Why is more power required for BASS?

Discussion in 'Pro Audio' started by Mark, May 31, 2007.

  1. Mark

    Mark Guest

    Why is more power required for BASS?

    This seems to be a common rule of thumb in PA work, most of the power
    is needed to provide the bass. This seems consistent with my limited
    experience in PA and certainly consistent with my experience listening
    at home.

    But this does not seem consistent with my limited experience mixing.

    When mixing, the bass (drum and guitar typically) are set to a nominal
    level just like anything else and per the meters they do not require
    more power than anything else. If I solo these bass parts, they do
    not move the meters any more than any other parts solo.

    So how do I reconcile these two views?

    I think the answer is the typical smiley face EQ most everyone uses
    when listening to music. Even if not intentional, many amps have a
    "loudness curve" that provides bass boost.

    So my question is: Is this "listeners EQ" the reason for more power
    needed for the bass. If we actually listened to music with a flat EQ
    would more power not be needed for the bass? Or is there a more
    fundamental reason having to do with speakers and acoustics that more
    power is needed for bass?


    Mark, May 31, 2007
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  2. It takes a lot more power to move the air around a 12" speaker than around a
    1.5" tweeter, I guess...

    Meindert Sprang, May 31, 2007
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  3. Maybe the clearest explanation is to say that bass production/reproduction
    moves lots of air. Here are some peak power levels of orchestral
    instruments (Tremaine):

    36" bass drum ~ 24.6 watts
    15" cymbal ~ 9.5 watts
    Snare drum ~ 11.5 watts
    Piano ~ 0.267 watts
    Piccolo ~ 0.084 watts
    French horn ~ 0.053 watts
    Violin ~ 0.025 watts

    The power is not in the mixing, where meters display voltage levels of the
    signals, but in the reproduction. Power relates to the area under the
    waveform. A 1 volt 100 Hz sine wave has a lot more area than a 1 volt 1000
    Hz sine wave. Further, power relates to the square of the voltage.

    Note: It is incorrect to say "Even if not intentional, many amps have a
    Roy W. Rising, May 31, 2007
  4. message
    Perhaps the fact that the top octave of the audio spectrum
    takes as many frequencies as exactly half the entire audio
    spectrum and the lower octave of the audio spectrum takes one
    thousandth of the audio spectrum holds a clue.

    Number of distinct frequencies/Total audible bandwidth
    Top octave 10,000 Hz to 20,000 Hz 10K/20K=.5
    Lower octave 20Hz to 40 Hz ---20/20,000=.001

    How many octaves go to the bass speakers and how many go to
    the mids/tops?

    Deputy Dumbya Dawg, May 31, 2007
  5. Don, you're looking at voltage representations of the signal. Please see
    my other respons to the OP, you're a long way off base when you say "just
    as much power is needed for reproduction in both areas (lower and higher
    Roy W. Rising, May 31, 2007
  6. Mark

    Scott Dorsey Guest

    Because conventional bass speakers are very inefficient. They are generally
    omnidirectional, throwing signal everywhere and not just where you want it.
    They have to move a lot of air.

    If you built a bass horn with the same pattern as your treble horn, it would
    take something in the same ballpark to produce the same amount of signal.
    But it would be the size of the Empire State Building.

    In general, bass devices make severe efficiency and extension compromises
    in order to get reasonable size. Life is like that. If you want to
    reproduce something whose wavelength is huge and you don't want to do it
    with a huge cabinet, you pay in efficiency.
    Scott Dorsey, May 31, 2007
  7. Mark

    GregS Guest

    I was going to say something like that. Another thing is the time. HF's don't usually
    last long like a bass note.

    As a very general statement, tweeters are more efficient than woofers.

    The car audio buffs need about 100 times more power for the bass than the HF.

