terry, I think everything is already answered here:
http://www.mehlau.net/audio/multisub_geddes/
http://www.mehlau.net/audio/multisub_geddes/
Hi Terry
Does it function?
What I do is simply increase volume and X-over on the sub, in order to have more over lapping between mains and sub. Then let my wife handle the phase control until I'm satisfied. That is about the only time my vife has control over my stereo.
Maybe we are a weird family but my children, 4 and 6 years, can hear when it's correct. Out of phase sounds like ear drums are sucked in different directions, so-to-say, + one has a bass increase when correct. It's easy to detect when once heard.
Ooops, here comes wifey, better turn off computor
Does it function?
What I do is simply increase volume and X-over on the sub, in order to have more over lapping between mains and sub. Then let my wife handle the phase control until I'm satisfied. That is about the only time my vife has control over my stereo.
Maybe we are a weird family but my children, 4 and 6 years, can hear when it's correct. Out of phase sounds like ear drums are sucked in different directions, so-to-say, + one has a bass increase when correct. It's easy to detect when once heard.
Ooops, here comes wifey, better turn off computor
Phase in the context of a plate amp mostly means + -, nothing more. Some amps have continuous phase, but not many. With a DCX I believe you also have delay. This is even more effective - has huge effects. But the bottom line is whatever gets you the response you are looking for is correct. No need to worry about what that actually is just so long as the end result is right.
hi markus, rest assured I have read your little article, and I even bookmarked it for ease of discovery for when I give the distributed subs another go (this time I'll do it right, promise!!)
I guess my question came out of the mucking about I did with delay (I do recall mentioning what I found in the setting up the nathan thread) where basically at the low frequencies I was playing with I could not detect any change no matter the delay I set. (That was significant to me because previously I was 'certain' I could in fact hear sub delay)
I was trying to accurately measure (rather than calculate) the delay required, was trying to use audacity to do it IIRC, but there was nothing I could find that gave accurate measurements.
Same with phase, unless it's simply a 'smoother FR thruout the region in question'???? Which may be backed up by this little snippet from your writeup to see if you can get a better response by changing the gain, the low pass point, the phase and or delay if you have it
Think I even asked this question in the nathan thread, and not sure it really got answered (maybe I asked it elsewhere, dunno), but in any case what exactly is phase and why do we adjust for it?
basic question I know, but hey let's at least all get on the same page. Is phase and delay kinda two sides of the same coin, ie they are important simply because of distance? ie distance is a factor in both?
peter, maybe I can borrow your wife? might be quicker and simpler?
EDIT thanks earle. so basically the measurement I was chasing is simply FR as I posited just before?? Huhh, now delay is important again??? my poor head is spinning heh heh, esp as I recall that it was you thatalways maintained that my belief that I could hear different delay between subs was 'not supported by the data' (whilst I in my arrogance believed I was right....until I did my own experiment described before.....and realised to my own satisfaction that delay in the order found in normal rooms is not significant)
I guess my question came out of the mucking about I did with delay (I do recall mentioning what I found in the setting up the nathan thread) where basically at the low frequencies I was playing with I could not detect any change no matter the delay I set. (That was significant to me because previously I was 'certain' I could in fact hear sub delay)
I was trying to accurately measure (rather than calculate) the delay required, was trying to use audacity to do it IIRC, but there was nothing I could find that gave accurate measurements.
Same with phase, unless it's simply a 'smoother FR thruout the region in question'???? Which may be backed up by this little snippet from your writeup to see if you can get a better response by changing the gain, the low pass point, the phase and or delay if you have it
Think I even asked this question in the nathan thread, and not sure it really got answered (maybe I asked it elsewhere, dunno), but in any case what exactly is phase and why do we adjust for it?
basic question I know, but hey let's at least all get on the same page. Is phase and delay kinda two sides of the same coin, ie they are important simply because of distance? ie distance is a factor in both?
peter, maybe I can borrow your wife? might be quicker and simpler?
EDIT thanks earle. so basically the measurement I was chasing is simply FR as I posited just before?? Huhh, now delay is important again??? my poor head is spinning heh heh, esp as I recall that it was you thatalways maintained that my belief that I could hear different delay between subs was 'not supported by the data' (whilst I in my arrogance believed I was right....until I did my own experiment described before.....and realised to my own satisfaction that delay in the order found in normal rooms is not significant)
I have 0-180 continous variation and it goes quite a long way with placement also, but I (probably) agree as I have never been fully satisfied with a sub. Or better to say, with the tested subs.(And do not mention several subs as I hate to have cables everywhere in the room
)Could be other issues of course. But for now, I still prefer to hear the whole (or at least some of it) register coming from the mains.
Oboy! wife=quick'n'simple. Equation impossible!!
