what is transmission line speaker

[MomurdA]

What is it, how is it different than conventional speakers, and how much do they cost?

[RGA]

PMC is one of the best known for Transmission line loudspeakers, but many other speakers utilize the technology in some of their speakers -- simply it can be used to get more bass depth out of the speaker - Audio Note is another off my head that uses transmission line technology to get more bass depth from some of the speakers in their line-up. It is not new and it does not mean better - it all depends how it is used...but I personally think PMC does a good job. http://www.pmcloudspeaker.com/transmission.html

[Rock789]

is that what bose does with their wave radio?

[RGA]

It may very well be and Bose may call it by a different name -- many do. The difference is PMC knows what they are doing when designing and building loudspeakers - Bose knows what they are doing marketing and selling loudspeakers.

[kexodusc]

Transmission lines are technically suppose to be a speaker with an enclosure that routs the back-wave of a speaker through a long tunnel that eventually exits via the front of the speaker (though I've seen other, oddball designs that have the "port" elsewhere with much success). The theory of the transmission line is to make a line length equal to 1/4 or 3/4 of a wavelength, therefore the front and rear waves will add to each other upon exiting the front of the line, instead of subtracting...this is good...Awesome bass accuracy, realism, tightness, phase, etc...!!!
Resonance (Helmoltz) gets to be a problem problem in the low end of T-Lines though, and is very difficult to predict even with good software programs, which makes these designs quite difficult to produce. But when they're done right, there's no substitute IMO, it's as close to reproducing the soundwaves an instrument makes (ie: low bass frequency cancellation, better attack/decay, response, etc...).

You can typically use the T-Line design with a less "bass-heavy" woofer that perhaps has much more pleasant midrange response and a higher F3 to save some costs. This improves performance as well.

Inexpensive T-lines sound terrible, and there aren't many out there because T-lines are quite difficult to make properly, no sense in going cheap on the drivers, crossover parts, etc...a cheap T-line probably won't compete with other budget speakers, but once you get above the $3000 range, they really start stealing the show...

Real T-Line enthusiasts will tell you not to judge the T-Line design by PMC's offerings as they're the so-called "mass production version" of this design, but I think that's a bit harsh, PMC's sound as good or better than most other speakers you'll hear for the money.

[Rock789]

The theory of the transmission line is to make a line length equal to 1/4 or 3/4 of a wavelength, therefore the front and rear waves will add to each other upon exiting the front of the line, instead of subtracting...

what frequency do these company's use mostly?

[skrivis]

Transmission lines are technically suppose to be a speaker with an enclosure that routs the back-wave of a speaker through a long tunnel that eventually exits via the front of the speaker (though I've seen other, oddball designs that have the "port" elsewhere with much success). The theory of the transmission line is to make a line length equal to 1/4 or 3/4 of a wavelength, therefore the front and rear waves will add to each other upon exiting the front of the line, instead of subtracting...this is good...Awesome bass accuracy, realism, tightness, phase, etc...!!!
Resonance (Helmoltz) gets to be a problem problem in the low end of T-Lines though, and is very difficult to predict even with good software programs, which makes these designs quite difficult to produce. But when they're done right, there's no substitute IMO, it's as close to reproducing the soundwaves an instrument makes (ie: low bass frequency cancellation, better attack/decay, response, etc...).

Well... no.

A pipe closed at one end and open at the other is a 1/4 wavelength pipe. Make it longer and it's a 1/4 wave pipe for a lower frequency.

If done correctly, low frequencies pass completely through the line and arrive in-phase with the front wave from the woofer. You normally would want the line terminus to be on the front baffle (in the same plane as the woofer) so that the outputs are indeed in-phase.

Some t-lines are actually designed to competely lose the back radiation from the driver...

Research by King and Augspurger now allows t-lines to be designed pretty easily, and with good results.

Fried talks about "resistive" speakers, as opposed to "reactive" ones. (In other words, there is no resonant system to store and release energy.) Good horns and t-lines are "resistive," while most bass reflex and sealed boxes are reactive.

