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Which way do you point your sound pressure meter?

Discussion in 'Archived Threads 2001-2004' started by ScottAndrew, Jan 10, 2002.

  1. ling_w

    ling_w Well-Known Member

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    Jeremy,

    Your method doesn't make sense. For method 2, where you want every speaker to be roughly off axis by the same amount, why would you not just use method 1, where it would put almost all speaker at 90 deg off-axis? Plus, if one points the mike directly at each individual speaker, would this not solve that problem completely?

    Also, if we want it to simulate the ear/head, we would actually want to use the "A" weighting. Since the response perceived by us is modified by the ear/head, therefore, what is outputted by the surround would not necessarily sound like what is coming from the front, thus needing the freq modifier of the "A" weighting so it sounds equally loud when the sound is coming from the rear.
     
  2. BruceD

    BruceD Well-Known Member

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    Ling,

    Please read the RS manual.

    "A" weighting DOES NOT measure any pink noise test signals below 500Hz. That means you will not be able to balace a subwoofer at all, much less match it's SPL to the other speakers.

    That's why you want to use the "C" weighting scale.

    All the other stuff you said is nonesense.
     
  3. Jeremy Anderson

    Jeremy Anderson Well-Known Member

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  4. Chris Moffitt

    Chris Moffitt Member

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    So, I've followed the advice here, purchased the Radio Shack analog SPL meter and calibrated my speakers using the internal reference tone on my Marantz 5200. Yes, I use a camera tripod, mounted in the sweet spot an angled straight up or at 45 deg.

    Everything on the SPL measures right at about 75db (as close as I can get it), but when I play music (2 Ch - CD), my sound stage seems to be "anchored" to the right. I wouldn't say it's coming directly from the right speaker, but it doesn't seem quite right to me.

    If I go in and manually tweak my levels so it "sounds right", when I go back to using the SPL, I'm off by around 5db or so.

    I figure it's one of a couple things:

    1. Some sort of weird frequency problem related to my room

    2. Toe-in not correct

    3. Problems with my ears

    My next step might be to use video essentials and see what that gives me.

    Does anyone have any ideas or hints. I'd greatly appreciate it.

    -Chris
     
  5. Jonathan_M

    Jonathan_M Well-Known Member

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    Chris,

    I would investigate your toe-in again. That's likely where you'll find the problem. Someone in another thread suggested taping a laser pointer to the speakers to aim them. Just a suggestion.

    Good luck!

    -Jonathan
     
  6. ling_w

    ling_w Well-Known Member

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  7. BruceD

    BruceD Well-Known Member

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    ling,

    quote:

    -----------------------------------------------------------

    I am talking about using "A" weighting for LCR and surrounds, not sub. As for using it, the purpose would not to get equal balance of energy distribution, but to create equal perceived loudness.

    -----------------------------------------------------------

    Why do you want to confuse people by directing them to use different scales "A" and "C" to measure speaker balance, because they do or don't also measure a sub ?

    The whole purpose of the "A" and "C" weighting as described in the RS manual is: "Select A-weighting for noise-level determinations, and C-weighting for measuring sound levels of musical material".

    Last time I checked we were measuring for musical material reproduction in our Home Theaters.

    The whole point of using an SPL meter is to get an equal SPL response from all speaker/room interfaces at the measurement location (regardless of speaker type or orientation).

    quote:

    -----------------------------------------------------------

    e.g.

    If my surrounds are dipoles mounted far far back in my room. The sound I measure from it would include alot of reflected sound, and by the fact that it is a dipole with the transducers 90 deg off axis from the listener, the upper midrange freq has been attenuated and maybe the upper bass/lower midrange has been enhanced. So the energy distribution has shifted to the lower part of the freq spectrum, where our ear are less sensitive. So if we measure with "C" weighting, most of the sound pressure picked up does not translate to sound heard by listener. But with "A" weighting, the sound energy in the lower freq spectrum will have less affect on the final reading, just as the way our ear would perceive.

    -----------------------------------------------------------

    The above is simply not a smart way to measure.

    Frankly the "C" weighting simply captures all that your speaker/room is actually delivering to your measurement location.

    Why not measure what your room is truly producing instead of artificially throwing away actual room/speaker response as you suggest with the statement; "But with "A" weighting, the sound energy in the lower freq spectrum will have less affect on the final reading"?

    Certainly seems counter-productive to me.
     
  8. ling_w

    ling_w Well-Known Member

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    "A" weighting's purpose is not to measure noise, but to simulate a human being's hearing across the frequency spectrum. It drops drastically below 500hz not because there is no noise there, but the fact that human hearing is less sensitive at lower frequency.

    That is why the mentioning of using "A" weighting for calibration for equal loudness in situations where the energy distribution is widely varying between sources.

     
  9. Jason Wolters

    Jason Wolters Well-Known Member

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  10. Bill Lucas

    Bill Lucas Well-Known Member

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    ling,
    I think you have your hz's mixe3d up. [​IMG]
    If our hearing dropped drastically below 500hz we'd have a tough time understanding normal conversation. I *think* you meant to say 50hz and even that number is quite debatable. "C" weighting is best used when calibrating speakers. I know of NO loudspeakers (even Bose) that doesn't have useable output below 500hz. regards.
     
  11. ling_w

    ling_w Well-Known Member

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    Bill,
    Our hearing becomes less sensitive below 500hz (how one interprets the term drastic is another thing.) That drop in sensitivity is gradual until around 20hz, where it would take so high a level of sound at that freq for us to actually hear it (as oppose to feeling it) that we define that as our low end freq threshold.
    Here is a little description on "A" weighting and its purpose:
    http://www.norsonic.com/web_pages/correlation.html
     
  12. Ken Smith

    Ken Smith Well-Known Member

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    Ask a simple question and 31 threads later.........?
     
  13. Pete Mazz

    Pete Mazz Well-Known Member

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    But if the recording engineers are using the C weighting, then we should too, to faithfully try to reproduce what the levels were in the recording studio.

    Chris,

    Try swapping your speaker wires for the mains and listen again. That may give you a clue as to what's going on.

    Pete
     
  14. BruceD

    BruceD Well-Known Member

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    Chris,

    If you have VE, use the phase test and see if all speakers are in phase, especially Left, Right, and center.

    You can also use the round the room test to see if something is off on the balance between speakers.

    Also with VE I think you can use a mono test on the front L&R speakers to adjust the balance between L&R before setting the SPL levels on all the speakers.
     

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