By definition, if you have enough power then you don't need more.
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It was explained to me this way many years ago and I always reflect. My previous understanding was that amplifiers provide power to the speaker to use. It was best to get an amp that could match the power rating of the speaker. Now I think that the speaker DRAWS power from the amp. At different peak frequencies it will draw more or less. Also the more complex the music becomes. The amp one chooses must be up the task of provided all the power the speakers demand. If not, it will strain the amp and that can lead to distortion. The best amps have enough current to provide the power needed for the speakers demand. Be aware some speakers dip to a 2 ohm load or lower. Quality amps never sound strained to me. I always pick amps of high current capability, even if they exceed the power requirements of the speaker. To me, good quality watts means less distortion. This comes from quality parts, smart design and well built (often large) transformers. Anyone out there with electrical engineering backgrounds, please feel free to correct my simple understanding here.
The key is, how can you know what "enough" power is? I read an article recently that discussed the power requirements of transients. It could be a quick slap of a snare drum or a tympani, really any sound that is instantaneous can cause the speakers to try to accurately reproduce the sound. Those transients can cause the speakers to draw a huge amount of power in a very short period of time. The ability of your amp to handle these transient peaks will affect the overall sound quality.
My speakers are 4 ohm rated at 96db which is very efficient. I recently traded amps (solid state) and went from 220w per channel which drove the speakers very well, to an amp of the same brand at 470w per channel. The difference in sound quality was amazing. I couldn't believe how much better defined everything was. The bass was tighter, the mids clearer, it was as if I had purchased new speakers. So back to that article; the author noted that due to the high power requirement of transients, the more power the better even with efficient speakers.
This is a key problem with speakers - especially audiophile designs. At higher levels they compress and sound dull and flat. It is a problem in Xmax excursion of the drivers as well as overheating issues prevalent in small voice coils (less than 4 inch diameter). It is extremely expensive to make good drivers that still sound great when pushed hard and therefore designers most often choose cheaper parts (cheaper speaker parts can still sound great at lower levels but the sound falls apart when really pushed). Note that speaker efficiency is only measured at 1 watt so it does not tell you if the speaker can play very loud cleanly (lower efficiency designs with better parts may play much louder than high efficiency designs with cheap parts).
A very powerful amplifier is actually safer for the speaker as clipping at lower power can damage tweeters more quickly than clean signals at higher power. As Falconquest notes above - 4ohm speakers are much harder to drive than 8 ohm and will benefit from a beefy amplifier that can handle extreme levels of current necessitated by the very low impedance....
Soundstage speaker measurements show a test at 90 dB and at 95 dB and many audiophile designs show compression and high distortion levels at a mere 95 dB - so transients more often than not are a problem that the amplifier cannot fix as it is an inherent limitation of the accuracy of the speakers themselves. Here I am referring to high end audiophile favourite designs like Wilson etc.
I have no idea what you're talking about with speakers showing compression at a couple of watts. It looks like you're just throwing silliness out there with no context to buttress nonsensical ideas.
As for power supplies, they're a huge expense in an amp, and a lot of folks won't drop a power supply into an amp that will supply more power than the outputs will push into 4 ohm. The little 37.5 watt amp I built has a supply in it that'll belt out 400 watts and it sounds like it. Aside from the risk of melting the outputs, that power supply is the only real limit to what the amp will produce.
Not sure where I said 2 watts. Speaker drivers have an Xmax after which they are nonlinear and compress dynamics.
Speaker voice coil could run at 100 degrees and may be rated up to 200 degrees. 98% of power into a voice coil is dissipated as heat.
Your knowledge of Amps may be outstanding. However many or most people have a lack of understanding of speakers and make the mistake of treating them like linear devices with no power handling issues....
If your speakers compress at all within normal listening levels (i.e. other than the ear damage zone) you have crappy speakers and/or a crappy amp. Also the thing with amps sounding good is the overall design which should produce a great sounding "first watt" and the following watts are simply gravy. The speaker impedance and efficiency will pretty much tell you most of what you need to know about matching an amp to speakers, but it's gotta sound good to YOU. I've designed (and mixed with) systems for live sound using multi thousand watt amps and speaker systems that in terms of efficiency and power handling make home audio gear look weak and silly, but in my active listening home rig I use a 12 watt per side single ended Class A amp with reasonably efficient mains and a couple of powered subs…it will play louder than I need it to and sound sublime with any either calm or dynamic music I put through it because it's supposed to.
Soundstage readily admits that many speakers deviate from linearity at 90 dB and most will deviate significantly at 95 dB. Few if any audiophile speakers that Soundstage have tested can handle 100 dB.
Take a $5000 audiophile speaker like the Monitor Audio PL100
Examine Chart 4 - Linearity at the following link
Is this a crap speaker or simply a very common issue with audiophile speakers? 4dB of compression (non-linearity) at 95 dB shown on the chart for BOTH the woofer AND the tweeter response!
OMG and Soundstage says it is common and they have tested thousands of speakers.
Quote "Many speakers show slight deviations at 90dB. Most speakers start to show serious deviations at 95dB. Very few speakers can be tested at 100dB without damage. "
If most speakers can’t even cope with the dynamic range needed to represent realistic sound levels of real instruments and audiophiles are not even aware of this issue then "Houston, we have a problem."
.....perhaps people get so used to distortion from compression as a lot of pop and rock is compressed to begin with.....
I welcome comments but I don’t regard a speaker as "high fidelity" if it can’t accurately represent real music...so big power amps will only go so far unless the speaker is a very rare bird indeed.
Roger Sanders who designs and sold electrostatics once explained to me that a speaker that is 4ohm say with a rating of 94db (Decwares I used to have) are not really 94db efficient because of the 4 ohm rating. I Don't recall what his current company is now. What had got my attention though is he was pretty determined in explaining how that works and unfortunately I can't recall how to explain that. It did have me feeling a bit though that speaker manufacturers are mis representing . I do remember that he said for the db rating to be as stated it has to be for example -- 96db @ 8ohm 1 watt/1 meter.
Meant to add that the rating would be a lot less.. below 90db in the case of my Decwares. I think he said more like 86db something like that. I had meant at some point to ask Steve at Decware about it but I have since moved up the chain to Harbeths and so glad I did. Something else that seems to be pivotal is a lot of manufactures are using polypropylene for cone material and from what I gather that is not what you want in the ongoing pursuit of better sound. The only good thing about poly cone is very cheap to make .. I found this out as well when I prices the drivers for the Decwares I had and they were like 36 bucks apiece.