simple bracing question...

[SkinnyBoy]

Skinny,

64L seems quite big for that woofer. What Q are you aiming for? Ported? ( tuning?)

I remember reading the following guidelines (one of Ray Alden's books?):

- if you have a rectangular panel, then better to run your brace longways and not widthways

- angle bracing? - I don't think that would provide as much rigidity as a perpendicular brace (eg. as each side flexes out, the perpendicular brace is providing maximum stiffness). However, an angle brace can help make different panels of different sizes therefore you don't 2 or more panels combining and resonating at the same frequency

- as you would using golden ratio type numbers for the box dimensions, so to the internal bracing spacing (such that you divide panels into golden ratio quantities)

as for the number of braces - not sure (that's really what you are probably after - not my mumbo jumbo . Maybe there is a "brace calculator" out on the net somewhere? (eg. brace position to "tune" a panel to a desired resonance frequency).

If you go overboard with braces - do take them into account with box volume (they do make a slight difference - about 8% when I made my sub box)

Reality?:
- with 1 x 6.5" woofer per box (< 5mm xmax?) - you aren't going to create huge pressure (further reduced if ported)

- 25mm is a good wall thickness to go for. Based on an MDF spec sheet I have, and my crude analogy - it will flex 35% less than 18mm MDF

- you will probably get better bass definition by having a heavy box that doesn't wobble

Dave.

I was aiming for 60litres, if I have more than that with speaker, bracing and port displacement then I will add some more bracing...

60 litres is one of the reccomended for this woofer, tuned to 40Hz...

I'm not using are ratios, I worked out the best way to make the boxes with the least waste from ONE 1200 X 2400 sheet of MDF.. lol

Its an 8inch driver with 4mm X-max (I think, one way) I know its not going to generate any pressure at all.. lol

Angle bracing... so the surfaces aren't parallel...

When I was trying to figure out if I wanted to add bracing to my last project I did the following sort of fun experiment. I don't recall where I learned about it.

I drove the woofer installed in the cabinet with my function generator feeding an amplifier. I layed the speaker on it's side on some carpet and sprinkled some table salt across the side facing up. With the tone playing at a moderate level, I changed the frequency of the generator. When a fundamental frequency of the cabinet structure is reached, the salt dances on the side of the box and shows the "mode shape" of the box that is being excited.

This was helpful in finding the first (lowest) resonant frequency of the structure. The test can be repeated after braces are added to see where the lowest mode as moved up to.

Unfortunately this method requires that the box be completed first.

Umm... I can't really add bracing in once the box is made... lol I am glueing EVERYTHING!!