more adjectives to help define 'fatigue' vectors?

OutSTANding, Duke. Thank you for this and your email as well. I really appreciate your POV and expertise, and your taking the time to explain this at the High School level for me. :-) Will be back in touch via email.

In addition to Duke's comments, fatigue can be caused by the presence of odd-ordered harmonics in the amplified signal. Our ears use the odd orders (5th, 7th and 9th) as a means to determine the loudness (sound pressure) of a sound. If these harmonics are distorted (enhanced) by amounts of only 1/100th of a percent, we will perceive the sound as louder. In addition, these harmonics also contribute to brightness, in fact we audiophiles have terms like bright, hard, harsh, brittle, clinical, etc. to describe this type of distortion.

One of the primary ways that these harmonics get emphasized is through the use of loop negative feedback in electronics. Loop feedback is used to *reduce* distortion, but due to timing effects that occur in any gain stage, the loop feedback is always a little late in doing its job. Its this 'lateness' that enhances odd ordered harmonics. Not by much, mind you, but it happens that this is a fundamental violation of what you might call human hearing rules; how we figure out the volume of a sound is pretty important.

This is why you see some audio manufacturers pushing zero feedback circuitry, as it is less fatiguing to listen to if they have their ducks in a row.

I am not going to argue with Duke as he surly knows a lot more on the subject (audio) than I do. I am sure all of those things contribute in one way or another. But it really comes down to volume.

As to others claiming metal domes are the cause of fatigue/brightness get real. Yes some aluminum domes will break up around 20khz but I would bet 90% of the population on this forum could not hear jack above 17khz. With all of the new alloys out there the breakup node is pushed MUCH higher and well out of the audible range. But yes the highs will wear out your ears much faster because of the higher cycle rate.

Anyway a lot of fatigue comes from where the ear is most sensitive, the upper mids lower treble 3000-4000hz. People tell you metal domes are the down fall like a dark color to their sound (nothing wrong with that) but to push the opinion as fact is a joke.

But really turn down the volume your ears are tell you what they need. If you like the volume very loud you may like a slightly darker speaker or one with a small dip in the upper mids. Also keep in mind distortion can cause a lot of energy and the excessive energy can also wear out your ears. Typically speakers will less distortion can be played louder for longer before fatigue sets in.