#166387  by Jblue76
 Sat Nov 02, 2019 9:59 am
Cab advice needed!
I was about to build a 15x15x13 1x12 cab but I just spoke with a guy that used to build cabs and he said you don’t want any of the sides the same length because of the standing waves, even in an open back cab. Is this true? For a small little 1x12 that approaches HT specs, what should be the dimensions?
Thanks!!!
 #166392  by TLRSIDP_Graduate
 Sat Nov 02, 2019 7:35 pm
A couple thoughts:

First, the go to material for the GD cabs is 13 ply, marine grade Baltic birch. This is a high grade void free, resonant free Baltic Birch ply and is usually imported. You may be able to find sheets locally, or online.

Second would be the precise joinery used to construct cab. Dados, or mortise and tenon were the preferred method and guaranteed a very rodust, rigid cab

Acoustics: a speaker will coil (+ wave cycle) and recoil (-wave cycle)

Parallel walls within a cabinet will cause reflection from speaker coil and recoil. Reflections can lead to "flutter" phasing issues and other very unpleasant residual sounds. When the speaker baffle, 4 inner walls and back are assymetrical then you deflect any kind of reflections away from each other rather than towards each other. This allows the acoustics of sound to dissipate and decay with very little interference between sound waves.

However, there is a serious science to cab design, acoustics and sound reinforcement. That's why high quality sound gear gets so pricy. This shouldn't be discouraging, but more of an insight into intricacies of sound. I have built a couple amp cabs, both with dovetail joinery, quality woods, hand built hand wired 5e8a tube circuit and quality speaker. Both cabs are air tight, closed back cabinets for maximum punch and limited bleed through from sides and rear. Stick with very hard wood, tight joinery and Quality speaker. Preferably a closed/open back design where you can experiment by removing back panel, using absorbative foam treatment when closed etc. You'll probably be pleasantly surprised by the results
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 #166393  by TLRSIDP_Graduate
 Sat Nov 02, 2019 8:06 pm
Here's a scaled down "Wall of Sound" speaker cab design. This is a Rudson mix cube studio reference monitor. It's the real deal and best sounding speaker I have that isn't an electrostatic ribbon speaker.

Dimensions: speaker 5.25"

Sides: 7"X7"X7"X7"

rear and speaker baffle are fixed within a channel, not simply glued to bracing. Scale this design to your 1X12 and it'll blow you away. I'll post picture when I figure out how. (New to forum)
 #166394  by Jblue76
 Sat Nov 02, 2019 9:59 pm
Thank you so much for that explanation. If you scale for a 12” speaker that 7” design for the 5.25” speaker, do you basically wind up with a 16”cube?
 #166401  by ac4468
 Sun Nov 03, 2019 1:50 pm
While not a direct answer to the 15x15x13 question, this is direct from JBL.

"An enclosure should be made of 3/4" material throughout, either plywood or particle board.  Outside dimensions ARE NOT CRITICALLY IMPORTANT but no single dimension should be more than 3 times any other"
 #166403  by lbpesq
 Sun Nov 03, 2019 3:26 pm
ac4468 wrote:While not a direct answer to the 15x15x13 question, this is direct from JBL.

"An enclosure should be made of 3/4" material throughout, either plywood or particle board. Outside dimensions ARE NOT CRITICALLY IMPORTANT but no single dimension should be more than 3 times any other"

I guess that would rule out linear arrays?

Bill, tgo
 #166404  by ac4468
 Sun Nov 03, 2019 4:13 pm
Good point. From what I've seen, the linear array cabinets are pretty heavily engineered and segmented with all sorts of ports and baffles.
lbpesq wrote:
ac4468 wrote:While not a direct answer to the 15x15x13 question, this is direct from JBL.

"An enclosure should be made of 3/4" material throughout, either plywood or particle board. Outside dimensions ARE NOT CRITICALLY IMPORTANT but no single dimension should be more than 3 times any other"

I guess that would rule out linear arrays?

Bill, tgo
 #166413  by TI4-1009
 Tue Nov 05, 2019 8:52 am
For GD/HT style cabs hard (Baltic birch type) wood is normally used. However, Fender usually used pine or other soft wood. You can sometimes tame an over-brittle JBL by using softer wood. Horses for courses. Remember that the Dead and their sound people were building for durability, touring, big halls, stadiums, and HUGE volume as much as anything, not bedroom playing. But it resulted in the sound we know and love.
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