signals before peak?

[zangaidaige]

Hi
I test a open baffle speaker and find signal before peaks. I test several times and signal is always at -197ms before peak so it is not random noise.
Just confused with measurement!
anyone with similar experience?

 

[John Mulcahy]

Probably a distortion image.

 

[zangaidaige]

Probably a distortion image.

impulse is ifft of frequency response so I think harmonics should merge with peak?

I use window separate the peak from harmonics, however the distortion plot still show the harmonics?

 

[John Mulcahy]

impulse is ifft of frequency response so I think harmonics should merge with peak?

I use window separate the peak from harmonics, however the distortion plot still show the harmonics?

No, the frequency response is the FFT of the windowed IR. Log sweep deconvolution places distortion images at defined times before the linear response, those images are individually windowed to generate the distortion data when the measurement is made.