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SPL meters and subwoofer level setting

Discussion in 'AV Receivers & Amplifiers' started by NicolasB, Aug 1, 2003.

  1. NicolasB

    NicolasB
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    God alone knows which forum this ought to be in; we'll try it here first. Mods redirect at will....

    Recent threads on the subject of setting up subwoofers (and BFDs) have made me wonder just how accurate my faithful £25 SPL meter is when it comes to setting the subwoofer level. There's a much-referenced Excel spreadsheet which includes corrections for a standard SPL meter - reading vs actual value at different frequencies.

    Obviously subwoofer adjustments - positioning as well as level - are a big subject, and as I haven't yet found a satisfactory position, or dealt with some obnoxious room acoustics issues, or hooked up my BFD, results at this stage are going to be a shade sub-optimal. :)

    But as a general point: if one is using a processor-generated pink noise test-tone to set one's speakers to the same level, is a standard SPL meter actually accurate enough to adjust the subwoofer level in this way? Or is it a given that one should actually adjust the subwoofer several dB up or down from what the meter suggests is the right level, because the meter is inaccurate when it comes to bass frequencies? And, if so, what sort of correction factor should one use?

    (I would assume that the meter would read a level that is lower than the true volume at low frequencies, and hence the subwoofer would tend to be set too high if you trust the reading).
     
  2. Nic Rhodes

    Nic Rhodes
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    The good old faithful meters aren't accurate per se but they are accurate enough for proper setup. I always prefer a few extra dB anyway on that sub :)

    Each old faithful Tandy meter is different so the calibration is a moot point anyway. My digital differs from my analogue which differs from the unit I gave my father! I think I have often seen 3 dB difference.

    A meter doesn't actually have to be very accurate at all, you just need to get the balance right which they should be capable of :) If you want to try a really accureate meter, PM me your details and I will send you one to 'play with', don't think it does C weighted though which is a shame. I think it was calibrated last time to 0.1dB.
     
  3. stranger

    stranger
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    don't know why but it was the same in my last house too-but I've set my levels many times using an analogue R/S meter but to get the best results (for me) I always finish up with the centre and surrounds (and the sub:) ) 2 or 3 db higher than L and R. it just doesn't sound 'right' any other way.
     
  4. NicolasB

    NicolasB
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    Thanks Beekeeper, but I wouldn't trust myself not to drop it or step on it, I'm very clumsy.... :(
     
  5. NicolasB

    NicolasB
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    On the subject of meter accuracy: for the purposes of balancing it doesn't matter too much whether the actual reading the meter is producing is "correct" - what matters is whether or not it's consistent. I.e. if you set all channels to what the meter says is 75 dB, it doesn't matter whether that's actually 72 dB or 78 dB; but it does matter that all of the channels adjusted to the same 75 dB reading are actually all at the same real level (regardless of what that level might be).

    My concern is that the meter may do a reasonable job of producing consistent readings for the other channels but produce an inconsistent one for the subwoofer, because of the drop-off in sensitivity for bass frequencies.
     
  6. HotblackDesiato

    HotblackDesiato
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    I use a meter that's supposedly linear down to around 5Hz, i calibrate it using a 114dB tone generator but it goes back to RS for a proper tweak.
    That said... i don't use the meter for setting the sub, and prefer to do this by ear...then i just make a note of the reading once i'm happy... for the sake of reference/resetting.
    The meter does come in handy when messing around plotting the dreaded dB/Freq room curves.
     
  7. buns

    buns
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    Just out of interest, we are generally setting sub levels using pink noise. Now, why dont we work out our crossover location and simply set the sub's level at that frequency to match that of the main speakers? Or does pink noise already achieve this and more?

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  8. Jase

    Jase
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    Doesn't pink noise cover a wide frequency range anyway? Think that's why they use it.:confused:
     
  9. buns

    buns
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    it does....... but why do the other frequencies count? Assuming you have fairly flat sub and speaker responses at the crossover frequency, then surely this is all that matters?

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  10. Jase

    Jase
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    I would imagine if the crossover frequency was flat, ideally you would need all other frequencies to be flat as well. You wouldn't want a frequency response that looked like the Himalayas! :D

    I would say all frequencies count or am I looking at it too simplistically?? LOL
     
  11. buns

    buns
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    Well ideally! :D But in order for good integration between sub and mains, the crossover must be smooth. Im sure there is a good reason for it all..... but im going to try it both ways! :D

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  12. avanzato

    avanzato
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    I've found recently that setting up with the SPL metre and test tones doesn't take in to account my room modes. So I end up with really loud peaks.

    On one of my test discs I found a swept tone with frequency readouts. Using this I set the sub to a sort of average level which was about 5-6db lower than the SPL setting. I could also see if there were any problems around the crossover region.

    Having said that the most successful way I've tried is to set the amp to stereo and swap between the small and large settings for the speakers. When the sound is the same on both settings I consider the sub level to be right. I don't think this last method is strictly 'correct' but it gives me good subjective results.

    Next week I think I'll get a BFD, so hours of plotting nasty little graphs, and then maybe even get second sub as with the Harman white papers.
     
  13. micb3rd

    micb3rd
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    I usually calibrate the subwoofer about 2db over tha main spakers for movies, I listen about 15-20 below reference a slighter higher bass level seems to sound better to me.

    I think you most poeple have to play with the level a bit to get a satisfactory reasult.
     
  14. Nic Rhodes

    Nic Rhodes
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    intereting short thread ont this at the Tag web site at the moment
     

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