I bring mid-highs down quite a bit and use a ribbon tweeter coming in quite a bit louder (it´s an active system) at 9khz. I need to hear that sparkle or it will sound dull and unexciting to my ears. I also find a subwoofer necessary to make it fall into balance or it will sound plain bright. It´s amazing how the lower and higher ends of the spectrum need each other to shine.
The short answer is *yes*.
The second part of the short answer is that this is "holy grail" in audio.
At least a significant part of it.
In order to do this you need to really get the carp out of your system in a big way.
There is no easy answer.
But, the key to it all is to at least have a very low distortion "high freq end" in your speaker system - then you have a shot at it.
The other way to do it is to essentially "gloss over" the highs - some tube amps with a rolled off top end will give a sonic result that is free of apparent sibilance...
I do not subscribe to the idea that you can attenuate a band of frequencies and eliminate sibilance - rather it is a series of harmonics that are perceived as "sibilance", those harmonics sounding objectionable to the ear. You could reduce the apparent presence of sibilance via EQ, but then you've also altered the overall sonic presentation as well. If one assumes a nominally "flat" response of the system, then the application of EQ will create a deficit in an important area.
Just my views.
Eliminating sibilance is non-trivial, and requires a very clean signal path throughout.
_-_-bear
The second part of the short answer is that this is "holy grail" in audio.
At least a significant part of it.
In order to do this you need to really get the carp out of your system in a big way.
There is no easy answer.
But, the key to it all is to at least have a very low distortion "high freq end" in your speaker system - then you have a shot at it.
The other way to do it is to essentially "gloss over" the highs - some tube amps with a rolled off top end will give a sonic result that is free of apparent sibilance...
I do not subscribe to the idea that you can attenuate a band of frequencies and eliminate sibilance - rather it is a series of harmonics that are perceived as "sibilance", those harmonics sounding objectionable to the ear. You could reduce the apparent presence of sibilance via EQ, but then you've also altered the overall sonic presentation as well. If one assumes a nominally "flat" response of the system, then the application of EQ will create a deficit in an important area.
Just my views.
Eliminating sibilance is non-trivial, and requires a very clean signal path throughout.
_-_-bear
Unnaturally high treble makes transients and strong vocal attacks annoying.
I have my system equalized as flat as a 15 band equalizer make it. No problem at all with sibilants. But the big improvement that the EQ made was doing away with "shout" when vocalists, females in particular, attack a note strongly. It also helped to remove the passive baffle step correction circuit and use just the active EQ. I do not know why. I did not expect any improvement. Maybe it is a matter of reduced heat in the 1/4 cubic foot boxes.
I have my system equalized as flat as a 15 band equalizer make it. No problem at all with sibilants. But the big improvement that the EQ made was doing away with "shout" when vocalists, females in particular, attack a note strongly. It also helped to remove the passive baffle step correction circuit and use just the active EQ. I do not know why. I did not expect any improvement. Maybe it is a matter of reduced heat in the 1/4 cubic foot boxes.
You may find the following helpful:
Below is a chart from Martin Collom's "High Performance Loudspeakers" book:
_________________________________________________
COLORATION
Boomy, 50 - 80 HZ
Chesty, plummy, 100 - 150 Hz
Boxy, hollow 150 - 300 Hz
Tube like, tunnelly 400 - 600 Hz
Cup like, honky, 700 - 1.2 kHz
Nasal, hard, 1.8 - 2.5 kHz
Presence, upper hardness, wiry 2.5 - 5.0 kHz
Sharp, metallic, sibilant 5.0 - 8.0 kHz
Fizzy, gritty, 10 -15 kHz
Interactive Frequency Chart - Independent Recording Network
Below is a chart from Martin Collom's "High Performance Loudspeakers" book:
_________________________________________________
COLORATION
Boomy, 50 - 80 HZ
Chesty, plummy, 100 - 150 Hz
Boxy, hollow 150 - 300 Hz
Tube like, tunnelly 400 - 600 Hz
Cup like, honky, 700 - 1.2 kHz
Nasal, hard, 1.8 - 2.5 kHz
Presence, upper hardness, wiry 2.5 - 5.0 kHz
Sharp, metallic, sibilant 5.0 - 8.0 kHz
Fizzy, gritty, 10 -15 kHz
Interactive Frequency Chart - Independent Recording Network
The short answer is that you probably can't. This demonstrates the importance of accuracy in reproducing acoustic sounds. If a sound system cannot reproduce the sound of a human voice correctly, it probably can't reproduce anything else correctly either but usually you aren't aware of it because a human voice is the sound most humans are most familiar with.
