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Q: TMREQ - UrbanT method

Discussion in 'TAG McLaren Audio Owners' Forum' started by Bogi, Sep 13, 2004.

  1. Bogi

    Bogi
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    Hi guys

    I've been looking to check out UrbanT's method and am quite fascinated by the fact that one does get a true spl on each freq. :)

    However, I need a bit of advice regarding the db level and volume on the DP unit. If I use speaker calib. the volume on the unit is set automatically. However when using the Sine feature on the unit one can adjust the volume.

    Well, the problem is that what volume should I use as I need a reference Hz point as starting point? I have some major peaks (around 103Hz) and it would be weird to use that as a reference Hz point. Am I to use 0 db on the unit and then check the db setting for each freq. My crossover freq is default 80Hz, but I'm suspecting I might have a dip tendency there. :blush:

    I've used ETF with very good results and am quite at ease with that method, but upon checking with the Sine UrbanT method I discovered that there are still peaks and troughs, so I wanted to try his method out.

    Any suggestions on a reference starting point volume wise using the sine method? :lease:

    Cheers
     
  2. JohnMulcahy

    JohnMulcahy
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    Try setting the DP's volume level to -20dB.
     
  3. Bogi

    Bogi
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    Thanks John!

    I'll try that. I had -25dB and was a bit concerned if I had to go up to 0dB as my SVS sub started outputting some really serious SPL values at 20Hz in the sub -20dB area that actually made me frightened! :D

    Cheers
     
  4. UrbanT

    UrbanT
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    Yep, my volume setting was -20db, and my peaks hit approx 95db maximum.

    You may possibly want to reduce the target level down slightly to compensate for a lower volume.

    I'm actually in the process of writing a brief guide to this method which should be ready in a week or so :)

    Can I also stress I can take no credit for this method, it was kindly shown to me by John :)
     
  5. GrahamMG

    GrahamMG
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    When doing TMREQ via the JM/Chris method, I am curious if final setting of the ref volume in speaker cal (nominally 75dB) has some sort of sliding scale effect on the overall result depending on what volume you normally listen at? I wouldn't normally listen at 0dB for instance, is this partly a reason for going with -20dB when measuring the true SPL of each frequency? i.e. measure them at the volume you normally listen at?
     
  6. Bogi

    Bogi
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    Fantastic, looking forward to that one! :thumbsup:

    Thanks and kudos to John, ever helpful in times of need! :thumbsup:


    BTW Urban, checked your set-up at your web site. The screenshots look fab! Really impressive the little TX100. :D

    Cheers!
     
  7. JohnMulcahy

    JohnMulcahy
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    At -20dB on the volume control the sine wave test tones should be around the 75dB mark (room effects excluded). I don't have the info to hand to check exactly what the result should be at the moment, if you are feeling really keen Graham you could get your scope out and measure the sine wave amplitude coming out of the processor's line outputs at that setting.

    I might make some enhancements to the wizard to provide better support for this method if that would be worthwhile. I have a few ideas for that, but unfortunately we did not get around to adding the additional support in the code for automating the measurement and correction process (e.g. commands for activating the test tone and setting its frequency) so there is a limited amount that can be done.
     
  8. GrahamMG

    GrahamMG
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    Hi John.
    I suppose I am that keen........Out with the scope then.....What would you expect it to be in the region of?

    Any enhancement you make to the existing wizard would be most welcome naturally. I'd go as far as asking, if you and Steve were up for it, to add the support in the code regarding the automation for a small fee or if take-up was just me in exchange for a rummage through by PC bits......
     
  9. Stevesky

    Stevesky
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    Now we're digging into the dark depths of THX and AV192R land ...

    On a calibrated system 0dB FS digital domain = (approx) 105dB inroom per channel. Subwoofer channel has assumed 10dB headroom, hence 0dBFS on SW channel digital domain = +10dB analog domain = 115dB inroom (=LOUD!).

    TMREQ sine wave generator is -10dB down at 0dB vol position and the AV internally hacks off another 10dB when doing the sub channel to take the extra headroom into account. So to sum up at the -20dB volume pos it should be about 75dB inroom.