A t-line can add the mass of the column of air in the line to load the back of the driver and actually reduce the driver's resonance frequency. T-lines also reduce the magnitude of the impedance peaks. Other types of enclosures don't provide these benefits.

I'm still working my way through King's work, but it's very interesting in that it applies to bass reflex, Voight pipes, and horns, as well as t-lines.

[Beckman]

It may very well be and Bose may call it by a different name -- many do. The difference is PMC knows what they are doing when designing and building loudspeakers - Bose knows what they are doing marketing and selling loudspeakers.

Bose knows what they are doing designing building and marketing their radio. I don't know if there is any other company out there that could make $50 dollars worth of plastic and electronics sound as good as bose does. I think bose is a case of excellent engineering and very low quality components.

[RGA]

Beckman -- you can read reviews of the bose Wave radio out of Britain -- several other manufacturers have apparently built far better for much less money -- but their name isn't Bose -- The Wave radio scored the worst in the group tests of similar devices.

kex

Who else makes great audiophile calibur T-lines -- I'm surprised by the comment against PMC which is first and foremost a Professional Monitoring company who decided to throw their hat into the hi-fi ring -- that alone may be seen as a cop-out amongst DIY crowds -- but that doesn't mean it's reality -- note there is room for improvement with PMC but that;s true of everyone's products.

[Sir Terrence the Terrible]

Bose knows what they are doing designing building and marketing their radio. I don't know if there is any other company out there that could make $50 dollars worth of plastic and electronics sound as good as bose does. I think bose is a case of excellent engineering and very low quality components.

What good is excellent engineering when it is lost on cheap parts? That is like saying a woman has got a great body, but ugly face.

[skrivis]

It may very well be and Bose may call it by a different name -- many do. The difference is PMC knows what they are doing when designing and building loudspeakers - Bose knows what they are doing marketing and selling loudspeakers.

They're certainly good at marketing and selling, but there's also some real talent there.

For instance, they're excellent at getting the most from really cheap drivers.

The end result isn't what I would call accurate, but they didn't design for that...

Companies like Bose and Polk follow a different design philosophy, and it isn't at all what the high-end industry strives for. Nevertheless, they're good at what they do, and they're competent at doing it.

Perhaps I'd put it this way: "Bose speakers are, in my opinion, crap, but it's very well done crap."

[skrivis]

is that what bose does with their wave radio?

The Bose Wave Radio actually uses several very resonant pipes to boost apparent bass response.

The first product I saw from them that did this was a PA speaker with two ported chambers with very high Q. (No stuffing or lagging inside at all.)

You get a tremendous boost, but only at the frequencies the pipes are tuned to. Think of organ pipes.

I suspect it could be rather complicated to design something like this, but a clever design doesn't always equal accuracy.

[E-Stat]

PMC is one of the best known for Transmission line loudspeakers, but many other speakers utilize the technology in some of their speakers...

One of the commercial pioneers over thirty years ago of TL speakers was the late Irving M. Fried. He designed and sold many a TL line speaker under the IMF brand name. Later in the 70s, ESS marketed some TL speakers as well.

When done right, it is a relatively expensive way to get good bass response. I am amused with Bose's notion that somehow they came up with the "acoustic wave" principle. I do admire their marketing expertise, if nothing else.

rw

[RGA]

Audio note uses a Quasi horn T-Line in their AZ series floorstanders and the review said it sounded very much like Quad but with bass.

The original Snells had a Wave Launch system -- hmmm wonder is there is a resemblance?

[kexodusc]

I've heard of some odd-ball designs that use T-Line's for the tweeters etc, never actually listened to these.
I should add that T-lines aren't ONLY a means of improving bass, most T-Line enthusiasts (myself included) would argue the bass improvements are the smallest benefits of a T-Line, though this is often the first thing picked up in initial listening tests because it is such an improvement.

Some of the rest of the theory (which I'm not even going to pretend to fully comprehend) involves preventing the back wave of the woofer from bouncing off an interior wall so as to radiate back into the room through the thin cone of the woofer as in sealed and ported enclosures. These reflecions or echoes add to coloration quite a bit. Instead this energy is tranferred through the system in an a deliberately organized fashioned "in synch" with the forward wave - I have a book that has some research on harmonic ringing or some such term, but basically it's talking about the back wave radiations spilling over into all frequencies.

