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Path: utzoo!linus!philabs!cmcl2!harvard!think!mit-eddie!genrad!panda!teddy!rdp
From: rdp@teddy.UUCP
Newsgroups: net.audio
Subject: Re: Speaker Sensitivity
Message-ID: <1555@teddy.UUCP>
Date: Thu, 31-Oct-85 14:02:31 EST
Article-I.D.: teddy.1555
Posted: Thu Oct 31 14:02:31 1985
Date-Received: Sun, 3-Nov-85 14:21:27 EST
References: <480@uvaee.UUCP> <601@bonnie.UUCP>
Reply-To: rdp@teddy.UUCP (Richard D. Pierce)
Organization: GenRad, Inc., Concord, Mass.
Lines: 30
Summary: 

In article <601@bonnie.UUCP> saf@bonnie.UUCP (Steve Falco) writes:
>
>Now here's my question:  If you seal the box for acoustic suspension,
>how do you handle changing barometric pressure - it tends to displace
>the cone from center...  Maybe there should be a valve on the side of
>the box to allow mountain dwellers to bleed off some of that extra air
>the factory put in the box.  (Guess I'd better put a :-) in to avoid the
>flamers...)
>

Two answers: first, have YOU ever tried to build a wooden box that was
absolutely airtight? It's real tough, especially when you start cutting
holes in it to put drivers, terminals, etc. Secondly, I have, myself,
never seen an absolutely airtight enclosure that would suffer from the
problems you describe. In fact, many manufacturers seem to be acutely
aware of this problem and build a deliberate leak into the box. Probably
not worth the engineering and manufacturing time to worry about. These
leaks have a long time constant (2-4 seconds) and, because of this, are
of no consequence in effecting the performance of the enclosure as a sealed
box. The time constant should be, of course, much longer than that of the
woofer/enclosure system. This means that for a 30 Hz system, whose time
constant is on the order of 10's of milliseconds, anything substantially
greater than that is suitable to make the driver think that the box is truly
sealed. The danger arises from having the leak "whistle" under certain
conditions. 

Of course, if the :-) you have is global to the paragraph, then you shouldn't
have read my reply :-).

Dick Pierce