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Question on answers for underpowering cabinet thread

Discussion in 'Amps [BG]' started by fxopx264, Jan 8, 2013.

  1. fxopx264

    fxopx264

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    After reading through the stickies, I still have a question on underpowering cabs

    So apparently the deal with underpowering cabs is if you turn the volume up to a certain state, the amp will start clipping. The clipping causes the cab to output a power much higher than it is designed for, causing it to overheat and later lead to failure

    However, how does a matched amp and cab set avoid this problem?:confused:
    Say I have a 300W amp with a 300W cab, if I crank the volume up, wouldn't that still result in clipping and potentially destroying the cab?
    :confused:
  2. hdracer

    hdracer Supporting Member

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    Yes,
    clipping is clipping
  3. fxopx264

    fxopx264

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    Ah, so the matched power in the amp and cab does not solve the problem...?
    So no matter what clipping can easily result in a higher power output and should be avoided?

    Thanks for the quick reply btw
  4. Rune Bivrin

    Rune Bivrin Supporting Member

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    A completely clipped signal will result in twice the average power being output compared to a clean signal. However, that sounds like s**t, so you'll not want that. A slightly clipped signal will result in slightly more power than a clean signal.

    Nothing magical going on. More speakers per watt of amp power is safer, it's a simple as that. And as a rule, speakers are rated in a way that makes it not very relevant for bass players (thermal vs. excursion limited) so a wide margin is a good thing.
  5. Bassmec

    Bassmec

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    The point here is to differentiate between what happens with the passive crossover and tweeter if fitted and what happens to the woofer.
    The woofer has no preference for clipped distorted or clean it will handle
    whatever it says it will handle in terms of watts thermally.
    Yes amplifiers do produce more power than their clean rated power if overdriven.
    Tweeters may blow with distorted signals as they will see an unusual increased signal level from clipping or distortion because the crossover mistakes the squaring of the wave form as a set of harmonics at a much higher frequency.
    Loudspeaker ratings are to do with the power it takes to melt the voice coil, and are next to useless as what we bass players really want to know is how much power they can they take still operating within Xmax.
    This is usually about half the rated thermal power handling.:bassist:
  6. bassgod0dmw

    bassgod0dmw Supporting Member

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    Yes and yes

    To further confuse you...

    Amps generally have (generally!) a correct wattage rating. Or close enough. 500w usually means it can put out 500w.

    Cabs on the other hand, are all over the map. There is no standard to follow, so ratings are just what the manufacturer wants to say. A cab rated for 500w realistically may only be able to take half that.

    There are certainly exceptions to both of these.
  7. 1958Bassman

    1958Bassman

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    Power handling specs are for clean, undistorted power. Speakers aren't usually tested with sine wave, it's pink noise, over a specific time period that used to be 8 hours. If it handles this, it will usually last a long time as long as it's not subjected to signals it was never designed for.

    This link may help-
    http://www.jblpro.com/catalog/support/faqgeneralaudio.aspx

    "Under-powering" isn't just a matter of sending low power to a speaker, as some of the other threads debated, it's using a speaker rated for higher power than the amp and the amp is run WOT for extended periods in an attempt to get more from it than it can produce well and as intended in it's original design.
  8. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member

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    There's no such thing as "underpowering" a loudspeaker.

    There is such a thing as not having enough power for what you're trying to do with that loudspeaker, and the end result would be clipping--i.e., the tips of the waveform are clipped off, or flat-topped. When an amp clips, the power it's putting out exceeds its stated power rating, which would've been measured with a steady sine wave signal right at the threshold of clipping. This is important to understand.

    A small amount of occasional clipping is usually not even audible. A large amount of clipping will tend to sound harsh and objectionable.

    Clipping is, by itself, not harmful to loudspeakers. Too much power is, whether it's clean or clipped. Clipping generates higher harmonics, but that doesn't really threaten HF drivers unless the frequency of the fundamental is fairly high, like less than an octave below the crossover frequency or above, or if the HF driver's power rating is really low.
  9. Jerrold Tiers

    Jerrold Tiers

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    Sure there is.............

    Some speakers seem to need a certain amount of input to "open up"...... which may mean in reality "to get the THD up to where they sound good"......

    Whichever......... if you don't supply enough power they just sound dull and dry.
  10. Mr. Foxen

    Mr. Foxen

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    That is just bad sounding speakers.
  11. AdamR

    AdamR Supporting Member

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    Thats not harmful to the speakers though. Theres a difference between working a speaker and blowing it out of the cabinet. Even a 100 watt amp will have enough power to work just about any cabinet.
  12. Bassmec

    Bassmec

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    I also don't need to use loudspeakers as audio compressors, I find they are nothing like as good at it, as tubes, power supplies and big output transformers.:bassist:
  13. Jerrold Tiers

    Jerrold Tiers

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    Curiously, most of the speakers that act like that need the power not to "compress", but rather to "stop compressing".....

    So it looks like you are off on the wrong track there.....

    Generally, they seem very constrained/compresssed/ until driven with enough power..... which is usually in the 150 to 300W area at most......

    But the flip side of the point is that the things don't sound very good until they are hit with a fair amount of power...... i.e. thay CAN be "underpowered"

    Yep, different from what most people think of.... and not a huge point, but there is is.....

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