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Other Stuff Thread, Pa system in Fun Stuff; Originally Posted by laserblazer I'm not sure I would agree with getting an amp that's rated higher than the speakers. ...
  1. #16


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    Quote Originally Posted by laserblazer View Post
    I'm not sure I would agree with getting an amp that's rated higher than the speakers. The tendency is to turn the volume up to 11.
    Generally that's OK. The real danger is from amplifiers that are underpowered for a speaker.

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    Quote Originally Posted by pcstru View Post
    As I read it, the article says it's not a problem to underpower a speaker but it is a problem to overpower it. Which is how I've always understood it. Anyway, the long and the short is have a decent matched system.

    I suppose it would be ok to have a bigger amp if the speaker cables are fairly long. There's quite a lot of loss on a cable and a higher powered amp would compensate for the loss. Trouble is, someone will then use it with short cables and overdrive the speakers.

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    Sorry, yes it does. The thing with underpowered amps is they are more likely to clip before you hear distortion from the speaker, so when you turn it up to 11, it clips, the power doubles and your speakers very suddenly go bang. With an overpowered amp, you approach the limits of the speakers gradually and you can generally hear them start to distort (they tend to reach the limits of the cones excursion and make a fart like noise). It starts to sound very bad usually long before you actually damage the speaker.
    Last edited by pcstru; 10th October 2012 at 02:51 PM.

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    dhicks's Avatar
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    Quote Originally Posted by pcstru View Post
    The thing with underpowered amps is they are more likely to clip before you hear distortion from the speaker, so when you turn it up to 11, it clips, the power doubles and your speakers very suddenly go bang.
    What do you mean by "clip"? Do you mean that if I have an underpowered amp it might at some point suddenly stop powering one of the two speakers and put all of its power in to the one speaker, damaging it? I currently have our amp turned up as far as it will go, I generally then connect either one or two speakers before switching the whole thing on with the volume on the mixer board turned right down. I've not had a problem up until now, but is there the potential for me to forget to make sure the volume is right down on the mixer one day and blow the speakers? I think we have a properly matched amp and pair of speakers, by the way, so this might not be a problem for us.

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    Clip means that the signal peak is cut off - the output of the amp effectively changes from AC to DC and as a consequence of that, the power increases (twofold is about right). It doesn't put the power from one speaker to another, you can happily blow two speakers at a time :-)!

    When setting up, you should connect up the cables to the power amp before switching it on (inputs and outputs). I personally tend to set up with volume switches turned down. Occasionally I've had components in the chain go awry in peculiar ways and apart from anything else the results can be very horrible and very loud. It's nice to catch them before they cause hearing damage.

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    Andrew_C's Avatar
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    A more powerful amp is correct, but... You do need to set the gain structure correctly, or the speakers are toast. Less likely that with an over-driven, underpowered amp, but possible all the same.

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    Quote Originally Posted by pcstru View Post
    Sorry, yes it does. The thing with underpowered amps is they are more likely to clip before you hear distortion from the speaker, so when you turn it up to 11, it clips, the power doubles and your speakers very suddenly go bang. With an overpowered amp, you approach the limits of the speakers gradually and you can generally hear them start to distort (they tend to reach the limits of the cones excursion and make a fart like noise). It starts to sound very bad usually long before you actually damage the speaker.
    I see what you mean. A sensible person would back off the power when the speakers started to show signs of distress. There's just one problem with that. We don't tend to work with sensible people So, what we need are amps that have a lot of built in protection. I didn't know about the clipping effect. Thanks for that.

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    cpjitservices's Avatar
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    being a Hi-Fi enthusiast I advise to get an amp rated to match the power of the speakers,

    if you under-power your speakers you'll damage the amp as the amp has to work harder to power the speakers possibly even blowing caps if you don't have proper relay protection inside the amp circuitry, you also don't want to over power your speakers as you can blow them if you don't have speaker protection within the amp, some amps will detect what power speakers you have an add cut in protection if the speakers are being over powered if you've cranked the volume.

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    Oaktech's Avatar
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    Quote Originally Posted by laserblazer View Post
    We've got one of these Kustom KPRO100 PA System 100w that we used to use in the hall until the PTA funded a bespoke system. We use the Kustom one for Sports Day etc., but with hindsight I'd get the 200W version.

    The speakers are wedge shaped and by connecting the "line in" to the "line out" of the hall system, they make great stage monitors, laid on their side.
    Please don't do this... it sounds awful and is almost impossible to prevent feedback on.

    Any time you have a PA problem, rub some yamaha on it.

  10. #25

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    Quote Originally Posted by cpjitservices View Post
    being a Hi-Fi enthusiast I advise to get an amp rated to match the power of the speakers,
    You might want to do that in your living room, that is not what we are discussing here. The correct thinking is that the amp should have a rated power higher than the speakers.

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    Blimey, I wouldn't even want to do that in my living room. But "hi-fi" does send people down peculiar paths in the name of alleged improvements in sound.

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    Stand by for a descent into Russ Andrew's "Snake Oil" territory...

  13. #28

    localzuk's Avatar
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    I designed and put in a system here, consisting of a Crown amp, Behringer EQ, Behringer rackmount mixer for 'day to day' use, Denon multi-disc cd/dvd player, and a Yamaha mixer for performance usage. XLR looms all over the place - so things can be plugged in easily.

    The system is split in 2 - the mixer/eq/patch panels are locked in one cabinet, and the rack mixer and cd player are in a second. That way we set the levels on the amp etc... and lock it away. Then the day to day users can't break the speakers or amp.

    We've also just ordered 4 Sennheiser XSW mics in a portable rack flightcase, which we can pull out when needed.

    We followed a similar approach for our lighting. We have a Jester desk for the performance stuff, but day to day, they use a simple, cheapo 6 channel one in drama.

  14. #29

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    Hey localzuk,

    May I ask what speakers you're using with your setup? I've been roped into a meeting later and they want to know estimate costs. (Yeah I found out I was involved in this an hour ago). Our current system uses 4 speakers (old tinny things) and there's no bass what so ever. We're losing out on potential external business because it's not fit for purpose. A dance class was cancelled because it didnt sound good. Could I also be cheeky and ask how much your setup cost (ex fitting) please? The amps, speakers, mic's and mixer.

    Sorry, I'm honestly not being too lazy but it'd give me a good idea what to put forward. We have a hall that sits about 300 people (using chairs) to give you some scale.

    Thank you!!

  15. #30

    localzuk's Avatar
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    They are DAP speakers, 2 x 15 speakers. Can't remember what it cost sorry, something around 2k IIRC. We sit about 300 kids in our school without chairs.

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