Terry,
I am not sure what is built in the DCX2496 but I have seen some circuits claiming doing 0-180degree phase shift doggy. The problems could be too much phase shift at undesirable frequencies (say above 200Hz) or having a 4dB roll-off at 20Hz, etc. So I don't trust the phase shift nobs provided by normal commercial subs any more. Fortunately, I don't buy them but am building my own. The Linkwitz Pheonix subwoofer is excellent and you get the free plan from Linkwitz' site.
Two days ago while designing my PCB for the implementation of multiple subs I managed to work out a simple single stage phase shift circuit based on the standard allpass filter that can change the phase between 20Hz to 200Hz from about 9degree to 160degree with flat frequency response by turning a 100k trimpot. This would be good enough to do the work. Unfortuately, I have changed my ISP so I don't know the URL for my new web space therefore, can not post it here in the forum to share with others. For 180degree to 360degree, you can simply swap the +/- speaker leads or add an inversion stage with one opamp and 2 resistors.
Moving the subs around the room can achieve the same thing as phase shift (of course, other paramters, such as SPL and room modes would change as well). For example, a 100Hz signal has 3.4 metre wave length, moving the sub by 3.4 / 4 = 0.85 (metre) would cause a phase shift of 90degree at 100Hz, and 45degree at 50Hz.
As discussed earlier, I am a "Geddes multiple sub" convert and believe that there are numerous, unpredictable room modes in a typical room with "irregular" shapes due to openings, furnitures, etc, and it is impossible to change a single sub's phase to solve all room mode problems. So I am not surprised that you heard no difference by changing the phase of a single sub.
Don't we get a big head when we need to analyse all those room modes, the peaks (reinforcements, standing waves, etc) and nulls (cancellations, etc) in a typical room? Simulations would give us good education about room effects and help us understand them, but serves barely any value in real life room set up - they simple don't work with real rooms, as we simply have no accurate data for absorption efficiency, etc.
Even though I had a pure maths degree ages ago, I still don't bother to look at the maths involved, as I would be heading to a wrong path. We could align a single subwoofer to change one room mode, effective only at a narrow bandwidth and worse, possibly at specific location within the room, and even worse, cause some new peaks and dips in other frequencies or at other locations in the room.
Using multiple subs at random locations may solve the problem. Let me make an analgy - If there is only one or two fish (room mode) in a fish pond (room) and we want to catch it (them), we can directly target it (them). If there are hundreds of fish in a small pond in a fish farm and we want to catch the fish, we don't target the fish individually, we would just use a net (multiple subs) and swipe through the water (i.e. at random) and we would catch most fish that way. The remaining a few fish can then be targeted (by using a couple of notch filter, etc).
I guess moving multiple subs around the room and turning the SPL and phase nobs to obtain the best sound by ears or (best) by measurement is a simple and effective solution.
Regards,
Bill
I am not sure what is built in the DCX2496 but I have seen some circuits claiming doing 0-180degree phase shift doggy. The problems could be too much phase shift at undesirable frequencies (say above 200Hz) or having a 4dB roll-off at 20Hz, etc. So I don't trust the phase shift nobs provided by normal commercial subs any more. Fortunately, I don't buy them but am building my own. The Linkwitz Pheonix subwoofer is excellent and you get the free plan from Linkwitz' site.
Two days ago while designing my PCB for the implementation of multiple subs I managed to work out a simple single stage phase shift circuit based on the standard allpass filter that can change the phase between 20Hz to 200Hz from about 9degree to 160degree with flat frequency response by turning a 100k trimpot. This would be good enough to do the work. Unfortuately, I have changed my ISP so I don't know the URL for my new web space therefore, can not post it here in the forum to share with others. For 180degree to 360degree, you can simply swap the +/- speaker leads or add an inversion stage with one opamp and 2 resistors.
Moving the subs around the room can achieve the same thing as phase shift (of course, other paramters, such as SPL and room modes would change as well). For example, a 100Hz signal has 3.4 metre wave length, moving the sub by 3.4 / 4 = 0.85 (metre) would cause a phase shift of 90degree at 100Hz, and 45degree at 50Hz.
As discussed earlier, I am a "Geddes multiple sub" convert and believe that there are numerous, unpredictable room modes in a typical room with "irregular" shapes due to openings, furnitures, etc, and it is impossible to change a single sub's phase to solve all room mode problems. So I am not surprised that you heard no difference by changing the phase of a single sub.
Don't we get a big head when we need to analyse all those room modes, the peaks (reinforcements, standing waves, etc) and nulls (cancellations, etc) in a typical room? Simulations would give us good education about room effects and help us understand them, but serves barely any value in real life room set up - they simple don't work with real rooms, as we simply have no accurate data for absorption efficiency, etc.
