Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/3/84; site teddy.UUCP Path: utzoo!decvax!ucbvax!ucdavis!lll-crg!seismo!harvard!talcott!panda!teddy!rdp From: rdp@teddy.UUCP Newsgroups: net.audio Subject: Re: subwoofers and xovers Message-ID: <1459@teddy.UUCP> Date: Mon, 21-Oct-85 10:13:50 EDT Article-I.D.: teddy.1459 Posted: Mon Oct 21 10:13:50 1985 Date-Received: Tue, 22-Oct-85 08:15:36 EDT References: <1395@teddy.UUCP> <1556@hammer.UUCP> <1431@teddy.UUCP> <1575@hammer.UUCP> Reply-To: rdp@teddy.UUCP (Richard D. Pierce) Distribution: na Organization: GenRad, Inc., Concord, Mass. Lines: 80 In article <1575@hammer.UUCP> seifert@hammer.UUCP (Snoopy) writes: >>> You can go to larger drivers, but transient response will probably suffer. >> >>If the crossover limits the high-end cut-off to something like 200Hz, >>and any loudspeaker system can get up at least that far reasonably, >>transient response will suffer only because of the crossover (neglecting >>the fact that the lower cutoff also affects it as well). > >Perhaps I am using the wrong term? A larger driver will have more >mass (other things being equal), and will be more sluggish getting >started and stopped. I suspect that several 10-12" drivers would >sound better than a single large one (18-24-40") for this reason. > In fact, if the response time ("sluggishness gettin started and stopped") is very slow, the upper bandwidth of the driver WILL be severely limited. If you have three woofers, an 8 inch, a 12 inch and a 65 foot, and ALL of them can respond linearly to 200Hz, then imposing the 200 Hz upper limit will make their response time quit similar, regardless of what their unfiltered response time is. My memory may not serve me correct, but I recall the relationship between rise time and bandwidth to be something like: Tr = k/F where Tr is the rise time, F is the upper bandwidth (usually measured at the -3db point, and k is some fool constant I remember as being .35 or something. The exact value here is unimportant, the point is the intimate relationship between bandwidth and response time. Note that the equation is for simple critically damped response, but the point remains the same, bandwidth and transient response are intimately related. In fact, one can be viewed as a transform of the other. giving our three examples some hypothetical numbers, and my (possibly) erroneous constant, we might find: UNIT BANDWIDTH Tr ---- --------- -- 8" woof 2000Hz .2 mSec 12" woof 1000Hz .4 mSec 65' woof 500Hz .8 mSec Well, you say, obviously the 8 inch woof will make a better system because it's MUCH faster. Not so, the same drivers in our 200 Hz system will now have the following (approximate) characteristics: 8" woof 200Hz 2.0 mSec 12" woof 200Hz 2.0 mSec 65' woof 200Hz 2.0 mSec These figures are approximate because there will be a slight additional delay because of the fact that the characteristics of the drivers bandwidth does interact somewhat with the crossovers, but the steeper the corssover cutoff, the more dominent it is in determining transient response. (For those reeady to flame, yes I have made some simplifying assumptions here, but the basic relation ship of transient response and bandwidth still hold true) In fact, you might try the following experiment. Take a tweeter, whose response extends from 1 Khz to 20 Khz, and limit it's bandwidth to say 3 kHz. Now, compare it to the 8" woofer above. Which will have better transient response? Which will be "faster"? Which will be slower? Well, the answer is that the 8 inch will be just as fast as the tweeter, but over all, it's transient response will be significantly better. Why? The tweeter has a bandwidth of 1 kHz to 3 kHz, whereas the 8" has a bandwidth of maybe 50Hz to the same 3kHz. It's transient response (more specifically step response) will be vastly superior to the tweeter's, but it will be no faster or slower. >>Well, let's note that the poster lives in a small dog house, so bass >>really isn't an issue :-) > >Perhaps you have forgotten that the visible doghouse is merely a shelter >for the entrance to the underground mansion. :-) > No, I haven't, but I thought I might have some fun anyway. Dick Pierce