caculating internal cabinet volume when converting to curved sides

[justinthorpe]

Hi

My maths is not that great, and im having trouble working out how to calculate internal volume with curved speaker cabinet sides. I have permission to replace the main speakers, however her one requirement is that they have nice curved sides, not "big ugly boxes"

I have two ways,
1. Build the boxes as per plans, and add a second curved skin over this.
2, re calculate internal volume with the new curved sides, which is my preferred option.

Preference would be to keep the height and width same, and make them deeper to make up for the lost volume. The curve would be quite noticeable, rear panel width just enough to put the binding posts on.

Im looking at something around the size of Zaph's Dayton Tower 3.5 etc.

Any assistance and ideas appreciated.

Regards

Justin

[TEK]

What do you want the interal baffel width to be?
What do you want the internal volume to be?
Do you want a "half-circle" as B&W Nautilus or a flat back plate as many designs seen here has?

I can think of some methods.
1) draw the inner part of the speaker in sketchup and use sketchup to calculate volume.
2) a curved speaker can be looked at as several geometrical shapes put together.
Volume of a sylinder is just area of bottom x height.
So the volume of your speaker should be possible to calculate as this:
Vtotal = (Area of a segment of a sircle + Area of a triangle + Area of a rectangle) * Height

[TEK]

[justinthorpe]

Hi Tek

Thanks for the reply. I was looking to keep front of speaker size as per the plans, and same height, and have a narrow flat rear panel, pretty much as you have drawn above.
I will look at what you have suggested, never used sketchup before.

Regards
Justin

[PMazz]

Try some of these:

http://abe.msstate.edu/~fto/tools/vol/

[Juhazi]

The volume is not very critical, so you don't have to get exact volume - an educated guess is just fine in this case!

[TEK]

If you dont need an exact value, you could problably - in my example above - just take
width (of the front baffel inside) * depth * height
As the sides are wider in the middel and more narrow in the back, the average would problably be approx ok.

[fbov]

The volume is not very critical, so you don't have to get exact volume - an educated guess is just fine in this case!

+1

While the attached shows port length effects, the message is similar. I like to tune the box low, where F3 is flat. Very little difference in F3 going from 20cm to 30cm port length...

Have fun,
Frank

[Martyn]

I like to do a full-size drawing of the cross-section before I start cutting wood. If you do this on a large piece of squared paper, you can draw the original cross-section and then overlay your proposed shape. If the number of squares lost in the narrow part is about equal to the number gained by fattening the mid-section of making the box deeper, you'll be OK. Even drawing it half-scale would be close enough as long as your shape is accurate. I wouldn't wrap a rectangular box in curved sides - you might pick up some strange resonances.

[Steve Manning]

I second Tek's suggestion ...... try SketchUp. It's very easy to learn and allows you to make changes on the fly rather than having to re-draw something from scratch, it's also free! I believe the free version will let you calculate area but not volume, unless that has changed since the initial release. That is easily solved though by by downloading free plugins from the community, http://sketchucation.com/forums/view...culator#p14555 is a great place for plugins and help.

I laid out my entire build, having to maintain specific cabinet volumes, with SketchUp, before I cut a single piece of wood. It was well worth the up front time to get problems worked out before wasting material.

Steve

[BigguyZ]

I'm not a sketchup user, and I don't mind having to play around with things too much.

Assuming you don't have any change in height, the internal cross sectional area should be the same in the curved cabinet as the box cabinet. So if you take graph paper that's sized with 1/4" squares, you can draw it out and count up. I think I saw that a 10% variance won't affect the sound too much (though I aimed for as close to the actual area as I could).

Then that cross section becomes the template for your support ribs of your curved cabinet.

[justinthorpe]

Hi , yep, this is the way I will go, may take a little longer, but should get where I want to.
Now all I need to do is decide on a design. What are the speakers in your pics BigguyZ??

[BigguyZ]

The speakers are Clearwave 4TSEs by Jen Kunz. They were big a few years ago, and I know several people on the forum have built them. He still offers the kits, but it's not actively advertised on his website (he's mostly selling fully built speakers now).

I've been working on these speakers for about 3 years now. Work and other events have gotten in the way... I spent my tax refund on the internals (crossover, drivers, etc), so I finally don't have to worry about Jed not offering them anymore. Now I'm hoping that in the next 8-10 months I can piece enough time together to get the cabinets completed.