Setting up a 3-Way Speaker with MiniDSP 2×4 using REW

It’s been about a month since the completion of these speakers and it’s about time I do a write-up on how I set up and tuned these speakers. I’ve spent the last several weeks and many hours setting up and dialing in these speakers and overall I’d say I am very happy with the results of this setup. I doubt this will be my final tuning/crossover setup with the MiniDSP but for now I’m just enjoying the new speakers and how awesome they truly do sound. Because overall the speakers sound fantastic. Better than I could have hoped for. Of course, my opinion is somewhat/mostly biased. But they literally sound just how the response plots would indicate – flat and neutral. No frequency range sounds out of balance, neither too forward nor too timid. But before I get into the subjectivity that is describing hi-fi sound, let me share the setup.

The above block diagram details the setup for measuring and tuning the speakers. The setup starts with a pair of laptops, one running windows 7 with the MiniDSP 4-Way Advanced Crossover Plug-in while the other is running Lunix Mint Cinnamon and REW 5.19 Beta 4. The sound card is a Behringer UCA222 connected via USB. My measurement mic is a Behringer ECM8000 using the cal factors available from Behringer’s website. Home Theater Shack also has a popular cal table for the ECM8000 (newecm.cal) but I felt like it over-corrected above 10 kHz and wasn’t realistic of the actual response of my microphone. When I use it, it causes almost every speaker I own to have this rising tail at 20 kHz that I just don’t believe. Behringer’s correction factor is more subtle and even though I am sure it still does not perfectly represent my microphone, I feel like it’s close enough for casual home use. See my comparison plot below.

Also the Behringer cal table includes phase. I think the main reason people use the newecm.cal is because the correction factor goes all the way down to 5 Hz to satisfy all the bassheads need for insanely low frequency measurements. Since the mic needs 48V phantom power, I use a Behringer XENYX 1202FX mixing console (which is normally part of my home recording studio) between the mic and the UCA222. A Schiit Audio SCH-13 Sys Preamp allows simple volume adjustment of two different sources. For my modest setup at the moment, I have an old Sony DVD/CD player and an Apple Airport Express. Better sources are in the works, including a real pre-amp, but for now, this is what I’ve got. The Airport Express is more for just convenience of listening than any kind of critical listening. Check out this post here on my whole house audio system.

So I debated doing a really nice all-aluminum housing for the MiniDPs and in the end just installed everything into an old VCR enclosure. The big spring-loaded slot in the front makes for easy access to the USB cables that I keep tucked away in there when not in programming mode. It’s not super glamorous, but is functional and practical. Both MiniDPSs are mounted on standoffs along with four LM317 linear regulator kits I picked up for $2 a piece on Amazon. I had an old 15 Vdc wallwart that after tearing it apart realized it was complete garbage. It claims an output current of 1000 mA which is just about right for two MiniDSPs (they draw 150 mA each) while maintaining some overhead. But with only a single transformer, a full-wave bridge rectifier and one capacitor, this would not be my first choice in powering any audio gear. But it’s nothing we can’t clean up nicely with some decent linear regulators. The wallwart provides 15 Vdc and feeds the first LM317 which takes the voltage down to 10 Vdc. The second LM317 takes the voltage down to 5 Vdc and over to the MiniDSP. Each LM317 claims roughly 65 dB ripple rejection so long as Vin-Vout > 5 Vdc at 150 mA. So with two in series, we probably get around 100 dB rejection which should be enough for even the most demanding audio needs. Since the MiniDSP outputs feed the UPA-700 amp with a fixed 29 dB of gain, everything in the signal path and DC bias paths needs to be dead quiet in order to provide quiet, hum-free and hiss-free experience. I think I succeeded because even though there exists what I would call traditional background white noise in the setup, you only hear it from less than 1 foot away from the tweeter with your ear directly in front of the speakers. Once you back up a couple of feet, everything is dead quite. And this is with the original MiniDSP kit which only claim >98 dB SNR. It’s definitely plenty for me. And yes, the MiniDSP’s are on all the time. For curiosity sake, I plugged my little VCR/MiniDSP setup into a Killawatt meter and measured a measly 3 watts (or 0.003 kW/h) which if left on year-round amounts to only 26 kW/year (24*365*.003). I pay about $0.1/kWh at my house on average which amounts to a grand total of $2.60/year. So to leave on a pair of MiniDSP’s 24-7-365 costs less than a side of fries at Five Guys. In other words, it’s basically peanuts. Which oddly enough, you can also get at Five Guys.

I made six sets of speaker cables that are each 14 feet in length from a 100-foot spool of 12 gauge OFC speaker wire from Parts Express. I bought 12 sets of black/red screw-style banana plugs which dressed up the cables nicely and provide a clean transition from speaker cable to the binding posts at the back of the speakers. I wanted to do something fancier on each side, like bundle each set of cables into some nice black expanded cable sleeving but just ended up leaving the speaker cables exposed for now. It’s functional and does the job. No complaints here.

Here’s a quick shot of the back of the upper cabinet with the nice Dayton Audio Premium gold-plated binding post terminals and aluminum face plate from Parts Express. Normally I wouldn’t go all out and buy such fancy binding posts, but for this build I decided they would complement the high-end feel of the speakers overall. They are super nice and provide a robust quality and feel to the speakers. I definitely recommend them for that great premium look.

Here’s the basic microphone setup for doing near-field measurements of just the midrange driver. I moved the microphone around a lot during my measurements. I did near-field plots of each driver at 0.5″ distances and then 6″ and 12″ and 30″ and 1M distances (approximately) as well as in-room measurements. I haven’t done a lot of off-axis measurements yet. But I do plan to take more measurements as time permits. This mic orientation and distance do not represent all of the measurements taken/shown here.

So this is sort of how the setup looked. The old Dell Inspiron was used to connect to each MiniDSP and provide instantaneous crossover and PEQ changes while the HP Elitebook on the right was running REW for taking and recording all the measurements. I only played with one speaker at a time, so I could make all the adjustments to just one MiniDSP unit. Once I was satisfied with the settings, I saved a configuration file and then loaded the settings onto the second MiniDSP. I did some casual listening of various types of music with each setting. Then I would go back to making adjustments as needed and redo the process of tweaking one unit, taking a measurement, loading the second MiniDSP and then doing some listening. I basically did this for about a month. What I’ve really been doing with this whole experience is educating myself on not only the basics of crossover design but some of the more complex elements as well. I figured I have a really nice set of speakers built into a great enclosure, now is my opportunity to really understand the benefits of different slope rates or crossover types on a really nice set of speakers. I have at my disposal the ability to test multiple filter types and slopes and take tons of measurements to see just what makes one filter better than another.

