Jump to content

technical help needed


Recommended Posts

  • Members

 

Oh, you mean the sound of a flanger turned all the way up. Robin trower played out of phase on every song he ever made. LOL!

 

 

Yea and only Robin guitar was out of phase the rest of the band was in phase. Is the phase switch on your subs?

Link to comment
Share on other sites

  • Members

If you're talking about the switch on the mixer. It's really only used if you are using 2 mics to listen to 1 sound source. Let's say you put a mic on the top and bottom of a snare. As the stick hits it pushes down on the head. This is going to pull the diaphragm of the top mic and push the diaphragm of the bottom mic. The positive voltage will cancel out some of the negative voltage resulting in a hollow kind of sound like you're listening to something through a conch shell. You can determine whether or not there is a problem by listening to the pa and just flipping the switch back and forth or you can solo both mics and watch the meter. If the meter becomes much louder with 2 sources it's ok. If the meter actually gets quieter you have a phase issue.

Link to comment
Share on other sites

  • Members

 

Well on my sub it says "Polarity" and it has normal and reverse.

 

 

Okay doubt you ever use it unless your subs are to close together which can cause the subs to be out of phase.

So if your low end has the swooshy sound then hit the switch.

Link to comment
Share on other sites

  • Members

As a bass player you'll really want to get a handle on the phase and polarity concepts. If you have the Yamaha Sound Reinforcement book or similar that's one place to start.

 

Many people use the word phase when they mean polarity. On your sub the switch seems to mean polarity. If there's a time delay switch then that would be applied to phase issues, which could help to align some of your sound waves that are emanating from multiple sources.

 

Both polarity and phase will have an impact on your sound, often more noticeable in the lower end - except for that easy to hear whoosh sound!

Link to comment
Share on other sites

  • Members

 

Okay doubt you ever use it unless your subs are to close together which can cause the subs to be out of phase.

 

 

Huh??? Has nothinbg to do with being close together, and if anything, there will be less issues that way and certainly not one magically jumping out of phase.

 

If your subs are of like polarity, leave them alone. If one of the subs is incorrectly wired, reverse only that sub.

 

For the JBL's mentioned, using the onboard crossover, leave them alone.

Link to comment
Share on other sites

  • Members

 

Huh??? Has nothinbg to do with being close together, and if anything, there will be less issues that way and certainly not one magically jumping out of phase.


If your subs are of like polarity, leave them alone. If one of the subs is incorrectly wired, reverse only that sub.


For the JBL's mentioned, using the onboard crossover, leave them alone.

 

 

So speaker distance can't cuase phase problems and phase problem can only happen to mics being to close together since they have smaller voice coils then speakers do. So much for that 1/4 wave length advice you gave me a few years ago.

Link to comment
Share on other sites

  • Members

 

So speaker distance can't cuase phase problems and phase problem can only happen to mics being to close together since they have smaller voice coils then speakers do. So much for that 1/4 wave length advice you gave me a few years ago.

 

 

It's not the size of the cone. One has to do with electrical waves and the other has to do with air pressure waves. It's the same principle. Imagine you try to open a door and someone tries to close the door. Not a whole lot of door swing is going on.

Link to comment
Share on other sites

  • Members

 

It's not the size of the cone. One has to do with electrical waves and the other has to do with air pressure waves. It's the same principle. Imagine you try to open a door and someone tries to close the door. Not a whole lot of door swing is going on.

 

 

I was referring to air waves since most subs are omni directional and being to close together could cause phase problems if their to close together maybe I misunderstood Age wouldn't be the first time I didn't understand Age's advice because he not the type that gives layman term advice so some times it hard for me to decipher his advice. As far as the electrical wave can't that be checked with old battery trick to make sure the cone thrusting outward in the right direction.

Link to comment
Share on other sites

  • Members

Phase/polarity switches. Well just switch one back and forth. Does it make a difference to the sound quality? If it does leave it in the position that sounds best (typically it makes very little difference.

 

Usually on a channel input it only has an effect if you have two (or more) mics picking up essentially the same sound source.

 

With subs ... play a low frequency sine wave 40-50 Hz. Flip 'em back and forth and leave it in the position that has the most bass.

Link to comment
Share on other sites

  • Members

 

I was referring to air waves since most subs are omni directional and being to close together could cause phase problems if their to close together maybe I misunderstood Age wouldn't be the first time I didn't understand Age's advice because he not the type that gives layman term advice so some times it hard for me to decipher his advice. As far as the electrical wave can't that be checked with old battery trick to make sure the cone thrusting outward in the right direction.

