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.

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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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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 really 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 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 its effectiveness is more or less just dependent 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, so I’d have something scientific to back up my damping technique, 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 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 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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