A little background first: I’ve been actively involved in the audio community for quite some time, and have built many, many speakers and subwoofers. Full range, multi-way, front loaded horns, rear loaded horns, transmission lines, open baffles, isobaric, you name it. I don’t believe in fancy cables or mystical noise filters, just sound engineering along with repeated listening and measurements. The purpose of this instructable is to demonstrate a different way to build subwoofers, which has become my absolute favorite method for low frequency reproduction: the tapped horn.

The tapped horn is a relatively obscure subwoofer arrangement, only recently brought to prominence by Tom Danley. A tapped horn is unlike other horns, in that it uses the radiation from both the front and rear of the driver, and combines them at the mouth. This allows for many possibilities, including greater efficiency, smaller enclosure size, and deeper extension. One of the greatest benefits a tapped horn exhibits over other arrangements is lower excursion (the distance a woofer moves from rest). Because of the acoustic load placed on the driver, excursion is reduced, leading to increased maximum SPL and lower distortion.

My goal of this instructable was to build a versatile, affordable, small, and high performance tapped horn that someone with reasonable woodworking skills could assemble. Don’t just think of this as another common sealed or bandpass subwoofer tutorial, this is a much different realm, and is also significantly harder to build. It utilizes two 8 inch MCM 55-2421 drivers, which cost $28 each, and perform at a level of drivers costing magnitudes more. Add a sheet of plywood and few bits of hardware, and you have an excellent tapped horn subwoofer for $120. How much would a tapped horn cost commercially? Well, the most affordable tapped horn sub I know of is the TH-Mini, which runs about $1300 per piece. For less than 1/10th the price, you can see what all the fuss is about. Now, without further delay, let’s make some sawdust!

What would I do with a Shopbot? Tom Danley had hinted at offering a kit for a multiway tapped horn speaker, but because of limitations with time and a focus on the professional market, it is something that will not happen. However, he was very supportive of the idea, and offered to license the technology to a third party if they wanted to tackle it. If I were to get a Shopbot, I would pursue a licensing agreement with Danley Sound Labs to provide these kits at a very low price. It would be my way of giving back to the community for a Shopbot that I didn’t have to pay for. A Shopbot can precisely cut the complex angles and provide the precise alignment that is necessary for such an undertaking, not to mention do it at a rate that would allow production costs to be kept very low.

Step 1: Designing the Horn

I designed this tapped horn using three different programs: Hornresp (horn response), AkAbak, and Sketchup. All are free, but all have a learning curve, some of which are steeper than others. I won’t go into how to use these programs, as there are tutorials online if you are interested. If you haven't worked with speakers in the past, you will have to spend some time educating yourself on the various parameters and meanings. If you need any help, or want guidance on where to find info on using HornResp or AkAbak, feel free to ask questions in the comments section!

The arrangement of the driver is roughly similar to the TH-Mini, which has the driver on the bottom of the cabinet firing down into the throat. I designed mine in a similar fashion, as it works well in a cabinet this small. I’ve attached my Hornresp input file, as well as the Sketchup file with a 3D model. The cabinet is approximately 30”x30”x10”, but the 10” width can be increased to smooth out the response if materials and space allow. Please note that I did not follow the model I made in hornresp exactly. I changed the flare at the end to use as much space/wood as possible. The predicted response won't be far off, subtle changes so far down the horn have little effect.