Here's a more detailed explanation of why the current paradigm of a high fidelity sound system falls short IMO.
Sibilance along with explosive sounds are a normal part of human speech. Without them important sounds that make words comprehensible are lost. Voices sound muffled. The problem for most modern sound reproducing systems comes when they are either muted, absent, or exaggerated. Since these sounds are characterized by having a high proportion of their energy in the treble range, overemphesis indicates a problem with treble reproduction. When the treble is not properly reproduced nothing else matters. Audiophiles know that it is so important there have been and still are probably more kinds of tweeters manufactured and marketed than all other types of drivers combined.
There are several sources of the problem each sufficient by itself to distort the sound. Here are the most common and obvious ones.
One is the focusing of high frequency energy by deliberately designing tweeters to have very narrow dispersion. All of their high frequency energy is directed at the listener. It arrives along a narrow beam on axis all at once. Although the the sound human voice as it is heard is more directional than most musical instruments, much of its energy arrives from many angles in most rooms. Not so the case of speakers because of tweeter beaming.
Another problem is recordings themselves. In the bad old days of vinyl phonograph records, it was common practice for recording studios to have their monitors equalized by a technician often once a week to be sure that recorded sound was consistent. Even with different brands of speakers there was at least some uniformity.Today with the word equalizer meaning a path straight to hell, spectral balance of recordings is all over the map, many with exaggerated peaks somewhere in the treble range often deliberate. This may be to compensate for deliberate dips in the FR of their audiophile monitors or to be more ear catching when heard on a radio. Studies show that the human brain likes the ear hearing high frequencies. They give clues to direction which is very important to those whose focus is on what is called imaging instead of accurate tonality. Experienced listners of acoustic music know that exaggerated treble while ear catching at first results quickly in listener fatigue. Inexperienced audiophiles don't know this and so products are targeted at them. Manufacturers may have only a few seconds during dealer switching comparisons to attract prospective buyers.
Another problem is that for voices that are heard in large spaces live the acoustics of these spaces causes the treble to fall off faster than middle and bass frequencies. When they are played in a small room where the acoustics of the large space was not fully captured on the recording (never is), this phenomenon doesn't happen and the net result is that the total sound has a greater proportion of hf energy than was heard live.
Decades ago, most speakers did not produce sufficient treble. A few such as those manufactured by Acoustic Research and Alison Acoustics used very wide dispersion tweeters which helped a lot but those concepts are not popular today and have largely disappeared from the market. They also needed a treble boost to make them sound flat, their HF often rolling off.
Use of bipolar speakers such as electrostatics (where the treble is bi-polar as well as the rest of the range) and careful equalization is used, the problem can be mitigated but not completely resolved. Far better understanding of acoustics and hearing will be required before this problem is actually solved. Buying silver bullets such as vacuum tube amplifiers, expensive wires, and other expensive gimmicks that supress the treble is invariably a waste of money. If they work at all to mitigate or cure this problem, they just create others.
Fwiw, I agree with much of what soundminded said... but as far as decades ago, a lot depends on how many decades ago you want to go.
If you go back to the 50s and early 60s, pre solid state, speakers of quality had quite a bit of HF response. Examples include things like the Altec 604 and Tannoys. Both have issues, but an awful lot of your favorite older recordings were monitored on Altec 604s...
However the quality of the *average* driver today is far better than of yesteryear thanks to slick computer software including measurement systems, AND the incremental improvement in basic design based on better understandings of the way that speakers work...
Although most folks do not have it, you can build and perhaps purchase a speaker system that is a full order of magnitude lower in IM and THD than was possible two decades or more in the past... also the typical signal path of the better equipment has much lower *objectionable* harmonic distortion than in the past. The better source material (downloaded high bitrate/bit depth for example) is substantially cleaner than the typical source material available to a home enthusiast in the past... playback of redbook source also has risen to a higher level on average. An inexpensive CD player today arguably can be better sounding and have better specs than the most expensive units of even 10 years ago.
This means that the demands are greater in one regard, and in another the potential is greater than ever before...
_-_-bear
If you go back to the 50s and early 60s, pre solid state, speakers of quality had quite a bit of HF response. Examples include things like the Altec 604 and Tannoys. Both have issues, but an awful lot of your favorite older recordings were monitored on Altec 604s...
