You misunderstand the reason for power. It has little or nothing to do with volume. There are several reasons why a comsumer might want to go with a higher powered amp.
1) Certain speakers depending on their efficiency require large amounts of power to work as they are designed. A very efficient speaker can run with very low power. Some of the favorite amps right now put out only a couple of WPC. These low powered amps though cannot drive most speakers to the satisfaction of the speaker owner.
2) More powerful amps are more able to reproduce difficult musical passages because of the amount of power the are able to store. For example; if the listener is playing a recording with quiet strings and suddenly a portion comes along with lots of brass or drums played much louder a low powered amp will not have the reserve to 'accurately' reproduce the passage.
I use a 4 ohm speaker, my amp is capable of 400 WPC into a 4 ohm load. I have never turned up the volume of the pre-amp over half way. For sheer volume I have no need for this amount of power. For the enjoyment of the music I want an amp with the kind of power that will reproduce the details of portion I am hearing. So the issue remains, quality rather than quantity is what the average buyer is seeking.
Personally, i would consider an amp rated at 250 wpc @ 8 ohms to be "good sized" and not "big". Like all things in life, points of view will vary based on one's perspective : )
As to why someone might need that much power, I had temporarily hooked up an amp that is rated for 200 wpc @ 8 ohms / 350 wpc @ 4 ohms to my HT mains today. These speakers are a nominal 4 ohm load and are about 85 - 86 db's in terms of sensitivity. As such, they are less than average sensitivity and what most would consider a low impedance load. Into this type of load, the amp should be delivering 350-375 wpc rms and probably at least 4-500 wpc on peaks.
Upon playing a classical piece by Rimsky-Korsakov entitled "Allegro Molto" at what i consider to be "good volume", the amp was noticeably going into compression and lacked bass sustain during the "high impact" parts of the selection. Instruments were getting smeared together due to amplifier saturation. Switching back over to the amp that i usually use to drive these, which is rated at 1200 wpc and clips at 1400+ rms, i had no problems. The bass had much greater impact and sustain and instruments did not get as "bunched up" sounding. This was because the amp was still "coasting" and not being pushed hard. As such, it was easily able to keep up with the demand for power and the result was cleaner operation with less smearing, compression and distortion.
And just in case you were wondering, it was wonderfully dynamic, loud and still crystal clear : ) Sean
A few years ago I switched speakers from generally efficient ones to a quite inefficient pair. The amps driving my old speakers did so beautifully with 100 watts of class A power per channel. However,they were totally inadequate to drive the new speakers--it was as if there was a lid on the speakers, which had nothing of the openness they had had at the dealer's showroom. I had to buy a pair of 350 watt per channel amps. Now, those same speakers have been reconfigured by the manufacturer, and are much more efficient. The 350 watt amps just coast, the volume control on the preamp is much lower, and I am sure my old amps would work just fine again.
Mgottlieb, can you expand on what you consider to be efficient and inefficient? Where does the line cross?
How loud do you "high powered" guys listen to music? How big are your rooms?
Matchstikman: I just checked things out playing the same recording set to the same volume level. The mains are spread appr 12.5' apart ( center to center ) and toe'd in a bit. While this is not ideal for two channel reproduction with these specific speakers, this is my HT system and i have things dialed in for optimum use with a large ( two eight's, dome mid, dome tweeter ) center channel. As such, i need to spread the mains out just a bit more than normal, which also results in a very wide soundstage with excellent center fill due to the center channel taking over on movies. Even with this wide of placement and the center turned off for standard "stereophonic reproduction", imaging and soundstage is quite acceptable. Since I was using the system in 2 channel mode via the mains only when i made the above comments, that is how i measured it.
Ambient noise level in the room is below 50 dB's, which is as low as i can measure. At my seated listening position and the meter just behind where my head would normally be, I am hitting peaks of 108 - 110 db's sitting 10' away from the speakers. The average level of the recording is easily 20 - 30 dB's ( and sometimes much lower ) than this. As such, there is a great deal of dynamic contrast as the tempo and volume changes during this specific performance. This is a very exciting Classical performance, even for a "rocker" like me : )
For those that are "playing along", i'm using a stock Realistic 33-2050 analogue SPL meter. It was set to the "C" weighting and fast response. I also have a highly modified version of the same meter that is much more linear in response ( and would have shown higher peaks ), but i used the stock RS meter so that others with such units might be able to do a more direct comparison. Sean
More important than playing "extra loud" is the ability to play music at a moderately loud level without the clipping distortion and compression you would hear when using an amp that is not quite up to driving the speaker load. Its not all about your amp playing louder, just being able to handle the demanding peaks and keep control during complex passages.
Another dividend can be improved bass control and quality. Some speakers dont need much power but still respond in the bass region. Matching the speaker to the amp is the most important aspect.
I leave my amp on all the time. Will a 300 wpc amp consume about 3 times more electricity than a 100 wpc amp when idle?
Also, a speaker with 8 ohms impedance harder or easier for an amp to drive than a 4 ohms speaker?
More power hopefully mean a more authoritative and controlled sound with more of a relaxed ease in the musical presentation with greater and more life-like dynamic swings. By relaxed ease, you do not feel that the amplifier is pushing it's limits as it's just humming along beautifully.
But all the above can certainly be accomplished in a lesser powered amp to a certain degree. Generally, it's just cheaper and more conventional to add more wpc.
Ulimately, the wpc is only one of many factors that determine whether an amp is worth living with.
But still wouldn't want to be without those wpc's. At least not with my current speakers.
Matchstikman--to answer your questions to me: (1) there are simple formulations as to efficiency. If I remember correctly, and I'm a listener, not an engineer, speaker efficiency is measured in decibels of output per watt of power input. Speakers rated under 90 db. are considered more or less inefficient, over 90 more or less efficient. But it's more complex than that: my speakers were just upgraded, and while their output rating only increased by 2 db., the manufacturer's power recommendation went from 200 watts per channel minimum to no upper limit to 30 watts minimum, 300 maximum. Inefficient speakers driven with inadequate amps tend to sound opaque and closed in. The inevitable tendency is to turn up the volume at the preamp, which only makes the problem worse, because the power amp is now working even further outside its comfort zone. My own experience is when I have added a more powerful amp or switched to more efficient speakers, I wind up listening at a lower volume because more detail reaches me, both on quiet passages and loud ones. (2) I listen at a volume I can get away with in a New York apartment, which isn't all that loud. (In fact, I use a 4-channel system, because the rear speakers increase the sense that the sound is filling the room without my having to blast the overall level.) (3) 22 X 13.5 X 9.
Paraphasing the better explanation:
the ability to play music at a moderately loud level without the distortion and compression you would hear when using a lower powered amp that is "clipping". Its about your amp being able to handle the demanding peaks and keep control during complex passages
Ideally the available dynamic headroom should be in the neighborhood of 20dB, a power multiplication factor of 100 times. So if you're running at only 2 watts per ch. average power, then you need a 200 w/ch amp to have 20dB of headroom & stay out of clipping. You don't use all of that amplifier power continuously, but you do need the large power reserves.
Excellent point Bob. I remember watching a fast responding wattmeter show me peaking well in excess of 900 watts on more than a few occasions. The funny thing is, i don't think that anybody here would have called the sound being produced as being "loud". The speakers were simply BIG-TIME power suckers.
Having said the above, if you have your choice between two "good" sounding speakers that perform relatively evenly, always go for the one that is more efficient. Higher efficiency, non-reactive loads of reasonable impedance make amplifier selection SO much easier. Sean