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 Vandersteen VR-5 speakers. It’s sort of a marriage of the two designs, taking the best of the aesthetics of both and incorporating them into one awesome speaker. The dimensions are 12-1/2″ at the bottom with a 7° slope on each side 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 at 14° to mimic the VR-5 and reduce the effects of edge diffraction. 1/4″ chamfers around all exterior edges finish off the cabinets 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. But it’s not just the looks, the dimensions, the angles, the top chamfer all serve a purpose, too. Read on to find out why. Or skip my mumbo jumbo ramblings and move on to the pictures at the bottom. Your choice.

How I came up with 14° sloped front baffle was by drafting up side views of the raw drivers in Delta CAD using the .pdfs from Parts Express’s website. Phase/time alignment is achieved by placing the acoustic centers of each speaker in the same vertical plane. It is generally believed that the acoustic center of a speaker sits roughly at or around the voice coil location. The exact acoustic center is much more difficult to ascertain, so we are simply going for a best approximation. 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 active (MiniDSP), I will have independent control over the time/alignment of the woofer and tweeter. But if someday I decide to re-purpose these speakers, I may design a passive crossover for them and in that case I’ll be all set with the speakers 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 dimensional design consideration is the 3″, 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 Watt doesn’t have it, so it is even necessary? The answer is both yes and no. Aesthetically, it completes the speaker, in my mind, it’s that final detail that just makes the speakers, 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 almost 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. Baffle edge diffraction occurs anywhere there is a discontinuity on a surface where sound is present. Wilson’s Watts combat this problem with a type of acoustic foam attached directly to the front baffle around the tweeter and woofers. This way the sound waves traveling across the front of the baffle are attenuated before they even get to the edge, therefore reducing the audible effects of edge diffraction by the listener. While in principle this works, it also looks ugly. Just my opinion though. 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, voice coil, materials, glues, 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 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 the microphone is still picking up in your measurement graph that you just can’t let go. But that’s not to say that some speaker designs 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 with their 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 design. So a designer must balance form with function. The complexity of the shape of the DM-4 Cabinets doesn’t lend itself to an easy edge diffraction model and Jeff’s tool doesn’t exactly allow the sloped sides or a single 3″, 14°chamfer across the top to be modeled. So I don’t have a good estimate going in how much these cosmetic changes will really alter or improve the sound. But I certainly intend on taking a whole bunch of measurements to find out. 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.

So to sum up there are three things with these speakers that help to reduce the effects of edge diffraction:

The first is flush-mounted drivers. Measured response plots can easily 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. The second design feature that is helping to reduce edge effects is the top 3″ chamfer which looks like a 118° corner (instead of 90°). This provides a smoother transition from the front baffle to the top baffle. This results in less disruption in the waves traveling over it. The last design feature that helps reduce edge diffraction is the 0.25″, 45° chamfer along every edge of the enclosure. This creates a similar effect to diffusing the edge and thus reducing the disruption of sound waves as they travel over/around it. Granted this contour is small, only 0.35″ across its surface, it is just enough to help smooth the frequency response of the most critical frequencies from the tweeter. Edge effects are a peculiar thing because at low frequencies, the wavelengths are so long that the edge does little to disrupt the wave since it represents such a small fraction of its total wavelength. But baffle step losses do occur for this very reason where the driver transitions from radiating from 2pi space to 4pi space. Edge diffraction effects sort of start to take over just above the 2pi frequency point but then decay again as the tweeter frequency increases so much that it begins to operate as a single point source radiating directly into the air without ever reflecting across the front baffle to the edges. So there’s this really critical area in all speaker designs that is roughly from only a few hundred Hz to upwards of 10 kHz where you must be concerned about both the baffle step losses and the edge diffraction effects of a speaker cabinet. That’s actually a lot of bandwidth if you think about it! You don’t want to screw this part up. Anyway….

The only other thing I didn’t go into was the bracing technique I used. I’ll save that for another post, but even the bracing has some intentional design behind it and isn’t random. Recently with some of by builds I’ve sort of adopted this design that starts with the bracing and enclosing a box around it, instead of building a box and adding bracing to it. The other thing I considered was doing enough bracing to push the fundamental panel resonance out of range of the woofer (>2 kHz) as much as was practical and to mimic the lower cabinet design. This box will have so much insulation (carpet pad, cotton fill, polyfil) so it shouldn’t make a whole lot of difference but I did have some concept going in to stiffen the sides/top/bottom panels as much as possible. 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, if you made it this far, I’m impressed. Now you may view pictures. Which is all you really wanted to see anyway. Check them out below. And check out the video montage as well. Enjoy!

