SPL Noise Contour plots

[donegalstevie]

Hi everyone,
I'm have an array of microphones (13 x 17) measuring pressure over a certain time period. I want to create a sound pressure level contour (SPL) plot from the pressure time histories for frequencies in the range (416 - 2,780 Hz). If I apply a fourier transform of the pressure time histories for SPL, I get a range of [dB] values for the associated frequency range but I only want 1 value per microphone in order to create my contour plot. A paper I have referenced says the pressure time histories should be frequency averaged. What does this mean?
Can anyone help me with this problem?
Thanks for any help.

Regards,
Stephen

 

[btrueblood]

Freq. average SPL = [(integral over freg. range) of SPL x freq.] (divided by) [(integral over freg. range) of freq.]

 

[GregLocock]

...and they almost certainly don't mean the average dB. I'm a bit surprised they don't want RMS SPL/freq range.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[donegalstevie]

Thanks for your replys. Thanks Greg for the links.
I'm measuring the noise generated form a model helicopter on a CFD software. After reading their results again, I realised that they averaged the frequency over a number of revolutions of the rotor blades to eliminate any random portions of the signal whereas I only measured the acoustic signal for 1 revolution. Sorry for any confusion.
I am still confused about how to generate my contour plots. I get very different values when I calculate the SPL using the RMS conpared to the values generated by the software.
The software seems to be taking the max SPL at each microphone to create the contour plot. Is this logical?

 

[GregLocock]

Not especially logical but they might be trying to measure annoyance which would be related to peak SPL



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[donegalstevie]

Thanks for the reply Greg. I think I found the solution. The SPL values can be combined using the following equation;
Combined dB = 10log(10^(dB1/10) + 10^(dB2/10) + ....... + 10^(dBn/10))