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Someone Please Explain Response & Range

Discussion in 'Home Cinema Speakers' started by cjob68, Mar 9, 2003.

  1. cjob68

    cjob68
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    Hi,
    I am looking at the specs for the B&W ASW600 and it shows the following:

    Freq. Response -3dB 26Hz – 33/150Hz adjustable (EQ at A)
    Freq. Range -6dB 22Hz – 40/180Hz adjustable (EQ at A)

    The part I am unsure about is the following:

    What's the difference between the response and the range ?
    What do they mean by -3db or -6db ?

    If a subwoofer's specs don't show -3db in the response what does that mean ?

    Thanks
    cjob68
     
  2. MikeK

    MikeK
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    Response and range have no "official" meaning really - although it's generally accepted that response means within +/- 3dB limits.
    Not it seems to some marketing departments though - where response means whatever looks best on paper. Some companies quote subwoofer response at -10dB for instance (or worse) - and some then conveniently omit this in the blurb.

    Range has a much looser definition IMO.
    To B&W it looks like it's the response but to a 6dB limit instead of 3dB.
    To others it can mean the range over which a driver/loudspeaker will produce any usable output - hence a subwoofer may have a response of -3dB at 36Hz while it may have a "range" of say 24Hz at -10dB. It's easier to sell a sub if you quote 24Hz.

    The other spec trick is of course to quote "typical in room response" - where room gain has boosted the low-end output when compared to a similar meaurement taken anechoically.

    This is why you can get two subwoofers with seemingly identical spec sheets, but very different real world performance.
    Hence the often touted advice that it's very difficult to choose just by going off paper specs.
     
  3. Marshan Man

    Marshan Man
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    mesa still :confused:
     
  4. cjob68

    cjob68
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    Hi,
    I'm still not sure what youy mean by -3dB at 36Hz while it may have a "range" of say 24Hz at -10dB.
    What does it mean to be "-3db" ?

    Thanks
     
  5. EvilMudge

    EvilMudge
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    Half the actual volume. If something is 3dB down at 36Hz, then if you play a 36Hz Tone and a 50Hz tone (both at the same volume) through it, the 36Hz output will be half the volume of the 50Hz output.
    6dB down is a quarter volume. 9dB is an eighth. 12dB is a sixteenth.
     
  6. MikeK

    MikeK
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    Put simply, the -3dB point (F3) is the frequency at which the ouput power has fallen to half, for the same input signal.
    The -10dB point (F10) is the frequency at which the output power has fallen to one tenth of the original, for the same input.
    As we don't hear in a linear fashion, the -10dB point is also the point at which the average human would perceive the sound to be half as loud.
    Hence, because of our ears it takes 10x the power to create a sound which we perceive to be twice as loud, and 100x the power to be 4x as loud, and 1000x the power to be 8x as loud, and so on.
     
  7. Marshan Man

    Marshan Man
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    just a side point.. why is it always '-'xDb ? ie... why is the DBina negative form... ? tho cheers MikeK for clearing up the other bit
     
  8. Steve.EX

    Steve.EX
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    0db (often refered to as "reference") is the input signal, (say from a cd player) with no attenuation applied.
    This is then the maximum output the amplifier will achieve from a given signal (i.e line level)
    In the case of speaker respnse the ideal would be a totally flat response across the entire audio bandwidth (typically 20hz-low through to 20khz-very high).
    Subs are often quoted with a +/-db range, this simply "indicates"
    that if a subwoofer extends down to 20hz @-3db then if you were to measure the subwoofers output at 50hz and then at 20hz the output would be 3db less (quieter) than the former.
    0db represents in this instance "the norm"
    3db is a figure/term that is commonly used simply because in audio terms it represents a doubling or halfing (50%) dependant on whether it is +?db or -?db
    Another example would be if you had an AV amp with 5 speakers connected for ease of explanation lets assume that it is a commoner garden AV amp and that when you test the output (spl-sound pressure level) of the center speaker in relation to the other speakers so they are all identical. the setting on the amp for the center speaker is 0db. (to obtain an SPL of 75db from the speaker itself).
    If you were to add a second identical center speaker and connect it in series to the first center speaker so that the amp is effectively "seeing" twice the load (or impeadnce) now on the center channel you would have to raise the amplifier setting for the center channel by 3db to obtain an spl reading of 75db from the center speaker itself (that you originally got when only using one speaker)

    Steve
     
  9. MikeK

    MikeK
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    Just because they are quoting the low frequency performance.

    If you say that in an anechoic chamber, the response of a subwoofer is -3dB at say 36Hz, it means that's the frequency at which the response begins to tail off.

    Many other factors come into play here though - it's really taking a bit of a flier to attempt to judge a subwoofer's subjective performance from just reading this figure.

    These factors include how the measurement was taken - if it wasn't taken in the same way, then two (or more) such "specs" cannot be compared directly.
    What type of subwoofer is it - for instance a ported design with an 8" driver may read -3dB at 36Hz, just as a sealed design with a 12" driver may have the same spec.
    Trust me, with all things being equal (which, fair enough, they often aren't), the two units are very unlikely to sound the same in real life!!!


    If we are talking purely subwoofers - take claims of true 16Hz reproduction with an 8" driver, 100W amp and a 10"x10"x10" box, with a pinch of salt - it simply wont do it. I wish it would, but the laws of physics dictate otherwise, whatever some marketing dept might claim.
    Put simply, while there is a fair bit of room for manoevre, generally speaking, very low bass requires a good quality, purpose designed large driver in a large box with a powerful amp.
    That's not to say that anything not fitting this description is crap though - I'm just saying that performance expectations have to be realistic.
     
  10. Marshan Man

    Marshan Man
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    cheers guys... clears it up alot thanks:smashin:
     

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