How does the Q of the driver affect the performance of a TL speaker? I heard that drivers with a low Qts (0.25-0.4) , low Qes(0.3-0.4) and fairly high Qms(3-6) is used is used . What will happen if the driver is greater of smaller than these ranges?
A driver used in a transmission line will have the same response as a driver used in an infinite baffle arangement. The free-air f3 of the driver will be the same in the TL enclosure. The theory is that the "transmission line" is of infinite length and therefore places no load on the rear of the driver which is isolated from the listening space. The driver's front radiation is all that is used. Pratically, the TL is stuffed with absorbing material to absorb all of the back radiation, and just "looks" like it's infinitely long.
Drivers designed for this application need to have a stiff suspension to support the cone and voicecoil and extra mass to get the f3 low enough to be useful for hi-fidelity. That forces the motor to be very powerful to drive the stiff suspension and high mass. High mass tends toward high Qms, powerful motors tend toward low Qts and Qes. If you go in the opposite direction with the Q values, you'll get higher f3's and/or lower efficiencies.
Quote Roddyama: "The driver's front radiation is all that is used. Pratically, the TL is stuffed with absorbing material to absorb all of the back radiation, and just "looks" like it's infinitely long."
There are two kinds of speakers called "transmission line". Those two kinds are broken down into variations, but no matter.
In the first, there is little or no radiation from the open end of the line. This is the kind that Roddyama is talking about. There is also a fellow named Jon Risch who is a major advocate.
In the second, there is substantial output from the open end. This is probably the more popular kind. I believe the requirements for this type of speaker might be different for the driver.
Here is really good site with all kinds of links and examples. The webmaster posts here frequently under the name Planet 10.