    SW for PC cast-offs - dream on Goodbun!!! :eek:)
     
  10. GrahamMG

    GrahamMG
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    My definition of "cast-off's" is rather different to most.....try nod nod wink wink ask and see what might materialise.....
     
  11. JohnMulcahy

    JohnMulcahy
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    I've made the spl checks (by direct measurement of line outputs to exclude room) and the volume setting to match the sine test tone spl to the speaker cal level is -22.0dB. What this means is that if the speakers have been calibrated to 75dB, the sine test tone should also be at 75dB when the system volume is set to -22dB, if there were no boost/dip from the room at the frequency being measured. As the approach using the sine wave test tone uses actual spl levels, the wizard target level should be set to 97dB+system volume setting, i.e. 75dB if measurements were done at -22dB, or 77dB if measured at -20dB etc.

    Note that if the spl meter offers a "flat" setting, that should be used for the measurements. Meters that only offer a choice of A or C weightings should use C, but the C weighting curve will cause some under-reading at low frequencies (effect is -6dB at 20Hz, -3dB at 31.5Hz, -2dB at 40Hz, -0.8dB at 63Hz). I'll look into providing automatic compensation for C weighting in the Wizard (at low and high frequencies, at the upper end effect is -0.5dB at 3.2k, -2dB at 6.3k, -3dB at 8k, -6dB at 12k and -11dB at 20k).

    As an aside, if making measurements in a room with strong resonances it is not necessary to endure high sound levels at the resonances. Simply reduce the system volume setting at those frequencies to keep the level reasonable and add the volume adjustment to the measured value, then increase the volume again beyond the resonance - just make sure not to forget to account for these adjustments in any readings for which they applied.

    Postscript: Steve's measurements show the required volume setting to be -20dB, which was what I originally expected to see :confused: . Will investigate further and see if the 2dB disparity can be explained.
     
  12. GrahamMG

    GrahamMG
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    All these early morning starts must have woken up my brain...I actually understand all that :thumbsup:

    I, for one would love for John's suggestions to be included in the wizard especially the auto-compensation for everyone without a "flat" setting (i.e. almost everyone!).
    I wait with much anticipation.
     
  13. GrahamMG

    GrahamMG
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    Actually, are we not a million miles from fully automatic setup here?

    I assume that if the TMREQ could be set to do a sweep of all the frequencies (say five seconds of each one) and the RS meter's line out connected back to the laptop running the wizard so auto filling in the txt file (so to speak),we could just sit back and watch it do its stuff. Now that really would be cool.....

    It would certainly help with those of us who move stuff around in search of the perfect setup and try new kit (never quite doing it justice due to the time overhead of setting TMREQ well) which I'll wager is quite a few of us.

    I'd consider opening my wallet for this and allowing access to Aladdins cave :D
     
  14. JohnMulcahy

    JohnMulcahy
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    Graham,

    That's more or less what I was planning (and I've already implemented the C-weighting correction BTW, did it last night :)). The difficulty is in driving the test tone generator as there are no simple-RS232-over-Tt-bus commands for that, so I'll see if something is possible with cursor navigation commands - but user would have to make sure the cursor starts out in the right place in the menu or pandemonium could ensue! Before I get to that I need to set up the wizard to make spl measurements via the line input, and provide a means of calibrating the record level. All in "free" time of course, so it will take a little while.
     
  15. GrahamMG

    GrahamMG
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    Your a star!

    I was wondering on the control issue if Steve's old TAG interface on the PC program (in the days before you employed him) might be a way of telling the AV to do things? I know it was one way at the time but your both very clever people. If there is anything I can do to sweeten the deal just let me know.
     
  16. Bogi

    Bogi
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    Wow! :thumbsup:

    I'm really impressed. Extremely informative, and I'm so excited over the fact that there are new exciting hidden possibilities in the DP-units! :clap:

    I too would be willing to open up me wallet... :hiya:

    Cheers
     
  17. Welly123

    Welly123
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    Interesting stuff....

    I'll happily open my wallet for this as well.... :thumbsup:

    Regards
     
  18. GrahamMG

    GrahamMG
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    I'll even offer to keep John's 993 "warm" whilst he works on this, after all the car is only going to distract him from the task ahead :D
     

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