View Full Version : How large does an aperture have to be for sound to pass through it?

thadman

07-24-2007, 08:22 PM

I'm just curious, how wide (relative to wavelength) must an aperture be for 100% (or near 100%) of a sound wave to pass through it? F. Alton Everest specifically stated in the Master Handbook of Acoustics that if 13% of a thick steel wall was free (ie holes/slits) then 97% of the energy would pass through...Is this wavelength specific or universal to all wavelengths relative to the aperture?

Think of it like this

____ ____ ____ (3 4" obstacles with 2 .5" apertures, a 1700hz wave (~8") would easily diffuse around the 4" obstacle, but is the opening large enough for the 1700hz wave to pass through?)

for reference, the sound waves wavelength must exceed the fundamental baffle width (wavelength>baffle width) before the 2pi to 4pi transition can occur

BassAce

07-24-2007, 08:25 PM

Are you in Indiana?

Tough question, though.

thadman

07-24-2007, 08:32 PM

Are you in Indiana?

Yeah:)

BASSMEKANIK

07-24-2007, 08:37 PM

I'm just curious, how wide (relative to wavelength) must an aperture be for 100% (or near 100%) of a sound wave to pass through it? F. Alton Everest specifically stated in the Master Handbook of Acoustics that if 13% of a thick steel wall was free (ie holes/slits) then 97% of the energy would pass through...Is this wavelength specific or universal to all wavelengths relative to the aperture?

Think of it like this

____ ____ ____ (3 4" obstacles with 2 .5" apertures, a 1700hz wave (~8") would easily diffuse around the 4" obstacle, but is the opening large enough for the 1700hz wave to pass through?)

for reference, the sound waves wavelength must exceed the fundamental baffle width (wavelength>baffle width) before the 2pi to 4pi transition can occur

umm.... yes!!! :escape:

ballstothewall

07-24-2007, 10:56 PM

Hmm, very interesting topic and I can't say that I've really given it much thought. I am anxious to see if anyone here has a article or three to link to for more reading information. *Thylantyr....*

I think I'm going to see about buying that Masters Handbook of Acoustics for some background reading, looks like a good reference book.

Rich B

07-24-2007, 11:01 PM

If long wavelengths (such bass) were blocked by small apetures, ported enclosures wouldnt be feasable since the ports only pass long wavelength frequencies.

thadman

07-24-2007, 11:37 PM

If long wavelengths (such bass) were blocked by small apetures, ported enclosures wouldnt be feasable since the ports only pass long wavelength frequencies.

I think you have a flawed understanding of how a ported enclosure works, the rear wave does not actually leave the enclosure. The rear wave modulates the mass of air inside the port (sort of like a passive radiator) and creates additional sound pressure and only works in narrow bands. If the rear wave (180* out of phase) left the port, we'd have some serious phase cancellation issues and a huge reduction in SPL.

diminishedpower

07-24-2007, 11:41 PM

hey whats ur job/ major if you have a degree?

thadman

07-24-2007, 11:46 PM

I'm 18:crap: No degree yet, just passionate about sound and feel some serious improvements are readily achievable in acoustics as well as loudspeaker design.

ballstothewall

07-24-2007, 11:52 PM

While I'm thinking about it, its completely off topic though... I'm curious about the distinction between near field and far field. I've know the actual distinction between them but I was curious is there is a mathematical way to predict where the near field transitions into the far field, some equation or set of equations to predict. I was curious about this while reading on line arrays awhile ago and couldn't find my answer.

Got an idea Thadman?

*EDIT* No worries, found my answer. :) Not sure how I missed it....

diminishedpower

07-24-2007, 11:53 PM

Just curious as im studying to be an engineer and these are kinds of concepts we talk about in some classes so was just curious

thadman

07-25-2007, 12:13 AM

While I'm thinking about it, its completely off topic though... I'm curious about the distinction between near field and far field. I've know the actual distinction between them but I was curious is there is a mathematical way to predict where the near field transitions into the far field, some equation or set of equations to predict. I was curious about this while reading on line arrays awhile ago and couldn't find my answer.

Got an idea Thadman?

*EDIT* No worries, found my answer. :)

Yes there is such an equation, hope you like math:)

d=(1.5 times f times h squared) times the (square root of (1 minus (1 divided by (3 times h times f) squared

-or-

d=1.5hf^2 times (sqrt of (1-(1/3hf^2)))

d=distance, h=height, f=low frequency cutoff

bk12321

07-25-2007, 12:18 AM

Yes there is such an equation, hope you like math:)

d=(1.5 times f times h squared) times the (square root of (1 minus (1 divided by (3 times h times f) squared

-or-

d=1.5hf^2 times (sqrt of (1-(1/3hf^2)))

d=distance, h=height, f=low frequency cutoff

ermmmmmmmm...

let me get out my quak yoo lator

ballstothewall

07-25-2007, 12:21 AM

Yes there is such an equation, hope you like math:)

d=(1.5 times f times h squared) times the (square root of (1 minus (1 divided by (3 times h times f) squared

-or-

d=1.5hf^2 times (sqrt of (1-(1/3hf^2)))

d=distance, h=height, f=low frequency cutoff

I've made it through college calc II with a B so math doesn't scare me to much any more. Thanks for the equation though. :)

ballstothewall

07-25-2007, 12:22 AM

You thinking of doing EE with comm. systems or something of the sort Thadman, or are you thinking more physics and acoustics related field?

thylantyr

07-25-2007, 06:57 PM

[TV game show] "How large does an aperture have to be for sound to pass through it?

[Press buzzer fast]

"zero.................................... cause I hear the hoe in the upstairs apartment through the

walls bangin' every night" :nerd: :groovy: :*******:

joetama

07-26-2007, 10:45 AM

I think the better questions is what the hell does this have to do with.

It is hard to help you with the concept with out having the overall idea.

In all honesty it sounds like you are going to be loading the sound some how. If so, why?