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In Reply to: Yes, I'd like to hear more about it, especially the sealed vs. ported issue. posted by powermatic on April 3, 2007 at 19:59:34:
I think the relatively poor bass pitch definition of many ported designs is a result of unfortunate choices on the part of the designer - going for the quick-cheap-wham-o thrill of the boom instead of has-to-grow-on-you accuracy.The in-room frequency response curve seems to be a reliable predictor of subjective bass naturalness (hence my use of scattered multiple low frequency sources to smooth out the in-room bass). I've read mixed results as to the audibility of group delay - apparently it is audible if you have too much, but it's apparently not audible in many practical vented systems.
Now most vented systems are designed for "flat" or even exaggerated bass, and in my opinion this is wrong for a subwoofer that is going to get the benefit of a lot of boundary reinforcement. Instead, you want a subwoofer with a very gentle rolloff (maybe 1 or 1.5 dB per octave) starting at about 100 Hz, and no bump at port resonance. This shape frequency response curve isn't practical in an unequalized sealed box system, but it is not that hard to get in a vented box. Briefly, just use a big box and tune it lower than normal. Now this won't work with all woofers, so you have to model several different woofers until you find one that gives the target curve you want.
Getting specific about sealed box subs for a minute, the "critically damped" Qts = .50 alignment is in my opinion overdamped. I hear better impact from a bit higher Q alignment, and I don't start hearing objectionable heaviness until you get up around Qtc = .85 or so. This based on relatively few data points gathered informally back in the 80's, but it convinced me that ultralow Qts wasn't necessarily the answer.
As far as box size, I start out with an enclosure volume that would give me a Qts of between .45 and .5 if the box was sealed. Then I tune low enough to get the shape frequency response curve described above. I try different woofers until I find one that gives me no peaking at system tuning frequency while meeting these other requirements.
In the Swarm I wanted bass extension to an honest 27 Hz, as that's the lowest fundamental of orchestral instruments. The Swarm goes down to about 25 Hz. To really do justice to heavy synthesizer rock you'd probably want to go to 20 Hz, and organ enthusiasts would probably prefer extension to 16 Hz or lower. Maybe one day I'll build a version for organ music fans - but it will be a lot larger and a lot more expensive.
Hope this helps.
Duke
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- Re: Yes, I'd like to hear more about it, especially the sealed vs. ported issue. - Duke 20:56:36 04/03/07 (0)
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