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Old 18th May 2012, 07:48 PM   #1
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Default Current state of TL speakers?

What's the current state of transmission line speakers in terms of modeling and predictability? Is the style in favor? Recommended driver types? Stuffing or lining?
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Old 18th May 2012, 08:40 PM   #2
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Originally Posted by Conrad Hoffman View Post
What's the current state of transmission line speakers in terms of modeling and predictability?
Both Martin J King's MathCAD worksheets, and George Augsperger's TLx software, are very accurate. The former also helps us better understand a lot of the myths and phenominon at play in loudspeaker enclosures, and is highly recommended. There are a lot of myths about TLs that I think MJK's software has helped dispel.

Quote:
Is the style in favor?
Well, Martin King's research on transmission lines has sort of revealed why a lot of ported loudspeakers "sound bad". Because his mass-loaded transmission line worksheets can more accurately model the internal standing waves for ported speakers, I think traditional TLs have become redundant - Tapered TLs and ML-TLs basically seem to sound the same in their passbands, but the ML-Tl will normally extend deeper. Either way, though, regardless of what you pick, both are inherently inferior methods of bass reproduction to a good, properly equalized and distrubuted multi-sub setup.

I would certainly rather model a tower as an ML-TL than a ported box program, even though they're probably the same thing for a tower speaker as far as the resonance at play - the only difference is the accuracy of the sim IMO.

Tapered Tls can have a nice, low Q shallow rolloff similar to the Q = .25 type vented/ML-TL speaker, which can work nicely with some room's gain functions. This can lead to a very tight sounding bass similar to a sealed speaker, but with a lower F3. However to get it you need a very big box, and it simply may not be worth it.

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Recommended driver types?
Generally a qts between .35 and .4 is a good idea as a starting point for a TL, OR sealed IMO. A qts between .25 to .5 is just well for an ML-TL. But really, just pick a driver and start simming it and see what you think - is this the sort of frequency response you would live with? Because it's frequency response (a combination of the native response and the room's impact) that will dictate what you hear.

Remember that what looks flat in a sim, may not be flat at all in-room - and likewise what looks like it rolls off early may not roll off early in-room. Placement will dictate the excitation of modes from stereo speakers - what your room does to the sound is a big determinant in SQ below the shroeder frequency.

Last edited by RockLeeEV; 18th May 2012 at 08:49 PM.
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Old 18th May 2012, 11:16 PM   #3
pkitt is offline pkitt  United States
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I've modeled many, many, many TLs of both the tapered and mass-loaded varieties and built quite a few for personal use. For the same line length F3 a folded, tapered TL needs to be about 20% larger in volume than the equivalent ML-TL. Both have pros and cons but both sound and perform quite well.
Paul
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Old 19th May 2012, 04:03 PM   #4
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Thanks! I have a couple pairs of odd 8" drivers around and was thinking about what to do with them. I've built lots of conventional vented and sealed boxes, but have never tried a TL. I've done a few open baffles and thought a TL might give a similar sound with less cancellation on the bottom end. I'll have to try the sims- that was my main curiosity as to whether sims have advanced for TLs and it seems they have.
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Old 19th May 2012, 04:37 PM   #5
Jay is offline Jay  Indonesia
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Originally Posted by Conrad Hoffman View Post
I've done a few open baffles and thought a TL might give a similar sound with less cancellation on the bottom end.
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Old 19th May 2012, 06:57 PM   #6
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Confused? Note I said open baffles, not infinite baffles. That backside wave interacts with the front wave, highly dependent on where the speaker is in the room. Getting extended LF response is, IMO, harder with open baffles. I'm not always the sharpest tack in the box, so what am I missing?
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Old 19th May 2012, 07:23 PM   #7
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Open Baffles are dipolar in the bass. Yess, their global measured response rolls off 6db/oct below the dipole frequency + 12db/oct near resonance, but this is also the reason they produce great bass. Their frequency response is much less altered by the room because much of the bass in various directions aside from forward and back cancels out before it can reflect and return as a peak or valley. So you hear more speaker and less room.

A transmission line won't get you that level of SQ, but it can get pretty good SQ/clean bass as can lower q sealed and ML-TL alignments. It's still dominated by the room, but the box won't contribute coloration of its own.

IMO dipole or cardioid down to ~100hz with a 15" woofer, plus multiple sealed 15" - 21" subs + linkwitz transform below 100hz, is the way to go for the best bass.
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