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In Reply to: Oops :-) you're right - it's watts rather than power (nt) posted by Christine Tham on December 5, 2005 at 11:11:59:
Some comments to your thread:
<"..you're right - it's watts rather than power">
Watts is the SI unit of power..
.
.
<"Basically a doubling of power is required for every 6dB increase in volume.">The rule people need to remember is that the input power must double for every 3dB increase in output.
Volume isn't a term used in engineering practice when describing a signal. It is thrown around loosely and may describe current, voltage, or power all of which are very different phenomena.
Your following example calls for a 6dB increase instead of 3dB per doubling of the input power..
.
.<"so, whilst 1 watt is required for 85dB, 10 watts are required for 91 dB, 100 watts for 97 and 1000 watts for 103dB, and 10000 watts is required for 109dB! Thus, in this particular situation, you do need more than 10000 watts for 110dB peaks! but that's not taking into account the effect of wall reflections in a contained space. And, you don't need 10000W to get 109dB">
The reason why you don't need 10kW isn't due to wall reflections, it is because you have illustrated the relationship between decibels and watts incorrectly.
The formula to use is:
Power in dBW = 10 * log ( Power in Watts / 1 )
Given your example of a speaker with a sensitivity of 85 dB W/m, the amplifier needs to provide 256 Watts to the input terminal of loudspeaker.
Here is table illustrating the relationship between input power and speaker output - dB SPL.
Watts (input) dB SPL (@1m)
------------- ... -----------
1 ...................... 85
2 ...................... 88
4 ...................... 91
8 ...................... 94
16 ..................... 97
32 ..................... 100
64 ..................... 103
128 .................... 106
256 .................... 109
I hope this helps.
-Jack
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Follow Ups
- You don't need 10000W, just 256W - Jack100 16:05:30 12/16/05 (0)
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