Intermodulation-distortion and Doppler-distortion ??

[Grasso789]

Thanks! The code must be wrong, for what i see in the spectrum plot, is amplitude modulation, say f2 +-(n*f1) with n=1,2,3 and so on. Frequency modulation does not show as discrete frequencies but as an even plateu with a center frequency of f2 and a width which is proportional to f1 and its amplitude.

 

[TMM]

Thanks! The code must be wrong, for what i see in the spectrum plot, is amplitude modulation, say f2 +-(n*f1) with n=1,2,3 and so on. Frequency modulation does not show as discrete frequencies but as an even plateu with a center frequency of f2 and a width which is proportional to f1 and its amplitude.

Nope, it's PM. Check the files with an audio editor and you'll see the amplitude never changes. An even plateu in the frequency domain only occurs if the modulation signal is evenly distributed noise - same for FM and AM so you can't really tell what kind of modulation you are looking at just by inspecting the spectrum. In the case of a sinusoidal modulation you get side bands at multiples of the modulation frequency. See:
Phase modulation

 

[Grasso789]

Thou are right about the appearance of the spectrum of a frequency-modulated signal, i stand corrected. Having let Cool Edit 96 generate sines modulated by 50 Hz, i can easily hear 2% Doppler at 200 Hz, 1% at 400 Hz, half a percent at 800 Hz, a quarter percent at 1600 Hz, an eighth percent at 3200 and a fourth percent at 6400 Hz. Hence, if i expect serious excursions, it is important to me to cross over before the presence range. Amplitude intermodulation seems to be different, having its easiest detectability at lower frequencies. It may also depend of the frequency of the modulating signal.

 

[MITsound]

A more thoro solution is to lower excursion by raising source size. This again introduces beaming. All ways lead to Rome, but there are only a few ways.

Uli[/QUOTE]

I used to use horns for their constant directivity, now I use dipoles above 800 hertz for this. Using stacked 15" woofers (in Onken cabinets for deep bass loading) limits their vertical radiation somewhat, and placing them nesr sidewalls allows allows boundary reinforcement to be eq'd down at lower frequencies. This results in still lower excursion, free clean bass, and subjectively cleaner sound, although I have no way to measure this, aside from movie sound being much easier to follow dialogue at low volume.