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From: keithe@tekgvs.UUCP (Keith Ericson)
Newsgroups: net.audio
Subject: Re: Homemade Speakers
Message-ID: <1779@tekgvs.UUCP>
Date: Fri, 26-Sep-86 13:58:14 EDT
Article-I.D.: tekgvs.1779
Posted: Fri Sep 26 13:58:14 1986
Date-Received: Sat, 27-Sep-86 19:24:30 EDT
References: <1147@houxa.UUCP> <3300014@datacube> <3133@teddy.UUCP> <1241@mhuxo.UUCP> <1592@vax135.UUCP> <3210@teddy.UUCP> <854@abic.UUCP>
Reply-To: keithe@tekgvs.UUCP (Keith Ericson)
Distribution: na
Organization: Tektronix, Inc., Beaverton, OR.
Lines: 34
Keywords: double-tuned versus single-tuned

Regarding bass reflex speaker designs: the advantage offered by the
bass reflex cabinet, aka a Helmholtz resonator (or is is Hemholtz?),
is that it provides another degree of freedom to the speaker-system
designer.

The speaker (driver) itself has its resonance, due to the weight
oops - mass) of the cone, the springiness of the suspension, and there
are losses in the suspension, et cetera, et cetera, et cetera. The first
order approximation is a parallel LCR circuit.

The enclosure has a similar resonance, losses, and so on. Again the
first-order approximation is an LCR circuit. (Now don't jump on my
case, already, Dick: I said FIRST ORDER APPROXIMATION, OK?)

By properly designing three parameters the system designer can take
advantage of these resonances to improve the frequency response - at
the loweer frequencies - of the overall system. The parameters are the
driver resonant frequency, the enclosure resonant frequency, and the
degree of coupling between the driver and the cabinet. Those of you
familiar with designing double-tuned filter circuits (aha, I see we
do have some amateur-radio enthusiasts in the audience) have seen
this before. By properly designing the system the two circuits
will interact so as to reduce the effect of the separate resonant
peaks and thereby smooth the overall response.

But you don't just look at the front panel and say "Well, this looks
like a good size for the reflex port" and attack it with your saber-
saw. Check out some reference material - Olson's (isn't that the name?)
book from the 50's (40's?) is a good place to start. From there - you're
a big boy - go look it up.

keith

PS - #define  "you're a big boy"  "you're a mature person"