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Tapped Horn for Dummies
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Old 13th August 2008, 04:18 PM   #51
GM is offline GM  United States
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You're welcome!

Indeed it does, though at the expense of gain BW for a given path-length. Not many 'free lunches' in sound systems design.

The stepped response is the price you pay for a small net bulk, i.e. there's only true horn loading in its HF BW. Design it as a max gain BW TH where Fs = Fc and watch it smooth right out, though now its size will be measured in thousands of liters just like a traditional 'ideal' bass horn.

Bottom line, as in any optimum speaker alignment you want to use the right driver for the app and if you can't find or mod an existing one to suit, then you either accept its trade-offs and work around them as TD does with his DTS-20 or rethink your system design.

IIRC 'JH' posted that while the HF 'ripple' wasn't nearly as bad as predicted, the folds didn't have much (any?) affect on them either like in a typical folded horn. Not surprising considering the typical driver-in-mouth TH designs that folks here seem to prefer.

No, my speaker design/building avocation for a variety of reasons has been on hold for many years now, so my postings are based on what I think I know about TL, horn, etc. design from prior experience and of course the much appreciated published efforts of others and last, but not least, rely on Prof. Leach's well proven math to calculate the throat, etc., values of any low frequency horn alignment.

Note that just plugging numbers into his math will probably not give you a viable alignment or even a decent starting point, especially WRT TH alignments, i.e. GIGO applies (garbage in/garbage out), hence the tiny throat predicted (the byproduct of a low Qes/Qts) would probably quickly destroy even a 'bullet-proofed' horn driver if used in a prosound app and probably cause audible distortion via surround deformation using a thin, high compliance half roll one, but the 2421 is robust enough for prosound apps, so I see no reason why it wouldn't be fine for a much less stressful HIFI/HT one. Only one way to know for sure though.........

Yeah, not being math savvy enough to learn from acoustic engineering textbooks I was forced to make many 'proof-of-concept' cabs to create enough of a pattern of each type of basic alignment to see trends, which then allowed me to skim past much of the higher math to design conservative alignments I could tweak to suit since making something acoustically smaller was far easier than stretching it to sound big enough.

GM
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Old 13th August 2008, 05:00 PM   #52
Milkduds is offline Milkduds  United States
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Greg,

Could you please email me? (You designed a cabinet for at 515-8G a couple years back for me.)

Thanks,
Jim D.
jrclwd@embarqmail.com
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Old 13th August 2008, 05:06 PM   #53
Milkduds is offline Milkduds  United States
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Can someone define the parameters required to design a TH box from GM's simulation in Post 49?

Thanks,
Jim
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Old 13th August 2008, 10:21 PM   #54
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally posted by Jimmy D.
Could someone design a tapped horn using the MCM 55-2421? I've been wanting to try out THs. I would need a rough sketch or description with dimenstions. Something from the high 30s to about 100 hz would be good and a small as possible footprint would be ideal.

Thanks,
Jim D.
Hmmm, where to start with this one?
I started a thread called "Tapped Horn for Dummies" because all the tapped horn designs on William Cowan's thread were no good for people who weren't good with a table saw. So this design is ideal for beginners, and you guessed it, it uses the very woofer you're asking about.

I'm listening to my tapped horns as we speak.

Construction plans are here : http://www.diyaudio.com/forums/showt...95#post1565695

That's page 1 of the thread.

I'll post pics soon...
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Old 13th August 2008, 11:44 PM   #55
aznboi3644 is offline aznboi3644  United States
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I still don't understand how this enclosure is assembled. Could we get some more pictures
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Old 13th August 2008, 11:56 PM   #56
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally posted by aznboi3644
I still don't understand how this enclosure is assembled. Could we get some more pictures
I need to find the reader for my camera. 'Til then, it boils down to this:

