Woofers getting workout, but no bass

Acoustat,
I don't know the circuit details (probably wouldn't understand them if I did) but Mapman's comment seems about right from what I remember Nick saying. It's certainly not switchable. I got the impression there's no active filter *added* to the circuit, but rather its a characteristic of the circuit itself. Sorry to sound so mystical about it.

Agree with Dan_Ed, with some elaboration. Certainly if the amp stage or its power supplies clip due to the extra LF energy you'll have sonic problems.

More subtly but more commonly, if the amp or its power supplies are easily modulated by the extra LF energy then it will congest on complex or dynamic passages. Dan's amp and mine (more Doshi stuff, sigh!) are about the best we've heard in their power class for the ability to resist such congestion. The power supplies are radically overbuilt and very carefully grounded, which reduces signal modulation of the PS to very low levels. Similar class amps played side by side are often less transparent, and I'd expect those amps would suffer more from woofer pumping.

If the amp has sufficient isolation and headroom then I agree the sonic effects would be lessened.

The Wikipedia seems to indicate that rumble affects the sound even when not audible.

"Even when not audible, rumble can cause intermodulation, modulating the amplitude of other frequencies. The ‘unweighted’ response curve is intended for use in assessing the level of inaudible rumble with such intermodulation in mind"

Also, one has to wonder how a speaker can produce accurate bass when the woofers are pumping violently.

That being said, I've given up on doing anything about it for the time being.

I just look at mine when they do it...and it hypnotizes me. INTO WANTING MORE EQUIPMENT!!

"11-01-09: Vandermeulen
I just look at mine when they do it...and it hypnotizes me. INTO WANTING MORE EQUIPMENT!!"

Want more equipment?
Try a subsonic filter

Bob

Definitely, you are reproducing the record warps. You need a subsonic filter. Your amps are using a lot of power to reproduce frequencies that you cannot hear, and that you don't WANT to hear. Also, if you are using a heavy arm with a high-compliance cartridge, this makes the problem even worse.

Tell us what cartridge and arm you are using together.