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Lbk

F20 braces

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Kirby and I were talking about MDF the other day. I took him outside to my flatbed trailer and showed him a piece of 3/4" baltic birch under the tongue jack where it has been for months in a very wet period and with freezing and thawing. There it sits stained but otherwise as good as new. No delamination no warping no rotting. You want strength in all ways and good acoustics BB is what I choose to use. Here in Nashville this is what the lumber yards tell me. MDF goes into car boom boxes and BB goes into speaker cabinets. They sell so much BB that even with  the 9.75% tax a 60" x 60" x 25mm sheet costs $48.00 out the door. Music City has spoken and it's preference is BB.

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12 hours ago, Lbk said:

What material did use, MDF -  BB?

18mm baltic birch.  I did use the mouth brace, but that's it.

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12 hours ago, Dave A said:

Kirby and I were talking about MDF the other day. I took him outside to my flatbed trailer and showed him a piece of 3/4" baltic birch under the tongue jack where it has been for months in a very wet period and with freezing and thawing. There it sits stained but otherwise as good as new. No delamination no warping no rotting. You want strength in all ways and good acoustics BB is what I choose to use. Here in Nashville this is what the lumber yards tell me. MDF goes into car boom boxes and BB goes into speaker cabinets. They sell so much BB that even with  the 9.75% tax a 60" x 60" x 25mm sheet costs $48.00 out the door. Music City has spoken and it's preference is BB.

Agreed but this time of year money is tight and time is  not. Got a good deal on some 23/32 inch plywood and thought I would give one a shoot. If it does not work out I will build another in a month using BB. I'am anxious to hear a folded horn sub.

Edited by Lbk

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Sorry, I misspoke  about braces, I did put some in.  Went back and looked at the pics from the build.

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15 hours ago, Lbk said:

Carl do you remember how far the mouth  brace is from front edge, looks to be about 6 inches? Thanks.

No set dimension.  You can run it out to the front edge if you want to or leave it shy.

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I braced my F20, it's not that much extra work.

And it's not like you can go in after the fact and add them.

 

F-20_Layout_SM2.thumb.jpg.8b3b43dc60ce3daf8a7b5fe3833c2d41.jpgF-20_4_sm.jpg.6db48254447394a36f160b8748bc2e44.jpgF-20_7_sm.thumb.jpg.6846c7c5f9531e49ee769b2b98335801.jpg

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That front panel where the woofer is firing needs bracing the most, not one yet i have seen has bracing.

 

Move the woofer 1-2" so the woofer is centered in the driver chamber, then you will have plenty of material to glue up that brace properly.

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Has anyone tried moving the mouth of the horn to the adjacent face? The dimensions would work better for me if the mouth was moved to the panel opposite of the woofer access panel. I have seen some tapped horn subs with options for moving the mouth to different panels (Danley I believe). I have just not seen an F20 folded horn sub configured that way. It looks as though some expansion may be lost so I don't know if it's viable. Been looking at the Lil Wrecker as well.

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1 hour ago, capo72 said:

Been looking at the Lil Wrecker as well.

I think it's about 9 cu ft bigger than the F-20.  It's a load.

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Leave the driver where the plans say it's supposed to be and brace like the picture above.  You'll be fine.  There's no vibration anywhere on the cabinet even when you're airing it out.

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On 2/19/2020 at 3:03 PM, CECAA850 said:

Leave the driver where the plans say it's supposed to be and brace like the picture above.  You'll be fine.  There's no vibration anywhere on the cabinet even when you're airing it out.

I think that's good advice since this my first f 20 build.  But would it help any if the brace next to sub was extended to run in front sub and connect to the mouth exit panel? Bad idea?

 

Hpower I like the black finish on your sub, is that duratex?

Edited by Lbk

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2 hours ago, Lbk said:

I think that's good advice since this my first f 20 build.  But would it help any if the brace next to sub was extended to run in front sub and connect to the mouth exit panel? Bad idea?

Not sure what you mean.  Are you talking about putting a brace in front of the driver?  If so it isn't necessary. 

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9 hours ago, Lbk said:

I think that's good advice since this my first f 20 build.  But would it help any if the brace next to sub was extended to run in front sub and connect to the mouth exit panel? Bad idea?

 

Hpower I like the black finish on your sub, is that duratex?

 

Yep, Duratex.

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9 hours ago, CECAA850 said:

Not sure what you mean.  Are you talking about putting a brace in front of the driver?  If so it isn't necessary. 

Yes in front of sub by extending the first brace. I will follow existing plans with above bracing, thanks!

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1 hour ago, HPower said:

 

Yep, Duratex.

Do you remember how much you used?

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Just now, Lbk said:

Yes in front of sub by extending the first brace. I will follow existing plans with above bracing, thanks!

Yes, no need to brace across the face of the driver.  The driver baffle is close to adjacent panels on all 4 sides which provide support.

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Just now, Lbk said:

Do you remember how much you used?

I'd estimate at least 2 quarts.  Let's see what he says.

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6 minutes ago, CECAA850 said:

I'd estimate at least 2 quarts.  Let's see what he says.

 

Hey Carl,

He says, he can't remember but I bet your guess would be close.

 

I would suggest buying 1 gallon, and a roller.

If you keep the bucket sealed up good, your left over Duratex should last, ready for your next project.

 

https://www.parts-express.com/acry-tech-duratex-black-1-gallon-roller-grade-speaker-cabinet-coating--260-101

 

https://www.parts-express.com/acry-tech-9-textured-roller-for-duratex--260-113

 

To get a slightly smoother finish, I usually mix a very small amount of water into the Duratex.

 

Tips-for-Storing-DuraTexR.pdf

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6 minutes ago, HPower said:

To get a slightly smoother finish

Or just go over it with a long nap paint roller while it's still wet.

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40 minutes ago, HPower said:

 

Hey Carl,

He says, he can't remember but I bet your guess would be close.

 

I would suggest buying 1 gallon, and a roller.

If you keep the bucket sealed up good, your left over Duratex should last, ready for your next project.

 

https://www.parts-express.com/acry-tech-duratex-black-1-gallon-roller-grade-speaker-cabinet-coating--260-101

 

https://www.parts-express.com/acry-tech-9-textured-roller-for-duratex--260-113

 

To get a slightly smoother finish, I usually mix a very small amount of water into the Duratex.

 

Tips-for-Storing-DuraTexR.pdf 87.36 kB · 1 download

Sub measures approx. 51square ft. According to PE one quart will cover 20 to 24 sq ft. So looks like a gallon to be safe.

Edited by Lbk

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