#1: Get a 8ft tall sonotube that's 10.5" across. Home Depot doesn't sell eight foot long sonotubes, so just buy two that are four feet tall. Also, bring your tape measure with you. The sonotubes at Home Depot and Lowes come in various sizes. The ones that are labeled 10" are actually 9.5", 10", and 10.5". The reason they do this is because it allows them to put more on the shelf. You want the ones that are 10.5" across, not 10" across.
2. Get a piece of plywood, cut it to 9" x 90". I used 1/2" stock. You could use MDF too I guess. I like plywood because it doesn't split as easily as MDF.
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 16" from the end of your 90" piece of plywood. See this pic here, from the 1st page of this thread?
http://www.diyaudio.com/forums/attac...amp=1216524591
Note that L1 is 50.8cm, which equals 20". Our hole is at 16" because that's the center of our 8" woofer. Get it? 20" - 4" = 16".
4. Put the MCM woofer 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. The reason there's a five inch gap is that a five inch gap is equivalent to the midpoint of our tapped horn.
7. Put a cap on the other end that covers up one HALF of the sonotube. The reason that we're covering all of one end and half of the other end is that the mouth of our tapped horn is on one side. If you covered up the whole thing it wouldn't work too well
8. That's it!

THESE ARE THE FINAL DIMENSIONS. I know I've posted two or three variations on this, but these dimensions are what I'm using for the tapped horn that I'm listening to RIGHT NOW. It's done, it works, it's cheap
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Old 14th August 2008, 12:28 AM   #57
Patrick Bateman is offline Patrick Bateman  United States
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A couple o' notes for people who actually build this beast. This is kind of a post-mortem, and things to consider when you build it.

#1 - OMG this thing is more work than I thought. Seriously, I thought I could build two of these in a day and it took me a month to finish one 90%, and the other 50%. (One works but needs carpet.)

#2 - The reason why it's such a P.I.T.A. to build is because it's so TALL and SKINNY. I never even considered this before I fired up the table saw. When you build a horn you need to make that thing AIRTIGHT, and I couldn't figure out any easy way to do this!!! Sheldon recommended cutting the sonotube lengthwise, sealing up the board, then stitching everything back together. That might work for you.

What I wound up doing, which is anything but elegant, is chopping up the sonotube into 9" chunks. The idea was to build it from the ground up (literally), piece by piece. So I stood the board vertically, attached a piece of sonotube with glue and screws, then used plumbers caulk to seal both sides of the board.

If I had to do it again, I'd chop it into 24" chunks. 9" chunks are too small. If you cut it into 24" chunks it's short enough that you can get inside and caulk everything up, but not so short that you'll spend the rest of your life assembling this thing. YMMV

If anyone can come up with a better method of insuring that the enclosure is airtight, I am all ears. This project would be much easier if the sonotube wasn't so narrow. 10.5" doesn't sound that small, but it really is. The inside is so narrow, I can barely fit my arm inside of it. I don't have massive guns, it's just really difficult to work inside of this thing.

Also, if you don't put in the effort to seal this thing properly IT WON'T WORK. PERIOD. It has to be AIRTIGHT.

#3 - If I had to do it again, I might use this woofer instead: http://www.partsexpress.com/pe/showd...umber=295-456. You see, the whole idea of this project was cheap and easy. Yeah, it's cheap, but damn these enclosure take a long time to build. If you're going to invest a month building a subwoofer, you might as well use a driver that costs more than $25 I think. Having said that, the MCM woofer is a much MUCH better deal than the Dayton. Another thing about this subwoofer is that you'll end up spending $50 on carpet, wood, glue, screws, styrofoam, sonotubes, etc. It seems a little silly to spend $50 on the enclosure and $25 on the woofer.
Does the Dayton offer any huge advantage over the MCM? Not really, just the peace of mind that the build quality is superior, and MCM isn't known for their reliablity. Again, you get what you pay for.
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Old 14th August 2008, 01:51 AM   #58
GM is offline GM  United States
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Please explain again why you didn't make it out of straight cut boards? Folks have been doing just fine with BIBs and Weems style Voigt pipe horns without any angle cuts.