So the measurement and tweaking process is definitely on-going. One of the banes of active crossovers I suppose. The constant fear that just another tweak will make it sound so much better, or 10 times worse. I had started with a Linkwitz-Riley, 24dB/octave, 200 and 2,000 Hz crossover with almost no PEQ and 3 dB padding on the mid and tweeter with a 0.08 ms time delay on the tweeter. The slope rate and frequency was mostly just pulled out of the air, though loosely based on tweeter Fs and cone break-up modes of the RS-180P-4. I think this woofer works admirably up at 2,000 Hz. My near-field measurements matched very closely with PE’s measurements showing 1st, 2nd and 3rd cone break-up modes at 4 kHz, 5.3 kHz and 6.4 kHz and then rolling off sharply after that. I picked 200 Hz for the mid because it is simply 1/10th the tweeter crossover frequency. That’s really the only reason. The overdamped sealed enclosure actually starts to rolloff at around 100 Hz naturally (according to my measurements) so 200 Hz is basically double that. Mainly, I didn’t want the speakers to be a 2.1 way where the lower cabinet is just a subwoofer producing only bass. It seems like anything between 200 and 400 Hz would be appropriate for this setup though I have no real reason to limit the upper frequency response other than perhaps to match the natural frequency where baffle step losses occur. From my measurements baffle step losses look to occur between 400 and 200 Hz and is about -5 dB.

As far as tweeter minimum crossover point, I remember from times gone past the rule of thumb being 2x the fs of the tweeter minimum with a 12 dB octave slope. Though this may work in general, distortion levels will rise as the tweeter crossover frequency approaches fs and power handling will decrease. So from that perspective, it’s better to maintain a minimum crossover of 3x the fs and 18 dB / octave slopes or higher, but only as a rule of thumb. I still would like to experiment with the RS28F-4 down at around 1,200 Hz with 24 dB/octave slopes and see what it sounds like. So far the lowest I’ve run is 1,700 Hz, which is where it is at right now with 24 dB/octave Butterworth slopes. Besides setting the overall level of the three drivers (in amplitude), I feel like the crossover frequency has the largest overall impact in providing the desired tonal quality of the speaker. So while it may seem like an arbitrary selection point, it can make or break your speaker system. But how do you exactly determine the best crossover point? For me it’s about trial an error. Try something out, give it a listen for few days/weeks and then try something else. Ultimately whatever crossover point sounds best is invariable the best point. Though it’s doubtful that any single point or crossover type, or slope is “the best”, there must be dozens if not hundreds of viable options. I know many textbooks tend to favor crossover points that will sum acoustically with the natural roll-off of a driver. Thus allowing an acoustical slope that is steeper than the electrical slope of the crossover alone. These crossover points have to be very specific to coincide with the natural roll-off of the driver so as to sum appropriately and provide the desired response. But does this actually sound better than simply picking any other appropriate frequency regardless of the driver’s natural roll-off?

I look at it somewhat theoretically and ask myself, which driver do I feel has the best opportunity to reproduce a given frequency range the most accurately? In the broader sense this is probably obvious from looking at the natural (without crossover) frequency response plots and distortion plots of each driver. 1″ tweeters do a horrible job reproducing bass/mid frequencies and woofers can’t produce treble/highs worth a darn. Obviously, but what is more subtle to me is the overlap frequencies of the different speakers. Take the case in these 3-way speakers where the 100-500 Hz region could easily either be covered by the dual 8″ woofers or the 7″ midrange. As is the case with the 1,200-2,400 Hz frequency region, could either be played by the 7″ woofer or the tweeter. Yet different crossover points even within these small frequency regions will certainly cause significant tonal balance and sound quality to change. Something a simple on-axis frequency response plot or phase response plot probably wouldn’t even capture. However distortion plots may reveal a little more into which drivers can produce which overlapping frequency range better, in addition to off-axis response plots. I bet the the 1-1/8″ dome tweeter produces 2,500 Hz tones “better” than the 7″ woofer when you consider phase, on and off-axis frequency responses, impulse response and distortion. Good crossovers are about the creating predictable polar response patterns as a result of multiple drivers at different Y and Z axes and have them sum appropriately. If I had enough time I could compare such measurements of each driver in the ranges where they have natural overlapping usable ranges and pick which one does it best. At some point the crossover point that is selected should be based upon the crossover of where the woofer begins to sound better than the tweeter and vice versa.

Here’s a quick shot of my little Schiit Sys passive pre-amp. I bought this mainly as a stop-gap until I made a decision on what pre-amp I really wanted to purchase long-term. As a passive little unit, it basically provides a completely neutral response to any fixed output analog signal and allows attenuation of that signal with reasonable resolution. Once I received the unit, I ran the Schiit Sys through REW because, well, why not! I was really curious about overall flatness and left-right amplitude balance. I wanted to see just want this thing actually looked like electrically. I uploaded some of the plots here.

Basically to sum up the plots, at full volume (the 5 o’clock position) the SYS is about 0.4 dB down and nearly perfectly from 20-20,000 Hz with only a subtle low-frequency roll-off of about -0.05 dB at 20 Hz. Left-right balance is also excellent differing less than 0.05 dB between the two channels. I then took ten additional measurements with the dial at the 4 o’clock, 3 o’clock, 2 o’clock, etc. locations and continued to watch for frequency flatness and channel imbalance. The left-right balance began to diverge once the dial was moved off of the 5 o’clock position (full volume). At its worst the balance is separated by only 0.6 dB left to right while the flatness remains about -0.2 dB down at 20,000 Hz. I ran into noise floor limitations at low frequencies in my setup once I exceeded about 30 dB attenuation or the 10 o’clock position. At minimum volume the attenuation is basically infinite, equal to disconnecting a cable, but the limitation of my setup was around 70 dB (above 1,000 Hz). Overall the volume adjustment feels natural and increases appropriately based on dial location. The flatness and imbalance isn’t perfect, but it’s likely inaudible. It’s quite good actually considering the simple use of just a wiper-type potentiometer. Also, the switch which selects between inputs causes no click or pop in the output, even with the output driving a fixed gain amp straight to the speakers. So I am happy with this unit and feel it was a worthwhile addition to my little setup and can recommend it easily. It’s got a solid feel to it, construction is nice, and it’s really small, so it fits just about anywhere.

So I have no real stereo rack, everything just sits on the floor underneath an end table next to the couch. This is my best chance at having this system pass the WAF.

Another shot of the setup. An Airport Express ($25 on Craigslist) and a Sony DVP-S300 DVD/CD player (a $6 steal from Goodwill), the Schiit Sys, two MiniDSP 2×4’s in a VCR and an Emotiva UPA-700 amplifier. Quite compact and mostly unobtrusive.

And here’s a shot of the whole room. The speakers are close to the walls but it’s the only practical location for this room.