However the quality of the *average* driver today is far better than of yesteryear thanks to slick computer software including measurement systems, AND the incremental improvement in basic design based on better understandings of the way that speakers work...
Although most folks do not have it, you can build and perhaps purchase a speaker system that is a full order of magnitude lower in IM and THD than was possible two decades or more in the past... also the typical signal path of the better equipment has much lower *objectionable* harmonic distortion than in the past. The better source material (downloaded high bitrate/bit depth for example) is substantially cleaner than the typical source material available to a home enthusiast in the past... playback of redbook source also has risen to a higher level on average. An inexpensive CD player today arguably can be better sounding and have better specs than the most expensive units of even 10 years ago.
This means that the demands are greater in one regard, and in another the potential is greater than ever before...
_-_-bear
I also think alot of non audiophiles see a bright treble response as a sign of high fidelity, probably due to the horrific treble produced by some bugdet systems, and cheapo midi systems with rubbish FR drivers. I have even found that although in GENERAL i like the sound of the A6 and other FR drivers, i do find the rising response around 5-8k fatiguing, despite the intention of improving off axis power response, (which it does), Id still prefer a FLAT response. the TB w3-1285sg im using has a rising response above 10k which i find less objectionable, esp since it seems to be over a very narrow angle indeed. Soundminded makes some great points, which i cannot really improve on 
hmmmm the 'over-spaciousness' of some large hall recordings seems unduely compressed, (even though it ISNT intentionally so), due to the reproduction in a small room, and NOT as some would believe, because of compression in studio mixing. studio compressors are very good nowadays, and compression CAN be used which is almost imperceivable.
hmmmm the 'over-spaciousness' of some large hall recordings seems unduely compressed, (even though it ISNT intentionally so), due to the reproduction in a small room, and NOT as some would believe, because of compression in studio mixing. studio compressors are very good nowadays, and compression CAN be used which is almost imperceivable."If you go back to the 50s and early 60s, pre solid state, speakers of quality had quite a bit of HF response."
IMO the horn speakers of the 1950s and 1960s all had harsh high ends and their dispersion was awful. Horn speakers by their very nature have limited HF dispersion. AR3/3a had much better dispersion but their high ends were rolled off. Most speakers of that era had almost no high end to speak of. The Lansing Heritage site says I think on the page for JBL Paragon that until 1958 they didn't have to contend with any program material above 12 Khz. These horn speakers came from the motion picture industry where efficiency and high SPL from small amplifiers was the design goal.
If speakers are so well designed to day, why the topic of this thread which is a very common complaint, the shrillness and excessive sibilance of many modern loudspeakers? They are not that good, their flaws are just different.
"you can build and perhaps purchase a speaker system that is a full order of magnitude lower in IM and THD than was possible two decades or more in the past."
I'm not so sure about that. The AR 12" woofer had 5% THD at 30 hz and could be equalized flat to the lowest audible frequencies 55 years ago. The same basic design was used by them from around 1955 to 1985. It's still a pretty tough benchmark to beat.
The issue is HF dispersion. In general the common goal for today's designers is to restrict HF dispersion to improve "imaging" in a sweet spot and increase efficiency. Excessive sibilance is one result.
Interesting debate with a lot of good points.
My tactic is to use the HF drivers perpendicular to the listening axis. EQuing them is a compromise between direct axis measure and 30°, but with the stuff I have, it's the best way of managing some spaciousness without the "shhh" and without falling on the dull side.
I use bipolar drivers, open back 1" CD with small horns
My tactic is to use the HF drivers perpendicular to the listening axis. EQuing them is a compromise between direct axis measure and 30°, but with the stuff I have, it's the best way of managing some spaciousness without the "shhh" and without falling on the dull side.
I use bipolar drivers, open back 1" CD with small horns
I said "you can" - not that most are.
There are numerous examples of tweeters today that are much lower in distortion than in years past, and many that extend past 20kHz very nicely.
There are woofers that are quite superior to the AR woofer today. Many.
And, at what level was that "5%"??
Besides the AR woofer didn't produce any sibilance, did it?
I am not in agreement as to the "cause" of sibilance being the one you're suggesting.
Imo, sibilance is a type of distortion, plain and simple.
The question is what is the cause.
Imo it seems like it is not due to a single cause, and does not occur in a single component. My experience with it seems to indicate that it can be generated anywhere and everywhere in a given system, not just in the tweeter. Perhaps it is a summation of harmonics due to non-linearities. I don't see it being the result of the polar response of a given driver, per se. That's not to say that a given driver might not be able to generate sibilance because of the way it is designed - be it due to the way it was designed for narrow dispersion or not.
