Underpowered speakers

Discussion in 'GENERAL AV Discussions' started by jdub15, Mar 23, 2009.

  1. jdub15 Audiophyte

    jdub15
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    What is the harm of underpowered speakers? For instance, would it be bad to have only 130 watts going to a speaker rated for 50-500? What would the speaker performance be related to a lower speaker rated for 20-250 getting the same power? Looking at the Polk RTi A9 versus the RTi A7.
  2. lsiberian Audioholic Overlord

    lsiberian
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    For every time you double the wattage you increase the db by 3. Which is the first time you notice it in non-critical listening.

    500 watts is probably the point at which the driver excursion reaches it Wmax. However many drivers distort badly at about 1/3rd of wmax. This varies but 130 would be plenty of power for a Polk RTi IMO. I don't suggest ever feeding it 500 or 250 watts respectively. You will probably not like the sound.

    If your concerned about power the RTi 9s then I suggest you pick up a Behringer Ep2500 do the fan mod and use that to drive the speakers.

    you will need some kind of pre-amp, but you would have plenty of good clean power.
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  3. skers_54 Full Audioholic

    skers_54
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    Just for clairification, the property is xmax, not wmax :).

    Think of an amp as a car engine. Cruising around town doesn't require much power. But accelerating to reach highway speed will require much more, as well as show if your car is underpowered.

    The issue with underpowering speakers is that they can be damaged when an amp is driven into clipping. This will occur when trying to achieve higher and higher sound levels. At moderate levels, speakers will essentially sound the same if the amps are operating within thier limits. If you have a large room or inefficient speakers, more power will be required to reach the same spl. This increases the demands on the amp and makes clipping more likely.

    Most of the time, only a couple watts will be used (continuously). In your case, there probably won't be a noticible difference between 130 watts and 500 watts as you will not be using the reserve power (except on dynamic peaks). Many speaker power ratings are also misleading, as a speaker can fail in several different ways.

    Basically, it will be fine to use a lower power amp as long as you're responsible with the volume control. Just turn it down if you hear distortion. More power will give you better dynamics and more reserve, which are both good things.
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  4. jdub15 Audiophyte

    jdub15
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    This is what I am kicking around in my head....Denon AVR-3808CI with the Polk RTi A9 or A7, CSi A6, FXi A6, and a sub. Is this a good system? Any recommendations? Looking to stay around $5K. Totally new to the audio world.
  5. mtrycrafts Audioholic Slumlord

    mtrycrafts
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    Right:D wmax is one of our fine contributors here:D
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  6. speakerman39 Audioholic Spartan

    speakerman39
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    Fine contributors? I would say a term like genius would be more fitting. ;);)
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  7. no. 5 Audioholic Field Marshall

    no. 5
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    There is none. Speakers are only damaged by too much power, ether by exceeding the mechanical or thermal limits of the speaker.

    500 watts would put a lot of consumer loudspeakers past both the maximum linear excursion (Xmax) and the mechanical excursion limit (Xlim), I could be wrong, but I think Polk is being optimistic in saying that that speaker can handle 500 watts.
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  8. mulester7 Audioholic Samurai

    mulester7
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    .....example....a pair of speakers are rated 150 watts-rms continuous....they are being pushed by a receiver rated 2 X 50 watts-rms-continuous, and the amp-sections clip at 67 watts asked....clipping the amp-sections in such a manner sends maximum-distortion to the voice-coils, many times frying them....I see Mtry is still alive and well :D.....

    .....Samurai my butt.....
    Last edited: Mar 25, 2009
  9. annunaki Moderator

    annunaki
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    Welcome back fine sir. :)

    Distortion is not what causes driver failure in and of itself. It is the increased power level and lack of linearity caused by distortion which can result in thermal or mechanical failure.

    Full on amplifier clipping is typically double the output of the .1% thd output rating of the amplifier.

    Example: If an amplifier will do 70 watts rms at .1% thd it will do around 140 watts when fully clipped. This easily exceeds the thermal limit and mechanical limit for most 100 watt rms rated speakers.

    Let's say that this amplifier partially clips and is still doing 120 watts regularly. Thermal failure will set in albeit not as quickly. Mechanical failure is still a high probability.

    Thermal failure is too much heat built up over time.
    Last edited: Mar 25, 2009
  10. mulester7 Audioholic Samurai

    mulester7
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    .....thanks, Moderator Annunaki....the soup kitchen shut down :eek:.....
  11. lsiberian Audioholic Overlord

    lsiberian
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    Heheh but I thought since he's such a great contributor that we could rename the parameter. What it's named is really a matter of semantics:)
  12. skers_54 Full Audioholic

    skers_54
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    Agreed. Maybe we could rename cabinet resonance or invent a parameter to measure subwoofer integration after him. Since he knows more about those two areas that pretty much everyone.
  13. mtrycrafts Audioholic Slumlord

    mtrycrafts
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    I didn't want him to perish due to a swollen head:D
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  14. mtrycrafts Audioholic Slumlord

    mtrycrafts
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    Still here, yes:D I guess if the kitchen shut down, no more hungry folks out there;):D
  15. speakerman39 Audioholic Spartan

    speakerman39
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    LOL, too funny. :p:D:p But, you do have a point. :eek::eek:

    Cheers,

    Phil
  16. mulester7 Audioholic Samurai

    mulester7
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    .....hey, MtryCrafts, you are doing fine, I see....Guys, Mtry told me a couple of years ago subs hum when they don't know the words....yes, others will verify this....just kidding, I actually accused him of saying it....MtryCrafts is sharp for sure.....

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