I’ll start off with a final response plot of the three drivers with the crossover settings at 170 Hz and 1700 Hz, they are Butterworth filters at 24 dB/octave on all drivers. The response is smoothed with 1/24th octave smoothing. Measurements are taken in-room at approximately 20″ from the top of the midrange driver. There is some active PEQ on just the two 8″ drivers and some subtle PEQ settings for the entire speaker. Overall, the speaker itself really needs no PEQ. Most of the EQ I added was just to compensate for room modes, not necessarily driver response imperfections. I grabbed a couple of screen shots of the REW auto-tuning mode. These pics don’t represent the final settings, but show you how it’s possible to create a target response from measured data and what PEQ settings in the MiniDSP are required to achieve it. I balanced the output of the drivers by adding 4 dB of attenuation to both the mid and tweeter equally. This roughly accounts for most of the baffle step losses and provides the overall flat on-axis frequency response you see here.

The above plots show multiple overlays of various different settings used while dialing in the PEQ, levels and crossover settings. The measurements are also done at varying distances. For any given tuning session I would quickly fill all 30 measurement locations in REW with multiple measurements from multiple settings. Either changing the slope type, rate or other settings. Even this graph only shows a handful of settings. Most of the time I don’t even write down what the settings are for a particular measurement. Again, I’m just trying to see what settings affect what and how it changes the what can be measured in REW. I used the target filter response option in REW to auto-generate PEQ settings and then just typed them into the MiniDSP. It does a remarkable job of predicting the new response each time. I was quite impressed.

This graph shows the basic final on-axis frequency response plot of the entire speaker with 1/24th octave smoothing and includes the phase response. Frequency response is roughly 30-20,000 Hz ±2 dB. I unwrapped the phase for a better visual depiction of what the phase response actually looks like. Phase is nice and linear (though not flat) and changing at a rate of about 120°/octave from 20-2,000 Hz. Then from 2,000 – 20,000 Hz the phase begins to reverse slightly and flattens out somewhat changing no more than 100° over this entire range. The tweeter alone pretty much produces this kind of phase response no matter what EQ/crossover settings I used. The tweeter phase is not inverted from the woofers and there is no electrical time alignment on any of the drivers. Since most people don’t talk about what phase actually sounds like, I don’t really have a good feel for whether or not this kind of phase response is good or bad or just otherwise unremarkable. I’m going to start playing around with the timing and crossover slopes to see if I can shift this phase response around and see what that sounds like.

Lastly, here’s a few screenshots of the 4-way Advanced Crossover Application from MiniDSP. Here are some of the windows available for setting up the MiniDSP, such as the crossover freq, slope rate and type, the PEQ for the woofers and the output level settings for the woofer and midrange which shows the -4 dB for the mids. The tweeter is also -4 dB with no time delay on any of the drivers. Nothing too fancy otherwise. The interface is functional and intuitive and changes are made instantaneously.

So that’s basically it. Not much more I can say about these things. Though there is one other thing I can share that I did that I thought was kind of fun and hadn’t seen anyone do. I put the mic in the exact location that I took most of these measurements and then recorded an entire song through the mic at a reasonable volume and imported the recorded song into a track in Audacity along side the original .wav file. Then I bounced back and forth between the recording and the actual song with a pair of headphones and I was honestly quite amazed at how similar they were. Aside from the recording sounding more “live”, everything else was spot on, the bass, treble, midrange, vocals, they all sounded fantastic and balanced nicely with the original source. If my room had more acoustic treatment on the walls and floor, I bet I could have narrowed the gap even more between the recording I made and the original, since that was really the only defining different between the two recordings. That and the fact that I converted the song to mono since I was only capturing a single speaker with the mic.

But you be the judge, click play on the audio clip in the media player below to listen to a song recorded with a mic in front of the speakers against the original source CD. The first 15 seconds is the original CD while the the next 15 seconds is a recording of speakers and so forth. The audio alternates every 15 seconds between the source music and the speakers until the song ends. The song is I Only Have Eyes for You by Harry Connick Jr. It’s an okay song for speaker auditioning, though arguably I could have picked something more jazzy and upbeat, it’s got some good vocals, a decent bass track, some piano and strings that can help showcase a speaker’s overall range. Put some headphones or use some good computer speakers and have a listen. See if you can spot the transitions without watching the time. Enjoy!

I Only Have Eyes for You – Harry Connick Jr., Recorded with the DM-4 Speakers

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DM-4 Reference Speaker Build Part V – Finally Complete!

The speakers are done! I’m super excited to finally unveil the completion of the DM-4 Reference Loudspeaker. It’s been crazy though, the last few months have been such a roller coaster of different, unexpected projects, as is evidenced by my last few posts. It seemed like with each new project this speaker build kept getting put off more and more. At some point I said to myself, I just need to finish a couple of these other things on the to-do list and then hit the speaker project full-time and just get them done. This has probably been the longest time I’ve spent doing a single speaker build. From conception to completion this project taken almost 3 years. It got the point where in the middle somewhere I completely lost interest in the whole project and began designing a completely different set of speakers. But alas I persevered and now I can say that I am super happy I did because these speakers turned out amazing! Well, in looks at least. As of this post I haven’t hooked them up and actually listened to them yet aside from my initial tuning of lower enclosures which I did a few months ago. The method for creating the crossovers and doing the measurements will have to be saved for another post. For now I just wanted to get the rest of the build pics up and of course the final shots of them sitting in my living room just looking awesome.

It’s funny because as with so many DIY projects, at some point you just have to accept the little flaws in a project and recognize that this thing is made by the hand of an imperfect person. I know I get way too picky about the fit and finish of the final product that can’t enjoy it for what it is. Overall these speakers went together without too much fuss. I’ve been working with wood and MDF and building speakers for many years so I’ve come to understand what it takes to get the job done without making too many mistakes. But when it comes to the final paint and finish work, I’m a complete mess. For this project things were looking good all the way up until I added the Polycrylic clear coat. Staining the birch was a piece of cake, it went on like any stain, really cleanly and looked flawless once complete. I went out on a limb and did the black surfaces with just spray paint and to my surprise that also went on really well. I think I did 3 coats of gray primer and then 2 coats of flat black. I had masked off the birch while spray painting and when I lifted the masking for the first time I got a glimpse of what these speakers were going to look like and I was super excited.

The gray stain contrasting the black just made a killer combination that just looked different from the usual speaker. So I was excited and pumped to put on that first coat of clear coat to give it that clean, smooth, subtle shine to it. This is where it all fell apart. I seriously have to find a better method for clear-coating speakers. There has to be a better way. I won’t go into the details, but I ended up with 4 coats before I just gave up and said it’s as good as it’s going to get. After each coat I’d find a drip, or a spot where I’d brushed it again when I shouldn’t have, or a spot I missed completely. So I’d sand it down and put on another coat, only to miss another spot, over-brush a different spot and end up with a run somewhere else. After sanding down that coat and doing it again and again I just quit and said it is what it is. So that’s when I decided you know what, they’re not perfect and overall they look as good as I ever could have expected them to look so I’m just going to say that I’m happy with them for now. But if and when I learn how to do a proper clear coat, I’ll remove all the drivers, sand this top coat down once again and finish them proper. But that’s down the road, like, way down the road.

