I meet a 4 dB gap in CFD-Post SPL calculation

- September 14, 2023 at 2:06 pm
  
  Liang Yifan
  Subscriber
  
  Hello,
  
  I start studying acoustics by CFD-Post these days. And I know the formula of SPL (sound pressure level) is SPL=20*log10(P/ref), ref=2e-5. So while P=1 Pa, the SPL should be 93.9794 dB.
  
  But when I use a sin signal to test the settings in CFD-Post, I do FFT and turn Y axis from magnitude to SPL, then I find it give a SPL 97.9588 dB at P=1 Pa. There is a 4 dB gap with the 93.97 dB it should be.
  
  Dose anyone meet the same problems? Can anyone tell me how to fix it, thanks very much.
- September 20, 2023 at 2:15 pm
  
  Federico
  Ansys Employee
  
  SPL = 20*log10(Prms/Rref).
  Also, why are you getting 2 tones from your sine wave?
  - September 23, 2023 at 10:35 am
    
    Liang Yifan
    Subscriber
    
    I give a signal like S=0.7*sin(2*pi*50)+1*sin(2*pi*70).
    So there are tones at the 50Hz and 70Hz.