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Author Topic: Speaker position for best GBF. Which parameter is more important?  (Read 3520 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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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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Ivan Beaver
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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

David Allred

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #10 on: October 20, 2016, 12:59:53 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).



The MC is 6'2".  The following speaker is Molly McOompaLoompa.  Then followed by "the low talker" from Seinfeld, pitching her puffy pirate shirts.  I am trying to remove all variable except distance and angel off axis.
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David Allred

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #11 on: October 20, 2016, 01:14:20 pm »

The speaker in question is the Yorkville E12.  I have used this general set-up for 6+ years.  Always been able to have sufficient GBF, but would like to squeeze 3-6db out.
Most of the rooms have 13' ceilings.  I use  Global ST-132 stands and 15 deg tilt adapters (with COG compensation), so I can run the cabs against the ceiling if I need.
Moving the stands in interferes with sight lines, and get in the way when the stage layout is changed (widened and extended forward) and banquet tables replace theater seating.
Even with the dual coverage from both speakers to every seat, delay causing intelligibility problems is not an issue.
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Keith Broughton

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #12 on: October 22, 2016, 06:48:28 am »

Get the speakers up high, away from the stage (as Ivan said) and cut lows (as Reily said) and put a note on the lectern to "please speak close to the mc"
With voice, intellegibility does not require the FM DJ voice  sound so don't be afraid to use that high pass filter. Even if it sounds a bit "thin" it will be clear.
Then...hope for the best  :D
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Stephen Kirby

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #13 on: October 23, 2016, 01:29:55 am »

In such situations I've actually moved the speakers out into the room a bit.  As has been said, the biggest factor (in terms of set up) is the distance from the mic to the speakers.  But the other reason is that quiet speakers get scared when they hear their voice amplified and back off even more.  The closer the speaker cabinets are to the presenter, the more aware of them they are.  In order to get them up on the mic, you want the system to be as quiet on stage as possible.

As was also said, people in the front rows will hear some sound from the presenter.  And if the SOS are a couple of rows back up high and pointing to the rear of the room, some sound from them will still reach the front rows.  Maybe not the ultimate in clarity and HF but usually intelligible.  And the extra gain and bit of proximity will really help the rows further back.
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Roland Clarke

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #14 on: October 23, 2016, 09:17:15 am »

Give or take that speakers will be as close (or not) to the microphone as they can or feel comfortable being although this is technically the difference this is not going to factor.  Distance from microphone to speaker and volume are going to be the main factors.  Choose your microphone sensibly for the application and work accordingly.  Also consider height as this will effect your front to back level and hence intelligibility for the audience.
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Ivan Beaver

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #15 on: October 23, 2016, 09:36:26 am »

And to put "another twist" into it.

Having the speakers  so that they put less sound onto the microphone actually accomplishes TWO things.

The obvious is more GBF, that is measurable.

The second is psychological.

Some people don't like to hear themselves through a PA system.

So when they hear themselves-they talk QUIETER, and if you turn them up, they talk even quieter.

So by having the speakers put less energy around the mic area, those people will not think they are as loud, so they will speak up a bit.  Or at least not speak quieter
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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 maddox

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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #16 on: October 23, 2016, 11:07:13 am »

Okay, i'll attempt to answer the question.  :)

In truth, i think there are too many variables to know for sure.  Ordinarily i would vote for the position farther up stage as that puts more of the pattern away from the mic.  However, seeing as the speakers are now 5 feet farther away from the audience, they'll have to be slightly louder in order to achieve identical volume at the seats.  They're also a tiny bit closer to the mic which will tend to cause low end feedback to occur sooner.  And it's low end feedback that you're liable to fight the most.

My suggestion since this is a real world scenario would be to put one speaker in one position and one in the other and see which one you can make louder.  My prediction is that they will end up being very close to the same.
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Re: Speaker position for best GBF. Which parameter is more important?
« Reply #16 on: October 23, 2016, 11:07:13 am »


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