# Power spectral density plot converted to sound pressure level

112 views (last 30 days)
S_saleem on 3 Jun 2023
Commented: Star Strider on 4 Jun 2023
I have analysed a voltage signal and plotted the PSD. However, I need to produce a power-spectral-density plot from the data in terms of non-dimensional frequency. How do I calculate the Strouhal number for the frequency range and generate a power spectral density per unit Strouhal number plot for it?
nfft=2048;
window = hann(nfft);
overlap = 0;
[PSD, freq] = pwelch(det_data, window, overlap, nfft,fs);
figure;
plot(freq, 10*log10(PSD), 'b');
title('Power Spectral Density');
xlabel('Frequency (Hz)');
ylabel('Power Spectral Density (dB/Hz)');

Hiro Yoshino on 3 Jun 2023
The simplest way is this; try the following code without receiving the result from the function:
pwelch(det_data, window, overlap, nfft,fs);
It will show the PSD plot with the x-axis set normalized frequency.
S_saleem on 3 Jun 2023
I need to convert this PSD into SPL and then plot dB/St vs St plot. St=strouhal number. Can you help me with it?

Star Strider on 3 Jun 2023
To generate an SPL plot, and assuming compatible units (among other things) —
nfft=2048;
window = hann(nfft);
overlap = 0;
[PSD, freq] = pwelch(det_data, window, overlap, nfft,fs);
figure;
plot(freq, 10*log10(PSD), 'b');
title('Power Spectral Density');
xlabel('Frequency (Hz)');
ylabel('Power Spectral Density (dB/Hz)');
Pref = 20; % microPascals
SPL = pow2db(PSD/Pref^2);
figure
plot(freq, SPL)
grid
Calculating the Strouhal number is not possible.
While we can assume that f is frequency, and are nowhere defined, miuch less calculated.
.
S_saleem on 4 Jun 2023
Thank you very much. This is really helpful!! Please let me know how should I scale the ampltiude to a dB/V scaling factor of about 230 for this plot?
% %% PSD in terms of NON-DIMENSIONALIZed frequency
St= ((freq*Dj*0.001)/(Uj));
ss=(psd*Dj/Uj)/St;
plot(St, 10*log(ss))
title('Sound Pressure Level (SPL)');
xlabel('St');
ylabel('SPL (dB)');
xlim([0.1 1.5])
Star Strider on 4 Jun 2023
My pleasure!
I do not understand what you are doing, particularly with respect to ‘scaling factor’. (I am specifically helping only to get your code to run correctly.)
Please let me know how should I scale the ampltiude to a dB/V scaling factor of about 230 for this plot?
I do not understand what you are doing well enough to respond to that.
.