When using a tapped horn, one has to be very careful about low frequencies that are out of the pass band, as excursion rapidly increases. An active high pass filter is what I generally use, but a passive high pass filter would work just as well. I'll explain later this in greater details later.
<p>Hello. Excellent guide. I will definitely tackle this as a project to get started in the world of tapped horns. Can you please tell me if this particular driver is well suited for use in a tapped horn enclosure? Once I get more confident, I would like to experiment to see how small I can make one of these things while still achieving low frequency extension. </p><p>Aurum Cantus AC-130MKII</p><p><a href="https://www.parts-express.com/aurum-cantus-ac-130mkii-5-1-4-carbon-fiber-kevlar-woofer--296-404" rel="nofollow">https://www.parts-express.com/aurum-cantus-ac-130m...</a></p>
<p>wil it works with 2 8inch philips subwoofers 120watt</p>
<p>Is anyone able to help with the wiring of the drivers - particularly the positioning of the capacitors and inductors if the drivers are wired in parallel. I'm trying to work this out from stuff on the net and it is doing my head in! I can't even work out where to just buy a unit from... aarrgg!</p>
<p>If you're wiring in parallel; both positive and negative hooked together to share the same output, here is a simple diagram... </p><p><a href="http://www.diyaudioandvideo.com/Tables/ButterworthCrossover/2ndOrder/" rel="nofollow">http://www.diyaudioandvideo.com/Tables/Butterworth...</a></p><p>L1 is the coil and C1 is the cap. You're following the LOW PASS filter, 12dB.</p>
Many times I thought build something like this, but always left it for later. I think it's very interesting design. <br><br>I wonder if it would be a good idea rounding the edges inward, to facilitate the &quot;flow&quot; of sound. It is to say, to put a quarter of PVC tube in the interior of the angle joints.
At the long wavelengths involved, it really doesn't matter. When I built my first few horn speakers, I made angled pieces to fit the corners, thinking it would help. The only differences I noticed I attributed to the bracing these pieces provided. When building larger horns, I'll use any extra wood for bracing instead of angled corners. It certainly looks nice though!
well, even with lower frequencies you still might get diffraction and reflections from the momentum of air through the guide, this is often described in both transmission line and horn loaded sub's and speakers though you are correct in that higher frequencies need it more since they are more directional and are affected by reflections more easily.
Is this a variation of a &quot;Folded Horn&quot; design? or the same only named differently? I have made several folded horns, home, car, and other applications.... Great 'Ible btw.
usually a folded horn refers to a sealed enclosure with an extended, typically &quot;folded&quot; horn to act as a waveguide to extend frequency response and improve loading and acoustic impedance matching. Though I've never built one, I believe bill fitzmaurices designs are based on folded horns. in addition, there are back loaded horns with the front of the driver radiating into the listening area (often used to increase the frequency response of full rangers in older vintage designs) and the tapped horn like this one which combines both front and back loading with the waveguide effect of the horn as well and frequency reinforcement from the length of the line. There's a lot to learn about the different designs and sometimes youll find a few designs that overlap a couple different categories of horns or enclosures.
<p>Hello,</p><p>would it be possible to get a drawing with sizing? Especially the first angle would be interesting...</p><p>Or am I just stupid not to see it?</p><p>Thanks for your help</p>
<p>HI,</p><p>Thanks for this material. I am planning to build this soon and I have few questions</p><p>1. Can I use the same dimension for a single 15&quot; sub?</p><p>2. Is there any other material that I can replace with plywood to reduce the totwl weight.</p><p>My plan is to use this sub for mobile parties where i will be carrying this in my bike.</p><p>Thanks again</p>
<p>I am no speaker builder and I don't know a ton about horn design, but I think I know more than you. I would say:</p><p>1. Probably not. A lot of math goes into designed the size and shape of these boxes, and they are calculated based on the driver size. A single 15&quot; driver would probably request at least a different size, and maybe shape too.</p><p>2. Plywood? I don't know of any horn subs that people are building out of plywood. Maybe you could, but your sound would probably suffer. Use MDF if you want to go cheaper, but that will drastically increase your weight. If you are worried about weight, you shouldn't be building a tapped horn sub at all, and you definitely should not be carrying this on your bike. </p><p>I've been using this sub in my home for a year and a half, built almost entirely to spec by a horn builder in Boulder, CO, and I love it. The only thing different that he did was use a more durable, harder wood, actually salvaged from an old desk. I don't know what kind of wood it is, but the sub is very heavy and rock-solid. </p><p>I am using probably the same plate amp that one of the users below posted. It sounds great, especially in a small to medium-sized room. Definitely do not use this in a large room. Even for a medium sized too, I would probably recommend two of these, or perhaps a different sub. One of the more difficult things with this sub has been playing with the placement. It truly sounds best corner-loaded. However, I have found that it does not sound that great simply in a corner firing out. It is a very &quot;directional&quot; sub, and you loose a lot of the bass if you are not standing right in front of it. Best to fire it directly into the corner of a room (either right at the corner or at a right angle to one of the corner walls, which is what I am currently doing, just a few inches from the wall). This way, the bass expands around the room to fill the entire room. If you are doing this, and also because it is a folded horn, you will want to incorporate delay into your speaker tops, as the bass frequencies will be exiting the mouth of the horn after the high frequencies exit the tops. I use a Behringer external PA crossover (CX-3400) and crossover at about 180 Hz. Really sucks that the plate amp doesn't have a crossover built in, but oh well. The CX-3400 gives me a lot more control with other things too.</p>
