School project, small driver but "big" enclosure

[Rullknufs]

Something like this:


The purpose of this is to have something to write about, relating to the physics and math subjects in school. The idea is to use a small driver, like 3-4" and use a big enclosure to amplify the sound and extend the bass.

I don't want to build a 300l cabinet that requires extreme woodworking skills. I'm more looking for something in the picture above. Does not require extreme skills yet it could provide me with lots of things to write about (like pipe resonances and such) and also achieving a good sound.

The budget is maximum 500SEK per driver, that equals ~$75/~€60/~£47

The finished product is not important as the work and writing, so therefore I'm looking at pretty cheap small drivers.

[chrisb]

Originally Posted by Rullknufs

Something like this:


The purpose of this is to have something to write about, relating to the physics and math subjects in school. The idea is to use a small driver, like 3-4" and use a big enclosure to amplify the sound and extend the bass.

I don't want to build a 300l cabinet that requires extreme woodworking skills. I'm more looking for something in the picture above. Does not require extreme skills yet it could provide me with lots of things to write about (like pipe resonances and such) and also achieving a good sound.

The budget is maximum 500SEK per driver, that equals ~$75/~€60/~£47

The finished product is not important as the work and writing, so therefore I'm looking at pretty cheap small drivers.

Fostex FF85WK? - might not necessarily work in the pictured style, but maybe something like the Woden Vampyr?

[Rullknufs]

Originally Posted by chrisb

Fostex FF85WK? - might not necessarily work in the pictured style, but maybe something like the Woden Vampyr?

Seems a bit complicated to build though, including lots of angles and such.

[Kindhornman]

Seems like a simple transmission line project with a cheap speaker if you are just trying to demonstrate the principles here. Would be a fun project in school and some easily cut wood from the wood shop and some glue. Another easy thing is to use round plastic pipe and one 180 degree bend or two 90's and some pipe glue with a flange to mount the driver to the tube.

A second idea, just about as simple is to install the speaker in the middle, actually offset so you have two different length and you have a twin tuned transmission line a la a boss wave radio design. Each length is set to a different frequency and you have two frequencies instead of one emanating from the tube ends.
simple to calculate the tuning frequencies and so it also becomes a math problem for the students to solve.

[chrisb]

Originally Posted by Rullknufs

Seems a bit complicated to build though, including lots of angles and such.

fair enough

[Rullknufs]

Originally Posted by Kindhornman

Seems like a simple transmission line project with a cheap speaker if you are just trying to demonstrate the principles here. Would be a fun project in school and some easily cut wood from the wood shop and some glue. Another easy thing is to use round plastic pipe and one 180 degree bend or two 90's and some pipe glue with a flange to mount the driver to the tube.

You've got it!

The idea with pipes seem interesting, and would require less woodworking but still provide a good sound, I guess? Is there any limit to how long the pipe can be? I mean, I have no problems making it several meters long but with many bends. I was thinking of setting maximum height to ~180cm just to reduce handling problems

[Rullknufs]

Originally Posted by chrisb

fair enough

Well, it's a school project and since I'm studying nature science the main focus of the project is not the actual construction process. What matters is documentation and researching about what I've done.

[chrisb]

Originally Posted by Rullknufs

Well, it's a school project and since I'm studying nature science the main focus of the project is not the actual construction process. What matters is documentation and researching about what I've done.

Good opportunity then to document your study of, and use of formulas and math related to Quarter Wave behaviour*

You could do far worse than to immerse yourself in the work of Martin King, to name only one

*fortunately I "have guys" for that, otherwise the math would get embarrassingly mangled - I'll just stick to slapping together boxes made from other folks' designs

[Rullknufs]

Originally Posted by chrisb

Good opportunity then to document your study of, and use of formulas and math related to Quarter Wave behaviour*

You could do far worse than to immerse yourself in the work of Martin King, to name only one

*fortunately I "have guys" for that, otherwise the math would get embarrassingly mangled - I'll just stick to slapping together boxes made from other folks' designs

Yes. I just started with wave studies in physics class talking a bit about standing waves, pipe resonances and such and that's the area I want to "dig deeper in" and construct something using the principles of it.

[Nanook]

How deep into wave mechanics and math are you?

If you have some calculus, the math is not difficult. Look at the Helmholtz resonator and it's equation. It all starts here.

Perhaps the simplest is what I made: a37" straight pipe using a good (but) cheap co-axial. With a proper cross-over, quite capable. TLs, BRs, horns, etc all rely on the Helmholtz equation at some point. These things are ridiculously easy to build, and rely on the same math.

So your efforts will be spent in the documentation aspects of the project and the correspondence of the end result to theoretical performance, just remember that the output will be into "4-pi" space, not "8-pi" space. So the length of the TL should be halved.

MJ King's work (while helpful and of great use to folks concentrating on completed projects and perhaps less theory), would not help you demonstrate your understanding of wave theory. Your time would be better spent developing the math from first principles, and why you might limit the solution to "4-pi" space. This requires that you differentiate between the Physics (where boundary conditions help you limit the solution(s) to those conditions) and Mathematics . Remember that Physics is NOT Mathematics .