If you have a speaker rated at 350W @ 8 ohms and you hook it up to an amp rated at 150W at 8 ohms would the speaker or amp get damaged if pushed hard?

Most speaker damage is due to using a small amplifier over driven into clipping. It's better to run speakers from a larger output amplifier that is going to give a clean signal at high volume but still runs within its capabilities.
The use of excessive tone control will also push an amplifier into distortion & clipping again burning out the speaker voice coils.

Graham,
I've been playing thru amps/speakers for 40+ years, and it was just recently, that I learned the importantce of what you stated.
(I think that I will ask Nigel to change my name to "The Student")

Also, a friend of mine uses a 1000 watt Peavey digital amp, going into 1 Bose 802. He is doing this multiple times, weekly. It sounds fantastic, super clean, crisp hi-quality sound.
I told him, granted you are driving 8 or so drivers in that 1 Bose, but still, 1000 watts...its going to blow some night.
He says no and stated what Graham noted.

Although, for the record, he uses 2 of the 802 speaker cabs when he is playing the large 800+ annual things he's involved with.
But that would be logical to carry over the larger area with the amp working continuously at that high output.

MrEd and kkmusic2001,

Think of a speaker and amplifier like they were automobiles. Let's say your car has 500 horsepower. When you are driving down the road at 35 mph you are not using all 500 horsepower.

Even though your friend has a 1000 watt amp doesn't mean he is pumping 1000 watts into the speaker. If your friend has all the volume controls turned up all the way maybe then he is using all 1000 watts. The same for a car, if you put your foot to the floor and keep it there maybe you are using all 500 horsepower.

Think of the extra watts in an amp as extra horsepower to be used for passing and climbing hills and pulling boats. When the musical passage reaches a loud point or really heavy bass is needed you have the reserve power to handle it.

A 350 watt speaker means you should be able to pump a CLEAN 350 watt signal into it and it will not self destruct. If you are outputing a clean 150 watt signal your speaker has an extra 200 watts of reserve capacity before it goes boom.

Tom

Makes sense Tom. That is what I was thinking till the local music store refused to rent me a larger speaker (to be used as a monitor). Their explaination was I will fry the amp as it can only handle 150W and the speaker was 350W. To me this did not make sense. The monitor I was using was and 8" outputting 120W which they said was ok. Only that this small monitor was not sufficient for me on stage, so I wanted a 12"

[This message has been edited by kkmusic2001 (edited 03-31-2006).]

assuming the 350 watts is the RMS rating, NOT peak!!!!

[QUOTE]Originally posted by kkmusic2001:
Their explaination was I will fry the amp as it can only handle 150W and the speaker was 350W. To me this did not make sense. The monitor I was using was and 8" outputting 120W which they said was ok....

Your right. This does not make sense, but MOSTLY because the renter has no problem with you using the 8-incher.

Something else must be going on here that involves ohm load, not speaker wattage.

Is your 8" at 8 ohms too?
If so the 350W at 8 ohms is going to put the same amount of strain on the amp as the 8".
Right friends?

Might that 8" be at 16ohm? That would be less strain on the amp.

Both 8" and 12" are 8ohm speakers

I know only some basic stuff about ohm load, speaker impedance, series and parallel connections, but in my opinion, I still feel that they are wrong on this.

If they allow the 8" 8ohm, they should allow you to use the 12" 8ohm. The watt capacity of the speakers should not be an issue here when the speaker impedances are the same.

If you were planning to connect both monitor speakers, than they have a valid point.

Well, its a bummer but they own the goods and they have the right to set the rules.

Good luck. Hope you resolve the issue, find and alternative, or another supplier.

Hi,

The issue with an amp being ruined by driving too a
powerful speaker has been nagging me some time. How
could it get ruined? The ohms are the same 8 ohms so the
same power will be drawn through the speaker whether it
has a low power rating or a high power rating. Right??
WRONG!! I also could not understand that concept until
someone partly explained it too me.

Here is the best explanation which I can give:
A speaker designed for more power has to push more air,
the cone must be stronger. The coils are definitely
heavier. All this makes for much more mass. All this
mass has too be vibrated back and forth at incredible
speed (although you can't see it move much at higher
frequencies.) In order for the cone and coil to vibrate,
its inertia has too be overcome. Now, let’s say you are
putting in 300 watts to a 300 watt rated speaker, the
moving mass is RELATIVELY small and takes a certain
percentage of the input power too overcome its inertia.
The rest of the power is given out as sound energy into
the surrounding air. So lets say that our lightweight
300 Watt coil is consuming 50 Watts and the remaining
250 are being put out as sound. If you take the same
scenario but with a speaker rated at 1000 watt, say 150
watts will be consumed by vibrating the speaker and only
150 watts will be put out as sound. The result is of
course a much lower sound level. Ahhh, so Mr. DJ goes
and cranks up the amp to get the proper sound volume.
Guess what, the amp is now putting out say, 500 watts.
That's it: to get the same audio volume into the air,
the higher power rated speaker must draw more power from
the amp WITHOUT YOU REALIZING IT.

I am not a sound engineer, but I believe that the above
is true. It just makes so much sense. What do others think?

There have been some valid points made here.

Certainly, one wouldn't want to use an amplifier to drive a speaker whose impedance was significantly below the amp manufacturer's spec; not only might the amp be damaged from over-current, but the amp's damping is reduced as well, possibly leading to "loose" bass and perhaps excessive voice coil excursion causing speaker damage.

Nor should an amp be driven into clipping, as the harmonic content of the "squared off" waveforms will often overheat voice coils, especially in high-frequency drivers (tweeters).

However, one of the most important aspects of choosing an amp/speaker combination hasn't been mentioned yet, and that's speaker efficiency, or sensitivity. Two speakers having identical impedance characteristics, and even cone size, can vary considerably in what their SPL (Sound Pressure Level) output is. I won't go into how SPL is determined ("Google" it if you'd like). What's important to understand is how it affects your choice. Let's assume two speakers of the same impedance and using the same method of determining SPL have ratings of 88dB and 91dB. That may seem like a small difference; the less-sensitive (some would say less "efficient") one (88dB) is "only" 3dB lower. But the 3dB needed to get the same sound level from the 88dB SPL speaker requires twice as much power as the 91dB model. A 6dB difference in SPL translates to a 4-times drive-power requirement difference.

There's more to matching amp/speaker/venue than impedance and watts.

Jim, QuietDIN,
Thanks for adding your information.
I have multiple situations, now and in the very near future, where the more knowledge on this subject that I have will help me to make some better decisions.


[This message has been edited by MrEd (edited 04-03-2006).]