Pensil 10.2 - To brace or not to brace?

[ElEsido]

Hi

I'm close to getting a pair of pensils 10.2 built. I expect them to be the only speakers I'm allowed to own for the forseeable future so I want them to be right. I've got a couple of questions before I pull the trigger:

- The builder suggested to use 18mm birch plywood. Is internal bracing recommended with this kind of material and will it bring audible benefits? I believe it would be rather hard to add bracing later?

- If no holey brace is fine, are two little braces at the bottom recommended, like in the third picture here?

- Do you reecommend to champher the back of the driver cutout the way Mark or the way Planet10 does it?

Thanks!
ElEsido

 

[planet10]

- The builder suggested to use 18mm birch plywood. Is internal bracing recommended with this kind of material and will it bring audible benefits? I believe it would be rather hard to add bracing later?

The primary purpose of the holey brace is to shunt driver energy to the back panel (away from the baffle). It is probably as much work to do the holey brace as the rest of the box, but i feel worth it. Skeeter just added his after-the-fact. But whole lot easier i expect during the build

- If no holey brace is fine, are two little braces at the bottom recommended, like in the third picture

Those aren't really braces but to hold the damping above the vent so you can't see it (cosmetic... a "net" would work if you are concerned.

- Do you reecommend to champher the back of the driver cutout the way Mark or the way Planet10 does it?

dave

 

[Bob Brines]

I put a pair of Pensil 10.2's together simply to have something to break in the drivers. 3/4" cabinet grade plywood, no bracing, no finish. Once I get my own design cabinets built the Pensil 10.2's go next to the curb.

The Pensil10.2's desperately need bracing. I understand P10's opinion on bracing, but I think that a holey brace the full length on the cabinet front-to-back is overkill. It's the side panels that are ringing, so much so it is smearing the imaging, If you feel the need to brace the driver front-to back, then do so only for the top 12" of so. Brace the rest of the cabinet side-to-side.

The holey brace is a real bug-bear to do with a router or a hole saw. Of course, if you have a CNC machine, then you start the machine and have a cup of coffee. The simplest and a very effective approach is to glue a 2" strip of plywood to the side panels. Start the brace below the driver to avoid splash back into the cone and end it a couple of inches above the vent. Offset the braces at least the thickness of the braces off of the center-line so that the braces are asymmetrical in the sides.

Bob

 

[skeeter99]

Dave is right, its MUCH easier to do while you're building the cabinet. I have just finished adding mine (last night) and they turned out really good. It was A LOT of work though and took quite a while. I think I cut close to 75 holes then of course rounded the edges on BOTH sides. Couple that with the fact that I had a 1/2" long bit and was using 3/4" material I had to cut each hole twice. UGH! I will say that panel resonance is SIGNIFICANTLY less now. I will do more side/side bracing at the top of the cabinet but probably dowels cut to length (much less work). I have the SuperPensil cabinets but I believe they all need the bracing, especially like Bob says on the sides. The panel resonance on mine is quite strong. That could be party due to the fact that I used MDF instead of ply but I still feel like a rock solid cabinet with no resonance will yield a truer response and less smearing. Just my 2cents though

Scott

 

[planet10]

If you feel the need to brace the driver front-to back, then do so only for the top 12" of so. Brace the rest of the cabinet side-to-side.

I can't disagree with Bob on that. Our build had additional side-to-side bracing below the driver. You can see the kind of thing Bob is suggesting in the microTower documents.

dave

 

[ElEsido]

Thank you for all your feedback. I'll ask the builder for a cost estimation with added bracing.

 

[chrisb]

certainly the larger pensils such as for Alpair 10 and 12 are in much greater need of a sturdy bracing regime than those for the smaller drivers

and yes, since I'm the guy actually building the damned things, I sometimes question the overkill holey braces myself , but they have become somewhat of a signature - there are simpler approaches .

 

[skeeter99]

and yes, since I'm the guy actually building the damned things, I sometimes question the overkill holey braces myself , but they have become somewhat of a signature - there are simpler approaches .

Agreed, there are definitely simpler approaches but these look so good when they're all done and you KNOW you have a superior braced cabinet

 

[jimbro]

I used a scroll saw and cut squares and odd shapes in my holey braces. A jig saw would work also. Didn't take all that long.

 

[Rullknufs]

and you KNOW you have a superior braced cabinet

That's why I decided to add holey braces to my Mar-Kel70, just to know that the sound as good as a Mar-Kel70 in 12mm particle board can
I can barely feel the cabinet resonate, even at high volumes.

 

[skeeter99]

That's why I decided to add holey braces to my Mar-Kel70, just to know that the sound as good as a Mar-Kel70 in 12mm particle board can
I can barely feel the cabinet resonate, even at high volumes.

That's great! I picked up a broom stick yesterday that I'm going to cut down and add some extra bracing in the top portion of my cabinets. The bottoms are pretty solid but the top is still too resonant for me. I want those babies dead

 

[dainrobert]

Do you all believe the classic golden ratio box would need side panel bracing? The side panels are only 5 7/8" wide.

 

[planet10]

No, you can get away without there.

dave