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!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