Stepped Sine or Pink PN in LIMP? - diyAudio
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Old 22nd October 2011, 05:05 AM   #1
sebDIY is offline sebDIY  Belgium
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Default Stepped Sine or Pink PN in LIMP?

Hi, I've done some measurements with LIMP. With resistances, no problem, it's very accurate, Stepped sine ou Pink PN gives similars results. But on loudspeakers, Pink PN gives peaks a little higher than Steppedd Sine. All over the curve is similar.

So what curve lies? Why these differences in loudspeakes testing and not resistances?

Thank.
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Old 24th October 2011, 07:13 AM   #2
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As you will have found, measuring the impedance with the pink noise signal is much quicker than with the stepped sine wave, but the measurement result usually shows much more noise on the resulting plot. A stepped sine wave will give a more accurate result. A lot of the problem is because the loudspeaker is also acting as a microphone and so the input to the sound card (that is measuring the voltage directly across the speaker) will also show this room noise. The stepped sound wave averages the input signal at each of the sine wave frequencies, so the effect of the room noise is much less.
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Old 25th November 2011, 04:49 PM   #3
JMB is offline JMB  United States
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There is also a difference due to the signal level. In general, there is voltage applied via Stepped Sine than via Pink noise and this will also impact T/S readings. I compared my results and then ultimately the box design and the impact was pretty small. There is much more error from other issues of design such as Qb, Qp, Ql issues, stuffing, port issues, etc. You are probably safe using either method but make certain that you are using small signal numbers with limited excursion of the driver as this was the foundation of the original T/S work.
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