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In Reply to: Sorry guys--dark is correct, sser2 is wrong. Double or half power is a difference of 3 deciBels, not 6. posted by jeffreybehr on November 23, 2006 at 14:40:56:
on decibels and power in Wikipedia.One quotation from that article:
"A practical example
A fictional 2 way speaker (A box with separate driver for high("Treble") and low("Bass") ) has the following specs:High driver: 92 dBSPL @ 1W @ 1m. A Low driver: 86 dBSPL @ 1W @ 1m.
Now if we want to match the output of the two speakers so the sound is "equally loud" we need to do the following:
Get the difference between the two by subtracting the sensitivity:
Difference in sensitivity = A-B
= 92 dBSPL - 86 dBSPL
= 6 dBSPLAs we concluded earlier this 6dB difference requires that we double the power delivered to the low driver. Since a doubling in [power] relates to 3 dB, we need to adjust the cross-over unit in this system so that the [gain] of the Low signal is 3dB more than the Highs. If there is no crossover you can always adjust the Amplifier's output to be 3dB more."
Follow Ups:
Sorry, you can't use Wikipedia as proof text. It's user driven. I mean I could go there right now and make up anything I want and post it. It's true that over time someone will correct it but.......For something more definitive read Tremaine, page 1635, fig #25-105A. "DB versus power in Watts"
This graph shows if 1 watt is 30DB above reference then 10 watts is 40DB above reference. 2 watts is 33DB, 4 watts is 36DB and 8 watts is 39DB.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Just because it is written somewhere does not mean it's true. Look at the foolishness supported by a few authors like Crowhurst on the PP loading...:)if you can't get there from first principles( as in Tremaine ), one should consider conducting more research.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
...of a ratio of 2 different amounts of power. A deciBel (that's 10 times a Bel in metric terminology) is 10 times the base-10 log of the ratio.The base-10 log of 2 is 0.301. Ten times that is 3.01, and that round to 3, so double the power is 3dB.
Do not confuse subjective expressions of twice as loud or half as loud with the very precise definition of deciBel. And as for 6dB, I've read elsewhere that many people require a change of about 10dB before they'll say a loudness is twice or half.
-------------------------------------------------------
Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
For amplitude, e.g. voltage and sound pressure difference:XdB=20lg(X/Xo)
For power difference
XdB=10lg(X/Xo)
Hence 3 dB of power increase brings about 6 dB of SPL increase.
http://www.jblpro.com/pub/manuals/pssdm_1.pdf chapter 2http://www.analogrules.com/dbwatts.html good math, nicely explained
http://sound.westhost.com/class-a.htm table #2
http://www.bassbacke.de/hints/bass/cabproperties.htm another power vs.sound pressure chart
http://users.chariot.net.au/~gmarts/amppower.htm "double the power is equivalent to only a 3dB increase in volume! "
The math.
8 ohm speaker with 2.83 vrms is one watt.
2.83/8=.3538amps X 2.83 = 1 watt
with 4 volts rms we have 2 watts
4/8=.5amps X 4 = 2 watts.voltage
XdB=20lg(X/Xo)
4/2.83=1.1434.....log = .150723....X 20 = 3DBpower
XdB=10lg(X/Xo)
2/1=2 log=.301029..... X 10 = 3.01029..... DBTre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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