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Thread: Sensitivity VS headroom

  1. #1
    JBL 4645
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    Arrow Sensitivity VS headroom

    This one is for bop/Widget

    Does a speaker with say 95db sensitivity means it sounds better played at 85db SPL with headroom of 10db if that makes any sense as, 85db is loud enough?

  2. #2
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    Nope. The sensitivity is actually taken using only 1 watt! It is basically a measure of how loud the speaker is compared to another. If one speaker with a 95dB rating is compared to another of 92dB, we know that it is much louder.

    Allan.

  3. #3
    Senior Member pos's Avatar
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    a 95dB/1W/1m speaker will only need 0.1W to achieve a 85dB/1M sound level, whereas a 92dB/1W/1m speaker will need 0.2W for the same sound level.
    That means that you can use a lower power amp, of better quality (maybe class A, or tubes...), and also that the voice coil of the driver will see less power and will have less heat to disspiate. That means lower power compression, more dynamics...

    But then if you sit 2m away from your speaker you will need 4 times the power you needed at 1m, that is 0.4W to achieve 85dB with your 95db/1W/1m speaker...

    But the logic remains: the more sensitive the speaker the less power you need to obtain a given SPL level at your listening location.

  4. #4
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    Dynamic range

    Quote Originally Posted by pos View Post
    a 95dB/1W/1m speaker will only need 0.1W to achieve a 85dB/1M sound level, whereas a 92dB/1W/1m speaker will need 0.2W for the same sound level.
    That means that you can use a lower power amp, of better quality (maybe class A, or tubes...), and also that the voice coil of the driver will see less power and will have less heat to disspiate. That means lower power compression, more dynamics...

    But then if you sit 2m away from your speaker you will need 4 times the power you needed at 1m, that is 0.4W to achieve 85dB with your 95db/1W/1m speaker...

    But the logic remains: the more sensible [sensitive] the speaker the less power you need to obtain a given SPL level at your listening location.
    And, as it follows, the more sensitive the loudspeaker. the less power it takes to produce a given listening level at a given listening distance, and the more headroom there is remaining for cleanly reproducing peak transients. Another way of saying this is that highly efficient systems have a greater dynamic range than less efficient systems. There are some remarkably good sounding systems that sound "remarkably good" only at relatively low volumes because they may have the capacity to produce only (for instance) 87 dB at 1 watt at one meter; as much as ten times the input power may be required to produce a relatively realistic volume only a few feet away at the actual listening position. In actual live music, peaks may be perceived as four or more times as loud as the "average" level. Psycho-acoustically speaking, an increase of ten times as much power is required to produce an output that will be perceived as "twice as loud." The inefficient system soon runs out of steam, regardless of the amount of input power that is applied, for it will reach its maximum output level at some point far below its rated "maximum input power," and any increase is simply converted to heat inside the enclosure. For example, in Bell Labs, Klipschhorns were long used to reproduce sonic booms at over a measured 140 dB, while the typical "audiophile" system maxes out around 110 dB. A symphony orchestra, listening to it from a few rows back in the center, can produce in a typical performance, dB readings averaging 90 dB, with peaks 20-24 dB above that level. Most low efficiency systems cannot accurately produce this wide of a dynamic range given a 90 dB level at the actual listening position. This is perhaps the most serious shortcoming of modern "audiophile" type designs. That symphony orchestra will sound different, tonally, from one venue (listening environment) to another, but of course sounds no less "real" in any one of them than in another--that is, tonality is the principle variable--but all within the "musicality range," but, on the other hand, the dynamics of the playing are remarkably constant. Any hack can learn to play the right notes in the right order, but the virtuoso knows what to emphasize. The virtuoso musician understands dynamics, but, unfortunately, many loudspeaker designers evidently do not.

  5. #5
    Senior Member MikeBrewster77's Avatar
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    Quote Originally Posted by whizzer View Post
    The virtuoso musician understands dynamics, but, unfortunately, many loudspeaker designers evidently do not.
    Nor do record companies, unfortunately. A bit OT and a rather long article, but worth the read and relevant to a discussion of dynamics in music reproduction.

    http://www.stylusmagazine.com/articl...nd-forever.htm

    You can scroll down to the section titled "Loudness War" to get straight to the point.

    Best,
    - Mike

  6. #6
    Senior Member BMWCCA's Avatar
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    Quote Originally Posted by MikeBrewster77 View Post
    Great article. Thanks for the link. We all feel the pain!
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

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    Quote Originally Posted by Allanvh5150 View Post
    Nope. The sensitivity is actually taken using only 1 watt!
    Allan.
    Maybe at one time, but I don't think so anymore. I think that sensitivity is taken at 2.83 volts input to the speaker.

    The amount of wattage is a function of the impedience and this varies with each speaker so the actual wattage also varies.