    GregS, May 31, 2007
  8. Mark

    Arny Krueger Guest

    (1) The power in most music tends to be more concentrated in the bass. This
    is at least partially due to the fact that the ear is far less sensitive in
    the bass range. In order to have well-balanced bass, it must have more

    (2) In order to produce a given amount of sound at lower frequences, a
    speaker has to be either larger or less efficient. The "make it larger"
    approach has practical limits, so efficiency is usually less in the bass
    Arny Krueger, May 31, 2007
  9. Mark

    jwvm Guest

    It might also be noted that humans are not very sensitive to low
    frequencies so bass needs to be louder to be heard. Modern recordings
    of pop music tend to have exaggerated bass also. Relatively little
    bass is heard in well-recorded symphonic works since the low-frequency
    components are muted unless the kettle drums are being struck
    jwvm, May 31, 2007
  10. Good clarification. The temporal aspect isimplicit in my note that power
    relates to the area under the curve.
    Roy W. Rising, May 31, 2007
  11. Mark

    jwvm Guest

    On May 31, 10:56 am, Roy W. Rising <rwrising@dsl[omit]extreme.com>
    You might want to rethink your power statement. There is no
    relationship between power and frequency for a purely resistive load.
    The areas are the same for any 1 volt sinusoidal waveform regardless
    of frequency assuming some reasonable number of cycles are applied to
    the load. Also note that power is energy/time. The energy in one cycle
    of a 1 kHz waveform is the same as 10 cycles of a 100 Hz. waveform and
    both would require the same time interval.
    jwvm, May 31, 2007
  12. If that meant anything, it would mean the treble end, with all its
    frequencies, required MORE power than the bass, surely? :)
    Laurence Payne, May 31, 2007
  13. Mark

    hank alrich Guest

    But he's not talking "frequencies", he's talking _octaves_.
    hank alrich, May 31, 2007
  14. Mark

    Arny Krueger Guest

    "Deputy Dumbya Dawg" <>
    wrote in message
    That would be relevant if music usually contained equal power per frequency.
    That can happen, but it is relatively rare.

    Speaker builders and system designers would be wise to assume that music has
    about the same power content as red or brown noise. Pink noise has equal
    power per octave, but red or brown noise takes things to the next step. As
    the frequency goes down, each octave has twice the power.

    That varies quite a bit from speaker to speaker.
    Arny Krueger, May 31, 2007
  15. Mark

    Mark Guest

    There are a lot of interesting answers to think about but this one is

    I am 100% positive that a 100Hz 1 Volt RMS sine wave has the same
    power as 1 kHz a 1 Volt RMS sine wave or 10 kHz or any other frequency
    (into a fixed load resistance).

    Mark, May 31, 2007
  16. But is that ratio musical? If not then is it realistic for
    anyone listening to mistake those tones for something they
    want to listen too?

    Deputy Dumbya Dawg, May 31, 2007
  17. I might be mistaken, but I think you have that backwards.
    Roy W. Rising, Jun 1, 2007
  18. Maybe I could have expanded on that a little more. Sorry!

    Not that I believe this is "the answer" but perhaps if one
    spreads out a little bit of power over an octave with 10,000
    individual frequencies and averages it out ....... that would
    be the same number as averaging a 20 frequency octave with
    proportionally higher power for each frequency.

    Another consideration is looking at a spectrum analyzer
    playing music over a period of thousands of hours of music
    listening. Any decent sounding program will show a distinct
    downward amplitude slope from bass to treble. Good sounding
    music spectrum naturally has more power in the low

    Deputy Dumbya Dawg, Jun 1, 2007
  19. It shows the sound levels. It doesn't show the power required to
    produce those sound levels. You're chasing the wrong rabbit :)
    Laurence Payne, Jun 1, 2007
  20. Perhaps not we are changing the question from...Why is more
    power required for the bass? To : Does it take the same power
    to produce nSPL at low freq x than nSPL at high frequency y?

    The new question would have to cover.
    1) the radiation space of the SPL - and ways to hold them
    equal for comparisons.
    2) the driver efficiencies and sensitivities scaled back to
    the amplifier power.
    3) measurement techniques which remove any room effects from
    the acoustic measurements.
    4) differences caused by measurement distance
    5 ????

    I suggest that the answer to the OP question falls into these

    Why do you need a bigger amp on the bottom of a bi amp PA
    system than on the top?

    1) there are usually more low frequency octaves in the low end
    than the high therefore more program to be reproduce by the
    2) the program (usually and especially in rock music) requires
    more low frequency energy to sound natural.
    3) High frequencies are usually reproduce with comparatively
    sensitive compression drivers mounted on horns that beam the
    energy where you need it .
    4) Low frequencies are usually produced by comparatively less
    sensitive cone drives mounted in boxes which radiate the
    sound all around the box where a lot of it is wasted and only
    some if it goes where the HF frequencies are beamed by the
    horns--that is at the listener(s) are listening.

    Deputy Dumbya Dawg, Jun 1, 2007
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