High output 8" Tapped horn - AVS Forum
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post #1 of 49 Old 04-03-2010, 07:40 PM - Thread Starter
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Here is my first foray into building tapped horns. It uses the MCM 55-2421 8" driver and the 115W Foster plate amp from Jack Hidley. This entire build cost less than $100 including wood and hardware.
It has external dimensions of about 29.75"x35.125"x9.5". I actually built this sub about 2 months ago and have been enjoying its clean sound in my living room since then. It is tuned to 28Hz and will provide 110db down to this frequency.

Here are my new arrivals. For $25 each I had to get a few extras.


I hung these in my basement and drove all 6 of them with a single 115w amp to break them in. These were broken in at 30Hz for 48 hours.


These parameters were slightly different than my originals but have been adjusted slightly due to folding which changed them a bit.


The schematic. It was kept at 3.5 cubic feet before folding.


The SPL response at 2.83v input. Nearly 95db down to 28Hz.


Phase response


Group Delay


Impulse Response


Max SPL--Over 110db down to 28Hz


Driver Displacement--According to HR it is slightly over Xmax but the amp rolls off at about 28Hz as well which should help to protect the driver.


Here is the drawing in AutoCAD which makes it very easy to fold the horn. In this drawing the amp will fit at an angle in the upper left of the pic. The driver will sit directly next to it.


The enclosure is nearly completed at this point. It took a mere 3 hours to assemble once all of the pieces had been cut. The 1/2" plywood that I used is some inexpensive stuff from Lowes that was slightly warped that they marked down to $7 a sheet just to get them out of the way for them. I used the PL premium and a brad nailer which made assembly very easy. Highly recommended!!!


I really didn't want to stick an amp in my entertainment center so I built the amp into the box. I know that BFM strongly frowns on this but the amp is plugged into the same outlet as my receiver as well so no ground loop issues here. I also wanted to make the enclosure as slim as possible so I made it 8.5" wide internally. This required me to mill down the amp to fit. Good bye warranty!!


Here is a pic showing the driver and amp installed in the box. Note that airflow from the enclosure will also help to cool the amp, not that it gets very warm anyways. It's a very tidy slim package.


This is the completely assembled enclosure. To this day I have not finished the enclosure. A buddy of mine wanted to buy this one but hasn't picked it up yet. He wants to finish it himself.


Here is the home so far of this tapped horn. For scale that is a 50" Samsung Plasma next to it and my latest project, my 64" tall TLAH's. Sitting back in the corner like they are and aimed towards the corner they really don't use up any extra floorspace. If I do end up keeping this sub I may paint it to match the walls to better help it blend in.


With a total outlay of less than $100 I have been extremely pleased with this overall package. Although they don't hit the lowest notes they sound amazing with movies and just incredible with music. Clean and loud explain it well. Keep in mind that this replaces my Onkyo 5100 HTIB sub with its 10" "sub" and 290 peak watt amp. For hardcore movie watching I still rely on my 4 sealed IXL18's in my basement.
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post #2 of 49 Old 04-03-2010, 08:32 PM
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Sounds like the perfect sub for a TV/music room!

"The boom is dead, long live the bass"
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post #3 of 49 Old 04-03-2010, 08:43 PM
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Really nice job.

Thanks for the plans.

I didn't realize the MCM 55-2421's were on sale again
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post #4 of 49 Old 04-03-2010, 08:57 PM - Thread Starter
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Quote:
Originally Posted by mynym View Post

Really nice job.

Thanks for the plans.

I didn't realize the MCM 55-2421's were on sale again

I bought mine a few months ago and used a code to get them for $25 a piece with free shipping over $100. They may not be the most robust driver but for the money they can't be beat and sound great.
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post #5 of 49 Old 04-04-2010, 03:51 PM
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Nice work. Great job on the fold.

I'm still listening to something very similar, though I hope to change that this week.

Any chance you can measure SPL?

The 55-2421 is on sale more often than not, just try all the codes.

Free shipping is icing on the cake.
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post #6 of 49 Old 04-04-2010, 04:06 PM
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cool build...would it be fair to characterize the currency used to buy added performance in this case is complexity of the build?

