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Old 12th March 2002, 04:07 PM   #1
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Default What REALLY Matters?

I have been (again) weighing some different design approaches for building my subwoofer. I seem, to keep running across a handful of factors that are alleged to be the main offenders standing between my sub and real fidelity. Chief among them are: Harmonic distortion, IM distortion, Transient response, Phase response, Group delay and cabinet resonance. I am sure there are hundreds of additional more esoteric measurable parameters of acoustic systems of which I am admittedly ignorant.

I just want good bass extension and the highest fidelity I can reasonably afford - I don't need 130 dB and I don't think subwoofer induced sheet rock cracks are the sign of a 'real man'.

So.....let's separate the sonic wheat from the chaff eh? What is it that really matters? What characteristics can be empirically shown in repeatable double blind tests to effect AUDIBLE performance???

Where should I spend my time and money: a massive driver with 2000W Pe and a flat BL to X plot? Push-pull or Isobaric designs? A massively braced cabinet with 3 inch thick walls? Sealed design with some expensive parameteric EQ? Or should I just plead with the wife for that 8 cubic foot box? ( sorry, I forgot that's not an option).

I know the Canadian National Research Council did just such research a few years back but I can't seem to find the source material.


Enough R&R for one morning. Any information/feedback highly appreciated.

regards
<peter>
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Old 12th March 2002, 07:01 PM   #2
subwo1 is offline subwo1  United States
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I am only going to let you know what I have learned from my personal experience. I have no sound lab, etc.. But the work I have done leads me to conclude the easiest way to get the best results centers around a few critical points.
1) Use speaker design software so that you can model your design's frequency response, SPL, and cone excursion.
2) Like you alluded to, make the cabinent solid and stiff so it will not color and distort the sound in the bass region. Fill it with insulation to muffle the resulting higher frequency standing waves. Don't rely on internal resonance to reinforce the sound. The result is boom and mud. Ideally you want an infinite baffle, but since that way is unreasonable to enact, you must take the opposite approach and make the box small. Do not use a woofer with a Qts above .4. Exceeding that figure moves you beyod the point of optimization. The higher the excursion rating ot the woofer, the better.
3)Use active equalization to obtain the best response you can get. There is no way it will be perfect, but you should be able to do very well.
I am not sure if I have mentioned all I have found out. But hopelfuly these thoughts will help you.
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Old 12th March 2002, 09:23 PM   #3
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Javaman,

In my opinion nearly all you points mentioned are no design criteria for me. If I were to design a sub, my goals or better " design criteria" would be f3, Impulse behaviour, Speaker Sensitivity and of course size. This would lead to a initial enclosure pick ; Sealed, Vented, Bandpass, Pushpull, Isobaric passive radiator and so on...
The better your woofer the better your results. Look for high excursion possibilities
A well designed box does not suffer from measurable distorsions or bad responses.
I would bed my money on a good/excellent speaker. Activly equalized and amped. Then again, try to design a box that meets you design standards as close a possible without the use of any "active" aids. And do not use active amping and/or equalizition out of ease.
For closed enclosures i would use a speaker with Qts above 0.3
Vented ones i would use one between 0.2 and 0.5 (Qts).
Don't know what "subwo1" means by Qts below .4

The only two criteria you're talking about which are worth while measuring (For a subwoofer) are Phase response and Group delay. You ears are totally not made for detecting IM distorsion. Harmonic distorsion is more easilly detected. If you woofer can handle the requested power, HD is not a problem.
Cabinet resonance is controlable. Bracing, sandwiched material, sand, etc. or even double woofer designs.
More important is the a airtight enclosure.

Try and start with a closed design. Open a new tread and there are some very experienced guys how can help you with the design of you "perfect" subwoofer.

Hope not to confused you,

regards Mazz.
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Old 12th March 2002, 11:43 PM   #4
Super is offline Super  United States
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Transients are clearly audible. A sub with poor transient response tends to sound "lagged" behind a pair of decent mains, and just doesn't sound natural.
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