  8. #8
    JBL 4645
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    Quote Originally Posted by pos View Post
    a 95dB/1W/1m speaker will only need 0.1W to achieve a 85dB/1M sound level, whereas a 92dB/1W/1m speaker will need 0.2W for the same sound level.
    That means that you can use a lower power amp, of better quality (maybe class A, or tubes...), and also that the voice coil of the driver will see less power and will have less heat to disspiate. That means lower power compression, more dynamics...

    But then if you sit 2m away from your speaker you will need 4 times the power you needed at 1m, that is 0.4W to achieve 85dB with your 95db/1W/1m speaker...

    But the logic remains: the more sensitive the speaker the less power you need to obtain a given SPL level at your listening location.
    Good point there kinder like when I heard Rich JBL diy 43 series a few years ago. He was running less power and they where TUBE and yet they where of high sensitivity the JBL, the slam kick range was uniform.


    Given my distance for JBL control 5, from front is about 2.4 meters only 5 watts to achieve 85db. Sensitivity 89db leaves only 4db out for minimal safe headroom for peaks no?

    For the JBL 4645 diy sub only 1 watt required for 85db and that leaves 13db headroom no?

    Surrounds JBL control 1 about 1.5 meters watt required for 85db 3 watts for sensitivity 87db leaves 2db, no its half that sorry, 82db plus 82db = 85db for the two sides, so that would 1 watt not 3 watts, so that would leave only 5db headroom no?

    Also the high end, the tweeter for the JBL, control 5 what is the sensitivity of that individual speaker?

  9. #9
    Senior Member timc's Avatar
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    The headroom is not linked to sensitivity. If i have understood correctly it is the difference between the playback level and the peak output lvl of the speaker.


    so if you play at 85dB and you speakers can put out 100dB, then you have 15dB of headroom. At the most, music can have a crest factor of about 30dB i think.



    -Tim
    2213 + 2435HPL w/aquaplas + H9800 (Matsj edition)

  10. #10
    JBL 4645
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    30db at what distance 1 meter or other?

    Hmm, I’m going to do a few tests with pink noise measured at 1m/1w then listen to few moments form Quantum of Boredom it was Bond Rubbish! The plane VS helicopter has assorted use of ranges of loudness

  11. #11
    Senior Member timc's Avatar
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    Quote Originally Posted by JBL 4645 View Post
    30db at what distance 1 meter or other?

    Hmm, I’m going to do a few tests with pink noise measured at 1m/1w then listen to few moments form Quantum of Boredom it was Bond Rubbish! The plane VS helicopter has assorted use of ranges of loudness

    Crestfactor doesn't have anything to do with distance. If you increase volume by xdB at one distance you also increase it by the same in every other distances.


    -Tim
    2213 + 2435HPL w/aquaplas + H9800 (Matsj edition)

  12. #12
    JBL 4645
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    Quote Originally Posted by timc View Post
    Crestfactor doesn't have anything to do with distance. If you increase volume by xdB at one distance you also increase it by the same in every other distances.


    -Tim
    Can you, please show me an example I catch on fast.

  13. #13
    JBL 4645
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    Quote Originally Posted by BMWCCA View Post
    Great article. Thanks for the link. We all feel the pain!
    I agree that was a fascinating read, “The Loudness War” interesting subject.

    There are some films/CD music that I wouldn’t dare push too far, as the dynamics is too LOUD, Jarre In China is one musical example that I have on DVD.

  14. #14
    Senior Member timc's Avatar
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    Quote Originally Posted by JBL 4645 View Post
    Can you, please show me an example I catch on fast.

    If you play at 80dB/1m. Then you play at 74dB/2m 68dB/4m and so on.

    The crestfactor say something about the difference between nominal/average level on the source material and the peak level. You then need a headroom equal or greater than the crestfactor at any given time.


    -Tim
    2213 + 2435HPL w/aquaplas + H9800 (Matsj edition)

  15. #15
    JBL 4645
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    Hmm, I have a few other speakers I can use on the centre channel to see which one sounds the best?

    JBL Control 5 sensitivity 89db
    JBL HT1F sensitivity 87db
    JBL MR Centre sensitivity unknown
    JBL control 1 sensitivity 87db
    AWIA SX-77 sensitivity unknown
    AWIA SX-N7 sensitivity unknown
    Ariston acoustics MSX-07 sensitivity unknown

    I’ll see which one sounds best, I have feeling the JBL control 5 will win LOL.

    I’ll use a test program and microphone up the centre with spectrumlab at 1m distance and test a monaural program source, how about JAWS 2 chapter 4 time 19 minutes 13 seconds to 20 minutes 19 seconds.

    I’d have to set the graph spectrum for a wide window from 0Hz to 400Hz I’ll also run a frequency sweep of each speaker, not sure what this would prove? It’s only fun.

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