T39 Build, Perth Western Australia

[SimonD]

11 1/4 Inches between the Mouth Brace and outside panels is too large.

Are you refering to the curved mouth braces? If so what panel do you think is going to flex, Panel 6?

[Grant Bunter]

S,

You might not even feel the flex or movement of any or all of the panels, but if it's there it can be quantified as causing a 3dB loss in output. If you built only 2 cabs, that would be like throwing the second one away.

It should be in your plans that mouth braces should be spaced no greater than 9" apart.
If not check out the sketchup file.

Your cab is 24" wide. With one vertical mouth brace, that means a spacing of 11 1/2".
There should be 2 vertical mouth braces, spaced at roughly 7 2/3" from inside edge of either side...

[SimonD]

Ok, I get the idea, I need more bracing

Let's concentrate on how to achieve that. Two more braces in the horn mouth is not a problem and that will deal with the panel 8 & 6 issue. That just leaves the panel 5 & 3 issue. I don't know jack about speaker design but I do know about structural analysis and I believe that my solution of two or even three dowels through panel 3 to panel 5 on each side of the cab as per my drawing will provide the same support as a flat panel brace.
I could model it in Space Gas and get a definitive analysis but I really can't be bothered

Any other suggestions greatly appreciated

[Bill Fitzmaurice]

Thanks Bill, I seem to have saved a section of the drawing and labled it 21" for some reason
Either way, what do you think of my fix?

That will work.

[DJPhatman]

Thanks Bill, I seem to have saved a section of the drawing and labled it 21" for some reason
Either way, what do you think of my fix?

That will work.

SimonD's "fix" looks like it will work, but I think 3/8" (9mm) dowels, using at least 3 per missing brace. IOW, smaller diameter but more of them. Bill?

[SimonD]

Sorry for the delay folks but I have been up north (Western Australia) for a few days messing around with control systems for making big rocks into little rocks and putting them on ships (what a legacy I'll leave....)

I picked up some nice 9mm Tasmanian Oak dowel. I haven’t seen this before but it has a serrated edge running lengthways along the dowel giving it a much larger surface area for the glue to hold on to. I’ll install the extra bracing this weekend.

[SimonD]

Bracing operations are complete, I put four 9mm braces each side of the central brace.



and two braces each side of panel 3. I also put three 20mm posts between the driver mounting bracket and panel 3. There is no flex anymore



Almost ready for Duratex, just a bit more internal cleanup around the horn mouth. Is it ok to use the Duratex inside the horn mouth and on the mouth braces etc?

[Tom Smit]

Almost ready for Duratex, just a bit more internal cleanup around the horn mouth. Is it ok to use the Duratex inside the horn mouth and on the mouth braces etc?

Absolutely! If you have any adhesive left, try to chisel it out, and then spray the adhesive joint with latex paint. This will allow the Duratex to grip. Otherwise, the adhesive will show right through because the Duratex rolls right off.

[SimonD]

Thanks Tom. I have done a bit of a search for Latex paint locally but not comming up with anything

I have sanded all the glue remnants off the bracing so don't think I'll have an issue. My system is to let the glue dry for about four hours, then I use a cheap craft snap-off knife, the type with the blades that you break the end off when it becomes dull, to cut the excess glue off. I extend about an inch and a half of blade from the knife and that allows the blade to bend easily so that I can run it along flush with the timber on each of the two faces and cut off all the excess glue in a single piece.

[Rich4349]

There is no 21" T39 model, there is a 23" panel width model.

Alright, I know this is going off the reservation and risking the wrath du Bill, BUT...
Would a 96" wide, 4 x 3012lf, braced every 8" titan 39 (or 48 with appropriate drivers) "work"? Yes, it would be for permanent install (or a masochistic roving dj).

Also: do 4 slim t-39s that are <30" wide have a lower frequency capability than a pair of 30"ers? (Assuming all of the above are equally v-plated.) I don't have my plans with me; is the narrowest version 15" wide?

[Bill Fitzmaurice]

Would a 96" wide, 4 x 3012lf, braced every 8" titan 39 (or 48 with appropriate drivers) "work"?

It will, but by about the third panel you'll find it too big and too heavy to move to install any more panels and will wish you'd built four 1x12 instead.

[SimonD]

Hi Folks, Just a quick update. Driver burn-in is in progress as per the picture.



The cabinets are complete and ready for mounting the drivers this evening

The moment of truth is fast approaching!

[escapemcp]

Sorry for the delay folks but I have been up north (Western Australia) for a few days messing around with control systems for making big rocks into little rocks and putting them on ships (what a legacy I'll leave....)

Totally off topic, but I saw in a TV program that some geezer from a quarry said that 20% of the world's power was spent crushing rocks. I was pretty amazed by this if true, but I don't believe it... 20%... that's a lot! Any insight on this figure Simon?

Sorry for derail.

[SimonD]

Very interesting escapemcp, I had a quick look at what Perth, Western Australia, was using right now and it was 3125 Mw. I know of many mines around the state that have power stations raging from between 20Mw to 160 Mw. Add to this the towns that support them (the towns would not be there if the mines weren't there) and we could easily get past 20%, probably closer to 40%. So for Western Australia that would definitely hold true. The rest of the world I couldn't comment on but I would presume that countries like Canada etc. would be similar?

[escapemcp]

Sorry for the off-topic, but I just couldn't believe it when I heard it and then you come along with your rock crushing experience.

Back ON-topic, nice build and nice recovery on the bracing. Not long now