Tapped Horn for Dummies

[iand]

Hi Earl


Hi Ian

I am not sure how you modeled the TH-115, but what I got was about 3dB down in sensitivity.
Also, as I said earlier, I am happy when a computer model for a horn is within a dB or two of what you measure when you build it.
In my case, we sell the actual thing and not the computer model so how it measures trumps the model (normally the model is a bit better than the real thing).
We measure at 10 meters most of the time because one would literally be in the mouth bubble at one meter with large woofers. This also compensates for the fact that the speakers aren’t buried in the ground firing up into half space.
We have a mic calibrator, Earthworks mics, use an HP3456a Voltmeter and send some stuff to an independent company for measurement also.

I have made a fair number of boxes, which didn’t work out for one reason or another so this appears to be “the way it is” so far as some computer ambiguity or at least indicates that something’s are still left out..
Your reference to excursion discrepancy is puzzling with David’s reply , yes the cones do move and the models I use tend to overstate the Q’s on its predictions like magnitude and excursion.
The best bet is to observe the motion while in operation.

Best,
Tom

Hi Tom

Do you mean that the modelled reflex was 3dB down compared to the modelled tapped horn, or the modelled tapped horn was 3dB down compared to the measured tapped horn, or the modelled reflex was 3dB down compared to the measured tapped horn?

When I model them in Hornresp they both average about 101.5dB from 40Hz to 100Hz; the dual 18" reflex has about 2/3 the cone travel of the single 15" tapped horn -- but 3x the cone area so the drivers are having to shift twice as much air for the same output.

This is with my best guess at the TH-115 design, which has close to an exponential taper and includes some added series inductance to flatten out the passband.

If my guess is wrong that could explain some difference, but I spent a lot of time playing around with the tapped horn parameters and this was the best I could do with the 15TBX100. If you are willing to tell me exactly what is really inside the TH-115 (or post your results of this from Hornresp if you don't want to give too much away) that would be great.

Still looking for the missing 3dB -- this might not seem like much, but it actually represents a doubling in efficiency which is an enormous difference between simulation and measurement...

Cheers

Ian

 

[Patrick Bateman]

I would be curious what a BP system would look like if one fixed the sensitivity low corner and size as the boundaries.
As the TH-115 has a known driver (15tbx100) and has been carefully measured outdoors, that might be a good reference.
It has an exterior volume of 420 Ltrs, is �2dB at 38Hz and has a sensitivity of about 105 dB 1W/1M below 70Hz.
The measured response and impedance curve is on the data sheet.
Alternately, the TH-215 has two purpose built drivers, has an outside volume of 505Ltrs, a sensitivity of 102dB 1W/1M and is �3dB at 28Hz.

Anyway, if you or one of you other guys feels like crunching some numbers, I�d be curious to see what it takes in a BP speaker to get this low corner, enclosure volume and sensitivity with any realistic �low pass� corner.
Is there an acoustic B.P. analogue for a Tapped Horn TH-115 or TH-215?
I don�t know if there is a free lunch in it or not, those are so rare it�s not worth looking for them or worrying about, but it has allowed me to make products that I couldn�t have made otherwise.
It will be interesting to see how easy it is to equal the TH-115 or TH-215 with a BP alignment.
Best,
Tom Danley

If anyone is interested, there are 3rd party measurements of the TH-115 online. Based on these measurements, we see a few things:

1: It's a heck of a lot flatter than hornresp predicts. This is consistent with what Danley and Cowan have measured.
2: It doesn't have the surreal efficiency level that some people would expect. For instance, a labsub appears to be more efficient. Having said that, a lab sub is 50% bigger, *dramatically* more difficult to build, and has a nasty dip, like all front loaded horns in an enclosure that's too small.

I didn't want this thread to turn into a "let's bash tapped horns" kind of situation. For my money, bandpass and tapped horn are about the best options in subwoofers these days. As I see it, a bandpass is ideal if you don't have a ton of space, and they're easy to build. A tapped horn is compelling if you can afford a much larger enclosure, you're handy with a table saw, and you want big SPLs.

Here are the measurements:

http://www.cobrasound.com/MDSubwoofers

 

[David McBean]

Hi PB,

yes and yes.

Thanks for the confirmation. Known Problems 3 and 4 in the Readme.txt file supplied as part of the Hornresp download package, refer.

I was running hornresp on my girlfriend's laptop with a intel processor and a vista OS, and noticed it crashes quite a bit less.

I have not had the opportunity to test Hornresp on a Vista OS machine, but I do know that Intel processors seem to be far more "Hornresp-friendly" than AMD ones .


Kind regards,

David

 

[David McBean]

AMD processor and firefox 3.x running is a 'crash all the time' scenario.
However, I don't care... I can just shut down firefox and work just fine. THANKS for an awesome tool david.