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Damping Methods, First Listen and Measuring the DM-4 Speakers Part III

dampingdm4smallThe time has finally come! The moment when a speaker design has reached the stage where you finally get to install the drivers and have a listen to your masterpiece. I have to admit, I struggled through this middle phase of building these speakers. The part where I spent hours and hours tediously cutting strips of carpet pad, spray gluing them into the cabinets, only to repeat the process with another layer of carpet pad and glue, then two more layers of a cotton/poly (80/20) blend fabric (and glue) and finally another two layers of 100% polyester batting and once again, more spray glue. This whole job just stunk. My garage was HOT (middle of summer here in AZ) the glue was sticky, it got all over everything, including me and halfway through the process I realized the glue wasn’t holding and all the pieces were coming off! Complete nightmare. I remember the days when all I used to do was cut a big piece of fiberglass insulation and staple gun it the box and be done, 1/2 hour job, tops. (Okay, I did that just recently, but still).

So I don’t know what I was thinking when I decided to do this whole multi-layer-different-material-glue job catastrophe. It didn’t help that each panel in the speaker is so compartmentalized, what with all the bracing every 4″ to 8″. Every piece had to be measured and cut to fit a specific location and then repeated over and over again. It was so stinking time consuming and honestly I have no idea if it’s any better or any worse than just putting a big wad of fiberglass in there. For the sake of argument, I am just going to say that it is better. So much better than I am super excited to get to do it ALL OVER again when I build the upper cabinets for the midrange driver and tweeter. Yeah. The fun has just begun.

So enough bemoaning, I chose this hobby, it’s my own fault. The basic idea behind the damping method was to start off with a relatively dense material up against the MDF and progressively use lesser and lesser dense materials working my way outward (or inward?). The idea being that in order to absorb the most bandwidth, I would need multiple different types, or densities of materials. There is no one-size-fits-all when it comes to good broadband sound absorption. I started off with 2 layers of 6-lb carpet pad which makes up about a 3/4″ layer of sound absorption that I suspect does a good job in the low-to-mid frequency range. Next up I have the 80/20 cotton/poly fabric winch is also about 3/4″ thick. This was sort of an impulse buy at Walmart but I liked it because it felt denser than the 100% polyester but lighter than the carpet pad. A perfect “in-between” weight for those middle frequencies. I used two layers on all the sides except for the back panels which has 4 layers. And last in the stack-up is the famous and favorite, 100% polyester batting. This material probably works well over a fairly broad frequency range and really depends on how much you use. I lined what was left of the inside of the boxes with with another 2 layers (which looks more like 4 layers) of the polyester fill making up another 3/4″. So in total the walls are lined with this custom-fabricated, multi-layer, sound-absorbing compound that is 2.25″ thick and should have good overall acoustic properties. When you consider the wood in the mix, that’s another 1″ for a total of 3.25″ of sound-deadening, sound-absorbing action. The only thing you will hear coming from these speakers will be from the actual drivers themselves. That’s the hope anyway. It’s a concoction all right, but it’s my concoction and I like it. One day I will recreate each layer in a sounds booth or something and measure them independently just to see what it really does.

So along the way I did very unscientific sound checks with each new layer which consisted of me sticking my head in the box and singing different tones and simply listening for how much the boxes echoed or resonated. The boxes without any damping had a very apparent resonance in the mid-to-low vocal range. The lowest note I could sing, the boxes just resonated like crazy. Once completed however, the boxes felt very “dead” and had very little echo or resonance. In hind sight, I wish I had measured the cabinets throughout the process, but like I mentioned earlier, I hated this part enough already, add in the complexity of trying to take frequency and impedance plots along the way, I probably would have gone absolutely crazy. It seems like most people just take the trial-and-error approach to speaker damping anyway (me included) and so I fell victim to the same ploy, I guess, just out of shear laziness on my part. Sorry folks, but I will say this, this damping technique seems to have worked out perfectly in this 4th order cabinet to satisfy the requirement of “walls lined” and matching the corresponding Absorption (Qa) factor. To the best of my measurement ability, the measured frequency response and impedance plots line up very closely with the modeled performance. My plan is to carry this method into the upper mid/tweeter cabinet but instead of merely lining the walls, the entire cabinet will be filled with the 100% polyester batting in addition to the layers of carpet padding and cotton/poly blend fabric as previously defined. But since that enclosure will be sealed, and will have a high-pass active filter at around 300 Hz, I am really only looking for maximum sound absorption over a very broad frequency range and not too worried about over-damping or loss of bass response. So I am going to fill that cabinet up.

Okay, so now it’s time to drop in the drivers and the port and take some measurements! For now the only measurements I am going to show is nearfield FR and impedance plots. I have my entire setup in my garage and so room modes were apparent in all my measurements and I wasn’t in the mood to tear it all apart and re-build it outside in the backyard. That is coming, just not yet. My main thing for now was just to do a quick check on the damping and tune the boxes so everything is as close to modeled as I can get before I stain and paint the boxes and call them done. And of course just to give them a quick listen!