Really, you could probably come up with a design that used standard width boards as I've done for some driver alignments (no TH though), so only their lengths need cutting.

GM
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Old 14th August 2008, 02:00 AM   #59
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally posted by GM
Please explain again why you didn't make it out of straight cut boards? Folks have been doing just fine with BIBs and Weems style Voigt pipe horns without any angle cuts.

Really, you could probably come up with a design that used standard width boards as I've done for some driver alignments (no TH though), so only their lengths need cutting.

GM
The board is straight. The dimensions are posted above. The tricky part is that you have to be sure that the board and the sonotube are airtight. Because the internal dimensions are so small, and the tube is so long (eight feet!), sealing the board is tricky.

If the board was centered, this wouldn't be a big deal. For example, if the sonotube was 10" across you could cut the board to 10.125" across. The extra eight of an inch would seal the board along the entire length of sonotube, and you'd be good to go! That's because the tube is kinda flimsy, and the board would cause the tube to flex, accommodating the extra width. But the board ISN'T in the middle of the tube, it's off center, so that one side has more volume than the other. That makes construction much trickier.
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Old 14th August 2008, 02:06 AM   #60
GM is offline GM  United States
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I meant why use Sonotube at all? Make it all out of straight boards.

GM
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Old 14th August 2008, 02:11 AM   #61
Patrick Bateman is offline Patrick Bateman  United States
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The usual reasons. A sonotube sub is lighter and stronger than a MDF or plywood sub of the same weight. Whenever possible I use sonotubes for subs.

These subs are MASSIVE. Their footprint is less than one square foot, but they're EIGHT FEET tall. If I built the same thing out of MDF they would be almost unbearable to move.

Also, I live in a three story house, and the idea of hauling three 100lb subs up the stairs isn't too appealing
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Old 14th August 2008, 03:02 AM   #62
GM is offline GM  United States
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~100 lbs isn't my idea of 'massive', but I always had a cheap hand-truck for heavy and/or awkward size loads such as my ~245 lb speakers (less drivers), which I have moved by myself up/down stairs before a car accident ended such endeavors.

Anyway, the way I've dealt with your problem is to buy a second one to mount the baffle at each end, trimming off the large side so the seams can easily be sealed up, then glue it up and slide it down the other tube and add the end caps.

GM
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Old 14th August 2008, 03:10 AM   #63
Patrick Bateman is offline Patrick Bateman  United States
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I've been working on this for a few weeks, and I just came up with THE PERFECT SOLUTION!

The problem with a sonotube tapped horn is that the board has to be ABSOLUTELY airtight. When the inside dimensions are small, it's practically impossible to get your arm inside to seal things.

But how's this for a solution:

Cut four discs. Each disk is the EXACT size of the sonotube. So if the sonotube is 10.5", each disk is 10.5". Then you cut the discs down the middle, and attach them to the center board. By doing this, the discs will insure that the sonotube is PERFECTLY cylindrical. And that will solve the problem with gaps between the board and the sonotube.

See, the reason there are gaps is that the sonotube isn't perfectly cylindrical. The discs solve that. In addition, they also reinforce the sub in a big way.

Of course you would have to cut holes in the discs, otherwise they would turn your tapped horn into three six sealed chambers.
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Old 14th August 2008, 03:22 AM   #64
winslow is offline winslow  United States
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John, I built my tapped horn in haves and assembled it in my apartment. There was no way I could have gotten the blame thing home if it was in one piece. Sealed it up with silicone and screwed it together.

Also didn't break my back moving the smaller half sections.
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Old 19th August 2008, 08:44 PM   #65
Patrick Bateman is offline Patrick Bateman  United States
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In a strange turn of events, my 2nd tapped horn threw itself off the deck of my house, plunging fifteen feet in the process. This is the first time I've seen a subwoofer commit suicide. Sure, I've murdered a few subwoofers, but never seen one kill itself. I woke up on Saturday morning, couldn't find my tapped horn, only to see it's crumpled body laying in the weeds in front of my house.