Well I should do a write-up on the final build of these speakers. They definitely deserve it, there are so many little details that went into every aspect of making this speaker. You can probably gleam how they were built from all the pics but a few words won’t hurt. I’ve already written quite a bit leading up to this point. A lot of finishing these speakers is just duplicating what I did to the lower cabs. I had just finished building the upper cabinet when I stopped late last year. So I will pick up this post with adding the 1/4″ MDF to the front/top/back/bottom and cutting the 45° chamfer around the edges. The 1/4″ MDF worked out great and gives a clean finish to work with as far as painting goes. Plus it allowed a perfect flush fit for the Dayton Audio drivers. I used Parts Express’s sweet Jasper Jig Model 240 to router perfect holes for the woofer and tweeter. This took a lot of trial and error though! I think I went through 5 different boards before I found a size that allowed the drivers to fit just right without the gap being too big or too small. I was shooting for a gap that was at least 0.005″ but no more than 0.015″. That’s basically a baffle diameter that is 1/32″ larger than the diameter of the driver basket. This allows for some growth from paint/clear coat but no so much that the driver can actually move around. The smaller the gap, the better the finished speaker looks, in my opinion. I did error on the smaller side for the tweeter and I had a tough time getting it fit after the 4 coats of clear coat that lined the inside edge. But since it is probably the only driver anyone is really going to look at, I wanted to make sure the transition from the tweeter’s faceplate to the baffle was absolutely seamless. Plus with the Jasper’s fairly course 1/16″ increments (or 0.062″) I didn’t have much choice with the tweeter as one size was spot on at 0.000″ and the next size bigger left a whopping 0.0315″ gap around the whole tweeter. That was more than double what I had already agreed was reasonable from an aesthetics perspective. So I cut it with no gap and then sanded it slightly to get the tweeter to fit. I then just tried to be careful with the paint and clear coat so as to not decrease that size too much. It worked out, because the tweeter fit by the skin of its teeth and the gap is nearly zero.

The next step was adding the acoustic insulation – I reiterate what I had stated about doing this insulation technique on the lower cabinets that it was an absolute pain and was super time consuming but I think in the end it is going to provide superior damping and absorptive properties than some of the traditional (and simpler) methods. I took a bunch of pictures of each layer going into the cabinet and then made a “sample coupon” on a separate piece of MDF just so show a cool cutaway view of the built-up layers of materials. In short each upper cabinet is covered with 2 layers of 1/2″ (6-lb.) standard carpet pad following by 4 layers of a 80/20 cotton/poly blend fabric/fill and then 4 layers of a 100% poly batting material. The total thickness ends up being almost 3″. Each layer is glued onto the previous layer with spray glue to create one cohesive material that won’t move around and hopefully provide consistent absorptive properties throughout the enclosure and in both enclosures. The upper cabinet is sealed and will have an approximate high-pass filter of around 200-400 Hz so for the most part I was shooting for a nearly-full enclosure, but still ended up with a solid pocket of just air with no fill in just the middle portion. So it’s probably like 75% filled if I had to guess? The lower cabinet only has the walls lined and is probably only 15% filled.

Alright so now the cabinets are done it’s time to start working on the finish. I picked up a can of Winwax “Classic Gray” and put 3 coats of stain the on birch sides for all four speakers. I didn’t bother masking the bare MDF since I was planning on painting it anyway. I should have stained those raw MDF edges better though because the spots I overbrushed with the stain actually sanded nicely and cleaned up that rough MDF edge look and then painted even better. But I did what I could to sand the bare MDF edge so it didn’t look like crap. In the end they are not perfect, I could have done some better edge prep, but they look fine overall and am not going to worry about it too much. After letting the stain dry I masked off the sides and began preparations to paint everything else. I picked up 3 cans of Painter’s Touch 2X gray primer and 3 cans of the flat black. Over the course of the next couple of months I went out to the garage and painted a coat of the primer, then sanded it, then did another coat and sanded it, until I had a really nice flat base finish. Then I moved on to the flat black paint. I also sanded between coats until I had a near-flawless black finish. This spray paint went on really well and I would definitely use this spray paint again. The flat black is extremely flat and I wouldn’t recommend it as a final top coat. It needs a satin or semi-gloss clear coat of some kind to finish it off.

Once the paint was all dry I brought the speakers in the house for the first time. I didn’t want to do the clear coat/top coat in the garage because seriously anything that sits in my garage for more than 5 minutes is immediately covered in a layer of dust/saw-dust/paint-dust/you-name-it-dust. It’s not like I’ve got a 10,000 clean room at my disposal so the house will have to be good enough. I masked off the floor and my coffee table and set up the speakers for their first coat of Minmwax Polycrylic Satin clear coat. I’ve used this stuff before on countless projects and usually praise the ease with which this product goes on. It’s usually forgiving of brush strokes, provides a really consistent sheen across its surface and it’s water based so clean-up is a breeze. But I realized that painting over a solid black surface is not as easy. Every blemish in the coat was readily visible. Any imperfection in the base finish showed through and any area in the top coat that wasn’t applied perfectly evenly was visible when the light shown off it at certain angles. Thus began the paint-sand-paint-sand-paint-sand-paint nightmare that lasted about a week. And yes, with the speakers sitting in my living room just like this pretty much the entire time. Anyway, I called it good enough after that last coat and accepted the fact that once again I’ve nearly ruined a perfectly good project with a shoddy top coat. I started looking at past speaker projects and realized that none of them are perfect and that surely after a while I’d soon forget all about it anyway. I can say that birch sides look great. The clear coat went on and after only the second coat looked great. So I will say that real wood, with a grain and some texture to it, is way more forgiving of the irregularities in the top coat. But that solid flat black was something else. Especially since the fronts have the holes for the drivers, brushing around the driver openings and trying to get it look seamless was just a pain. I’m doing a spray top coat next time. I’m sure that goes on easier.

Alright so now to the last part, the installation of the drivers! This part was probably the most fun. I took my time on this part, I did only a pair of drivers a day for basically a week until all four speakers were complete. I made up the internal wiring using 14 gauge 100% OFC copper wire and crimped them to a set of 0.250″ gold plated female disconnects from Parts Express. I went all out and bought the fancy Dayton Audio 5-way binding post kits with the black aluminum faceplates from Parts Express. These things look super nice and are definitely a step up when compared to a good old fashioned terminal cup. I won’t claim they offer much sonic benefit other than being a robust, gold-plated, low-loss connector, but they look stinking awesome and definitely match the high-end look of the speakers overall.

I attached each disconnect to its appropriate spot ensuring I maintained proper polarity on each connection. I’ve been know to look right at a red connector and plug it straight onto the black connector like a moron. I took pictures of each connection just so I could be sure. Nothing’s worse than trying to diagnose polarity issues in a speaker system via measurement techniques alone. It is possible though, but I’d rather not get into that situation where I don’t know if the polarity is inverted or not or double-inverted and therefore not inverted. The MiniDSP allows inversion of any of the 4 outputs so there’s flexibility in the processing to get the polarity right but it’s better that everything be correct from the get-go.