Even though I had a pure maths degree ages ago, I still don't bother to look at the maths involved, as I would be heading to a wrong path. We could align a single subwoofer to change one room mode, effective only at a narrow bandwidth and worse, possibly at specific location within the room, and even worse, cause some new peaks and dips in other frequencies or at other locations in the room.
Using multiple subs at random locations may solve the problem. Let me make an analgy - If there is only one or two fish (room mode) in a fish pond (room) and we want to catch it (them), we can directly target it (them). If there are hundreds of fish in a small pond in a fish farm and we want to catch the fish, we don't target the fish individually, we would just use a net (multiple subs) and swipe through the water (i.e. at random) and we would catch most fish that way. The remaining a few fish can then be targeted (by using a couple of notch filter, etc).
I guess moving multiple subs around the room and turning the SPL and phase nobs to obtain the best sound by ears or (best) by measurement is a simple and effective solution.
Regards,
Bill
Terry
Delay is phase, that is correct, except that delay can extend to many times around the phase angle. So if you have continuos phase from 0 - 180 degrees there is nothing more that you can do with delay than you can with phase. There is no "right" delay or phase. Its just what works. Its all too complex to calculate - I mean it could be done, but it wouldn't be worth it. You'd spend months modeling only to end up within a dB or so of what you could do with the simpler approach that Markus posted in a few hours.
Delay is phase, that is correct, except that delay can extend to many times around the phase angle. So if you have continuos phase from 0 - 180 degrees there is nothing more that you can do with delay than you can with phase. There is no "right" delay or phase. Its just what works. Its all too complex to calculate - I mean it could be done, but it wouldn't be worth it. You'd spend months modeling only to end up within a dB or so of what you could do with the simpler approach that Markus posted in a few hours.
hi Bill
hmm, think your analogy is a bit fishy.
wanna know what I thinks a great idea? a gang of us get together and go thru this procedure. I know that sounds like I'm making out that it's complicated (and prob the hard thing to grasp is actually how simple it is) but hey! any excuse for a pissup tight? brett would no doubt be interested too.
and being the nice guy that I am, I'll even let everybody experiment on my system heh heh.
Earle, so very quickly just to confirm, the results of phase being right is reflected in the FR measurements, either a sweep (which is what I've gotten used to using, have to learn to do RTA) or RTA using pink noise, in any case the 'hole gets filled'...is it as simple as that?
Using multiple subs would tend to randomise any particular 'phase problem' of any one sub I guess, ie it all comes out in the wash.
so all those questions to peter about his wife, you was just czeching?
hmm, think your analogy is a bit fishy.
wanna know what I thinks a great idea? a gang of us get together and go thru this procedure. I know that sounds like I'm making out that it's complicated (and prob the hard thing to grasp is actually how simple it is) but hey! any excuse for a pissup tight? brett would no doubt be interested too.
and being the nice guy that I am, I'll even let everybody experiment on my system heh heh.
Earle, so very quickly just to confirm, the results of phase being right is reflected in the FR measurements, either a sweep (which is what I've gotten used to using, have to learn to do RTA) or RTA using pink noise, in any case the 'hole gets filled'...is it as simple as that?
Using multiple subs would tend to randomise any particular 'phase problem' of any one sub I guess, ie it all comes out in the wash.
so all those questions to peter about his wife, you was just czeching?
terry j said:
Yes - exactly!
You need to go to Prague to understand the other part. There is no place like it. Its my favorite place on Earth!! I was there just after the Wall came down - Wow! Then I went back twice more. Its a beutiful place with fantastic women and the best beer in the world. Whats not to like!?
Why is Audio so sexist? I don't understand.
gedlee said:
because there are people like us in the hobby???
In any case, thanks.
Now whilst I do remember, I very much enjoyed you 'comments' in some sort of article/writeup regarding the relative importances of the electronics in the final outcome. However, the last link I has to them (there were two IIRC) now comes up page not found.
If you know which ones I'm referring to, are they somewhere else?? Or you were responsible for their disappearance?? dunno, copyright or something?
If you're not sure I can go and dig up the old links, dunno if they'd help at all. Would like to have another look at them, hopefully for some sort of audiophile test coming up
(expensive front end vs cheap front end, all done blind of course, a la the matrix test)
gedlee said:
Hi earle, this is one of the ones I was talking about
http://www.gedlee.com/downloads/Comm...20Comments.pdf
but it has 'disappeared'. Do you know why?? or where it can be found now?
I can't imagine too many 'audiophiles' agreeing with you on the importance of the electronics, which I find interesting in a weird way. For example, in one of the traditional areas of audiophile dispute, valves vs ss amps, you are probably a 'hero' to some of the valve guys because finally 'we have an explanation of the various distortions differences between the amps'. BUT, on the other hand you'd be a villain because of your stance on electronics as a whole.
An interesting insight into human behaviour sometimes, we pick and choose what we want to accept in order to defend our positions and reject the rest.