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Post by Gary Cook on Apr 27, 2014 0:51:51 GMT -5
I beleive way back kef use to provide kits for transmission Line enclousure that were huge . It used a 9 by 15 inch flat piston woofer, a matched 6 inch mid and 1 inch tweeter. I built such a monster about 40 years ago and my neveux still has it in his home. They went down to almost 20 Hz at the time. They had a huge front opening 9X15 inch bass port and they were about 2 x 2 x 6 feet high and of about 150 + pounds. Mel KEF transmission lines, that brings back memories. I recall seeing a pair of the legendary IMF TLS80 9 (designed by Irving M Fried), unfortunately beyond my woodworking skills at the time. There was also a multi folded transmission line labyrinth design by C. J. Rogers, there is actually a pair for sale in the UK currently; Cheers Gary
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Post by Canuck_fr on Apr 27, 2014 10:49:00 GMT -5
Generally, in a labyrinth design, the idea is that the overall length of the labyrinth (tunnel) works out to be half the wavelength of the lowest frequency you expect it to produce. This way the sound coming from the back of the speaker (which is 180 degrees out of phase from the front wave) is shifted another 180 degrees by the time it gets to the port - and so it adds to the front wave and reinforces it. This doubles the output from the front of the driver at that frequency, and the cabinet should be designed such that it provides damping for the driver as well. (Usually transmission lines include stuffing in the tunnel - which increases its "effective length" and adds damping. There is also an intent that higher frequencies shouldn't "make it out of the tunnel". Even without stuffing, the author says his does pretty well in that regard, which makes sense since, while bass travels through the tunnel as a pressure wave, higher frequencies would have to ricochet back and forth until they find their way out. You do get about 3 dB of "boost" at the tuning frequency by doing this, but the biggest advantage is supposed to be cleaner, more well damped sound (very sharp; very little ringing). As for maximum capacity, you will get about 3 dB more than the driver alone can do, which is not going to be much low bass with a 4" driver (think "punchy"; not "thunderous"; putting the vent opening in a corner or on the floor may help there - this author did not.). You're also going to get some high-frequency roll off - because the driver isn't a tweeter. (And, even though some tiny drivers can be EQed to go pretty high, you usually get all sorts of distortion and beaming effects when you try to make a midrange work as a tweeter. You've also got the fact that the cone is moving quite a bit to make low frequencies - and that moving cone is trying to make high frequencies at the same time - we call that MODULATION - as in "intermodulation distortion"; you're basically moving the tweeter back and forth with the bass. ) For anyone looking to try a DIY labyrinth or TL design, but dubious of their woodworking skills, you should note that several (supposedly successful) designs have been made using 4" (or larger) PVC drain pipe for the "cabinet". It's strong, rather inert, easy to work with, and you can make any shape you want by combining elbows and corners. I've seen ones that zig-zag, ones that spiral, and long straight ones..... (you can even make a long one and snip off - or add - length to tune it) Link works now. The design seems to compromise his premise of "Elongated sound passages". Based on the design, I really can't see how this speaker would sound good across the normal audio frequencies. I'll admit it is braced very well but that's not the only tenet of good loudspeaker design. Seems overkill on the bracing. Normally one just needs to stop the cabinet from flexing and doesn't need concrete-pillar solidity. A single 8cm driver won't cut it IMHO. For a start, there'll be nothing in the mid-upper frequencies. Just my 2 cents. While this is true, the new transmission lines are now doing the same by using dimensions that 1/8th or 1/18th wavelengths.
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Post by Canuck_fr on Apr 27, 2014 10:52:50 GMT -5
I beleive way back kef use to provide kits for transmission Line enclousure that were huge . It used a 9 by 15 inch flat piston woofer, a matched 6 inch mid and 1 inch tweeter. I built such a monster about 40 years ago and my neveux still has it in his home. They went down to almost 20 Hz at the time. They had a huge front opening 9X15 inch bass port and they were about 2 x 2 x 6 feet high and of about 150 + pounds. Mel KEF transmission lines, that brings back memories. I recall seeing a pair of the legendary IMF TLS80 9 (designed by Irving M Fried), unfortunately beyond my woodworking skills at the time. There was also a multi folded transmission line labyrinth design by C. J. Rogers, there is actually a pair for sale in the UK currently; Cheers Gary As you can read from my signature, I currently own 4 Ariel TL speakers in my dedicated room setup for both Stereo listening and Home theater. These IMF speakers were what hooked me to TL speakers back in 1977! I just love the tight bass they produce. To my ears there is never a better base than that coming from a TL speaker.
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