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Author Topic: Speaker position for best GBF. Which parameter is more important?  (Read 3521 times)

David Allred

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Situation is conference setting.  Singular lectern mic (Crown LM-300A).  Those addressing / speaking range from bold to timid, eager to be heard to afraid to be heard.  So gain before feedback trumps pretty much everything else.
Below are 2 speaker placements with different parameters in play for each.
One has a greater angle outside the theoretical dispersion pattern to the mic.  (10 deg - 5 deg)  (Angle marked with an ellipse)
One has a greater in-line (parallel?) distance from the speaker face to the mic.  (10' - 5') (Marked with a box)
The one with greater distance also has a greater distance to the theoretical pattern intersection.  (13' - 10.5')  (Marked with a circle)
The off-axis distance from the mic to the speaker is not changed, though the direct distance does change a foot or two.  But let's not get that deep.

I am not concerned that the "pattern" varies by frequency so the "number of degrees to the mic is not valid".  This is for the practical application of a principle.

Which parameter, degrees the mic is outside the pattern or in-line distance from the mic to the speaker face?

Thanks,
David


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David Allred

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #1 on: October 20, 2016, 11:14:38 am »

Maybe this is easier to view and compare.
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Ivan Beaver

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #2 on: October 20, 2016, 11:25:22 am »

Since this is for speaking, I would point the speakers our into the room more.

Point the center of the cabinet towards the furthest listener.

You don't need to worry about covering the front seats.

They should hear enough of the natural voice.

And the added delay time would bother them the most.

As you have it, the back of the room is going to be lacking in level.

Remember that the loudest part is the center of the coverage pattern.

The edges of the pattern are 6dB (quarter power) lower in level-so when you add the added distance loss, it would be loud in the front-middle and quiet in the back.
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Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Riley Casey

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #3 on: October 20, 2016, 11:42:23 am »

One practical element of any loudspeaker small enough to put on a tripod stand is that at low frequencies it is essentially omnidirectional so you can't just ignore directivity vs frequency considerations.  You have to consider that what you are trying to 'throw' to the last seats in the house are the voice articulation frequency bands while the frequencies most likely to feed back are the lows.


I am not concerned that the "pattern" varies by frequency so the "number of degrees to the mic is not valid".  This is for the practical application of a principle.


David Allred

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #4 on: October 20, 2016, 11:59:13 am »

Thanks. All the info is useful, but I am still interested in the main principle.  Which plays a bigger role in avoiding feedback, greater angle out of the pattern with less distance or less angle with greater distance?

Riley,
The mic has a high-pass engaged, the Mixwiz has the hpf engaged.  I also have a Driverack 260 inserted on the mic channel (overkill I know) but it gives me as many tools as a digital board on 2 inputs, if needed.

Side question.  Is it bad to stack HPF's for a mic?  Does is cause any sonic chaos?
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Ivan Beaver

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #5 on: October 20, 2016, 12:18:55 pm »

Thanks. All the info is useful, but I am still interested in the main principle.  Which plays a bigger role in avoiding feedback, greater angle out of the pattern with less distance or less angle with greater distance?


If you want to learn a little about GBF, put some numbers into the PAG-NAG equation, and teach yourself what parts of the "whole puzzle" make the most difference.

WHile not useful in real life-it will teach what makes the biggest differences in getting the most gain before feedback.

It IS a good excersize.  Be sure to vary each of the variables and see what difference it makes.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
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Brian Jojade

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #6 on: October 20, 2016, 12:36:37 pm »

With extreme angles like you are showing, you're going to create 2 points of sound for just about every listener that have different arrival times.  This will result in a significant reduction in intelligibility.

If it was me, I'd bring the speakers closer together and point them more straight out towards the audience instead.  The straighter out that you point the speakers means less energy on stage, especially at higher frequencies.  Doing this may create a hole for the front center seats. If this is a problem, it can be resolved with a center fill speaker.
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Brian Jojade

Josh Millward

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #7 on: October 20, 2016, 12:45:18 pm »

Generally speaking, when dealing with your average "speaker on a stick", it will have minimal control of the coverage pattern down low.

Ergo, you can not use the coverage pattern of a typical speaker on a stick in the manner you are attempting because it is not valid at frequencies below 1000 to 5000 Hz, depending on the specific loudspeaker that is being used.

Distance between the microphone and the loudspeakers will be the greatest factor in gain before feedback.

Generally, you want the loudspeakers as close to the audience as you can get them, and as far away from the mic as you can get. The problem with this is if you can not get the loudspeakers high enough in the air, it will be deafeningly loud up front and quiet in the back.

If you have the height to work with, the best thing you could do in that space is to put a single loudspeaker overhead center and aim it towards the back of the room. It may be a little dim on the front corners, but at least the people in the back can hear.

If you are stuck with speakers on sticks, get them up high and point them towards the back center of the room. Do not get too caught up on the dispersion pattern of the loudspeaker if it is a typical 2-way front loaded woofer and small HF horn. The pattern is only in reference to the horn in the top part of its pass band. At low frequencies the woofer will be omnidirectional and will become gradually more directional as you go up in frequency.

Distance will be the biggest factor in this situation, not dispersion pattern.

What specific loudspeakers are you using?
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Josh Millward
Danley Sound Labs

Ivan Beaver

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #8 on: October 20, 2016, 12:47:54 pm »


Distance between the microphone and the loudspeakers will be the greatest factor in gain before feedback.


Actually if you play with the PAG-NAG equation, it should be realized that the item that makes the biggest difference is the distance between the mic and the sound source (mouth).

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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Josh Millward

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #9 on: October 20, 2016, 12:51:35 pm »

Actually if you play with the PAG-NAG equation, it should be realized that the item that makes the biggest difference is the distance between the mic and the sound source (mouth).

That is absolutely true.

However, that is something that only the source (the person speaking) can control.

I was speaking purely from the perspective of what the sound operator can control with his setup. It is assumed that the source will vary widely, and he specified that in his original post. So the point was to maximize the performance of the rest of the system to accommodate a poor source. A good source will be good, regardless.
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Josh Millward
Danley Sound Labs

ProSoundWeb Community

Re: Speaker position for best GBF. Which parameter is more important?
« Reply #9 on: October 20, 2016, 12:51:35 pm »


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