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<blockquote data-quote="thch" data-source="post: 1315933" data-attributes="member: 562032">or a good DMM and a lot of time and blissful ignorance of engineering basics.for one you have to be sure you want the gain to be the same as the DMM method reccomends.second you have to assume that the charging sysem never changes, ever.&nbsp; the speakers cannot signifigantly affect the amp (or test with the speakers in).but if you ignore those, you can determine distortion based upon iteritive tests.&nbsp; a high pass crossover is a great tool because it will filter out the normal signal but pass&nbsp; distortion from clipping.&nbsp; as you turn up volume, you alternate between 2 settings on the HU.&nbsp; you know that this should give a 2dB increase*.&nbsp; if the AC voltage on the highpass filter output increases by more then 2dB then extra energy is in the system (highpass sytem i mean).&nbsp; or if the output before the highpass jumps by less then 2dB then some energy is not being output = clipping.the highpass filter gives better resolution.&nbsp; i&#039;m not sure either method is any better then the ear method.&nbsp; you probably can&#039;t distinguish THD less then 5% with this method.&nbsp; at least without building custom hardware (a bandstop filter to completely cut out 60hz, so that only distortion is measured)***example only, actual HU could also have 1dB or 3dB steps.** among other things.</blockquote>

[QUOTE="thch, post: 1315933, member: 562032"] or a good DMM and a lot of time and blissful ignorance of engineering basics. for one you have to be sure you want the gain to be the same as the DMM method reccomends. second you have to assume that the charging sysem never changes, ever. the speakers cannot signifigantly affect the amp (or test with the speakers in). but if you ignore those, you can determine distortion based upon iteritive tests. a high pass crossover is a great tool because it will filter out the normal signal but pass distortion from clipping. as you turn up volume, you alternate between 2 settings on the HU. you know that this should give a 2dB increase*. if the AC voltage on the highpass filter output increases by more then 2dB then extra energy is in the system (highpass sytem i mean). or if the output before the highpass jumps by less then 2dB then some energy is not being output = clipping. the highpass filter gives better resolution. i'm not sure either method is any better then the ear method. you probably can't distinguish THD less then 5% with this method. at least without building custom hardware (a bandstop filter to completely cut out 60hz, so that only distortion is measured)** *example only, actual HU could also have 1dB or 3dB steps. ** among other things. [/QUOTE]

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