Transmission Line Speakers
Ed
that have deep bass. He commented that transmission-line speakers often have
muddy, poorly controlled bass with little dynamic or attack. Does anyone have
any thought on the bass from speakers utilizing transmission line loading?
Ed Devlin
Richard D Pierce
:Ed (EDW...@tiger.hsc.edu) wrote:
:TL woofers he's listened to. Possibly, this is his way of saying "the
:bass response is not at boomy as I like it".
:Transmission Line designs, done well, are better controlled and "tighter"
:than any other design short of servo'd woofers. This is because a TL
:woofer system has a first-order (6dB/octave) bass rolloff initially.
:It's response looks like a very over-damped sealed system.
Not correct at all. This is an assertion that dates back to as early as
1971, when Bud Fried was making this claim (unubstantiated).
A transmission line designed to augment the total system output with
radiation from the end of the line looks, behaves and measures just like
a reflex system. It shows the phase response, it shows the transient
response and it shows the frequency response of a 4th order system.
Period. If you arrange the Fs and the Fb of any reflex system
appropriately, you can get it to behave in such a way that it exhibits
something other than the commonly supposed 4th order butterworth rolloff.
But exhibit 1st order rolloff? Sorry, it can't do it.
If, on the other hand, the line is either so heavily damped or it is
closed, it will exhibit the same phase, transient and frequency reponse
behaviour as a 2nd order system. Period.
The advantage to transmission lines comes in two ways, NEITHER having
much to do with low end extension or roloff rates. First, in the upper
bass and lower midrange, cabinet coloration due to internal reflections
can be greatly reduced if the line is done properly. Second, if the line
is designed and assembled properly, the effect of all those baffles on
stiffening the cabinet can be substantial. These, however, are secondary
benefits, even though their effect can be important.
In terms of extending the low end or somehow making the transcient
response better or reducing the roloff rate, there is nothing a
transmission line is doing in that respect that's any different than
other 4th order systems. In fact, if you model a transmission line at low
frequencies as a system with a relatively high compliance ratio/high port
mass/high port loss/high absorbtion loss 4th order system (just like it
looks, small, heavily damped enclosure with a long, damped port), the
response predicted by such a model matches extreemely well the actual
measurements ofreal systems. The common stransmission line model fails in
its ability to prodict actual performance.
:Unfortunately, if you want good bass extention you need a very big
:enclosure (long line) compared to typical consumer boxes. The complexity
:of the cabinet and size have made them unprofitable, relatively speaking,
:for manufacturers. Some people swear by them, and I rather like them
:myself.
Well, unfortunately, any speakerr that's required to go to low
frequencies with any degree of efficiency MUST be large, magic and claims
not withstanding.
:For subwoofers, though, I'm a servo'd woofer fan, myself.
:Mine is flat +- .5dB from 16Hz to 300 Hz, and the transient response and
:honesty is a delight. Surprising, even. I've recorded waveforms from my
:sub, in -vs- out, and when the serve system is on, the two match
:beautifully.
Uh, how can this be? A subwoofer is a band limited device. It is
impossible for ANY band limited device of ANY technology to reproduce an
exact (or even "beautifly matched") copy of an input waveform. I
challenge you, for example, to demonstrate that your woofer can produce a
perfect copy of a step response, or a 1 msec wide pulse, and so on.
Unless, of course, you're willing to abandon all notions of causality.
--
| Dick Pierce |
| Loudspeaker and Software Consulting |
| 17 Sartelle Street Pepperell, MA 01463 |
| (508) 433-9183 (Voice and FAX) |
Robert Slugg
good." I built my TL's from a kit after demoing them with "Another brick
in the wall" being powered by an identically modified ST70. The transient
attack is phenomenal, and the extremely narrow front baffle really improves
imaging. Granted, they don't have the "natural" bass of a 15" Cerwin-Vega
woofer, but they do make the most of a small cone. Tranny's are big and
heavy. Mine weigh about 80 lbs apiece. The 10" model weighed 120 lbs. They have been replaced by cheaper power and less efficient speakers. If you have
a wood shop or access to a table saw, get some 3/4 fiberboard and build a
pair, you'll never regret it.
Bob
Bob Olhsson
I'd go find another dealer!
No design method has an exclusive on good sound. Some of the most convincing
bass response I've ever heard came from the old IMF transmission line
systems.
Modern ported designs do better than a "TL" (which can mean many things) in
bang/buck but across the board condemnations make both the depth of
knowledge and the integrety of the dealer suspect to me.
I won't even go into the issue of bass "attack" as there are far more
qualified folks here than me to comment on that one.
busenitz
:in the wall" being powered by an identically modified ST70. The transient
:attack is phenomenal, and the extremely narrow front baffle really improves
:imaging. Granted, they don't have the "natural" bass of a 15" Cerwin-Vega
Why is the front baffle very narrow? Is it because
a small driver is used, and if so, why is a small driver
used for TL enclosures?
Uli Bodenhausen
|> Ed (EDW...@tiger.hsc.edu) wrote:
|> :that have deep bass. He commented that transmission-line speakers often have
|> :muddy, poorly controlled bass with little dynamic or attack. Does anyone have
|> :any thought on the bass from speakers utilizing transmission line loading?
|>
|>
|> Well, your dealer is either full of it or is speaking of poorly designed
|> bass response is not at boomy as I like it".
I agree with Philip and not with this sales guy. It is true that poorly
designed TL's can have a muddy characteristic. It can be best described as
"each bass guitar sounds exactly the same". The sound of TL's is not only
depending on the length of the line, but also on the damping of the line.
Some modern designs also use woofers inside the line to control the sound.
Uli