My measurement setup consists of an old laptop running REW 5.16, an ECM8000 microphone and stand, a Behringer 1202EQ Mixer (for phantom power) and a Denon AVR-1801 receiver (for the amp). This was the first time I had done actual impedance plots using REW and it worked out flawlessly. I love REW, it impresses me every time I use it! Thanks again to the guys who developed it for people like me. =) Impedance plots can serve several purposes: they show you box tuning, box damping, can reveal if there are leaks and of course, they show you the overall impedance vs. frequency of your speaker system. It’s more useful in that sense when combining multiple drivers and complex crossover networks, but even a simple 2-driver set-up it’s nice to see a solid 4 ohm impedance for two 8 ohm drivers in parallel.

So what I chose to do was deliberately cut the port long and take measurements with progressively shorter and short port lengths just to show how the port length affects FR and impedance. I didn’t really do any exhaustive listening tests since the speakers were being driven full-range (and yes, they sound terrible that way) and I was doing the measurements in my garage, which is not the final destination for these puppies. So as I mentioned earlier, the alignment I was shooting for in this design was a BE4 (Bessel) alignment according to Vance Dickason which should result in improved transient response (for a 4th order design) and has the lowest tuning of all the various alignment options. Which in a 78 liter enclosure is 32 Hz given the T/S parameters of the RS225P-8 drivers.

So what the plots show is that for every inch I cut off the port, the enclosure Fb increased by ~1 Hz. Enclosure Fb can be measured using the Impedance measurement tool in REW in addition to a 100 ohm resistor. Fb is located at the lowest point between each of the two largest impedance peaks. A more accurate way to measure Fb is to measure each peak, label them Fl and Fh and then seal or plug the port and measure the peak again can call if Fc. Then you can calculate Fb with the following equation: Fb = sqrt(Fl^2+Fh^2-Fc^2). So I made 4 measurements with the port length starting at 10″ and ending up at 7″. The tuning corresponded by starting at 29 Hz and ended up 32 Hz in these tests. This can be seen in the impedance plots below. I am happy with the 32 Hz tune for now. It represents the lowest tune that still fits within a classical alignment type and doesn’t give up too much in way of lower midbass extension. But it does not represent a flat response either, which would have needed to be tuned way up at 38 Hz with a modeled f3 of 43 Hz. That just wasn’t low enough for my liking especially considering how big these cabinets are. I’m a little disappointed that I won’t get extension into the 20’s. But that’s okay, because I already have a matching subwoofer in the plans to compliment this whole setup that will get me into the teens. So there’s no sense wasting that low frequency stuff on these little 8 inch speakers. Besides, I did get a change just to play some extremely bass heavy music (just to break in the drivers a little bit) and even with a 32 Hz tune, they can drop some extremely deep bass. At one point my entire garage was bumpin’. Of course, not the intent of these speakers, but they really sounded quite awesome.

So I ran a whole bunch of frequency response plots with the speaker in the corner and in the middle of the garage, with the garage door open, near-field, mid-field, far-field, near the top cone, near the bottom cone, near the port, etc. There’s a huge room mode at about 25.5 Hz, which showed up in all the plots. That calculates out to be exactly 1/2 wavelength at 22 feet – the distance wall-to-wall in my garage. So I left it as good enough for now and will wait to do the measurements outside once I finish the upper cabinets. The frequency plots looks very good though. They match up nicely with the predicted responses as modeled in Unibox. See the Excel screenshot above. Even the impedance plots look very good as well. The impedance peaks are a little higher in my enclosures which suggests I do not have quite as much damping as the model, but that only means I can easily go up from here and add more as needed. Besides, if I had to error on one side or the other, I’d rather be a little less damped and pick up some extra bass then to be overdamped and bass shy.

So that’s about it for now. The plan from here forward will be to start the upper cabinets for the mid and tweeter. I have finally finalized the design and am ready to start cutting wood! I’ve got the materials all ready to go, I just need a nice long weekend to get to it. Hmmm, wonder when that will be? I’m thinking probably Christmas. That way it’s cooler outside and my garage won’t be a sweat shop. Enjoy the photos until then! And of course the cheesy Google video montage.

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DM-4 Reference Loudspeakers Part II – Bottom Cabinets Nearing Completion

So it’s been a couple of weeks since my last post and I’ve made significant progress on the ‘ole speaker project. I figured it was time to do a quick write-up and post some more pictures. Last I left off I had completed 5 of six sides and left all of the internal bracing exposed. The plan for damping is still in work as well as figuring out some means of measuring the enclosures in stages with progressive amounts of damping with different materials in different quantities until I achieve what I would call “reasonable expectations” with regard to resonances. Or in other words, I want to get the structural and acoustic damping “just right”, and only my ears and some measurement equipment is going to be able help me get there. Which means the speaker enclosures needed to be done so I can get to point of dropping in the speakers and taking some measurements. Besides, I still haven’t come up with the perfect combination of glue/foam/carpet pad/cotton/egg crate/wool/polyfil to dampen these puppies just right.

