What are phase issues/problems

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MrStitch

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When digging around researching some home recording material, or even live audio setups, i keep coming across people talking about phase issues and how to correct them.

Pardon my ignorance, but what is this 'phase problem' that seems to be decimating the audio industry? Can it be explained in text, or do i need to hear it? Info, samples, websites would be great. Any information at all would be greatly appreciated.
 
Funny - I did a google search in the form of a question (can't remember how i worded it), but the first website that came up was titled "Am I gay?"

LOL

Fark you google... fark you! :)
 
When two waves of the same frequency are in different parts of their cycle they are out of phase. If you combine them they can add or subtract from each other, depending on their phase relationship. If they are less than 90° out of phase they will add. If they are more than 90° out of phase they will subtract. If they are exactly 180° out of phase and the same amplitude they will cancel entirely.

The simplest kind of phase issue is a difference in arrival time. For example the sound of a drum reaches two or more drum mics at different times. Most frequencies will be out of phase by varying degrees. When you plot that on a frequency response graph it has a series of deep notches at many frequencies which is called comb filtering due to its resemblance to a comb. Usually things like that sound bad. Often a polarity swap is used to try to reduce the damage caused by the phase problems, but don't confuse phase with polarity.
 
Interesting. Sounds like you'd have to have a pretty well trained ear to spot something that ISN'T there. Hahaha. But good to know! Our drummer has mics all over his set, so i just might apply some of this by muting mics here or there to see if anything appears to drop (or sound funny) vs. one single active mic running. Maybe i'll iron out some other issues with that too...
 
The easiest way to check for phase issues is switch to mono....phase cancellation shows up more pronounced then. Read that tutorial I linked in my first response, I think it goes over that in there.

Where at is SD? I am originally from SD...transplanted to ND now.
 
showstone said:
The easiest way to check for phase issues is switch to mono....phase cancellation shows up more pronounced then. Read that tutorial I linked in my first response, I think it goes over that in there.

Where at is SD? I am originally from SD...transplanted to ND now.
Click to expand...

In the Mitchell area. Where you from?

This whole phase discussion gives me an idea. I have a pair of Yamaha subs and running them with a QSC 2400 (or whatever the model is), and it seems like we get very little sound from them.... extremely little. Given that we're pushing roughly 1000 watts combined, you'd think our subs would be pounding hard, but like i said, it's very faint.

We were told that we need to run these with a crossover (which we don't have). Do you think a crossover would fix the issue, or do you think i have some sort of phase problem?
 
MrStitch said:
This whole phase discussion gives me an idea. I have a pair of Yamaha subs and running them with a QSC 2400 (or whatever the model is), and it seems like we get very little sound from them.... extremely little. Given that we're pushing roughly 1000 watts combined, you'd think our subs would be pounding hard, but like i said, it's very faint.

We were told that we need to run these with a crossover (which we don't have). Do you think a crossover would fix the issue, or do you think i have some sort of phase problem?
Click to expand...

Most likely it's a polarity mismatch. The positive and negative leads on one are swapped. If you turn off one of the subs and the sound gets louder it would confirm the diagnosis.
 
bouldersoundguy said:
Most likely it's a polarity mismatch. The positive and negative leads on one are swapped. If you turn off one of the subs and the sound gets louder it would confirm the diagnosis.
Click to expand...

First good news i heard on this subject in a while! To be clear, one channel on the amp is driving one sub, and the other channel of the amp is driving the other sub. There are no other speakers attached. Also, our amp has a selection to gang the channels (or whatever its called), so basically we only have ONE input running to the amp (from ONE channel on our 31 band EQ), but the amp splits the signal internally to both channels. I cannot turn off an individual channel, but i can change the settings so that it doesn't do the 'gang' thing anymore and also completely disconnect the cable running to one sub.

Does this situation still sound like a polarity issue, phase issue, or missing crossover issue? If it's a polarity issue, then what leads are we talking about... you talking about the cable from the - mixer to eq? eq to amp? amp to speaker? internal speaker wiring? (got me all excited now! LOL)
 
The polarity mismatch would occur from the amp to the speaker since your running the amp in a bridged mode.

