Helmholtz Resonator from wine bottles?

[flintan]

I'm planning to build a recording booth in our rehearsal/project studio. It's in a 200m² (~30x6x2,4m) concrete bunker comprised of a big recording space/stage with local acoustic treatment and a small control room. The main need for a booth is to get control of the lower frequency room resonances and to reduce outside noise and room reverbartion. The booth will mainly be used for vocals, acoustic guitar, all types of brass and woodwind instruments, strings etc but it would also be nice to have room for bigger instruments like upright bass and drums. So i think the size of the booth will end up being something 10-15m².

Anyway i got this crazy idea yesterday of building a combined diffusor and helmholtz resonator from empty wine bottles, or alike. Pile them up over one of the walls with the bottlenecks facing the room and fixing them with some type of glue. A 75cl wine bottle has a resonance frequenct of something 100Hz. An easy way to find out the frequency is achieved by blowing into the bottle..

My first idea was to use lots of different sizes of bottles with different bottlenecks to achieve a wide absorbtion of the desired frequencies. But the i got the idea of using only one type of bottle, easier to find many of the same and easier to pile up, and tune them afterwards by placing plastic or paper pipes of different lenghts into some of the bottles. This could then be done while measuring/listening to the room.

I realize it's a lot of bottles.. How efficint do you think it would be? Approximately how many would be needed for say a 10m² room with 2,4m height?

If it would work it would be a simple way to build a bass absorber at practicallt no cost at all that also has the possibility to be tuned afterwards. What do you think? A stupid waste of time or something worth trying?

[John Sayers]

I've had the same idea but I never got around to it. You could hook up a mike to a real-time analyser and find the resonant frequency of the bottles. I was going to start with 2 litre (4 quart) bottles on the floor building up to small coke bottles. You have to add insulation to the bottle but I thought it would be easier to squirt expanding foam into them. Once they were all up I was going to spray paint them.

If you mount them off the wall you would also create further deep resonators in the shaft created between the bottles

[jbassino]

That would indeed look "cool", but.. isn't it cheaper to just buy some wood, insulation and do a membrane, or any resonator you like?
or maybe... easier?

[John Sayers]

but flintan is after the diffusive aspect as well as the resonator

[Soundman2020]

Sounds like a fun idea! But you'd need an awful lot of bottles! If you need help emptying them all of their original contents, then I'm sure you'll find many volunteers here, willing to assist you with that task! (Of course, assuming that you only buy the best bottles, with the best quality contents... )

- Stuart -

[John Sayers]

Actually it would be rather expensive in Sweden - doesn't Sweden have the highest alcoholic beverage prices in Europe?

[flintan]

I've had the same idea but I never got around to it. You could hook up a mike to a real-time analyser and find the resonant frequency of the bottles. I was going to start with 2 litre (4 quart) bottles on the floor building up to small coke bottles. You have to add insulation to the bottle but I thought it would be easier to squirt expanding foam into them. Once they were all up I was going to spray paint them.

There must be quite some people that have had the same idea but i have not seen or heard of anyone who realized it. Would this type of foam do? Sorry it's in swedish but it's a cheap normal type of polyurethane foam. And also with foam inside, will it lower the frequency further? I won't be able to test the frequency of the single bottles once the foam is in there.

If you mount them off the wall you would also create further deep resonators in the shaft created between the bottles

Hmm.. That could make a really deep absorber i guess. But now the mathmatics gets way over my head. How to calculate the volume of the openings between the bottles? How far off hte wall would be appropriate? One could of course "close" some of the openings with some foam or glue..

It would for sure involve a lot of bottles and make a reallt heavy construction and it's probably easier to build a normal membrane or slat absorber.. But i'd like to ruminate this idea some more before abanoning it.

Actually it would be rather expensive in Sweden - doesn't Sweden have the highest alcoholic beverage prices in Europe?

Indeed we have but a lot of people are buing from germany or other near by countries. But for this project i would rather rob a bottles recycle bin than buing and drinking every bottle myself.

[Soundman2020]

But for this project i would rather rob a bottles recycle bin than buing and drinking every bottle myself.

Aww geee! But that would take all the FUN out of the build! and like I said, I'm sure there would be plenty of volunteers here that would be only too happy to help you empty the bottles and build your wall! Of course, after emptying the bottles, the wall might not end up very straight, but at least everyone will be happy!

Seriously, I'm intrigued by this idea. I've heard it mentioned before, but as far as I know it hasn't actually been done yet.

By the way, the purpose of putting foam in the bottle is to dampen the resonance, taking energy out. It will also broaden and lower the Q of the bottle, which is a good thing.

- Stuart -

[John Sayers]

I first presented the bottle wall idea in the studio construction forum of Home Recording.com back in the late 90s.

[g-slam]

My idea was, to Build à wall from this bricks.

then you can fill the holes with absorbent Material.
On top you put in a circle formed MDF with a hole in it.
Use different lengths like in a qrd diffusor.

So you will get a "qrd abfusor"!

[Soundman2020]

So you will get a "qrd abfusor"!

And if you built the wall in the shape of a variable radius curve (convex) you could have a "poly-cylindrical-QRD-abfusor"...

[g-slam]

Damn.
We are good!

[flintan]

I've been trying to calculate the optimal room dimensions. The hight is 2,4m so 3,07x3,7m seem to make a good startpoint according to this page: http://www.mh-audio.nl/

My question is from wich point should i measure the dimesions? From the wall behind the cavity behind the bottles? Or from the "surface" of the bottle diffusor? I guess it depends on wich frequencies you care about..

[Soundman2020]

My question is from wich point should i measure the dimesions? From the wall behind the cavity behind the bottles? Or from the "surface" of the bottle diffusor? I guess it depends on wich frequencies you care about..

My guess would be from the wall behind the diffuser, since that is the boundary of the actual room, and you will have numerous gaps between the bottles.

[donal_finn]

I can help with the drinking!!