So I left off with the second back panel, main front panel and one side incomplete. So I glued and screwed on the second side to each speaker. I then installed the back panel which is glued to the oval-patterned frame/brace which makes the back panel 1.5″ thick but not throughout the entire panel. This stiffens it without adding too much additional mass and buys me over 1 liter of extra internal volume. And I need every liter I can get in these puppies!

The front panel went on next and was measured with a makeshift compass (nail, envelope from Ace and a pencil) and cut with a jigsaw to mount each 8″ Dayton driver and the 7″ port. The driver opening is oversized by 1/16″ of an inch to allow some wiggle room for each driver. The backside of each opening was routered with a 1/2″ round-over bit to provide breathing room for the back/rear of the driver into the cabinet. Note that the internal panel, or the first main front panel, the opening was oversized by 1″ which leaves even more breathing room for the rear of the driver. The front panel is now 1.5″ thick with a pair of 2″x3/4″ cross braces between the drivers and between the lower driver and port. The cross braces also connect to the sides as well as the first window brace internal to the cabinet. The idea here being the more braces that are structurally tied to one another, the better damped the braces will behave, and therefore the entire enclosure. Doing a simple knuckle tap test reveals just that, this sucker it well braced and solid! But it still sings like a canary since nothing is actually damped, yet.

At this point I am basically done with the 3/4″ MDF (except for the 2nd bottom piece which will go on last) and the boxes look awesome but they also look terrible! Screws and holes and glue are everywhere. There’s no way I’m going to try and putty and polish this thing up to paint it. It just wouldn’t be worth my time. So instead I did my old trick of using sheets of 1/4″ MDF panels to “finish” the speaker cabinet. The 1/4″ front panel provides the exact depth required to flush mount each driver. Then a piece on the top and back provide a super-nice and even finish which I will ultimately be able to sand and paint to a beautiful semi-shine. All those crummy MDF edges and screws get covered up in one shot. The 1/4″ MDF plus the 3/4″ MDF means the top is now 1″ thick and the front and back panels are 1.75″ thick. The enclosure is getting stiffer and not to mention heavier!

So while I was considering installing all these 1/4″ MDF panels, I decided I didn’t want a uniform finish on all six sides of this speaker. I didn’t want just an all-black speaker and I didn’t want to to have to try and paint the entire speaker and make it look perfect, because I knew I would not succeed. So the idea came to me to use a real-wood veneer for just the sides of the speakers and then do the other 3 faces in the 1/4″ MDF. This is a design scheme that I’ve grown rather fond and I’ve done it on several speakers I’ve built in the past. The real wood stained combined with a nice semi-gloss black should look awesome together. Plus I can stain slightly better than I can paint, or at least staining seems to be more forgiving for me. So if I can get the stained sides to look great, then all I really need to get perfect is the front and the top. I think I can handle that.

I picked up two 4’x4’sheets of 0.20″ (1/4″) Birch plywood from Lowe’s. I rummaged through the only 8 pieces they had and picked two that had some nice, unique natural wood grain patterns that I thought would look cool. I cut each piece to fit the sides of each enclosure and oversized each piece by 1/8″. Each piece was glued to the cabinet wall using Liquid Nails. I applied pressure via my own body weight to press the Birch into the glue as much as possible. Once it was well seated, I popped in a some 1″, 18 gauge brads into each corner to prevent the panel from drifting, flipped it over and did the other side. Then I did the other speaker and stacked them on top of each other. I added two really old speakers I use in the garage for music along with 240 pounds worth of QuickSet concrete bags. One of which got wet from the rain and is literally a block of concrete. This was just enough to keep some even pressure on the entire surface of the 4 newly glued pieces of Birch plywood. I let that dry for 24 hours before tearing my tower down.

This is the point where I added the 1/4″ MDF to the front, top and back. The front baffle was cut using a Jasper Circle Jig from Parts Express. This tool is awesome! Since this is a visible cut, I didn’t want to use my jigsaw, I needed that cut to be a perfect circle. With 1/16″ increments, I made some practice cuts to pre-fit how much gap I wanted between the edge of the frame of the drivers and the edge of the baffle. One size was too big, so I dropped it down, then it was too small, so I picked a spot right in the middle. Perfect fit! The overall size ended up being 0.031″ larger than than driver (or ~1/32″) which leaves about a 0.015 inch gap all the way around the driver. This gives me some wiggle room to fit the driver as well as some room to grow from paint. You can see from the pics though, the fit is perfect, if anything I went too small and drivers won’t fit after I paint them. I am going to have to be careful and watch that inner diameter. I may even need to mask it off after a certain number of coats to keep it from being undersized when I’m done.

