How Much Difference Does a More Powerful Amp Make?

When would you notice a real difference in sound quality with a more powerful amplifier?

I have a Simaudio W-7 driving Dynaudio Sapphires, and at some point, I may upgrade to Sonus Faber Amati Futuras.

My W-7 is 150 watts at 8 Ohms, and Simaudio makes the W-8 at 250 W at 8 Ohms. Would I notice any difference if I moved to the more powerful amp in a medium-sized room (14' x 22' x 8')?

The Sapphires are 89 db efficient, the Futuras are around 90 Db, but I've read that with most speakers, the more power the better.
Given your speakers are quite efficient, I doubt you'd notice any difference at all. Yes, more is always better, but 150 is already more.
going from 150 to 250 isn't such a big a power boost as it would sand amps, high current designs are most powerful...i.e. doubling in power when going from 8 to 4 ohms.
Larry - Sand Amps ? :-) what does that make the other variant "Lack of Air Amps" Made me chuckle though.

In my experience, a more powerful amp does not necessarily translate into better sound. I had Dynaudio C4's powered by a Plinius SA-102 (125 WPC), then thought I'd get more out of them moving to Simaudio W-6 monoblocks (425 WPC). Ended up being the wrong move and I sold the W-6's three days later. IMO, it's often the quality of the power that counts... not the number of watts. Based upon my experience with Simaudio & Dynaudio, I suggest you try something other than Simaudio with the Dyn's... maybe a higher powered tube amp from McIntosh (MC275), VAC or Conrad Johnson... or if you must stick with solid state, try the Plinius SA-102 class A amp, or a class A amp from Pass or Clayton.
According to perceived loudness calculation

k^(1/3.5) where k is ratio of powers

your loudness will increase by 15.7%.
Greater power may or may not offer a 'better' sound. The quality of the power matters also.
As has been mentioned, the increase you are interested in is not really much. However, if you are at the point of running out at your current power usage, it might be all you need.
The issue IMO is not quantity of power, but the quality of the power along with the quantity.
If you buy a cheaper sounding, but more powerful amp, you will be disatisfied with the sound, louder or not.
A good amp can last a long time. My last amp, A Forte 4a i used for 17 years.. and my current amp, i hope to use for the next 20 years (Bryston 4B-SST2)
Since you are moving within the same make and lineup of the amp you will probably not have "inferior" watts. So it is all about 150 vs 250 watts. With your speakers it is a big thumbs up to go higher in watts. What you will most probably hear is a more resolute, disciplined performance because of the grip the amp will have on the drivers. The sound might be bigger as well but it will be more graceful. To me these are important improvements. I have owned and heard many Dynaudios in the past BTW.
This Sims are very high current so I doubt you need more power. The W-7 is more than capable.
How would someone know if they were "running out at current power usage"? Is there an easy way you can tell that an amplifier is not powerful enough for your speakers? Or does that just manifest in "bad" sound?
How can you tell whether an amp has high current? And, pardon my ignorance, but what's the difference between currents and watts?
more power doe snot always mean better sound ... if power was the only consideration, old amps like the Crown Macro Ref or newer 1000w class D's would be the pinacle of amps

some of the best sounding amps (IMHO) from major manuafacturers include the Levinson 29, Krell KSA-50's, Jeff Rowland Model One and the Plinius SA-50 Mk III or IV. the Forte IVa is a "giant killer" in what could be termed inexpensive high-end amps.

Plinius amps are nice in that you can switch from pure class A to class A/B. the older models are an excellent value on the used market.

Generally, an amp that doubles its output from 8 ohms to 4 ohms is a high output amp. Only very robust power supplies are able to go from 200 watts @ 8 ohms to 400 watts @ 4 ohms. An excellent solid state amp that does this is the Clayton M200, plus its output is all Class A. Occassionally they pop up for resale on Audiogon. I know, because I recently bought one at around $4,500. You won't find a better solid state amp than the Clayton. They even make a M300 with 300 watts/channel @ 8 ohms. These amps are built incredibly well and likely will last decades, due to their military spec building quality. They are plain looking, but beautifully sounding with most speakers.

An alternative solid state that is about as good as the Clayton's are the McCormack DNA-500's. Both these amps are significantly better than most of the famous named solid state amps, such as Levinson, Krell, Rowland, etc. And they are less expensive to boot.