It is important to differentiate in the discussion between the "best" available and the "norm" (be that of yesteryear or today). Also to differentiate between outcomes and causality.
As far as there being drivers today - especially HF drivers that are an order of magnitude lower in distortion than decades past, I am quite sure this is true, although there were still exceptional HF drivers of note from decades past, some of which are still worthy of use and consideration...
_-_-bear
There are numerous examples of tweeters today that are much lower in distortion than in years past, and many that extend past 20kHz very nicely.
There are woofers that are quite superior to the AR woofer today. Many.
And, at what level was that "5%"??
Besides the AR woofer didn't produce any sibilance, did it?
I am not in agreement as to the "cause" of sibilance being the one you're suggesting.
Imo, sibilance is a type of distortion, plain and simple.
The question is what is the cause.
Imo it seems like it is not due to a single cause, and does not occur in a single component. My experience with it seems to indicate that it can be generated anywhere and everywhere in a given system, not just in the tweeter. Perhaps it is a summation of harmonics due to non-linearities. I don't see it being the result of the polar response of a given driver, per se. That's not to say that a given driver might not be able to generate sibilance because of the way it is designed - be it due to the way it was designed for narrow dispersion or not.
It is important to differentiate in the discussion between the "best" available and the "norm" (be that of yesteryear or today). Also to differentiate between outcomes and causality.
As far as there being drivers today - especially HF drivers that are an order of magnitude lower in distortion than decades past, I am quite sure this is true, although there were still exceptional HF drivers of note from decades past, some of which are still worthy of use and consideration...
_-_-bear
Excessive sibilance is caused by excessive high frequency energy reaching the listener's ears from a single direction in phase at the same time. It's the same cause that makes modern speakers sound unbearably shrill and bright although this FR distortion is less easily identified in much music by those who are not familiar with the sound of real acoustic musical instruments. The way in which they propagate sound into space and the way it arrives at the listener whether in a small room or a vast auditorium is entirely different from the way loudspeakers work. Walk around a street busker or a piano at a piano bar and the timbre (tonal balance) of what you hear hardly changes at all. Walk around a speaker placed in the middle of a room or better yet outdoors and it changes drastically. Bose was so annoyed by this shrillness nearly 45 years ago he marketed a speaker that seems to me not to produce any high frequences in the top ocatave at all.
Efforts to mitigate this effect usually include devices or equipment that reduces system HF output to the speakers. Wires with high shunt capacitance and/or high series inductance, vacuum tube amplifiers with output transformers having high HF losses due to eddy current and hysteresis losses, heavy tracking moving coil phono cartridges which shave the HF components of phonograph records off with excessive pressure are just a few. From the industry's point of view, the more expensive they are the better. That is why bass and treble controls and equalizers which do the same thing are shunned, there's no money in them. Ultimately the listener throws his hands up and buys another speaker which invariably suffers the same defect.
Efforts to mitigate this effect usually include devices or equipment that reduces system HF output to the speakers. Wires with high shunt capacitance and/or high series inductance, vacuum tube amplifiers with output transformers having high HF losses due to eddy current and hysteresis losses, heavy tracking moving coil phono cartridges which shave the HF components of phonograph records off with excessive pressure are just a few. From the industry's point of view, the more expensive they are the better. That is why bass and treble controls and equalizers which do the same thing are shunned, there's no money in them. Ultimately the listener throws his hands up and buys another speaker which invariably suffers the same defect.
Soundminded, please explain where the "excessive HF energy" comes from??
If one has a nominally "flat" FR on axis (for example), or pick any other curve you wish, where is this "excessive HF energy" from??
So, will and Ohm F or MBL speaker produce "sibilance" due to the phenomenon you claim?
How about a Magnat plasma tweeter (the round one)??
How come I can swap out amp A) with amp B) - both of which are "flat" way beyond 20kHz, probably into >200kHz+ - and have the characteristic of said "sibilance" change? By your theory there should be no audible change whatsoever, if the cause is in the design of a HF driver in a speaker. Clearly, if the characteristic of sibilance changes when one changes amps, the issue can not be solely in the driver or the driver's polar response shape.
The example you gave of a live music being played and how you hear it as one moves about does nothing to explain "sibilance" in a reproduced sound. While it is generally true that live sound is propagated differently than sound from most speakers, that has little to do with why there is "sibilance" or what causes it when sound is reproduced by speakers.
