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melindamusil
11-08-2013, 08:24 AM
How rare is it to find a cave/cavern that has really lousy acoustics?

It makes sense to me that it would be difficult, maybe impossible, to eliminate noise within caves (without covering the walls in nice absorbent material). So I'm not talking about a lack of noise, but instead too much noise - the sound echoes so much that it becomes confusing (ie you can't tell where it is coming from, or the sound becomes so loud it is overwhelming).

I'm imagining a large cavern (about the size of an auditorium), but full of stuff (kind of like a warehouse). FMC is at one end of the room; MMC enters the opposite end of the room, but I don't want him to be able to locate the FMC based on audio cues.

Underground would be swell, but it could be moved above ground if absolutely necessary. I'm also open to a man-made cave (vs a natural cave).

I may alter the shape of the room - making it an L-shaped or S-shaped room. Not sure if corners and bends would help or hinder.

Or am I just grasping at straws?

Thanks!!

GeorgeK
11-08-2013, 08:27 AM
If you have tinnitus the sounds can reverberate and be painfully loud and many people without tinnitus get confused with the location of sounds unless they are either rhythmic or at least repeated several times with enough time for the echoes to die down.

Helix
11-08-2013, 08:35 AM
I was going to suggest filling it full of bats, bat poo and bat poo-feeding cockroaches, but that would make it a very icky warehouse. So what about having water flowing through the cave? Would that be a problem for the gear being stored in it?

kevinwaynewilliams
11-08-2013, 09:03 AM
Caves frequently have very confusing acoustics. Hard surfaces reflect sound very well, and you tend to be hearing echoes nearly as loudly as you hear the direct sound.

blacbird
11-08-2013, 11:50 AM
Underground would be swell, but it could be moved above ground if absolutely necessary.

How exactly do you move a cave "above ground"?

In any hollow space, acoustics depend upon the geometrical configuration of the space and the acoustic characteristics of the walls. Theater designers are acutely aware of this. But theater designers don't design caves.

caw

DeleyanLee
11-08-2013, 06:20 PM
I just toured a set of natural caves located nearby in PA, out by Altoona (Lincoln Caverns). It was great, with a lot of stalactites and stalagmites and oft-times we had to squeeze and duck from cave to cave. Some of the area was still "active" (meaning water still ran through it, still making formations and carving rock), but most of I was "dry" and very fragile.

But what I thought was most interesting was how the formations messed with sound. We were in a cave that had 30' tall ceilings and you could easily fit 100 people in--if it weren't for the formations--and the tour guides voice was swallowed up. It didn't bounce or carry at all. We couldn't hear the school group (about 20 high schoolers) ahead of us (they'd exited the cave we were in, but hadn't left the 'tunnel' we were about to go down).

It was very weird to know that they were that close and not be able to hear them.

Not what you were going for, but it's recent cave experience.

ClareGreen
11-08-2013, 07:18 PM
Having visited (twenty years ago) a cave which had a cafe in it, the acoustics were as confusing as a very, very confusing thing.

Most caves have confusing acoustics, but that one was special.

melindamusil
11-08-2013, 09:14 PM
If you have tinnitus the sounds can reverberate and be painfully loud and many people without tinnitus get confused with the location of sounds unless they are either rhythmic or at least repeated several times with enough time for the echoes to die down.

Thank you for giving us the medical side, GeorgeK!
I was also reading yesterday about total silence (in an anechoic chamber). Without fail, it will cause auditory hallucinations. Fascinating!


I was going to suggest filling it full of bats, bat poo and bat poo-feeding cockroaches, but that would make it a very icky warehouse. So what about having water flowing through the cave? Would that be a problem for the gear being stored in it?

Actually, that might be interesting in terms of adding to the confusing sounds. I like it - thanks!


Caves frequently have very confusing acoustics. Hard surfaces reflect sound very well, and you tend to be hearing echoes nearly as loudly as you hear the direct sound.

This is exactly what I am thinking, Kevin. Thanks!

melindamusil
11-08-2013, 09:22 PM
How exactly do you move a cave "above ground"?

In any hollow space, acoustics depend upon the geometrical configuration of the space and the acoustic characteristics of the walls. Theater designers are acutely aware of this. But theater designers don't design caves.

caw

Last night I asked my father this question. He is brilliant with engineering and acoustics, but SO not a writer! His response, and I quote: "I don't see why you need a big room, or why it has to be underground." (Because that's the plot, dad!)


I just toured a set of natural caves located nearby in PA, out by Altoona (Lincoln Caverns). It was great, with a lot of stalactites and stalagmites and oft-times we had to squeeze and duck from cave to cave. Some of the area was still "active" (meaning water still ran through it, still making formations and carving rock), but most of I was "dry" and very fragile.

But what I thought was most interesting was how the formations messed with sound. We were in a cave that had 30' tall ceilings and you could easily fit 100 people in--if it weren't for the formations--and the tour guides voice was swallowed up. It didn't bounce or carry at all. We couldn't hear the school group (about 20 high schoolers) ahead of us (they'd exited the cave we were in, but hadn't left the 'tunnel' we were about to go down).

It was very weird to know that they were that close and not be able to hear them.

Not what you were going for, but it's recent cave experience.

Deleyan, that is FASCINATING. Thanks for the name of the cave - I'm going to look into that!


Having visited (twenty years ago) a cave which had a cafe in it, the acoustics were as confusing as a very, very confusing thing.

Most caves have confusing acoustics, but that one was special.

I read that those caves in France (with the cave paintings) have acoustics that are as good or better than many concert halls. It's pretty easy to find other examples of caves with "good" acoustics; it's much harder to find information on caves that have BAD or at least confusing acoustics!

Siri Kirpal
11-08-2013, 10:55 PM
Sat Nam! (literally "Truth Name"--a Sikh greeting)

The problem is that exceptions tend to be interesting so they get written about. Then people think they are the rule.

Lots of hard surfaces will cause painful acoustics.

Blessings,

Siri Kirpal

thothguard51
11-08-2013, 11:05 PM
Acoustic noise is reflected off of hard surfaces. The more obstructions you have, the less distinct the reflection, thus, the less echo you have.

In a cave system, the more obstructions you have, like winding tunnels, rocks that jut out at irregular intervals, or even sudden elevations changes, the acoustics will vary depending on the composition of the cave and its material.

Or something like that...

skylark
11-08-2013, 11:25 PM
If it's literally full of stuff, that's going to affect the acoustics even more than the shape of the walls will. If you want to get rid of a lot of the sound, have your "stuff" be endless stacks of cardboard boxes.