Easy, just think the differences in horse power in a car, as you are climbing Pike's Peak.
For inefficient speakers with low impedance drops a more powerful amp can make a dramatic difference. For your average speaker you may perceive better or tighter bass and more "ease" at louder volumes. But then again you may perceive nothing different at normal listening levels and sometimes lower powered amps do indeed have better sound than their big brothers.
Amp rated at lower continuous power might have higher momentary power. Average power needed for music is only few percent of peak power unless you listen to sinewaves.

Power specifications give only general guidance but all depends on particular amp design. Chances are, when comparing amps from the same line/company, that higher rated amp will be louder but 15.7% difference in loudness might not be worth extra money.

Comparing to a car is a little misleading since 10x power is only 2x louder (exponential scale).
The point has already been made but here it is in a cute form.
If the first watt sounds bad why would you want several hundred more of them?
Quality is the key and the usual recognition that some speakers really do need high current amplification to sound best. Essentially I am just agreeing with most of the comments thus far.
The W7 is the sweeter sounding of the two amps . I would never trade finesse for more power , and although the W8 may sound more powerful we are only talking about a 2dB difference .
A couple of years ago Hi-Fi+ published and interesting review, where they compared three Conrad Johnson's power amps- LP70, LP140, LP280, which use essentially the same design, circuit and type of output tubes, the only difference being, as you could probably guess, an output power-70, 140, and 280 Wt. respectively.
Without going into much detail, the bottom line was, that in the same system (actually with some fairly efficient speakers), every more powerful model sounded better, than the one with the lower output. LP 280 was an overall winner.
I completely concur with the above based on my personal experience.
Power of the amplifier has very little to do with the loudness, or efficiency for that matter. It has more to do with the ability of the power amp "to control" the speaker, allowing it to play at it's full potential. Obviously, it has direct impact on how the dynamic aspects of music are being handled.
In essense, you can make 10 Wt. amp to play almost any speaker loud enough, but it won't sound good doing it.
Maril555 - Imagine 100W class AB transistor monoblock that dissipates 100W of continuous power into heatsink while driven with the sinewave test signal.

Now, get rid of this large expensive heatsink and replace it with 25W heatsink and use saved money to oversize power supply and up the voltage. You'll get an amp that is rated only 25W continuous but is louder with better control of the speakers at the expense of continuous power rating that is useless since average music power is only few percent of peak power. Peak power is what counts.

Most likely it will not sell very well since most of people, you including, believes that higher continuous power rating means better sound. Tubes might be different story - we need to ask Atmasphere (he knows tubes).
I have a 100 watt solid state amp that controls my speakers better than a 150 watt solid state and a 400 watt digital amp that I tried.
Approaching your question from the speaker side.
Sensitivity is not the end of the amp/speaker problem. 'goodness' of load is more about phase angle then just sensitivity. A very highly reactive load will be worse, even if much more 'sensitive'.

From the amp side. were driving just a resistor, the more powerful amp would indeed be slightly louder. Not even 3db, which would hardly be worth it. But, the load you are driving is not a resistor so as it turns out, amps vary in ability to drive such non-resistive loads. It is just possible that the lower power amp will be a better electrical match for your current or proposed speakers.

For the above reasons, 'hi-current' amps may be a red herring non-spec. Since speakers are not a resistor, the real measure of an amp is how well it does into a real load. Which the published specs don't help with.

As for 'real world' performance? Read Kijanki post above. 10x power=2x loudness. Not much for such a huge increase in power. If all speakers were of the sensitivity they advertised, much better leverage could be gotten with more sensitive speakers than the amount of amp power you are talking about.

Check out this link for real-world amplifier testing.
IMHO, and perhaps more so with ss amps, having some extra power beyond actual use, is worthwhile in that it can keep an amp from stressing near it's clipping point.
I had a Classe CA 300 on a pair of PMC MB2 once and turned the amp up to its limit and then put on a Classe CA 400(only 100w more But 1kv bigger transformer)and that made a huge difference when pushing a great song up into the bigger SPL's.
I have had a Simaudio Titan(200w/ch) and it would hold its own..
The $$ value vs power may not be worth it...maybe W7M's
The C.J. LP280 used a more complex circuit than the LP140 or 70 .
A better amp is more important than a more powerful amp. Don't be mislead by the numbers game.
Isn't that what the Pass "first watt" thing is all about? There are a hundred things that make up a great amp, and power is only one of them. I think 100 clean high gain watts per side is just about right for my rig and room, but I was at a friend's place recently and he had some little triode tube mini watt thing and it sounded amazing, although not very loud. Note that for live stuff I've always used VERY large wattage amps...350 watts minimum into each speaker or uncompressed things don't fare well.
But there are some very good high powered amps that compete with and beat their lower powered siblings, like the Mccormack DNA 500. But it's always about synergy with your speakers and using the power that THEY need, not that your ego needs.
The first Watt of a more powerful amplifier need not be worse than the first Watt of a less powerful amplifier. Furthermore, a more powerful amplifier can often provide better power longer than a lower powered amplifier, even though it hasn't exceeded the total power output of the lower powered amplifier.
Definitely maybe. Speaking as one without the technical experience to even provide you with an all costs audition in your system compared to your current component.

