The importance and in fact the audibility of Doppler distortions in loudspeakers is a hotly debated topic, not a certain problem. And definitely no big deal unless the music contains low bass notes mixed w treble and nothing in between. Moreover it’s the same issue or nonissue with electromagnetic speakers as with ESLs.
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Dear @lewm : Always will be an issue if the main speakers crossover 250-300hz or even a little lower and the speakers goes as the neonnigth around 30-35hz. It's a certain problem depending on that crossover frequency and yes depending of the quality of the drivers will be more lower/higher audibility, but the problem is there. Like it or not.
" low bass notes mixed w treble and nothing in between " this makes no sense to me: do you? because harmonics are there.
It is not a theory and there is nothing to debate. It is much less of a problem for two and three way speaker systems because the bass driver's range is limited. It is a huge problem for our ESLs because they are full range. It is extremely noticeable with bass below 40 hz which few recordings have, but it still modulates the sound up to about 80 Hz. You hear it as a warble almost as if the speaker is shaking at high volumes. I think some do not notice it until it is gone. It bothered me right away as I tend to listen to bass heavy material at higher volumes. This resulted in my getting RH Labs subwoofers, a Dahlquist LP 1 crossover, and a pair of used Kenwood L07 M amplifiers. In typical audiophile fashion went things are getting too hot you turn up the temperature. This was back in 1979 and I am still trying to get it right although I think I am very close, 95% of the way there.
We had a lot of fun with the HQD system back in the day. Even though the Quads were crossed to subwoofers we blew them left and right giving demonstrations. I can still see Peter McGrath running back in the store room to come running back with a Quad on his shoulder, teeter tottering on a ladder replacing the upper unit. That people actually bought these things is beyond me. The Decca ribbon tweeter was even less reliable. I have no experience with modern quads because they are all point source speakers and I am a line source kind of guy. You might message skos and see what he thinks of the subwoofers and SLs. He has heard the system twice and is very opinionated.
I never said it was a “theory”. But there is plenty of debate about its significance and audibility. The only reason it’s of particular importance for ESLs is because they tend to be full range or nearly full range sources. The best reason to use a subwoofer with an ESL is far and away relieving the main amplifier and the main speaker of reproducing extreme low bass frequencies, not because of Doppler distortion, in my opinion. Also, and with respect, you do tend to choose from a list of causes to explain a list of objectionable effects without much experimental proof of a relationship between the two. If you heard what you heard and it was fixed by adding a subwoof, that’s not proof you heard Doppler distortion.
Dear @mijostyn : I refer to you because lew don't took in count my post to him, aniway here I come with you:
""" It is much less of a problem for two and three way speaker systems because the bass driver's range is limited. """
Not exactly " much less " because in a 2-way speaker normally its woofer goes from 50hz-60hz up to around 2.5khz and this kind of speakers ( its woofer ) goes down to 40hz even if you don't noted so there exist a really high IMD kind of distortions that subs relief the bass down there and midrange and HF shines as never before. Same with 3-way speakers.
We can't just stop the developed IMD that as you pointed out modulates/color the whole speaker reproduction. Maybe we don't noted because we already are accustommed to that color/modulattion but when we add a pair of self powered true subs and through high pass filters only a deaf audiophile can't hear that new and lowered distortions " color " with ( between others ) additional advantage that any amplifier will increment its headroom due that now is liberated of that main bass range.. If we like it the new " color " is not the main issue.
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