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Re: A correction on one point

Hi Bill

Well I have not tested every implementation but MLS as supplied with Lspcad, or as software for the TEF machine, does not accurately measure acoustic phase.
Also, Smaart for example, does not.

A phase “reality check” I devised.

Take a crossover or filter design program, model up a “perfect speaker” with the following parameters. High pass , 4 th order at say 100Hz and a 2nd order low pass at say 5KHz.
One gets a phase plot one expects from those amplitude changes.
Now, using a dsp speaker controller, construct this filter alignment and add say 3ms fixed time delay to simulate the speaker to mic distance.

Now, test this instead of a real speaker and set the measurement delay.
If the phase plot is the same as the predicted one for a filter with no delay, then it measures phase.
If its like the ones above, the phase curve is not the same, it is a different (wrong) slope at each end.
Best,

Tom

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