Transmission line speakers!

The bottom line of any design is how they perform and how musically satisfying they are.  

American made Acoustic Zen Crescendo Marl ll.  Great speaker.   

is a loudspeaker enclosure design which uses the topology of an acoustic transmission line within the cabinet, compared to the simpler enclosures used by sealed (closed) or ported (bass reflex) designs. Instead of reverberating in a fairly simple damped enclosure, sound from the back of the bass speaker is directed into a long (generally folded) damped pathway within the speaker enclosure, which allows far greater control and use of speaker energy and the resulting sound.

Inside a transmission line (TL) loudspeaker is a (usually folded) pathway into which the sound is directed. The pathway is often covered with varying types and depths of absorbent material, and it may vary in size or taper, and may be open or closed at its far end. Used correctly, such a design ensures that undesired resonances and energies, which would otherwise cause undesirable auditory effects, are instead selectively absorbed or reduced ("damped") due to the effects of the duct, or alternatively only emerge from the open end in phase with the sound radiated from the front of the driver, enhancing the output level ("sensitivity") at low frequencies. The transmission line acts as an acoustic waveguide, and the padding both reduces reflection and resonance, and also slows the speed of sound within the cabinet to allow for better tuning.

Transmission line loudspeakers designs are more complex to implement, making mass production difficult, but their advantages have led to acclaim for a number of manufacturers such as IMF, TDL, PMC. As a rule, transmission line speakers tend to have exceptionally high fidelity low frequency response far below that of a typical speaker or subwoofer, reaching into the infrasonic range (British company TDL's studio monitor range from the 1990s quoted their frequency responses as starting from as low as 17 Hz depending upon model with a sensitivity of 87 dB for 1 W @ 1 metre), without the need for a separate enclosure or driver.^[1][2]Acoustically, TL speakers roll off more slowly (less steeply) at low frequencies, and they are thought to provide better driver control than standard reflex cabinet designs,^[3] are less sensitive to positioning, and tend to create a very spacious soundstage. Modern TL speakers were described in a 2000 review as "match[ing] reflex cabinet designs in every respect, but with an extra octave of bass, lower LF distortion and a frequency balance which is more independent of listening level".^[4]

Although more complex to design and tune, and not as easy to analyze and calculate as other designs, the transmission line design is valued by several smaller manufacturers, as it avoids many of the major disadvantages of other loudspeaker designs. In particular, the basic parameters and equations describing sealed and reflex designs are fairly well understood, the range of options involved in a transmission line design mean that the general design can be somewhat calculated but final transmission line tuning requires considerable attention and is less easy to automate.

any of those wishing to differ..can..see how your corrections, edits and such fare on Wiki, or better yet on the….speaker market…. 

I had a rather lengthy conversation w Richard Vandersteen yesterday, we talked about other exotica like tanking circuits and Zobel networks, his use of transmission line didn’t come up…but when we get past Sunday the day of rest, i will certainly ask him….

Since 1977, not everyones cup o tea. How freaking boring that would be

Carry on

Pick your expert carefully….music is AC…. ha

tomic601,

I can't thank you enough. I was feeling like the odd man out. I appreciate your thorough description of TL design. Having owned the large TDL Monitors, I can attest to the scary extension of their bass. It didn't make itself known above other frequencies except when called for.

I recall a short while after I bought them in the 80's, I had a couple of friends over and we were listening to the first Enya disc at a lower level as we chatted in the living room. Suddenly, the synthesizer hit a subsonic note, and it felt as if a very heavy object had hit the floor. I'll never forget the first time I had that experience with them.