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Author Topic: Better to overpower or underpower speakers?  (Read 21276 times)

Jeff Hague

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Re: Better to overpower or underpower speakers?
« Reply #70 on: June 16, 2009, 10:56:58 PM »

Stephen Dranger wrote on Tue, 16 June 2009 13:09



How does one figure out how far they can push their speakers if you're giving them 2x their RMS rating?


That is determined by properly setting the gain structure through the system as a whole. There are many posts here and elsewhere on how to do that so I wont go into it but the idea is to set everything up such that, if you clip the output of the console, you also clip the input of whatever devices follow that and you clip your amps at the same time - every device clips at the same level. When the system is set that way you wont send an organ sound to the amp that will cause a problem unless you clip the output of the console. Keep in mind that just because the amp can send 1.5 to 2X the RMS rating of the speaker , generally its really nowhere near that (unless you just don't have enough "rig for the gig" to begin with). In fact, it probably isn't sending even 1/8 of that most of the time. Even with an organ / synth patch, its still music after all and it is generally very dynamic. Thats 1 of the reasons that you want all that extra power to begin with - the dynamics. It needs to get really friggin loud for a split second every now and then but most of the time it wont be "sending" anywhere near that amount of power to the speakers. The term "RMS" is the key here and it can be a difficult concept to grasp in these terms. It is roughly equivalent to "average" and amps have an RMS rating and so do speakers but they don't necessarily mean the same thing. An amp that can produce 500 watts RMS typically wont do that. It can, but typically (when the band is playing) it may only really produce 100 watts. A speaker may be rated at 500 watts RMS and that means that you could send a 500 watt sine wave to it all day long and the voice coil wont heat up to the point that it melts. Again, typically that wont happen. The reason you want an amp that can do 2X the RMS rating of the speaker is so that the music can have the dynamics that make it sound good - if you do actually send 1000 watts to the 500 watt speaker, it is only for a split second - not enough time to overheat and melt the voice coil but enough time for the peak to make the music sound natural. Clipping an amplifier generally makes it output behave more like a sine wave (in simple terms) such that you will be sending far more "average" power to the speaker and will heat the voice coil up much faster - not good. Unfortunately, compressing your mix can be similar - it increases the average power sent to the speakers (and limits the dynamic range) so it can also lead to voice coil failure. That is why most folks here suggest that you never compress the overall mix, use limiters if you can and if you have the capability, use RMS limiters whenever possible but always use amps that can deliver 1.5X to 2X the RMS rating of your loudspeakers. The problem is that far too often, even when these suggestions are observed, there just simply aren't enough speakers to handle the gig - that causes clipping and speaker failure...

Edit:
Quote:

that causes clipping and speaker failure...



Thats not really what I menat to say... What I meant to say is that not enough rig for the gig causes the Operator to run the system to its limits in an effort to get "enough" sound and that causes voice coils to heat up and fail...
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