(Yet ANOTHER) DR250 Build Thread!

[escapemcp]

Has no-one spotted the deliberate mistake??

No-one? The 'deliberate' mistake was locating the cutout so that the driver had to be touching the top of the cab to get it inserted into the chamber. This allowed no room for the bit of wood that has to go between the 2 uprights which allows the airtight seal. You probably all knew this and were waiting for me to find out

To correct this problem the uprights had to come out. I thought of miked's problems that he had with his braces... or was it Mr. Bunter, when he had to move the throat horn support up a touch... I think it was Grant as I remember him using a plastic saw and breaking it - miked used a sawzall IIRC. Sorry.. anyway.. I thought of Grant's problem and looked for a similar saw (top saw in pic). This was until I realised that I could just as easily use the bendy saw (below it - I'm not sure of the name - I think that's bad ):


Once removed, I tidied up the area and started again. After a lot of messing around and PITA small cuts, I ended up sorting out the problem, and I'm happy that I did. The driver fits in much easier now, and I'm not sure if it's just me, but there seems to be more wood in the thin bit. It probably IS just me, as I can't see how this is possible.

I also installed the top and bottom braces, along with a reinforcement for the top hat - I have countersunk the TH 6mm (1/4") that allows it to sit flat on the base. I decided that one big piece would be better than a couple of small strips, although I doubt it would make much difference either way. I like the industrial-ness of the one piece.... that sucker isn't moving, and I don't want to take any chances. A DR falling from a couple of metres up isn't going to end happily.

So without any more of my yap here's what you've been waiting for (prepare to be disappointed though! ):

Here's all the progress on cab #1


Reinforcement for top hat (hole yet to be cut out of the centre):


Who can see the DR monster?

I like the fact the the piece of wood comes all the way forward to the back of the tweeter module. If I hadn't don't this, I would have been worried about the plies splitting when the chunky screw is driven straight in to the edge of the ply of the brace. And yes, the 3 degree angle is there, so it's all nice and flat ready for the array back.

Finally, sorry for my bad grammar in this post (well, all my posts actually ), and for making this build look bloody awful. I have posted some ropey looking pictures in the last couple of days, mainly due to me having to correct mistakes/things I wasn't happy with. I'll promise it'll get better in the next few days I'm sure removing the extra tube of PL that has ended up on the cab will help loads. Sheaths tomorrow, so I can hide all my dodgy work!

Oh, and another finally... would anyone care to comment on my PVC pipe situation please? My 100mm (4") ID pipe won't fit where it's supposed to, as that is about 1/2" wider than the pipe's outside diameter. Should I look for pipe that has 1/4" thick walls (as that's what sketchup is suggesting).


Thanks,

Aidan

[rogerc]

Would upvc half round guttering work in place of the 100mm pipe? It is around 115mm across the open side and slightly flexible.

[escapemcp]

Yeah, possibly. I just want to be certain of the OUTSIDE diameter of the pipe, as this is the one the soundwaves will see. Once I know that, i can adjust.

[escapemcp]

A new day bought about new ideas (inspired by Roger), so I decided to head off to try and find some 110mm OD PVC pipe. This is what I found (shown next to the old stuff I had):


This is looking much more like the pipe I saw in sketchup

It only came in 3m sections and I had forgotten to take a saw with me to the shop. I had to squeeze it into a Volvo 850 saloon. With a bit of jiggery-pokery, I managed to get it in and the boot closed - the clearance was in fractions of an inch. The static coming off the thing was unreal. If I moved my arm within 6 inches of the pipe, I could feel it moving all my hairs! Once home, it was onto the mitre saw and time to chop it down into managable bits:



That static that I was talking about continued to let it's presence known. Despite using a hoover attached to the mitre saw, the chippings went everywhere and stuck to everything. I was orange by the time I had finished all the cuts!

I then had to rough up the edges to give the glue something to bite into. I was going to use sandpaper or perhaps an electric sander, but I realised that would have produced even more static orange bits... these ones would be even smaller - just the right size to inhale, in fact I therefore opted to use the saw from yesterday (now known as my Grant saw). I ran it up and down the edges like so:



You can see the 'before' and 'after' quite nicely in the following shot:



Once they were all ready, I broke out the glue gun and attached them. I also filled the area that this created behind the pipe with the stuffing, as I know that it has been mentioned on previous builds that if you leave it until where it is in the plans, you'll have a hard time getting that 'stuff in' there



Talking of stuffing, the stuff I have managed to grab (for free) has quite short fibres, which means that it doesn't really hold together well. I envisioned all the stuffing coming out of place once these cabs start to get lugged around all over the place. I therefore grabbed a pair of tights from my draw and used this to block up the holes. This makes for a much neater look when looking into the driver chamber (I told you I'd get neater!!)



Next up.... horn sheaths. Been looking forward to this bit. The cab really starts to look the part once you get these on. Nothing much really to report here, so here's a pic of the end result:



So after all my work today, this is now how cab #1 is looking:




Much neater than yesterday!

Tomorrow it's more of the same, will probably try to work on cab #2.

