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Using SPL meter to set subwoofer

Discussion in 'Subwoofers' started by Dr.Rock, Jan 7, 2005.

  1. Dr.Rock

    Dr.Rock
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    I just want some pointer from anyone who uses a SPL meter to set the level of their subwoofer. My mains, centre and surrounds have been set to give 75 dB with a test tone (SPL meter set to Slow, C-weighting). I am now running a test tone into the sub. Theoretically, should that level be set so the SPL gives the same reading as with the rest of the speakers (ie 75 dB) ? When I do so, the sub still sounds damn quiet, even for film scenes which are well-known for thir LFE's....unless I turn the sub up, but then I'm not sure if it's turned up too much and it's delivering extra base which the film director doesn't intend the audience to feel. Any advice about the theoretical level setting dfor subwoofers using a test tone?

    Thanks in advance.
     
  2. danny daniell

    danny daniell
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    I cant get on with subwoofers at all (& i guess i have one of the best available) All i seem to do is keep altering the bloody crossover or volume.Like you,i set it with a spl meter,but it sounded too low.Anything above this & the sub is considered to be running too "hot" :confused:
    Sometimes i feel like throwing the bloody thing out the window! :devil: but it weighs too much :rolleyes:
    Help! :suicide:

    Dan
     
  3. Jules

    Jules
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    A digital SPL metre works well here as you can set it to 'slow' and 'max'.
    This will then record only the highest peaks during the test tone cycle.
    The 'average' readings can read way,way too low as the peaks last only a fraction of a second during the test tone cycle.

    If after setting with this method your sub is too quiet, you've probably got your phase, speaker size and delay time settings wrong.... or you've simply become used to an overblown sub level.

    The occassional 1 or 2 db boost 'on the fly' may be needed with different material, but on the whole if it is set correctly you should be able to leave it well alone.
     
  4. Nimby

    Nimby
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    Lets try and clear up some basic misunderstandings. :)

    Firstly test tones don't have peaks. They are steady state for as long as they last.

    Then there are room peaks and troughs in your sub's output.

    Poor subwoofers may have their own peaks and troughs regardless of where they are placed. (Or the room's own sound characteristics)

    If you match your sub to your speakers at some nominal frequency that coincides with a peak in your sub's response. Then your sub will only match at that frequency. The rest of the time the sub will sound too quiet. Possibly leaving the peak as a badly exposed "boom".

    If the nominal matching frequency coincides with a trough in the sub's response. Then the sub might sound too loud all the time except at that particular frequency. Though troughs aren't easily noticable. Partricularly if the sub is too loud over the rest of its range.

    The speakers themselves may also have troughs or peaks in their response curves. So the increased number of variables is beginning to cloud the process of speaker/sub matching.

    My advice would be to use your spl meter and test tones to get a rough frequency response curve above and below the calibration (level matching) frequency. Try and determine if the calibration point coincides with a peak or a trough. Or is fairly representive of the average in your sub's and speakers' response curves.

    Ideally your response curves should be perfectly flat lines. But the world is rarely that fair in real rooms. Which is why some people use BFDs.

    Do not be afraid of setting your sub level to your own tastes. While perfect matching is theroretically desirable many like their subs "hot" by 2-3dB on film watching. Reading the American AV forums I regularly see people mentioning having their subs up to 6dB hot on film. And some also have a "house curve" on top of that! So they could (theroretically) be running 10-12 dB hot at 30Hz!

    This is way way too hot for most people and certainly isn't kind to a sub that can't effortlessly match this required output. Probably well over 115-120dB at very low frequencies.

    On music the general concensus is a flat sub/speaker setting. But even that is open to interpretation. If you find you like your bass at a certain level then go for it. It may not be realistic on acoustic music or classical. But who's going to know except you? (and the neighbours)

    Remember that the human ear's sensitivity falls with frequency. But this fall is also dependant on the actual level (dB) at which you're listening. If you are listening at low levels then a bit of bass boost isn't too harmful and may sound more realistic and exciting to your ears.

