Hello!
I am a newb, and have never done physics so I am wondering if ye can help me. I am conducting an experiment in which people have to distinguish between sound coming from above and sounds coming from below. Due to the nature of the task, the speakers need to be placed relatively (within 10") close to the screen. I have conducted pilot studies and people have no problem ascertaining which sound came from left or right but when it came to up or down, they reported hearing majority of sounds coming from the lower speakers. I checked the decibel reading using a decibel meter, the sounds coming from the speakers are even. I have the speakers angled towards the person so sound is not (totally!) bouncing off the table or the ceiling before they hear it. But people are still having difficulty identifying whether a sound is coming from top left speaker as opposed to bottom left and same with right hand side also. ANY HELP WOULD BE GREATLY APPRECIATED!!

Quote Mavis Davis:

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I have conducted pilot studies and people have no problem ascertaining which sound came from left or right but when it came to up or down, they reported hearing majority of sounds coming from the lower speakers. I checked the decibel reading using a decibel meter, the sounds coming from the speakers are even.

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The human physiology isn't very good at determining sound source directions in the vertical plane. Essentially the only clues available are those formed by frequency responses notches and resonances caused by the effects of sound relecting and diffracting around and off the pinnae (outer ears), the imposed response alterations varying with source direction.

The ability to determine sound direction is also affected strongly by previous experience. Play the sound of a plane passing and most people will perceive it as being overhead even if it's generated by a speaker on the floor, just because prior experience has taught that planes live in the sky!

Also, the spectrum of the source sound is important, as some types of signal don't include sufficient spectral content to be modified adequately by the pinnae reflections etc -- specifically, content in the 6-10kHz region is particularly important.

It is important to remove any possible source of sound reflection to minimise any confusing and counter-indicative signals -- desks, screens, walls etc -- and if they can't be removed, then position them in such a way that any reflections won't reach the listener.

There's quite a lot of research available on line into the directivity of human hearing.

hugh

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Technical Editor, Sound On Sound

Thanks Hugh,
I know, I've done some preliminary tests just moving stuff in different ways and I think the best I can hope for is people identifying the sound source correctly MOST of the time! I had a read around and Universal Audio recommended placing the speakers at a 30 degree angle to the centre point (after creating a three point equilateral triangle using the speakers and hearing position). As I'm using 4 speakers, two up, two down, I was going to replicate this but also angle the top speakers so they face down towards the hearing position, and angle the bottom speakers up towards the hearing position. I know it won't eradicate the localisation problem completely, but if you have any further recommendations as to placing the top speakers differently to the lower speakers to make them more identifiable, I would be very grateful.
Cheers,
M.

Quote Mavis Davis:

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I think the best I can hope for is people identifying the sound source correctly MOST of the time!

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It's all anyone can hope for! If I recall correctly the papers I've read on hearing directionality I think the typical success rate was around 83% with speakers at +/-45 degrees.

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I had a read around and Universal Audio recommended placing the speakers at a 30 degree angle to the centre point (after creating a three point equilateral triangle using the speakers and hearing position).

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This is the usual arrangement for conventional horizontal stereo.

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As I'm using 4 speakers, two up, two down, I was going to replicate this but also angle the top speakers so they face down towards the hearing position, and angle the bottom speakers up towards the hearing position.

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Good plan. It might be helpful to have a non-reflective surface onthe floor to prevent the top speaker sound bouncing staight back up.

hugh

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Technical Editor, Sound On Sound

Great! Thanks for all the info,
Cheers,
M.

Good post! Its really useful information to me. Could anyone tell me some ideas of how to position speakers to get the maximum benefit from them? Thanks in advance.

Edited by James Perrett (30/04/12 09:13 AM)

Quote aeroalexer:

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Good post! Its really useful information to me. Could anyone tell me some ideas of how to position speakers to get the maximum benefit from them? Thanks in advance.

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You've established that people don't take much notice of up/down when localising sound. Possibly for the same reason we perceive a mirror image as laterally inverted, but not vertically. Now, what's your aim? Can you just accept this result and count the experiment as successful? Or do you have a scenario where you NEED people to recognise up/down?