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Tandy SPL correction values.

Discussion in 'Home Cinema Speakers' started by Steve.EX, Mar 28, 2003.

  1. Steve.EX

    Steve.EX
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    As no one has posted these for a while and there may be new members here playing with new subs and/or anyone dipping their toes into room acoustics, here are some correction values for the Tandy (Radio Shack) spl meter (both the analogue and digital versions as they use the same "engine") to be applied due to mic inefficiencies.
    The left column represents a/the test tone frequency
    the right column represents the value to be added to the recorded value of the frequency of the left column.
    16hz Add (+) 11.5db
    18hz Add (+) 8.0db
    20hz Add (+) 7.5db
    22hz Add (+) 6.5db
    25hz Add (+) 5.0db
    28hz Add (+) 4.0db
    31.5hz Add (+) 3.0db
    36hz Add (+) 2.5db
    40hz Add (+) 2.5db
    45hz Add (+) 2.0db
    50hz Add (+) 1.5db
    56hz Add (+) 1.5db
    63hz Add (+) 1.5db
    71hz Add (+) 2.5db
    80hz Add (+) 1.5db
    89hz Add (+) 1.5db

    Steve.
     
  2. nathan_silly

    nathan_silly
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    So if you're calibrating all speakers (bar sub) then the values are not important?

    It's only if you want readings from the various freqencies?
     
  3. Steve.EX

    Steve.EX
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    Nathan

    Firstly, these frequencies and their respective correction levels are very useful for ascertaining your rooms peaks and troughs when trying to iron such lifts and bumps via whatever methods (BFD, second sub, sub placement, TAMREQ etc) most rooms, mine included will have a lift around 50hz (mine is 17 db up at 48hz)
    clearly the frquencies listed are those that lie within the common THX filtered sub bandwidth.
    These frequencies are where the Radio shack in particular is telling lies.
    Although it has a much smaller +/- degree of error further up the audio spectrum you would be well advised not to attempt to measure such frquencies (commonly known) as high mids - tops as many many acoustic effects compound to make this method too crude and results useless to be of any meaning.
    Software running real time analysing with a tripod mounted mic or the like is really the way to go for these frequencies (and even still is not foolproof), which requires an obsessive type to want to get involved with this.

    Steve
     
  4. Steve.EX

    Steve.EX
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    Nathan

    To add, the frequencies listed are pretty much generic values and can be found on many test cd's etc.

    Secondly and this is IMPORTANT and is perhaps not realised (although it stares us in the face) as to what impact on integration it holds.
    When you callibrate your sub via the amp/whatever internal test tone do you know what frequency(ies) this is at?
    Without doubt be it pink/white/brwon/whatever the tone will contain frequencie(s) that your room responds too, and, if as i you have big lift (+10db is common) at some point you will be callibrating your sub to the room mode enhanced spl. (generally speaking TO HIGH/LOW, there will of course be the very very odd exception to this)
    Enter the benefits of TAMREQ and the like- (just HOW much better are my sub's sounding after only 15 minutes work? - oh baby! just wait till i have a few days to spare! (BTW i am so overtly biased to towards anything that might be related to Tag developements by even the slightest degree that this paragraph and the one following should be considered as coersion)
    TAMREQ actually is very similar indeed in application to the BFD, but has more filters per channel and more filter type choices (as i recall).

    Steve
     
  5. Steve Bate

    Steve Bate
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    Looks like I wont need to spend that £1.5K on the twin sharks then ;)

    Steve, is it really just a BFD with bells on it?

    Steve
     
  6. deckard

    deckard
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    Steve/anybody else

    What test disc do you use - Stryke? Are there any others out there, partic this side of the pond?
     
  7. deckard

    deckard
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    Perhaps I should clarify that, what disc do you use to get tones at these exact frequencies. I use Avia for my system setup but it only has sweeps, not exact frequencies.
     
  8. Steve Bate

    Steve Bate
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  9. Steve.EX

    Steve.EX
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    Steve
    The BFD certainly serves the same purpose as TAMREQ but the Tag implementation has several key (obvious) advantages.
    Firstly (and i had a BFD for a week or so and then returned it)
    the BFD is accepting an analogue signal from a processor/whatever AFTER any processing and has already undergone D-A conversion to which the BFD then A-D adds some more processing and then back to D-A. REGARDLESS this will impact on the signal to varying degrees as well as interfering with posiible time alignment and possibly to a far lesser extent phase.
    Obviously with TAMREQ this never leaves the digital domain until fully treated with all relevant criterea.
    I did think the BFD worked well (especially given it's modest price) but TAMREQ and it's implementation is a little more than bells and whistles.

    www.stryke.com
    I have used this disc for years now, it only took 5 days or so to arrive but there are others around but similarly are only mail/internet orderable (CPC, Maplins, RS) so the likelyhood of getting one quicker will only amount to a day here or there.

    Steve
     
  10. Steve.EX

    Steve.EX
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    Steve.
    I should add (although of no particular relevence) that the up-grade also includes a required restructuring/replacement of the power supply.
    As you may or may not know/care i have bought a new av32r DS and can i say that the sound quality particularly in full 6.1 discrete is fantastic, it really is a better cleaner sounding machine with lightening fast pannig abilities with even the most delicate of effects.
    I think there will be a lot of positive press/posts about this latest incarnation of the 32r.

    Regards

    Steve.
     
  11. deckard

    deckard
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    Steve B thanks for the links, unfortunately I don't have a HTPC or a CD burner so I've taken the plunge and ordered from Stryke.

    Should have a nice new Velo CHT-15 in a couple of weeks to test it out on. :D :D
     

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