Trace arithmetic.

sm52

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John, hi. I have the impedances of four drivers connected in parallel to a signal source. Using trace arithmetic to find out their total impedance. But it is difficult. There are 17 mathematical operations to be done, as I calculated. If A,B,C,D are impedances, then A*B*C*D/(A*C*D+B*C*D+A*B*C+A*B*D) is needed. Is there an easier way to do my task with REW?
 

John Mulcahy

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If for some reason you can only measure the impedance of each driver individually you could try generating the inverse of the sum of their inverses, otherwise just make a measurement of the 4 connected in parallel.
 

sm52

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Inversion of measurement A Is 1/A?
I have not yet managed to get what I wanted in the first post using trace arithmetic. I have the total impedance of these four drivers from the crossover simulator. It is not the same as it turns out if 1/(1/A + 1/B + 1/C + 1/D).
 

John Mulcahy

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Yes, inverse is 1/A. Perhaps it would be easier to put the impedances in a spreadsheet and calculate the overall impedance there.
 

sm52

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Question about the generator.
I want to write files from generator with noise. There are several additional options there. What settings of these parameters would you recommend for general purposes? So that the noise signal is more consistent with the musical one with more instruments.
 

John Mulcahy

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For general purpose I would use Pink Periodic Noise. What constitutes a more music-like signal is a topic of debate (what kind of music would also be a factor). Meyer sound have created M-noise to have a dynamic profile closer to music for maximum level testing.
 

sm52

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Pink Periodic. Minimise crest factor is better to leave? Sequence length is also 16k by default?
 

John Mulcahy

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Sequence length should match the RTA FFT length. Not minimising the crest factor will produce a signal that is a bit more like music in its peak to rms ratio.
 

sm52

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Sequence length can be changed in the generator. But RTA FFT length is missing from the generator. These two parameters must match. What changes if they are both 16k, and in the other case 256k?
 

John Mulcahy

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REW automatically adjusts the sequence length to match the FFT length selected in the RTA. If you manually change the sequence length afterwards you get the effects shown in the help.
 
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