Do I have this right? A question on watts

[Mark_IDT]

Ok I think I have this right so let me know if I go wrong. Lets say I have a pair of 250w speakers and I'm running a 250w amp to them. As I turn up the volume the watts double for every 3 db until I reach 250w which would be the point where the amp clips and another 3db of volume would push it to 500w or more blowing everything up. So then lets say I run a 500w amp to the same speakers once I reach the volume where it's putting out 250w I'm close to or at the point where the speaker clips. Another 3db of volume from that amp would probably blow up the speakers but that last 3db of clean power is reffered to as headspace. Therefore it's better and dare I say safer to have a bigger amp if your going to play your speakers at a volume close to there limits because a small amp quickly doubles watts when it starts to clip.

[Geoffcin]

Ok I think I have this right so let me know if I go wrong. Lets say I have a pair of 250w speakers and I'm running a 250w amp to them. As I turn up the volume the watts double for every 3 db until I reach 250w which would be the point where the amp clips and another 3db of volume would push it to 500w or more blowing everything up. So then lets say I run a 500w amp to the same speakers once I reach the volume where it's putting out 250w I'm close to or at the point where the speaker clips. Another 3db of volume from that amp would probably blow up the speakers but that last 3db of clean power is reffered to as headspace. Therefore it's better and dare I say safer to have a bigger amp if your going to play your speakers at a volume close to there limits because a small amp quickly doubles watts when it starts to clip.

IF you have a speaker rated for 100 watts, and you hook a 200 watt amp to them they will be just fine unless you loose your mind and intentionally drive them past the limit. The 3db thing that gets bandied around is a bit of a misnomer. A 100 watt amp can make a sinewave that is 3db louder than a 50 watt amp. Music for the most part is NOT sinewaves, but complex waveforms wth lots of transient peaks in it. It's these peaks that can get clipped first, and sometimes even at a moderate overall SPL. A more powerful amp can give you more headroom, and these transient peaks will remain unclipped.

[Mark_IDT]

A more powerful amp can give you more headroom, and these transient peaks will remain unclipped.

Ok so do these transient peaks stay unclipped only if they remain within the rms watt rating or within the peak power? Is a sinewave just a constant frequency?

[kexodusc]

Without knowing what your amp is it's hard to answer your question on the clipping of the transient peaks, but these peaks won't be clipped if the amplifier still has headroom (peak power)

Geoffcin was right.

The 3 dB thing does assume sustained signals, but these are can often be more demanding than musical passages which are instantaneous draws of power of varying amounts on an amplifier. Except for probably bass heavy orchestras in classical music which are pretty intense.

The added headroom the transient peaks enjoy in a larger amplifier is directly proportional to the amount of headroom the sine waves enjoy though. There's a function that determines the output based on the input signal, this remains constant in an amplifier. We could state that the transient peaks also only get 3 dB's more of volume as the power doubles, but that's not exactly true. In some cases it will be more, with frequencies below 500 Hz or so it's probably less than 3 dB's.

Most amps have no problem exceeding their (for example) 200 watt ratings for instantaneous transient peaks that aren't as demanding as sustained signals. Some manufacturers will give you a peak power rating which is not really useful, but can give you an idea of how much room beyond the rating there is.
Say you had a 100 watt amp. It likely won't have a problem with 200 watt transient peaks and sometimes more (depending on the manufacturer). Most amps I've seen will have at least 3 dB headroom at max power...3 dB isn't really enough for peaks which can be 9 dB -12 dB louder though, so if you expect to be drawing 100 watts of power to your speakers sustained, you'll want a much beefier amplifier.

Power's hard to gauge as it swings up and down almost instantaneously.

All things equal it's good to have more. But there's a point for many of us where the extra power becomes useless or wasted, and you'd be better off to invest money into another part of your system.
Best to take into consideration your room size, your average listening volumes, your peak listening volumes (as in as loud as you'll ever play it), your speakers maximum input, their senstivity, and whatever flexibility you want in case your speakers change, you move into a bigger room, etc.
Some speakers need more power to play loud than others. People say there's no correlation between speaker efficiency and sound quality, but I've actually found speakers with lower sensitivities to sound pretty darn good. Not sure if it's because cheap speakers are all really efficient or if there is a link there...

My tower speakers in my studio are about 88 dB, not the most efficient. At my listening position in that room (about 10 feet back), 1 watt of power from my amp to each channel will produce 85 dB at the listening position. I've actually used a multi-meter and spl meter to test this. My room is adding about 3 dB of volume since the speakers are only a few feet from the walls. Most of the time, I don't actually listen to music that loud, I'm usually in 10 dB lower or so. I'm not even drawing 1 watt of power.
I can listen to music at about 95 dB or so in there, this is where the cheap sound proofing really starts to fail though and you can hear stuff in the rest of the house. Kind of sucks when the boys are over practicing, but it was the cheapest solution when I built the room and lady of the house is patient with me. Anyway, at 95 dB I'm drawing about 10 watts per channel. My Rotel Integrated is rated conservatively at 100 watts per channel. I have probably 15-18 dB of headroom at 10 watts for any musical peaks...maybe more. This is ear bleeding loud, and I could turn it up even more, but it becomes unenjoyable at that point.
In that 20 X 18 room with those speakers, I don't need anymore power. I could probably get by with some older 40 watt/channel NAD amps I have actually, but I like the Rotel.

[N. Abstentia]

I don't think you have to worry about getting 250 clean watts into a home theater speaker...unless of course you're trying to make those speakers fill up the Superdome or something.

You normally won't use more than 20 watts to get to a level where you can't stand it for more than 30 seconds. It's nice to have 50 watts or so for headroom/transients.

Now keep in mind I'm talking CLEAN watts here..not the "100 watts per channel!" you see in the receivers at Best Buy. Even on their best day you'll never get 100 watts per channel from one of those.

[Mark_IDT]

I thought learning about 2strokes buy reading on the net was sometimes confusing but audio is just mind bleeding painful physics. I'm going to go buy a spl at ratshack tomorrow to see how loud I listen to music.

[kexodusc]

Good idea on the SPL meter...you might be shocked at how loud you actually listen to music at versus what you think you listen to musica at, I was...I've heard so many people say they crank their stereos to 120 dB. Yeah right.
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