Bass leaves after amp warms up?

Are your speakers in phase? Are the cables in phase. Is there an inverting switch somewhere?

I didn't read through the entire thread but this is exactly what happened to a friend of mine. He opened the cabinets and found one of the woofers had the polarity reversed. Damnedest thing I ever heard, but it made sense after we put all of the clues together-our position in the room, the musical content.

It was one of those unexpected issues, if you know what I mean. He thought outside of the box (or inside, in this case). I would have never suspected the woofers came from the factory wired in reverse.

It was a simple case of wave cancellation.

(Sorry if this was discussed, I didn't feel like reading 10 pages of this thread).

Rich

Are you?

Unnecessary. Comments like that are the reason I rarely look at this site.

BTW-Only one woofer was out of phase in my friend's system. The other speaker in the cabinet was in phase.

Why does it take time to perceive any difference? That could be due to musical content and aural acclimation. It took a while for me to notice the drop off at my friend's house depending on the musical mix, seating position, and volume level. Consider also that perfect wave cancellation can only occur with monaural material, so the musical mix plays a big factor in the listener's perception.

One of the reasons the old preamps had a mono switch was to help set the azimuth when mounting a phono cartridge. Wire one channel of the cartridge or speakers out of phase, place the preamp in mono and adjust the cartridge's azimuth till the bass response seemed minimal. This procedure works on the principle that wave cancellation can only occur when both channels are in phase, which can only occur when the cartridge is properly aligned. After the alignment procedure, the speaker or cartridge was restored to it's proper phase and the preamp was returned to stereo operation.

guys,
I'm sorry if I came across terse and offensive.
The point I was trying to make was that the OP needed help, not humor to solve his problem. I realize everyone here is friendly and all, but when you're the guy suffering, answers are what you need, not jokes. I've been there, still am in many ways and use other forums that are more instructive when I have a problem.

I was offering an obscure suggestion (one driver out of phase) because I've heard the effect at a friend's house. We tried everything and nothing helped. I don't know what prompted him to check the internal wiring of the speaker cabinet, but once corrected, all was well.

And yes, it makes sense that the listener, no matter how well trained his ear was would only notice the problem after about an hour. That's about how long it takes for your ears to adjust. Your eye's have to adjust to darkness, your ears have to adjust to volume. It's in your brain, what else can I say. I remember back in the 70's everyone thought Infinity speakers were the bomb because they were bright and sounded so clear when first heard. But after an hour, listener's fatigue set in and they didn't sound so good.

If you think about wave cancellation and augmentation, it's very easy to imagine that the way the music is mixed and seating position have a great affect on your perception.
Try it for yourself, reverse one speaker's phase and play something recorded in mono. As you move around the room, the sound just disappears as you hit that spot near the middle where the sound waves cancel. It's very cool. Even if the recording is in stereo, the bass or drums may be on both channels (effectively Mono), so cancellation can occur.

Again, very sorry to come off terse, I was really only trying to help. If you've been in the same situation as the OP, the last thing you want to hear is jokes. I've been there and would rather get it fixed than joke.
I mean, look at the length of this thread, ten pages and still going. With the other forums I've been on, it's problem solved, thank you. Next question. That's why I hardly visit this site anymore. But you guys are great, and I've made friends here. I was just trying to help, just too serious I guess.

Rich