help with round enclosures

flaevor · 17th February 2005, 03:37 PM

I really want to build some round enlosures and I have read that some of you have or are planning on it. I fond some round styrofoam balls at a craft store that are hollow and can be separated into two halves. The have them in 20cm, 25cm, 30cm and I think two size above that. I figured I could just encase the styrofoam with fiberglass. The question I have is should I use resin and fabric or just use fiberglass filler or filler and fabric or, or...I have never worked with this stuff. Tto me the resin and fabric approach seems to be more work but for whatever reason I suspect that it would be stronger. I'd appreciate any feedback unless it is to denounce rond enclosures ; ).

BTW my first post...

tiroth · 17th February 2005, 03:46 PM

Great idea for a frame.

Remember, spherical inner chamber is quite possibly the worst possible enclosure shape...you may wish to build some kind of box inside the sphere. (spherical outer shape is great though)

gary f · 17th February 2005, 05:12 PM

I don't about spherical enclosures. I did a small two-way with curved pannels. I used many layers of thin wood, with epoxy glue and lead layer in between. The result is great, both in apparence, rigidity and damping. I highly suggest this, but this is quite long to do

gary f · 17th February 2005, 05:14 PM

Other image
Is that the kind of things you had in mind? Maybe it's not round enough.

F

scone · 17th February 2005, 05:25 PM

Quote:

Originally posted by tiroth
Remember, spherical inner chamber is quite possibly the worst possible enclosure shape...you may wish to build some kind of box inside the sphere. (spherical outer shape is great though)

I was under the impression that a spherical inner chamber is the most ideal enclosure design.

I thought people didn't build them that way simply because it's very hard to implement.

flaevor · 17th February 2005, 05:42 PM

My aim is something sphereical and the real heart of the question is purely structural, should i work with resin and some fabric or use filler or use both.

I like your design and had though about doing something similar but it would be a lot of work for a lot of tools I don't have.

Peter M. · 17th February 2005, 06:07 PM

A spherical chamber will have only one main resonance, but much more intense than the three main resonances in a rectangular box.

One could possibly make a helmholtz resonator tuned to the resonant frequency inside the spherical chamber, and place it where the resonace is at the most intense (in the center of the sphere) A tube placed from top to bottom inside the sphere with tuned holes in it should probably do the job, or a smaller sphere suspended inside... Well just an idea...

Peter

tiroth · 17th February 2005, 06:12 PM

Yes, I think that option has been discussed as possible. I don't know that anyone has ever tried.

MarkMck did some great work where he demonstrated using real enclosures that rectangular prism was superior to egg/sphere shape. Think about it: if a cube is bad (three pairs of parallel sides with identical dimensions), how much worse is a sphere with an infinite number of parallel identical dimensions?

Peter M. · 17th February 2005, 06:23 PM

Some resins will melt or dissolve the styrofoam while curing, test the resin and let it fully cure before you cover the whole sphere.

Fiber glass and epoxy resin should work fine.

Peter

Peter M. · 17th February 2005, 07:02 PM

Yes, i totally agree with you, an infinite number of paralell dimensions would make an extremely strong resonance. But if we were able to kill that resonance, there would not be any other to worry about... Well, the multples of the main resonance could possibly make some trouble...

17th February 2005, 03:37 PM	#1
flaevor diyAudio Member Join Date: Jan 2005 Location: Germany	help with round enclosures I really want to build some round enlosures and I have read that some of you have or are planning on it. I fond some round styrofoam balls at a craft store that are hollow and can be separated into two halves. The have them in 20cm, 25cm, 30cm and I think two size above that. I figured I could just encase the styrofoam with fiberglass. The question I have is should I use resin and fabric or just use fiberglass filler or filler and fabric or, or...I have never worked with this stuff. Tto me the resin and fabric approach seems to be more work but for whatever reason I suspect that it would be stronger. I'd appreciate any feedback unless it is to denounce rond enclosures ; ). BTW my first post...

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17th February 2005, 03:46 PM	#2
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Great idea for a frame. Remember, spherical inner chamber is quite possibly the worst possible enclosure shape...you may wish to build some kind of box inside the sphere. (spherical outer shape is great though)

17th February 2005, 05:42 PM	#6
flaevor diyAudio Member Join Date: Jan 2005 Location: Germany	My aim is something sphereical and the real heart of the question is purely structural, should i work with resin and some fabric or use filler or use both. I like your design and had though about doing something similar but it would be a lot of work for a lot of tools I don't have.

17th February 2005, 06:07 PM	#7
Peter M. diyAudio Member Join Date: Jan 2005 Location: Østfold	A spherical chamber will have only one main resonance, but much more intense than the three main resonances in a rectangular box. One could possibly make a helmholtz resonator tuned to the resonant frequency inside the spherical chamber, and place it where the resonace is at the most intense (in the center of the sphere) A tube placed from top to bottom inside the sphere with tuned holes in it should probably do the job, or a smaller sphere suspended inside... Well just an idea... Peter

17th February 2005, 06:12 PM	#8
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Yes, I think that option has been discussed as possible. I don't know that anyone has ever tried. MarkMck did some great work where he demonstrated using real enclosures that rectangular prism was superior to egg/sphere shape. Think about it: if a cube is bad (three pairs of parallel sides with identical dimensions), how much worse is a sphere with an infinite number of parallel identical dimensions?

17th February 2005, 06:23 PM	#9
Peter M. diyAudio Member Join Date: Jan 2005 Location: Østfold	Some resins will melt or dissolve the styrofoam while curing, test the resin and let it fully cure before you cover the whole sphere. Fiber glass and epoxy resin should work fine. Peter

17th February 2005, 07:02 PM	#10
Peter M. diyAudio Member Join Date: Jan 2005 Location: Østfold	Yes, i totally agree with you, an infinite number of paralell dimensions would make an extremely strong resonance. But if we were able to kill that resonance, there would not be any other to worry about... Well, the multples of the main resonance could possibly make some trouble...

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