Center Block vs Brace on the baffle

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idnotbe
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Center Block vs Brace on the baffle

Post by idnotbe »

Image

Image

the first picture is more traditional approach to give load to the baffle - the center block which is connected / contacted from the baffle to the back panel.
the second picture is Fryette's V-brace which gives more rigidity to the baffle.

i think they are the same in the perceptive that they strengthen the baffle, thus they raise up the overall frequency of the cab.
the difference is... the 1st makes the back panel to move in the same direction of the baffle, but the 2nd is not.

is "making the back panel to move in the same direction of the baffle" important ??

some ppl say it reduced the phase cancellation by synchronizing the movement between the baffle and the back panel.
but some cabinets do not screw the center block to the back panel, thus the baffle & the back panel do not move in the same direction.
(when the air pressure goes up, the baffle will move forward and the back panel backward because the center block is not fixed on the back panel)

want to hear your experience or imagination.
Geeze
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Re: Center Block vs Brace on the baffle

Post by Geeze »

I've built a number of 2x12 & 4x12 cabs and only use bracing on the slant 4x12s - no posts. Yield strength data on wood is so variable that the simple answer in most cases is to 'over engineer' the design. I only use 3/4" BB style plywood for the baffle and back and haven't had any vibration [resonance] or phase issues - I'll admit I'm a bit vague on the phase side. When using thinner stock bracing becomes necessary to control resonance. Several years ago on this forum we chewed on the idea of the lightweight cab using 3/8 or 1/4" stock with radial, fan or honeycomb styles of bracing and came to the conclusion it would be a waste of wood.


This cab has been blasted with 50 & 100 amps with zero issues to date.
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The other question you raised about movement of the panels in relation to each would require some sort of strain gauge to measure deflection and direction. I'm somewhat ignorant on the engineering side of sound. It would be very cool to be able to measure the impact waves / collisions flowing around the cab faces. There are so many variables that contribute to the produced sound and too many assumptions / conclusions based on subjective data that sifting through the internet flood is a challenge.

I welcome any engineering or scientific data on guitar sound production that you have.

Thanks for posting!

Russ
dbeeman
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Re: Center Block vs Brace on the baffle

Post by dbeeman »

If you secure a stiff brace to both front and back panels, tying them together, it will limit panel vibrations. They want to move in opposite directions in a closed back cab. Of course most center posts are only secured to the baffle, so they are not as effective
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Bill Moore
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Re: Center Block vs Brace on the baffle

Post by Bill Moore »

Would they actually move differently in a closed cab? All the speakers move in unison, so they are either pulling a vacuum on excursion, or creating pressure, when the lower wave is produced.
I'm no engineer, but is seems to me the vacuum/pressure differential would be a wash.
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TUBEDUDE
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Re: Center Block vs Brace on the baffle

Post by TUBEDUDE »

The cone movement, say backward, pushes the back panel out rearward. The cones push the front panel out forward in the opposite direction. The opposite and equal reaction as the speakers.are mechanically linked to the baffle. Cone moves back baffle moves forward.
Tube junkie that aspires to become a tri-state bidirectional buss driver.
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Reeltarded
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Re: Center Block vs Brace on the baffle

Post by Reeltarded »

I vote post. I remove a handle on my 4x12s and hammer in a wedge between the post and back to tune the cabinets. It's more than a little tension in that. Just like a violin. Without the post the cabs just don't focus and project at a similar frequency in pairs or quads. It's about annunciation and controlling the plate modes. I prefer A cabs to B cabs, and I also glue insulation to the back panels to clean up the air a little.

What can work in an uncontrolled stock Marshall cabinet at low volumes is impossible to get once the spl causes the cab to catch the low frequncies like a baseball glove. Untreated cabinets act like open backs throwing a tantrum.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
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cbass
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Re: Center Block vs Brace on the baffle

Post by cbass »

i need to try to put a post in this thing. I have diagonal braces glued and pocket screwed on the center of the baffle. Its pretty stiff already though pretty sure you cpuld trough it out of an airplane and be fine.already wieghs more than a 4x12
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