Also, unlike sealed and ported enclosures where resonances can never be fully eliminated (only managed and diminished), a good T-line theoretically removes ALL resonances because there's no pressure in the system to excite the resonances - again, reduced coloration. The result is a more stable, purer mid-range performance. Problem is some less expensive T-Lines make compromises, and this isn't always the case - these shouldn't be called T-Lines IMO, but oh well.

The T-Line also provides the driver coil with more control (ie: always within the accepted limits of its magnetic field) - less distortion, higher SPL, etc.
Ever notice how some speaker's sound changes as you crank the volume? Often this is caused by thermal compression on the driver coil as heat builds, which is also reduced in a T-Line (better dissipation).

Many T-line designs only concentrate on the bass aspects, not the rest of the possible benefits...a well designed T-line should incorporate all the advanatages.

[RGA]

KEX

That's interesting because parts of those statements seem to be what the AN boxes are doing the AZ series has a huge cut-out about 3/4 the way up the back of them --- your cat could jump inand get stuck -- there's no port just a big square hole and you can see down and inside them...Though my understanding is they use a semi horn as well to raise sensitivity -- a person more knowledgeable than me basically said it's a Semi horn loaded T-Line. I have not heard the AZ series but next time I'm out there It might be interesting.

They call it "Two-way folded, parabolic, rear-loaded, quarter-wave quasi-horn-loaded floor-standing loudspeakers" LOL

Suppose to be very room firendly as well.

A reviewer said

"Audio Note AZ-Three is a two-way speaker system of a hybrid transmission line, folded horn, and bass reflex design. Dimensions are 1000*280*344 mm (H*W*D). Crossover frequency is 4 kHz. The tweeter is the 25-mm impregnated cloth dome, and the woofer is the 200-mm paper cone. The speakers are nicely efficient, about 95 dB, according to our measurements. The shape of the bass response is dictated by the cabinet design providing installation versatility of the speakers. The boost at 3.5 kHz is possibly caused by the flexure of the paper cone; the corresponding coloration is virtually inaudible. As a whole, the frequency response looks well-balanced. The harmonic distortion in the essential frequency range is no more than 0.5% both at 0.5 (88 dB) and 1 Pa (94 dB) signal.../...In accurate, deep, and, above all, clear bass is not surprising at all; this is the family feature. In general, the fundamental advantage of AZ-Three is an excellent image clarity, which is due to the low harmonic and intermodulation distortion. The small value of the latter is responsible for the excellent quality of choral vocals, which is a rare and significant advantage even for high-class speakers. The voices in the monolith stream form a well-readable pattern, the ear relaxes listening to the harmony unobstructed by the characteristic dredge. I won't have the heart to speak about genre preferences; both rock and the most complicated classical music are played easily. Treble is very nice; its exhaustiveness, austerity, and the absence of unnecessary accents is to the audiophile's taste. The sound stage imaging is stable across the front. The sound stage is even as if it grows as a single solid wall; the third dimension is not thoroughly elaborated though. Nevertheless, the image is shaped rather eloquently. Note that the spatial effects are strongly dependent on the speaker position in the room. In this connection, we strongly recommend to follow the placement instructions given by the manufacturer.

In addition to the genre neutrality mentioned above, the indifference to the room size should be mentioned as an advantage. The speakers can be safely placed in a very small room without a risk of spoiling the bass. Their high sensitivity gives one a free hand in choosing an amplifier; in particular, a combination with a valve amplifier can be very interesting." ( by Dmitry Dmitrokopulo, Stereo & Video, November 2000, page 56)

Makes me want to hear it now. (pictures are of the cheaper smaller AZ two - $1kUS so I do want to hear it for the money.

[FLZapped]

What is it, how is it different than conventional speakers, and how much do they cost?

This should answer some of your questions:

http://www.quarter-wave.com/

-Bruce