How to ACCURATELY integrat subs with mains (and a little challenge heh heh)

[terry j]

hope this is in the right subforum, I hope so cause it also has a lot to do with loudspeakers as opposed to just subs.

Bit of a ramble I'm afraid, feel it's needed tho in order to explain. sorry

OK, been mucking around a bit with distributed subs, as per Harmon Kardon and of course a bit closer to home it is something Earl is a champion of.

All that is fine. I run a splitter off my bass outputs of the deqx and run the bass signal thru a behringer dcx 2496, which I'm sure most are familiar with. So the actual frequency response side of things is well and truly covered.

The problem I find (and have mentioned before in a few threads) is that (well I assume) because the subs vary in distance from the LP, both to each other and the mains, if not integrated properly then I can tell that the arrival time of the signal from the various subs do not exactly coincide with the signal from the mains. It's a very subtle thing, but both annoying and distracting.

That may also be complicated by the dcx having it's own internal processing delay.

OK, THE QUESTION IS, (caps lock, sorry) what is a good method for measuring the arrival times fo the sub signals, so I can set the appropriate delay on each of the subs to have them arrive at the same time??

What have I tried? Well, (can't find the link) I tried the 'trick' of putting the subs into opposite phase, and adjusting the phase whilst playing pink noise and looking for the biggest dip. Seemed a bit inaccurate (and listening confirmed I didn't have it right). Maybe that only works when the subs are low passed and the mains are high passed? As I run it off a splitter, the woofer is not high passed, so I'm just trying to fill in underneath.

I tried a variation of that, and just played a sine wave at the frequency of the sub low pass, and adjusted the phase whilst watching the spl meter.

BTW, what is the correct term I'm looking for? I think some of the confusion in the past when I explained this is that I may have been using the wrong terms. Just now I've been using 'phase'. I tend personally to think of it in terms of time and distance differences, but are they just opposite sides of the same coin??

I have hooked up long leads to the behringer so i can have it on my lap and twiddle while listening, varying the time (in terms of distance) but after a while it gets really confusing and frustrating...did I go the right way, too much, too little. You get the idea.

In another thread shinobiwan mentioned using audacity, which I downloaded and somehow got working. A thought occurred to me, if I stick the mic in the LP and played a signal thru the mains and the subs in turn, hopefully the captured recording will allow the delay (difference) between when the woofer does the signal and the subs do the signal, and adjust the unit accordingly.

That too somehow does not seem accurate enough, Admittedly I was only using an audacity generated signal (pluck I think) and am wondering if another signal would produce better results, and if so where to find it. I guess we would need a 'sharp' snap type signal that encompassed all the frequencies in question, hopefully something with a clearly defined leading edge we could read from the recorded trace.

Is there such a signal? Maybe audacity is not the correct program?

Or what other tricks do people use?? I really want to get away from trying to do it by ear and trial and error, it bugs me greatly when they are not in time (nothing to do with FR as I say).

Ahh, I mentioned a little challenge didn't I? In the other thread where shin mentioned audacity, he also mentioned that he was umm, 'discussed' on another forum by s/one named terrorizer, aka thylantr (I think)...hope I'm not wrong. will edit it if I am.

Hahaha, anyway I browsed around a bit and found MUCH to my amusement and surprise, that I TOO was ''''famous''''' and had (kinda ) been discussed on that site. (well, not me personally but my project, tho there was a few comments made about me personally if you get my drift).

http://www.createforum.com/petereuro...orum=petereuro

The site seems on the whole to be quite antagonistic and belittling of quite a few in audio and fora.

Naturally I signed up and had a bit of a chat, and to date there has been no real hostility or antagonism shown towards me, which is good.

Anyway, I kinda gave THEM the challenge of helping me integrate my subs properly. Admittedly I did not give them as much data as I just did here, but a slightly sarcastic comment was made about 'why are not my 'pals' on DIYA helping me with the problem'.

Well, in part that was because I had never put the problem before my pals, heh heh, but it did motivate me to put it here and see what help I get.

Then I can compare the help offered here vs the help offered over there, and over there they are quite scathing about DIYA.

So that's the 'challenge' heh heh. Where will I get the most help? This forum or the forum that bags this forum.

