A little over 2 years ago I was checking out my local Goodwill for any miscellaneous stereo/electronics/speakers (as one does on a Saturday morning) when I came across a pretty interesting find – 8 small carboard boxes with a familiar logo printed on the side – it said Dayton Audio. A closer look revealed 2 pairs of Dayton Audio Signature Series DA175 7″ aluminum cone woofers and 2 pairs of ND90 aluminum dish cone full-range midwoofers. I couldn’t believe what I was seeing. The boxes were opened but the drivers appeared to be brand new. And they were priced at only $6.99 and $3.99 each respectively. I immediately grabbed a cart and added the 8 boxes to it and headed to the checkout absolutely giddy with my find. For a total of $44 I basically had in my possession over $200 worth of brand new Dayton Audio drivers, for which at the time had no idea what I might do with them, but wasn’t about to pass up the opportunity to potentially make something great and do it for insanely cheap.
Fast forward 2 years and I have officially completed the Goodwill-inspired 4-way tower speakers that now adorn my small garage home theater. For nearly 2 years I tossed around almost every possible speaker combination I could come up with using these 8 drivers. Initially I was thinking of building two sperate types of speakers, like a Bluetooth speaker with the ND90s and maybe Zaph’s Bargain Aluminum MTM with the DA175s. Years ago I built a pair of speakers for my friend’s home theater using the DA175s and they were great speakers. But the more I thought about what do build with them, I just never could get over the fact these speakers need a pretty decent size box if you go the ported route. Going to a sealed box to remedy the size issue only brings about a major excursion issue above about 7 watts. So building a nice smaller 2-way or MTM just didn’t get me all that jazzed. And as far as the ND90s, I’m not too big on Bluetooth-based portable speaker systems in general. Parts Express sells some decent BT amp kits but I’ve got so many BT speakers lying around that just don’t really get used at all, so again I wasn’t super excited about that option either. So the speakers sat, month after month, with no plans in sight to every build them into the sweet speakers they deserved to be.
That’s when it sort of hit me one day to combine both sets of drivers into just one speaker design. It was an odd combo, the 7″ DA175 woofers and the 3.5″ ND90 full-range drivers, I thought there’s nothing I could possibly throw together where these two speakers would sound good together. Right? But I drafted up some concepts, taking into consideration the bass limitations of the DA175s and the lower efficiency of the ND90s and the upper frequency limitations (despite claiming to be full-range), I modeled up an WMTMW setup with a soft dome tweeter that I thought looked pretty good. I figured the ND90s would play great in just the midrange section and I could cross those to a nice soft dome in a 3-way setup. Add a sub and these could play great Left/Right duty in a home theater, with the receiver set to SMALL for the fronts. A potential design was coming together here, but it was still missing something.
Slowly that idea morphed into me deciding I really wanted a full-range tower speaker, something I could use in a 2-channel stereo setup without a sub. That’s when I added a pair of 8″ woofers to the design, making it effectively a 4-way speaker in a SSWMTMW (sub, sub, woofer, mid, tweeter, mid, woofer) configuration. After modeling up a bunch of different 8″ drivers from Parts Express, I settled on the DSA215-8 aluminum cone Designer Series woofers to act as the “sub” woofer in this 4-way monster. I liked that they matched the look of the DA175 speakers, they were offered in just a standard 8-ohm version so I could wire them in parallel for a final 4-ohm load (more power, easier crossover), they weren’t expensive, keeping in line with this being a budget speaker build, and they modeled great in a tower-sized cabinet that was exactly about the size I was shooting for. I drafted up some of the artwork you see here which helped give me an idea of exactly what this concoction of a speaker would look like. And you know what? I thought it looked awesome! You don’t see many commercial speakers in a configuration like this, but I knew it had the potential to sound amazing. For the tweeter I picked out the ND20FB-4 Rear-Mount 3/4″ Soft Dome Neodymium Tweeter. This ended up being an amazing tweeter for these speakers and was also pretty inexpensive. In the end, I think spent more on new crossover parts than anything else in this build. I was getting low on all my resistor/cap/inductor values from my last few passive speaker projects, so I stocked up on just about every value I thought I might need to build the massive crossovers for this 4-way speaker.
With the basic speaker configuration finally settled on, I played around in Passive Crossover Designer 8.0 (using the stock .frd and .zma files) to get an idea of what in the world the crossover for this thing would look like. Starting with 2nd order filters for all drivers, I came away with some candidate crossover frequencies that appeared to work. All the speakers would need is some attenuation to match the levels of the 8″ woofers after baffle step losses. So at least on paper, I knew I could get the response essentially flat from ~35 Hz to 20 kHz and I wouldn’t need any exotic notch filtering or any other overly complicated filter networks. Each driver was operating in what I would call its “sweet spot”, well below the cone break-up region but also above the bass region where the smaller drivers didn’t play as well either. The ND90s operate happily up to 10 kHz so cutting them off at a couple of kHz allowed the tweeter to pick up this critical region alone. And cutting off the DA175’s below 200 Hz prevented them from ever experiencing any over excursion. Also, limiting them to about 900 Hz, since they are in an MWTWM configuration and are over a foot apart from either, helped to minimize comb filtering effects, allowing the vertical off axis response of this speaker to be quite good despite the WMTMW configuration. Keeping the ND90s as close to together as possible and with a reasonably low crossover point also helps with improving the vertical off-axis response. Once I got the cabinets built I spent a good deal of time measuring all the drivers and ultimately designing the crossover real-time with REW, though PCD at least got me started in the right direction, especially when it came to picking a reasonable selection of part values from Parts Express. Inductors are not cheap, so I only bought what I thought I might use, and even then, I ended up purchasing iron-core inductors just to keep the cost down. Also purchased simple electrolytic caps for anything above about 20 uF. At 20 uF and below, they are all Dayton Poly caps.