 

 

You misunderstood my explaination.

 

Also, 1/4-wavelength at sub frequencies is in the range of 15-30 feet, but that's for constructive coupling, boundery issues, etc.

 

All waves ideally propogate in the polarity so there will not be destructive interference. If the polarity of one of 2 point sources is reversed, they will cancel out (on average) which is destructive.

Link to comment
Share on other sites

  • Members

 

You misunderstood my explaination.


Also, 1/4-wavelength at sub frequencies is in the range of 15-30 feet, but that's for constructive coupling, boundery issues, etc.


 

 

That's full wavelength. Half wave is where you get polarity cancellation so half wave distance between speakers is a problem ... which is also the same as 1/4 wave reflections. (but you knew that :-)

Link to comment
Share on other sites

  • Members

 

That's full wavelength. Half wave is where you get polarity cancellation so half wave distance between speakers is a problem ... which is also the same as 1/4 wave reflections. (but you knew that :-)

 

 

I understand where you are coming from, but your example is for pretty serious cancellation...

 

Cancellation really begins to become an issue where the phase response becomes 90 degrees (or 2 sources shifted lead/lag 45 degrees from the reference T0) but "full" cancellation occurs where the phase response becomes 180 degrees (or 2 sources shifted lead/lag 90 degrees from the reference T0).

 

At 30Hz (lowest practical sub frequency), the wavelength is ~12M or 40 feet. 1/4-wavelength is ~10' (I estimated a bit high but immaterial for this discussion) and there will be some measureable degredation where the distance is 1/4-wavelength (I will try to plot this later) and (theoretically) complete cancellation at 30Hz at 20' separation.

 

To Don't point however, as the frequency increases, the point at thich these effects changes. Go up to 60Hz and divide the distances in half. Go up to 120Hz and again the distance divides. This is why IMO, there's not much of an advantage once you get beyond a couple of subs clustering (for artifacts in the hiogher sub range) because you begin trading off one issue for another... ie. better low end coupling for a different upper sub range interference but at some point the room acoustics contribution make this more or less a moot point. There's no perfect solution but there are things that can be done to make things worse... things like incorrect polarity of a sub box releative to the others.

Link to comment
Share on other sites

  • Members

Let me see if I understand. Polarity refers to the wiring of the loudspeaker (in this example), and determines the direction of the movement of the cone when a given charge is applied. Two matching speakers that sit side by side should have the cones moving in the same direction if the polarity is the same.

 

If those speakers have their cones moving together in the same direction, the sound waves produced by each should have an additive effect for most/all listeners. The sound waves are "in phase" under those conditions.

 

If the speakers are located some distance from one another, it may be that a given listener receives the sounds produced by the two speakers at different times, due to being located different distances from the source of the sound. Under some circimstances, it may be that the sound waves appear at that location "out of phase", and thus there will be a subtractive effect. It is possible that the sound waves could " cancel each other out" if they arrive at the listening position exactly 180 degrees out of phase. In practical effect, since our two ears are not at the same point, we will probably not experience total silience. Changing the polarity of one of the speakers will change that effect, and thus (at that position and at certain frequencies) sound louder.

 

Do I have a basic grasp of the concepts? Mark C.

Link to comment
Share on other sites

  • Members

 

I understand where you are coming from, but your example is for pretty serious cancellation...


 

 

Well yes ... it's for the max. But that is relevent with "polarity switches" ... all or nothing. There are true "phase shifters" but I don't think anyone here is actually using one.

Link to comment
Share on other sites

  • Members

 

Well yes ... it's for the max. But that is relevent with "polarity switches" ... all or nothing. There are true "phase shifters" but I don't think anyone here is actually using one.

 

 

Right, but separation is variable so the effect differs with distance (and measurement position). The polarity switch wouldn't be a suitable correction tool of course.

Link to comment
Share on other sites

  • Members

 

. Not as significant as 180 degrees of course, but this is not an all or nothing world.

 

 

I'm saying that the "switch" is an all or nothing. If flips 180 or 0, your only two choices.

 

Which is why my original suggestion still stands ... flip it ... pick the best of the two, neither is likely a perfect fit.

Link to comment
Share on other sites

  • Members

I'm saying that the "switch" is an all or nothing. If flips 180 or 0, your only two choices.


Which is why my original suggestion still stands ... flip it ... pick the best of the two, neither is likely a perfect fit.

 

So how do they do the 360 array sound just kidding. :p

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...