I was quite above board about it, and to be honest quite a simple yet very good suggestion was made by terrorizer which I tired and it has helped me advance quite a bit (silly silly dumb errors on my part).

I hope it stays fun and lighthearted tho. Forums are sposed to be fun right?

[pacificblue]

Originally posted by terry j
OK, THE QUESTION IS, (caps lock, sorry) what is a good method for measuring the arrival times fo the sub signals, so I can set the appropriate delay on each of the subs to have them arrive at the same time??

Calculating gives a good approximation. The speed of sound is approximately 343m/s [1125ft/s). That means for each meter distance you can assume about 2,9ms of delay (~0,9ms/ft).

[Brett]

Very interesting Terry. I was just drawing up some sub ideas for just such an arrangement and my plan was to use a DCX 2496 in a similar way to what you've mentioned - up to 6 subs. I haven't tried to do the integration, but can't see why it can't be done, so I'll watch this thread with interest.

See you next weekend.

[terry j]

Originally posted by pacificblue


Calculating gives a good approximation. The speed of sound is approximately 343m/s [1125ft/s). That means for each meter distance you can assume about 2,9ms of delay (~0,9ms/ft).

yeah, I got close by that sort of method quite a while back, tho I don't recall using such accurate figures as yours. that may help a bit.

on top if that, is there an accurate figure for the delay thru the dcx as well?? If we want the absolute best accuracy, that will need to be taken into account to?? Idly wondering as I type, does ntha figure vary according to how much processing it does?? ie a moving target of sorts?

Originally posted by Brett
I haven't tried to do the integration, but can't see why it can't be done, so I'll watch this thread with interest.

See you next weekend.

Yeah of course I'm convinced it can be done, but right now I think I'll go back to just two subs...haven't got a lot of time to spend getting it right you know! It's not next weekend is it?? think it's two weekends away isn't it/? (tho you are welcome anytime as you know)

I really think any slight discrepancy really stands out because I'm using the deqx and the way the bass has been measured with it. It does such a good job that anything not up to the same standard really stands out.

It could be that everyone else is waaaay better than me in integrating subs, or maybe I'm more sensitive to it than most, but I do think nthe absolute quality that the deqx (using the new technique) gives to the bass has quite a bit to do with it.

[pacificblue]

Originally posted by terry j
on top if that, is there an accurate figure for the delay thru the dcx as well?? If we want the absolute best accuracy, that will need to be taken into account to?? Idly wondering as I type, does ntha figure vary according to how much processing it does?? ie a moving target of sorts?

I am probably the only person in this forum who does not yet have a DCX2496, so I can only guess. Usually DSPs give you either the possibility to set delays in mm or in ms. The better ones have both options.

How exact does it need to be? For one thing you won't be nailed to a place without moving, so it is probably not even practical to concentrate on settings up to the millimeter. And which setting is correct, if there are several listeners in the room at different positions?

Chapter F on this site gives hints about how accurate delay settings need to be.

Processing time should not affect the DSPs performance.

[Paul W]

Try using the DCX "auto align" function with the subs lo-passed and the mains on the hi-pass side. You may not want to leave the DCX in the main speaker signal path permanently, but it may help you identify the appropriate relative delay (it's not just distance, as the filters also play a role). You may find you need to delay the mains rather than the subs.
Paul

[augerpro]

Keep in mind that just because you have the mains crossed LR4 via the DCX, they may not actually be LR4 due to the natural response of the speaker. If you have a box modeling program that will allow you to apply active filters to sim the effect, then I would find a crossover frequency (and slope) for the mains that will correctly cross to the sub at it's given crossover frequency. So you will have different crossover frequencies and possibly slope for the main and subs, but the actual acoustic response will be closer to ideal.

For example I am building a 5.1 HT package. I have a sub that I want to cross at 50hz. My HT receiver will apply a LR4 filter @ 50hz for the sub, and the actual response should follow quite close since the sub is pretty much flat to 100hz. Now for the mains, the "standard" based off THX specs expects the mains to be sealed with Qtc=.7 (2nd order Butterworth) and the F3 at the expected crossover frequency. In my case, 50hz. The receiver will apply an additional BW2 filter to the mains, resulting in a net response of LR4 slope that is 6dB down at 50hz, in other words a perfect match to my sub. Now since my mains are ported-and yours probably are too- they don't have a response that looks like Qtc=.7 with F3 of 50hz. But I started applying BW2 filters at different frequencies (in the sim program) to find one that would most closely follow this ideal slope. I found that setting the filter to 60hz made the mains behave quite closely to the ideal sealed slope.

