A question regarding power and SPL

Discussion in 'AV Receivers' started by Cagri, May 27, 2003.

  1. Cagri

    Cagri Second Unit

    Joined:
    Dec 18, 2002
    Messages:
    415
    Likes Received:
    0
    Trophy Points:
    0
    Last night I put my RS SPL in front of one of my front speakers, 1 mt away. It is a floorstander, 91db, 8 ohms. I turned the volume on my Denon 1802 to read -18, which is almost half the way (Denon's volume scale is from -60 to +18) and the meter read 84db.

    I know there's the input level and the software in effect, but the speaker was just 10 feet away from the other one and 13 feet away from the sub. My question is; am I just using about 1 Watt when the volume is at almost half way up or am I missing something crucial here? Thanks
     
  2. Yogi

    Yogi Screenwriter

    Joined:
    Jul 25, 2002
    Messages:
    1,741
    Likes Received:
    0
    Trophy Points:
    0
    You probably are using less than a watt at -18db setting. The reason you are troubled is because you think this is half way and yet you are only getting a watt out of the amp. Power and SPL levels dont scale linearly but in a logarithmic fashion. So half way at -18db you are using, say, a watt of power. So at -15 you would be using 2 watts and going on like this you can see that:

    -15db = 2 W
    -12db = 4 W
    -9 db = 8 W
    -6 db = 16W
    -3 db = 32W
    0 db = 64W
    ....
    ....
    ....
    + 18 db = 4096W

    So you see you wern't even using a watt of power at -18db. At most you were using a small fraction of a watt at -18db to be able to get 100 (or so watts) at full power of +18db. So dont worry about the volume setting and your power usage because the relation is not linear. You didn't observe anything wrong and it all makes sense you see.

    Hope that helps.
     
  3. Cagri

    Cagri Second Unit

    Joined:
    Dec 18, 2002
    Messages:
    415
    Likes Received:
    0
    Trophy Points:
    0
    That helps a lot thanks. It is also very comforting to know in this regard that I will never cause the Denon clip in 2 channel listening as even in my largish room, I can't bear it if it is past -15, which equals about 2Watts usage. Great [​IMG]

    Actually I knew the relation wasn't linear, but I wasn't thinking that it would be such a proper one, i.e. 3 db increase = twice power for all voume levels... According to this rule being valid for the whole scale, I am using 0.00012 Watt when the volume is set at -57. Sounds surprising.
     
  4. Yogi

    Yogi Screenwriter

    Joined:
    Jul 25, 2002
    Messages:
    1,741
    Likes Received:
    0
    Trophy Points:
    0
    Always remember that at all volume levels the 3 db=2 x power relation holds true. If you are going from 1W to 2W or if you are going from 1000W to 2000W the gain is only 3db.
     

Share This Page