A quick question though... one of my tubes of PL seems to be foaming LOTS the other day. It has much larger air bubbles in it than usual. Luckily it was on the cleats that I discovered this, so it hasn't caused any critical issues. I have now swapped to using a brand new tube which seems to be ok. The weather here has been hotter here than usual - a balmy 23°C (73°F) - so I am wondering if this is causing it? Could this be an indication that the PL is not getting enough moisture to cure, and I should be using the damp the glue line trick? It all seemed to start when one of my tubes had a bit of an air in it. Once the air had passed it started spitting out extra foamy PL, which incidentally was also runnier than the stuff that had preceded it from the same tube! Any ideas? I'd hate to waste over half a tube of PL.

Thanks

[billkatz]

Great progress. This is motivating me to get back to the workshop...

[Bill Fitzmaurice]

A quick question though... one of my tubes of PL seems to be foaming LOTS the other day. It has much larger air bubbles in it than usual. Luckily it was on the cleats that I discovered this, so it hasn't caused any critical issues. I have now swapped to using a brand new tube which seems to be ok. The weather here has been hotter here than usual - a balmy 23°C (73°F) - so I am wondering if this is causing it?

PL expansion is more active in warmer and more humid conditions.

BTW, the horn sheaths are supposed to go on before the PVC reflectors, not after.

[Tom Smit]

I therefore opted to use the saw from yesterday (now known as my Grant saw).

It looks like a drywall saw to me.

[escapemcp]

PL expansion is more active in warmer and more humid conditions.

Should I do anything to allow for this??

BTW, the horn sheaths are supposed to go on before the PVC reflectors, not after.

Yes, I know (sorry ) - I'll explain my reasoning:

I remember that Grant stuffed the horn throat area before he put the sides on. I looked at the same problem, and realized that if I wanted to stuff the whole area - including behind the PVC pipes (as I believed that this was what you were supposed to do) - then the PVC reflectors have to go on before you can stuff that area. If you were to do this as the plans say, then you could stuff the area around the horn (with difficulty), but you'd then have to put loads of stuffing inside the PVC pipe just before gluing... and with my skills, that would mean it would have ended up everywhere!

However since doing this I have thought about it, and I expect it isn't necessary to stuff the areas 'behind' the PVC pipe. I'm no expert but I think that the stuffing is just to damp down internal reflections. If any sound was to get to the PVC pipe area and rebound back, it would have to go through the wodge of stuffing around the horn throat twice which would have killed any reflections - the bit behind the PVC pipe is therefore probably pointless! You'd get more of a reflection off of the 'letterbox' surround than you ever would with sound going into the area behind the pipe.

Here's a pic of the letterbox and the area 'stuffed' behind the PVC pipe , so that you might get a better idea of what I am on about:



Thanks for the heads up Bill... I hope what I said made sense and you can understand my reasoning (even if it was all based on flawed logic!)

[escapemcp]

Feeling pretty ill with this cold - although not so ill that I couldn't do a few light jobs tonight I am finding that although I am not enjoying the building quite as much whilst I am ill, it takes my mind off of the cold, the alternative being lying on my bed feeling lousy and sorry for myself.

Anyway, it'll be pretty brief tonight.

First I...



Then I...


And finally, I...


I ended up using 4x2.5mm speaker cable. I know this is total overkill, but I am planning to install the filters behind the buttcheeks & I prefered making one hole into the driver chamber rather than 2... therefore it had to be 4 core. It's only about a foot of cable anyway, so no biggie.

[Grant Bunter]

but I am planning to install the filters behind the buttcheeks

Errr, you sure you have room to do that?

[Bill Fitzmaurice]

but I am planning to install the filters behind the buttcheeks

Errr, you sure you have room to do that?

Plus if located there you won't be able to fix them if anything goes wrong.

[Grant Bunter]

but I am planning to install the filters behind the buttcheeks

Errr, you sure you have room to do that?

Plus if located there you won't be able to fix them if anything goes wrong.

IIRC ncgrove's build shows a slight mod allowing a detacheable back cover plate.
So that's a possible answer to that problem Bill.
I was more concerned with adequate room to have 1 inducter mounted perpendicular to the back cover to decrease cross talk...

[Bruce Weldy]

I am planning to install the filters behind the buttcheeks

My wife has requested this upgrade on me for years.

[Grant Bunter]

I am planning to install the filters behind the buttcheeks

My wife has requested this upgrade on me for years.

You made my spill my coffee lol...

[escapemcp]

They'll fit

I am planning to have a removable back (or probably a removable part back). I am aware of the issues and the diversion from the 'follow the plans' golden rule. I feel that this is an area where I am happy changing it slightly. The idea is that if I biamp down the road (which I probably won't, but it's nice to have the option), then I can easily wire it up as I have the 4 core coming from the driver chamber. Time will tell.

Quick one tonight. No real progress. Bondo & sanding sheaths. Got this new toy in the post today:



Drill & countersink:


Then flip:


Then screw:


Should speed up my builds quite a bit, especially the tubas with all those screws. Not bad for £16

More tomorrow.

Night