Suggestions for making a concrete dome sound good

[goat farmer]

I know, it's not ideal, but it's what we've got right now.

The dome is made of concrete and has a door with a glass window and no other windows or openings except for a small window unit.

The ceiling is about 10 to 12 feet high but has a 4X8 peice of plywood with foam egg crate hanging about 1.5 to 2 feet from the exact center of the ceiling. Also there is 4 egg crate peices about 4X8 stuck to the ceiling itself near the center of the cieling evenly placed around the hanging board.

There is also 7 or 8 3X5 loose panels that are covered in fabric. To me they look like what you would make and office cube out of, but for all I know, they may be some sort of sound proofing material and probably are because the room was used as an audio studio at one point to record commercials (not professionally) Anyway, we have these to play with

hardly any sound gets out of the room, but obvoiusly it reflects all over the place.

Our band is wanting to record here cause it's our pracice spot and a nuetral place to play, everything is perfect (excpet for the fact that it is a dome )




I have no idea what to do as far as improving the sound in the room. I was thinking of checker boarding the entire thing with panels of 4" thick pyramid egg crate type foam, but I would love to hear what all of the experts have to say on this site. I would consider myself a newbie as far as improving acoutics and sound proofing so take it easy on me I would REALLY appreciate any advice!!! Thanks.

[dymaxian]

Greetings and welcome!

That ceiling is going to be pretty hard on your acoustics if you leave it un-treated... however, it sounds like you've got plenty of headroom, so it'll be easy to take care of.

What's the size of the room? You gave us the heights... how much floor space do you have to work with?

Take a look at the SAE manual linked from this forum (take the John Sayers productions link at the top right) and read up on the acoustics stuff there. There are also ideas for building absorbers that, put in the right spots, can work wonders for your space.

The egg-crate foam is probably not doing much. If you could hang some rigid fiberglass panels up there, without a hard backing, they'd do a lot more for you.

Hope this helps!

[goat farmer]

Thanks for the response, I'd say it's probably 20 feet from one wall to the other across the floor and probably 10 to 12 foot ceilings. Of course, it's weird being in a dome cause the most space is on the floor and the distance from wall to wall quickly decreases as you go towards the ceiling. I won't be able to measure for 2 weeks unfortunately, but yeah, there is some room on the ceilings.

[knightfly]

Sheesh, what a freakin' nightmare; how much time, money, building expertise and tools do you have available?

Basically, square rooms suck, cubic rooms double-suck, and a dome is essentially one continuous and INFINITE pair of parallel walls, all focussed on ONE POINT...

Got a couple ideas, but you need to let me know on the above questions along with how much floor space along the walls you can afford to give up... Steve

[goat farmer]

I'm going to measure it out and post the results this weekend. I go out there Friday night.

What do y'all think about making a center column in the room made out of bass traps from the floor to the ceiling by stacking the small corner type traps on top of each other. Not the only thing that we would do, but since all of the reflections are focused to the center, do you think it's a good idea? We don't really use the dead center of the room and can sacrifice some space there. We can also sacrfice space all the way around the floor out to about 2 or 3 feet from the walls.

[knightfly]

The halfway point between two parallel walls is also the NULL point for sound pressure at the first and third harmonic of the mode, which means that the sound VELOCITY is at its MAXIMUM; so, if you can get a good absorber placed at that center point, it should work as well as it's going to anywhere else.

Basically what I was thinking for your room (sphere) is to build some slat resonators across some of the arcs of the circle, making your room no longer hemispherical; this would eat up a fair amount of space, but could tame the sound quite a bit... Steve

[goat farmer]

OK, got some more info for ya. Although I was pretty darn close on the measurements.


20 feet across, wall to wall along the floor.

The center of the ceiling in 10 feet.

The wall starts making a major bend (arch) around 5 feet high from the floor. Until about 5 feet, it's fairly vertical.

There is a 5X3 peice of board hanging directly in the center of the ceiling about 2 feet down. It has thin egg crate foam on both sides of it. The board looks like normal plywood, but it may be some sort of acoustic board.

There are 8 5X3 fabric covered fiberglass panels that can be positioned anywhere in the room. Before, I didn't realize they were fiberglass, but I checked the insides of one and it is. Looks like 1 to 2" thick fiberglass.

I bet these panels are making a big difference and it won't be hard to make stands for them to get them up a little higher.

So, you think the bass traps as a center column are a good idea?

I'm thinking maybe the center column idea, a few large thicker fiberglass panels along with the existing thinner panels raised up a bit around the room and placed several feet from the walls to make the room less of a circle like you said and some more foam scattered around the walls to help with the high frequencies may do it.

What do you guys think?


I know we are having problems with standing sine waves because you can walk around the room and listen to someone talking and it sound different depending on where you stand. I'm hoping these ideas can fix that problem. Other than that, the actual sound is not too bad, but I understand that is a major problem.