Matching amps and speakers

[Sk8boi]

I am looking at a pair of Yamaha s115 speakers (http://www.mwsound.com/commerce/ItemView.cfm?INV_ID=1017), and a yamaha mg166fx mixer. I have been told that a QSC RMX 850 or 1450 (http://www.qscaudio.com/products/amps/rmx/rmx.htm) would be a good choice for an amp for this setup.

Can someone explain optimal power output vs speaker watts, and etc? Do I simply want to match a 500 watt amp to a 500 watt speaker? Why not?

Do tell.

Thanks!

 

[Derek Verner]

What needs to be matched is output impedance of amp to speaker impedance, Amps may have different connections for various output impedances (4. 8. 16 ohms). The speaker should also be capable of handling the power (watts) of the amp. It is unlikely you will ever operate most amps or speakers at their maximum power handling capabilities.

 

[Sk8boi]

Okay, assuming that the speakers are 500W @ 8ohms, would you want an amplifier that is capable of outputting 500W at 8ohms, or would you rather choose a different output (over or under driven)?

 

[Garry Sharp]

Nothing in music is ever simple...

First point is that the Yammies are rated at 500W Peak power - not continuous or RMS. RMS (Root Mean Squared) represents an average level of signal over a period of time, and hence will be lower than the occasional peak, and therefore speaker RMS ratings will be lower (typically a half to 2/3) of the peak rating. So if you put a continuous, heavily compressed or limited 500W into one of those speakers you would turn it into a flower pot.

On the other hand, you can run into trouble running an amp at its full rated power - different people have different and forceful views on this, but in essence an amp running at max is liable to clip, which sends a highly damaging signal to the speaker, again adding to your flowerpot collection.

So the answer is to buy an amp which is at least up to the maximum RMS handling of the speakers (with those Yammie probably 350 Watts per side, 700 total, at 8 Ohms) or greater, and listen carefully for any signs of speaker distortion as the volume goes up.

Some bass players regularly run power amps rated much higher than the cabs, which gives them a clean signal and pushes the speakers up to the volume level where they operate best.

Hopefully some more erudite posts will follow this.

 

[Derek Verner]

It was not clear from the original post whether the system in question was to be used for a live performance or for recording monitors. If for monitors, you need far less power handling capability for both amp and speaker.