To the best of my knowledge, like a Pipe Organ, there must be an opening in the line.
The picture definitely shows two active drivers at the ends of the tube.
The "speaker stack" in my living room is almost 8-feet tall! Just an inch or two below the ceiling! I don’t know if an optimized TQWT has ever been Klippelized, but measurements I’ve seen of some tubes based on King’s work are pretty legit.P.S.
I thought about building a transmission line (or labyrinth) once (probably tuned at 20Hz). But it was going to be impractically large. 20Hz has a 56-foot long wavelength so even a half-wavelength is long.
I don't usually say "impractical".
I'm not sure what a true acoustic transmission line would look like. In the RF world, a transmission line is impedance matched to transmit a signal efficiently with no (or minimal) standing waves or return loss.
I drew it to represent my subs--but I don't know how many baffles or if the line tapers.
Those were VERY interesting speakers, which would likely do badly on current measurement suites but were terrific for symphonic music. What happened to them?
The main point of a Transmission Line loudspeaker is that it's NOT tuned. ALL the rear radiation is absorbed in the line, so theoretically it doesn't matter if the line is open or closed. If closed, then any energy still remaining has to travel back through the absorption such that there's really nothing left to reach the back of the cone and colour the reproduction. That's the theory. In practice, few so-called TL loudspeakers are true TLs, and the clue there is the open vent at the front, as there's still LF energy left that by the time it gets out, and with correct dimensioning, the energy left has gone through a phase change (due to the wave velocity being slowed down by the line stuffing) that now reinforces the energy from the front of the cone, helping maintain bass output. B&W's Nautilus is one of the few true TL loudspeakers, and they're pretty big. The larger PMCs also are true TLs (or very close to it).P.S.
I thought about building a transmission line (or labyrinth) once (probably tuned at 20Hz). But it was going to be impractically large. 20Hz has a 56-foot long wavelength so even a half-wavelength is long.
I don't usually say "impractical".
I'm not sure what a true acoustic transmission line would look like. In the RF world, a transmission line is impedance matched to transmit a signal efficiently with no (or minimal) standing waves or return loss.
You have described a labyrinth, not a TL.
In my view, a TL is so-called, because just like an RF transmission line, there is no reflection from the end when the impedance of the line is matched. In general terms, a TL loudspeaker has the TL tapering from wide to narrow, as the energy from the back is of the driver is progressively absorbed. There should be no energy left at the end of the line, so making it immaterial whether the vent is open or closed.
You contradict yourself in your own words. I agree with the statement that the open end of the line will support the driver with audible output which is in phase. So how could a line absorb all rear radiation AND have such output?
It can't. If a line absorbs the whole output, which it should in a real TL, then there's nothing to come out, which is why it doesn't matter if the line is open or closed.You contradict yourself in your own words. I agree with the statement that the open end of the line will support the driver with audible output which is in phase. So how could a line absorb all rear radiation AND have such output?
Regardless, TLs are tuned to the Driver Fs, for optimal performance and both King and Augspurger show the optimal tune to always be above Fs. Unless you are going to claim TQWT designs don’t count?
According to King, the placement of the driver at 1/3 the length of the line aids in damping that 2nd harmonic (an octave and a fifth above fundamental). The proper stuffing of the line helps damp the rest of unwanted distortions and brings the phase back in time 1cycle off. It also helps smooth out the impedance.
Bud Fried and Martin King nod.Well, clearly, everything I've read, and the designers I've discussed this topic with are all wrong. *shrugs
It's been quite a while now since he took that down. Bummer, too!
Fortunately, I hate Apples with a deep, white-hot, burning fury.
