Structural goals for subwoofer enclosure

[zrino8]

I am starting the planning phase for two separate 12-18” subwoofers and I am a bit confused as to what the structural goals are for the enclosure. I am a bit of a novice when it comes to audio design but I am a civil engineer (still an EIT) so I can figure out the design of the structure but I am not sure what my goals should be for the enclosure should be.

1. I have heard a lot of emphasis on stiffness; I assume that movement in the structure would cause distortion; I am assuming that this is one of the primary goals.

2. The term “Deadening” is still a bit confusing, I have a loose idea of the definition, but this seems to be in a bit of a conflict with the stiffness of the enclosure, can anyone provide a good definition for the term?

3. I have seen a lot of designs that have cross bracing on the center interior of the enclosure, suspended cross bracing has obvious structural advantages but does this have any negative impacts on the acoustic design of the enclosure?

4. After reading several posts on the shape, I still don’t know how important this would be, does anyone have an input on the importance of the shape.

5. I haven’t been able to find much about the importance of the interior texture or elasticity, does this have an impact on the output of the system?

Let me know if you have anything to add about the integrity of a subwoofer enclosure. I am open to the idea of using most materials (softwood, hardwood, steel or concrete). Also if anyone has input on good drivers to use that would also be helpful.

Thanks.

[planet10]

1/ you want stiffness for 2 reasons a/ stiffness helps push panel resonances above the passband of the woofer (if resonances are sufficiently high there will not be any energy to excite them), b/ the woofer envelope needs to be immune to ballooning.

2/ deadening usually implies adding mass without increasing stiffness, this actually counters 1a/

3/ bracing, if it is suffiently "holey", will not affect sonics as the wavelengths being reproduced are usually much larger than any of the structures inside Bracing is used to further stiffen the box in aid of 1a & 1b. Braces should divide a panel into unsimilar trapezoids (in practice these trapezoids are rectangular) and the aspect ratio of the sub-panels should be greater than that of the panel

4/ Shape is only important in that it may aid 1a or 1b (ie a sphere or cylinder will resist ballooning -- althou in a cylinder it means great stress on the endcaps)

5/ see 3.

6/ In a woofer it always worth considering push-push drivers as this provides the opportunity for active vibration cancelation. I always prefer 2 12s to a 15 or 2 15s to an 18,

dave

[Henkjan]

Dave said it all...

[Pashley]

I am in China. Wood products here are mostly relatively expensive imports. MDF is not common, though it is available.

However, locally produced compressed bamboo flooring material looks like it might work as a sub enclosure. The stuff is really dense, over 1100 kg per cubic meter vs 600-900 for oak or MDF. It is quite hard, and some of it is very nice-looking. I assume it is also quite rigid, do not actually know.

It comes in two forms, tongue-and-groove planks or 50 x 50 cm tiles maybe 8 mm thick. I'm thinking of gluing tiles together up to some convenient thickness (probably 20-50 mm range) then building a cube-shaped enclosure out of them.

Any comment or advice?

[planet10]

Originally Posted by Pashley

However, locally produced compressed bamboo flooring material looks like it might work as a sub enclosure. The stuff is really dense, over 1100 kg per cubic meter vs 600-900 for oak or MDF. It is quite hard, and some of it is very nice-looking. I assume it is also quite rigid, do not actually know.

The US made bamboo plywood should have an edge (that is what we have used), but this stuff is good. A Danish manufacturer we work with is using this stuff to build his speakers.

dave

[zrino8]

Thanks for the info.