Originally Posted by elZaphod
Old thread, but I have the exact same problem, and virtually the same equipment. I run an Onkyo TX-SR705, bought it used a couple years back to replace my Yamaha that died after many years. I've run it through a pair of JBL studio reference speakers (can't remember the model offhand right now). I would have to keep turning the volume down lower and lower to avoid distortion. I have my drum kit in the same room and like to play along while I learn, so I like to turn it up, yeah I'm beating the system pretty hard at times.
The JBLs are very nice speakers, but they were kind of small and needed more bottom end. I finally got a pair of Polk RTi A9 towers that I bi-amp with the Onkyo. It is running into the same issue. Sounds phenomenal at high volume, then an album or so in, I find I have to back off. The amp has always gotten damn hot, I'm suspecting the issue is there. The Polks can handle up to 500W, so the 200 I'm throwing at it shouldn't be a problem should it?
Should I try rigging an additional fan in the Onkyo?
I don't know if you read all of the posts on the thread, but the ones from Bill F. are particularly pertinent. Many amps run hot, and an external fan may help to protect the amp components if the amp is in a closet, or on a narrow shelf. But the amp producing heat is not the same thing as the speakers producing distortion. And as with the OP, it sounds as if you are simply over-driving your speakers. In the OP's last post it appeared that he had damaged his speakers by continuing to play them at volumes that the particular combination of speakers and amp couldn't support.
I will defer to others on the causes of thermal compression. But speakers audibly distorting at loud volumes is a pretty obvious problem with a pretty obvious solution. You need to stop playing those speakers, at those volumes, with that music, until you can upgrade something. What you to choose to upgrade first is a tougher question, but I like the suggestion to start by adding a subwoofer and off-loading the power-consuming low bass to the external sub amp.
Whether that will be sufficient to solve the problem by itself is hard to say. But I would back off the MV until I could add a decent sub and bass manage my speakers. And then I would go up in volume cautiously listening for distortion. If there is still a problem getting to the volumes you want without distortion, you will have to upgrade either the amp, or the speakers, or both. But anytime you hear distortion with loud volumes, you should simply back off the volume to protect your audio components.