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Old 5th August 2004, 10:04 PM   #1
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Default Need comments on a proposed sub design

This is my way of killing two birds with one stone. I have a large number of 12-inch Pioneer woofers sitting around that I want to "get rid of," and I also need a high fidelity subwoofer that is of reasonable finished size. These woofers are of high quality and go pretty low, but are not designed specifically for subwoofer use. That's another reason why I want to use multiple drivers. BTW I only listen to classical music, including pipe organ music.

I started off thinking of just building a simple sealed enclosure, using woofers in isobaric alignment to keep the size down.

Then I started to think, "How can I add more woofers?" One approach is to start putting woofers on more than one face of the sub. However, I wonder if that will tend to contribute to phase cancellation problems. Especially since I am also thinking of using more than one sub. (I lean toward a pair of subs -- one under each main speaker.)

It occured to me that I might be able to eliminate any phase-induced cancellation problems by making a design like the one shown in the drawing. (I'm not sure I would used woofers on four faces, but that's how I drew it.) Am I correct in assuming this is essentially a 4th-order bandpass design? If so, is my having the woofers firing directly into the port a problem? And how do I actually design something like this so it will work? I would be grateful for tips on free or cheap software that would help me work this out. If the design is going to be too daunting, I may just stick with a more foolproof simple sealed enclosure.

Thanks!

Christopher Witmer
Tokyo
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File Type: jpg subwoofer.jpg (88.1 KB, 233 views)
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Old 5th August 2004, 11:35 PM   #2
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I cant see how it will work, plus I dont see why you need 4 drivers in the box - have you quadrupled the volume to account for the added drivers?
I would check out http://www.diysubwoofers.org
If you like organ music then I would suggest a 1/4 wave TL - they are not that hard to design (Ive made 3 of them). Only drawback is size.
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Old 6th August 2004, 12:06 AM   #3
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Default Some clarifications on this proposed sub design

Regarding the size shown: first, it is just a conceptual drawing, --nothing even remotely to scale. Second, I was thinking of using electronic circuitry that would help me to drive the woofers below their resonant frequency, and also get away with a smaller cabinet than usual.

Thanks,

Christopher Witmer
Tokyo
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Old 6th August 2004, 01:22 PM   #4
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Hey, here's an idea: You said you had a load of these 12" drivers...how about isobaric push-pull to cancel out those pesky nonlinearities and lower distortion? You might be able to pull off a reasonable-size sealed box system that would extend fairly low. Isobaric Push-Pull If you had eight woofers, then you could do two subwoofers each with four woofers in two isobaric pairs.
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Old 6th August 2004, 07:23 PM   #5
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If you dont know the TS parameters, then should test them before choosing an alignment - much less running the saw.

12-inch drivers, not speced for sub use? If I absolutely had to get down low with something like that, I would go with horn-loading, but you've got to know the parameters before you start designing/building.

If you have some of those ugly-low QTS Pioneer woofers, you should use some of your "loads" as passive radiators. Pioneer also made some high QTS woofers, where a OB/dipole sub would be any easy build. If you're never going to check those parameters, I think I'd start with the dipole first.
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Old 6th August 2004, 07:51 PM   #6
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Use as many drivers in as many placements as you wish so long as the farthest distance from the cones is somewhat less than 1/4 wavelength. For a passband up to 100 Hz you will be safe with maximum cone spacing of up to about 2.5 feet.

To get a lot of bass from a bunch of cheapo drivers I'd go with a line array from floor to ceiling. With the drivers spaced edge to edge the phase issue won't arise as they'll act as a single source. For even more oopmh have the array facing into the room corner. Aside from working well this would also take up the smallest possible amount of floor space for the number of woofers used.
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Old 6th August 2004, 11:22 PM   #7
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How many is "a large number" of the 12's? Do they have big magnets or relatively small magnets? How much power do you have to drive them? Do you have an attic or basement above or below the listening area or a closet that could be used for an IB setup?
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Old 6th August 2004, 11:42 PM   #8
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Default Some more details of my woofers

Thanks to all who have replied so far. Some details on my woofers:

I have a total of 16 woofers -- eight woofers of the type shown in the attached image, and eight of an earlier version of the same woofer. The version shown has a "carbon graphite" polypropylene cone, dual voice coils, and is shielded. The rated efficiency of the speaker from which it was taken is 93dB/1W1m. The earlier version differs in that it lacks dual voice coils, has a paper cone, and the rated efficiency of the speaker was higher, 95dB/1W/1m. The power handling ability of the loudspeaker systems was about 120W rms, although I don't know if the woofers themselves are capable of handling more (it may have been the tweeters that were the limiting factor in determinng the allowable power input). The xmax for these is not huge like one normally expects from a modern subwoofer driver; that's why I'm inclined to use multiple drivers. Again, space is tight. (This is Tokyo!) I would like to fit however many woofers I use into a space that does not exceed 1.5 meters wide, by 50 x 50 cm tall and deep. (I suppose I could go a bit higher or deeper, to perhaps 60cm.)

Thanks!

Christopher Witmer
Tokyo
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Old 7th August 2004, 12:14 AM   #9
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Looking at the magnet size, they're fairly low Q drivers so you might need some EQ to get the lowest organ notes with a dipole. Otherwise you could easily fit 8 per side in a W Baffle cab as long as you can accomodate at 67cm or so height. You may even be able to fit 8 accross in WBaffles within your 1.5M limit. If it didn't get you what you to the output level you wanted, you could still use the small alignment and go with an aperiodic cab by stuffing the back chambers. You might even be able to have it be both with stuffed vents on the sides and/or top near the back and use a foam rubber seal around the back edges to form a seal with the wall. Then you'd have an aperiodic enclosure against the wall and dipole away from the wall.

That's such a good idea that I think I'll try that one myself.
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Old 21st August 2004, 12:15 PM   #10
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Hi,

I am new here but well with my knowledge of adding subwoofers like that,there are only 2 ways of hooking up a sub with single voice coil. I would ahve thought that if you ahd 4 subwoofers inside one enclosure they would cancell each other out?? sorry if I am wrong.
Cause I know from expirience that it would if you had the subs hooked the same one way.

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