Now your setup is a little different, but the basic idea is the same. This will at least get you ballpark correct. Now you have to adjust delays based on the varying distances of speakers. Ideally you would want to plot the response of each speaker and sub by itself, then check response with all of them playing (sine wave, pink noise, whatever) and look to see if they appear to be summing correctly.

[terry j]

yeah the dcx allows delay in metric and imperial, and also in terms of time. I mentioned earlier that I feel I could have confused some people in that past as I always mentioned this in terms of distance (as that was how I was using the unit) but I feel others though of it in time or phase or whatever.

Are these terms interchangeable??? If not, what is the essential difference?

Bit of further background, this is 2 ch only. Not into HT. That also means that I don't need (or even want) low bass. I HATE being shaken when listening to music!!! That may be fine for movies, dunno hate movies and don't watch them. In any case it's not what I want. That's fine, between the deqx and dcx I can tailor the extension to suit me.

OK the mains are three way, and the deqx is only three way. So in order to use the subs I run a splitter from the bass output of the deqx and pass that thru the dcx and amps to the subs.

That means the woofer in the three way is NOT high passed with the subs low passed (I do low pass the subs of course with the dcx, but I can't high pass the mains).

So it is a 'classic' case I guess of just adding a sub to fill in below a set of mains. I only need to add the subs now because I only recently moved my system orientation around (trying the article on the decware site about aligning the system to a corner).

In my old setup I could get extension to 29 hz, which is all I want (hate the shaking remember), but due to the new layout both the speakers and the chair are much more in 'open space' and I have lost a lot of extension that I can't get back with the mains no matter how much boost I apply (the woofers are 18 inch PHLs, can take a lot of power and boost). On the other side the advantages of the new layout (imaging, much less 'mud' in the vocals and midrange etc) mean I'd rather keep it this way and go to the extra hassle and complication of adding the subs back in to keep the advantages yet get the old extension back.

I have not tried the auto align function, it could work but my gut feel is that at bass frequencies it will not do too much good?? Still, worth a try.

All boxes sealed.

As a thought experiment, this is what I think. Lets say we have an appropriate signal (what would that signal be and where do I get it) and play it thru the system with a mic in the LP being recorded in say audacity (correct program??)

Lets assume that all the subs are at different distances from each other and the mains. Let's say that we have four subs.

Ok, when a bass 'thump' is played we record the results. By my reasoning we should see a 'thump' in the recording which comes from the two aligned mains woofers, then a succession of thumps from each of the subs in turn according to their respective distances. Actually that needs to be reversed.

The subs need to come earlier than the mains signal (as they are piggy backed off the bass output) so that using the delay function in the dcx I can delay the early arrival of the sub signal back to the woofer. Ie, if I delay the woofer in the mains via the deqx, it will also delay the signal to the dcx.

Anyway, the essential point is that with the appropriate signal and measurement program I should be able to see on the screen the actual time arrival of the signal from each source shouldn't I? The it would be a trivial matter to adjust to make them arrive at the same time.

The question is what signal and program is best suited to doing this?

Maybe we need to look at impulse graphs for example. Dunno.

Does any of this make sense?

[Brett]

Originally posted by terry j
It's not next weekend is it?? think it's two weekends away isn't it/? (tho you are welcome anytime as you know)

Today is Thursday isn't it?

[Robh3606]

"OK, THE QUESTION IS, (caps lock, sorry) what is a good method for measuring the arrival times fo the sub signals, so I can set the appropriate delay on each of the subs to have them arrive at the same time??"

Hello Terry

Do they have a adjustable phase controls?? I have 3 subs that I use in my HT. I used the phase controls and a test tone to set them the subs up for max output. Just used an RTA to measure level. I don't know how close you can get them time-wise but a a minimum they should all be in phase and summing properly where the listening seats are.

Rob