Sad really.
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Old 19th August 2008, 09:02 PM   #66
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Quote:
Originally posted by Patrick Bateman
In a strange turn of events, my 2nd tapped horn threw itself off the deck of my house, plunging fifteen feet in the process. This is the first time I've seen a subwoofer commit suicide. Sure, I've murdered a few subwoofers, but never seen one kill itself. I woke up on Saturday morning, couldn't find my tapped horn, only to see it's crumpled body laying in the weeds in front of my house.

Sad really.

Are you sure that this is not an "apparent suicide"? Maybe a hitman is involved.
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Old 19th August 2008, 09:54 PM   #67
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Quote:
Originally posted by GM
~100 lbs isn't my idea of 'massive', but I always had a cheap hand-truck for heavy and/or awkward size loads such as my ~245 lb speakers (less drivers), which I have moved by myself up/down stairs before a car accident ended such endeavors.
Hope you have repaired the stairs by now and given up the moonshine.
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Old 20th August 2008, 12:22 AM   #68
Patrick Bateman is offline Patrick Bateman  United States
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Here's a photo of the tapped horn's throat. The duct tape is there because I was too impatient to wait for the plumber's caulk to dry. I'll fix that.

Click the image to open in full size.
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Old 20th August 2008, 12:25 AM   #69
Patrick Bateman is offline Patrick Bateman  United States
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Now THAT'S an ugly subwoofer. Movie screen in the background (I only set up the screen when I watch a film.)

Click the image to open in full size.
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Old 20th August 2008, 12:28 AM   #70
Patrick Bateman is offline Patrick Bateman  United States
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The Gedlee Summas sure look a lot better than my subwoofer. As you can see in the picture, the finish is like a mirror. You can see the reflection of my front yard on the speaker, via the window beyond the speaker.

Tapped horn is in the corner; audio video cabinet in front of it.

I placed a 18sound waveguide there to give you a sense of scale, the Summa waveguides are easily twice as big.

I need to finish two more subwoofers, and carpet them.

Click the image to open in full size.
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Old 27th August 2008, 06:06 AM   #71
Patrick Bateman is offline Patrick Bateman  United States
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Since my 2nd tapped horn commit suicide, I built a pair of bandpass boxes to replace it. They're fairly similar to the boxes I considered on page two of this thread. I built two instead of one since the tapped horn should be much more efficient (and bigger!)

So here are some thoughts on a tapped horn versus a bandpass, using the same woofer:

The first thing I noticed was that the bandpass is more efficient. Which was quite a shock, I was expecting the tapped horn would be a good 3-6db louder. I didn't measure the response, so it's possible that the difference was psycho acoustice, due to fletcher munson curves. Because the tapped horn was *definitely* playing lower than the bandpass.

The second thing I noticed was a buzzing present in the bandpass that was mostly absent in the tapped horn. Both enclosures are quite inert, so I'm guessing that this buzzing sound is either 2nd or 3rd harmonic distortion, or a pipe resonance in the bandpass. It's a sound I've noticed in every bandpass box I've built, going back for years. It's not obvious once you turn on the main speakers, since they mask it. But it's quite prominent when listening to the subs alone.

To make a long story short, the tapped horn sounds pretty darn good. The bandpass box is much MUCH easier to build, but there's definitely something special about the TH.

Having said that, the bandpass IS easier to build, and the tapped horn doesn't appear to have an efficiency advantage over the bandpass. Of course in-room measurements should be done to confirm this.

Also, I checked the tuning frequency of the bandpass, and it's tuned a few hz too high, which gives it an additional DB of output.

I'll fix that in the next few days.
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Old 27th August 2008, 06:11 AM   #72
Patrick Bateman is offline Patrick Bateman  United States
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I just double checked the models, and it looks like the bandpass should have an F3 of 28hz & 70hz, while the tapped horn has an F3 of 18hz & 70hz.

So that confirms what I was hearing, the TH is playing much lower.

