$10 (plus wood) 18Hz ISOT-TQWP Sub - diyAudio
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Old 17th February 2012, 09:44 PM   #1
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Smile $10 (plus wood) 18Hz ISOT-TQWP Sub

Now that your attention is drawn, as is common with many manufacturers, the 18 Hz response of this cabinet is at a bit below 10 dB down from the average.

That said, the sub has a +/- 3 dB response from 24 to 72 Hz, and can play cleanly in the 90 dB one meter range, hitting over 100 dB SPL in room with moderate distortion using only 6.2 V input, which is 11.7 watts in to the minimum impedance of 3.27 ohms.

Although the SPL level is not huge, judging from responses of many posts, the level is in the high range of what many listeners choose.

At $5 apiece, the Sammi 10” woofers (made in Korea), a buyout (formerly) available from Parts Express, part number 299-284 is a good choice for filling speaker holes on a budget.

The sub sounds good with music, even with no fill, it sounds tight and punchy, and gets pretty loud.
The deep dip centering at 76.8 Hz would make crossing around there a good choice, phase and frequency response are very smooth below.

Sine wave testing at 14v (60 watts, rated RMS limit for the ISO pair) only resulted in 11 mm P to P displacement down to 1 Hz. The Xlim is near 22 mm (the voice coil hits the back plate) the 30 watt RMS speakers would probably burn up well before mechanical damage (or clacking noise) would happen. 14 V did result in a bit of glue smell.
The speakers have no back vents and there was very little mechanical noise, any normal music would mask the little noise present. In fact, a rattling wall some 30 feet away was louder to my ear than any non-fundamental noise from the woofers.

I still feel a bit queasy a quarter hour after the 14 v test from 1 Hz to 20 Hz.

This project started with the tragic loss of a pair of Acoustic Research woofers from an AR-2 variant used in a tapped horn, the demise of those woofers described in post #27 of this thread:
AR-1 woofer - new enclosure?
A post-mortem investigation of the drivers showed the spider hit the basket and the voice coils continued going backwards, ripping themselves from the cone.

I had been wanting to get the shop sub going again to fill in below the other three subs in use, but until finding cheap speakers it was not high on the priority list.
Needing to replace a sub in my travel trailer taking up space that will go to a Porta Pottie required a pair of 6” drivers to replace it. With the Sammi 10” speakers, some long mic cords, and a DtoA converter (that didn’t work with my new TV, drat) I was at the free shipping point.

This reincarnation uses the same “Totem Sub” box backwards as an isobarically reverse tapered tuned quarter wave pipe, a ISOT-TQWP.

I’m not normally an ISO fan, as it takes double the speakers and power to get the same output level (in a smaller box), but these cheap speakers and posts showing the advantage provided by a T-TQWP for low frequency extension made me decide to give it a try.

The isobaric loading allows the cheap low-Bl drivers to have very low frequency response in the box, and the cone to cone (back speaker is polarity inverted) isobaric arrangement cancels even order harmonic distortion. At lower volume levels the speakers sound quite clean.

The box interior dimensions are 15.5" deep at the top, 14" deep at the bottom, 11.5 wide, 78.5" tall, about 7.7 cubic feet. The center board is about 3.5” from the front panel, 8.125 from the back at the bottom, approximately 7” from the front and back at the top, 71” long.

Since the sub can’t take much power, bracing is not required. If you plan to upgrade speakers, add bracing from the start.

Knowing from experience that most users will push subs till they sound gross, then back off a bit, I tested with a voltage which Hornresp predicted would drive the speakers well above Xmax.
The speakers only hit a maximum of 10 mm peak to peak on the test, once the speaker’s 4 mm Xmax is exceeded, it simply won’t go much further.
Distortion with the 6.2 V sine wave input averaged 7.2% from 25-60 Hz, rising from 40% at 20 Hz to to over 100% at 10 Hz.

That said, the flapping shop walls don’t lie, this bugger is still kicking below 20 Hz, and since most content down that low is usually cannon shots and stuff blowing up, a bit of distortion is not very distracting.