What "efforts" are made that may or may not work or may be misguided are not really relevant to understanding what is actually going on.
_-_-bear
If one has a nominally "flat" FR on axis (for example), or pick any other curve you wish, where is this "excessive HF energy" from??
So, will and Ohm F or MBL speaker produce "sibilance" due to the phenomenon you claim?
How about a Magnat plasma tweeter (the round one)??
How come I can swap out amp A) with amp B) - both of which are "flat" way beyond 20kHz, probably into >200kHz+ - and have the characteristic of said "sibilance" change? By your theory there should be no audible change whatsoever, if the cause is in the design of a HF driver in a speaker. Clearly, if the characteristic of sibilance changes when one changes amps, the issue can not be solely in the driver or the driver's polar response shape.
The example you gave of a live music being played and how you hear it as one moves about does nothing to explain "sibilance" in a reproduced sound. While it is generally true that live sound is propagated differently than sound from most speakers, that has little to do with why there is "sibilance" or what causes it when sound is reproduced by speakers.
What "efforts" are made that may or may not work or may be misguided are not really relevant to understanding what is actually going on.
_-_-bear
I thought my explanation was plain enough however here's an example of what I mean by the focusing of high frequencies. Have someone whisper in your ear. You will hear considerable sibilance, all of the HF energy from each sylable is focused in one direction and arrives at the same time. Now move the source 15 feet away and make it 40 to 50 db louder. That's the effect you get from modern loudspeakers. If there is a HF peak anywhere along the chain including back to the microphones that recorded it, that only makes it worse.
A common but unsuspected cause of sibilance is crossing the tweeter too low, or using a shallow-slope crossover. Many designers - unfortunately, a lot of them in the high-end biz - forget that direct-radiator drivers increase excursion at a rate of 12 dB/octave. Thus, it takes a 12 dB/octave highpass filter to merely keep excursion constant in the frequency range between nominal crossover and the Fs of the tweeter.
For example, if the tweeter has a typical Fs of 700 Hz, and the intended crossover is 2.8 kHz (again, typical), it takes a 12 dB/oct electroacoustical filter to merely keep excursion constant in the very critical 700 Hz ~ 2.8 kHz range. Part of the reason that this range is so critical is that audibility of distortion is at a maximum in the 1~5 kHz region. (Perception of distortion similar to, but not quite the same as, the Fletcher-Munson curve.)
Staying with the same example, if the electroacoustical filter is 1st-order (6 dB/octave), then excursion actually increases from 2.8 kHz on down, until 700 Hz is reached. Below 700 Hz, the excursion finally starts to decrease, but not very fast, only 6 dB/octave. This is troublesome because the maximum spectral energy of many recordings is around 300~500 Hz, so energy from this range can crossmodulate with the tweeter output.
This is why auditioning with little-girl-with-a-guitar program material and a full choral piece sound different. The LGWAG is spectrally sparse, and there isn't as much chance the tweeter will be struggling with IM distortion. Throw a dense, high-powered spectrum at the loudspeaker, though, and the tweeter will start to scream - and it is very audible on massed chorus as complete breakup.
At any rate, regardless of distortion of a particular tweeter (none of them are free of IM distortion), crossovers matter. Many designers want to take the tweeter as low as possible because the polar pattern is prettier and certainly measures nicer, but the inevitable price to be paid is more IM distortion resulting from increased excursion (the linear region is most tweeters is less than 1mm). Choosing a crossover is a difficult tradeoff between narrowing of the vertical polar pattern, IM distortion from out-of-band excursion, and how close the designer wants to approach the region of midbass driver breakup. The tradeoff is made more difficult when a rigid-cone (Kevlar, metal, ceramic, etc.) midbass driver is chosen, because the onset of breakup commonly falls in the 3~5 kHz region, right where the ear is most sensitive to distortion.
As you can see, the worst possible solution is a 1st-order crossover combined with a midbass driver that has a severe breakup region (Kevlar drivers, I'm looking at you). The 1st-order crossover fails to control out-of-band excursion, so program material in the 700 Hz-2.8 kHz region results in IM distortion in the tweeter's working range, while plenty of midbass breakup in the 3~5 kHz range gets through as well. And midbass breakup sounds the same as a bad tweeter, since the distortion and resonances fall in the same frequency range.
