T39L attempt

[ncgrove]

I'm trying to break Harley's record by attempting an un-sanctioned and ill-advised T39L build. It's being built with 1/4" BB and is going to be a final width of 24", using 23 1/2" panels. It will be loaded with a 3012LF. I'm using 5 braces for the first few segments where I imagine air pressures are higher, and four braces for the last two spans. The driver chamber is also heavily braced.

Here are some pictures of what I've done so far. We'll see how it goes, and if it doesn't work, it'll make for a nice fire.

[ncgrove]

[Bruce Weldy]

Really cool and nice work.....but, I would have stayed with 1/2" for the baffle.....that may be tweaking the giant's nose just a bit too much.

[Rich4349]

Wow, nice work. I've pondered this, myself. My plan has been to add a bit of 1/4" horizontal bracing between the "proper" vertical bracing. Not the full length, as that would largely defeat the purpose of the exercise, but enough to reduce flexing. And lots o' Swiss cheese holes! I've also considered a "w" formation, accordioning across the span.

[Chris_Allen]

How old are your T39 plans?

I thought the square hole in the baffle disappeared years ago.

[ncgrove]

Thanks guys. I'm not sure how old the plans are, but I like this style better than the newer.

The drill press got quite a workout today:

[J_Dunavin]

THAT looks cool, and extremely time consuming.
Excited to see how it sounds.

[Rich4349]

Again, wow. Quite clever with the extra lateral.bracing inside the chamber.

[Bruce Weldy]

Thanks guys. I'm not sure how old the plans are, but I like this style better than the newer.

+1

Got a feeling that if there hadn't been a spike in neodymium prices, there wouldn't have been a new design.

[Rich4349]

Updates! We want updates!

[ripNdeb]

Again, wow. Quite clever with the extra lateral.bracing inside the chamber.

respectfully -1; looks like OVER KILL to me. Time better spent on making things square and correct with respect to the plans. I didn't do the math but, that bracing takes away quite a few square inches of chamber volume.
But don't mind me; I'm losing my skills at my age. My current T39s build is twisted and off by as much as a quarter inch in places.

[ripNdeb]

Sh**, didn't even pay attention to the original post.....sorry. Still, maybe a little overkill on the GOOD looking braces. I hate braces. You should see some of mine. If nobody else sees them, what the hell?

[ncgrove]

The sides of the chamber are likely to experience a great deal of pressure at high volumes and are going to require a good deal of bracing when they are 1/4" thick. Really, Bill did all the hard work designing the Jack Lite series. That's where I got my bracing scheme from. The side braces have the added benefit of bracing the baffle and the panel to the rear of the driver. The panel I'm most worried about is the panel opposite the baffle that the driver fires into. It's only going to be braced to the baffle with 5 braces across a 23 1/2" span, so I hope that's enough to keep it from vibrating too much.

As far as the chamber volume, when using 1/4" ply, preserving the horn geometry requires an increase in chamber volume. I haven't calculated by how much (it would be pretty easy to do), but the chamber bracing should reduce the volume close to spec.

I haven't been able to work on the cab for a while due to trips to New Orleans and Little Rock for semi-unexpected family reasons, and helping a friend gut his house after it flooded last week. I don't know if anyone heard about the flooding in Houston, but he had about 3 feet of water in there. Hopefully I'll be able to get in the garage this week.

[ncgrove]

Got some more work done this weekend.

[Rick Lee]

I can vouch for 1/4" T39s. Just finished up another pair about 3 days ago. You're definitely not underbuilding them...