audio-idiot question about speaker wattags vs. amp wattage.

Discussion in 'General Electronics Chat' started by s_mack, Jun 4, 2015.

  1. s_mack

    Thread Starter Member

    Dec 17, 2011
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    I'm sure this is a stupid question, but those are the type I like to ask.

    I have a device that needs a little speaker. My question about wattage is: do I need an amp rated higher than the speaker? Or a speaker rated higher than the amp?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Generally you want a speaker rated higher than the amp to avoid blowing the speaker.
     
  3. cornishlad

    Member

    Jul 31, 2013
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    Generally of course that is spot on. In this case though where the op is saying he needs a Tiny speaker, it may be that the "amp" is so weedy that it could cause no damage and possibly any speaker whose physical size fits in the project would be quite ok.
    In the world of PA the situation may also not so clear cut. Some amps of insane power ratings may be used with lower powered speakers if the final sound level the speaker can safely produce exceeds what is required. In other words the amp is coasting. In that case it's up to the operator to not overdrive the speaker(s) It's usually painfully obvious when distortion sets in !
     
  4. s_mack

    Thread Starter Member

    Dec 17, 2011
    187
    5
    Ok, thanks. I wasn't sure if it worked like electricity in general, where the speaker could be seen like a lightbulb and the amp like the voltage regulator, and it was the lightbulb that determined how much power was used... or if it was the other way round. If I understand you, it is the other way round and the speaker needs to handle what the amp is putting out.

    W.r.t. cornishlad's comment... if everything is under design's control (not user's), then it doesn't really matter because we just make sure we don't output enough to blow the speaker. In that case, does it make sense to "oversize" (in terms of wattage) both? Does straining either/both cause distortion, or just over-loading the speaker?

    FYI - we're just talking about voice, like a GPS sort of. Pre-recorded messages playing at certain events. The user will have digital volume control but, of course, we can constrain that.

    Sorry, I know nothing about audio at all.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    The speaker does look like a resistor, so the power it draws is proportional to the square of the voltage across it, as determined by the sound source and the amp volume setting.

    It's not uncommon to have an audio amp that's rated at a power higher than the speaker.
    Normally that's not a problem since the speaker will start to sound very distorted before it reaches the burn-out point so the user will not go past that when adjusting the volume.

    Both amplifiers and speakers will sound distorted when their respective power limits are reached.

    How loud a sound do you need for these "events".
     
  6. s_mack

    Thread Starter Member

    Dec 17, 2011
    187
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    Not that loud. It is a handheld device that you'd hold similar to, let's say, a geiger counter or r/c airplane controller. The voice needs to be easily heard in an environment that can range from dead-quiet to noise like someone mowing their lawn down the street.
     
  7. Lestraveled

    Well-Known Member

    May 19, 2014
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    The fastest way to destroy a speaker is to apply DC voltage to it. DC can not be converted into movement and will be converted directly into heat instead. This occurs when a too small of an amplifier is used. When an amplifier "clips" it is the same as applying DC to the speaker. It is always better to have an amplifier rated for higher power than the speaker.

    In other words, a sine wave that exceeds the speaker power rating, is less damaging then a square wave within the power capability of a speaker.
     
  8. s_mack

    Thread Starter Member

    Dec 17, 2011
    187
    5
    OK, I now have to exact opposite recommendations :)
     
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