To be honest, it can be hard to tell. It is not uncommon for people to conflate distortion with "too loud." One of the things people often note when they hear a system capable of much higher output limits is that suddenly they listen louder and it doesn't sound as loud. We often interpret sound that is distorting and compressing as being too loud.
There is a training factor too. If you listen to clipping amplifiers enough, you get a sense of what that sounds like. James and I have had a few situations where we ran sweeps at different levels and noted that we where hearing clipping, and then had the background realization that this also comes from experience. That to even notice this won't be obvious to everyone. That doesn't mean it isn't audible or objectionable, it just means that you might not recognize what it is you are hearing.
I've clipped receivers that measurably produce over 120 watts RMS into 8 ohms into my Geddes speakers. I was using the center channel and surround channel amplifiers in the receiver while using an outboard amp for the L-R speakers. I run the Geddes speakers full range, so do keep that in mind, that matters. I watched a bunch of movies and heard a distinct change in the sound, a kind of edginess or hardness as certain loud effects panned across the screen. I had a tweeter diaphragm move out of the gap once causing a similar effect, so I had worried it was either that or a blown tweeter (mind you, I couldn't figure out how I could have blown a pro audio compression driver). I asked a friend with more experience than I have blowing up compression drivers and he assured me it would be next to impossible to have blown the tweeter, and suggested it might be clipping. I thought that should be impossible, these are very sensitive speakers afterall. I decided to try a simple test, highpass just the center at 80hz, and rewatch the same sequence. Sure enough, the problem went away. A more objective test that followed was to run sweeps on the speaker at the same volume level with the same settings. Sure enough, amplifier clipping was evident in the distortion measurements, as was compression of the output. Adding the 80hz highpass filter added back some headroom. Since that situation (likely a decade ago) I have since noticed that same phenomena with many speakers connected to receivers or amps of lower power.
I've shared this view with a number of other enthusiasts and experts who have shared back similar thoughts and experiences. When I shared this experience with Martijn from Dutch & Dutch, he responded that amplifier clipping is far more common than people realize and he had to size his amplifiers accordingly. There have been some "studies" by engineers who developed clipping boxes who then claimed that clipping was exceedingly rare, but I would note that a) We don't know how quickly those devices could measure clipping and we don't know if any other measures of clipping or distortion were being captured such as the test I did, b) It is possible the type of content used was simply unlikely to stress the amp or that the levels played back were not the same levels I am talking about here.
This one was better, but only music was used. I'd love to see this device used with movies, I would guess that with the right amplifier, we might see that peak power double.
With average speakers of typical sensitivity (say 87dB to 90dB) you need amps with roughly 300-500 watts to be able to achieve reference levels. It honestly blows my mind that more people don't notice clipping issues and my honest opinion is that this is because they don't know what to look for, and they probably are clipping their amps more often than they realize.
As for my academic background, I've noted it a few times actually, and most people are shocked to hear this. I have degrees in human development, psychology, and statistics. Before heading in that direction, I had this dream of going into robotics, so my first year of college was in electrical and computer engineering at Rochester Institute of Technology. While working on a PhD at Purdue University, I had finished my coursework and needed to maintain a 12 credit hour course load outside of just research, so I was offered the option to take additional courses in anything else I want. I am sure the idea should have been something more relevant to human development, but there were no other courses available that I could take (It is not uncommon for PhD courses to be limited to just 10-15 students), so I chose acoustical physics. They had a lab doing research on human perception, and my background gave me expertise in studying human perception, which their physicists didn't have. As such, I worked on some projects in that lab and took a number of acoustical physics courses at the Masters and PhD level, though not for credit. Earl Geddes had been like a mentor to me at that time and had encouraged me to consider doing that. That gave me a lot of course background knowledge and some hands on experience. I then earned additional real world experience starting around 10 years ago when I began working with some experts I knew who needed help in either testing products (like A/T projector screens) or designing and setting up rooms (I did a few hotels and conference spaces, a broken down recording studio, and eventually residential spaces, which is what I now do on my own).