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post #7 of 49 Old 04-04-2010, 04:33 PM
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Absolutely - no free lunches anywhere.
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post #8 of 49 Old 04-04-2010, 04:47 PM
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"Absolutely - no free lunches anywhere."

i was curious to know if there were any other advantages/disadvantages as well.

one "free lunch" seems to be getting a good design--however that may be defined (i assume that was implicit in your post).

with multiple impedance peaks in the operating range, horns seem to offer the benefit of higher efficiency/less power causing distortion effects than other designs as well as multiple excursion minima and the related problems of that. is 2nd and 3rd harmonic distortion the best way to compare subs or is there something else? are folks measuring the right stuff i guess is part of my question.

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post #9 of 49 Old 04-04-2010, 05:02 PM
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Nice , seems like a lot of you guys are getting hornresp dialed in.

If at first you dont succeed , get a bigger hammer !
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post #10 of 49 Old 04-04-2010, 05:13 PM
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Quote:
Originally Posted by LTD02 View Post

..... is 2nd and 3rd harmonic distortion the best way to compare subs or is there something else? are folks measuring the right stuff i guess is part of my question.

Don't know.

I figure that a 1W 1M SPL sweep is most useful, as it can be compared to anything and easily repeated. Impedance is also useful. THD is tough to get with a real-world noise floor, but can be useful, but not alone.

If the frequency response is not flat, it probably won't sound good. Any other defects will likely be manifest in the frequency response. THD measured in two different places by two different people will be two different things. They really can not be compared in a meaningful manner.

I wish there were an "easy button" for measurements - that way we could all compare apples and apples.
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post #11 of 49 Old 04-04-2010, 06:08 PM - Thread Starter
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Quote:
Originally Posted by lilmike View Post

Nice work. Great job on the fold.

I'm still listening to something very similar, though I hope to change that this week.

Any chance you can measure SPL?

The 55-2421 is on sale more often than not, just try all the codes.

Free shipping is icing on the cake.

Thanks lilmike, fortunately I have AutoCAD on my work laptop so I also use that for drawing up my speakers. It's been pretty handy. I have been drawing out the boxes as a long taper, folding them in AutoCAD, and then remeasuring the length as I lose a little bit in overall length due to the folding. The parameters I gave here are the actual parameters after folding.

This build is actually pretty simple to build. The most time consuming part is drawing out all of the lines on the side panels where the internal boards need to go. Once these are all drawn out the assembly goes pretty quickly especially with the brad nailer. There is then no need to wait for the PL to set up.

I should be able to get some SPL measurements tomorrow after work with any luck.
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post #12 of 49 Old 04-04-2010, 06:41 PM
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Man, all these great builds going on lately, I love it. Thanks for the info/build thread and good job on the build man, it's looking really cool.
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post #13 of 49 Old 04-04-2010, 06:44 PM
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you autocad guys should hook up with some folks with cnc machines and deliver flat packs. that would make a lot of bass available to a lot of folks who are stuck between not knowing woodworking and not being able to afford commercial offerings.

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post #14 of 49 Old 04-04-2010, 07:35 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

you autocad guys should hook up with some folks with cnc machines and deliver flat packs. that would make a lot of bass available to a lot of folks who are stuck between not knowing woodworking and not being able to afford commercial offerings.

Man I wish I knew someone with a cnc machine. I could think of lots of ideas for one of those.
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post #15 of 49 Old 04-04-2010, 08:19 PM
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Nice build, I use Solidworks and could model every nook & crannie. Dadoe & rabbet all the panels and include all the pilot holes for all the wood screws as well. Send the file right to a cnc machine. That would be fun.
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post #16 of 49 Old 04-07-2010, 06:23 PM - Thread Starter
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Well unfortunately I cannot find the power cord for my Xenyx 802 in order to take measurements from this sub. I think I may order the M Audio MobilePre USB sound card to use with my laptop and to power my mic. I hope to have actual measurements within a week or so.
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post #17 of 49 Old 04-07-2010, 07:35 PM
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Fantastic!

Another great and low-cost option with great performance!

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post #18 of 49 Old 04-07-2010, 08:07 PM
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Quote:
Originally Posted by LTD02 View Post

you autocad guys should hook up with some folks with cnc machines and deliver flat packs. that would make a lot of bass available to a lot of folks who are stuck between not knowing woodworking and not being able to afford commercial offerings.

I mentioned in the Anarchy 25hz thread that I could look for a local cabinet builder and see if I could set up some flat packs. I have some room at my shop to store a lot of kits. I didn't get much response to it though.