    But if you are listening at a steady 100dB, then turning up the sub gain will sound as if the house is being demolished. Since any bass peaks will probably be 8-10dB higher than the average music level. I speak from (SVS) experience here. :blush:

    Nimby
     
  5. eviljohn2

    eviljohn2
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    Another good post from Nimby. To quickly add to the various response curves available, some people have their sub flat down to about 35Hz (for music) and then have a gradual curve upwards from there. Apparently it's a very good compromise which I hope to try when my BFD connectors finally arrive.

    To reiterate what Nimby's saying, the theoretical perfect sub response is next to impossible to achieve in a normal room so aim to be close and then tune it for your own taste. :)
     
  6. Jules

    Jules
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    Nimby is right of course.
    However, I would argue that, particularly on Denon AV amps, the test tones are not pure and do not make it easy to calibrate a sub.

    My experience has been that these 'peaks' represent the settings you'll end up when using AVIA.

    Also, I find phase shifts are introduced by the amplifier according to the crossover and delay time setings! And many people then boost the sub level by 3db or so when in fact they'd be better investigating other settings in their system first.

    Eventually, I settled for my speakers all set to 'large' as this eliminated the phase problems that gave inaccurate results after individual speaker calibration.

    I suppose personally I really hate those sickening, horrible peaks. So I find the absolute peak during calibration and then use all means at my disposal to minimise the troughs.
     
  7. bob1

    bob1
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    You will be setting the sub to a peak in the room response of the sub, i would run some tones and make a graph up to see if you have any peaks in room.Before i got my bfd i had the same problem i would set the sub up with the spl meter and it would sound too quiet except when it hit a peak,so i turned it up but the trouble then when i hit a peak BOOM BOOM.I now have it set at +2/3bd higher and i get the same effect as when i had set far too high before except the boom as gone because the peaks have gone.
     
  8. bob1

    bob1
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    Some people say that a curve is great for music but not so good for film.I did try for a house curve but didn't quite get there but you do turn the sub level up more than you should ,this does make movies seem OTT on the low stuff below 30hz.
     
  9. eviljohn2

    eviljohn2
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    Bob

    A house curve will be increasing from about 80Hz downwards so there will be quite a boost at the low frequencies, going flat to ~30Hz and then curving up a little is something of a compromise. I'll give it a try when I get my 1/4" connectors. :)
     
  10. danny daniell

    danny daniell
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    Sorry,but what is a house curve? (i dont frequent the U.S sites)

    Dan :)
     
  11. recruit

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    The Pink line is a House Curve Dan
     
  12. eviljohn2

    eviljohn2
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  13. Dr.Rock

    Dr.Rock
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    I think there should be some suggested demo-clip so we know we set the volume levels correctly on our subwoofer. eg, "if you play this chapter on this DVD, you should feel a lot of rumble when this bit happens in the film. If you don't feel anything, then you know you set your sub too low. In this other moment of the film, you should feel something but only a little bit. If you feel a lot of rumble, then you've set your sun too high." And since subs like the REL have separate voume controls for Lo-Level (dedicated LFE channel) and Hi-level (LFE recorded on main-speaker channels), maybe useful to have demo-clips for both ways.

    Thanks.
     
  14. bob1

    bob1
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    I don't think that would work ,some subwofers are better than others so for something you might feel on one subwoofer would never be felt on another.Room peaks and nodes are another factor so you might get a large peak in one room and not another so this would give diferent results.The best thing to do is set it how you like it and leave it like that.You won't hear /feel anything thats should not be there it just might be louder or quieter than it should be.When i changed to the svs sub i could feel more than i used to before ,this is because the sub is better on the lower fequencies something my last sub could not produce so i never heard /felt.Also people are not the same ,someone the other day on another thread said that most people can't hear below 30hz ,i can hear well below 30hz without a problem.
     
  15. Nimby

    Nimby
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    Good post Bob. :)

    I was having great fun rattling the windows today. :devil:

    Using Bass-Oldie's Cool Edit 96 tone generator. :cool:

    Sub gain was just above zero and I didn't dare use any more than a fraction of a second of continuous tone. :rolleyes:

    I got down to 14Hz before I was told to stop by SWMBO in no uncertain terms. :blush:

    It would have been an absolute piece of cake to completely shatter the windows. :clown:

    Now that is what I call a serious subwoofer. :D

    Nimby
     

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