Building a tapped horn

Picture of Building a tapped horn
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Rounded interior baffle.JPG
Ripping the sides.JPG
Looking like a horn.JPG
Lining up horn pieces.JPG
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Gluing bottom and back panels.JPG
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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.

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neumannjeremy made it!1 month ago

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.

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.

Anyway, thanks so much for the instructable. It's a good project and not expensive at all.

thebuffness10 months ago
So has anyone built this sub? Im thinking of trying it.
Is this a variation of a "Folded Horn" design? or the same only named differently? I have made several folded horns, home, car, and other applications.... Great 'Ible btw.
lesizz2 years ago
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.
thornsftw (author)  lesizz2 years ago
I have the measured response in a file on another computer, I'll try to upload that later in the week.
schkip19732 years ago
interesting 'ible!
Is there a link for the physical / acoustics principles behind this design?
I'd be interested to find out.
Some questions that are raised in my mind:
Is the driver as efficient 'pushing' as well as 'pulling' in both phase and amplitude?
I'm assuming that the housing causes the sound waves to be combined at the output aperture?
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.
Thanks in advance!
thornsftw (author)  schkip19732 years ago
Here's a pretty detailed explanation of how a tapped horn works:

It should answer your questions better than I can, let me know if you still need clarification.
ellisgl2 years ago
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.
zomfibame2 years ago
very nice design
Danielk2 years ago
I had never imagined you could combine the push and pull in one direction. I might try this with a 3" 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
rimar20002 years ago
Many times I thought build something like this, but always left it for later. I think it's very interesting design.

I wonder if it would be a good idea rounding the edges inward, to facilitate the "flow" of sound. It is to say, to put a quarter of PVC tube in the interior of the angle joints.
thornsftw (author)  rimar20002 years ago
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!
curbowman2 years ago
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.
thornsftw (author)  curbowman2 years ago
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.
You tilte needs work though "Design" 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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