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  • Matching Power amp to Speakers

    OK , correct me if I'm wrong or confirm if I'm right please , I always thought if you have a sub that is rated to handle 500w rms that you try and match that with the power rated output (rms ) of the power amp with maybe a bit more from the power amp for headroom , I know that underpowering speakers will not blow them . Am I thinking right ?

    Thanks 


  • #2

    When using unpowered speakers + amps.... I usually want an amp that has about 25-33% more maximum wattage over the speakers "continuous" wattage rating.

    So in your case,  a 500w speaker,  I'll go for an amp that can supply ~600-700w.

    Underpowering will only cause issues if you clip or peak the signal going into the amp.

    ​Boston Common Band - Boston Wedding Bands
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    • #3

      djrnno wrote:

      OK , correct me if I'm wrong or confirm if I'm right please , I always thought if you have a sub that is rated to handle 500w rms that you try and match that with the power rated output (rms ) of the power amp with maybe a bit more from the power amp for headroom , I know that underpowering speakers will not blow them . Am I thinking right ?

      Thanks 


      Yes, you are thinking correctly. If you look at how the manufacturers of powered speakers power their own products, most fall into this catagory even though the marketing may lead you to incorrectly believe otherwise.

      You COULD provide substantially more than the continuous power BUT if you have an accident, or momentary lapse of good judgement, you will have considerably less margin for error and that can be a costly lesson to learn.

      -------------------------------------------------------------------------------------------------------------------------------------------------------------------
      Former product development engineer: Genz Benz, a KMC Music/Fender Musical Instruments Company, continuing factory level product support and service for Genz Benz

      Currently product development engineer: Mesa Boogie

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      • #4

        So first here's a paper I did years ago.  Please read it so I don't have to type it all again ...  http://www.peavey.com/support/technotes/poweramps/HOW_MUCH_POWER.pdf

         

        Now let's ask this question, are you asking about the best possible sound quality or the safest power level?  It makes a big difference although I can say there is no "safe" power level except off.

        The best possible quality sound would be to use an amp that can cleanly supply the rated peak power handling power of the speaker.  The peak power rating of a speaker usually does not specify a time limit or how long you can supply that peak power but  it is an intregal part of the noise used for the "continuous" test.  Now this test usually involves a 2 hour or an 8 hour rating so it's reasonable to assume that they are not talking about one single peak that would burn out your speaker.  It depends on a bunch of things but when I've measured the number of peaks in pink noise it averages somewhere between 50 and 200 of them in every second of the signal.  So when you run a speaker up to max you are sending it both the continuous average power and the max peak power at the same time.

        As far as the continuous power rating of a speaker ... it's measured in hours but most power amps can only deliver their continuous rated power for a second or two.  So it makes no sense that the continuous power from an amp rated somewhere near the power rating of a speaker could ever cause damage (we're talking thermal damage, not mechanical damage).

        How much power can your 1000W amp actually deliver?  Well assuming you have the available voltage and current (and you likely don't unless you are using a professional distro ... that's another story too) typically you are pushing about 100W of continuous power at the same time as your limit lights begin to fire.  So even if they fire a lot you are still only pushing out that power for fractions of a second if you are running typical live music through your system (I know, there is no typical music).  Most commercial pop stuff released these days probably still has about 8 dB of dynamic range so that would be 160W.  Remember though whether it's 100 or 160W it IS delivering the full peak power of the amp which is probably 2000W but again thats basically only happening for the fractions of a second that the limit lights are on.

        Just to be fair, when it comes to subs you would likely be somewhere around 300W with occasional 500W short bursts (remember the definition of continuous is speaker power handling is 2-8 solid, always on, never off power)

        So if you hook up a 1000W speaker to a 1000W amp you could be hitting it with 2000W peaks and somewhere south of 200W of continuous power.  Of course a 1000W speaker typically has a 4000W peak rating.  Are you scared yet?

        I remember a test we did back in Mississippi where we took a 500W speaker, set it outdoors, powered it up with a 2500W amp, turned the built-in limiters off and cranked up the CD player until there was pretty audible distortion.  It ran non-stop for almost 2 hours (til the cops shut us down).  Yea, they bust manufacturers too.  We broke down the box and measured the speakers. And all the components still met their specs for frequency response, distortion and power handling.  So you tell me.

         

        So if you stopped reading right now you might think I'm a proponent of really big amps.  Well I am ... BUT ... having them and using them to the max are not the same thing.  Speakers will likely put out 95% of their possible level when you hit them with half their rated power.  So I use big amps but I take all kinds of precautions to not deliver any more power to the box than I deem safe, necessary and sounding great.  Once you get past a point and the speaker starts sounding bad, who cares how much more power it can take before the smoke leaks out.

         

        My very best suggestion is just use self powered speaker systems if your system is less than a dozen speakers for mains.  Let the factory engineers worry about it and then you can go make some great music.

        Don Boomer

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