Can Physics and Engineering Help Attenuate Sound in a Large Indoor Firing Range?

[Physics_Kid]

i am looking for some ideas on where i can look within physics and engineering to help solve my problem.

i want to attenuate the sound blast from a rifle muzzle, however, i want to engineer a large deep room to do it. think of this like a indoor firing range. i know opera stages many times don't need amps and speakers so that the sound can reach the back of the room with little attenuation. my problem has some physical constraints that limit the max dimensions of the room. width is fixed at 153ft, depth(or length) is fixed at 300ft, height is 10ft(min), height and the interior surface profile can be adjusted. although the far end needs a bullet catch, the end wall can be, as example, open to the outdoors in some way to reduce sound pressure reflections.

just as example, wild ideas, etc

 

[.Scott]

i am looking for some ideas on where i can look within physics and engineering to help solve my problem.

i want to attenuate the sound blast from a rifle muzzle, however, i want to engineer a large deep room to do it. think of this like a indoor firing range. i know opera stages many times don't need amps and speakers so that the sound can reach the back of the room with little attenuation. my problem has some physical constraints that limit the max dimensions of the room. width is fixed at 153ft, depth(or length) is fixed at 300ft, height is 10ft(min), height and the interior surface profile can be adjusted. although the far end needs a bullet catch, the end wall can be, as example, open to the outdoors in some way to reduce sound pressure reflections.

just as example, wild ideas, etc
View attachment 207782

More important that the shape of the room will be the material you use for the walls. You want something anechoic.
Google "anechoic materials" or "anechoic tiles" - both web and shopping.

 

[Physics_Kid]

yeah, the surface shape and treatment is the ez part, but what about main design/shape? the floor must remain bare smooth concrete.

 

[.Scott]

yeah, the surface shape and treatment is the ez part, but what about main design/shape? the floor must remain bare smooth concrete.

If you want to muffle the sound as heard from outside, you will need to limit openings to the outside. And where there are openings, they should be baffled with anechoic material. To muffle the sound for people inside the range, keep the ceiling low where you can - to minimize the problem with the floor. Of course, anyone inside will be wearing hearing protection.

 

[Physics_Kid]

its the sound of shooter(s) that needs to be attenuated. environmental (outside) noise is a factor. areas that may be open to the outside might be there to help release the sound pressure energy.

and yes, shooters inside would be wearing hearing protection, but the design of the space should be engineered to attenuate.

i have to go back and look again, i saw some other setups where a shooter with rifle shoots down a ~36"dia steel tube and the sound seemed to be very attenuated.

 

[.Scott]

My question was who was being protected from the sound - not where the sound was coming from.

They can shoot through a 48"x24" (width x height) rectangular "pipe" made of sound absorbing material and it should be even better. And if they are shooting at target that are more horizontally distributed, they will have more room for motion.

The floor needs to be solid concrete, but can the target wall be anechoic?

 

[Physics_Kid]

attenuation of muzzle noise to help protect shooters and nearby folks. the room is connected to other rooms in the bldg. but in general, trying to attenuate as much as possible.

walls and ceiling can have sound deadening panels. the target wall is a bullet catch. tubes will not be feasibility, the lane dividers are made to adjust (slide&lock) on the floor for various types of training.

so what type of shape would the room be to help attenuate? just a std rectangle, a < sign, a polygon, corrugated, a < shape where the ceiling has a sin(x) ripple, etc ?

 

[David Lewis]

No two walls should be parallel. That reduces standing waves.

 

[Physics_Kid]

No two walls should be parallel. That reduces standing waves.

this is a method o know of from a recording studio design.

so, flat floor, ceiling that opens up like <, and then one side wall that comes in at an angle.

i am looking at a panel system for the ceiling that has end result like corrugation. then i plan to use sound deadening foam sheets to cover walls and ceiling.

 

[David Lewis]

The anechoic panels I've seen have pyramid shapes molded into foam elastomer material. I believe ceiling and wall finish panels have a noise reduction coefficient (NRC) in dB, a flame spread rating (seasoned red oak = 100), and smoke developed rating. Ordinary foam rubber is a fire hazard.

If you are concerned with how much sound passes through the wall and gets outside, there is also a sound transmission coefficient (STC).