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larryk

Cornwall Bracing

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Last weekend I decided to try bracing the motorboard on my Cornwall 1.  I had seen an old post regarding this.  I put an 18" 3/4 X 1 3/4 piece of oak half way between the mid horn and the woofer and secured with 5 screws.  This rather simple bracing made a huge difference eliminating any of the boominess I had as well as improving the midrange clarity.  I was concerned about taking up cabinet volume but this takes up very little.  Have many others tried this?

 

Bracing.jpg.a51f72401e8dbe11957081002675f374.jpg

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Run a 2x4 or two front to back.

 

Just use glue to attach to the motorboard, let it dry and then screws through the rear panel.

 

 

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Not sure how that would work.  If you glue one end of a 2x4 i would think the weight would not support it until you got the rear panel in place to secure with screws.  Maybe i am not thinking this right.   I have also heard that others have added a 3/4” panel to the back of the existing panel to keep the back panel from flexing.  Am curious what results that may bring.

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18 minutes ago, larryk said:

Not sure how that would work.  If you glue one end of a 2x4 i would think the weight would not support it until you got the rear panel in place to secure with screws.  Maybe i am not thinking this right.   I have also heard that others have added a 3/4” panel to the back of the existing panel to keep the back panel from flexing.  Am curious what results that may bring.

 

The back is more important than the motor board IMHO

The 3/4" ply works great! To my ear it made the back side of the woofer more pronounced

Just be careful and not screw into the mid driver.

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They have this wonderful invention called a tape measure that allows you to find out dimensions of a given area.  ;)  Find out where the mid isn't, and where there is a safe spot, or two, on the backside of the front baffle, attach the 2x4('s) to the back panel, put a little glue on the ends of the 2x4('s) and drop into place.  Obviously with the front baffle facing down so gravity helps with the glue.  Screw the back baffle in place and that should lock in the glued sides of 2x4('s) if measurements were done right.

  • Haha 1

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7 hours ago, larryk said:

Not sure how that would work.  If you glue one end of a 2x4 i would think the weight would not support it until you got the rear panel in place to secure with screws.  Maybe i am not thinking this right.   I have also heard that others have added a 3/4” panel to the back of the existing panel to keep the back panel from flexing.  Am curious what results that may bring.

 

Added weight and an unsatisfactory look.

 

Measure from motorboard to flange face, this will be 2x4 brace length.

 

Glue brace to motorboard between the woofer & squawker, set in place with glue and let dry. If you are worried about exact placement you can remove the squawker or woofer and test fit the new brace using a pencil to mark placement before anything else. This step will make drilling the rear panel hole placement easy.

 

Simply drill the holes in the rear panel slightly larger than the screws to avoid binding on the plywood.

 

I don't own Cornwalls ( so no measurements) just make sure to avoid brace placement under the rear jack.

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4 hours ago, jason str said:

 

Added weight and an unsatisfactory look.

 

Measure from motorboard to flange face, this will be 2x4 brace length.

 

Glue brace to motorboard between the woofer & squawker, set in place with glue and let dry. If you are worried about exact placement you can remove the squawker or woofer and test fit the new brace using a pencil to mark placement before anything else. This step will make drilling the rear panel hole placement easy.

 

Simply drill the holes in the rear panel slightly larger than the screws to avoid binding on the plywood.

 

I don't own Cornwalls ( so no measurements) just make sure to avoid brace placement under the rear jack.

 

Unsatisfactory look ???  I always kept mine with the back to a wall or a corner....Didn't look at the back unless moving :D

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On 10/3/2019 at 12:58 PM, larryk said:

Last weekend I decided to try bracing the motorboard on my Cornwall 1.  I had seen an old post regarding this.  I put an 18" 3/4 X 1 3/4 piece of oak half way between the mid horn and the woofer and secured with 5 screws.  This rather simple bracing made a huge difference eliminating any of the boominess I had as well as improving the midrange clarity.  I was concerned about taking up cabinet volume but this takes up very little.  Have many others tried this?

 

Bracing.jpg.a51f72401e8dbe11957081002675f374.jpg

 

That's a stiffener.  Glad it helped.  Now, use that as a shelf, glue and screw similar material to the stiffener and run back to the rear panel.  Be sure they are just long enough to touch the rear panel and screw the back panel the your new "braces".  Using that thin material won't reduce the interior volume much, so I don't think it will change the tuning. 

 

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23 hours ago, IB Slammin said:

 

The back is more important than the motor board IMHO

 

:emotion-21:

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Let's think this through guys, What is the bracing for?

 

I believe it is to minimize vibration of the baffle. If your thinking is that the back panel moves and that motion in turn "generates sound" into the room, then that mechanism would lead to a trivial impact. 