Anyway, I used liquid nails again on all the 1/4″ pieces mainly because the viscosity of Liquid Nails is so much thicker than wood glue that I have a much better chance of controlling the squeeze out. The reason this is so important at this stage is because both of the enclosure sides have that beautiful Birch ply finish which does not take kindly to a smattering of runny wood glue. Since it’s only Birch ply, the actual Birch is extremely thin and doesn’t give me much option to sand down/away any place that the wood glue would have touched. With the Liquid Nails I can ensure that the Birch is untouched while the other panels are being glued in place. Even then I still covered the Birch with 2″ blue painters tape, just in case. The old speakers and 240 pounds of concrete sat on top of the speakers for another 24 hours while all the 1/4″ panels dried in place. Again, the 1″ brads held the panels in place to keep them from walking while it was drying.

So now that all the panels are installed and dry (and they aren’t coming off), since I had oversized all the pieces, I needed to use my router to trim each piece flush to each side. This was accomplished using a 1/4″ flush bit and a router. I took the router to each side and zipped along its edge at just the right depth so as to only trim the MDF without touching the Birch. Once complete, this left a perfectly flush edge on each side of the speaker from the MDF to the birch and the MDF to the MDF (front-to-top-to-back). Oh yeah, I had done this already to the Birch plywood before installing the 1/4″ MDF since it was also oversized when installed. That was made near-flush to the 3/4″ MDF leaving some room to account for the thickness of the Liquid Nails (about 0.015″).

I am almost done at this point but there’s one more finishing cosmetic touch to add, and that’s the 1/4″ 45° chamfer on all the 1/4″ edges. This look, I have to admit, I borrowed from the VR-5’s but it really does give the speakers just a little bit of extra class, something notable, something different, that overall fits the look and style of this speaker perfectly. I will still have to seal this edge, since it’s just MDF, but having that angle to it on each side meat at a point at each of the four corners just looks so cool. Totally subjective sure, but for the cost of a 45° chamfer router bit and the 20 minutes it took to router it, in my mind, it was well worth it. From a baffle edge diffraction perspective, a roundover would have had less diffraction than the 45° chamfer but it’s still better than a 90° edge. And in practice to get any significant benefit or reduction in edge diffraction, the roundover needs to be quite large which in my opinion ruins the aesthetic of the speaker. Arguably the upper frequency limit of these cabinets will neither benefit nor suffer from edge diffraction effects but I intend on carrying this design into the upper enclosures which will run all the way to 20 kHz. So it’s at least important to keep it in mind. The overall shape of the upper cabinet should help with diffraction effects anyway, but I’m getting off topic.

So with that, that’s about it, I’ve reached by 1000+ word limit so it’s time to just put up the rest of the pics and let them tell the rest of the story. Enjoy!

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The DM-4 Active Reference Series Speaker Project Has Begun!

20160403_102731I have officially broken ground, or cut wood, as the case may be, on my latest and greatest speaker project – The DM-4 Active Reference Series Loudspeaker. This is one of those projects that has been in the back of my mind for what seems like forever that is finally coming to fruition. I wrote a lot of the history and background over on my website Audio Innovation (which is dedicated to all of my speaker projects) so I won’t go into it again here. But I find it much easier to do write-ups and post pictures in WordPress than trying to do it on my old-school web site (which I still use Frontpage to create!) So to document some of the build process, I am going to post pics and details here out of simplicity (laziness) on my part.

So this will be Part I of the DM-4 Active Reference Series Loudspeaker build write-up and pictures blog. As I get further and further along I will continue to update this site with pictures and descriptions of how the build is coming along. I expect this build to be a work in progress and to extend over the course of the next few months. The goal would be to complete this project by Christmas time this year (2016). I’ve waited this long to start this project, I might as well take my time actually putting it together.

So yes, if you haven’t noticed, the inspiration for this design stems from two fairly popular high-end commercial speakers – the Von Schweikert VR-5 and The Watt/Puppy by Wilson Audio. So read my introduction over at Audio Innovation if you’re curious as to why I would attempt to build a pair of speakers based on these $$$ speakers, call it nostalgia, call it crazy, call if whatever you like, but this is the base design I’m shooting for with plenty of my own DIY throw into the mix. So with that, let’s get onto the build pics!

