Sound Spectrum For CV-1800

B

bababrown

Member
Today I recorded my CV-1800 sound and ran an FFT on it. This CV-1800 does not have the stick. The program I'm using (LAMA 1.3) doesn't let me print if you can believe that! But there is a surprise. The line at roughly 350 Hz is in the noise. The strongest line is at about 700 Hz. The line at 1050 Hz is down 11 dB while the line at 1400 Hz is down about 8 dB.The levels drop off for the next few lines and then are down about 13 to 11 db at 2450 and 2800 Hz.The levels drop off thereafter. There is near continuous spectrum from 300 Hz to about 6 KHz below the spectral lines which I think is from air noise.(?)
We all thought the six blades at something under 3600 RPM should yield a strong line at about 350 Hz but that line is really in the mud. For some reason each blade apparently is making 2 pressure pulses per revolution.
bababrown
 
Spectrum Update

Spectrum Update

I used "Grab" to get a screen print of the spectrum. I'll see if they attach here.
 

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Thanks for posting that. Any thoughts as to why your spectrum shows a drop off below 500 Hz, vs the relatively flat spectrum below 500 posted by Eric a while back?
Bob
 
Spectrum Update

Spectrum Update

Bob,
I hadn't seen Eric's post. Interesting. His shows the dominant frequency near 350 Hz like I would expect. I'm beginning to think I have a low frequency rolloff somewhere in the hardware I used. I'll keep working it.
Bababrown
 
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