Whats my reference level?

Discussion in 'Home Theater Projects' started by Ken Bock, Jun 5, 2005.

  1. Ken Bock

    Ken Bock Auditioning

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    Yesterday I recalibrated my home theater because I bought a tripod to put my spl meter on. Need some clarification on what my reference level is. I used the Sound and Vision Home Theater Tune Up DVD. SPL meter was set at 70db and used the front left test tone to set the volume on the receiver which ended up being -10db. The results of the test were FL: 1.0db, C: 0.0db, FR: 0.5db, Surrounds: 1.5db, SUB: 0.0db. For movies the volume is normally between -10db and -13db and is comfortable listening wise. Music is between -17db and -22db. Equipment used Fronts: Polk R50, Center: Polk CSI20, Surrounds: Polk R15, Sub: Polk PSW250, Recvr.: Denon AVR2805, DVD Player: Pioneer Elite DV45A. Any help would be appreciated.
     
  2. Bob McElfresh

    Bob McElfresh Producer

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    Hi Ken.

    I'm not sure what you are asking. A "reference level" is like a yard-stick. In theory, we all have a yard stick exactly the same length.

    A better description of what you did was "level adjusting". Your reciever, speakers, distances, angles, room sizes are all different from someone else with the exact same equipment.

    You used the SPL meter to compensate for all the distances so that each speaker produced the same volume at your main seat.

    What newbies often think is they use the SPL meter to produce about 75 db, then they think they should freeze the volume control at this position. You just use ~75db as a yard-stick to get all your speakers adjusted. You adjust your volume control up/down differently for each movie or for music.

    Does this help?
     
  3. Ken Bock

    Ken Bock Auditioning

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    Thanks for the reply Bob. I was just wondering what it means when I read people say I watch movie whatever it may be 10 to 15 clicks above reference level. The other thing that I was wondering was the volume setting that I used for the test was -10db so it doesn't matter if I listen to something higher or lower than this setting because its just a benchmark. Bottom line is I want to make sure I've done everthing correctly and I don't want to abuse my equipment by pushing it too hard. Thanks again for the help Bob.
     
  4. Bob McElfresh

    Bob McElfresh Producer

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    short answer: If you have level adjusted your speakers, and have good clearance on your reciever to allow cooling - you did things right.

    We have a primer/FAQ that helps explain FAQ: Reference Level

    If you notice the sound distorting or your receiver getting excessively hot - you have the volume control turned too far up.


    Ok, first off - your front-panel display lies to you. It does not really tell you the volume at your chair.

    Different companies adjust the display differently, but here is how I suspect your Dennon display was adjusted:

    - They took a "reference" speaker, put a SPL meter 1 foot in front and turned the volume knob to the max-rated power with a test-tone. They made the display say "0 db" for this amount of power.

    - Then they turned the knob down and when the volume on the SPL meter dropped by 10 db, they made the display say "-10 db". They repeated for 20/30/... db.

    (Ok, the engineers in the audience know they did not really do this with every receiver. But I am trying to explain the concept. [​IMG] )

    So your display is an aproximation of the volume and an aproximation of the power your reciever is putting out.

    Are you within 10% of max power? - I can hear this question in your mind. And the answer is NO - you are well-below the max power setting.

    There is a strange relationship between volume and power. It goes something like this: To increase the volume by 1 db, you must DOUBLE the power.

    So lets do the math:

    Here is the power your reciever is putting out when your display reads 0, -1, -2, ...

    0 db - 100 watts (according to the spec)
    -1 db - 50 watts
    -2 db - 25 watts
    -3 db - 13 watts
    -4 db - 6 watts
    -5 db - 3 watts
    -6 db - 1.5 watts
    -7 db - 0.75 watts
    ..

    Do you see? In truth, most of the time your reciever is putting out about 1-3 watts of power (per channel).

    So why do we need 100 watts of power per channel?

    An audio sound track is very complex. While we deal with an "average power of 1-3 watts", not every sound takes the same amount of power, and there is a HUGE range of volume in a movie. Your 1-3 watts of power includes moments of 50-120 watts (Yes, your reciever can/does go above it's rated output at times). But as long as these are short times, and the average volume is low enough, your receiver does not over-heat.

    (whew - sorry if I over-loaded you with info.) A simple turn of the volume knob seems simple - but it is really complex to put numbers to it.

    Did I loose you or does this make sense?
     
  5. Ken Bock

    Ken Bock Auditioning

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    Yes that makes sense. You explained everything vey well and I appreciate you taking the time to write me back.
     
  6. David_Rivshin

    David_Rivshin Second Unit

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    Just one minor correction, 10dB = 1/10th difference in power, not 1dB = 1/2 difference as you showed. The correct table would be:
    0 db - 100
    -1 db - 79 watts
    -2 db - 63 watts
    -3 db - 50 watts
    -4 db - 40 watts
    -5 db - 32 watts
    -6 db - 25 watts
    -7 db - 20 watts
    -8 db - 16 watts
    -9 db - 12.5 watts
    -10 db - 10 watts
    or more simply, every 3dB is (roughly) a doubling/halving of power.

    Of course the point remains that an amplifier very rarely works at it's max output. Anyone who consistently listens at even 20 watts of power on reasonably efficient (say 89dB@1watt@1m) speakers is just asking for hearing damage.

    -- Dave
     
  7. RobWil

    RobWil Supporting Actor

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    Reference level is the sound level at which your neighbors "refer" you to the po-lice [​IMG]
     

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