more adjectives to help define 'fatigue' vectors?

My apologies in advance for posting a naive question, and perhaps erroneously posting this in 'speakers' rather than 'amps' as well, but my efforts to find this answer via search are failing me...

I understand, I believe, what 'fatigue' itself means. But I don't understand in the slightest the causes/mechanisms of it in a listening situation.

I assume there must be myriad causes - but can they be grouped or categorized...and explained in something approaching layman terms?

Fatigue induced by speakers, amps, poor power, they all have something in common that I'm missing?

Or are they all completely different conditions that result in the same general 'fatigue' outcome?

Perhaps fatigued, perhaps not;
In my experiece,fatigue came from overly bright highs that I was getting from my speakers with metal domed tweeters.I struggled with this for a while until some of the members here suggested I try a speaker with soft dome tweeters.Since changing speakers I have not experienced any listener fatigue until I introduced a silver speaker cable into my system.I have since gone back to all copper wire and everything is as it should be.Again,this is just my experience,yours may be different.
this thread is helpful, but still confusing to this newbie:
It's a nebulous term at best but for me fatigue is when I reach the point of not enjoying the presentation. Could be 5 minutes or 5 hours.

I'm sure you'll get dozens of descriptions, none of which are wrong due to the pure subjectivity of the term.
The decreased capacity or complete inability of an organism, an organ, or a part to function normally because of excessive stimulation or prolonged exertion.
love that Entrope. it generally safe to say that the type of excessive stimulation audiophiles experience, and describe as fatiguing, is generally high frequency information? That the HF portion of the experience is where folks are finding themselves overly exerted?
I've experienced fatigue and it was the high frequencies. If you really want to experience it, I know for sure that Rotel and B&W speakers with the metal domes will fatigue most anyone. Add in the silver speaker cable and prepare for fatigue gone wild.
Soundgasm said, "But I don't understand in the slightest the causes/mechanisms of it in a listening situation."

Its all about room acoustics. Bad room acoustics will do this
See this post,

Bob, that might be what i've got going on, although this question was really academic at the time I posted it...I was reading the word fatigue used here and had no idea what part of the spectrum it came from, if everybody was talking about the same thing, or what it was. I'm less than a year into this. The consensus I'm gleaning is that it's a HF phenomena, some kind of shrillness. I can certainly see how that that kind of energy would be made much worse in a bright reflective room for sure.

bridging these two posts, guess my question would be...can a non-fatiguing system be deployed in a brighter-than-ideal room and have it remain not-fatiguing?
"Can a non-fatiguing system be deployed in a brighter-than-ideal room and have it remain not-fatiguing?"

The short answer is, "yes". But that's not very interesting, so you're going to get the long answer too.

Let's look at a couple of causes of fatigue that relate to room acoustics, and then come back to your question.

A significant spectral discrepancy between the first-arrival and reverberant energy can be a cause of listening fatigue. Sorry but I'll have to delve into psychoacoustics a bit at this point.

The ear localizes sound sources primarily by the first .68 milliseconds of a sound impulse. This corresponds to the time it takes for a sound wave to travel the roughly 9 inches around the head from one ear to the other. After .68 milliseconds, something called the "precedence effect" or "Haas effect" (after Helumt Haas, who first described it) kicks in and the ear ignores repetitions of the original signal (reflections) as far as directional cues go. After about 40 millisecond or so (I forget the exact figure) the precedence effect wears off, and a reflection is heard as a distinct echo.

Now how the ear does this is very interesting: It takes each new incoming sound and puts it into a short-term memory for the duration of the precedence effect. Any and all incoming sounds are compared to all of the sounds in this short-term memory to see whether they are "new" sounds or "old" sounds - and if the latter, they are classified as a reflection and ignored as far as directional cues go.

What do you suppose is the criteria the ear uses to determine whether an incoming sound is a repetition of a sound that's already stored? It compares their spectral content! Very simply, it looks at whether the incoming sound "sounds" like one that is in the short-term memory. This is where the fatigue factor comes in: When there is a substantial spectral discrepancy between an incoming reflection and the stored original, it is literally more difficult for the ear/brain system to correctly classify that incoming reflection. More CPU usage, and so the CPU heats up. After about half an hour, listening fatigue can set in.

On the other hand where there is only a minor spectral discrepancy, and preferably where said minor discrepancy is caused by the room's characteristic acoustic signature, listening fatigue does not arise, at least not from this cause. I am not saying that a spectral discrepancy between the direct and reverberant energy is the only cause of listening fatigue, but I believe that in many cases it is a primary one.

The way to quickly check the spectral balance of the reverberant field is to walk out of the room and listen through an open doorway. All you can possibly hear from outside the room is the reverberant field. If it still sounds realistic, then the reverberant field has a good spectral balance.

Let's briefly go back to what happens between .68 milliseconds and the fading of the precedence effect. Although directional cues are suppressed, loudness cues are still picked up (singing in the shower as an example). So if there's a lot of extra reverberant field energy around, say 2-5 kHz (not uncommon with a typical small two-way system), the ear picks up on it and that region sounds louder than the rest of the spectrum, even though it might measure perfectly flat on-axis! Which brings up another potential source of fatigue: Excess energy in the 2-5 kHz region. The ear's sensitivity peaks at about 4 kHz, and many speaker systems have excess off-axis energy in this region because of the tweeter's wide radiation pattern at the lower end of its passband.

One elegant solution to both of these issues is for the speaker's radiation pattern to remain uniform over as much of the spectrum as is practical. How to do that is another topic for another day.

Okay, let's look at the question again:

"Can a non-fatiguing system be deployed in a brighter-than-ideal room and have it remain not-fatiguing?"

A brighter room simply means that the reflections are full-spectrum instead of rolled off at the top end. If the reverberant sound generated by a speaker sounds bad, then you probably want to absorb as much of it as possible. If the reverberant sound from a speaker sounds good, then you can preserve it and have a fine-sounding, non-fatiguing system. And now you know why.

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.