does flat frequency response mean LOUD flat freq. response?

Discussion in 'Archived Threads 2001-2004' started by John Doran, Nov 9, 2002.

  1. John Doran

    John Doran Screenwriter

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    if a speaker is flat down to, say, 20hz, and the same speaker is capable of doing 124db clean SPL, does that mean that the speaker can do 120db at 20hz?
    i guess what i'm wondering is if an otherwise flat frequency response is degraded by increasing volume; and if so, at what volume? i mean, i realize that if volume has an effect it will probably be a different volume for different speakers, but what i'd like to know is when volume starts wrecking a flat freq. response, why and what is it about the volume that does the wrecking...
    and would it be safe to assume that volume would have a more significant effect on the low-end of a flat response curve?
    thanks for the help.
    - jd
     
  2. Tom Brennan

    Tom Brennan Screenwriter

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    John---All speakers suffer from dynamic compression as volume increases, most suffer from it quite severely. What this means is that power produced by the speaker lags behind the power going in, an increasing proportion of the power is turned into heat instead of sound and this will effect the frequency response of the speaker at higher volumes because not all frequencies may compress at the same rate, generally woofers compress more than tweeters.
    An exaggerated example would be an 8" woofer matched with a compression driver and horn. The woofer would start to compress before it even reached 100db but the horn wouldn't start to compress until 115-120db. So when listening at 105 db the woofer would be several db down in level because it could no longer keep-up with the compression driver; what sounded balanced at 90db would no longer sound balanced at 105db.
    Don Keele used to do speaker tests in Audio magazine with graphs that clearly showed the effects of compression and how it skewed frequency response.
    www.chicagohornspeakerclub.org
     
  3. John Doran

    John Doran Screenwriter

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    thanks, tom; very clearly put.

    - jd
     
  4. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    Hi John,
    Tom is correct.
    Unless the manufacturer gives you the frequency,source input,measured harmonics,and measuring environment(say 1 meter from a corner loaded unit ---or 2m ground plane for example) then you can't be sure of anything.
    In your example, the FR(freq response) was probably measured using a low 85-90dB SPL output(that is the industry standard). So at 85dB---the speaker specs to -3dB at 20hz(or whatever). We also know the maximum output measured from the speaker was 124dB.
    But I bet if you ran a sweep that peaked at 124dBs thru the speaker---the FR would look a *little* different than it did at 85dB [​IMG]
    TV
     
  5. RichardH

    RichardH Supporting Actor

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    Yep, you know that Bag End Infrasub?? They say it goes down to 8 Hz, but only at like 75 dB (!!)
     

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