Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83 based; site hound.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!hound!rfg From: rfg@hound.UUCP (R.GRANTGES) Newsgroups: net.audio Subject: Re: subwoofers and xovers - principle of a TL spkr cabinet Message-ID: <1417@hound.UUCP> Date: Wed, 16-Oct-85 23:56:15 EDT Article-I.D.: hound.1417 Posted: Wed Oct 16 23:56:15 1985 Date-Received: Fri, 18-Oct-85 01:11:46 EDT References: <1395@teddy.UUCP> <30200019@siemens.UUCP> Organization: AT&T Bell Labs, Holmdel NJ Lines: 42 [] TL = Transmission Line ? If so the principle is something like this. If I error, I'm sure that I will be corrected. One basic problem with speakers is that they have two sides. What happens to the sound coming from the back side? If you do nothing about it it will sneak around front and cancel out most of what's coming out there. One school of thought says: get rid of it. That's not as easy as it seems. You can build a big box, stuff it full of lamb's wool and hope for the best, you can do lot's of things. One thing you can do is try to build a transmission line to carry the back sound wave away, far far away. If you succeed, you have gotten rid of it. So you build this transmission line and you try to make it very lossy so that if anything bounces back from the other end, which really isn't far, far away after all, it will be very weak by the time it gets back and won't cause any bad feelings. A variation is to figure on taking advantage of the delay in the back wave as it moseys along down the TL as a form of phase shift. At just the right point you suprise the wave into radiating into the room in just the right phase to aid the front side speaker radiation instead of messing it up. If that is pretty hard to do right (more like impossible) then at least your lossy TL will hopefully have weakened it so its too wimpy to matter anyhow. Presumably while the TL may not work perfectly in practice, it will beat the stuffed box as a better "infinite baffle." Unfortunately, it also loses the opportunity to use the sealed volume of air in the box as a more linear spring than speaker mfrs know how to build with their voice-coil supporting "spiders." This is the secret invented by Ed Vilchur and used in the AR speaker. The AR uses the air as an "acoustic" suspension. It uses the box stuffed with lambs wool to lose the sound it doesn't want to use for springing. No question it works mighty good at low frequencies where the wool doesn't absorb much but you need the spring action. the english used to have a TL speaker which sounded very good. I forget its name. I