I’ll try to keep the narrative to a minimum and let the pictures do most of the talking. I’ve CAD’d up the design using DeltaCAD (which is a great tool for drafting speakers, or any other project for that matter) as well as I just sketched up some drawings on paper of what the speakers will look like (my kids think the only thing I know how to draw are speakers). I’ve only cut wood so far on the lower cabinet. I’m still tweaking some of the design/dimensions on the upper cabinet as well as drafting up the cut sheet. So far now I have just got the lower cabinet started.

cad-drawing-1Each cabinet measures 12″W x 30″H x 21″D and is made from 3/4″ MDF with extensive window and cross bracing. Front and rear baffles are double-stacked 3/4″ MDF with an additional 1/4″ MDF baffle board for flush mounting the drivers. Total expected volume will be 75L-80L for both drivers. Tuning frequency will be between 32 and 39 Hz using a Precision 4″ flared port from Parts Express. Volume and tuning was initially modeled using Unibox 4.08. This design represents nearly a perfectly aligned “Standard Tuning” enclosure with minimal fill and minimal leaks. I picked up my old copy of Vance Dickason’s Loudspeaker Design Cookbook and calculated some different 4th order alignments given the formulas in his book. Unibox doesn’t assign an alignment descriptor such as the ones that Dickason described. I guess the assumption is that since you can plot the desired response you don’t need to design to any of the traditional filter types since the possibilities are infinite. I’m not even sure any of the modern tools really mention filter type/alignments anymore. So I calculated three other classic alignments, the SBB4, QB3 and a BE4 (Bessel) and put those values into Unibox so I could plot them and see how they compare. Note that Parts Express also recommends a volume based on BassBox 6 Pro which appears to align somewhat with a SBB4 or a QB3 alignment but they don’t tell you what to tune the box to. Telling us f3 does us little good, without fb one cannot know what the correct tuning is suppose to be, which the the most important part of a 4th order vented design! Anyway, I may shoot for the BE4 alignment, for two drivers the enclosure is 77 L with a tuning of 32 Hz. It’s got a gentler slope than the Standard Alignment or the SBB4/QB3 alignments which should result in improve transient response, according to Dickason. Using the Step Response function in Unibox confirms this theory to some degree though the difference is marginal.

DSC_4908The drivers that will compliment these cabinets are a pair of Parts Express 8″ Reference Paper Series woofers which were recently released (2015). I haven’t seen too many builds with these speakers but when they first came out, I knew they would make a perfect driver for my VR-5/Puppy clone lower cabinet. Besides, they model well in the enclosure size I was shooting for. They have a matched set of 7″ drivers for the midrange plus that great Dayton Audio 1-1/8″ dome tweeter. All around, I thought this would make a great Dayton Audio-based speaker system.

Just some quick notes about the cabinets so far – the design intent for the cabinet is to increase/maximize stiffness while reducing mass, i.e., maximizing internal volume – light but stiff panels to increase the resonance frequency of each panel with the objective being zero audible panel vibration within the passband (and beyond) of the two drivers. There is a lot to read about the subject, as I have learned, and as it would seem there’s more than one way to brace a box from the overkill to the simplistic to the complex to the, how the heck did they do that? After reading all about calculating panel resonances in MDF, I had originally set out to design the perfect balance of bracing, stiffness, volume and mass using straight up science (as in, math) but later bored with the all the numbers and figures and decided to just wing it – as I think most DIY’ers do. But all is not lost, even though the project is already underway, it’s still fun to figure out just what I’ve got and perhaps I can tweak the bracing if I haven’t already over-engineered it. I have found some great tools online that I have been playing around with, LISA being one of them (www.lisafea.com) which is a FREE Finite Element Analysis modeling tool for up to 1300 nodes. This program is so cool! I’ll go into the details another time, but so far I am able to model and show animations of the panel modes and calculate the frequency of several modes. It’s pretty slick.

2unbracedpanelmode1Anyway, so what I have come up with is both simple to cut, easy to build and should provide the largest panel surface area of no more than about 20-25 sq.in. before being constrained by either a 2″x3/4″ brace, a full 3/4″ cross brace or a panel edge. So let’s break this down (before we get into the real FEA portion), if you take the largest surface area on this speaker box, the sides, you end up with a panel that is 630 square inches. Without any bracing, worst-case scenario, this panel is held, supported, constrained, fixed or “bound” on a total of 4 sides. This panel will have a fundamental resonance of, let’s just call it fs (which is a function of Young’s Modulus, Poission’s Ratio and the density of MDF). This will be the main mode, or the 1st mode (and in most cases will follow a classic drum mode), with the center of the panel flexing in and out at fs with an amplitude of z. There will be other modes, higher order modes, 2nd, 3rd and 4th and so-on, but with each higher-order mode, the frequency increases and the z amplitude decreases for the same input energy. So emphasis can be placed on killing the first couple of modes with all other higher-order modes improving respectively as bracing is added and stiffness is increased. It should be noted that the z axis motion, or amplitude of the resonance corresponds to damping. Increased damping results in the decrease of the amplitude of the resonance and does not move or change the frequency of resonance. Both concepts have real implications in speaker enclosure design and both principles need to be considered when shooting for a “solid” speaker enclosure. My plan was to shoot for optimizing (increasing fs and stiffening) panel resonance modes first and then attacking damping second. Lastly is to consider internal cabinet fill material which serves a much different purpose than the aforementioned techniques. That requires a blog for another day (as well as the FEA models which I’m cooking up using LISA).