I applied a strip of the 1/8″ x 1/2″ open-cell foam gasket to backs of the 7″ and 8″ drivers and applied two strips to the back of the tweeter, since the faceplate is thinner. The basket thickness of the woofers is about 0.210″ and my baffle thickness is 0.250″ which leaves 0.040″ (about 1mm) of uncompressed gasket to provide a perfectly flush fit. The gasket I received from Parts Express was actually about 0.140″ thick and was not easily compressed to 0.040″. (I had purchased another role of gasket but it was only 0.110″ thick and was significantly softer so I didn’t use it). It could compress more under the pre-load provided by the six (6) 8×1 screws but since I shooting for a flush fit I only tightened the screws enough such that the basket sat flat to the surface. This is the only downside to using just a piece of 1/4″ MDF to flush mount the drivers. The drivers are not seated tight against the baffle, I mean they are tight, but there’s still 1 mm of foam between the driver and the baffle. Normally you would tighten the screws super tight, or reasonably tight such that the gasket reaches “full” compression. Whatever that is, you decide. It’s not going to zero no matter what, so when you do design for a flush-mounted driver you have to account for some amount of gasket under the driver that makes it sit higher than just the thickness of the basket. As it is this material has a fairly soft durometer, it’s probably in the 20-30 region based on a Shore 00 rating, if I had to guess. Uncompressed the thickness is 0.140″ and and final compression in my design it is 0.040″ which represents a compression ratio of 71%. Honestly I couldn’t turn the screws much more to get that compression any higher without stripping them out. After all it’s only MDF with a pilot hole, I did not use any kind of hurricane nut or t-nut (I just find them way more hassle then they are worth for small drivers such as these). The drivers are definitely in there and the seal is surely air-tight. Taking them out later on will be a pain since I’ve found this soft gasketing material tends to bond itself to both surfaces once compressed and proved quite the challenge when removing drivers years later.

Anyway, that pretty much brings me to today. The drivers are installed, the speakers are set up in their (probably) final location in my living room and so I snapped some pictures so I could show them off. Oh yeah, the other thing I ended up doing for the feet was I bought a set of sixteen (16) of the Penn-Elcom rubber feet from Parts Express. They are 1″ in diameter and 0.375″ tall. They were only 57 cents a piece and worked out awesome. I have wood floors so moving them around on the floor is a piece of cake plus they stick quite nicely. The top cabinet is definitely not going anywhere and the height it just perfect. So if you’re debating on getting a full set of toe spikes at 10x the cost, my recommendation is just go with the rubber feet. I doubt they provide any measurable difference in sound in the end over anything else but they are super easy to install and are essentially invisible in the final product.

Here’s the gallery of pics starting with the upper cabinets and putting on the 1/4″ baffle boards forward to completion. I can’t believe this took five blog entries to complete. And I wrote a lot. I’m sorry for being so long-winded, but hopefully some of this information is helpful if you are working on speaker project of your own. There is so much that goes on behind the scenes with a good speaker design. I’ve only really touched on a handful of design concepts and ideas that I considered while making these speakers. Not to mention I still have to measure them and design the crossover for them, sot that’s all to come. Until then here’s a bunch of pictures of the completion of the DM-4 Reference Loudspeaker System!

And if weight provides any indication of the build quality of a speaker, here’s the stats on these puppies: the lower cabinet weighs in at 96.0 pounds and the upper cabinet is 45.6 pounds bringing the total weight per speaker to 141.6 pounds! No wonder I nearly bust a gut every time I have to move these beasts.

Click here to go to a complete gallery of final build pictures!

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How I Built an Awesome Classic-Style Bookcase from Scratch with Mixed Lumber from The Home Depot

So I’m trying something a little bit different. I’ve been blogging for a long while now and while I feel like it’s still a great venue for sharing DIY projects and what-not, the bigger and better trend these days is vlogging – the video version of blogging. YouTube is way bigger than Blogger ever was and for most people it’s the sharing platform of choice. Me, I honestly hate shooting video of my projects. It just takes extra time, it distracts me from the work I’m doing, and most of the time I just don’t know what to say on the video. But for this project I made a conscious decision from the very beginning, for good or bad, that I was going to turn this bookcase build into a video blog. Just to try it out, see what I could turn it into. So in addition to a very short write-up on my blog, I’ve created a 4-part video series of this entire project from beginning to end for your viewing enjoyment!

Honestly though this will probably be the last time I do this kind of thing. As much fun as it’s been working with one of the most useless and frustrating video editing tools known to man (Windows Movie Maker), I really don’t think that many people are going to sit down and watch this thing front to back. But I feel like if you are interested in building a project similar to this, then I hope there are some nuggets of useful information in the 30+ minutes of video I pieced together of this project. I will say that did have a lot of fun throwing in old songs I had written, some from as old as 20 years ago as well as some songs I wrote just last month, to back the videos and at least make it somewhat more watchable (though depending on your music tastes, that’s debatable). I’ve got hundreds of these old songs I’ve composed over the years that I never know what to do with, most are just synth beats with some melody and a bassline, reminiscent of synth pop music from the 80’s. My son enjoys listening to them, and so for some reason I keep writing them even if they are lame. Anyway, I hope you enjoy the soundtrack to the Benjamin Bookcase Project. I think I will leave it at that for now. I will do a more complete write-up here in the future. For now I’ll just post a few pictures as well as links to all 4 videos on YouTube.

As always, thanks for stopping by and I hope you enjoy the pictures and my first ever video blog of the Benjamin Bookcase Project – A classic DIY bookcase featuring victorian styles including crown and fluted mouldings mixed with old-fashioned farmhouse comfort with the shiplap backing and clean white features. This is an all-white, 6-shelf, classic-style bookcase measuring 12-1/2″ deep by 70″ wide by 100″ tall. This bookcase looks great in almost any home mixing a little bit of old with a little bit of new to make a unique center piece for any living or family room. More info about this project will be posted here. Pin it if you love it!

Benjamin Bookcase Video Part I

Benjamin Bookcase Video Part II

Benjamin Bookcase Video Part III

Benjamin Bookcase Video Part IV

Mega-Picture Gallery

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Just Jumped on the Painted Piano Bandwagon

Last weekend I found some time to squeak in a quick little makeover project that my wife has been anxious for me to do for a while now. I’ll admit it, painting a beautifully-stained, vintage-style, classic Kohler & Campbell piano felt just a little bit wrong. How could anyone take something so original, so natural, probably hand-stained by some really old guy, and just slap a dull, ordinary coat of paint on it? I’m glad you asked, because I’m going to show you just how I did it!

