Need HELP Bass Cab Problem

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DaveWell
Posts: 246
Joined: Wed Feb 25, 2009 9:59 pm

Need HELP Bass Cab Problem

Post by DaveWell »

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
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ChopSauce
Posts: 1038
Joined: Wed Mar 15, 2017 12:08 pm
Location: So Paris, France

Re: Need HELP Bass Cab Problem

Post by ChopSauce »

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)
Geeze
Posts: 379
Joined: Fri Jul 12, 2013 3:41 am

Re: Need HELP Bass Cab Problem

Post by Geeze »

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
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DaveWell
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Joined: Wed Feb 25, 2009 9:59 pm

Re: Need HELP Bass Cab Problem

Post by DaveWell »

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
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DaveWell
Posts: 246
Joined: Wed Feb 25, 2009 9:59 pm

Re: Need HELP Bass Cab Problem

Post by DaveWell »

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