As bouldersoundguy mentioned, just disconnect one of the speakers and if the volume increases then it's most like that one
of the speakers is connected with the leads swapped.
 
So here's a question. I have a Firestudio and a Presonus HP60 headphone amp. I have it connected almost exactly like this...
hp60-hookup.jpg


The only difference is that where it shows "Vocal direct out from DAW" I'm going direct and not using the monitored signals from the DAW.

Now the idea with the HP60 is that you can have a main mix and each guy can adjust the level of his own instrument. But what happens is that when you turn up the level of say the Bass it actually makes the bass sound lower. When you turn either source off the Bass sounds fine. SO I suspect a phase problem but have no idea how to correct it.

Any ideas?
 
@tetra
HMMM,,that is strange.

What cables are you using to feed daw outputs to the hp60?
Diy ones? Balanced or unbalanced?

I guess if the outputs are balanced mono and you used a TS cable you could cause problems.

@stitch
It still sounds like polarity.
The cables you're looking at are the amp->sub ones.
Are they bare wire connectors? If so, swap the two wires around on ONE of the subs.

Crossovers wont help. All a crossover will do is stop high frequencies getting to the subs.
You should probably have one, but the lack of one won't cause the problems you're having.
 
Steenamaroo said:
HMMM,,that is strange.

What cables are you using to feed daw outputs to the hp60?
Diy ones? Balanced or unbalanced?

I guess if the outputs are balanced mono and you used a TS cable you could cause problems.
Click to expand...

I'm using 1' TRS patch cables, All new.
 
Does it just do it to bass, or will it happen with any instrument?

Is this a one off that just happened, or has it always done this?

One thing that comes to mind is if you are monitoring direct rather than from daw, then you'd be hearing
the live direct instrument and the version of it that has latency from the daw main outputs right?

Or are the individual instruments that you're monitoring omitted from the main mix?
 
Since it was new, and it does it with all instruments. I ended up just using a different mix for each guy, but that cuts it down to 4 so a couple people had to use the same one. I'd really like to get this solved one day so it works like it should.
 
So, say you have a song with drums bass guitar and vocals in the main mix.

You patch the bass to one of the headphone mixes as you're describing.

Would bass still be sent to the main mix?
 
One end of the cable is a skeakon(?)... goofy big round plug, and the other end of the cable is a 1/4" jack.

The one guy here mentioned 'bridged' mode- i really don't think we're running in bridged mode. We have the option to do so, but we're not utilizing the amp in that fashion, at least according to my limited understanding. Both channels still have independent volume controls, and we did NOT go the process lined out in the manual to run it in bridged mode.

Here's the product specs (better than i stated) RMX 2450 - QSC - RMX Series Amplifiers

Here's the manual - See PDF page 10 called Parallel Input Mode - http://media.qscaudio.com/pdfs/manuals/RMX_User_Manual.pdf

However, i will still reset the amp and disconnect a cable to test this all out. I should download some bass beats or something for testing, and run just the subs. In doing so, i should be able to make these things pound hard, correct?
 
Ok, you're right. You should be set up in parallel as per page ten.
One input, two outputs, independent volume control.


If this is the case though, and you're using a pair of speakon on jack cables for your output, i can't see how the polarity would be out on one of them.

Have the cables ever been repaired or toyed with? Same for the subs?


Bridged mode is the opposite of what you want. It takes one input and uses one output, but couples the power of both channels together.

Check that bridged is off and parallel is on, like the pic on page 10.
 
The cables are brand new. The speakers are used though. We brought them in once and the techs said they worked fine (not the same guys that sold us the subs).

Interesting situation though - We have a similar situation on our mains (sort of), but not quite nearly as bad. We're getting good sound from our mains, but it seems like we're getting a LOT more sound from our horns than from our mids. We had these in once too and the techs say everything is just fine. I even heard them in their shop, and they sounded pretty good (though they had a much smaller amp). They still sound great right now, it's just that i would think we'd be rockin those mid speakers. Same situation too - Mains are hooked up with a separate RMX 2450, using the OTHER eq channel, parallel input, new speakon cables, etc.
 
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