What does -3dB mean on my new subwoofer

Discussion in 'Home Cinema Speakers' started by 89JT, Mar 3, 2013.

  1. 89JT

    89JT
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    Hi, I've just got a new subwoofer, and in the technical specification it says this:

    "28Hz – 150Hz (–3dB)
    24Hz – 180Hz (–6dB)"

    Would anyone care to explain what the -3dB and -6dB refer to?

    I'm sure it won't affect how I set up my system, i'm just interested to know what it means! Thanks
     
  2. PSM1

    PSM1
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    The 3 and 6dB means that it will go to 28 or 24Hz but that at that frequency there is a drop off of 3dB and 6dB respectively. so you sub will go down to 24Hz but it will be 6dB quieter than a higher frequency (assuming a level response higher up. So if you set your sub up to give 75dB from the listening position then if you played a tone of 24Hz (assuming no room interactions etc.) then this in theory would read 69dB from the listening position. Anything much above -6dB is really dropping too much to be particularly useful in terms of range (although some manufacturers will quote -9dB or more to try to make their speakers/system look better than they really are.
     
  3. Soundmangt4

    Soundmangt4
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    Also, just for reference -6db is half the volume.
     
  4. 89JT

    89JT
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    Thanks for the extremely helpful responses. Does that mean my speaker will in fact produce much lower frequencies, but they will just be inaudible?
     
  5. PSM1

    PSM1
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    You are correct.
     
  6. BlueWizard

    BlueWizard
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    -3dB is essentially Flat Frequency response. -3dB is just the slightest noticeable change in volume. -6dB is a slightly more noticeable change in volume but still represent the proper working range of speaker.

    -6dB is NOT half the volume. It is two slightly noticeable changes down ward in the volume. I think something like -10dB is half the actual measurable volume.

    However, -3dB is HALF the Power. Which means every time you make a slight but noticeable change in the volume, the average power either doubles or drops in half. Power and volume are not linear; huge changes in power equal small changed in volume. At typical casual volume levels, you are not even using 1 watt of AVERAGE Power, So, it takes a lot of small 3dB increases in volume to ramp the average power up to something substantial.

    More Power does not really give you more volume, it gives you more headroom. As pointed out, if you double the power, you only get a slight +3dB increase in volume. The average power may be cruising along at a watt or two, but peak levels are jumping up near the limits of the amp. The more power you have, the higher that peak limit is. Though there are other aspects of power that are also of value.

    For what it's worth.

    Steve/bluewizard
     
  7. Alan Mac

    Alan Mac
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    1 dB is usually considered to be the smallest noticeable change in loudness, though I can hear 0.5 dB increments without too much difficulty. Certainly 3 dB is a very noticeable change.


    A change of -6 dB corresponds to a halving of the sound pressure. Sound pressure is measured in newtons per square metre, aka pascals.

    The sound pressure is proportional to the amplifier output voltage.


    A change of -3 dB corresponds to a halving of the sound intensity. Sound intensity is measured in watts per square metre.

    The sound intensity is proportional to the amplifier output power.



    Sound pressure and sound intensity are physical quantities.

    The subjective measure of sound “volume” is Loudness.

    A change of -10 dB

    (corresponding to 0.3162 times the sound pressure or 0.1 times the sound intensity)

    is generally considered to correspond to a halving of the Loudness.



    Alan
     

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