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jason str

K400-401 horn damping

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A few weeks ago i finally got around to damping my K401 horn with damping spray, what a difference a few bucks and a little time makes.

Here is what i used, 1 can per horn.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=268-250

There is probably other options out there but i had to order other stuff from there anyways.

I may also use this on the inside & outside of my LaScala bass bins when i get a chance to make my braces.

Anybody have a brace template to make things easier ?

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Anybody have a brace template to make things easier ?

If you mean the little wedgies that go inside... my understanding is there are enough variations in the dimensions that no single template would fit them all the same.

I've got a third laScala, beaterbox. Black with part of the rear (above crossover) brace broken out. I'm looking to maybe make this a little test bin and wrap (blue/screw) another entire layer of 3/4" plywood around the sides and perhaps top. Might also do the front where the 400 mounts if I put a K510 in there. I prefer the 402 sitting on top so we'll see. My hope is this extra layer of plywood glued & screwed will do the same thing as the wedgies and perhaps allow me to make it look a little nicer (hahahahahahaha)

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I may also use this on the inside & outside of my LaScala bass bins when i get a chance to make my braces.


I think that damping some slight vibration/resonance on the mid horn is different from trying to stiffen a sheet of plywood, like the sides of the LS bass bin. That needs mechanical stiffening, like adding braces or adding a layer of plywood on the outside. I don't think the spray would be much help in that application.

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I've put an old 5 pound soft dive weight on the 400's before (soft weight = the small bag with the lead shot). Never had any problems with the 401's, but I have also isolated them with a rubber gasket on the face and a rubber washer on the vertical metal support at the back.

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A speaker builder/audio hobbyist in the area gave me this response to my question to him about the LaScala bass cabinet dampening situation. He was very familiar with the bass cabinet design. I have not performed this mod, but would like to sometime in the future.

As for the LaScallas modification I have what I think is a much better improvement to the side wall issue. Take 16# or 30# felt paper and cut and glue a full sheet to each outside of the original side panels. Contact cement applied to original side boards and to the felt works good. Next take a cut to fit sheet of 1/4" void free plywood (birch veneered looks and finishes great) and again use generous contact cement on both sides and glue into place. Be sure and weight or clamp them together well- no nails are really needed. Let set up well.
You can band trim the exposed edge to finish. This modification makes a good, sturdy effectively thickened side wall that will not "breathe" with sympathetic vibration like the old panels once did! Bass response/ clarity is improved.
Sounds like it would work and no need for the braces. I have a pair of beaters I want to do this to.
I responded with some questions to the builder and his reponses are as follows...
Thanks for the great instructions. My only questions to your instructions are:
The 16# or 30# felt is the somewhat tar covered roofing felt that you get from a Home Depot or Lowes, right ?
correct
The instructions are for the left and right sides of the LaScalla cabinets only and not the back?
you could do the back as well would not hurt!
Can you recommend a specific contact cement?
I am thinking it was TightBond? (Don't use the water base type!)
When you say "use generous contact cement on both sides and glue into place" are you saying to use glue as well as the cement or only the contact cement?
Contact cement is all you need and good clamping/ drying time- nails if you like for extra strength
Wrinkles

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Anybody have a brace template to make things easier ?

If you mean the little wedgies that go inside... my understanding is there are enough variations in the dimensions that no single template would fit them all the same.

I've got a third laScala, beaterbox. Black with part of the rear (above crossover) brace broken out. I'm looking to maybe make this a little test bin and wrap (blue/screw) another entire layer of 3/4" plywood around the sides and perhaps top. Might also do the front where the 400 mounts if I put a K510 in there. I prefer the 402 sitting on top so we'll see. My hope is this extra layer of plywood glued & screwed will do the same thing as the wedgies and perhaps allow me to make it look a little nicer (hahahahahahaha)

No big deal, a little measuring never hurts i guess.

I would love the 510 combo but the funds are just not there at this point in time.

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I think that damping some slight vibration/resonance on the mid horn is different from trying to stiffen a sheet of plywood, like the sides of the LS bass bin. That needs mechanical stiffening, like adding braces or adding a layer of plywood on the outside. I don't think the spray would be much help in that application.

Yes, brace first then some damping spray was the plan.

Nothing is planned for the outside of the cabinet, my plan was to install the braces, remove the driver and go to town with the damping spray on the driver enclosure and inside of the bass bin & maybe the back of the cabinet if i can't find my big roll of self stick damping material.

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jason, the driver enclosure, or doghouse as it's often called here (after all, it's where the woofer lives), has no issues with rigidity or resonance. The only "problem" area (and it's not a problem to many LS owners) is the large side panels that are secured on only three sides, and on those sides, the supported edges are two feet apart.

The back is secured on four sides, plus it has the chevrons attached to its inner side, which also attach it to the doghouse, so it's secured in the middle as well. Those chevrons are the beginning of the bass horn. Meanwhile, the doghouse is smaller and is secured on all sides. It's pretty solid.

As for the bass horn, adding anything to its insides will change its engineered dimensions, changing the sound in the process. Besides, wood is not like metal. It has a much higher damping factor by its nature. Wood doesn't ring, which is why it's never used to make bells.

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I've put an old 5 pound soft dive weight on the 400's before (soft weight = the small bag with the lead shot). Never had any problems with the 401's, but I have also isolated them with a rubber gasket on the face and a rubber washer on the vertical metal support at the back.

Did you also use rubber grommets to insulate the screws from the horn ? Otherwise all your insulating may not be useful.

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jason, the driver enclosure, or doghouse as it's often called here (after all, it's where the woofer lives), has no issues with rigidity or resonance. The only "problem" area (and it's not a problem to many LS owners) is the large side panels that are secured on only three sides, and on those sides, the supported edges are two feet apart.

The back is secured on four sides, plus it has the chevrons attached to its inner side, which also attach it to the doghouse, so it's secured in the middle as well. Those chevrons are the beginning of the bass horn. Meanwhile, the doghouse is smaller and is secured on all sides. It's pretty solid.

As for the bass horn, adding anything to its insides will change its engineered dimensions, changing the sound in the process. Besides, wood is not like metal. It has a much higher damping factor by its nature. Wood doesn't ring, which is why it's never used to make bells.

Makes sense, my idea was to mainly hide the glue that will be needed for the braces and i figured it would not hurt to do the whole thing.

Wood does not ring but it does have its own tone.

Good news on the back of the cabinet, i was wondering how much support was back there.

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