mid-bass absorbtion using bottles on the wall -idea

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smidgie

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I'm going to try gluing 2L pop pottles with some type of insulation in them on to fibre board and laying it up against the walls in my basement. I'm going to do this in my live room. Can anyone tell me exactly how it works? Does the insulation in the bottles absorb the frequency that the bottle makes to get rid of the frequency? Or does it absorb just because there's insulation in the bottles just like if i layered my walls with insulation? What type of absorbtion material should i use inside the bottles? should i use fibre glass?
Can anyone show me any different methods of getting rid of bass feqeuncies that are relatively cheap and easy to make and don't take up so much room?
 
Before you waste a lot of time.... Why do you think this is going to work??? Is this another egg-carton type of thing - 'cos that doesn't work either...

Check out this link for more info on acoustic treatment:
go to http://www.auralex.com/, then click on Intro To Acoustics - inside that, click on Acoustics 101....

Bruce Valeriani
Blue Bear Sound
 
I read it on John Sayers site and i think on this board too. I thought i'd give it a try. thanks for the link.
 
Hmmm... John oughta know!!! I'll have to ask him about that - I've never heard of it!

Also, wouldn't there be a big problem then because of the reflective nature of the plastic???

Bruce
 
All i really want to do is absorb the bass, i want the highs to be diffused, which the pop bottle should do. i trying to get a really live sound.
 
Yeah I put it up as an idea. I haven't tried it but I believe it will work. Each bottle acts as a slot resonator with it's own note. The insulation in the bottle absorbs the resonance. If you vary the size of the bottles i.e 1 gallon on the bottom going up to small coke bottles on the top you should get a broadband low-mid absorber. Also the bottles will have a diffusion effect as they will have a multifaceted surface which will diffuse the reflections.

Give it a go smidgie - It sure is a cheap system and the more you drink the more you will absorb. Now that can't be too bad. ;)

Incidently the Romans used to line their theatres with clay pots to do the same thing.

Cheers
John :D
 
Pretty slick there John... only problem would be the strange looks I'd get from clients if there were pop bottles lining the walls from floor to ceiling!!!

;)

Bruce
:D
 
Com'on Bruce - a good studio owner should be able to convince a client that this is the latest thing in new technology - i bet you tell them that about your old teac DAT. :)
 
No - although fewer and fewer studios seem to be using DAT, clients still feel it's "fancy-schmancy" technology - then when they spot the Masterlink - lookout!!!! ;)

Teac -- yeah, gimme a break!!! (it's a Tascam!!!) :p

Bruce
:D
 
Thanks for the replys. I guess i'll try it as soon as i get enough bottles. so pink fibre glass would be the best insulation to use??

is there any other ways of absorbing bass without using too much room? i could make slat resonators but don't you have to put them a certain distance away from the wall?
 
John put it best a while back in a different thread:

"[Two things stop sound, mass and air. Either use ALOT of mass (basement) or divide your air into variable-width layers (double-walling, spaced sheets)]"

The "certain distance" from the wall determines what frequencies get damped the most. Figure out what dominant frequency you want absorbed/stopped and then figure out the wavelength. Unfortunately, the lower the frequency, the longer the wavelength, so you may need to just settle on an "even" fraction of this wavelength. Someone mentioned that a regular low-E bass note takes 33 feet to develop (although I still don't understand why you would then want to be 33 feet away from the monitor, didn't make sense), so maybe try 33 feet/8 or 16, which may lead you to spacing a "layer" of air two or four feet apart from each other.

Yeah, it takes a lot of space, so then add your mass into the mix, using heavier material for the "spacers."

Anyway, that's how I go about killing sound in my dream hall. Right now we play in a 14'x16' room, and, well, thank God for forgiving neighbors! We're actually thinking of building walls and a roof AROUND the building we're using now (lawnmower shack, basically).

But if you're going to do it right the first time (like we SHOULD), go underground. Lotsa mass there.
 
oh, hey, thought of two things about the bottle idea, which otherwise would be GREAT...

You'll need to REALLY wash those bottles out. Like rinse them 40 times or something. Otherwise, you'll get ants and mildew and cheese and smell and roaches and flies and funk...

And make sure your temperature and humidity don't change suddenly (which happens in our little shack all the damn time). And that the air conditioner isn't blowing over them. Then you get condensation, which leads to mold and mildew and smell and funk and sustained humidity and whatnot...

For a brief moment, I thought it would be cool to mix cans and hollow things into the mortar with which to build walls. But concrete block already has this built-in air pocket system, so that idea sucks (good recycling thingey, though!).

And Drstawl has a billion carbouys he'll be glad to sell you. His cats might get pissed, though...
 
You actually don't need a lot of wall space for slots. I'm using slots on a 3" depth and they will be broadband from around 800Hz down to around 180HZ. You can increase the depth but it will only take it down to around 120Hz. Panel absobers or hangers are the best solution for frequencies below 200Hz.

cheers
John
 
How would you make panel absorbers and slat resonators? I looked one you're site, John. i was somewhat confused. On the diagram for panel absorbers, the panel looks like it is not connected to the box...so would you hang the panels or something? would you also line the whole box with insulation? for slat resonators, where do you put the insulation exactly? do you know any websites where there are real pictures of these absorbers?
do you know anything about polycylindrical diffusers? how do they work? i read about it on http://www.mcs.net/~malcolm/fuzpoly.txt. the thing is i would like pictures, or else i don't understand. haha. just kidding.

I thought up an idea for bass trapping in corners. i'm wondering if it would work. what if i wrapped pink fiberglass insulation around a 2x4 for support and made it about 1 or 2 feet wide and 7 feet high and wrapped the whole thing in cloth and shoved it in the corners of my room? would this work to get rid of bass?

i know i'm asking for a lot but anything else you could show me would be helpful.
thanks.
 
One small, dumb question. Are we talking bout plastic or glass bottles here? Will plastic ones work??
 
Plastic or glass... shouldn’t matter much.

Actually a few things determine the frequency and efficiency at which the bottle will absorb - the volume of the bottle, length and diameter of the neck, and the amount of insulation you fill it with. The following factors lead toward lower frequencies: larger volume; longer neck; smaller diameter neck; more insulation(up to a point). A long neck beer bottle, for example, has a lower resonance than a 1 gallon plastic milk jug because the longer, narrower neck more than offsets the smaller volume. But, larger volume, wide neck bottles with more insulation(to a point) are more efficient absorbers.

This all is actually pretty tricky. If you don’t put enough inulation in the bottles you can color your room with multiple resonances. Pack the insulation too tightly and you reduce the efficiency of absorption. What you want are “critically damped” absorbers. Without test equipment, it will be difficult to know how or if you have achieved this. One rule of thumb is you should have enough insulation so, when you play the bottle by blowing over the lip, it does NOT make a note. You should just hear the hiss of your breath.

Also the air in the neck of the bottle needs to be free to move. Push the insulation back into only about the bottom 1/2 or 2/3’s of the bottle away from the neck.
 
Oh yeah. Mix it up, but concentrate the lower frequency bottles in the corners of the room.
 
good ideas barefoot. i still reckon it's worth a go cos it's real cheap. Glass bottles would be more diffusive as the surface has more mass.
cheers
John :)
 
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