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Old 3rd May 2007, 04:22 AM   #1
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Default 15HZ Sub (you can build in an hour)

Inspired by an argument on the tapped horn thread, I threw together a design for a subwoofer that reaches down to 15hz. This is serious bass folks - and you can build it in an hour.

It's a tapped horn tuned to 18hz. The driver that I used is a Diyma 12, which costs about $122 at www.diymobileaudio.com. The biggest challenge with this design is that the Diyma only works in a very VERY small box! In fact, the box is so small that the woofer doesn't even FIT! So I took a novel approach - the "tapped horn" bolts to baffle, but the horn has a diameter that's SMALLER than the woofer itself! In fact the "tapped horn" is simply sixteen feet of PVC tubing, with a 180 degree bend in the midpoint. You have two choices - you can use four lengths of 3" PVC tubing. Or you can use a single length of 6" tubing. Take your pick. The 3" PVC is much easier to find.

First, here's a diagram of the enclosure:
Click the image to open in full size.

Here's the diagram above in PDF

Second, here's the modeled response:
Click the image to open in full size.

One thing you'll notice about this design is that the efficiency is VERY low for a horn. This is due to the fact that the Diyma has an efficiency of just 84db. But there's an upside - this is easily the smallest 15hz subwoofer you're going to find. Remember that horns, like all subs, can be made smaller if you use a driver with a VERY low VAS. And the Diyma has a incredibly small VAS. In fact, if you try to increase the volume of the enclosure it will become "peaky." So it's ideal to keep this tapped horn on the small side, and feed it lots of power.

Here's the AkaBak model I used.

System 'S1'

Def_Const
{
Xwidth = 13.5e-2;
Xthroat = 13.5e-2;
Xmouth = 13.51e-2;
Lhorn = 488e-2;
Ldriver = 26e-2;
}

Def_Driver 'Diyma12'
dD=25.2cm |Piston
fs=25Hz Mms=327g Qms=4.75
Bl=22Tm Re=3.6ohm Le=1.3mH ExpoLe=0.618

Driver 'D1' Node=2=0=100=101 Def='Diyma12'
Duct 'Dr' Node=101=102 WD={Xwidth} HD={Xthroat} Len={Ldriver}
Duct 'Dd' Node=100=104 dD={Ldriver} Len=3cm
Duct 'Df1' Node=103=104 WD={Xwidth} HD={Xmouth} Len={Ldriver/2}
Duct 'Df2' Node=104=105 WD={Xwidth} HD={Xmouth} Len={Ldriver/2}
Waveguide 'W1' Node=102=103 WTh={Xwidth} HTh={Xthroat} WMo={Xwidth} HMo={Xmouth}
Vf=50mm3 Len={Lhorn-Ldriver-Ldriver} Conical
Radiator 'Rad1' Node=105 Def='Df2' WD={Xwidth} HD={Xmouth}
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Old 3rd May 2007, 04:24 AM   #2
Glowbug is offline Glowbug  United States
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Very cool design.

I was extremely disappointed with the DIYMA 12" that I got to test, the cone flexed way too easily and actually dented due to normal use

But it sounded alright.
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Old 3rd May 2007, 04:39 AM   #3
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Quote:
Originally posted by Glowbug
Very cool design.

I was extremely disappointed with the DIYMA 12" that I got to test, the cone flexed way too easily and actually dented due to normal use

But it sounded alright.

was that for the subwoofer shootout? what enclosure did you have it in? i've found that this driver is quite sensitive to enclosure volume increases (beyond optimal), moreso than others. i'm curious because i think it sounds quite good.
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Old 3rd May 2007, 04:48 AM   #4
Glowbug is offline Glowbug  United States
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It was part of this: http://bigbassman.realmofexcursion.com

I was doing most of the subjective SQ reviews.

It was in a little over 1cF sealed, IIRC.
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Old 3rd May 2007, 04:51 AM   #5
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Default Good work!

it would be interesting if you could run some sims with either a conical or exponential horn to compare to the pipe. Wondering how much gain a horn would provide over the pipe and if it is worth the added effort to build.
In terms of shear bulk Vs bass extension I think that you may have set some kind of record so kudos to you mate! Oi Oi Oi!!! Regards.
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Old 3rd May 2007, 05:04 AM   #6
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Default Re: Good work!

Quote:
Originally posted by moray james
it would be interesting if you could run some sims with either a conical or exponential horn to compare to the pipe. Wondering how much gain a horn would provide over the pipe and if it is worth the added effort to build.


Oh definitely, I tried that!

Here's what I found:

If you increase the volume on the tapped horn, the response begins to get "peaky." Danley mentioned that the tap smooths out the response. So this seems to be key - it actually works BETTER in a smaller volume.

Increasing the flare raises the F3. For example, the design I posted has a flare of one-to-one. Which means that the throat is the same volume as the mouth. If you increase the ration from 1to1 to 4to1, the overall SPL goes up... but the F3 goes higher too. Personally, I'd rather have a low F3, and it's easier to build with a straight flare too!

Last but not least, you can make it even smaller by reducing the length of the pipe. The response stays pretty flat... But the F3 goes up. The reason why I chose a length of eight feet is that it's JUST tall enough to fit in a house. Any longer and you'd need to raise the roof!

Quote:
Originally posted by moray james In terms of shear bulk Vs bass extension I think that you may have set some kind of record so kudos to you mate! Oi Oi Oi!!! Regards.
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Old 3rd May 2007, 05:07 AM   #7
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Quote:
Originally posted by Glowbug
It was part of this: http://bigbassman.realmofexcursion.com

I was doing most of the subjective SQ reviews.

It was in a little over 1cF sealed, IIRC.

yea. the first enclosure i listened to it was just around there and it was overly bottom heavy. this sub really needs a small box. i wasnt at all impressed with those reviews tho, some numbers and worthless graphs with hardly any substantial comments. pretty much only useful for those interested in which sub gets louder in the arbitrarily chosen enclosures (close for most woofers but shortchanged woofers like the diyma imo, another huge flaw with the test imo). then again, i'm just too used to klippel results followed by extensive reviews explaining the listening sessions.
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Old 3rd May 2007, 05:16 AM   #8
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Using 3" PVC, there are 4 pipe sections, but there are only 2 "tubes", correct?
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Old 3rd May 2007, 06:05 AM   #9
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Quote:
Originally posted by 454Casull
Using 3" PVC, there are 4 pipe sections, but there are only 2 "tubes", correct?
Take your pic:

Use one length of 6" tube that's a total of sixteen feet long. The 180 degree bend will burn up about a foot, so use TWO pieces of 6" x 78" pipe.

::OR::

Use FOUR lengths of 3" tube that's a total of sixteen feet long. The 180 degree bend will burn up a bit less than a foot, so use EIGHT pieces of 3" x 78" pipe (approximately.) Four piece of 3" PVC tubing have an IDENTICAL volume as one piece of 6" tubing.

If the total length is off by half a foot or so, it's no big deal.

The general idea is cheap, easy and fast.
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Old 3rd May 2007, 06:16 AM   #10
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OK, so 4 tubes if I use 3" PVC.
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