As a side note, most transistor amplifiers (including very expensive high-end products) go from Class A operation to Class AB around 1 watt. Feedback helps, but cannot fully overcome the two-to-one shift in transconductace as the AB region is traversed. In addition, thermal tracking is typically several seconds to a minute late (depending on the thermal mass of the heatsink and location of bias sensor), so the correct AB bias point is actually several seconds behind the program material. There are various sliding bias-tricks available (which avoid complete turnoff and associated switching transition), but they are all several seconds late. The more output transistors, the more AB transitions there are, since it is impossible to have transistors exactly match the switching transition - in production, they are matched for beta (current gain), but not usually for other parameters. Change the die temperature a bit, and the careful hand-matching goes away.
To recap, if you want lots of sibilance, use a midbass driver with severe breakup in the 3~5 kHz region (this is usually obvious from unsmoothed FR curves), pick a tweeter with limited excursion capability (not always spec'ed), select a 1st-order crossover at a low crossover frequency, and use an amplifier with a very large heatsink, many transistors, and somewhat unstable Class AB biasing (thermal overshoot). That should do the trick. Plenty of distortion from many different sources, even though the overall FR curves may look harmless.
For example, if the tweeter has a typical Fs of 700 Hz, and the intended crossover is 2.8 kHz (again, typical), it takes a 12 dB/oct electroacoustical filter to merely keep excursion constant in the very critical 700 Hz ~ 2.8 kHz range. Part of the reason that this range is so critical is that audibility of distortion is at a maximum in the 1~5 kHz region. (Perception of distortion similar to, but not quite the same as, the Fletcher-Munson curve.)
Staying with the same example, if the electroacoustical filter is 1st-order (6 dB/octave), then excursion actually increases from 2.8 kHz on down, until 700 Hz is reached. Below 700 Hz, the excursion finally starts to decrease, but not very fast, only 6 dB/octave. This is troublesome because the maximum spectral energy of many recordings is around 300~500 Hz, so energy from this range can crossmodulate with the tweeter output.
This is why auditioning with little-girl-with-a-guitar program material and a full choral piece sound different. The LGWAG is spectrally sparse, and there isn't as much chance the tweeter will be struggling with IM distortion. Throw a dense, high-powered spectrum at the loudspeaker, though, and the tweeter will start to scream - and it is very audible on massed chorus as complete breakup.
At any rate, regardless of distortion of a particular tweeter (none of them are free of IM distortion), crossovers matter. Many designers want to take the tweeter as low as possible because the polar pattern is prettier and certainly measures nicer, but the inevitable price to be paid is more IM distortion resulting from increased excursion (the linear region is most tweeters is less than 1mm). Choosing a crossover is a difficult tradeoff between narrowing of the vertical polar pattern, IM distortion from out-of-band excursion, and how close the designer wants to approach the region of midbass driver breakup. The tradeoff is made more difficult when a rigid-cone (Kevlar, metal, ceramic, etc.) midbass driver is chosen, because the onset of breakup commonly falls in the 3~5 kHz region, right where the ear is most sensitive to distortion.
As you can see, the worst possible solution is a 1st-order crossover combined with a midbass driver that has a severe breakup region (Kevlar drivers, I'm looking at you). The 1st-order crossover fails to control out-of-band excursion, so program material in the 700 Hz-2.8 kHz region results in IM distortion in the tweeter's working range, while plenty of midbass breakup in the 3~5 kHz range gets through as well. And midbass breakup sounds the same as a bad tweeter, since the distortion and resonances fall in the same frequency range.
As a side note, most transistor amplifiers (including very expensive high-end products) go from Class A operation to Class AB around 1 watt. Feedback helps, but cannot fully overcome the two-to-one shift in transconductace as the AB region is traversed. In addition, thermal tracking is typically several seconds to a minute late (depending on the thermal mass of the heatsink and location of bias sensor), so the correct AB bias point is actually several seconds behind the program material. There are various sliding bias-tricks available (which avoid complete turnoff and associated switching transition), but they are all several seconds late. The more output transistors, the more AB transitions there are, since it is impossible to have transistors exactly match the switching transition - in production, they are matched for beta (current gain), but not usually for other parameters. Change the die temperature a bit, and the careful hand-matching goes away.
To recap, if you want lots of sibilance, use a midbass driver with severe breakup in the 3~5 kHz region (this is usually obvious from unsmoothed FR curves), pick a tweeter with limited excursion capability (not always spec'ed), select a 1st-order crossover at a low crossover frequency, and use an amplifier with a very large heatsink, many transistors, and somewhat unstable Class AB biasing (thermal overshoot). That should do the trick. Plenty of distortion from many different sources, even though the overall FR curves may look harmless.
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