That said, I heard the Sanders Magtech amplifier in a somewhat familiar system, not mine, compared to the owners Bryston 7B's. Similar power but the difference in presentation was very noticeable.

Level 4 skier. Haven't skied in six years. New boots and skies last season, WOW, talk about gear related improvements!
06-21-11: Pani
Since you are moving within the same make and lineup of the amp you will probably not have "inferior" watts.
not necessarily true, AP. the bigger amp *could* have inferior watts; it could have superior watts. It's 50-50 without knowing any more about these 2 Sim Audio amps.
There are several such examples in the industry: the vintage Krell KSA-50 was acknowledged by many users to be a very sweet class-A sounding amp, while the bigger amps in the KSA series such as the 160W or the 200W monos did not have that sweet class-A sound. These bigger Krell amps were really very good but didn't have the 50W amp's sonics. Same could hold true for these Sim Audio amps....

With your speakers it is a big thumbs up to go higher in watts.
based on what???? where's the info or data to support this? have you been reading the manuf website & that's how you know??

What you will most probably hear is a more resolute, disciplined performance because of the grip the amp will have on the drivers. The sound might be bigger as well but it will be more graceful.
based on what?? where is the information or the data to support such a statement. it's pure conjecture on your part....

To Level8skier (from Level0skier!): the question you are asking does not have a definitive answer thru mere written discussion on this forum 'cuz there isn't enough data to supply a good/correct answer.
If you increase the wattage to 250W from 150W, you increase dynamic headroom by 2.2dB. Increasing dynamic headroom is always a good thing for music - you have more peak power that can be delivered into your speakers when there is sudden need from the program material.
That said, another aspect of power amplifiers is its ability to deliver current into the load. That's what sets up the instantaneous voltage in the drivers which creates the amount of pistonic action in them. If your stated wattages are correct, the 150W amp uses a 35VAC transformer whereby the DC rails are +/- 49VDC & the 250W amp uses a 45VAC transformer whereby the DC rails are 63VDC. If the only thing different between the 150W & 250W amp is the power transformer, then, the 250W amp has less load current ability (vs. the 150W amp) 'cuz at higher DC rails, the power transistors can source/sink less current (for a set bias level) according to the SOA graph.
OTOH, if Sim Audio increased the power transformer AND increased the number of output power transistors, you have a higher wattage amp which will have the ability to deliver a higher load current. My understanding is that higher load current is better because the amp is able to maintain is damping factor (DF) better ('cuz as load current increases, the amp output impedance stays relatively unchanged hence DF remains relatively unchanged). In such a case, the 250W amp is a better amp.
You have not told us which way Sim Audio went with the 250W design. Maybe you do not know? Maybe you will never know? Depends on how much Sim Audio wants to share with you....
If you are unable to decide after reading all the available info &/or talking to Sim Audio, it might be better to audition the 250W amp in your house or at your dealer. That would be the best route. In the mean time, all of us can speculate galore for you.... ;-)

It's interesting that no one has yet discussed the downsides to powerful amplifiers, as they are significant.

If a person is running an inefficient speaker (let's say 85 db. or less) or one that requires significant current due to low impedances in the bass or steep phase angles, then an amp with really stiff power supplies will, all else being equal, control the woofers better. When I write "amp with really stiff power supplies", however, I do not mean one that simply has a high wattage rating - as correctly noted above by several other posters, the fact that an amp has a high wattage rating does not necessarily mean that it has first-rate energy storage, e.g., Audio Research's 600 watt/channel monoblocks have less energy storage than CAT's 100 watt/channel JL-1 monoblocks.