In fact, this entire post deserves another post for another day. So let’s just get to the pics and I’ll stop talking for now. Enjoy!

The following week I accomplished a little bit more. They are starting to really take shape now! Also the upper cabinet design is getting a few bracing tweaks.

Here’s a video montage of the above picture gallery and some short video clips just for fun.

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Weekend Project: Two-way Bookshelf Speakers with Spunk

Mini J Two-Ways (42)We listen to a lot of music in my family, there are a vast array of speakers and stereos and mp3 players in this house. Whether on the go, in the car, or relaxing at home, there’s always a song playing somewhere. As my oldest daughter’s birthday was approaching, I decided I wanted to build her a small pair of bookshelf speakers for her room. Something that she could enjoy for many years to come. Something that was made by Dad just for her.

And so I present the “Mini J” two-way bookshelf speaker system. This speaker starts with a Dayton Audio Designer Series 5″ woofer and a 1″ Vifa soft dome tweeter. The DS series woofers from PE represent an excellent value, have a great look, and surprising bass response for a driver this small. Decent Xmax and a low fs make this little driver perform very well in a small cabinet size. The great upper frequency extension make crossing over to almost any tweeter a walk in the park. And for the tweeter I picked the Vifa DX25TG59-04 which has great power handling, low fs, and a smooth, flat response out to 20 kHz. It’s got a wide-roll surround around the dome and just has a great overall look to it. Besides, I’m a big fan of Vifa drivers and have been using them for many years.

miniJcadAfter picking the drivers I started with the cabinet design. I drew up some initial plans and started tweaking the cabinet volume and shape until I came up with something I really liked. I used Unibox to model the speaker response and ended up going with the Standard Design model which yields an f3 of 59 Hz in a 5.4L cabinet tuned to 56 Hz with no hump or dip in the response. This requires an enclosure size of 11.25x7x9 (HxWxD) using a mixed panel thickness of 1/4″, 1/2″ and 3/4″ MDF. Parts Express had also recommended a similar enclosure volume but they also recommended specific dimensions that meet what’s called the Golden Ratio. So I gave it a shot and I intentionally made the height and width conform to this Golden Ratio which is 1.618:1. There’s some great reading about the Golden Ratio over on Wikipedia if you’re interesting in killing a few more minutes. Aesthetically the most pleasing rectangular shape to look at and quite possibly exhibits superior sonic properties than other ratios. Hey, but I won’y get into that here. They look great to me and they sound fantastic too, but now I’m getting ahead of myself.

With the cabinet design complete, I moved onto the crossover design. I love the Designer Series drivers from PE because they provide FR and ZMA data for easy import into crossover designing tools such as Passive Crossover Designer. While the Vifa tweeter did not have raw data, I still made good use of SPL Trace to create data from the datasheet by tracing the FR and ZMA plots into data I can actually use. I don’t know why ALL driver manufacturers don’t provide this type of data. A picture of a plot in a .pdf file is hardly enough for doing any kind of real crossover design. You could argue that the manufacturer raw data isn’t exactly ideal either, but it’s a start.

summedresponsemodeledI’ll try and be brief on the crossover design and my methods of doing crossover design because quite frankly it’s just that, my method, and I’m still tweaking and proving my method with each new speaker design. I’m not sure I’m there yet, but this is actually a big part of the fun of speaker building. I always shoot for the simplest crossover with the fewest elements to achieve the flattest FR and a decent impedance. I typically add a Zobel network to the woofer to flatten the impedance above fs which helps with the high-frequency roll-off. The woofer is a 12dB/octave set at about 2,700 Hz with a cap value that is about double the textbook design value. This provides a sharper roll-off without peaking just before cutoff. The tweeter also ended up being a 12 dB/octave but wired in phase with the woofer. The inductor in this case is also slightly tweaked to be lower than the textbook value which also increases the slope slightly and according to the simulation blends/sums well with the woofer on-axis. I also added a 4 ohm series resistor and a 20 ohm shunt resistor (aka L-pad) to pad the tweeter and match the overall level of the woofer. It also brings my impedance of the system up to around 8 ohms which is where I wanted it for an easy load to even the cheapest amps.

crossoverimageNow that I had some crossover values assigned I started putting parts in my cart at Parts Express. Another fun part about building speakers, getting to buy everything. Since the crossover design at this point was just a model, I do like to buy multiple different values of capacitors and resistors so I can tweak things in a listening environment. I didn’t buy a bunch of different value inductors because they are quite expensive and I just hoped that my simulation was close enough to allow me to only tweak the caps once I got closer to being done. Caps are cheap, especially electrolytics, so I bought every value from 3.3uF all the way up to 15 uF which would allow me several tuning options on both the woofer and the tweeter and the zobel network. I also bought several values of resistors so I could adjust the tweeter level as needed. One day I would like to have every standard value inductor/cap/resistor just so I can have the ultimate freedom to tweak but that project will have to wait for another day.

