Subwoofer calibration

Discussion in 'Speakers' started by Eric_AP, Nov 17, 2003.

  1. Eric_AP

    Eric_AP Stunt Coordinator

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    I know the theory and what you are "supposed" to do, but it seems like I can't bring myself to lower my sub's level so that it reads the same as my other speakers on the spl meter.

    I have my sub at between 6-7 db higher than my other speakers (using the SPL meter). This is both on my receiver's internal test tones, and using audio calibration DVDs.

    When I lower it much below that, I just don't seem to get the oomph from my sub that I like. I also don't feel that my sub is overpowering the DVD soundtracks, where I have it right now. My current setting seems to be a good compromise between a nice sub impact, and blending of the soundtrack.

    The one thing that bothers me is that I don't feel the room shaking in movie theaters. Yet I hear alot of people talking about the room shaking in their home theater (and mine does too on certain explosions and where you might expect to feel shaking -- not the whole time). Is this because most subs are cranked too high at home? Is 6-7 db too high?

    Why don't the walls/floor shake in the movie theater? And I'm talking new multi-plexes with supposedly the latest and greatest in sound set-ups.

    So where do most of you calibrate your sub relative to your other speakers?

    Am I nuts for having it 6-7 db higher?

    In case it matters in your analysis, I have a Paradigm PDR-10 sub. My receiver would be playing DVDs at reference level at a reading of 82 on the main volume display. I play DVDs generally at about 67 (which is plenty loud). My receiver is an Onkyo TX-sr701.
     
  2. Robert AG

    Robert AG Stunt Coordinator

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    The THX gods are not going to strike you down if you like to run your subwoofer "hot". If it sounds better to you this way, by all means do it. I have a room that is calibrated to exactly match the levels on a movie dubbing stage since I do mixes of music that end up there for final mixing. But when watching movies for myself, I crank the subs by about 5db for the extra rattling of the walls - I just like bass.

    I spend a good deal of my time on dubbing stages where the movies are mixed, and can tell you that the subs don't rattle the walls there either. The "rattling of the walls" you hear in some home theaters are caused by two things. One is that the relative size of the subwoofers relative to the room which they are in with a home environment is different in a home than a movie theater (or dubbing stage). There is more subwoofer to room size in a home. To equal this ratio in a theater would mean more subwoofers than would be practical in a lot of installations, and thus cost.

    The other reason is that in a home, the subs are simply more likely to be cranked beyond the level they would be if calibrated critically to reference level. In a movie theater, they are more likely to be calibrated to reference level.

    The ideal method to properly calibrate a system is to use spectrum analysis and a calibrated microphone along with full bandwidth pink noise. In a home, the test tones (which are not full range pink noise except for the "Avia" test DVD disc) suffice quite nicely.
     
  3. WayneO

    WayneO Supporting Actor

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    There is also a lot less things to rattle in a movie theater than at home. You got shelves and knick-knacks and all that jazz that vibrate so easy. If you could tie everything down you'd probably find the bass response "tighter" as well.
     
  4. MarkyM

    MarkyM Agent

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    My SVS 25-31PCi runs about 3 db hot on the meter but if you
    factor in the 3db correction then it runs about 6db hot, which is the way I like it......[​IMG] [​IMG] [​IMG]
     
  5. ChuckRG

    ChuckRG Agent

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    Assuming you are using a RS meter for measurement, then a 2 to 3 db increase of the subs over the mains is actually setting the subs equal to the main (given the RS documented calibration issues for low frequencies).

    The reason walls move in your HT is due to compressing the air in the room and hence moving the walls. I have 4 subs (12 drivers) so my room moves a bunch with explosions even if the level is set below the mains -- it's all about moving air. The reason walls don't move in your local cinema is that the woofer driver area to the cubic feet of the theater is miniscule compared to your HT.
     
  6. ChuckRG

    ChuckRG Agent

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    My bad:

    I said that wrong. You have to add 2db to 3db to the RS meter reading to have it be correct, so you would set the subs 2 to 3 db (according to the RS) BELOW the mains.

    Sorry.
     
  7. Eric_AP

    Eric_AP Stunt Coordinator

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  8. Wayne A. Pflughaupt

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    Eric,

    It’s not unusual to have to boost the sub in a home theater in order for it to sound right. The fact is, the smaller the room the more boost is needed.

    If you’re feeling brave you might want to slog through the information at this thread.

    Regards,
    Wayne A. Pflughaupt
     
  9. JohnnyG

    JohnnyG Screenwriter

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    I've pretty much given up on the SPL meter entirely on my home system. DVE gives one result, AVIA another and the built-in test tones something else entirely. None of them are even close to a consensus. The receiver is an H/K AVR8000 (THX Ultra) and part of the THX certification process is supposed to be the accuracy of the built-in test tones. THX says to use these tones exclusively for setting the speaker levels, but the bass is off the charts if I do this.
     
  10. Wayne A. Pflughaupt

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  11. JohnnyG

    JohnnyG Screenwriter

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    Wayne, I ran all those tests in exactly the same room - even one after the other. I just don't get it! My gut feeling is that it has something to do with actual LFE channel information. AVIAs tests do not use the LFE channel - just low bass in the main channels that will be crossed-over to the sub. The H/Ks test tones do use the LFE channel, and I suspect DVE does too.

    There is one AVIA test with real LFE channel, but that's always measured -10dB for me. I've seen those results on several different H/K receivers, and a Panasonic model too.
     
  12. Edward J M

    Edward J M Cinematographer

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    The RS meter reads LOW in the bass region.

    It is C-Weighted and there are correction factors for the C-Weighted curve (the equation is log based and rather complex).

    The RS meter also introduces its own additional error (beyond the C-weighted correction factor) at extremely low frequencies.

    This has led to the development of "RS correction factors", which include both the correction for the C-Weighted curve, and also correction for the meter error.

    Anyway, if you are running the sub 6-7 dB hot on the meter for the sub calibration tone, that is really about 8-9 dB hot since the meter reads about 2 dB low on the typical rumble test tone.

    If you like the sub that hot, I say FINE. As long as you aren't stressing it or bottoming, go with what makes YOU happy.

    Ed
     
  13. Eric_AP

    Eric_AP Stunt Coordinator

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