Posted by Wayne Parham [ 192.35.232.241 ] on September 28, 2006 at 21:44:40:
In Reply to: Wayne - What are the fundemental differences between .... posted by Derro on September 28, 2006 at 18:58:13:
First off, I guess I should point out that there is no Thermionic four π loudspeaker. There used to be, but I pulled it from the line a couple years back. It was very large, and I felt it was just too big. The Q of the Alpha 15 driver is so high it needs an open baffle or a really big box.
The difference between the Theater, Stage and Professional Series four π cabinets are all related to the midwoofer driver. The Theater Series four π uses a relatively inexpensive midwoofer that needs a large box. It is tuned to have a nice slow rolloff, so it works well near boundaries, taking advantage of boundary loading and room gain. The Professional Series midwoofer is like that too, but the box is much smaller and its midwoofer generates lower distortion because of its use of a shorting ring. The Stage Series is right in between, but doesn't have a shorting ring. It also is better with less boundary loading.
The thing with low power SET amps is they have high output impedance. That makes electrical damping less effective. So woofers that have low Qes will act like they have much higher Qes when a tube amp is used. Speakers generate back EMF, which is not damped by the amp, so response can suffer in some cases. If a loudspeaker's impedance curve has large spikes, then this will act like a voltage divider with the tube amp, which in turn causes response spikes.
The Theater four π Speaker has a tube-friendly impedance curve, meaning there isn't a lot of fluxuation. The Professional Series four π is pretty good too. All of the six π and seven π cornerhorns have flat impedance curves. The Stage four π and Premium four π have more fluxuation, as does the Theater three π. They work well on some low power amps, less so on others. All of the Thermionics and Studio Series models work well on any amp, including low power SET amps.
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