 

If the baffle is relatively stationary, then there is little motion transferred to the back panel. In terms of reducing the energy in the cabinet due to the back wave, then flexing of the rear panel actually converts some of sound energy (SPL) inside the cabinet to mechanical energy (flexing, heat etc).

 

Stiffening and dampening the baffle's motion is where you want to focus your efforts, IMO.

 

Good Luck,

-Tom 

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This is the method I plan to use. This picture is obviously a Heresy so you wouldn't need the notch for the K-55 as shown here, but this gives you the idea. I plan to screw to the baffle and sides with pocket screws, then through the rear panel into this brace. This picture was lifted from another member's Heresy resto.

IMG_6344_thumb_JPG_16829c1150a389c0c592f8cedb94bad7.jpg

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Strips on all sides like in the first post, a "plus sign" / "diamond" (diagonally-connected endpoints) shape with 1" wide "members", cut out of one piece of void-free (underlayment quality) lauan 1/4" thick, fastened to side strips like shown in the first post should be entirely sufficient for the task without altering the internal volume too appreciably.

 

I wouldn't do what's shown in that Heresy.  Takes up too much volume and I don't like those doglegs.

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On 10/4/2019 at 4:42 PM, IB Slammin said:

 

Unsatisfactory look ???  I always kept mine with the back to a wall or a corner....Didn't look at the back unless moving :D

 

Absolutely, looks unprofessional and lowers the resale value.

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On 10/5/2019 at 9:01 AM, capo72 said:

This is the method I plan to use. This picture is obviously a Heresy so you wouldn't need the notch for the K-55 as shown here, but this gives you the idea. I plan to screw to the baffle and sides with pocket screws, then through the rear panel into this brace. This picture was lifted from another member's Heresy resto.

IMG_6344_thumb_JPG_16829c1150a389c0c592f8cedb94bad7.jpg

This type of bracing would be my preference though some reduction on the meat of the H framing would be appropriate.  Make it excellent an fitting frame to avoid the cleats and use a lot of glue to avoid too much volume loss.

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Added all that bracing is reducing the internal cabinet volume which is not a good thing.

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On ‎10‎/‎5‎/‎2019 at 12:10 PM, glens said:

I wouldn't do what's shown in that Heresy.  Takes up too much volume and I don't like those doglegs.

 

2 hours ago, Frzninvt said:

Added all that bracing is reducing the internal cabinet volume which is not a good thing.

I have not done this on my Cornwalls yet, but I plan to. I will most likely use round holes with large radii on edges instead of the windows and doglegs. I plan to calculate the volume of the brace; I don't think it will be as big of a percentage of total cabinet volume as it appears to be in the Heresy photo. I have a plan for that though if the volume change is deemed detrimental. Knowing the volume that the brace consumes, I can shim the rear panel out an appropriate amount to gain internal volume to compensate. If you think about it, the brace would be no more than half the size of the rear panel. If you shimmed the rear panel out half it's thickness (3/8") that would compensate for the brace volume. Now figure the volume gain of the swiss cheese holes in the brace and we are talking maybe a 1/4" shim out of the rear panel. I will do actual calculations when the time comes, but this is my current line of thought. I plan to use pocket screws so this modification would be completely reversible if it is a bust. Feel free to keep shooting down this plan and I will try to keep coming up with solutions.

 

Jeremy

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If you are worried about the volume displaced, then consider adding some pressed fiberglass. JBL does this with their cabinets. About 1 inch thick on 5 out of the 6 panels, is said to increase the "apparent volume" of the box by about 10%. 

 

Please remember I said "pressed fiberglass" and not something recommended by "someone on the internet" who makes wild claims. The closest thing you can easily get is probably the material that HVAC guys use when they fabricate the large plenums up in your attic. Alternatively, the "blanket" material used in the old Cornwalls is good also. Check the Lansing forum and do a search - plenty of good info. 

 

Good Luck,

-Tom

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Dimensional lumber front to back is exactly how Klipsch updated the newer Cornwall series cabinets, that is the cabinets weak spot.

 

 

Cornwall braces..JPG

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20 hours ago, PrestonTom said:

If you are worried about the volume displaced, then consider adding some pressed fiberglass. JBL does this with their cabinets. About 1 inch thick on 5 out of the 6 panels, is said to increase the "apparent volume" of the box by about 10%. 

 

Please remember I said "pressed fiberglass" and not something recommended by "someone on the internet" who makes wild claims. The closest thing you can easily get is probably the material that HVAC guys use when they fabricate the large plenums up in your attic. Alternatively, the "blanket" material used in the old Cornwalls is good also. Check the Lansing forum and do a search - plenty of good info. 

 

Good Luck,

-Tom

Yes, or use angle iron or I-beams in aluminum or fiberglass framing.  Not near as easy or inexpensive but won't eat up the space.

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