Still trying to decide what design to go with, for "portable" DJ / Rock band subs. I'm afraid this question may have to easy answer, but I'll try, anyway:
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I REALLY like the PPSL concept, but I'd probably have to use dual 12". (Or maybe those B&C 14's, but I dunno...)
The other way is to build two (maybe four) single 15" TH horns, but make them push-pull when grouped together. Easy enough to do. I wouldn't get the odd-order distortion reduction of PPSL, nor the phase improvement, but at least I'd still get good 2nd order harmonic reduction. Plus, using really good drivers, the other artifacts could be minimized to some degree.
I would MUCH rather do the PPSL, and the efficiency loss isn't too horrible. By my calculations I will be fine. I can probably also get decent extension to at least 40 Hz, without too much compromise.
## HOWEVER, the one thing that really bugs me is how much cone excursion I'd have with the 12's. I assume that, for any given volume, those 12's are going to be doing the Harlem Shuffle all night long. That means more modular distortion, and more doppler distortion.
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So I'm wondering:
Given the long wavelengths involved, and the relatively small amount of excursion even in worst case situations, should I be worried about this? Would the 12's sound more muddy due to this, all other things being equal?
And a stranger thought:
With PPSL, the drivers are mounted "sideways" relative to the listening position. I realize that bass is almost completely non-directional. but could this minimize doppler distortion? (I can't wrap my head around this, though I figure there's probably no free lunch at this event.)
------------------------
I REALLY like the PPSL concept, but I'd probably have to use dual 12". (Or maybe those B&C 14's, but I dunno...)
The other way is to build two (maybe four) single 15" TH horns, but make them push-pull when grouped together. Easy enough to do. I wouldn't get the odd-order distortion reduction of PPSL, nor the phase improvement, but at least I'd still get good 2nd order harmonic reduction. Plus, using really good drivers, the other artifacts could be minimized to some degree.
I would MUCH rather do the PPSL, and the efficiency loss isn't too horrible. By my calculations I will be fine. I can probably also get decent extension to at least 40 Hz, without too much compromise.
## HOWEVER, the one thing that really bugs me is how much cone excursion I'd have with the 12's. I assume that, for any given volume, those 12's are going to be doing the Harlem Shuffle all night long. That means more modular distortion, and more doppler distortion.
-------------------
So I'm wondering:
Given the long wavelengths involved, and the relatively small amount of excursion even in worst case situations, should I be worried about this? Would the 12's sound more muddy due to this, all other things being equal?
And a stranger thought:
With PPSL, the drivers are mounted "sideways" relative to the listening position. I realize that bass is almost completely non-directional. but could this minimize doppler distortion? (I can't wrap my head around this, though I figure there's probably no free lunch at this event.)
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When drivers are pushed beyond Xmax, the HF distortion compliment is modulated by the frequency of the lower tones- Amplitude Modulation (AM) distortion. "Doppler distortion" in speakers is a myth.
"Doppler Distortion" does not exist in the true sense, as the frequency shift caused by cone movement is far to little to be heard (it would be on the order of one millionth of a musical note), but AM distortion is a very real phenomenon, and sounds horrible.
AM distortion occurs when a driver's excursion exceeds the linear range of operation, which causes a change in level (amplitude) of the higher frequencies at the same rate (modulation) of lower frequencies. The effect is quite pronounced, making voices sound like they are gargling, and the onset is rather rapid after Xmax (the limit of linear excursion) is exceeded.
Take a 20 Hz tone to a woofer, turn it up so the cone is moving beyond Xmax, (probably only a few watts needed below Fb) then play a vocal track through it at the same time- the vocal track will sound "garbled" until the tone is reduced below Xmax.
As long as you don't push your subs beyond Xmax/Xvar, AM distortion is of no concern.
If the subs are crossed over at 100 Hz or so, AM distortion won't be a problem no matter how hard you push them- it's a problem with woofers used wide range, like over a decade- 30-600 Hz, 50-1000 Hz, etc.
Dave Rat has some online videos demonstrating the sound.
"Doppler Distortion" does not exist in the true sense, as the frequency shift caused by cone movement is far to little to be heard (it would be on the order of one millionth of a musical note), but AM distortion is a very real phenomenon, and sounds horrible.
AM distortion occurs when a driver's excursion exceeds the linear range of operation, which causes a change in level (amplitude) of the higher frequencies at the same rate (modulation) of lower frequencies. The effect is quite pronounced, making voices sound like they are gargling, and the onset is rather rapid after Xmax (the limit of linear excursion) is exceeded.
Take a 20 Hz tone to a woofer, turn it up so the cone is moving beyond Xmax, (probably only a few watts needed below Fb) then play a vocal track through it at the same time- the vocal track will sound "garbled" until the tone is reduced below Xmax.
As long as you don't push your subs beyond Xmax/Xvar, AM distortion is of no concern.
If the subs are crossed over at 100 Hz or so, AM distortion won't be a problem no matter how hard you push them- it's a problem with woofers used wide range, like over a decade- 30-600 Hz, 50-1000 Hz, etc.
Dave Rat has some online videos demonstrating the sound.
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You are a gent, Art, thank you for taking the time to explain technical things in detailed 'plain english' for those of us learning! 🙂
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