Bass leaves after amp warms up?

Should I ask where you plug in the ground?

I will preface my comments by saying I have not read everything said above, so I may be covering ground that has been rehashed to death. If the problem persists after certain components have been switched out, it lies with those that have not been switched out. If it happens with different sources, it is probably not the source components. If it happens with different sources, or when a source has been switched out, or with different components in the amplification chain, that really leaves the speakers to be suspect. If one overheats speakers the sound does change dramatically. If, for example the woofer voice coil gets too hot, resistance will shoot up and the speaker will sound lighter in bass. The crossover components can also heat up and this will affect the sound dramatically as well-component values will shift and change crossover points, filter characteristics, etc. and could lead to the loss of bass.

Such obvious change in sonic characteristics, if due to overheating of the speaker, constitutes pretty rough treatment of the speakers. Perhaps something designed to produce higher volume is needed for this particular application.

Does the dealer you bought from still sell the PSBs?

Maybe go there, talk to the dealer, and listen to your speakers there off a few different amps if possible. Maybe even take yours in and see what happens there off various amps if possible. Maybe even take the amp in to test out. See if same thing happens there.

Some of the recent posters have, understandably, not read through all of the 130+ posts in this thread. So here is a summary of some of the key facts that have been stated:

The same problem has been exhibited with two different models of PSB speakers (the Synchrony One and the Synchrony Two), both having impedances that are specified as 4 ohms nominal and 4 ohms minimum. JA of Stereophile measured the impedance of the Synchrony One that is presently being used as being between about 2.7 and 4 ohms throughout most of the bass and mid-range regions. The OP does not play the speakers at high volume levels.

The same problem has been exhibited with three different integrated amplifiers. There is reason to believe that driving low impedances is not a forte of any of those amplifiers.

The same problem has been exhibited with two different sources.

Connecting only one speaker to the amplifier considerably increases the amount of time between a cold start and the appearance of the problem.

When the bass disappears, it can sometimes be made to reappear by switching between sources, disconnecting and reconnecting the speaker cables, or other seemingly innocuous things. The integrity of all connections appears to be good.

My suggestion, at this point, in addition to the planned electrician visit, and attempting to borrow different speaker cables: Try to borrow a separate power amplifier that is known to be able to deal with very low impedances, and drive it from the pre-outs of the integrated amp.

Regards,
-- Al

I wonder if the problem could be better addressed if the OP had a SPL meter and a test disc so he could actually measure the SPL's at the listening seat. That way he would know if it was in his audio system or in his head. It would also help to know at which frequencies this loss of bass occurs and the actual amount of the loss.