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Old 21st August 2004, 07:48 PM   #11
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How about two towers about 400mm x 400mm x 1400mm high?

You can put the drivers push - push ( 4 on the front , 4 on the back) and have them either side of your mains. (you said you wanted stereo subs )

Build them, measure the response and do a linkwitz transform / eq on them.

Cheers,

Rob
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Old 21st August 2004, 08:59 PM   #12
Thunau is offline Thunau  United States
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Default Re: Need comments on a proposed sub design

Quote:
Originally posted by cdwitmer
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

I suggest you take look around the infinite baffle forum http://f20.parsimony.net/forum36475/
What you drew up is very similar to some of the manifold designs that the guys on that forum build.
Your idea of operating the drivers below their resonance is the idea behind BagEnd's ELF Infrasubs. There are circuits and descriptions for that design on ESP website:
http://sound.westhost.com/
look for ELF.
I don't think you should mix woofers in the same enclosure. It's been done before, but it's definitely not amateur hour.
Good luck.
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Old 22nd August 2004, 01:29 AM   #13
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Hi CDwitmer,
"I lean toward a pair of subs -- one under each main speaker"
IMO you are on the right track there for several reasons... but don't use those speakers just because you have them. Get some drivers designed to act as subs. In my project studio I listen to and produce mostly orchestral music and so need truly full range un-hyped response from my system. To avoid room modes interfering with equalization as much as possible, I monitor in the near field so I had to get my speakers on my countertop - including, after a lot of messing about with single centrally located sub and various crossover points, stereo subs. I now
have two 8" Peerless subs in closed boxes 10" square face, 14" deep OD, of 3/4" mdf actively crossed over to full range Jordans @ 110hz (bi-amped) sitting on top of the subs which are themselves on 4" or so stands which effectively isolates the speakers from the counter. Each combination collumn stands just over 22" tall including stands and is 14" deep. This is the first of many monitor systems I tried that I can stand to listen to! These little subs go subsonic in my cabs with ease. For example, the first time I ever really heard (and felt!) the 16 and 32 foot pedal pipes in Holst's Planets #5 (in about the 8th minute) was through these speakers. It had me scrambling for the score to see what
the hell was making that sound. They get pretty loud - granted, I listen at moderate levels, but a pair of these would do for a medium sized room. A system like this can render organ the way you want to hear it. Peerless subs $40 each at Parts Express,
http://www.partsexpress.com/pe/showd...ID=16242&DID=7
Specs: * Power handling: 150 watts RMS/210 watts max * Voice coil diameter: 1-1/4" * Voice coil inductance: 1.2 mH * Nominal Impedance: 8 ohms * DC resistance: 5.0 ohms * Frequency response: 25-5,500 Hz * Fs: 25 Hz * SPL: 87 dB 2.83V/1m * Vas: 3.07 cu. ft. * Qms: 2.65 * Qes: .54 * Qts: .45 * Xmax: 5.5mm *

Cheers.
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Old 22nd August 2004, 06:58 AM   #14
ScottG is offline ScottG  United States
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for something a little different..

8 drivers per side

4 drivers facing the listener in a vertical array on an open baffle(the single voicecoil drivers). 4 drivers immeadiatly behind them in a sealed box with an aperiodic "vent", (the dual voicecoil drivers). The single voice coil drivers and one voicecoil of the dual voice coil drivers are series/parallel wired and are either driven by your main amp or a plate amp. The second voicecoil of the dual voicecoil drivers are series/parallel wired and are conected to a subwoofer plate amp with variable crossover and eq.. The front and rear line both operate in-phase (i.e. push-push).

Physically the "box" would look similar to the Legacy Audio Whisper's bass drivers, EXCEPT it would have a box on the rear drivers (and of course you would see 4 drivers in a line). (Note: the black edge on the baffle of the Whisper isn't a black edge - its an opening where the front driver's rear radiation "exits" and where the rear driver's front radition exits.)

http://www.legacy-audio.com/2003/whisper.html
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Old 22nd August 2004, 01:53 PM   #15
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ScottG,

I was looking at a clone of the Whisper the other day and wondered whether the woofers were wired push/push or push/pull. If they are in phase, what is the point? It's just a very loosely coupled isobarik and virtually no sound will come out of that center gap.
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Old 22nd August 2004, 07:32 PM   #16
ScottG is offline ScottG  United States
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I believe the Whisper is an in-phase design. though with a little delay and out-of-phase it could be configured as a 2nd order gradient (i.e. a hypercardoid/superdirectional.) hmmmm, that reminds me.. me thinks I erred on my post on the dipole vs. horn thread - the minimal rear-wave on the hypercardoid is in-phase (not out of phase), though the principal I was getting at was correct (that the null pressure zone was reducing room mode influances).

The design will reduce non-linearity and cone-flexing to an extent. Additionally there should be some reduction in off-axis spl.. whether this is more or less than a dipole, I don't know. (I'm suspecting that it will be less.. with less roll-off than the traditional 6db reduction per octave, but it is purely a guess.) Don't you have a bunch of woofers for dipole use? If so, you could run a quick test to see what the real-world effect is.

The design I suggested is obviously quite a bit different.. the effectivness of both a reduction in non-linearity and side axis nullification will be freq. dependent. The directivity should act more like a dipole as freq. increases and more like a monopole as freq. decreases. In otherwords combine something similar to a dipole midbass driver to a monopole subwoofer with a 1st order filter, while reaping the benefits for both drivers of reduced non-linearity.
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Old 23rd August 2004, 09:56 AM   #17
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With so many woofers there are many options that sound promising for high fidelity use.

* push pull mounting this is one thing I'd definately suggest no matter what alignment

* infinite baffle - one of the best options as it has a good balance of output and fidelity, probably better than anything except dipole but with more output and it takes up no space in your room

* dipole - with this many woofers you can get good ouput with a dipole and the best in room response

* TL - very good transient response and very good for classical music. Size will probably be a problem though.

I'd suggest two approaches that I think will suit best:

1. infinite baffle with all drivers mounted push pull - eq to boost low end response and to deal with room modes

2. hybrid dipole/monopole - for this you need to do some room measurements and find out where the lowest room mode is. Use monopole below the lowest room mode. The monopole might be sealed boxes or infinite baffle but won't need any eq if used below the modal range of the room. Then in the modal range use dipoles - either W frame or U frame (the latter has 6db more output but isn't as effective with room modes). You might cross from dipole to monopole at say 40 Hz, use some eq on the dipole to get down that low. This approach is used by Thorsten Loesch and I think it's one of the best for accuracy in a small to medium room. You would have to experiment with how many woofers you would need for the dipole and monopole. Although sealed for the monopole would work well, the IB will have a transient response matching the dipole which I think would be better.
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