Tube Amp Archive

Hi
I built a Bass cab and the back rattle,
The Amp is a 5F8-A with 4 x 6550 bias at 70%
The Speaker is a Eminance Beta 15A 300W http://www.eminence.com/pdf/Beta_15A.pdf
dimension of the cab.
27'' x 27'' X 10 1/4''
Contour made with Pine 3/4'' and front and back made with Russian plywood 3/4''
Should I add a Port? And what Seize ?
or, 2 stripe of solid wood on the back pannel each side of speaker magnet + isolating Wool, exemple:onpen cab picture
other pictire is my cab.

Thanks

I'd vote for ports. Firstly because it is always reported as working well and secondly for physical reasons : the speaker is otherwise working against pressure and it doesn't seems to me that's what we're after.

About the ports themselves. As I see the speaker centered, I guess symetrical ports on each side - and for the ports size... what could be an average value, in between the area of the speaker and what's recommended for the 15" Thiele cab (was that TL606 ? ) - for a rull of thumb example?

These two pic-cents of contribution still remaining to be deburred - or ignored -
(this does not preclude reinforcing the back, though)

The solution depends on your sound requirements. Closed cab yields a tighter punchy and 'faster' sound. Relieving the pressure with a port goes somewhat the other way - looser and possibly more developed low end.

I use 3/4" BB style plywood for baffle and backs and haven't run into resonance issues yet but I play guitar. If you plan to brace I'd look at multi axis style bracing like an X pattern or a fan pattern. The pic of bracing you show only controls one direction of flex and might not completely solve this issue.

Russ

The Bassman tell me that the problem is really the back panel ripple...
renforcement of back pannel and a small port , together may be the solution.

Side brace may work too

Hi !
I modify the back pannle bu adding 2 brich wood pieces
not test for now , but it might helpfor the FK ripple