Putting the issue of energy storage aside, there are two major disadvantages to high-powered amplifiers. First, it is very difficult to control a high-powered circuit without global feedback and virtually every high-powered amplifier therefore uses it. Global feedback sucks the life out of music by destroying three-dimensionality and giving it a closed-in, deadened quality, and can create highly complex distortion products. Most triode tube amps do not use global feedback, and well-known solid-state amps that do not use it include the darTZeel (Herve Deletraz HATES feedback), the Ayre monoblocks (Charlie Hanson HATES feedback), the new Rowland 625, a variety of Pass amps, and speaking of Sim, the Sim Audio W-5. Pass has made some very high-powered amps that do not use negative feedback, but most amps that eschew feedback are lower powered (the darTZeel and Sim put out roughly 150 watts/channel into 8 Ohms - the Ayre monos and the Rowland put out 300 watts/channel). For technical papers about negative feedback, see the Pass and Atma-Sphere websites.

The other downside of powerful amps is that they feature many output devices (by "output device", I mean output transistors in the case of solid-state amps and output tubes in the case of tube amps). All of those devices muck up the sound in systems that are otherwise high resolution because, among other reasons, it is very difficult to match output device pairs, every device adds noise, and they make the circuit more complex. For this reason, it is often said that the best sounding amp in an amp line is the lowest powered one. Most high-powered amps use a dozen or more output device pairs, while the darTZeel, in contrast, uses a single pair of transistors per channel. Circuit simplicity is indeed highly desirable - it's why many serious audiophiles put up with 8 watt (or less) per channel single-ended amps that use only one output device per channel.

If a person runs inefficient speakers in a large room and listens to electronic music (anything amplified and then recorded, like rock or pop), then high-wattage, brute force amps are arguably desirable. But if a person has reasonably efficient speakers (87+ db.), a normal-sized room, and listens mostly to unamplified acoustic instruments (classical, jazz), a high-powered amp will, relatively speaking, sound less like real instruments and more like an electronic reproduction.

So, how much difference does a more powerful amp make? It can make a huge difference - go listen for yourself.
If one listens to music at levels that come near the levels one might hear at a live venue, and that includes unamplified concerts, under powered amps can be subject to clipping during peaks. Fairly high powered SS amps without global feed back have been available since at least the 1980's. Some ss Class AB amps lines are able to stay closer to a Class A bias longer, as their total power output levels increase.
"The other downside of powerful amps is that they feature many output devices (by "output device", I mean output transistors in the case of solid-state amps and output tubes in the case of tube amps). All of those devices muck up the sound in systems that are otherwise high resolution because, among other reasons, it is very difficult to match output device pairs, every device adds noise, and they make the circuit more complex."

Great sounding Coda Technologies S5, 50W/8ohm class A (no global feedback) has 60 output devices. As for noise it is exceptionally quiet with S/N=120dB.

State of the art Atmasphere MA-3 (also no global feedback) amplifier uses even more output devices (about 40 tubes per channel).

In both cases a lot of output devices doesn't "muck up the sound" but makes it better (at the expense of complexity).
Like someone stated earlier they make a difference for inefficient speakers with low impedence drops, they also make a difference with many multi driver speakers with complex xovers as the xovers are known to eat up as much as half the power before ever reaching the drivers
Metman - that's true, but I would rather have lower power amp that can perfectly drive very low complex loads. 50W/8ohm Coda S5, I mentioned, can output 200W at 2 ohm and according to Stereophile test can even drive 0.47ohm.

Half of the power loss in crossover, that you mentioned, is only 22% of loudness loss.
06-22-11: Raquel
First, it is very difficult to control a high-powered circuit without global feedback and virtually every high-powered amplifier therefore uses it. .....
Raquel, I believe that this is *not* a true statement. I think that you are confusing power amplifier gain with power amplifier (output) wattage. They are different. You need global negative feedback when you have many cascaded gain stages (wherein the power amp has a lot of output to input voltage gain) so that you can keep the entire design stable (oscillation free), lower in distortion & lower in overall noise.
To design a high wattage power amp you need to design in the correct transformer size, the correct number of output devices to handle the output current, the correct size & quantity of power supply caps to handle the charge being delivered to the load. This can be done using minimal number of power amplifier gain stages (for example, Pass does this often with just 2 gain stages hence he can avoid global negative feedback & still deliver to the market a X600 beast of an amplifier).

