Wattage Question

Discussion in 'AV Receivers' started by BryanMM, Jul 10, 2004.

  1. BryanMM

    BryanMM Extra

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    I'm worried that my Yamaha 5740 receiver won't be able to handle the Ascend CBM 170s I'm getting well. Advertisers list it as 100w a channel but the manual I got with it says 85w a channel. The speakers are 200watts.

    I've never understood this wattage thing, will having less than the speakers are rated for be bad? How does it affect everything? And is my receiver bad and in need of a replacement?
     
  2. John Garcia

    John Garcia Executive Producer

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    The speaker rating is a MAXIMUM input before the x-over or drivers give up, not a recommended power level. You basically don't need to worry about this rating. Even with a 200wpc or greater amp, these speakers will be fine - you are not using all of that power most of the time, especially at average listening levels. Though less power can be dangerous (clipping), I don't think you will have a problem since these speakers will want to be crossed over and used with a sub, allowing slightly better usage of power on the receiver's side.

    If you are really concerned, try out the ascend forum.
     
  3. Jack Briggs

    Jack Briggs Executive Producer

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    Bryan, most of the time you're listening to a fraction of a single watt in real-world conditions. The power rating that actually means anything would be whatever the receiver puts into an 8-ohm load across the entire 20 Hz-20 kHz range with all channels driven. As John notes, a speaker system's power-handling capacity rating simply means the speaker can handle peak loads at 200 watts without frying the voice coils. Very, very few power amps put out 200 watts.

    Also, as John notes, it can be more dangerous to underdrive a speaker with an amp going into clipping at peaks.

    You're okay.
     
  4. Phil Iturralde

    Phil Iturralde Screenwriter

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    When evaluating SPL in your room between the speaker and AV Receiver, the easiest way to get a snap-shot of how loud in can get, in SPL @ your 'sweet spot', ... is to use this quick Watts vs. SPL chart.

    It's based on your speakers Sensitivity Rating.

    Your CBM-170 Sensitivity rating is 89 dB @ 1w / 1 m. So, in other words, it takes 1 watt to generate 89 dB SPL @ 1 meter or approx. 3.28 feet from the speaker.

    Here's the basic RULES:

    1. SPL = To HEAR an Audible Increase in loudness, the SPL source must increase by 3 dB min.

    2. Watts = To Increase SPL by 3 dB would require Doubling the power output (Watts x 2 )

    Watt(s)..SPL(dB)
    1w............89 (CBM-170s rating)
    2w............92
    4w............95
    8w............98
    16w..........101
    32w.........104 (Dolby Digital Home Theater SPL Levels)
    64w.........107
    128w.......110
    256w.......113

    So a quick snap-shot shows that an honestly rated 64w x5 / x6 will rattle your windows and can disturb your neighbors.

    For a more accurate SPL @ your 'sweet-spot', use the excellent SPL CALCULATOR tool by C.M.Collins. This calculator will compute the predicted maximum sound pressure level (loudness) at the listening position.

    Phil
     
  5. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    Phil's table doesn't take into account distance (sensitivities are rated at 1 meter). Farther than 1m awayt the SPL will drop. Also, room gain is not taken into consideration which will usually increase the SPL, atleast over certain frequency ranges. That said, it does give a good overall description of how power affects spl and how you are RARELY using the amount of power you have.
     

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