Distortion...can a low pass filter change the breakup in the woofer at higher frequencies

[Nwickliff]

Take the Klipsch RP600m speaker. It shows some distortion in the woofer around 600hz but this is playing full range. If 80hz is cut and passed to the sub does this also lower the distortion at the 600hz since the woofer is having to do less work overall? Furthermore, how important is 2nd order harmonic distortion compared to the rest? My understanding was that it was not as audible or objectionable to others as it will be masked by the fundamental. Why does the 2nd order equal the THD if the other distortions are so much further down in percentage?

can I measure the distortion myself using REW?

Thanks, everyone.

 

[Juhazi]

REW is OK, but doing measurements reliably is not easy, everything is relative...

https://www.audioholics.com/loudspeaker-design/loudspeaker-measurement-standard
https://audioxpress.com/article/Measurement-and-Perception-of-Regular-Loudspeaker-Distortion
https://www.audioholics.com/loudspeaker-design/audibility-of-distortion-at-bass

 

[Nwickliff]

REW is OK, but doing measurements reliably is not easy, everything is relative...

https://www.audioholics.com/loudspeaker-design/loudspeaker-measurement-standard
https://audioxpress.com/article/Measurement-and-Perception-of-Regular-Loudspeaker-Distortion
https://www.audioholics.com/loudspeaker-design/audibility-of-distortion-at-bass

I could measure the relative difference, however though, could I not? Before and after LPF?

 

[Juhazi]

Yep. Just use high enough spl. Actually random distortion measurementes that we can see in www cannot be compared to each other at all. Measurement conditions must be fixed or standardized. A diy person can dot that at home and especially tests like you proposed, changing just one parameter at the time without touching anything in the environment.

https://www.roomeqwizard.com/help/help_en-GB/html/graph_distortion.html
https://www.diyaudio.com/forums/software-tools/338511-howto-distortion-measurements-rew.html
https://www.audiosciencereview.com/...w-to-measure-speaker-distortion-in-rew.14397/

 

[ebslo]

Distortion is usually measured with a frequency sweep so there is only one frequency on the input at a time. So no, high-pass filtering (you did mean high-pass, right?) at 80Hz will not make any difference to the measured distortion at 600Hz. But it may still make a difference to distortion while playing back actual music. You can test for this by playing two tones simultaneously, one at 600Hz and one < 80Hz, and use the REW RTA to measure harmonics of the 600Hz tone. Compare result with another measurement with only the 600Hz tone playing.

 

[hyperplanar]

Take the Klipsch RP600m speaker. It shows some distortion in the woofer around 600hz but this is playing full range. If 80hz is cut and passed to the sub does this also lower the distortion at the 600hz since the woofer is having to do less work overall? Furthermore, how important is 2nd order harmonic distortion compared to the rest? My understanding was that it was not as audible or objectionable to others as it will be masked by the fundamental. Why does the 2nd order equal the THD if the other distortions are so much further down in percentage?

can I measure the distortion myself using REW?

Thanks, everyone.

High passing the speakers would improve their intermodulation distortion, but not its harmonic distortion (which is the graph REW shows you from doing a sine sweep measurement). This is because the sine sweep only plays one frequency at a time, so there is no possibility of the low frequencies affecting the high ones in that scenario. To compare the difference in distortion, you'll need to use the multitone generator in REW and compare the before/after.

Arguably, IMD is much more important than HD as it is much more sonically disagreeable, but I don't think a standardized measurement has been agreed on for easy comparison between speakers. There is also a correlation between more HD -> more IMD, but IMD is affected by the ranges that the drivers are allowed to play. If you had a hypothetical 2-way and 3-way speaker that had identical HD graphs, the 3-way speaker would have less IMD simply due to each driver not playing as wide of a range of frequencies at once, limiting the potential for intermodulation between frequencies.

 

[ebslo]

WRT 2nd harmonic, it's included in Total Harmonic Distortion (THD) because THD includes all harmonics by definition. Power-of-two harmonics (2, 4, 8, etc.) are more benign than others because they are the same musical note as the fundamental but in different octaves, nevertheless all harmonics are weighted equally for THD calculation (up to the measurement bandwidth).

 

[Juhazi]

Yes, IMD measurements are the ones to use in OP's dilemma. REW gives good possibilities for that with it's signal generator. Then RTA option is used for measurement, toggle Distortion display! User can set frequencies free. https://www.roomeqwizard.com/REWhelp.pdf

 

[dualazmak]

This is an interesting and important discussion, I believe.

Not only for distortion measurements, but also,,,

For the frequency response (relative SPL) measurements, I always struggle with the choices of rapid sharp sine sweep, cumulative pink noise averaging, or cumulative white noise averaging, especially in my multichannel multi-driver (multi-way) multi-amplifier system with software digital crossover in upstream within PC. And, also the choices FFT size depending on the Fq zones, as well as the choices other smoothing algorisms (REW's psychoacoustic smoothing is one example), would be important.

I believe there should be no single best method, but I need test these methods, analyses and FFT representations having enough knowledge and understandings on why I see the different results depending on these.

I am really interested in frequency response (relative SPL) measurements not only in actual SP sound at listening position with measurement microphone but also in digital level in PC, in multichannel-DAC's analog output level, and in amplifiers' SP output level. I am currently working on these as you can find my post here and thereafter. Currently starting this weekend, I am intensively testing the cumulative white noise averaging, and the method and results will be shared there within a month or two.