Also, you use the term "high-powered circuit". what, according to you, is a "high-powered circuit"?? you probably mean 'high wattage circuit'? Might be better to use the correct terminology to avoid ambiguity esp. if you are sharing some of your technical views on a subject. Just FYI.

I was trying to keep it simple to make a point. Most amps, powerful or not, have anywhere from three to five gain stages (very few have two), and we all know that using global feedback with such designs makes the amp builder's job a lot easier. I do not agree that feedback ultimately lowers distortion - it changes the types of distortions to those that are different from the harmonics of live instruments (which is why it screws things up so much). Nelson Pass wrote the following:

"We have seen that nonlinear distortion becomes larger and more complex depending on the nonlinear characteristic of the stages, the number of cascaded stages, and the number of spectral elements in the music.

Negative feedback can reduce the total quantity of distortion, but it adds new components on its own, and tempts the designer to use more cascaded gain stages in search of better numbers, accompanied by greater feedback frequency stability issues. The resulting complexity creates distortion which is unlike the simple harmonics associated with musical instruments, and we see that these complex waves can gather to create the occasional tsunami of distortion, peaking at values far above those imagined by the distortion specifications."


PS - Pass makes a no-global-feedback amp that is even more powerful than the X600 monos: the X-1000, which also has only two gain stages.


I really respect Ralph Karsten's (Atma-Sphere's) designs, and I have no doubt that his amp with 40 tubes is really good for what it is, but this is precisely the type of amp that will be noisy ("mucky"!) compared to an amp having, say, 4 tubes. 40 tubes?! Or 40 transistors? Have you ever heard an amp with that many tubes or transistors in a really resolving system? More importantly, have you heard an amp with only a small handful of tubes or transistors in a really resolving system? Come on.
06-23-11: Raquel

I was trying to keep it simple to make a point.
ok, thanx for the clarification. I now know where you were coming from.

Most amps, powerful or not, have anywhere from three to five gain stages (very few have two),
OK, if you say so. i will not contest this as I certainly do not know this for a fact. I have not popped the lid of various amps nor studied their schematics to know any better. So, i'll take your statement at face value....

and we all know that using global feedback with such designs makes the amp builder's job a lot easier.
there was never a contest here - we are in full agreement.

I do not agree that feedback ultimately lowers distortion
I think that you should! ;-) any electronics book that discusses feedback will discuss 'feedback effect on distortion' & you will see mathematical equations showing that negative feedback does reduce distortion.
Having said that, in audio where we are talking about human hearing which is very sensitive to distortion components, I tend to agree with Pass' following statement (taken from your post):
Negative feedback can reduce the total quantity of distortion, but it adds new components on its own,...
I believe that you are in agreement with this statement as well.
this might be a better way of stating the distortion, negative feedback relationship.
Raquel - I've never heard either amp that I mentioned but specified S/N=120dB was confirmed by Stereophile measurement and audition of Coda S5. It is dead quiet and very resolving. As for Ralph amps - reviews praise them just for being quiet and very resolving. Putting two tubes in parallel doesn't make it less resolving or noisier than one tube. Part of SixMoons review of Atmasphere MA-1:

"Compared to my BAT VK-75, the Atma-Spheres just offered more of everything: More detail, more extension, more transparency, better soundstaging, greater micro and macro dynamics, more extended and luscious high frequencies"

You assessment of matching output devices is not accurate because it is easier to get average characteristic by connecting many output transistors in parallel. Linearity also improves since each transistor works at smaller current range.
Noise voltage that limits resolution of bipolar transistor is defined by resistance of the Base and resistance of the Emitter that can be reduced by reduction of emitter current (inversely proportional) while Base resistance become dominating reason for the noise. Placing transistors in parallel not only reduces emitter current but also reduces resistance of the Base (in parallel). Placing many bipolar transistors in parallel is well known noise reduction technique in microphone preamps.

As for negative feedback - It is not the complexity that screws up the sound but lack of bandwidth. Limited bandwidth amp delays the signal (shifts phase). When input signal changes fast, feedback loop is momentarily open creating overshoots (or odd harmonics in frequency domain). Our ears are very sensitive to odd harmonics (especially higher order) because loudness clues lie in them. It is called TIM (transient intermodulation) and is known since 70s.

One way is to compromise THD, IMD, DF and make an amp without global feedback but the other is to use just enough feedback to reduce THD to about 0.2-0.5% and then limit input bandwidth (before feedback summing stage) to one that amp had without feedback applied. There are many great amps designed with or without feedback - there is no simple answer. Some of these great amps are very simple some are very complex.

