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Author Topic: phantom image with loudspeaker array  (Read 3486 times)

chepotenza

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phantom image with loudspeaker array
« on: January 24, 2013, 10:39:45 AM »

Hello everybody,
I am a newbie, I hope I am addressing the correct post.

I have a loudspeaker array of 4 small speakers (each one as big as a Rubik's cube), linearly equally spaced by 2 cm (0.8 inches). I would like to play a sound source (pink noise) from the first to the last speakers, to give the illusion of a moving sound source.

One trivial solution would be, for right-to-left movement:
0 0 0 1 at time t
0 0 1 0 at time t+n
0 1 0 0 at time t+2n
1 0 0 0 at time t+3n

But this obviously gives me the impression of sound "jumping" from one speaker to the following.

Another solution would be updating the intensities twice more frequently:

0 0 0 1
0 0 0.5 0,5
0 0 1 0
0 0.5 0.5 0
0 1 0 0
0.5 0.5 0 0
1 0 0 0

but I am not sure it is the correct way.

The question is: which sound intensity should I set the speakers so that the sound is "smootlhy" perceived as moving?
I guess this is related to how to create a phantom image.
Please help!

Thanks a lot!


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Fletcher

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Re: phantom image with loudspeaker array
« Reply #1 on: January 25, 2013, 08:51:53 AM »

While I have no idea why you would want to do such a thing... it would seem that your first scenario would give you more of a "jumping" effect while your second scenario would give you a smoother transition between the boxes.

My guess is that you're planning to automate this in some way... if that is indeed the plan then you'd want an automated switching system for the first plan... and perhaps some kind of "4 way panning" system for the second plan.

Even if the speakers are set up in a straight line you could place them as LR LF RF RR and run through an automated panning scenario that panned from Left Rear to Left Front then Left Front to Right Front and finally Right Front to Right Rear which will indeed give you the smoothest transition between the cabinets.

I hope this is of some assistance.

Peace
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CN Fletcher

mwagener wrote on Sat, 11 September 2004 14:33
We are selling emotions, there are no emotions in a grid


"Recording engineers are an arrogant bunch
If you've spent most of your life with a few thousand dollars worth of musicians in the studio, making a decision every second and a half... and you and  they are going to have to live with it for the rest of your lives, you'll get pretty arrogant too.  It takes a certain amount of balls to do that... something around three"
Malcolm Chisholm

jaykadis

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Re: phantom image with loudspeaker array
« Reply #2 on: January 25, 2013, 11:31:51 AM »

If you want to do this convincingly, you need to research Ambisonics. Simply panning works left-right but will not work front-to-back.

Fletcher

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Re: phantom image with loudspeaker array
« Reply #3 on: January 26, 2013, 12:07:50 PM »

Due respect Jay -- the only reason I mentioned "front - back" was because that is the most common labeling of master output busses... I could just as easily have said it as busses 1-4 -- my point was to use common nomenclature -- nothing more, nothing less.

Peace
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CN Fletcher

mwagener wrote on Sat, 11 September 2004 14:33
We are selling emotions, there are no emotions in a grid


"Recording engineers are an arrogant bunch
If you've spent most of your life with a few thousand dollars worth of musicians in the studio, making a decision every second and a half... and you and  they are going to have to live with it for the rest of your lives, you'll get pretty arrogant too.  It takes a certain amount of balls to do that... something around three"
Malcolm Chisholm

Patrick Tracy

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Re: phantom image with loudspeaker array
« Reply #4 on: January 27, 2013, 12:14:04 PM »

What audio production software are you using to do this? Do you want to more than just move some pink noise from one side to the other once? Is there some bigger purpose for this you haven't mentioned?

I would be tempted to split the pink noise to separate tracks assigned to separate outputs and edit them rather than automate a bunch of volume curves.