First things first, Pinterest. There’s no shortage of painted pianos out there to get some ideas from. Everybody who’s painted a piano has a slightly different approach to it and it helps to see what’s out there. For purposes that suited me, I chose one of the simpler methods in terms of complexity. Though the results surpassed my expectations. Color options range from white, to off-white, teal, baby blue, green, gray and black and I even saw a few red pianos out there for the truly bold. In my case the color choice came down to the paint type I wanted to use. The wife wanted a classic gray and I agreed. So gray it was.

Now, if you’re willing to buy wall/house paint (such as the Behr brand from The Home Depot) you can pretty much pick the color of your choice. I’ve had decent success using Behr paint to paint furniture (and speakers). I’ve painted with brushes (tends to leaves brush strokes). I’ve painted with rollers (looks good but takes A LONG time). And I’ve painted with an HPLV sprayer (Wagner) though the finish has that “sprayed” look to it, it’s not as smooth as the other two options but is quick and the coverage is high considering the cost. This has just been my experience though and I am in no means an expert in painting techniques.

But there was always one paint type I avoided like the plague when painting furniture and that was good old fashioned spray paint. I always discounted spray paint as a legitimate painting medium because to me anything sprayed with spray paint looked just like that, like it was spray painted. Spray paint was reserved for those cheap projects, like a pinewood derby car, or a homemade set of roof racks for the car, or for people on HGTV who are trying to take junk from a flea market and sell it for 10 times what they paid to unsuspecting consumers looking for something “different”. So basically anything, almost anything but furniture is where spray paint was best suited. But until recently my opinion of spray paint has done a near 180 and when done right can truly look beautiful, yes, even on furniture. I’d venture to say that spray paint has come along way just in its engineering and chemistry alone in terms of quality, consistency and coverage since the last time I used it. Bare in mind however, not all spray paint is created equally and there is some pretty crappy spray paint out there that can be purchased for very cheap but I would recommend avoiding them or you may end up saying to yourself, yup looks like crappy ole’ spray paint.

The spray paint I used is Rust-oleum Painter’s Touch 2x Ultra Cover in a Satin Granite (gray). Each can of paint sells for about $3.89 at The Home Depot and for this piano makeover I used just about five cans. But before I get onto the painting details, let’s talk about prep work. Step one: If you’re going to spray paint your piano, you have to move it out of the house first. This alone is a deal breaker for most people who are looking to paint their old piano if they want to use spray paint. I don’t care how many square yards of 1 mil plastic you have, masking off half you’re living room to spray paint inside the house just seems like a bad idea all around. I had some friends stop by the house to help me move our piano out of the living room and onto the front patio. Took less than 5 minutes with their help. But it’s not a one-man job for sure.

Step two: Once out on the patio I began to disassemble nearly everything on the piano that had screws and could be removed. This is the second deal breaker for those looking to paint their piano. It’s just too much work and you risk either breaking something or losing some random piece of hardware or not being able to put everything back together just right. But if you feel inclined and up to the task, I recommend taking off as much hardware as possible and taking off as many pieces as possible and masking off everything else. This way each piece is fully painted on all sides so when it’s put back together, you don’t have any seams or cracks or small joints that still show through the original stained wood color. It also makes painting each piece much easier. You can see above all of the pieces I was able to remove and paint. I masked off the keys and the piano strings and hammers with some 1 mil plastic and blue painters tape. I also removed that long skinny piece of wood that sits right over the keys which has the strip of felt on it and painted it separately just so I could mask off the felt and get a good painted edge on the wood that sits right up against the keys.

Step three: repair and sanding. The main reason people don’t feel bad about painting an old piano, and the same reason why I caved as well, is because an old piano is just that, it’s old. The wood is usually damaged in multiple places, the finish has worn and it just doesn’t look as nice as it once did decades ago. This is where the repair part comes into play. My wife has had this piano in her family for a very long time. This was the same piano she played when she was 8 years old and it’s the same piano my kids play today. So with a little bit of wood putty I went around and filled all the cracks and broken wood parts and then sanded them smooth with 150 then 220 grit sandpaper. With my palm sander I sanded almost all of the piano with 220 grit sandpaper just to take off the very top layer of clear coat. I was not attempting to remove the clear coat or the stain and never intended on getting down to bare wood. I just went over each piece really quickly to take off the sheen and provide a somewhat roughed up surface for the spray paint to adhere to. This step you could probably skip, however. Depending on the existing finish of your piano. The parts I didn’t sand looked just as good in the end as the parts I did sand, so it probably wouldn’t have made much difference. The overall sheen was a little different in the sanded parts though, it ended up duller than the parts I didn’t sand. Perhaps another downside to the use of spray paint is that the finish ultimately is very dependent on the base finish. Since the paint goes on so thin, most of the underlying texture shows through. If the piano was really smooth and shiny to start with, then the paint will also go on and look and feel smooth and be shiny. But if it’s rough, the paint does nothing to make look smoother. Additionally the sheen is affected by the undercoat as well. Smoother wood looks shinier than rough wood, regardless of the sheen of paint you’re using. This satin Rust-oleum paint has just enough sheen to look nice without looking dull. But still varied based on quality/texture/ of the base finish. Test out a small section if you’re worried, like under the bench or under the piano top/lid.

I painted three light coats one after another all basically within the 1 hour timeframe allowed for re-coats. I started on one side and just worked my way around the entire piano and then to each disassembled piece and then started over back at the beginning. The trick, I think, is just not overdoing it in any one spot, allow the first coat to go on and not cover everything. The first coat won’t even look that good and you’ll be cursing yourself for even trying this whole project. But be patient. The second coat will fill the gaps once that first coat has had a chance to adhere and dry and by the third coat it will all just look like one seamless band of paint and you’ll be giddy with excitement. Okay so now I’m just describing how it all went down for me. It was panic and fear, then anxious relief and finally awe and bewilderment. Just take your time, don’t sand between coats, light and easy on the spray nozzle in quick short bursts from 8-12″ away at all times. If you do overdo it in a spot or two, let it dry a bit, sand it down lightly, and re-spray. That’s about it, take a step back and check out your wonderful work and don’t forget to snap a few pics for FB/IG.

Step four: let dry for 24 hours. I skipped this part and moved the piano back in the house the same day. I let everything dry for only about 4 hours but due to an impending storm I had to get that thing back inside before the rains came (which they did the very next morning). When moving the piano we tried not to handle the painted parts as much as possible, lifting from the back and undersides. But this job can be done in one day if you start early in the morning. I reassembled the piano once in the house and luckily managed to figure out where all the screws went. We set the piano up in its new location in the living room and sat back in amazement at the transformation. It looked fantastic. The best that piano has looked in all the years we’ve had it.

