Question about power

[tom]

So I'm building some new speakers for myself, and I was trying to get the combined RMS rating for all the drivers to equal that of the power rating on the new reciver (100 watts per channel, front at least.) Then I stopped and thought, does it really matter so long as the rating isnt too low? I.E. would there be a differance if I had a 75 watt woofer as opposed to a 150 watt woofer? I'm guessing that I should probably look at the efficiency more. Thanks in advance!

[Chris Roemer]

> So I'm building some new speakers for
> myself, and I was trying to get the combined
> RMS rating for all the drivers to equal that
> of the power rating on the new reciver (100
> watts per channel, front at least.) Then I
> stopped and thought, does it really matter
> so long as the rating isnt too low? I.E.
> would there be a differance if I had a 75
> watt woofer as opposed to a 150 watt woofer?
> I'm guessing that I should probably look at
> the efficiency more. Thanks in advance!

If you overdrive your woofers, they'll bottom out and you'll hear them pop. Do that too much and you'll wreck them.

If you clip your amp, most commonly tweeters get ruined due to the distorted high frequency material.

If you have a required SPL, pick drivers that are efficient enough and that can handle enough power to achieve your levels. If you have a speaker that's rated at 88dB 1w/1m, then it can produce 98 dB at 1 meter with 10 watts, and 108 dB at 1 meter at 100 watts (provided the voice coils can handle that much power). I believe that at twice the distance (2 meters, or about 6-1/2 ft) the spl drops by 6dB (IIRC).

Most people don't worry about any of this unless they're doing pro sound and NEED to fill a certain size venue with power.

[jeffman]

Step one is making sure you're pouring hundreds of watts into a tiny speaker that will fry.

Step two is counterintuitive. You might actually do better if your amp can deliver more than your speaker's rating. Not because you'll use all that power. But because a small amp asked to deliver more than it can will clip the sound, producing nasty square waves (I think) that can damage your speaker. Go for comfortable margins all around, based on your actual listening habits.

HTH, Jeff

[Paul O]

Yes there's more to it than just the power rating. So say you DO have a receiver that will output 100w per channel, that is the maximum peak power it will provide cleanly. In reality you probably only need speakers that are half that power in rms rating, because they will often handle double in peak. But.. speakers driven to the limits usually don't sound good, so it's better to have more capacity for this and upgrade purposes later. Also look at the sensitivity of the driver, because a higher 1w/1m rating will require less power to reach the desired sound level. And both the amp and speakers will sound better if they normally operate with ample headroom available for peaks.

[tom]

> If you overdrive your woofers, they'll
> bottom out and you'll hear them pop. Do that
> too much and you'll wreck them.

> If you clip your amp, most commonly tweeters
> get ruined due to the distorted high
> frequency material.

> If you have a required SPL, pick drivers
> that are efficient enough and that can
> handle enough power to achieve your levels.
> If you have a speaker that's rated at 88dB
> 1w/1m, then it can produce 98 dB at 1 meter
> with 10 watts, and 108 dB at 1 meter at 100
> watts (provided the voice coils can handle
> that much power). I believe that at twice
> the distance (2 meters, or about 6-1/2 ft)
> the spl drops by 6dB (IIRC).

> Most people don't worry about any of this
> unless they're doing pro sound and NEED to
> fill a certain size venue with power.

That's pretty much what I thought, the RMS and max power ratings really dont mean much as long as they can take the power. And I'm not too worried about clipping and the such, my room is small and I'm not one for anything too loud

[tom]

> Yes there's more to it than just the power
> rating. So say you DO have a receiver that
> will output 100w per channel, that is the
> maximum peak power it will provide cleanly.
> In reality you probably only need speakers
> that are half that power in rms rating,
> because they will often handle double in
> peak. But.. speakers driven to the limits
> usually don't sound good, so it's better to
> have more capacity for this and upgrade
> purposes later. Also look at the sensitivity
> of the driver, because a higher 1w/1m rating
> will require less power to reach the desired
> sound level. And both the amp and speakers
> will sound better if they normally operate
> with ample headroom available for peaks.

I guess what I'm tring to make sure of is if there's a lets say 200 watt woofer in there, would it be underpowered? If my combined RMS rating on the drivers is more than the reciever's per channel rating, it would still work well? (just want to make sure)

[damkor]

You always want all your drivers to have the highest possible sensitivity and power rating and flattest impedance. And you want your amps to have the highest possible power rating, into every impedance load.

Usually, the final speaker's power handling should be half of the amp's rating.

[damkor]

...you say you don't need much volume. So, it's fine.

The reason we want amps with more power than speakers is because speakers distort constantly and fairly gradually and so we turn it down. Amps distort suddenly and that can be dangerous to the speaker even before we hear the problem. So we want the speaker to max out before the amp.

[Paul O]

Don't worry about underpowering a woofer. If it delivers the sound level you want you're fine. A 100w woofer with 90db rating and a 1000w woofer with 90db rating will sound approximately the same from 1-100 watts. The only difference is the latter will be able to produce much more spl with it's higher power rating.

[tom]

> Don't worry about underpowering a woofer. If
> it delivers the sound level you want you're
> fine. A 100w woofer with 90db rating and a
> 1000w woofer with 90db rating will sound
> approximately the same from 1-100 watts. The
> only difference is the latter will be able
> to produce much more spl with it's higher
> power rating.

Ah yes, there we go. I kinda thought this before. Thanks for the help

[tom]

> Don't worry about underpowering a woofer. If
> it delivers the sound level you want you're
> fine. A 100w woofer with 90db rating and a
> 1000w woofer with 90db rating will sound
> approximately the same from 1-100 watts. The
> only difference is the latter will be able
> to produce much more spl with it's higher
> power rating.

But wait a sec, you said woofer. Is there something I should know about tweeters (or mid's for that matter)?

[Paul O]

Yes.. that's a bit of a catch 22. You could run a 100w amp wide open on a 1000w sub and likely never blow it. It would put out horrible distortion, and maybe 2-3 times it's rated power output, but the heavy duty VC windings of the woofer should handle it. How do you think guitar speakers live? Mids and tweeters are much more fragile, and won't tolerate much abuse. The key to keeping a speaker system alive is to never drive your amp to clipping, no matter how big it is. This is where the idea of having a bigger amp than necessary comes from. In a 2-way or 3-way system it's seldom the low frequency driver that blows, almost always the mid or hi driver. Usually when a smaller amp is turned up too much for too long, the distortion produced has much more hi-frequency content than in a typical music program, and a tweeter can actually be overpowered and blown. This is commonly called failure from "underpowering", but that is actually a bit of a misnomer. The amp is actually undersized, but the tweeter is still overpowered.