I just realized that Ralph Karsten has the same last name as first name of the Icepower (that I use) designer Karsten Nielsen. Karsten people design good things.
I have a similar consideration. Recently I added a second amp bi wired vertically into my system. Aragon 8002 125 watts. The second amp really helped in detail and yielded a more relaxed sound.
Now I have a chance to get a pair of Aragon Palladiums 400wpc
to drive my Snell CV's. I am thinking this too should make a nice improvement.
Will this extra power yields even better results? I will have a chance to test drive these puppies and they were top of the line @ $5 K. Hmmmmmmmm...
Consider the average wattage level that you will be playing your music at and consider that dynamic peaks can easily demand 10 db increases. In other words, if your music is played at 20 watts average and your cd played is very dynamic, you need 200 watts to play that 10 db peak. The 150 watt is sufficient in this case, but what if your peaks are 13 db higher? Now you need 400 watts of dynamic headroom. Continued clipping on your dynamic peaks can damage speakers. This is why they say smaller amps blow more speakers. Also, constant clipping can change from music that is soothing to music that fatigues. Consider how loud you play your music and how dynamic is the source. Check the dynamic headroom of each amp before you choose.
Every design, no matter how expensive or supposedly uncompromised, involves inherent tradeoffs. What compromise a designer finds intolerable or allowable accounts for some of the differences in products. For example, OTL amps are designed so as to eliminate the need for an output transformer (other designers actually LIKE what transformers do), but, in order to bring down the inherently high output impedance of tubes, a lot of tubes have to be wired in parallel (the high number of tubes is not just to increase output). Other designers might not like having many output devices. I happen to like the way most OTLs sound, compared to other higher power tube designs, so I would say that is a good compromise (the last thing that would come to my mind when hearing a decent OTL is "mucky"--they are the paragon of clarity and speed). In the SET world, there are a lot of purists who would never do parallel tubes to boost power (particularly tricky with SET amps), but, that is one way to increase power (I own, and love a parallel SET amp).

The same thing happens with solid state amps. DarTzeel and several other companies have tried to minimize the number of output devices, and NOT to save money, but for sonic reasons. This company also minimizes use of feedback, at the cost of lower measured linearity, more issues with instability, etc. I have no idea if these design choices account for the sound of their amps, but, I like the sound of the smaller DarTzeel amp I heard. Some designers even find it worth the trouble to avoid using complementary pairs of output devices--there are almost endless number of design choices.

I have NEVER heard an amp that just offered "more of everything" in all systems--and that is just based on my own preference. If you consider that each listener has a different set of priorities, I don't see any single design will every be crowned the undisputed champion.

I suppose there are some speakers that really demand a lot of power, but, as a general observation, I think there are far too many listeners who overestimate the amount of power needed to handle the dynamics of recorded music. Yes, in theory, the dynamic range of a live performance of an orchestra is extremely wide. However, recordings never actually capture that dynamic range;so, if I set my volume level at a reasonable level for softer passages, the peaks will NEVER reach realistic levels and I really don't need a super high reserve of power. For rock and popular music, my own preference is not to listen at "realistic" live volume levels. As I improve my system, I find that I get full sound and enjoyment at lower volume levels. I don't really care about attaining "realism" I go for sound I like (frankly, if my system didn't sound a whole lot better than ANY live amplified venue, I would junk it). As to the example above where the starting point of the analysis was an average level of 20 watts, that is a completely unrealistic starting point for even speakers of reasonably low efficiency. As an average, even a single 86 db/w efficiency speaker, in free field (no room) would be playing at 99 db at one meter (extremely loud). Actually, it would most likely be playing at a lower volume because it would be compressing like mad from overheating.
Larryi, I think in a typical setting, a single 86 dB/W efficient speaker playing at one meter in free field (no room)with only 20 Watts available, might be significantly less loud than 99 dB.

I would guess that very few actually listen in such a manner. In what I (admitedly arbitrarily) suspect might be a more typical setting, using two speakers that are 86 dB/W, placed within 2'-4' from a roomer boundary, and heard from a distance of 3 meters would require closer to 45 Watts to achieve 99 dB

Though often cited, I don't believe the reason one typically doesn't listen at average levels of 99 dB because (the speakers) "...would be compressing like mad from overheating.", but, though appropriate for musical peaks, 99 dB is just uncomfortably loud for sustained listening.