phase vs time alignment

[subharmonic]

I am having trouble wrapping my mind around the difference. If I precisely time align my cabs are they in phase? Is there a DSP that can put everything in phase?

[Dave Non-Zero]

I'm looking forward to a good answer to this.

[jjohnson]

I'm looking forward to a good answer to this.

+1

[subharmonic]

I'm looking forward to a good answer to this.

Dang. I thought you may have it with your cab spiel in the Titan/Tuba section.

[Bill Fitzmaurice]

Where time align is concerned you can only precisely time align on one dispersion plane. And even on that plane the differing phase responses of the different speakers/drivers make perfection impossible. So the answer is to keep things as close as is practical, because if you're trying to get it perfect it's a fruitless quest.

[BrentEvans]

Phase and time alignment are related. Time aligning everything does not necessarily put everything "In phase," because phase is relative. It does correct phase error due to physical delay, but not due to cab design.

Read my response in this thread. It might help clarify, particularly one of my line drawings. While the drawing is designed to represent degrees of phase, imagine a speaker sitting to the left of the drawing. The effect of delay on phase is equivalent to moving the speaker back and forth, and thusly the wave moves (so to speak).

[subharmonic]

Those drawings is why I started this thread. I didn't want to hijack the other one.

Well here's the bottom line. With the PA at war volume you should be able use an open mic within 3 ft of either stack and clearly understand it.If not either you EQ set up is drastically wrong or you are using a pretty crappy mic or both.Keep in mind systems that are not time aligned very well are more problematic with feedback.Especially those where their are phasing problems and the operator is trying to correct the timing error with amplitude correction.

This is from another thread I started since feedback (under mixers/processor-feedback) has/is always a nightmare for me. So I was wondering how you fix/avoid the phase issues?

Also I am still not comprehending how a Titan and Tuba can't play nice together. Given:

Where time align is concerned you can only precisely time align on one dispersion plane. And even on that plane the differing phase responses of the different speakers/drivers make perfection impossible. So the answer is to keep things as close as is practical, because if you're trying to get it perfect it's a fruitless quest.

[BrentEvans]

OK... let's see if this makes any more sense. Even if you time align the cabs to eliminate the phase errors that occur due to differences is travel, you cannot eliminate the differences in phase that occur because of cab response. EQing each cab separately can help this, as EQ affects phase just as much as amplitude. However, it isn't foolproof because it isn't perfect.

The vertical lines represent 180 degrees phase. Here are two representations of what the phase responses of two subs might look like:

phase 2.GIF (6.94 KiB) Viewed 1923 times

Notice that there are a couple of spots where the cabs are 180 degrees out of phase from each other (vertical line on one cab intersects zero degrees on the other cab). Time alignment does not change this because it is based upon the nature of the cab. Having cabs that aren't time aligned involves a whole new set of phase issues... in addition to the ones that are there because of mixing cabs with different phase response.

[Bill Fitzmaurice]

Also I am still not comprehending how a Titan and Tuba can't play nice together. Given:

Where time align is concerned you can only precisely time align on one dispersion plane. And even on that plane the differing phase responses of the different speakers/drivers make perfection impossible. So the answer is to keep things as close as is practical, because if you're trying to get it perfect it's a fruitless quest.

You're talking about two completely different issues. One is aligning two cabs/drivers in time so that they exhibit as close as possible to the same phase at the crossover point, specifically so that they're not in the vicinity of a cumulative 180 degrees apart. The other is using two cabs together within the same bandwidth, and as the phase response of both those cabs will differ at most frequencies across their pass bands you can't use time align to make them the same.

[subharmonic]

Thanks Brent, that clarified it a lot for me. I am still a little confused on one thing in the last part of the last sentence.

Thanks Bill, you answered my next question while I was writing it.

So you are saying although most of the time completely unnecessary (since tubas cut though the whole range) you can get different cabs to play nicely together in different frequency ranges.

I really don't want to drag both types with me but am interested in the workings of this.

So how does this work with DR tops or any tops for that matter? Wouldn't the horn section vs HF section suffer phase issues?

[Bill Fitzmaurice]

So how does this work with DR tops or any tops for that matter? Wouldn't the horn section vs HF section suffer phase issues?

No. If they're close to 180 degrees apart you'll get a cancellation notch. That's easy to avoid via placement. If they're too far apart in time you'll hear them as two different sources in time, ie., a double-hit, and that's also easy to avoid by placing the crossover above 800Hz, where the period of the cycle is too short to hear the two sources independently. The last consideration is precedence effect, where the frequency first heard dominates. So long as the highs lead the lows that results in a subjectively brighter sound, which is pleasing to the ear. When the lows lead the sound seems dull. All of our tops have the highs either leading or aligned with the lows.
BBE, BTW, works by delaying the lows, resulting in the highs either being aligned with or leading. That's useful in typical woofer/horn PA cabs where the HF driver sits behind the woofer, not so in ours.

[subharmonic]

BBE, BTW, works by delaying the lows, resulting in the highs either being aligned with or leading. That's useful in typical woofer/horn PA cabs where the HF driver sits behind the woofer, not so in ours.

BBE? Are you referring to sonic maximizers?

[Bill Fitzmaurice]

BBE, BTW, works by delaying the lows, resulting in the highs either being aligned with or leading. That's useful in typical woofer/horn PA cabs where the HF driver sits behind the woofer, not so in ours.

BBE? Are you referring to sonic maximizers?

Yes.

[subharmonic]

A DJ I was helping last weekend was using a BBE 882i maxed out on top and bottom, the feedback issues we were having was beyond obscene. There was no BFM cabs involved, no time correction, and I wasn't able to calibrate the room since the Maximizer was the only processing they had. I was able to bring in my Behringer 8024 as an afterthought put it in the wireless mic out before the mic in on the board. HPF 160hz, let the Behringer find the ringing frequencies and EQ them down 6-10db myself (didn't try full manual as we were short on time). This was my 1st attempt at semi-manual feedback correction. Didn't work and seemed to make things worse.

I suspected the Maximizer as part of the issue. Could the phase adjustments they do be part of the cause?

[doncolga]

A DJ I was helping last weekend was using a BBE 882i maxed out on top and bottom, the feedback issues we were having was beyond obscene. There was no BFM cabs involved, no time correction, and I wasn't able to calibrate the room since the Maximizer was the only processing they had. I was able to bring in my Behringer 8024 as an afterthought put it in the wireless mic out before the mic in on the board. HPF 160hz, let the Behringer find the ringing frequencies and EQ them down 6-10db myself (didn't try full manual as we were short on time). This was my 1st attempt at semi-manual feedback correction. Didn't work and seemed to make things worse.

I suspected the Maximizer as part of the issue. Could the phase adjustments they do be part of the cause?

Wow...even before I sold mine I never went beyond 1 o clock.