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Thread: Vocal cords and loudspeaker capabilities

  1. #1
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    Default Vocal cords and loudspeaker capabilities

    This is a video clip of stroboscopy of the vocal cords. Watch how we create sound.

    ST

  2. #2
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    Default Vocal cords and loudspeakers are fundamentally opposite devices - why?

    Quote Originally Posted by STHLS5 View Post
    ...stroboscopy of the vocal cords. Watch how we create sound.
    Fascinating. To me the essential point is that the vocal cords* are self-evidently created from pliable moist tissue, nourished by a warm blood supply and under muscular control. They are not like our bones or nails. Taken together, that means that the vocal cords are extremely well mechanically damped, and in audio we respect damping because it opposes the character we most seek to avoid: ringing otherwise known as undamped oscillation. The real live human voice is produced by wet, damped vocal cords at 38 deg. C with their normally smooth even sonic character and they are conceptually the opposite of what you find actually producing sound inside the loudspeaker. The speaker uses hard, rigid metal, plastic and cloth moulded parts at about 20 deg.C (ambient temperature) none of which have any 'give'. You can see then that if any or all of the speaker's parts have a tendency towards self-oscillation (ringing) there is no warm spongy tissue to damp that tendency.

    This very low damping in the loudspeaker parts has some important consequences:

    • If the speaker does 'ring' at some frequency or other, that may or may not be masked by music but
    • if clean, well recorded speech is reproduced over the speaker the ear may hear the unnatural character of the speaker imposed on what we expect natural speech to sound like and
    • once the ear has latched onto the self-evident loudspeaker coloration the subconscious mind cannot relax and
    • the listener is then in a state of psychological tension as he is not completely convinced he is in the presence of a real, live human

    The reason I have used human speech for so long as the primary arbiter of loudspeaker sonic quality is because most of the unwanted characteristics exhibited by loudspeakers cannot be heard in the live voice. Real human voice boxes cannot sound 'ringy' or 'brittle', descriptive terms we associate with hard, rigid materials.

    Perhaps surprisingly, the various colorations we associate with poor loudspeakers were characterised and named as far back as 1938 - before WW2 in the 78 era. From my archives, I've scanned this foolscap sheet to illustrate the point that speaker colorations were identified at the very start of the loudspeaker era, and are still with us to one extent or another as loudspeakers with their rigid parts try to mimic the human voice with its soft parts.

    *I cannot decide if the correct spelling is cord or chord. Any ideas?
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    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default Another word for unnatural ...

    Quote Originally Posted by A.S. View Post
    ...
    • once the ear has latched onto the self-evident loudspeaker coloration the subconscious mind cannot relax and
    • the listener is then in a state of psychological tension

    ...
    And these are other words for our old enemy ...... LISTENING FATIGUE.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default Efficiency our vocal cords

    Quote Originally Posted by A.S. View Post
    Fascinating. To me the essential point is that the vocal chords (UK spelling) are self-evidently created from pliable moist tissue......
    The reason I have used human speech for so long as the primary arbiter of loudspeaker sonic quality i...
    Quote Originally Posted by A.S. View Post
    And these are other words for our old enemy ...... LISTENING FATIGUE.

    I can't believe they actually described the effects of attenuation or boosting certain frequencies so long ago way back in 1938! I have seen similar excerpts from the Mixing Engineer's Handbook and thought they were modern findings.

    When you mentioned about the importance of a loudspeaker reproducing human voice as natural as possible and listening fatigue, these are qualities which somehow many modern speakers overlook. There are some speakers though nice to listen to, but I can't last 10 minutes without feeling fatigue. However, somehow these owners can listen for hours. Could one adjust themselves to listening fatigue?

    Another thing that I like to compare is the vocal cords and Harbeth speakers. I believe the speaker technology is much simpler and versatile compared to the vocal cord. Don't you think so? Even when we speak of efficiency our vocal chords is just about 0.0001 to 1% efficiency. At least speakers are about 10% efficient.

    ST
    Last edited by STHLS5; 10-01-2011 at 07:10 AM. Reason: Wiki says "cords", though "chords" also acceptable. The correct term is "folds".

  5. #5
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    Default Fatigue - marketing and engineering fighting together

    Quote Originally Posted by STHLS5 View Post
    I can't believe they actually described the effects of attenuation or boosting certain frequencies so long ago way back in 1938!
    Although seventy years or so that have passed since the GEC internal report I showed, today's speaker engineers still have not completely absorbed the knowledge of those pioneer audio engineers two generations ago. Or is that too simplistic an analysis? Do marketing trends have a bigger influence upon design than we believe? For example, although I don't buy hifi magazines (and we don't receive any gratis copies) I do occasionally stand in the newsagents shop and flick through editions to see if there are any interesting speaker reviews accompanied by a measurement of the speaker's frequency response. Such curves are as much music to my eyes as a manuscript is to a musician. Recently, one review caught my attention being representative of a trend I've noticed for some years. What surprised me was that a major manufacturer with an excellent brand name and doubtless the very best technical (measurement) resources had released a product - being typical of a marketing trend of similar product characteristics - with a much elevated high frequency response, according to the measurement graph. From recollection, the band around 10kHz was lifted by several decibels relative to the average level across the audio band. So if we look at the GEC 1938 paper, what would that say .....

    GECtoppy.jpg

    And the reviewer comments on the speaker's sound: the top end had a brightness of tone which was initially attractive (to the untrained listener) but he rightly cautioned the readers about longer-term listening satisfaction, which we can decode as listening fatigue. My question is this: what commercial forces arm-twisted the engineering department at this highly respected brand to deliberately boost the top-end when it's been known for seventy years that this is likely to result in lower ultimate fidelity? Imagine the arguments raging about whether this was the right direction to take the product development strategy. And obviously, the marketing department had the upper hand. We shouldn't be surprised by any of that; that's how corporations proceed internally. What should surprise us more is that one reviewer, backed by his measurement data, was willing and able to publish an opinion about potential listener fatigue which, in my view, scuppered the marketing department's prior justification (increased sales) and reinforced the hand of the brand's engineering department. Further arguments would have ensued!

    ... but I can't last 10 minutes without feeling fatigue. However, somehow these owners can listen for hours. Could one adjust themselves to listening fatigue?
    It is amazing what some people will tolerate. One professional studio user group constructed a blind listening tests to select new monitor speakers which neither included a reference loudspeaker, nor a real live human voice, nor put the speakers out to user testing to check for listening fatigue (a word they didn't seen to be aware of). Out of idle curiosity, I went and purchased one of the speakers that had reportedly done well under the brief tests. Enduring it is easily the most fatiguing listening experience I have ever heard. I wouldn't know how to begin to design-in such strong sonic characteristics into one of our loudspeakers. So the danger of immediate appeal over longer term fatigue is still ever-present despite the passage of so much time and common sense.

    ... Even when we speak of efficiency our vocal chords is just about 0.0001 to 1% efficiency. At least speakers are about 10% efficient.
    No. Think again. HiFi speakers are only about 2% efficient. That is, 98% of the energy pushed into them is wasted as heat, and doesn't produce sound.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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