Hi jbell,

Thanks for the feedback, and thanks for the THANKS .

Kind regards,

David

 

[just a guy]

I have vista and an amd processor and an older version of hornresp. It crashes the entire computer if hornresp does a calculation while connected to dial up internet, and when not connected randomly has errors and needs to close. It's to be expected, so I save frequently, use hornresp only while offline, and the random errors don't bother me at all. I'm just happy that it works.

 

[nuconz]

So here's how to build it:

1. Get a 8ft tall sonotube that's 10" across
2. Get a piece of plywood, cut it to 10" x 90"
3. Cut out a 7.5" hole for the woofer. The location of the hole is very important. The centerpoint of the hole must be 18" from the end of your 90" piece of plywood.
4. Put the two MCM woofers in the hole
5. Put the plywood divider right inside the sonotube
6. Cap one end of the sonotube completely. Leave a 5" gap between the end cap and your piece of plywood
7. Put a cap on the other end that covers up one HALF of the sonotube
8. That's it!

this is such a cool project. when i first read your post i was intrigued at the suggestion of doing a transflex/tapped horn in sonotube.

do you have more photos of the pipe? i'm unclear on the construction of the tapered end of the pipe. is the woofer underside (bottom)/end of the pipe closed?

 

[Patrick Bateman]

this is such a cool project. when i first read your post i was intrigued at the suggestion of doing a transflex/tapped horn in sonotube.

do you have more photos of the pipe? i'm unclear on the construction of the tapered end of the pipe. is the woofer underside (bottom)/end of the pipe closed?

Yes, that's correct. It sounds pretty awesome too. My only real disappointment with the project was that it was unexpectedly difficult, and I had expectations that it would have a much higher efficiency level.

 

[nuconz]

Yes, that's correct. It sounds pretty awesome too. My only real disappointment with the project was that it was unexpectedly difficult, and I had expectations that it would have a much higher efficiency level.

hate to bombard you with questions, but steady yourself!

what is the efficiency level? the woofer fs is about 25hz, so if it was tuned in the 25-30hz range, it should be ok, right?

can you add a different photo of the taper? what i'm getting at is "serviceability". how difficult is it to remove the woofer if it requires replacement?

did you screw the center "panel" into the sides of the sonotube?

what about using 12" sonotube vs. the 10"? might this increase efficiency?

you said to use a 90" length of plywood. what type of joints did you use to extend the pieces?

thanks.

 

[Patrick Bateman]

hate to bombard you with questions, but steady yourself!

what is the efficiency level? the woofer fs is about 25hz, so if it was tuned in the 25-30hz range, it should be ok, right?

can you add a different photo of the taper? what i'm getting at is "serviceability". how difficult is it to remove the woofer if it requires replacement?

did you screw the center "panel" into the sides of the sonotube?

what about using 12" sonotube vs. the 10"? might this increase efficiency?

you said to use a 90" length of plywood. what type of joints did you use to extend the pieces?

thanks.

No worries, happy to help!
I don't know what the efficiency is. If you download hornresp, you can get the data to model it from this post on the first page:
http://www.diyaudio.com/forums/showthread.php?postid=1565695#post1565695
The pic that I posted is modeled as if it's corner loaded. That's an incorrect assumption in my opinion; it's closer to half space than corner loaded, so the efficiency in the pic I posted is too high.

If the driver blew up, I would probably have to saw the tube in half to remove the woofer. Basically saw it in half, remove the woofer, then glue it all back together.

I've used these woofers in an autotuba in my car with something like 1000 watts, so they're surprisingly sturdy. I'm not telling you to use 1000 watts, but I think you'll run out of excursion before you smoke the voice coil.

If you made it bigger, it would raise the efficiency. It would also make the response peakier. Be sure to use the resistor - the response will be ATROCIOUS if you leave it out. It's essential to the design.

The center piece of plywood is simply glued in with liquid nails. I used some screws to line it up properly.

The *width* of the center piece is essential. The center piece is NOT tapered. The *width* of the center panel dictates the volume of air on each side of the center panel.

I don't understand the last question.

 

[nuconz]

I don't understand the last question.

thanks.

i don't understand the last question either. never mind.

were you able to obtain 8' sonotubes? they don't always have them in these parts.

 

[Patrick Bateman]

In my neck of the woods, Home Depot and Lowes have both stopped stocking 12" sonotubes. But they stock 6", 8" and 10". All of these sizes come in increments of +/- 1/2".

On the west coast, THE place to get sonotubes is White Cap. Not sure if they have them in Florida. White Cap stocks everything from 6" all the way up to 36"!!!