Speaking of measuring and designing the crossover, I’m getting a little ahead of myself on this writeup. DIY speaker building has so many fun phases to it and I honestly enjoy each one so much, as each part of the design and build process carries its own challenges and rewards. Starting of with the concept phase (one of my favorites) just picking drivers, drawing up some pictures, pricing out options, I spend hours on Parts Express’s website downloading datasheets, running enclosure response simulations, trying ported, sealed, passive radiators, with EQ, without EQ, I mean I can do this for weeks, months, even years when I’m designing a new speaker. And it never gets old. It’s kind of funny because I go through my DIY Speaker folder on my computer and there’s at least 20 unfinished, un-built, half-baked speaker ideas that just never made it for every one speaker project that actually sees the light of day. If I had endless resources, money and time, I could easily build a new speaker every month and I would never tire of it. For now, I’m basically limited to about one speaker project every year, or if I’m lucky, I might squeak in two in a year, or more if it’s just simple “upgrade” project, like I’ve done a few of recently. Then there’s building the cabinet, cutting the wood, gluing it up, sanding it down, using every tool I own and spending weeks in the garage just making these bare wooden boxes. I’ve gotten more creative with some of my speakers and have been adding some real-wood veneers, or rather, plywood veneers like Birch. Wrapping plain MDF in some real wood suddenly makes the hobby go from what I did in High School to something a little more meaningful. Getting to use my flush trim bit on the router to get a perfect seam between the real wood and the MDF just feels so good. I spend a lot of time sanding and routering once I get the boxes built in preparation for my least favorite part of every speaker I’ve ever built – painting and staining. I settled on a process that works for me, which is spray painting the painted parts with a regular flat spray paint and then finishing the speaker with a Satin or semi-gloss polyacrylic. This water-based clear coat is the most forgiving of imperfections and leaves very few lines, but still has to be done right, or it can look really bad. I’ve gotten better over the years, but am by no means an expert. This goes well over an oil-based stain which is what I usually do if I’ve added a real-wood plywood to the sides. The stain goes on fine and is usually pretty forgiving of bad technique as long as you don’t put on too much, wipe the excess after each coat and do 3-4 coats until the desired darkness is reached. I’ve also found that using a pre-stain treatment on the wood before staining it works wonders for getting that even, clean, professional, stained look. It prevents that botchy look you can get with softer woods if not treated beforehand.
Which brings me to another favorite and basically the final part of the speaker building process, measuring and listening, and designing the crossovers. This also is one of the more frustrating parts of the design, because it’s so tedious. The endless tweaking of crossover values, pushing the response up and down, listening to music, gauging if it sounds better now with a 4.7 uF cap on the tweeter and a 4 ohm resistor or if it sounded better with the 5.6 uF cap and a 5.1 ohm resistor. But that’s just the start, with a 4-way speaker such as this, I had to decide where each speaker sounded best in terms of crossover point, summing with its neighbor, overall volume of each driver, figuring out which phase/polarity sounded best, especially when I started to venture into 18 dB/octave (3rd order) slopes, it was like, I can’t keep everything straight! Keeping good notes of every adjustment is key and of course, using REW with every measurement so that you an actually see how each crossover adjustment affects the response. I rely almost entirely on REW to get the response of each driver flat, and summing properly, before I start to listen to anything as part of the listening tests. I like to have the crossover basically where I want it visually before listening to anything. And then the listening part of things just allows me to dial in my own personal preferences such as the overall tonality of the speaker, which is influenced a lot by just how loud I allow each driver to play. Oddly enough with these speakers, those little ND90s were just screaming, despite them being the least efficient drivers of the group, I have a pretty decent sized resistor on them (3.3 ohms) just to keep them balanced between the tweeter and the DA175s. Anyway, last but not least in this magical DIY journey is the day the speakers are officially done and you get just sit back and put on some of your favorite music or watch a familiar scene in your favorite movie and just get to enjoy the creation that you and your little hands have put together. The months of design work, and then weekends in the garage cutting, gluing, painting and staining, to weeks behind a laptop screen staring at REW plots all day, to finally come out on the other side with something you can be truly proud of. And in some cases, something that is really one of a kind. And something you will enjoy for years, even decades to come, as I recently just turned the corner on 25 years of owning my Swans M3s, which I consider some of the nicest speakers I’ve ever built. I’m hoping that I get to enjoy these speakers for at least that long.