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-   -   DIY 40HZ TH for DJ use (http://www.diyaudio.com/forums/subwoofers/159957-diy-40hz-th-dj.html)

NEO Dan 26th January 2010 06:40 AM

DIY 40HZ TH for DJ use
 
Hi All,
This is my first crack at a TH, the design is for a good friend that wants subs for a DJ rig. He had just ordered at GuitarCenter two low line commercial 1x18" ported bins that are very small, it leads me to believe they will not fill the bill. He has a right of return and he may use it and go DIY.

I have been out of audio for a long time but I still do testing and design as a hobby. I have a candidate driver that I tested for a friend in car audio that appears to be a good match for a TH in my noobish opinion. The driver is a 12" 4Ω DVC, the plan so far is to use two per cabinet with the coils wired series parallel for a final 4Ω load per cabinet. Driver specs are measured from a broken in driver, the 19mm figure for Xmech is ~where the suspension starts to limit itself without damage. The goal is solid output to 40HZ, I think I got it. But I came here for suggestions on improving the design.

http://i111.photobucket.com/albums/n.../1BSPL283v.pnghttp://i111.photobucket.com/albums/n...v01/HR283v.png

This is my first fold so..... DON'T HOLD BACK :)
Seriously. I can handle some constructive criticism.

http://i111.photobucket.com/albums/n...1/Layout3S.pnghttp://i111.photobucket.com/albums/n...THv01/1BSD.png

http://i111.photobucket.com/albums/n...1/1BDD283V.pnghttp://i111.photobucket.com/albums/n...Hv01/1BIMP.png

http://i111.photobucket.com/albums/n...01/1BPHASE.pnghttp://i111.photobucket.com/albums/n...THv01/1BGD.png

http://i111.photobucket.com/albums/n.../1BIMPULSE.pnghttp://i111.photobucket.com/albums/n...THv01/1BAI.png

I can see room for improvement in the impulse response, and I'm sure that you all can see other items and point me in the right direction.

littlemike 26th January 2010 07:43 AM

Great start.

Looks like a decent driver for a TH. What is it?

First thing I would do is shorten L12 to about 16 cm.

Second thing I'd do is mess with L34 a bit to see if you can clean up that dip at 100.

Third - it looks to me like that driver wants to play lower. See if the response clears up a bit by lengthening the horn a touch.

jbell 26th January 2010 12:26 PM

http://www.diyaudio.com/forums/subwo...ml#post1829572

If you want a 'proven' design, can't go wrong here with a 3015lf.

MaVo 26th January 2010 04:41 PM

If you want 40hz, its too large. This one will work to 30hz or maybe even lower. Highpass filter at around 25hz seems to be the right choice for this design. Also, your compression factor is only around 1, which is pretty low. If your woofer isnt really cheap, it should be able to handle at least a factor of 2-3.

NEO Dan 26th January 2010 07:40 PM

Thanks for the replies :)
The driver is an Asian built car audio driver of reasonably good quality. The only thing I remember not liking about it was the dust cap, it could flex because has a logo molded into it. I am working on obtaining another sample for testing to verify that it's still the same driver I tested 2 years ago. If it turns out to be a good match I will post the make and model once I've built and tested a cabinet.

Here are the TSP's for the driver I tested, note the 19mm figure for Xmech is based on my visual observation of self limiting of the suspension, not the point of bottoming. I don't think I was able to bottom it.
http://i111.photobucket.com/albums/n...01/XD12TSP.png

@littlemike
THANKS for the tutorials, and being so active on the topic of TH! Thanks for the input, I moved the L12 as suggested, adjusting L23 and L34 to compensate. It's a nice improvement in the upper response. I will spend some time with the L34 and re-folding for a better impulse response.

@JBell I read a large portion of your thread, it's been very helpful. Thanks. I've also looked at the furybox in some detail as I considered it as an option. The cabinet is larger without going lower and uses a more expensive driver. Also I have done some research on the 3015LF in the past, and IIRC the VC is .75" long so your true overhang on the coil is really only .25"/6.35mm.

@MaVo
Thanks for the heads up. I realize the cutoff is lower but I'm looking to keep the cabinet as small and efficient as possible. The goal is strong output to 40HZ for the single cab. The cabinet is intended for use in groups of four or more for DJ work. At that point the cutoff matches up better. So far the dimensions are about 37.5" x 15" x 31.5" hwd in 1/2" material. It looks like the compression ratio is 2.20:1 as shown above in the HR input screen.

Brian Steele 27th January 2010 01:44 AM

http://i111.photobucket.com/albums/n...THv01/1BSD.png

Looks closer to a tapped-pipe rather than a tapped-horn (same family). Probably as a result of a high Qts (from the results of most of my sims, higher Qts = lower compression ratio for flatter response). Quite likely you'll be able to go with parallel walls within the enclosure without any significant variation in the passband response.

How are you planning to mount the driver in the box? With Sd at the mouth so close to driver Sd, I'd be concerned about the driver's magnet "shading" the mouth and adversely affecting the output as a result.

NEO Dan 27th January 2010 02:44 AM

That's interesting Brian,
Your right about it being cramped, as the mouth configuration was to be with the driver magnets just far enough apart to facilitate installation of the drivers. I was thinking that It would appear to be a straighter taper. It never dawned on me to look at it as a tapped-pipe. The loss of SPL part didn't seem to be of concern as the throat of the horn is still much smaller. Is there a rule of thumb for restriction at the mouth in relation to S2/SD compression ratio?

Quote:

Originally Posted by Brian Steele (http://www.diyaudio.com/forums/subwoofers/159957-diy-40hz-th-dj-post2062919.html#post2062919)
Looks closer to a tapped-pipe rather than a tapped-horn (same family). Probably as a result of a high Qts (from the results of most of my sims, higher Qts = lower compression ratio for flatter response). Quite likely you'll be able to go with parallel walls within the enclosure without any significant variation in the passband response.

How are you planning to mount the driver in the box? With Sd at the mouth so close to driver Sd, I'd be concerned about the driver's magnet "shading" the mouth and adversely affecting the output as a result.


djk 28th January 2010 09:35 AM

http://i56.photobucket.com/albums/g1.../PD12SB30a.gif

http://i56.photobucket.com/albums/g1.../Ciare12SW.gif

I would rather use a single 8 ohm PA type 12 than a pair of inexpensive car stereo drivers. The Ciare is not as smooth, but it has about 6dB more maximum output due to its x-max.

NEO Dan 29th January 2010 02:24 AM

The Ciare is like $300 each plus shipping and has less x-max than the driver I selected. You are suggesting that I can get 6dB more maximum output with less than half the available displacement? Do you think it's wise to push drivers that hard? Using the driver I selected the largest cost item of the build by far will be the wood...

djk 29th January 2010 03:56 AM

The Ciare has twice the x-max of the first design I showed, A PD 12SB30.

"19mm figure for Xmech is ~where the suspension starts to limit itself "

X-mech is not x-max. Please specify the driver so we can look at it (or give us a link).

"The Ciare is like $300 each plus shipping "

Outside the USA the Ciare is not expensive, a Lab12 driver is more expensive in europe (for instance).

" can get 6dB more maximum output with less than half the available displacement? "

That remains to be seen. With your box tuning you have less output at 2.83V (and 2x the power into your impedance) and more excursion due to the lower tuning frequency of your box (and no output to speak of at the lower tuning frequency).


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