All in all, for $10 in speakers, a lot of screws, caulk and scrap wood, I’m pleased with the results.

Art Welter
Attached Images
File Type: jpg TotemSub.jpg (44.2 KB, 686 views)
File Type: png TotemFR&Phase.png (170.7 KB, 656 views)
File Type: jpg Exit.jpg (32.6 KB, 646 views)
File Type: jpg Displacement6V.jpg (20.5 KB, 640 views)
File Type: jpg HRinputs.jpg (56.5 KB, 627 views)
File Type: jpg Sammi 10.jpg (52.6 KB, 156 views)
File Type: jpg SPL,Disp 6.2V.jpg (33.3 KB, 136 views)
File Type: jpg PhaseImpedance.jpg (42.6 KB, 95 views)

Last edited by weltersys; 27th September 2013 at 08:02 PM.
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Old 17th February 2012, 10:06 PM   #2
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Cool! I love cheap stuff. You mention upgrading woofers... did you have any other drivers in mind?
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Old 17th February 2012, 10:12 PM   #3
GloBug is offline GloBug  Canada
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Yes!
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Old 17th February 2012, 11:37 PM   #4
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Quote:
Originally Posted by AdamThorne View Post
Cool! I love cheap stuff. You mention upgrading woofers... did you have any other drivers in mind?
I have not modeled others in this box, so can't say offhand what would be a drop in replacement.

This box is stretching the limits, but I had it laying around. I'd normally design for a higher Fb, which would go louder and be smaller, but the VLF response from a cheap driver is something you don't see every day.

The Hornresp information is in the OP, you could try plugging in other drivers with similar parameters with higher Xmax as a start if you are interested.
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Old 19th February 2012, 12:15 AM   #5
mdocod is offline mdocod  United States
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Have to admit, that $5 woofer is really looking like a steal. I think it could be used for anything from sound reinforcement to a car sub and everything in-between for someone on a budget. Assuming the listed specs are accurate.

Neat project. I just tinkered with the driver in hornresp and wow... if the characteristics are close to accurate, there are some really nice options for this driver. I like your approach here of using cheap leftovers to house the cheap driver. Someone could do well with some cheapo OSB from the hardware store also IMO.

I'm thinking closer to 10ft^3 with 4 of these drivers in 2P2S "dual" isobarak would be nice... I don't think I'd bother with trying to get 20hz out of them personally. A shorter wider horn would make better use of available materials, giving more box volume for similar material quantities, and allowing for more SPL in the more normal listening ranges. Though this is all personal taste...

@40W>
Attached Images
File Type: png Hornresp - SPL Response_023.png (16.5 KB, 110 views)
File Type: png Hornresp - Diaphragm Displacement_024.png (14.9 KB, 89 views)
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Old 19th February 2012, 05:09 AM   #6
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that sure is scrap wood! lol
great find art!
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Old 19th February 2012, 05:12 AM   #7
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maybe i'm blind, but i dont see a link to them, so i'm assuming you're referring to these, correct?

10" Ribbed Paper Cone Woofer Speaker 299-284
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Old 19th February 2012, 03:28 PM   #8
mista2 is offline mista2  United States
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Just ordered enough drivers to crank out 4 of them, or two and play with other designs...for the investment, why not? I could use a sub for the garage!
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Old 19th February 2012, 03:46 PM   #9
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Quote:
Originally Posted by m R g S r View Post
maybe i'm blind, but i dont see a link to them, so i'm assuming you're referring to these, correct?

10" Ribbed Paper Cone Woofer Speaker 299-284
Yes, that is the speaker mentioned in the fourth paragraph of the OP. The lower left attachment in the OP has the TS parameters, and shows the speaker in a ported box, the ISOT-TQWP goes almost an octave lower.

Art
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Old 19th February 2012, 03:52 PM   #10
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That must be the ugliest boxes I've ever seen! But hey, it probably sounds well and I guess it was dirt cheap, so why not? :P
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