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Author Topic: The all-important interface between box and PA system  (Read 14055 times)

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IanD

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Re: The all-important interface between box and PA system
« Reply #80 on: October 25, 2016, 12:50:28 PM »

OK, so how does it actually work?  I'm guessing that you're using one side of the mic, relying on the drop-off in sensitivity off-axis to try to extend the 'even response' length of the mic over the sound sources.  But surely, if you have a mic with that pattern of response, it's going to be equally responsive to sound from the other side of the mic, and therefore give you feedback problems?

Indeed, so you have to be careful about monitor placement as discussed earlier. There's no such think as a perfect solution...
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Chris Brimley

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Re: The all-important interface between box and PA system
« Reply #81 on: October 25, 2016, 02:24:21 PM »

Well, where exactly is the null area supposed to be?  The high frequency 180 deg off-axis attenuation is not good.  So is careful monitor placement going to help you much?  I suspect the only answer with this system is going to be to turn down the foldback level for the box in the monitor, and just rely on the player hearing it acoustically.  All very well if you have the luxury of separate mixes for different monitors, and the time to set them up.
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Anahata

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Re: The all-important interface between box and PA system
« Reply #82 on: October 25, 2016, 05:56:57 PM »

The 180° off axis attenuation should be best at mid-high frequencies; it's low frequencies where mics tend to become unidirectional (because it's hard to construct them otherwise).
That said, you are never going to get a perfect null pointing at the monitor anyway. You need to keep the amount of sound from the monitor getting in to the mic low enough to avoid feedback howls, and for best sound it should be well below that threshold. Knowing the mic's pattern helps with this, but it's not an exact science and you can't isolate the stage mics completely. The best you can do is understand all the possible paths between speaker and mic (bouncing of the wall behind the stage, or transmitted though floor vibrations, for example) and get the best compromise. In some situations you might have to turn the foldback level down to less than ideal for the player, but it entirely depends on the room acoustics, size of the stage, other instruments in the band etc. whether it will come to that.
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Chris Brimley

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Re: The all-important interface between box and PA system
« Reply #83 on: October 25, 2016, 06:57:44 PM »

Sure, all good advice, but it was just their 'ideal' claim that raised my eyebrow.
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Anahata

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Re: The all-important interface between box and PA system
« Reply #84 on: October 25, 2016, 09:00:11 PM »

Sure, all good advice, but it was just their 'ideal' claim that raised my eyebrow.

You're expecting too much from sales "literature"  ;)
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Chris Brimley

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Re: The all-important interface between box and PA system
« Reply #85 on: October 26, 2016, 09:30:32 AM »

You're right, there, Anahata!
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IanD

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Re: The all-important interface between box and PA system
« Reply #86 on: October 26, 2016, 10:22:39 PM »

The 180° off axis attenuation should be best at mid-high frequencies; it's low frequencies where mics tend to become unidirectional (because it's hard to construct them otherwise).
That said, you are never going to get a perfect null pointing at the monitor anyway. You need to keep the amount of sound from the monitor getting in to the mic low enough to avoid feedback howls, and for best sound it should be well below that threshold. Knowing the mic's pattern helps with this, but it's not an exact science and you can't isolate the stage mics completely. The best you can do is understand all the possible paths between speaker and mic (bouncing of the wall behind the stage, or transmitted though floor vibrations, for example) and get the best compromise. In some situations you might have to turn the foldback level down to less than ideal for the player, but it entirely depends on the room acoustics, size of the stage, other instruments in the band etc. whether it will come to that.

Actually most cardioid mics maintain pretty good off-axis rejection down to low frequencies; if you think of them as an omni pattern superimposed on a figure-8 you can see why this should be. But as Anahata says, playing on a stage isn't an ideal acoustic situation anyway, you're not playing in an anechoic chamber -- it does help to try and get the monitor somewhere near a pattern null, but once you have reflections this isn't so clear -- and this is another reason a mic with a tighter pattern than cardioid helps, the ratio between the peak signal on-axis and the average signal from every direction (Q) is bigger, so they tend to pick up more of the instrument and less background mush.
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