I was reading about Acoustic Zen Crescendo Speakers that are TL design. WOW $16,000.00 a pair and he used a Triode Corp.
20Wpc TRV-845SE amp $6,000.00. Anyone here own a pair of these? I had to Google Acoustic Transmission Line speakers ...Wikipedia and read about history,theory. Looks some what like what Paul klipsch does to the bass in the Klipschorn speakers.
Klipsch was a proponent of horn loading. Horn loading is totally different from TL loading. It is as different as a brass horn from an organ pipe.
I do not regard the Salk speakers as TLs. They are coupled cavity reflex speakers, and have two tuning peaks of impedance.
TL speakers have had very few good commercial designs, the vast majority being bad.
A TL is a specialized gadeckt organ pipe.
It is a reversed tapered stopped pipe, that is aperiodically damped and should have only one peak of impedance, like a sealed design.
Speaker placement is crucial, to avoid stimulating odd order harmonics.
The length of the pipe will set Fp and will have a close relationship to driver Fs.
The volume of the pipe Vp has a close relationship to the VAS of the driver.
Like sealed enclosures, they roll of 12 db per octave, however the F3 point is much lower than for the same drivers in sealed alignment.
The driver is given support over around 1.5 octaves, which is much broader support than for reflex loading.
This will illustrate what I mean.
Here is the impedance and phase angles of my R & L bass lines.
For the purposes of measurement the two 10" drivers were connected in parallel.
The peak of impedance roughly follows the area of support of the drivers. The calculated F3 is 27 Hz, however the measured F3 in their location is 20 Hz due to room gain.
The two drivers are in fact powered from separate amps. Both receive the same signal below 60 Hz, however the upper 10" driver also receives the BSC compensation signal for the 7" mid, to relive the smaller drivers.
This is the
impedance curve and phase angles of the mid lines in these speakers.
The peak of impedance is at 47 Hz, and measured F3 is 44 Hz.
So these dual transmission lines are tuned one half octave apart and give support to the drivers over 2 octaves, and the support is critically damped as the impedance curves show.
Since the pressure at the drivers in is very high over the area of support, the driver excursion is small and well controlled minimizing driver distortion.
These are the speakers from which these curves were obtained.
This is the configuration of the midline.
The bass lines were built round the midlines.
The only commercial dual line TL I'm aware of was the highly regarded TDL dual line designed by John Wright.
The US price in the early eighties was $23,000 per pair.
Done well TLs deliver powerful uncolored powerful bass.
These speakers were chosen as the reference speakers to audition the final senior student projects at the Minnesota Media Institute for that portion of the students final graduating grade. In part this was due to the outstanding bass definition of these speakers, along with their accuracy in the rest of the audio spectrum.