Having said that, the efficiency claims of the TH seem hard to believe; according to hornresp the TH is *12DB* more efficient than the bandpass. It doesn't sound like that at all. Also, the bandpass is exactly 1/2 the size.
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Old 27th August 2008, 02:52 PM   #73
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Quote:
Originally posted by Patrick Bateman


The second thing I noticed was a buzzing present in the bandpass that was mostly absent in the tapped horn. Both enclosures are quite inert, so I'm guessing that this buzzing sound is either 2nd or 3rd harmonic distortion, or a pipe resonance in the bandpass. It's a sound I've noticed in every bandpass box I've built, going back for years.

John

I am guessing this is turbulence. I am very careful to radius every corner in the ports as not doing so will create a turbulent noise that can be objectionable. I also often use foam in the port to quiet them down. The "smallish" ports on a bandpass are its Achieles Heal.

You comparison is not really fair since the bandpass in the same volume as the TH would go as low. I would expect the two devices to be quite comparable at these very LF in comparable volumes, etc. 12 dB more output from the TH is rather absurd.
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Old 27th August 2008, 06:06 PM   #74
Patrick Bateman is offline Patrick Bateman  United States
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Dr Geddes,

I've become accustomed to this buzzing sound in every bandpass I've built, assuming that it was a pipe resonance or perhaps mechanical noise from the woofer. But I trust your advice so I went and took a look.

First I took a look at the port, and there *was* a lot of turbulence. Which was a surprise, as the computer model indicated that my port was adequate. It turned out the turbulence wasn't from the port, but the SEAL on the port. In my haste I hadn't caulked the seal, and a TON of air was escaping through the seal.

That eliminated 25% of the buzzing, but the tapped horn still sounded more relaxed, while the bandpass buzzed away at the same power levels.

I noticed that the subwoofer was rattling quite a bit on my wood floors, so I pressed my entire weight against the cabinet, while the sub was playing. The idea was to keep it from bouncing off the floor.

And THAT solved the problem!

This buzzing sound was radiating from the end caps of the sontube! Honestly, the difference was night and day. So the woofer was turning the plywood end caps into a 10 inch passive radiator, on both sides of the subwoofer.

I am seriously kicking myself right now, because I've heard this distortion in every damn bandpass I've built for over a decade. If only I'd caught this years ago.

Once I placed some weight on the bandpass sub, to fix the problem with the end caps, the bandpass sub sounds *completely* different. It sounds a couple of DB less efficient, but also appears to be playing deeper, and there's isn't rattle or a buzz to be heard. It's very VERY clean, definitely cleaner than the tapped horn now.

Next up, I'm going to reinforce the heck out of BOTH subwoofers.
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Old 27th August 2008, 06:15 PM   #75
Patrick Bateman is offline Patrick Bateman  United States
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Here's the details on the bandpass sub. It's stupid easy to build. I put two of them together in under six hours with nothing more than a jigsaw, a drill, and a handsaw. One sub is about 80% complete, the other is about 50%. It is easily 10x easier to assemble than the tapped horn, which is MUCH more difficult to build than I realized.

First off, the bandpass sub requires modifications to the MCM 55-2421 woofer. In a nutshell, I add mass to lower the FS and raise the QMS, then I add a resistor to raise the QES. These modifications make it work much better in a single-reflex bandpass.

The front chamber of the sub is 15.8 liters.
The rear chamber of the sub is 34.1 liters.
The front chamber has a vent which measures 22" in length and 3" in diameter. The volume of the vent is 212."
The rear chamber is sealed; the woofer is in the rear chamber, and takes up 113".

The total volume of the front chamber, including the port, is 1176" (964" + 212").
The total volume of the rear chamber is 2194".

I juggled all the numbers so that this sub needs exactly ONE sonotube

The rear chamber is 31" in length; the front chamber is 17" in length. Note that you'll have to use a 180 degree turn to fit a 22" port into a chamber that's 17" long. No, I didn't factor in the volume of the front cap and the end cap, but it certainly wouldn't make more than a half DB difference :P
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