Need some education on Watts.

Folks

Can someone please define in layman terms what Watts really does for a receiver setup ?
I would like to know if I have a receiver rated 70W per channel and is hooked up to some to some good quality speakers rated 20-200W (8 ohm) , what difference I would notice if that is now hooked up to a 140/channel rx.

I know there are a lots of other floating factors here like room size , speaker type , etc etc .. but what role the numbers are playing here ?

Thanks

Re: Need some education on Watts.

Watts is a measure of power over time. Unfortunately, it is also one of the most abused ratings in consumer electronics and for most manufacturers, the ratings can't really be trusted. Plus, unless you are looking to drive really inefficient speakers at concert hall volume, the wattage required to fill average rooms is quite low receiver-wise, and you should worry more about:

Budget
Quality of Brand
A/V switching capabilities (component, HDMI, etc)
Upscaling capabilities
HD audio support
Any extras - iPod support, internet streaming

. . . and then worry about wattage, preferably only when comparing two models by the same manufacturer. Don't get lured in by the "easy to brag about" buzz words and concentrate more on getting the best quality and/or features you can afford.

Re: Need some education on Watts.

Ashish,

A quick overview of how watts relate to sound pressure (or loudness). For every 3db increase it takes double the watts. In other words, if it takes 100 watts to produce a 100db sound at 16', it will take 200 watts to produce a 103db sound at 16'. For reference, 3db is about the minimum increase that a human can detect. A 10 db increase is perceived as double the volume.

So to answer your specific example, the difference between 70 and 140 watts will be about 3 db. You can see it is not nearly as important as the marketing folks want you to believe.

Here's a good calculator to see loud your speakers will be.

Peak SPL Calculator

Re: Need some education on Watts.

Good stuff. Thanks a bunch

Re: Need some education on Watts.

There are a lot of other complications, too. However, there are some common "guidances of thumb" that are repeated early and often.... even if they're not always accurate.

A common story is that it's easier to "blow up" speakers with an underpowered amplifier than it is with an over-powered amp. However, if you start turning the volume knob up, and the sound level isn't behaving the way you think it should, back off! If your amp is getting unhappy, the distortion (which you may not recognize, depending on your experience) may cause harm.

That said, power is, as indicated two posts above, not always significant. Things to look at are the efficiency of your speaker. Somewhere, there should be something along the lines of "97dBA@1W@1kHz@1meter" or something like that -- at one meter, a foot, ten feet, whatever, a tone (in this case, 1kHz) played at 1-watt produces a pressure-wave that is measured as 967dB, a-weighted. Some or all of these parameters will be present. Combined with a 4-ohm/6-ohm, or 8-ohm measurement, this gives you a feel for how much power the speakers need, or how they will respond.

In the grand scheme of things? 97dBa is pretty loud. You might also be at 2 or 3 meters, and won't be listening to static sine-wave tones -- much.

Something to pay attention to is, "how much can the amp really do?" If you're lucky, the amp specs will indicate how they measured that 70watts/channel. Is that with a test-tone? White or pink noise? How many channels driven? And is that RMS or peak? Peak is a horrific thing -- what's the most power we can push in the shortest instant we can measure? That way, you can end up with 20w/c RMS, 250w/c peak! Which would they rather advertise?

Another thing to look at to see how much smoke people are blowing, is the back plate of the amplifier. Near where the power cord goes in, there'll be something about the amp: 560-watts @ 120VAC, for example. Or 180w@120VAC. Or 1450w@120VAC.

If it's a 5-channel amp, and it's claiming 55w/c RMS, all channels driven, it should at least be in the vicinity of 300watts. It should be at least close to the total output load.

On the last hand, I'd rather a well-built 20w/c amp than a shoddy 100w/c amp.

Leo