The last thing to do is to finish the fabric bench seat which for now is just a piece of fabric wrapped around the bench lid, but I will get it stapled down with a foam pad on it soon enough. The other thing that we didn’t get to do is put on a couple coats of Minwax Polycrylic satin clear coat. I bought a pint of this stuff expecting to use it but I was so impressed with the final finish of the spray paint that we decided to hold off for now. Now that the piano has been in the house for a few days I have noticed more inconsistencies in the sheen on the sides of the piano and the top. Basically a coat or two of the satin polycrylic will fix that right up. That step can be done anytime with a simple brush while in the house. So for another day we may get the final clear coat on this but even if that never happened, I would still be very happy with our new piano and hope to be able to enjoy it years to come.

Check out some of pics below of this little painted piano makeover project. Let me know what you think in the comments below and thanks for stopping by!

Obligatory Before and After Shot

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Updated Whole House Audio Setup with a New 12-Channel Amp

Last month I picked up a Niles SI-1230 Audio Amplifier from a guy on Craigslist for crazy cheap and completely transformed my modest whole-house audio system into one that became worthy of me actually wanting to write about it. I’ve always loved the idea of whole-house audio, a pair of speakers in each room and the ability to play the music throughout the whole house with just the click of a mouse or a touch of a button on your phone. My existing setup had 4 zones and was powered by three Lapai LP-2020 amplifiers with the outside patio speakers being powered by a SMSL-SA50. I had plans to add two more zones and a brand new pair of Theater Solutions SC-6 in-ceiling speakers (bought for $12.99 from Goodwill, #bargainhunters, thanks DC) and was just waiting to bite the bullet and buy a couple more Lapai/SMSL/Dayton amps to finish off the house but for some reason could never get the energy to do so.

Which is why when I saw the ad on Craigslist for a Niles SI-1230 12-channel amp for only $50, I knew this was my chance to not only finish off the last two zones in my whole-house audio setup, but to do a serious upgrade to each of the existing zones at the same time. And I was able to do it for less than if I had just bought another pair of “t-amps” like I was planning. The deal was too good to pass up. The unit was in perfect condition too, including the original packing. I didn’t want to tell the guy that he could have sold this thing for more than $50 but he said he wasn’t interested in making any money off it, just wanted it to go to someone who would know what to do with it. Apparently few people knew what to do with this amp since the ad was a week old by the time I saw it and the guy said the few people he talked to didn’t know what kind of amp this was. This amp boasts some seriously sweet specs: 12 channels, 30W per channel into 8 ohms, 37W into 4 ohms, all channels are bridgeable into 80W per channel, input options range from discrete inputs per channel, BUS input, L+R input, with selectable “always on” or sense. And it weighs like 40 pounds! So enough with babbling, here’s how I installed this thing into my existing setup and made it a permanent addition to my whole house audio.

First step was to create a location where I could put this amp that was close to my whole-house home run and be out of the way enough to not get in the way but be accessible so I could adjust the levels and get everything hooked up easily. My home run is currently in the laundry room so it made sense to keep everything here so I wouldn’t need to run any extension cables. I started off by building a shelf using some leftover bull-nose particle board from a previous closet renovation project. It’s 15-1/4″ by 26 inches. I installed the shelf above the cabinets in a “corner” location in the laundry room. I attached a pair of 3/4″ pine “cleats” to the wall so that the shelf had something solid to rest on. I attached the shelf to the cleats with a few 1-1/2″ drywall screws.

I could have left it at this point since it was functional, but looked like crap, so I caulked and painted the shelf to match the rest of laundry room. This really finished off the shelf and made it look good, like it belonged. After finishing the shelf I realized I should have made it run the entire length of the wall on that side so I could have more storage space for electronics, amps, routers, and whatnot, but figured for this project, the shorter shelf would suit just fine.

The next thing I needed to do was pipe over 110V and bring over the CAT-5 and all speaker wires. I cut two holes in the wall above the shelf and added a plug for the electrical and another for the low-voltage wires. The two locations are separated by a 2×4 in the wall. I tapped into an outlet in the attic that was close by and fortunately was also on the same circuit as the laundry room. Since there’s not a lot of load on that circuit, it made for a perfect tapping off point for the new amp.

I drilled a couple of 1″ holes in the top plate in the attic over the wall location where the amp would sit. I pulled out the speaker wire from the old location and dropped them down the wall in the new location. I made a new CAT-5 cable to run from the exiting switch to a new switch to feed each Airport Express. I bought a cheap TP-Link 8-port 10/100 switch for each Airport Express. My entire house is wired with Gigabit switches except this switch which doesn’t need it since the Airports only run at 100Mbps.

I bought a set of (8) 3-ft CAT-5 cables to run from the switch to each Airport and a set of (6) 3.5mm-to-RCA cables to connect the audio from each Airport to one pair of channels on the amplifier. I connected each set of speakers to each pair of channels of the amp and that was pretty much it. I bought a surge protector that provided 7 outlets that were rotated so one Airport would fit into each plug. I still need to dress the cables but for now the whole setup is functional, it’s out of the way and looks a lot cleaner than the old setup. I cleaned up the cables and wires for the rest of my network and called it done. I put on some tunes and adjusted the levels for each zone and just rocked out. The new amp sounds fantastic! I added one more zone in the den/computer room while I was it also. I still have one more zone I can add and was thinking about doing a whole-house subwoofer as a zone. Maybe put a 12″ sub in the attic and then it could be selected as a separate zone for when you want a little extra bass.

Here’s some pictures below of the making of my new whole-house audio setup including the new speakers in den. And the before and after of my laundry room home run. Enjoy!

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DM-4 Reference Upper Cabinet 2-way Speaker Build Part IV

cad_front_upperThe speaker project continues! I managed to find a few hours in the last couple of weeks to finally start the upper cabinet speaker portion of my sweet DM-4 Reference Speaker build. If you haven’t read my original introduction to these speakers, then you might want to start over there first. The inspiration for this design originates from both the Wilson Audio Watt and the Von Schweikert VR-5 hi-fi speakers. It’s sort of a marriage of the two designs, taking the best of the aesthetics of both and incorporating them into one totally awesome speaker system – and then ditching the passive crossover for a fully active DSP-based crossover with all the bells and whistles. It’s going to be my greatest achievement yet!

The dimensions of the upper cabinet are 12-1/2″ at the bottom with a 7° slope on each of sides ending up at a width of 9″ at the top. The speakers are 21″ deep at the bottom and 18-3/16″ at the top. The back baffle is perpendicular to the bottom but the front baffle is tilted back 14° to physically time align the woofer and the tweeter. The very top front edge has a 3″ chamfer cut at 14° (which mimics slightly the VR-5) which also reduces the effects of edge diffraction. There are 1/4″ chamfers around all exterior edges which finish off the cabinets (similar to the VR-5) which also aid in edge diffraction. These are the basics of the design which gives it that distinct look that I was shooting for with this whole speaker project. The sloped sides, the sloped front, the chamfered top edge all give the speaker that classic “Watt/VR-5″ look.

