Originally Posted by Stephan Mire
When I listen to music at very loud levels I notice voices and higher frequencies start to distort. Is that a function of the amp clipping or is that a function of the speaker not handling the volumes sufficiently?
How would a newbie determine the cause? I'm thinking of perhaps buying a power amp but if the amp isn't clipping and my speakers are being overdriven then adding a more powerful amp won't help my situation.
You said you hear distortion (noise?) with voices and higher frequencies, only at very loud levels, and later, you said your speakers are B&W 683s. Because of that, I believe you are not over-driving your amp into clipping, your speakers can't handle the high volumes.
B&W 600 series speakers that have a yellow Kevlar mid range or mid woofer, are notorious for high frequency break-up noise caused by those drivers. Your 683s have 6" Kevlar mid range drivers, and the crossover frequency between it and the tweeter is at 4,000 Hz. This frequency is high enough to include the noise from the mid driver's break-up at about 4,000 Hz.
Over the years, B&W has tried various methods to suppress or filter this break up noise. But they always avoided using a lower crossover frequency. Their efforts, usually notch filters of various configurations, seem to work only at lower volumes. At higher volumes, and with the right type of music, this noise becomes hard to ignore. The large number of B&W 600 series owners who complain of "listener's fatigue" attests to this.
This frequency response curve from a Stereophile review of the 683 s2
clearly shows a ragged looking response across the upper mid range (blue trace below). Look closely at the 4000 Hz range where the mid range crosses to the tweeter. If this nearly 10 dB variation is caused by break up noise, as I suspect, you might notice it best at louder volumes. If the review had shown separate mid range responses from the tweeter's, it might reveal this better.