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Tandy SPL conversion tables

Discussion in 'Speakers' started by , May 31, 2001.

  1. slingshot

    slingshot Member

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    There were several postings about error correction for the Tandy SPL meter at higher frequencies, however I've done a search and can't find them could anybody point me in the right direction ?

    Cheers

    Slingshot
  2. Guest

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    If i remember correctly it's for the lower registers (but i could be wrong)
    Raimus/Ramius (my most humble apologies) is the chap to ask.
    For what it's worth i have invested alot of time into this sort of thing (meter's, sub test cd's etc) trying to set these thing's up by exact spl readings etc is just really hard and not always satisfying experimentation. You've just got to go with your ears on this one, Example, the meter seem's to read "strangely" when trying to set correct phase alignment which "seems" obvious by ear. Odd!
  3. Ramius

    Ramius Member

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    Here you go-

    10hz.....+20db
    12.5hz...+16.5db
    16hz.....+11.5db
    20hz.....+7.5db
    25hz.....+5db
    31.5hz...+3db
    40hz.....+2.5db
    50hz.....+1.5db
    63hz.....+1.5db
    80hz.....+1.5db
    100hz....+2db
    125hz....+.5db
    160hz....-.5db
    200hz....-.5db
    250hz....+.5db
    315hz....-.5db
    400hz....0db
    500hz....-.5db
    630hz....0db
    800hz....0db
    1k.......0db
    1.25k....0db
    1.6k.....-.5db
    2k.......-1.5db
    2.5k.....-1.5db
    3.15k....-1.5db
    4k.......-2db
    5k.......-2db
    6.3k.....-2db
    8k.......-2db
    10k......-1db
    12.5k....+.5db
    16k......0db
    20k......+1db

    Have fun.

    Cheers.
  4. slingshot

    slingshot Member

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    Thanks for the help, time to get the test CD's out.

    Slingshot
  5. Matt F

    Matt F Member

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    A couple of quick questions on this:

    Where the table reads, say, +2.5dB does that mean that the meter over reads or under reads by this amount? In other words, if I want to sett the level on my sub at 75dB (and assuming it’s a 40Hz test tone) then should the meter be reading 77.5dB or 72.5dB?

    The second question relates to the test tones produced by my Tag AV32R. Does anyone know what at frequency the white/pink noise is reproduced for both the 5 full range and the LFE channels? Obviously I need to know this otherwise I won’t know what correction amount to use in the table.

    Thanks in anticipation,

    Matt.
  6. Dom H

    Dom H Guest

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    Matt take the value on the meter and add on the respective dB at whatever freq. to get the corrected value.

    So if you wanted to adjust 25Hz to 75dB (list is +5dB @ 25Hz) you would adjust the meter until it read 70dB. ie whatever the meter reads is 5dB too low and needs +5 to make it correct.

    You can't really put a Hz figure on some pink/white/sub noise, I always adjust mains to 75db and sub to around 72dB (then tweak by ear) on the meter.
  7. Matt F

    Matt F Member

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    Thanks for that Dom. However, are you 100% this is the right way around?

    The reason I question this is that I just noticed the subject came up a few months ago when "Chips" was calibrating his Servo 15:

    Chips said "Interesting point is that the servo needs to be set at 83db on SPL meter with satellites at 75db to get a subjectively balanced sound"

    Nic Rhodes then said "Meter calibration issue at low freq, especially if you are using a RS meter"

    So, they were saying that you need to get a reading of 80dB or more in order to get a genuine 75dB i.e. they are saying that at low frequencies the meter reads higher than the real SPL, you are saying it reads lower than the real SPL.

    :confused:

    Matt.
  8. Matt F

    Matt F Member

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    I have the answer on the Tag's pink noise frequencies - this is from Tag's Chief Engineer (Nick Clarke):

    For the 5 full range channels the test noise random with a "pink" spectrum, covering the band 500Hz to 2kHz (-3dB points).

    For the subwoofer the test noise is random with a "pink" spectrum covering the band 30 to 80Hz (-3dB points).


    I'd still like to know whether the SPL meters reads lower or higher than the real SPL at, say, 40Hz.

    Matt.
  9. Matt F

    Matt F Member

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    And now I think I do - according to what I have been reading here http://www.pitt.edu/AFShome/s/z/szekeres/public/html/sub/radslm/rshack.txt , the corrections are to be added to whatever the meter reads - so, if at 25Hz you want to set a level of 75dB then you need to get the meter to read 70dB.

    In other words, it's exactly as Dom says - the only strange thing is why Chips found he had to set an SPL of 83dB on his Servo 15 to get it to blend in with his satellites that were set to 75dB. Add on the correction and he must have been setting his sub at least 10dB higher than the satellites!

    Matt.
  10. Dom H

    Dom H Guest

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    76 for the mains and 73 for the sub (all on the meter) sound like a good starting point then.
  11. chips

    chips Member

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    Hi Matt,

    Sorry to have caused confususion. I had just upgraded from a PS1000 and I think that the lower distortion of the servo fooled me into thinking it was too quiet.

    After a week or so I turned it down to 78db, which sounded about right with my old satellites. However, since upgrading the satellites, I now find that 75db on all speakers sub & sats sounds best to me.

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