I'm still willing to check into it if anyone was interested.
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post #19 of 49 Old 04-07-2010, 08:24 PM
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Quote:
Originally Posted by Tom Bley View Post

Nice build, I use Solidworks and could model every nook & crannie. Dadoe & rabbet all the panels and include all the pilot holes for all the wood screws as well. Send the file right to a cnc machine. That would be fun.

You have to convert it from CAD to Gcode first. Some converters are better than others. The better ones usually cost big bucks too. The converter has to know what bits or end mills you're planning on using. If it doesn't have one already setup like you plan on using you have to define it yourself. If you've got an ABC you have to define that as well. 4 axis machines are only supported by 100 year old software it seems too. I wish it were just as easy as printing a CAD file but theres more to it. There always is.

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Even i, the genius, only vaguely understand what i am saying here.
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post #20 of 49 Old 06-07-2010, 11:52 AM
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Tsolsm, do you have the lengths of those interior angled braces and is the internal width of these braces 8.5 with 1/2 ply?
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post #21 of 49 Old 06-09-2010, 03:20 AM - Thread Starter
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Quote:
Originally Posted by stgdz View Post

Tsolsm, do you have the lengths of those interior angled braces and is the internal width of these braces 8.5 with 1/2 ply?

stgdz, I will get you some dimensions tonight. And yes, all of the internal braces are 8.5 inches wide so that it does not need any additional bracing.
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post #22 of 49 Old 09-05-2010, 04:04 PM
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Well I finished my build today, its really good for an 8" driver and compliments my D3 and unicc speakers. Its not over powering like the THT was with those.



I really dread having to do the finishing work on speakers.

I am driving it with a PE 240w plate amp though, I haven't run riducoulus voltage through it yet because I don't know if the high pass filters down at 28hz like jacks amp does.
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post #23 of 49 Old 09-06-2010, 07:40 AM
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Great build, looking forward to starting my own soon
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post #24 of 49 Old 09-06-2010, 07:52 AM - Thread Starter
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That looks great!!! It fits in behind your entertainment center very nice.

You made one huge mistake though. You didn't finish and paint the sub before putting it into it's home. I did the same thing when I built mine and it still hasn't seen any paint. Mine may never see paint.
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post #25 of 49 Old 09-06-2010, 07:56 AM
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Quote:


I did the same thing when I built mine and it still hasn't seen any paint.

lol, too funny!! My last speaker build was unfinished and 3 months later they are still in my HT room....unfinished

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post #26 of 49 Old 09-06-2010, 04:01 PM
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I'm staggering my finishing projects. The QSCinema speakers surrounds and 12" THT are getting their finishing touches on it now and it sucks. I hate the finishing part so much.

ssbario said building was easy compared to the finishing work.

Also here are some measurements. I don't know what the voltage was or the input as I just plugged the sub into my PC and used my work laptop with Soho's dvd (I didn't calibrate just run and gun'd it)

30hz 92dB
35hz 94dB
40hz 97dB
45hz 98dB
50hz 96dB
55hz 97dB
60hz 98dB
65hz 100dB
70hz 98dB
75hz 99dB
80hz 98dB

The mic was placed at about 1m on the floor and it seemed like there was still some gas left in the sub.
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post #27 of 49 Old 09-06-2010, 07:37 PM - Thread Starter
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That looks pretty good stgdz!!! Pretty impressive for a $25 driver!! You are reasonably flat until what seems to be about 30hz. Can you push it harder and see what kind of output you can get out of it?
Are you able to take readings below 30hz just to see if it falls off at that point? It should have good output until about 28hz. You can also gain output if you are able to flip the sub around and face the mouth about 12" away from the corner of the room. This will slightly lower the drop off knee as well.
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post #28 of 49 Old 09-07-2010, 02:04 PM
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I didn't want to run it that low but it looks like I will need that JH plate amp as the PE amp has an 18hz HPF on it. The farthest I can get it away from the wall, mouth facing it, is maybe 3" so I just placed it next to the wall.
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post #29 of 49 Old 09-13-2010, 09:38 AM
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well the plate amp is on order so I better get this thing filled and painted.



Sad day with out a subwoofer in the stgdz crit viewing area
I haven't had one in there for over 8 years and I can't believe how much I miss it now, hopefully I can get it done over the next two weeks.
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post #30 of 49 Old 12-25-2010, 10:18 PM
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Any updates on your sub? How did you finish and how is the new amp working? Did you ever take max SPL readings?
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