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X/M-32 Subs on DCA
Old 2 weeks ago
  #31
Lives for gear
 

Quote:
Originally Posted by jetam View Post
Cutoff frequency and crossover frequency aren't the same. Cutoff frequency of a filter is a frequency at which the amplitude is reduced by certain amount ( usually 3 dB). Crossover frequency is a frequency at which the amplitude of one signal starts overtaking the other i.e. both signals have equal amplitude.

I haven't mentioned anything about phase yet, although you keep implying so. But if you really want me to dive into this territory ...
If you have two speakers crossed over by a pair of L-R filters set to e.g. 100 Hz and time-aligned so that they are in phase at 100Hz and change the gain of one of them , this won't affect the phase at 100 Hz, but becuse most speakers don't have a flat phase reaponse and the filters aren't infinitely steep, you'll get some change in phase response in the overlapping area where the speakers weren't perfectly in phase from the begining.
c'mon! alignment between subs and tops can only be achieved for one frequency at the time (and hence for one distance) but cannot work over a large bandwidth (unless we add a bunch of allpass filters which, except for some processors and the ssl live desks not too many gear offers, so irrelevant for this thread).

generally, all we need to do in terms of alignment is to make sure we get phase coherence at the crossover frequency - again: adjusting the level of a frequency band does not affect the phase coherence (as any measurement will quickly reveal) but of course the overlap changes and a gradual phase shift over frequency can also be measured: the wider the overlap, the larger the phase shift

it is absolutely irrelevant however as a) the level will drop (according to the slope), b) lower level will get masked and c) absolute phase cannot be heard.

really, have a look at any visualisation or measure/analyze as you tweak a system - then come back (or better start a new thread in which you can try to challenge laws of physic in every way you want; be assured i will NOT chime in or hire you as a system tech)...
Attached Thumbnails
X/M-32 Subs on DCA-20191123_174019.jpg   X/M-32 Subs on DCA-20191123_174225.jpg  
Old 2 weeks ago
  #32
Gear Head
 

Look at your own images, x-over image1: 100Hz, image2: around 110Hz. You will now get a bump at new x-over as the filters are „magically“ not only coherent at 100Hz. But this is irrelevant as we are talking about acoustic x-over of speakers in a room not electrical of your filters (which everything relies upon, of course). You said it yourself, fire up smaart, measure top, align sub, look where magnitude meets (x-over), look at both phase graphs at ACOUSTIC x-over (I bet you done this before, lower sub volume, look at new x-over and phase at that new point. Phase response as a whole hasn’t changed a bit, but the relationship between sub and top surely not as coherent, because you aligned it to first (higher) x-over point. However, every system I looked at had a reasonable range of coherency around x-over, otherwise you couldn’t step away from your point of measurement. As your Highness of course knows everything within 90 deg phase shift still sums to 3db, how else would you align your subs to the whole venue? How else could sub arrays work? Sure this all is highly dependent on the individual phase responses of the speakers used, but every standard manufacturer like Meyer, L-Acoustics, Fohhn, d+b and cheaper ones will make it easy for you to get matching phase slopes in the x-over region. Some just wont match and there you’ll get your „coherence at just one frequency“.
Old 2 weeks ago
  #33
Lives for gear
 

Quote:
Originally Posted by Its Mork View Post
Look at your own images, x-over image1: 100Hz, image2: around 110Hz. You will now get a bump at new x-over as the filters are „magically“ not only coherent at 100Hz. But this is irrelevant as we are talking about acoustic x-over of speakers in a room not electrical of your filters (which everything relies upon, of course). You said it yourself, fire up smaart, measure top, align sub, look where magnitude meets (x-over), look at both phase graphs at ACOUSTIC x-over (I bet you done this before, lower sub volume, look at new x-over and phase at that new point. Phase response as a whole hasn’t changed a bit, but the relationship between sub and top surely not as coherent, because you aligned it to first (higher) x-over point. However, every system I looked at had a reasonable range of coherency around x-over, otherwise you couldn’t step away from your point of measurement. As your Highness of course knows everything within 90 deg phase shift still sums to 3db, how else would you align your subs to the whole venue? How else could sub arrays work? Sure this all is highly dependent on the individual phase responses of the speakers used, but every standard manufacturer like Meyer, L-Acoustics, Fohhn, d+b and cheaper ones will make it easy for you to get matching phase slopes in the x-over region. Some just wont match and there you’ll get your „coherence at just one frequency“.
we must live on different planets:

the pics i posted were a starting point for an emulation of a lake controller for a flaslight system which nirmally gdts driven vua lake/lab - could have been for any other system as well, i choose the example to illustrate my point that the phase does not change as the levels get changed - as anyone can see!

with a typical sub array along the stage and a pair of main hangs, the subs cannot get aligned to measure equally well in terms of phase coherence to the mais in all positions of a venue, no matter what gear you're using (unless the place is small enough so subs are used for loading the room/to smooth out room modes: alignment then indeed doesn't matter much)!

i stand firm: getting everyone the same sound in a venue ain't possible; multiple measurement positions will reveal it quickly - phase/delay would need to be different for each position (which let's me repeat that subs can only get aligned for one distance/frequency).

anyway, hope you get happy with your view on things...
Old 2 weeks ago
  #34
Gear Head
 

Quote:
Originally Posted by deedeeyeah View Post
i choose the example to illustrate my point that the phase does not change as the levels get changed - as anyone can see!
That's what I wrote about four times by now. Phase does !>_NOT_<! change. NOT!
Now forget the Lake and look of the phase response of a main hang vs the subs. You align the phase AT MEASUREMENT POSITION to say 100 Hz. Phase difference is now ideally 0 deg at 100Hz. Now you turn down the subs. Phase difference at 100Hz IS STILL 0 deg. But now the acoustic x-over point is say 90Hz where phase difference was say 20deg before you turned down the subs and STILL IS after you turned down the subs. PHASE DID NOT NOT NOT CHANGE, but you effectively lowered the x-over point to 90Hz by turning down the subs and therefore introduced 20deg phase shift THAT WAS THERE TO BEGIN WITH, but now it's at your new x-over point at the measurement position. Nothing happened inside your controller it's about where the speakers meet at measurement position. I don't know how I can make that more clear.

Quote:
with a typical sub array along the stage and a pair of main hangs, the subs cannot get aligned to measure equally well in terms of phase coherence to the mais in all positions of a venue, no matter what gear you're using (unless the place is small enough so subs are used for loading the room/to smooth out room modes: alignment then indeed doesn't matter much)!

i stand firm: getting everyone the same sound in a venue ain't possible; multiple measurement positions will reveal it quickly - phase/delay would need to be different for each position (which let's me repeat that subs can only get aligned for one distance/frequency).
Never said that, I agree completely. I mentioned sub arrays because you made it sound like there is one frequency like 100Hz where there is coherence and therefore coupling but at 101Hz there is no interaction. I see that you know much better, as you stated yourself that phase relationship is different for each position, which is also kind of my point
Old 2 weeks ago
  #35
Lives for gear
 

maybe me (not native english-speaking)...
Old 2 weeks ago
  #36
Gear Head
 

Me neither... so maybe both of us Next time we geek out in German
Old 2 weeks ago
  #37
Non! Plz keep it auf English. Great thread with a lot of useful points and much socratic push&pull. Subject confuses lots of us and the answer is as usual, it depends, but much food for thought here. Which is why we all come here.
WalterT
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