Sound Intensity Measurement

[ahfa]

Hi all,

If anybody can guide me about how to Calculate(predict) SPL at 1 m from the surface from Sound Intensity measurements. Basically I am trying to predict SPL(dBA) around motor at 1 m at left, right and rear side. Any spread sheet or guide will be much appreciated.


Thanks

ahfa

 

[Strong]

If you measured sound intensity at 1M, then why didn't you measure SPL? If you were using the 2-microphone method, then either of the two microphones will provide SPL.

Walt

 

[ahfa]

Hi Walt, I have measured intensity very close( approx 200mm) from the surface using grid system (Using Using LD 2900 LD 2250 Probe). I need to predict dBA value expected from this surface at 1 m from the surface.

Ahfa

 

[Strong]

I assume you know that Intensity integrated over the surface area is Sound Power, calculate SPL from area source and distance, and 1-m is in acoustic near field for mid to low frequencies. If I owned that expensive hardware, then I would measure the A-weighted SPL, in suitable environment, rather than inaccurately calculating it from precise sound intensity measurements.

Walt

 

[amanuensis]

Let's suppose you have carried out your measurement in semi-anechoic chamber.

Let Sm= Surface of the motor
Let Sp= Surface of a hemi-sphere = 2*pi*R^2=6.28
As Walt said,you can know Lw (Sound power Level) Lw=Li + 10*log10(Sm)

On the other hand, Lw= Lp + 10*log10(Sp)

So Lp=Li + 10*log10(Sm) - 10*log10(Sp)

 

[pcbman]

you need to either put the sensor closer to the source, or install multiple devices so that you can cover a wider area.