I was just about ready to cut wood at this point, so I drew up a cut sheet and got started. The cutsheet in this case is a little unique. The box design consists of (3) panels of 3/4″ MDF that make up the front, brace and back each piece being 6″x10.25″. The sides and top and made up of 1/2″ MDF which are cut at 8.75″x10.25″ (sides) and 8.75″x7″ (top/bottom). These cuts were a breeze on my table saw and were designed this way so as to allow the table saw to be set to each dimension only once and every cut made so that every cut that is dependent on a flush fit when assembled is exactly the same size, even if the saw isn’t cutting each piece at exactly the width it should. It doesn’t matter because all the pieces that fit together that require that dimension just end up being the same. The only cut that matters is the width of the top and bottom pieces which need to be cut to whatever the width of the front/brace/back ended up being +1.0″. With a table saw, every cut comes out near perfect anyway but even if they didn’t, this design allows for a little slop in each cut while still providing a perfectly flush fit.

Anyway, I cut the wood, built the boxes, sanded the boxes, painted the boxes, built the crossovers, tweaked the crossovers, measured the responses, installed the drivers, added some polyfill the port and the terminal cup and alas I was finally done. And just in time for my daughter’s birthday the next day. I was able to whip these out in only 4 days mainly just working a few hours each night after the kids had gone to bed. So they are a super easy project but were a lot of fun to design and build and they sound absolutely fantastic. I like the fact that I could tailor the sound a little knowing what type of music will be played on these speakers. While they don’t have a lot of low-end presence, they make up for it with a smooth, solid-sounding midrange and treble. I’m not all about that bass (no treble) and can appreciate a speaker’s ability to produce vocals without coloration. The boxes are rock solid too, very little resonances despite the 1/2″ MDF. But enough fluff, here’s the meat and potatoes. Click here for a parts list from Parts Express. Check out some of the build pics below as well as pics of the final product. Hope you enjoy!

Finally, scroll past the pictures for in-room measurements and near-field plots of various crossover options and L-pad values I had considered. In the end, I chose what “sounded best” to me regardless of what the plots actually looked like.

So with most speaker projects just getting that first listen is an awesome feeling. These speakers definitely sound great. Good balance between the woofer and the tweeter and they have a really good soundstage, so music doesn’t sound like it’s just coming straight out of these two drivers. You close your eyes and listen and you can’t really tell where the speakers are located. The music just fills the room in front and behind. And I love that. No harshness out of the tweeter either. You can put your ear right up to it and it sounds clean and smooth. So here’s some FR plots. I don’t try and read too much into every little bump and valley, I’m mainly looking for an overall balanced sound. The slight dip near the crossover freq is mainly due to the close proximity of the microphone in between the drivers which actually shows up in the PCD model as you move the listening position closer to the speaker. I suppose if I had a little more time and a few extra cap/inductor values on-hand I may have tried achieving a slightly flatter response, as I am sure it is achievable, but for now I’m going to call it good enough and overall I am happy with the results.

The last thing I did was take my measurement gear outside and ran some FR plots in basically a near-anechoic environment. I took a bunch of measurements at several different distances with both the tweeter wired in-phase and wired out of phase (meaning + to + and – to – on both woofer and tweeter) therefore actually making the speakers acoustically out of phase due to the 12 dB/crossover yet quite possibly back in phase due to the delta in physical relationship between the acoustic centers of the woofer and the tweeter. Confused yet? These plots at least tell me that everything is summing properly on-axis which yields the flattest FR. Notice that these speakers do not have baffle step compensation as is evidenced in the plots below. I decided not to incorporate it since these speakers will almost always be backed against a wall in a very small space, I didn’t want the bass and lower-midrange region to be too aggressive. You can see from all the measurements, in-room included, that there is a definite rise in amplitude between 500-700 Hz. John Murphy of True Audio came up with a quick formula for approximating the -3 dB point given the baffle diameter (or width) which is f3 = 380/W where W is the width of the baffle in feet. These speakers are 7″ wide, or 0.588 feet which amounts to a -3 dB frequency equal to 655 Hz. That matches well with the measured data shown here. Even without BSC, the speakers sound fantastic in-room, but if I were to implement it, I wouldn’t do more than 3 dB and I would shoot for a corner of about 655 Hz.

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