BillFitzmaurice.info

Hi Folks
I am currently in the process of building a couple of DR250s but don't have the drivers yet. How far can I practically go without them before I absoloutly have to have them? Is it feasible to work from a template of the drivers? I am using Kappalite 10s.

This is where I am at the moment.



I have only just managed to get the image hosting thig happening so I'll post the rest of the build pics with some descriptions soon.
Cheers S

I'll try not to bore everyone with the baisic construction info other than to say that I pretty much just used the instruction document and worked through it step by step. I did use Sketchup to familiarise myself with the basic layout but didn't refer to it during construction (so far ).
I am lucky to have a large workshop and some reasonable tools, not professional quality, but good enough to work to about 1/64 (0.2mm) accuracy if you take your time.
My main tools are my Triton workbench with various attachments and a Riobi belt/disk sander that I use to clean up each part after I cut it.




I deviated a little from Bill's instructions at the start and first attached the throat horn sides to the throat divider as I figured that the angle on the sides of the divider is more accurate than the 13deg chamfer on the edge of the throat horn supports.


I didn’t think that 7’ was really enough length on the throat horn top and bottom covers so I remade them to 8”, glued them on.

Used a reciprocating saw to cut off the excess

And sanded them back

Hey S,
Cool.

The thing to do normally is be sequential about it all.
Not having drivers on hand makes that a little difficult.
It's nice to put your recex screws, mount the driver onto that baffle and make sure everything is good before (removing it again and) moving on.

However, there's a whole heap of other things that can get you progressing more than you think, and you will be glad to have knocked over later on.
Examples:
Building jigs for melded array (if you're using one, but I assume that piezo's would also be on the way, and crossover/filter components). Or if you're going CD's, build the diffraction horn(s).
Prebending ply for the sheaths.
Getting a pillow for the rear chamber stuffing, and the underlay for the rest.
You could also cut up some of the parts for the module.
Think about your sides an back if you're going to have one.

All that can keep you busy while you wait...

To trim the complete assembly to size, I had to do a little re-configuration of the saw table but it came out perfectly



The baffles were actually less of a drama than I first envisaged as I used one of those vibrating plunge cutters for all the cut-outs and it worked better than expected. I had always considered it a bit of a gimmicky tool but it has earned its place in the shop 
I did however make the job last three hours longer than necessary by not checking the blank panels for square before I cut out all the bits, so threw them away and started again, after a very thorough re-alignment of the saw.



For the top and bottom panel round cuts I made a circle cutting jig from a 5mm stainless steel plate by drilling and taping a 6mm post into it. The results were well worth the effort and better than I had hoped for.




I have fitted the assembly and supports to the top and bottom panels but as you can see have not yet fitted the woofer spacer and throat filler as I don’t have the drivers yet.

Hi Grant
Good to hear from you again. I’m very happy to report that, as you can see, your advice has not been in vain and that the project is well underway

I'll definitely get onto the HF module next and the other bits you mentioned.

I suppose I could also start on the T39s as well

Yes, you could!
It's more important with T39's to have drivers on hand (slap test).
Though it may take up another day to cut T39 roughs.
Be careful of focussing on each build if you are going 2 different types of builds at a time.

Enjoying another DR 250 build thread

Got all the brace flanges and sheath cleats in last night. No real dramas just steady progress





Something that I meant to show before was the very handy angle cutting attachment on the Triton that I used to cut the 57deg angle on the horn top & bottom. I am thinking this will come in handy on the T39 build.

SimonD wrote:

That looks a lot like cured 'liquid' polyurethane glue, it will work but it simply is not going to be as strong as the type from the cartridge, essentially because the bubbles are bigger.

get this one
http://www.bunnings.com.au/selleys-390g ... e_p1210570

Thanks Horst, I have been using Sikaflex Techgrip, but if you think the Sellys is better I'll give it a go, especially for the T39s where I believe that the seal is more crucial (not that I have not been VERY thorough in ensuring that all joints are fully covered). I did read the datasheet for the Techgrip but can't find a datasheet for the Sellys. Techgrip tensile strength is 3030kpa. Does anyone have a datasheet for the Sellys?

As for progress, I got the rear frame for the compression driver completed and front flanges cut and dressed ready for installation.

I just rang Budget Group regarding some Locktite PL and got a reply from their sales guy within five minutes. The will have some stock late next week apparently.

Aha! Now you will have the right product!

yeah, a whole case of it.
There is nothing wrong with the Selleys product, it may even be better, not that I have used PL premium, but from what I observe here, it 'oozes' more and expands more than the 'Selleys ultimate strength' which tells me that on the broad spectrum of polyurethane products from the expanding foam to the 'construction adhesives' it is not as strong as this Selleys, even if it isn't the difference is not going to matter, whereas the difference of the liquid polyurethane to the thicker 'construction adhesive' variety is substantial.

Thanks Guys, I'll see what I can get my hands on. There is of course the reality that as soon as an adhesive is stronger than the substate that it is attached to (and the liquid that I'm using now certainly is) the the rest is pretty much a moot point

Unfortunately no progress planned for this weekend as we are heading off camping

Hi Folks, I managed to get a bit done on the weekend as campling was delayed by a day so I worked Friday night.
Got a few more sections of the compression horn assembly complete.



Cut out the centre braces (anybody spot the minor safety issue ?



And attached one pair.



Looking good so far

Horst, you will be pleased to know that I have changed to using the Sellys. I did notice that although the Sika did fill the gaps etc. it mainly filled them with bubbles ;-(.