Originally Posted by JHAz
If there is a difference it is after you pass the knee in the power to distortion curve. Because the flat part of the curve is, um, flat thd is identical throughout that part of the curve. If you never get past the knee in your actual use of your system without boa ping you cannot reduce the very low thd present.
A knowledge which we don't have when using our amp. My scope showed that one channel had clipped in a predictable signal, i.e. sine wave. Given that familiarity and an instrument like my scope, we could tell, using *visual* inspection that clipping had occurred. But where are we if I change the sine wave to real music and take away the scope? We would have to use our ears, right? Which gets me to the question I asked: what does clipping sound like? No one has answered that. What if someone compared two amps and heard a difference that is due to clipping in the lower powered amp. Would you believe him if he just said the Bryston sounds better than the amp in his AVR? I assume he would immediately be accused of sighted bias and many posts will be written to convince him that he has not heard anything. So if that is not the right observation and there is no instrumentation, how would one conclude that clipping had occurred?
The question that was asked a couple of times here is quite valid: how much power is enough? As was said, it seems even 30 watts should be good enough. Indeed in these discussions it seems any amount should be as no number is ever given for good enough. Surely this sufficiency amount can't possibly be the case for all listeners, content, speakers and rooms.
The tweeter amp and the woofer amp get exactly the same signal. In that sense they are not separated. It's like using a y cable to connect the output of say the left channel of a preamp to two separate amp inputs. Same signal in to both amps. Precisely zero difference.
Everyone is clear on this. What some folks are not clear on is that the output stage of the amplifier is load dependent and produces a different results at its peak performance. I explained the theory behind this (unregulated supplies) and showed measurements to demonstrate the same.
Whether the woofer amp clips sooner than the tweeter amp depends. But if you are at a thd of ten to twenty times the level present at the knee, like say the knee is at .001 percent and you have pushed it up to .02, you are probably below rated amp power since commonly used conservative ratings are watts at 0.1 percent or 0.05 percent. So all that nasty distortion is apparently considered unimportant by everybody from demon to Bryson.
The THD+N curve was computed using test signals not music. The amplifier (a real one as opposed to paper) works differently than these simple measurements show. And further there is no real science behind those thresholds of THD. If two amps clip differently, they will sound differently at that point even if their THD is the same number. Audibility of distortion simply cannot be computed as one number that sums up all the distortion products without regard to what is audible and what is not. Combine this with the fact that the curve we are using to determine THD is not representative of real content and we see why this kind of analysis is not proper for the situation at hand. And that is putting aside that the numbers we pick for THD as in your post have no proof behind them as being representative of any situation in anyone's home.
And we are still fussing over levels of distortion that could be reduced to acceptably even more I audible by turning down less than one typically would turn down if things were just a little too loud. Commonly folks adjust by three dB to achieve a meaningful slight decrease in volume.
Again, the assumption is that we know clipping has occurred. Someone should explain to me what it sounds like so that we can trust such observations which we normally dismiss without a double blind test of many subjects. This is a bit like redline of an engine. If that is at 5,400 RPM and you stay below 5,000 all is cool. But what if I took away the RPM meter? Can you judge by ear alone that you have hit 5,000? People with a lot of experience may be able to tell. For others, they will hear the engine getting very loud. But perception of loudness is subjective. Are they right in thinking the engine has gotten so loud that it is about to hit redline?
Really if it makes you feel better do it. But if you have no audible distortion without biamping, reducing the potential distortion that might be present at higher power output accomplishes nothing but psychological comfort.
We are not going to get anywhere until we understand how our systems work. If you knew nothing about engine redline in the above analogy, you would be lost in the woods in attempting to not damage your engine. We think we know what is going on here but so far in an amplifier with real music, that assumption has not proved correct. Lacking detailed knowledge of how real amplifiers work leads us to such dismissive comments. Run your engine anyway you like. You are not going to damage it. If it makes you feel better, stop when it gets pretty loud. But really, you will be doing that for psychological reasons. How does this read to you?