 

[just a guy]

nuconz, did you read this thread carefully? In particular the part where PB says how hard it is to construct this design? I wouldn't even want to try dividing a sonotube into half with a board. IIRC PB had to cut the whole thing into 2 foot sections for some reason or other and then glue it all back together, in which case it might make sense to make it totally out of flat panel wood. And then if you are going to do that, you might as well fire up hornresp and design something with a bit of a taper for a bit more high gain bandwidth. Or maybe just build one of the other designs.

As always ymmv, but just so you know, I don't like sonotube and would never use it, so I'm biased to begin with, but even if I HAD to, I don't think I could successfully build this design at all without turning the sonotube somewhat oval shaped and I'm pretty sure that would dramatically reduce the inherent strength of sonotube, which of course is because of it's shape.

 

[Patrick Bateman]

IF you cut the sonotube into 2 foot pieces, the project will come together quickly. The problem I had was twofold:

#1 : I couldn't figure out how to seal the gaps between the board and the tube, so I wasted a lot of time filling gaps. I would hold a flashlight into the tube, to see where the gaps were, then push liquid nails into the gap like I was frosting a cake. This was time consuming and messy.

The proper solution is to chop the tube into 2' sections, then stack them up piece by piece. If the pieces are that small, it's easy to get your hands inside to seal things, screw in the board, etc...

#2 : I tried a different method, which was to cut it lengthwise. That didn't work out as well. To add insult to injury, it FELL OFF MY DECK and landed 15 feet down the hill that my house is on

 

[nuconz]

nuconz, did you read this thread carefully? In particular the part where PB says how hard it is to construct this design? I wouldn't even want to try dividing a sonotube into half with a board. IIRC PB had to cut the whole thing into 2 foot sections for some reason or other and then glue it all back together, in which case it might make sense to make it totally out of flat panel wood. And then if you are going to do that, you might as well fire up hornresp and design something with a bit of a taper for a bit more high gain bandwidth. Or maybe just build one of the other designs.

ok, i admit that i did not explore all the responses in this thread. so thanks much for the tip.

i wonder if using simple weatherstrip on the sides of the plywood might avoid the necessity of cutting the tube in sections? you'd have to use screws every 6" or so (on the outside), but the thing would be (barely) serviceable. the 'strip could be nailed to the plywood with a brad nailer. you could use wax to assist sliding the plywood down into the tube. and you'd also want a dowel at the closed end top and bottom for extra support (for the 5" gap).

actually the design i like best is the AWC below. wonder if anyone has built it?

 

[just a guy]

The proper solution is to chop the tube into 2' sections, then stack them up piece by piece.

I'm really not sure that's a proper solution at all. Sonotube is cardboard and the only reason it has any strength at all is because it's completely round. I'm not really strong on physics, but when you jam a board up the middle and cut it into small pieces and glue it all together I can't see it having much strength at all left.

The only proper solution (IMO) is to not use sonotube for this particular design. As far as I can tell it would be much easier to just do it with flat panel wood.

 

[just a guy]

actually the design i like best is the AWC below. wonder if anyone has built it?

Not sure where you found that so I have no idea of the details. Can't tell from the pic, but it appears to have no taper, essentially making it basically a wave cannon with a rectangular look. No idea how it would work, but I wouldn't just cram any old driver in there. All of these designs that use gain building enclosures on the front AND back wave are as tricky as high order bandpass boxes to get right.

 

[Patrick Bateman]

I can stand on the sub with ease. I use nested sonotubes, with expanding foam in the gap. It's strong and light.

 

[nuconz]

Not sure where you found that so I have no idea of the details. Can't tell from the pic, but it appears to have no taper, essentially making it basically a wave cannon with a rectangular look. No idea how it would work, but I wouldn't just cram any old driver in there. All of these designs that use gain building enclosures on the front AND back wave are as tricky as high order bandpass boxes to get right.

this is in the tom daly top thread. it was proposed by diy member qi.

here is a similar one from the acoustic wave cannon thread.

 

[just a guy]

I can stand on the sub with ease. I use nested sonotubes, with expanding foam in the gap. It's strong and light.

Apparently it's not strong and light enough to withstand a 15 foot fall. I'm not sure if my traditionally constructed projects would hold up, but I'd like to think I could throw them off the roof without (too much) injury. I wouldn't bet money on it though.

this is in the tom daly top thread. it was proposed by diy member qi.

here is a similar one from the acoustic wave cannon thread.

I'm not familiar with wave cannons, just never really had any interest in them so I can't comment further.

 

[Patrick Bateman]

actually the design i like best is the AWC below. wonder if anyone has built it?

As the other person noted, that's not a tapped horn. It's a dual reflex bandpass with extremely long ports. To be tapped horn the output from the rear of the cone would have to cross the front of the cone at some point. The reason that it's not a wave cannon is that there is a distinct rear chamber behind the woofer. The volume of that chamber and the diameter of the port will shape the response. You can model this in hornresp btw, as a front loaded horn. I posted how to do this in the past couple weeks in one of my threads.