18” down-firing EGG shaped sub build…

[GMichael]

I agree with the extra bracing. It's not so much that you need it and would have to add it later, with the shape you have and the thick walls you don't really "need" bracing at all. But I would always do bracing as it's the most efficient way to get a stiff box. With bass it's all about stiffness and there is never too much.

There is no need to "break up sound waves." Design your bracing for maximum stiffness and you should be fine. With a sealed box, it's not so much what goes on inside the box, but what gets out. There are two ways to get out of the box:

1. Through vibrating the enclosure - this is what most worry about and it's important, but not as much as
2. Re-radiating through the cone itself - this is controlled by the damping of the driver

The second is a much overlooked problem, described here:

http://www.rythmikaudio.com/re-radiation.html

Consider this. You have very stiff and thick walls - 2" right? They will be as solid as you can make them. Now you have an 18" light weight cone that is designed to be compliant so that it can efficiently create bass. Which do you think provides the easier path for sound to get out of the box? Here we are not talking about transmission so much as the sound pressure waves from inside the box placing dynamic pressure on the cone, just like an active driver will cause passive radiators to move. It is the same except the active driver has an electric motor which resists interference. The driver Qts indicates the ability of the driver to reject this influence.

Thanks Paul. All great info.

I think the shape of the "box" in this case should help cut down on the re-radiating factor. What do you think there?
I also plan on adding 2 inch Mineral Wool inside. The driver manufacturer suggests a half fill.

Thanks for the link. I guess all those curved speakers (IE:B&W) are not just for looks.

Here are the specs on the driving I will be using.

Fs: 17.4 Hz
Le: 4.0mH
Re: 3.8 Ohms (Voice Coils wired in series)
Qms: 3.62
Qes: .42
Qts: 0.37
Mms: 525g
Cms: 0.16 mm/N
Vas: 313L
Sd: 1182 cm^2
BL: 22.9
X-max: 32mm
Pmax: 1500W
SPL: 87.8 db/1W/1M