Cancellation issue???

[5StringFool]

At a recent outdoor gig I experienced something new and very odd to me. At the sound board approximately 80-100 ft. from the stage there were almost no low frequencies present at all. If you were 20 ft. to the left or right of the soundboard the lows were thick and full. Mids and highs were equally present in both places.

What would cause something like this, perhaps some kind of phase cancellation? Ideas anyone??

[testing1two]

Usually this is from improper sub placement.

[Zooberwerx]

Almost sounds like comb filtering. Read this thread:

Subs missing on dance floor

Riis

[walterw]

yep, if the subs are spaced far apart, you get hot zones and dead zones.

[Groove Master]

Originally Posted by 5StringFool

At a recent outdoor gig I experienced something new and very odd to me. At the sound board approximately 80-100 ft. from the stage there were almost no low frequencies present at all. If you were 20 ft. to the left or right of the soundboard the lows were thick and full. Mids and highs were equally present in both places.

What would cause something like this, perhaps some kind of phase cancellation? Ideas anyone??

Yes that is phase cancellation. Were you playing?

This a common thing for us bassists when we have monitoring with a wedge or in-ear monitors. A quick fix is to ask the monitor guy to flip the phase of the bass strip. If this is not possible, if you have a banana plug for your speakers the trick is to invert it from normal.

[5StringFool]

Thanks for the links and replies. That thread and the Void Audio article are answering all kinds of questions about how we can better place our subs.

I have a fair amount of recording and mixing experience, but speaker placement for live reinforcement is still a relative new field for me. I've still got a lot to learn.

[fokof]

Originally Posted by Groove Master

Yes that is phase cancellation. Were you playing?

This a common thing for us bassists when we have monitoring with a wedge or in-ear monitors. A quick fix is to ask the monitor guy to flip the phase of the bass strip. If this is not possible, if you have a banana plug for your speakers the trick is to invert it from normal.

You are very lucky if the cancellation is exactly at 180°.
( That's what a phase switch do )

In those case , the soundman will have better luck to "align" the backline with the PA with delays.

[Zooberwerx]

To the OP: describe the speaker array / configuration. Were the subs separated to the L & R or were they centered and/or clustered?

Riis

[ggunn]

I have heard that when the FOH speakers were wired out of phase.

[Groove Master]

Originally Posted by ggunn

I have heard that when the FOH speakers were wired out of phase.

That would do it. As I described earlier it is a good habbit to check the phase of the bass on stage with the monitoring system. I do it on every gig even with in-ear monitoring when I have an amp on stage and/or a loud PA.

[5StringFool]

Originally Posted by Zooberwerx

To the OP: describe the speaker array / configuration. Were the subs separated to the L & R or were they centered and/or clustered?

Riis

Separated to the left and right of the stage about 30 feet apart.

[ggunn]

Originally Posted by 5StringFool

Separated to the left and right of the stage about 30 feet apart.

Active subs? Phase invert button depressed on one and not the other?

[Zooberwerx]

Originally Posted by 5StringFool

Separated to the left and right of the stage about 30 feet apart.

"There's your problem right there..." - my mechanic.

This would be the most reasonable explanation for the bass void in question. Did you read the thread I linked earlier?

Riis

[TimmyP]

Live Sound: The “Power Alley” - Discussion & Solutions To The Troubling Interaction Of Subwoofer Stacks - Pro Sound Web

[konodl18]

Originally Posted by TimmyP

Live Sound: The “Power Alley” - Discussion & Solutions To The Troubling Interaction Of Subwoofer Stacks - Pro Sound Web

Tim, I didn't know you were active on this forum as well. I'm a long time Lurker on psw. Good link.

And fyi, to the poster who suggested flipping banana jacks around, that is not phase reversal, its polarity. The words phase and polarity are not interchangeable.

Derek

[ggunn]

Originally Posted by konodl18

Tim, I didn't know you were active on this forum as well. I'm a long time Lurker on psw. Good link.

And fyi, to the poster who suggested flipping banana jacks around, that is not phase reversal, its polarity. The words phase and polarity are not interchangeable.

Derek

That's technically true for anything other than a pure tone (no amount of phase shift will simultaneously put every frequency 180 degrees out of phase like flipping the polarity will), but in the popular vernacular it's very often referred to as phase reversal. Some gear actually labels the polarity button "phase".

It's like tremelo and vibrato. Fender designers got it backwards - the vibrato channel on a Fender amp gives you tremelo and the tremelo bar on a Strat gives you vibrato.

And the Wicked Witch of the West wasn't melting, she was dissolving.

But whatcha gonna do?

[1958Bassman]

Originally Posted by 5StringFool

Separated to the left and right of the stage about 30 feet apart.

Any boundaries to the right, left or behind the stage, or behind the main seating area? That causes its own set of issues.

[fokof]

Is this a thread about show cancelled ?

[T-Bird]

Hi.

Originally Posted by 5StringFool

Separated to the left and right of the stage about 30 feet apart.

Originally Posted by Zooberwerx

"There's your problem right there..." - my mechanic.

This would be the most reasonable explanation for the bass void in question.

Riis

^+1000

180 deg phase difference between the subs don't behave like that unless the conditions (dimensions) are excactly "ideal".
If even then.



Stacking the tops onto the subs does look cool, the subs raise the tops usually just the right amount, the subs are usually sturdier and more adjustable "stands" than any other stand, it's the time-honoured way to do it, etc. the list for the reasons people separate the subs is almost endless.

That doesn't mean it's the right way to do it, just as every sound person finds out and learns, sooner or later. There will be situations and venues where the "traditional" stacking is the only way, but if clustering the subs is possible, that's the superior way to do it.

Regards
Sam

[konodl18]

Originally Posted by T-Bird

Hi.





^+1000

180 deg phase difference between the subs don't behave like that unless the conditions (dimensions) are excactly "ideal".
If even then.



Stacking the tops onto the subs does look cool, the subs raise the tops usually just the right amount, the subs are usually sturdier and more adjustable "stands" than any other stand, it's the time-honoured way to do it, etc. the list for the reasons people separate the subs is almost endless.

That doesn't mean it's the right way to do it, just as every sound person finds out and learns, sooner or later. There will be situations and venues where the "traditional" stacking is the only way, but if clustering the subs is possible, that's the superior way to do it.

Regards
Sam

I agree 100% with every you said here about clustering subs. But are you saying that the subs will only cause cancellations if they are exactly the right distance apart?

With left and right subs there will always be cancellations and hot spots or constructive and destructive interference. The distance between the subs only changes which frequency they occur the worst at, 60hz or 80hz or 100hz or whatever. I believe there is a link or chart floating around the web that describes which frequencies will cancel at a given distance based on the 1/4 wavelength.

I'm thinking it might be Tim P who has the link?

PS. This is also why putting subs up on a 2-3ft stage is a bad idea. It creates a deep notch in the frequency response of the subs based on the wavelength hitting the floor and cancelling at that height.

Derek