If  you want the image to be stable as it moves you may have to arrange the speakers in an arc around the listening position at its focus.

jaykadis

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Re: phantom image with loudspeaker array
« Reply #5 on: January 28, 2013, 11:43:49 AM »

Due respect Jay -- the only reason I mentioned "front - back" was because that is the most common labeling of master output busses... I could just as easily have said it as busses 1-4 -- my point was to use common nomenclature -- nothing more, nothing less.

Peace
The thing is, panning from front to back doesn't work because the same ear is hearing the two speakers and the interaural difference in time-of-arrival isn't functioning. There was an interesting talk at AES several years ago that showed that by adding a center front speaker, some of that interaural difference could be created and then there was better perception of front-to-back panning. But if you want convincing spatial placement in a surround situation, Ambisonics delivers.


The OP is interested in a line array, so this is academic anyway. I didn't pick up on that originally - should read better.

Fletcher

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Re: phantom image with loudspeaker array
« Reply #6 on: January 30, 2013, 02:40:48 PM »

I'm in complete understanding of the point you're bringing up -- but as you noticed he's putting the speakers in a "row" [a line array is really an SR term that doesn't really apply here].

Front & Rear would work fine in this application as Left Front and Left Rear would be discrete busses -- as would Right Front and Right Rear which would give him the switching / panning capability he seems to be after.

Peace
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CN Fletcher

mwagener wrote on Sat, 11 September 2004 14:33
We are selling emotions, there are no emotions in a grid


"Recording engineers are an arrogant bunch
If you've spent most of your life with a few thousand dollars worth of musicians in the studio, making a decision every second and a half... and you and  they are going to have to live with it for the rest of your lives, you'll get pretty arrogant too.  It takes a certain amount of balls to do that... something around three"
Malcolm Chisholm

John Roberts {JR}

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Re: phantom image with loudspeaker array
« Reply #7 on: February 05, 2013, 06:40:02 PM »

You may want to look at old AES journal papers about sound localization...  while IIRC most of that work was done with only 2 speakers in a L to R span, and more involved surround sound systems with 4 to 6 speakers, but lets try to KISS for now.

Our brain uses both arrival time and loudness information to localize where a sound is coming from. (Front/back and above/below localization also use comb filtering in our outer ear -google pinnae transform)

So for similar-same arrival time our brain uses relative loudness to guess localization, delay can trick us lock onto first arrival even if it is not the loudest.

You may want to experiment with a combination of varying relative delay and relative volume levels

Have fun..

JR
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Circular Science     http://RESOTUNE.COM

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Jerome Malsack

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Re: phantom image with loudspeaker array
« Reply #8 on: March 27, 2013, 01:28:46 PM »

I saw a paper on a University that did a theater with speakers in Middle Side as playback to give the stereo with depth image.   One speaker center stage and the middle of the room on opposite walls is a speaker this speaker is wired in opposite polarity.  creating the figure eight.  They used the Middle Side signal to the two channels of speakers.  Middle went to the center stage and the side channel to the two speakers opposite polarity. 

http://www.offbeatopenhats.com/OBOH/MS_Recording_%26_Playback.html

http://tdt.usitt.org/GetPDF.aspx?PDF=35-1winter99-02authenticity
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Fletcher

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Re: phantom image with loudspeaker array
« Reply #9 on: March 29, 2013, 10:02:41 AM »

If you further use a "summing matrix" -- that's how records were cut in the old days... M/S has been with us for decades -- not necessarily in a 3 speaker configuration, but with us none the less.

Peace
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CN Fletcher

mwagener wrote on Sat, 11 September 2004 14:33
We are selling emotions, there are no emotions in a grid


"Recording engineers are an arrogant bunch
If you've spent most of your life with a few thousand dollars worth of musicians in the studio, making a decision every second and a half... and you and  they are going to have to live with it for the rest of your lives, you'll get pretty arrogant too.  It takes a certain amount of balls to do that... something around three"
Malcolm Chisholm
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