100 watts enough for this size room?

Discussion in 'Archived Threads 2001-2004' started by Greg Warner, Nov 1, 2001.

  1. Greg Warner

    Greg Warner Auditioning

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    Hello,
    I plan on purchasing B&W dm303's all the way arround for my home theater as
    I have been reading nothing but good reviews (plus they fit my budget on an
    almost to good to be true level). These speakers are rated at 100 watts.
    Would 100 watts suffice for a room with the dimensions of 19 x 11 and a
    ceiling height of 7'? I will also be using a psb subsonic II to handle the
    base and set the speakers to small. Is there any formula, so to
    speak, for room size to power?
    Thanks
    Greg
     
  2. Brian Corr

    Brian Corr Supporting Actor

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    I take it you mean a receiver with a 100watt rating??
    If so, it should be fine.
    Do realize that a denon rated at 100 watts will sound different than a sony rated at 100 watts and a separate amp rated at 100 watts will sound different. Partly because at normal volumes, you are not listening with 100 watts (RMS vs. peak) and some amp sections will do a better job than others. Also, one brand's claim of 100 watts may be more wishful thinking than actual output. It's all relative though.
    Even a decent 65 watt amp can do the job. Of course, nobody ever cries about having too much power!
     
  3. Dustin B

    Dustin B Producer

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    Also remember sound pressure is not a linear beast, it's logarithmic. As a result power has to increase in a logarithmic way as well. One very important spec is the sensitivity of the speaker. The dm303 is rated at 88dB with 1 watt of power applied measured 1 meter from the speaker. Now to get a 3dB increase, you need to double the power input. So 91dB takes 2 watts, 94dB takes 4 watts, 97dB takes 8watts, 100dB takes 16watts etc. As you can see when you get up to above 60watts it starts to take huge increases in power to see a 3dB gain in output. 64-128-256-512-1024 etc.
    Now also remember that it takes approximately a 10db increase for your ears to perceive it as twice as loud. And the farther away you are from the speaker the quieter it gets, I don't know the number sequence for how that works, but again a doubling of distance from the speaker will cause such and such a dB drop.
    ------------------
    Dustin
    [email protected]
    My Adire Tempest Sonosub
     
  4. GarryW

    GarryW Stunt Coordinator

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    I use 5 MA-500 Monoblocks rated @125watts/pc with my Paradigms speakers (90+db eff.)rated at 125 -175 watts in a 11 x 19 x 8'room and watch movies from -17 to -12db on my preamp.
    Sometimes I think I've got too much power as at REF level (0db) it's pretty uncomfortable, especially coming from the center channel. My equipment is on the short wall though but I'll be moving stuff to a 15 x 24 x 9 room in a few months. [​IMG]
    Remember the rule: Sound pressure level increases only 3db when you double the watts! [​IMG]
    What kind of equipment are you going to be using with those B&W's? I heard they're harder to drive (
     
  5. Greg Warner

    Greg Warner Auditioning

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    Thanks for all the info. The receiver I am using is a Denon 3300 which I believe is 100 watts per channel. As of now I never go beyond -15 on the volume for a room that is 2/3rds the size of the one I plan on using the B&Ws in. My current set up is also coupled with speakers only rated at 75 watts, and that is plenty loud for me. I just wanted to make sure that I won't get these speakers home and over time ( as I loose my hearing ) realize that to get the volume I want I should have gone higher. Is a 100 watt receiver coupled with 100 watt speakers a good combo or is it better to have speakers that can handle more then your amp is capable of? Does the latter produce a cleaner sound?
    Thanks
    Greg
     
  6. Bob McElfresh

    Bob McElfresh Producer

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    Short answer: 100 watts is pleanty.
    Long Answer: You are NOT trying to use 2 speakers to fill every corner of a room with music like a concert hall/auditorium.
    You ARE putting an array of 5 speakers in a circle around 1 couch/chair to benifit 1/2 people.
    How much energy do you think you need to focus on that 3-foot area of your room? Not nearly as much as trying to fill a room to the corners with only 2 speakers.
    And lets face it. Your center speaker is being driven with sound 100% of the time. Your L/R speakers..about 40-60% (if you are lucky). And the rears.. 10-30%. (Try disconnecting the center and rear speakers and fire up a favorite DVD. You may be suprised at how little sounds come from the L/R speakers.)
    But your receiver is a power-plant rated to produce 100 watts to all 5 speakers continously. This tends to give you un-used capacity. And if you set your speakers to SMALL, the receiver wont even try to send the power-hungry low frequency sounds to the speakers.
    Hope this helps.
     

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