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Cornwall Bracing

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I added internal bracing to my Cornwall 1’s and I can say it made a big difference! I always had a lot of “resonance” at the upper end of woofer range, very annoying. Now the sound in very tightened up, much less boomy.  Now on to damping.  I got some 1” compressed fiberglass to play around with.  Should say in order to fit new squawker and Horn I had to move the back out 1”, so I think my interior volume is close to original.  

D20EE70A-B03B-44E5-98A8-CAA8FEB347F2.jpeg

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39 minutes ago, VDS said:

I added internal bracing to my Cornwall 1’s and I can say it made a big difference! I always had a lot of “resonance” at the upper end of woofer range, very annoying. Now the sound in very tightened up, much less boomy.  Now on to damping.  I got some 1” compressed fiberglass to play around with.  Should say in order to fit new squawker and Horn I had to move the back out 1”, so I think my interior volume is close to original.  

D20EE70A-B03B-44E5-98A8-CAA8FEB347F2.jpeg

The coupling cutout you have on your shelf brace is on the small side not to mention the cabinet wide slot (about 3/4"-1" wide) that you now have toward the back side of the enclosure is going to make noise and you have blocked off about a three inch wide section (wider actually, a significant portion of the vent) of your reflex vent with the horizontal brace you installed. This photo is a good example of how not to brace your Cornwall. I understand that your intentions were good but the result is a messed up cabinet.

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33 minutes ago, moray james said:

The coupling cutout you have on your shelf brace is on the small side not to mention the cabinet wide slot (about 3/4"-1" wide) that you now have toward the back side of the enclosure is going to make noise and you have blocked off about a three inch wide section (wider actually, a significant portion of the vent) of your reflex vent with the horizontal brace you installed. This photo is a good example of how not to brace your Cornwall. I understand that your intentions were good but the result is a messed up cabinet.

Huh, yeah I thought about the vertical 2x4, I could switch to a 2x2.  It is 6” from the back, so 2/3 from the front.  The cut out in the shelf is 4” x 12”, looks narrower in pic and the “shelf” is only 10” deep, so 5” from back.

the cabinet is far stiffer and audible resonance is noticeably decreased.  I hear you though. Your posts on the importance of bracing brought to my attention.  I will certainly consider having another go at it. Thanks

 

 

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I have made worse mistakes and I have found I learned the most when I made mistakes.

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8 hours ago, moray james said:

I have made worse mistakes and I have found I learned the most when I made mistakes.

Oh yeah, I wish I could make fewer mistakes as I age... but I do learn..  I am taking your critiques and mulling them over. 1 question is the behavior of low frequencies, which I only know a very little about, and how they are not as “directly reflective” as HF, less like Bullard balls? Wonder if my 2x4 really “blocks” my center port 8” in front of it?

anyway, I added a pice of 3/4” plywood, with a 1/8” sheet of rubber in the middle  to the outside, back.  Very little vibration on the surface of a formerly VERY vibrating back panel. 
overall I certainly have increased the impact of the base, less boomy, and seems more articulate to my ears.

of course this is my Cornwalls, in my room, with my amp, through my ears to my brain.  YMMV

Ted

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1 hour ago, VDS said:

Oh yeah, I wish I could make fewer mistakes as I age... but I do learn..  I am taking your critiques and mulling them over. 1 question is the behavior of low frequencies, which I only know a very little about, and how they are not as “directly reflective” as HF, less like Bullard balls? Wonder if my 2x4 really “blocks” my center port 8” in front of it?

anyway, I added a pice of 3/4” plywood, with a 1/8” sheet of rubber in the middle  to the outside, back.  Very little vibration on the surface of a formerly VERY vibrating back panel. 
overall I certainly have increased the impact of the base, less boomy, and seems more articulate to my ears.

of course this is my Cornwalls, in my room, with my amp, through my ears to my brain.  YMMV

Ted

yes the wide brace is having  a negative impact upon the vent action which is to begin with too close to the rear baffle for ideal function. The air in a reflex vent at full resonance will travel fully 1.5 times the vent length in both directions (into the cabinet and out of the cabinet). Turn that brace 90 degrees and you can minimize the impact. The next time leave out the 3/4" plates you used under and above the brace and make the brace smaller. The ideal brace ratio is 1.5 time the thickness for the width. Remember you want the air flow of the vent to be as laminar as possible to insure the best possible performance.

Low frequencies are long, they do bounce off of a reflective surface but they also shake most surfaces because of their length and high energy when you play loud.

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"Braces" rarely carry actual load.  They are intended to prevent the 1st fractional movement.  "Braces" have no need for "strength".  Most of the braces you see in a building of bridge are designed for 1/10th of the load in the braced member (just because) and enough stiffness for their length.  You can get equivalent cabinet stiffness with much less material and weight.  Light and stiff together means high resonant frequency.  If you wrap an acoustic guitar with your knuckles, you don't get a bass knock in spite of its resonant chamber.

 

20200920_181058e.jpgote

I built this stand for my RV out of 1x2s.  It is intended for sitting.  It is rigid and surprisingly light.  The joints are glued and air nailed.  Two or 3 boxes from 1x2s with a "V" brace inside is all you need for your cabinet.

V-brace(inverted)e.jpg

 

 

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