I am bussy with a corespondence course in electronics and got the following question in an assignment. It sound a bit wrong to me (the uninformed one) and want to know if it make sense and what would the answer be? I don't grasp the dB thing yet, so please excuse silly questions 
(Maybe somebody can give me a "dB for Dummy's" explanation. )
Q:
Determine the dB level from a given sound power of 15dB, and a reference sound power of 20dB.
(Don't you measure sound power in Watts?)
Thanx for all help.
(Maybe somebody can give me a "dB for Dummy's" explanation. ) Q:
Determine the dB level from a given sound power of 15dB, and a reference sound power of 20dB.
(Don't you measure sound power in Watts?)
Thanx for all help.
I think the text writer needs the "dB For Dummies" course more than you do. Or at least a writing course. Sound power is given in watts OR in dB referenced to some standard power level.
Here's the entire course:
For power ratios, dB = 10 log (P1/P2)
Since power = V^2/R, and log (x^y) = y log x, then for a voltage ratio, dB = 20 log (V1/V2)
That's all there is, there ain't no more. If the dB quoted in the question are both referenced to the same standard power level, the answer is -5 dB.
Here's the entire course:
For power ratios, dB = 10 log (P1/P2)
Since power = V^2/R, and log (x^y) = y log x, then for a voltage ratio, dB = 20 log (V1/V2)
That's all there is, there ain't no more. If the dB quoted in the question are both referenced to the same standard power level, the answer is -5 dB.
dB's are a logarithmic scale. They are not absolute, and can be referenced to any point.
In this case they have told you the reference point (20dB).
The magic formulae I keep in my head are:
10*Log (P1/P2) (for power)
and
20*Log (V1/V2) for voltage (and other non squared values)
In other words, the dB figuer is describing the ratio between the 2 voltages, powers, or whatever...
You'll need to do some substitution...
Cheers,
In this case they have told you the reference point (20dB).
The magic formulae I keep in my head are:
10*Log (P1/P2) (for power)
and
20*Log (V1/V2) for voltage (and other non squared values)
In other words, the dB figuer is describing the ratio between the 2 voltages, powers, or whatever...
You'll need to do some substitution...
Cheers,
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