<p>I am not able to edit my post. Sorry for the spelling mistakes. </p><p>After thinking more about it, one of these in a medium-sized room in a home would probably be fine. I should mention that I am a deep house &amp; techno DJ, so I play a lot of bass music. Heavy bass in the 30-40 Hz range is very important to me, and this sub does an excellent job at handling that. However, like I said before, playing my music in a slightly large room with this subwoofer would not suffice. I would need two of these probably. But if you play a lot of jazz, rock, or other music with significantly less bass, that would probably afford you more wiggle room with this sub. </p><p>Other notes: including about $100 labor for someone to build it for me, the sub probably cost me about $250 (not including the amp). Pretty great price for what you get. As you can see in the photo, I built it with parties in mind. I wanted it to be durable, portable (handles), and protected. I realized after two parties in my medium-sized basement space that this sub was not intended for that. It could not handle high SPL deep bass at a loud party. I blew one of the drivers after the second party I think, which was really not a big deal at all, because a new driver was about $30 and not difficult to install. For home listening, this thing is great. For PA applications, go with horn subs built for that. We are currently using Bill Fitzmaurice PA speakers. Specifically Titan 48 subs with DR280 tops. </p>
<p>I'd love to try building one of these, but know nothing about speaker design, so looking for a &quot;cookbook&quot;. If I learn a bit more about sketchup, can Iread off it the exact position of the internal baffles? (or are they somewhere in this article, and I am just not seeing them?</p><p>thanks!</p>
<p>I just built this sub with two 8 ohm Rockford Fosgate Punch 8's I used to use in my truck and a 250 watt plate amp. The results are excellent given the scale of the drivers and the high impedance. The scale is a bit obtrusive, but I've committed our family to hi-fi at all costs so they don't seem to mind the furniture being functional.</p><p>I'm still tweaking the gain and frequency on the plate amp to get the frequency response that sounds best in the room. I also made a modification to the design to accommodate the plate amp space (seen below middle). This seemed to have little effect on sound quality.</p><p>Anyway, thanks so much for the instructable. It's a good project and not expensive at all.</p>
So has anyone built this sub? Im thinking of trying it.
Really interesting project. Are you able to measure the response? If not, what would you guess as the bottom end. With less power requirement on the driver, I suspect that this system provides a nice accurate, tight bass.
I have the measured response in a file on another computer, I'll try to upload that later in the week.
interesting 'ible!<br>Is there a link for the physical / acoustics principles behind this design?<br>I'd be interested to find out.<br>Some questions that are raised in my mind:<br>Is the driver as efficient 'pushing' as well as 'pulling' in both phase and amplitude?<br>I'm assuming that the housing causes the sound waves to be combined at the output aperture?<br>If so, how does the design ensure the wide bandwidth required for audio? ie performing a 180o phase shift across the sub-woofer frequency range.<br>Thanks in advance!<br>
Here's a pretty detailed explanation of how a tapped horn works:<br><br>http://www.danleysoundlabs.com/pdf/danley_tapped.pdf<br><br>It should answer your questions better than I can, let me know if you still need clarification.
I wonder how well adding 2 speakers on the face would do. I was going to say something about using plywood instead of MDF, but since this isn't a closed box design I guess it doesn't matter that much.
very nice design<br>
I had never imagined you could combine the push and pull in one direction. I might try this with a 3&quot; speaker setup I have laying around. I need to put a volume control on the amp first though...that thing is already too loud. lol
I'm wondering if this could be used for live sound systems. As a bass player, I'd like to know if this design could be modified to handle up to 300W.
I actually used a pair of tapped horns with a single driver in each cabinet for a PA system, this should work even better. You can lay them on their side, and place the mains stands on top. Each horn is rated at 240W, those last 60W won't significant difference in overall output. Good luck!
Very interesting I will show this to a couple of friends I am meeting up with in a few days.<br>You tilte needs work though &quot;Design&quot; really does not get across exactly what it is your 'ible has to offer, if I were looking for information on speaker construction I could easially overlook it.

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