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<blockquote data-quote="Nick Hickman" data-source="post: 26422" data-attributes="member: 556">Re: Help me understand system limiting- setting itHi Charlie,With the numeric example I gave, I hoped to illustrate that no amount of hard (peak) limiting will prevent over-excursion because it ignores frequency.&nbsp; Take any waveform you want, lower it by an octave whilst keeping its amplitude (and peaks) unchanged and, all else being equal, excursion will quadruple.&nbsp; (&quot;All else&quot; pretty much will be equal for MF and HF drivers, but probably won&#039;t be for LF drivers where cabinet porting is involved.)Determining maximum excursion from the waveform isn&#039;t trivial and can be unintuitive.&nbsp; It&#039;s possible, for example, to change excursion without changing frequency content by fiddling with phase, and it&#039;s possible to have two signals with the same frequency content where the one with lower peak amplitude causes greater excursion.As an example of this, consider a signal containing three frequencies, F, 2*F, and 3*F all with peak amplitude 1V and all in phase.&nbsp; The RMS amplitude of the combined result is 1.22V RMS, the peak amplitude is 2.50V, and the peak displacement (in arbitrary units) is 1.08.&nbsp; Now, change only the phase of the 2*F component and shift it by 90 degrees.&nbsp; The RMS amplitude is unchanged, the peak amplitude is reduced to 2.03V, but the peak displacement is increased to 1.14.On a graph, a single cycle looks like this:<img src="http://100dB.com/misc/excursion.png" alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" />Of course, peak power is a danger to drivers, but not because of excursion.&nbsp; The right way to protect against over-excursion is with an appropriate HPF plus an appropriate power limiter.Nick</blockquote>

[QUOTE="Nick Hickman, post: 26422, member: 556"] Re: Help me understand system limiting- setting it Hi Charlie, With the numeric example I gave, I hoped to illustrate that no amount of hard (peak) limiting will prevent over-excursion because it ignores frequency. Take any waveform you want, lower it by an octave whilst keeping its amplitude (and peaks) unchanged and, all else being equal, excursion will quadruple. ("All else" pretty much will be equal for MF and HF drivers, but probably won't be for LF drivers where cabinet porting is involved.) Determining maximum excursion from the waveform isn't trivial and can be unintuitive. It's possible, for example, to change excursion without changing frequency content by fiddling with phase, and it's possible to have two signals with the same frequency content where the one with lower peak amplitude causes greater excursion. As an example of this, consider a signal containing three frequencies, F, 2*F, and 3*F all with peak amplitude 1V and all in phase. The RMS amplitude of the combined result is 1.22V RMS, the peak amplitude is 2.50V, and the peak displacement (in arbitrary units) is 1.08. Now, change only the phase of the 2*F component and shift it by 90 degrees. The RMS amplitude is unchanged, the peak amplitude is [i]reduced[/i] to 2.03V, but the peak displacement is [i]increased[/i] to 1.14. On a graph, a single cycle looks like this: [CENTER][IMG]http://100dB.com/misc/excursion.png[/IMG][/CENTER] Of course, peak power [i]is[/i] a danger to drivers, but not because of excursion. The right way to protect against over-excursion is with an appropriate HPF plus an appropriate power limiter. Nick [/QUOTE]

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