Speed difference for high and low frequencies

Discussion in 'Archived Threads 2001-2004' started by BenK, Dec 13, 2002.

  1. BenK

    BenK Stunt Coordinator

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    A co-worker mentioned while we were talking about audio equipment that the high and low frequencies have different rates of travel. Basically even in a perfect sound proofed room the sound waves from high frequencies would reach the listener earlier than the low frequencies. Enough to notice a difference. He said they was a "sound enhancer" device or circuit that fixes this. I've never heard of this and most of it didnt make sense to me. If this is true than basically I've been hearing music wrong all my life and everyone else for that matter. Anyone heard of this?
     
  2. Bob McElfresh

    Bob McElfresh Producer

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    I dont think this is correct.

    Sure, you get MORE CYCLES in one second of a higher-frequency sound. And this means it takes LONGER to hear 1 cycle of a lower frequency sound. But this is because the sound takes longer to complete. It does not mean it travels any slower or faster.

    There has been some audio myths that seem to support this:

    - Some wire companies claim to have super-secret windings in their speaker wire to 'temporially re-align' the sound.

    - Some audiophiles believe tilting their speakers back a bit to thrust the mid-range driver closer to the listener than the tweeter will align the frequencies.

    Both of these myths try to explain real-world changes in sound with fancyful theories about sound travel.

    Ex) Windings in a speaker wire DO make a difference, but it's because of capacitance issues changing the frequency response of the cable and not because of the speed of different frequencies. And tilting the speaker back - this fires the tweeter over your head, but keeps you in the middle of the radiation pattern for the mid-range driver. This is like using a equalizer to reduce the sound from the tweeter resulting in less high-frequency. This, by comparison, makes the mid-range sounds a bit louder which is also where human hearing is more sensitive. So this 'opens up' the sound.
     
  3. Kevin C Brown

    Kevin C Brown Producer

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    That's extremely incorrect. The speed of sound, ANY sound is about 1100 ft/sec.
     
  4. Vince Maskeeper

    Vince Maskeeper Producer

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    What he is likely talking about is aural alignment- a process executed by processing like BBE's Sonic Maximizer. While the reality behind the speed difference is less than accurate (the speed difference is not as much of an issue as directionality issues but...)- these device often do delay some freq slightly creating an illusion of "tighter" bass in some cases.
     
  5. Lewis Besze

    Lewis Besze Producer

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    I guess Thiel, Vanfersteen,and Dunlavy,don't know what they talking about then.They all favour and produce "time coherent" speakers,which features tweeters that,placed slightly further "away" compared to the mid/woofer.
    However it's not about speed but "directionality",higher ferquencies tend to "beam" at you compare to lower ferquencies,which could percieved as "faster".
     
  6. BenK

    BenK Stunt Coordinator

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    BBE's sonic maximizer. Thats what it was called. Thanks Vince...I couldnt remember the exact name of the device. So what I'm understanding is its a yes and no kind of answer. Am I right to assume there can be time alignment issues but not because high frequencies travel faster?
     
  7. Kevin C Brown

    Kevin C Brown Producer

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    No... Not Star Trek and "beaming". [​IMG]
    The reason why Thiel, Vandersteen, and Dunlavy (among very few others) slant their drivers is simply to make sure that the voice coils themselves are the same distance from you. Look at a tweeter vs a woofer from the side (or simply envision it). The voice coil is set further back in a woofer (because the cone is larger) than the tweeter. So you move the tweeter back to align *that part* of the drivers. That's why.
     
  8. Jason Wilcox

    Jason Wilcox Supporting Actor

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    different frequencies all travel at the same speed in the same medium. even if they didn't...why would we want to correct that to make them reach our ears at the same time...it isn't like they would do that at a live performance...and that's what we are trying to reproduce faithfully in our homes is it not?
     
  9. Paul Stiles

    Paul Stiles Agent

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    In multi-driver time coherent speaker systems, the drivers (tweeter, midrange and woofer) are placed at different setbacks so that the ACOUSTIC center of each driver (not the voicecoil) is equidistant from the specified listening position. So an electrical pulse into the speaker will result in an acoustic pulse (little or no time-smear of the waveform) at the listening position.

    The crossover feeding the drivers delays some frequencies more than others, this affects the acoustic center of a driver: the acoustic center is not just the average position of the radiating surface of the driver.

    Paul
     
  10. Lewis Besze

    Lewis Besze Producer

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  11. Jason Wilcox

    Jason Wilcox Supporting Actor

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    so that the frequencies reproduced by the tweeter and woofers are coming from points that are equidistant from your ear (also depends a lot on placement)...and reach your ear at the same time...
     
  12. Lewis Besze

    Lewis Besze Producer

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    Bravo! [​IMG][​IMG]
     
  13. Kevin Deacon

    Kevin Deacon Second Unit

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    In crossovers many folks incorporate baffle step compensation which in effect aligns the acoustic centers of each driver.

    If we are trying to reproduce live music through speakers why do we care about aligning the acoustic centers? Imagine an orchestra, the percussion and strings are not equidistant from the listener. Can someone explain?
     
  14. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    Myths anyone?
     
  15. Jason Wilcox

    Jason Wilcox Supporting Actor

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    "If we are trying to reproduce live music through speakers why do we care about aligning the acoustic centers? Imagine an orchestra, the percussion and strings are not equidistant from the listener. Can someone explain?"

    say you're recording that concert...the sound from the percussions and the strings would reach the microphone at different times...so that's already compensated for in the recording...

    now...say that you're playing a recording of a....classical guitarist...they hit the low notes that would be reproduced mainly by the woofer in your speaker....then the high notes that would be reproduced by the tweeter...now say the guitarist plays a note right around the crossover point...if the tweeter and woofers acoustic centers are not alligned with each other than the sound of that note would reach you first from the driver whos acoustic center was closer to you
     
  16. Kevin Deacon

    Kevin Deacon Second Unit

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    Ohhhhh, Thanks Jason. That clears it up.
     

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