SPL Question?

Discussion in 'Archived Threads 2001-2004' started by Shannon W, Nov 13, 2002.

  1. Shannon W

    Shannon W Stunt Coordinator

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    What SPL level would you you say Is Reference? I just checked my new HT Levels and it was 126 DB @ 3' away from speakers and 110 DB @ 10' from speakers. Would this be good for only running 90 watts x 7? The room size is 14' Width x 18' Length x 7' Height
    also What dose it take for a speaker to get a THX certification? Thanks

    Shannon
     
  2. jeff lam

    jeff lam Screenwriter

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    Dolby reference is peeks or no greater than 105dB from the listening position. This varies as soundtracs are recorded at different levels but as a standard, reference is 105dB(115 for LFE) peeks at the loudest scenes.
     
  3. Jeremy_Watson

    Jeremy_Watson Stunt Coordinator

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    Shannon,
    You need to get a calibration disc (Avia, Sound & Vision, whatever) and follow their instructions. Reference volumes should be measured from your "sweet spot" and are usually 70-75 dB, depending on the test tones. These are the levels for each speakers, too, not the total sound output.
    Hope this helps.
    Jeremy
     
  4. Shannon W

    Shannon W Stunt Coordinator

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    when i did test tone my speakers I did it @ 60-62 DB. Going to re calibrate.
    Shannon
     
  5. Dustin B

    Dustin B Producer

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    Dolby reference level can ask for peaks of 105dB from any of the 5 speakers at the listening position individually and 115dB from the LFE channel at the listening position. So the combined output of the 5 channels and the LFE channel can produce peaks of ~121dB at full reference level (this is from 120hz and below, above 120hz not quite that much will be asked for). If your speakers are all set to small, then the sub needs to be capable of the full 121dB on its' own to do full dolby reference level.
    If you haven't seen this yet Shannon I suggest you give it a read:
    http://www.hometheaterforum.com/htfo...553#post650553
     
  6. Shannon W

    Shannon W Stunt Coordinator

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    thanks guys for all you help. going to look into at calibration DVD.
    Shannon
     
  7. ChrisWiggles

    ChrisWiggles Producer

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  8. Dustin B

    Dustin B Producer

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    Exactly, not many subs are capable of this at the seats. Especially when placed at the front of the room and are several meters from the listening position. Remember that a speaker's output will drop 6dB for every doubling of distance. So when you see a sub claiming over 100dB at 20hz from 1m. When its' 4m (only 13') from the listening position you have to take 12dB off that number.

    Very few people in medium to large sized rooms have systems that can play reference level cleanly. A lot of people say they are running at reference level, but I don't know how they can stand the distortion that would be coming from their systems at that level. I know mine can't do full reference. Even if your system can do it cleanly I don't think many people would want to listen that loud, as it is very loud. My dream system could do it easily, and the system I hope to end up with in the next couple years should come very close (not that I'll ever listen at full reference, but headroom is never a bad thing).
     
  9. jeff lam

    jeff lam Screenwriter

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    Dustin,
    are you sure this applies to subs? Does room gain factor into this? Naturally this would make sense for mid and high frequencies but low frequencies have a much different characteristic and I was wondeing if it applied in the same way.
     
  10. Dustin B

    Dustin B Producer

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    As far as I've read it does. As always, could be wrong though.
     
  11. Chris Tsutsui

    Chris Tsutsui Screenwriter

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  12. Dustin B

    Dustin B Producer

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    I'm defining reference as 85dB on the Avia test tones. I think the biggest limiting factor on my system right now is my receiver. 70W just isn't enough to get my speakers up there. I don't find 5dB below reference that bad (still a little harsh), but full reference I can't stand. Sounds horrid on my system in comparison to 5 and especially 10 dB below reference. If I get a Denon AVR4800 like I want (I got a job now, yay should happen soon), 5dB below reference should be clean on my system. Full reference still won't be.

    It would take over 300W to get my JBL S38 to full reference peaks at my listening position (14'). They can't take that much power and I don't have anywhere near that much power to give them. A 90dB/W/m speaker 4m from the listener will need ~300W to hit a 105dB peak.

    Now people with much higher sensitivity speakers (>95dB), I could see them getting to reference just fine. People with the low 90dB/W/m range speakers that can handle over 300W and have the power to back it up I can see getting to reference. But people with under 90dB/W/m speakers and receivers with less than 100W claiming to be listening at reference level? They either don't mind horrid sound, are doing something wrong in the calibration or have their stuff setup in a closet.
     
  13. Geoff L

    Geoff L Screenwriter

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    Dustin

    Oh how you so speak the truth. I can reach true referance but my room is small and I run 3 subs. All 3 are SVS drivers. 2-sealed and 1-2039 clone.

    Referance is Damn loud!
    My room is only 13'W x 18'L x 8'H. I can't do 20hz at 121-db with 2 subs I need all 3 and a BFD. And even then I could be exceeding the 10% distort level that Tom N. uses when measureing. If they were all ported 2039 clones 2 might do it, but 2 are sealed and they them sevlves can't do it on their own. Regardless of a distort rating! At 20-hz and 120-db good god you think the place is going to littlerly come apart.

    Allot of pople have miss conseptions on Referance Level-SPL, and what proper calibration and true levels are and sound like.

    Jusy ask my neighbors, they could put the same movie in the player and not run any volume and watch the entire movie at their house and here everything easily!
    Live in a condo.

    If we are really into a film we may run 10-db below but most of the time it's more like 15-db or lower below referance.

    You guys that can take it, a full movie like ATOC, TPM, or Lord of the Rings at true referance are much tuffer than I. Maybe a larger room makes it more tolerable, I doubt it as 121+db is 121+db. I really don't know how you can handel it for 2 hours. Yes it's not a constant volume of 121 but good golly it's just toooooo much of a good thing for me!

    Geoff
     

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