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Author Topic: Sound waves vs gravity  (Read 637 times)

David Allred

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Sound waves vs gravity
« on: May 18, 2017, 12:47:10 pm »

If a speaker is tilted up so that the directionally controlled frequencies are parallel to the ground and elevated to a plane of 7ft, will these frequencies ever be pulled down to ear level of a person that is 6ft tall?  If so, what is the distance needed?  Does it affect the inverse law. 

Does sound fall?
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radulescu_paul_mircea

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Re: Sound waves vs gravity
« Reply #1 on: May 18, 2017, 01:07:05 pm »

No, it doesn't fall, it is an energy wave without any mass. The pressure difference will not behave the same as the heat pressure so it will not go up either . Plus, the total pressure remains the same because it's a fluctuation wave
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TJ (Tom) Cornish

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Re: Sound waves vs gravity
« Reply #2 on: May 18, 2017, 01:25:45 pm »

If a speaker is tilted up so that the directionally controlled frequencies are parallel to the ground and elevated to a plane of 7ft, will these frequencies ever be pulled down to ear level of a person that is 6ft tall?  If so, what is the distance needed?  Does it affect the inverse law. 

Does sound fall?
Yes, though not directly by gravity.  Temperature gradients cause the sound to refract upward or downward. Warmer air on top and cooler air on the bottom will refract the sound downward, and warmer air on the bottom and cooler air on top will refract the sound upward. 

This can be a factor for large-scale outdoor venues, but takes some distance for this to be a problem.

http://www.prosoundweb.com/topics/sound_reinforcement/whats_the_delay_the_effects_of_weather_conditions_on_sound/
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Jean-Pierre Coetzee

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Re: Sound waves vs gravity
« Reply #3 on: May 18, 2017, 02:16:42 pm »

I remember an article about sound pounds on the site, let me see if I can find it.

There she is
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Chris Grimshaw

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Re: Sound waves vs gravity
« Reply #4 on: May 18, 2017, 02:47:08 pm »

If a speaker is tilted up so that the directionally controlled frequencies are parallel to the ground and elevated to a plane of 7ft, will these frequencies ever be pulled down to ear level of a person that is 6ft tall?  If so, what is the distance needed?  Does it affect the inverse law. 

Does sound fall?

I can't think of any speaker that produces a laser-beam of output like that. It just isn't physical.

When you consider that "sound" is merely air vibrations (usually being transmitted approximately perpendicular to gravity), it seems odd that it even might be affected by gravity. Each molecule of air isn't being moved much before it hits the next one and passes the energy onwards.

We could get into a deep theoretical debate about how gravity is acting on each molecule and the microscopic details of how exactly the energy is transferred between molecules (think repulsion between electron clouds) and whether or not gravity affects those particular processes, but those effects are clearly swamped by other factors, like air density variations due to temperature.
It's been a little while since I studied interactions between particles, but I can dig the textbooks out if you like.

My short answer would be "maybe, but there are much larger factors at play that makes gravity irrelevant".

Chris
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Corey Scogin

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Re: Sound waves vs gravity
« Reply #5 on: May 18, 2017, 02:54:01 pm »

Maybe over significant distance given the right conditions.

(image from here)
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David Allred

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Re: Sound waves vs gravity
« Reply #6 on: May 18, 2017, 03:17:57 pm »

Maybe over significant distance given the right conditions.

(image from here)

So that is why sound carries so well on the water at night.  Pushed down, then reflected up, then pushed down, then reflected up, then........
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Geert Friedhof

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Re: Sound waves vs gravity
« Reply #7 on: May 18, 2017, 06:02:12 pm »

The waves travel by bouncing (vibrating) gas-molecules against each other, who in turn bounce against other molecules etcetera, but the molecules stay mainly in place. It's not like you fire gas-molecules from the speaker straight to the listener. So there is no gravity-trajectory like a bullit.

What is important though is temperature and humidity, because the conductivity of air is frequency dependent, and varies with those two variables. And ofcourse wind.
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John Roberts {JR}

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Re: Sound waves vs gravity
« Reply #8 on: May 18, 2017, 07:50:43 pm »

That's why good speakers are so heavy...

JR
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Doug Fowler

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Re: Sound waves vs gravity
« Reply #9 on: May 18, 2017, 08:18:48 pm »

If a speaker is tilted up so that the directionally controlled frequencies are parallel to the ground and elevated to a plane of 7ft, will these frequencies ever be pulled down to ear level of a person that is 6ft tall?  If so, what is the distance needed?  Does it affect the inverse law. 

Does sound fall?

I have seen line arrays pointed up outdoors. Surely the operators use gravity to pull some of that back down to the audience.
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Tim McCulloch

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Re: Sound waves vs gravity
« Reply #10 on: May 18, 2017, 08:21:40 pm »

I have seen line arrays pointed up outdoors. Surely the operators use gravity to pull some of that back down to the audience.

Yeah and I was critical of that until I started doing more detailed predictions and saw that while some of the HF might be playing to the flying critters the MF and LF lobes were not, in fact playing to the sky.

OTOH I've seen/heard vertical arrays that were aimed up for no apparent or defensible reason.  The last one I saw/heard like that, I asked the system tech how he arrived at the trim height, bumper clination and inter-box angles.  His reply was "we always do it this way."  SMH.
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David Allred

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Re: Sound waves vs gravity
« Reply #11 on: May 19, 2017, 07:57:18 am »

Yeah and I was critical of that until I started doing more detailed predictions and saw that while some of the HF might be playing to the flying critters the MF and LF lobes were not, in fact playing to the sky.

OTOH I've seen/heard vertical arrays that were aimed up for no apparent or defensible reason.  The last one I saw/heard like that, I asked the system tech how he arrived at the trim height, bumper clination and inter-box angles.  His reply was "we always do it this way."  SMH.

Maybe the sound shooting up, creates draft and pulls more of the sound that would "fall" otherwise, up.  Therefore increasing "throw" distance for the system.
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Geert Friedhof

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Re: Sound waves vs gravity
« Reply #12 on: May 19, 2017, 08:33:05 am »

www.electrovoice.com/downloadfile.php?i=1270

PDF about line arrays. See page 11.
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Robert Healey

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Re: Sound waves vs gravity
« Reply #13 on: May 19, 2017, 11:09:30 am »

Maybe over significant distance given the right conditions.

(image from here)

This was critical in some 19th century battles - wind and temperature inversions prevented commanders from hearing the sound of gunfire. Here is an Acoustical Society article summarizing research on acoustic shadows in the American Civil War:

http://acousticalsociety.org/sites/default/files/docs/echoes/v9n1.pdf
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