So just a few words on how I designed some of the shape and dimensions for this speaker because I think there are important factors with each parameter. This is not a just carbon-copy/knockoff speaker but is truly designed for the drivers I have selected. I came up with 14° sloped front baffle by drafting up side views (or cutaway views) for the 7″ Dayton woofer and 1-1/8″ Dome tweeter in Delta CAD using the .pdfs from Parts Express’s website and then played around with the angle to align the drivers until they were just right. Phase/time alignment is achieved by placing the acoustic centers of each speaker in the same vertical plane. It is believed that the acoustic center of a speaker sits roughly at or around the location of the voice coil. Since the voice coil location is not well defined in the datasheets, it can also be approximated by assuming the voice coil is centered within the top plate of the magnet assembly (not the magnet itself). I considered alignment was met by setting the baffle back such that the centers of each voice coil were aligned vertically. In the case of the Dayton RS-28F tweeter and RS-180P woofer, this turns out to be about 14° assuming the drivers are 1/2″ apart on the front baffle. This suits me just fine since most off-axis measurements are taken in 15° degree increments, so when seated directly in front of the speakers, you will be listening to both the woofer and tweeter at about 14°-15° off axis. The tweeters will sit at about 44” from the floor when resting on the lower cabinets. Based on the FR plots of both drivers, they both have a very well-behaved response at 15° off axis with only slightly more high-frequency roll-off than when listening to them head on. The exact baffle angle probably doesn’t matter too much as far as timing goes since the crossover is going to be MiniDSP-based (active), so I will have independent control over the time/alignment of the woofer and tweeter anyway. But someday I may decide to re-purpose these speakers without the active DSP so I will have to design a passive crossover for them and in that case I’ll be all set with the drivers physically already time aligned. I have to admit, my experience in this area is mostly textbook since I have not actually ever built a speaker with the drivers’ acoustic centers vertically aligned in this fashion. Like most speakers, I just allow the vertical offset to play out however it plays out on a normal, flat, vertical baffle. So this will be fun for me to see just how much it changes the way the speakers the sound.

Another cool dimensional design consideration is the 14° chamfer across the top/front baffle edge. So what purpose does this little design detail serve? It is just for looks? Did I just do it to copy the VR-5? The Wilson Watt doesn’t have it, so it is even necessary? The answer is both yes and no. Aesthetically, it completes the speaker, it’s that final detail that just makes the speakers great and sets them apart from the rest. It gives it that hi-fi, high-end look to it by simply cutting that corner at the top edge and smoothing its transition from the front to the top so that it, well, just looks cool. Sonically it should also reduce the effects of baffle edge diffraction around this surface. Baffle edge diffraction occurs anywhere there is a discontinuity on a surface where sound waves are present. I believe the Wilson Watt combats this problem with a type of acoustic foam attached directly to the front baffle around the tweeter and woofer. This way the sound waves traveling across the front of the baffle are attenuated before they even get to the edge, therefore potentially reducing the audible effects of edge diffraction by the listener. While in principle this should work, it also looks ugly. It’s probably one of the main reasons most speakers do not have some sort of acoustic foam on the front baffle surrounding the drivers, it can take a great-looking speaker and make it look terrible. Plus, I think it complicates the design in an area that does not need to be made complex. The construct of the tweeter, the voice coil, dome materials, doping methods, glues, the quality of construction, crossover type, frequency, etc. all play a much larger roll in whether or not a speaker sounds good. Once you start focusing on just baffle edge diffraction, even with a $50 tweeter, you’re really looking only to fine-tune what should already be a great-sounding driver. It’s taming that last little ripple in the response that your microphone is still picking up in the measurement that you just can’t let go. But that’s not to say that some speakers aren’t designed with edge diffraction as their sole feature with the entire focus being around proper driver/cabinet dispersion. Any speaker enclosure with huge rounded edges or extra ordinarily wide front baffles are taking into consideration these edge effects. Take almost the entire line-up of Thiel speakers for example or Sonus Faber. These guys believe whole heartily in the ill effects of edge diffraction and have designed in oversized front baffles and large-edge roundovers.

This effect can be modeled and there are tools out there for doing so. One of them is Diffraction and Boundary Simulator by our favorite Excel guru Jeff Bagby. Not only does the edge cause unwanted disruptions in sound but the location of the tweeter/woofer on the front baffle plays heavily into how bad these disruptions really are. Offsetting the tweeter from the center changes the distance from the radiating source such that the edge effects occur at different times with respect to each other. This can help reduce the overall effect of edge diffraction making the speaker’s FR response smoother. Unfortunately, the best-simulated design for diffraction tends to also be the worst-looking. So a designer must balance form with function in this sense. The complexity of the shape of the DM-4 cabinet doesn’t lend itself to an easy edge diffraction model and Jeff’s tool doesn’t exactly allow the sloped sides or a single 14°chamfer across the top to be modeled. But after researching it a bit more I came across another boundary simulation tool from the guys over at FRD Consortium called Baffle Diffraction Simulator. This tool will let me create the exact shape of the enclosure and then model its response. I’ve been playing around with it as well and it’s been pretty interesting the results. You can see a couple different screenshots below. I can say that the 1/4″ chamfer on all the edges, as small as it is, does provide as much as ±0.5 dB improvement in frequency flatness above 2 kHz. And the tapered sides and sloped front baffle provide a measurable difference as well when compared to a flat rectangular box with no chamfered edges. So moving on…

Another critical element to reducing edge diffraction effects is to flush-mount the drivers. Measured response plots can reveal the effects of edge diffraction for a tweeter mounted on the surface of a baffle (which might be only 5mm thick) compared to being flush mounted. Beside flush mounted drivers look soooooo much better. Finally a win-win for diffraction and aesthetics! I always like to flush mount my tweeters and depending on the design, will also do the woofers. Though the benefit of flush-mounting the woofers which have a lower crossover point is minimized due to the longer wavelengths. It still looks better to me!

So I’ve written plenty for this one post. The only thing I didn’t go into was the bracing technique I used. I’ll save that for another post, but the bracing definitely has some intentional design behind it and isn’t random. Recently I’ve adopted this design technique that starts with the bracing and enclosing a box around it, instead of building a box and adding bracing to it. It makes building the speakers really fun and is actually quite easy. The main consideration for doing the bracing this way is to brace each panel sufficiently such that the fundamental panel resonance is pushed out of range of the woofer (>2 kHz) as much as is practical. Also it mimics the lower cabinet bracing design. This box will be insulated using the same technique as the lower cabinets (with the carpet pad, cotton fill and polyfil) and should be extremely damped and extremely dead overall. The front and rear baffles are 1.75″ thick and the sides top and bottom are 1″ thick. Tapping/rapping on the cabinets with my knuckles provides a nice, dead, thump in response. So they sound very solid, very dead. Anyway, here’s the pictures, you may draw your own conclusions of the bracing design. Is it enough to do the trick?

Alright, enough talking, here’s all the pictures. Check them out below. And check out the video montage as well. Enjoy!

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