BillFitzmaurice.info

So, I finally got to start my DR 280 build last saturday, got the latest updates of the plans a few weeks ago, and I must say the feel like an easier and faster build, not that I´ve built to the previous version.

This is my second BFM build, did two 800mm wide Titan 48s last spring. The DR´s are for sure more complex, but I must say, a lot more interesting and enjoyable build Those of you who hesitate to build them, just do it:)

With my Titans I went very much CNC, watercutted all the plywood panels, just cutted the angled edges on a tablesaw. Since we used arauco, the panels twisted a lot from the water:P but it was no problem to straigthen them out, the cabs are very square '
But on the DR´s I felt that it would be to much work for not as much gain to do a full CNC-job, even more so taking in account that the construction probably wouldnt straighten out it self the same way as the Titans did.
So I went the middleroad, CNCed moulds for all parts that arent just square panels, or gets trimmed against the cab itself. This have definitly saved me time, havent had to measure so much, or convert to mm, I did that easily in Autocad And all curved surfaces are routered against the aluminium moulds:) I´ll take a few pictures today.

Sadly my landlord just moved his nice big professional tablesaw to a different workshop, the same day i started my build.. So I´ve used a circularsaw with a sled, a jigsaw and my router, and has worked out great:)

Today we are gonna put on the first curved panels, thats gonna be fun We didnt find any nice 6mm, 3 ply pine plywood, so gonna go with 2 layers of 3mm, laminated together, couldmoulding in boatbuilding terms. That should be atleast as strong, or even stronger.

But, now I run in to a "problem", the backhalves, and the compression horn "chamber" sides are to be made out of 1/8" 3mm plywood, I was thinking to use the pine I have here also, but now I´ve seen in the new plans that Bill says the 3mm ply must be either Birch or Poplar. That makes me wonder, is that because of the superior strength/stifness of the Birch compared to Pine, or mostly because its much easier to bend it without cracking the Birch? I may very well be wrong, but isnt Poplar a lot weaker then Birch, or even Pine?
I remember using poplar plywood to make floorboards on a lightweight race-yacht we built at a boatyard I worked years ago, and it didnt feel very strong, more like balsa then pine almost.

So, would there be an issue if I make the backhalves and HF chamber sides from 3mm pine? I did a testpiece yesterday, no problems at all to bend the backhalves with the pine, from flat sheet to full bend directly, no cracking noises or anything, and gets really nice and stiff when its held in place with one hand. I could laminate the HF chamber sides to get them stiffer, not so much bend in those, if that doesnt create any other negatives, the chamber would be slightly smaller of course, so the outside skins still match. But there are many stiffeners on the inside of that skin, so may be enough with one layer of 3mm, as per the plans, even if using pine.
Still gonna need to buy more plywood for the HF chamber, one sheet will be just enough for the backhalves and the woofer chamber sides. But it would be nice to not have to buy birch, mostly because birch is around 3 times more expensive then pine, and a lot harder to come by here in Gothenburg/Sweden, partly because the grossers who sell it are only open when me and my partner are at work, and its a bit of a drive to get it

So, whats the verdict, can I go with pine, or do I need to bite the financial apple and take the hassle of going to town to buy one sheet of BB?

I´ll upload some pictures of our progress so far later today

Good news, I just found a retailer that carries BB, that are opened at times when me and me partner are not working They "only" have 4mm, or maybe its somewhat thinner they said, I havent been able to find anyone who has thinner BB than 4mm, perhaps the RC model shop has some, in 100mm wide strips
The only bad news, is that the 4mm BB cost 475 sek, incl tax, for one sheet, the 3-3.5mm pine I have costed 200... Sadly birch is very much more expensive here in Sweden than in say USA, seems to be around twice the price, and its the same with a lot of stuff here... Thats why I order most of my sound and light stuff from Thomann in Germany, veeeery much cheaper for the exact same stuff..

I cant imagine that it would be a problem to use 4mm BB instead of 3? Except for where the backhalves meet, I´ll have to make some more room there..

1/8" (3mm) BB is specified as it's the only widely available species in the US in that thickness. Expensive BB in Sweden makes no sense, it's only coming from Finland. 4mm should be OK with the wide radii of the DR280 sheaths, so long as it's 3 ply.

Ah, I see Bill:) I know, its completly senseless that stuff made in our neighbor-country is more expensive here than in USA, but sadly thats how it is.. Part of it is ofcourse our 25% sales tax, but that I´ll get back from the state later, since I´m buying it to my company. But thats how it is in Sweden, most stuff is much more expensive here than the rest of the world, not only wood. Our government take very much of all money we make, and pay for stuff, so all prices needs to be high
If any other Swedish, or Scandinavian builders know any place to buy BB at a good price, preferably close to Gothenburg, please tell me:)

But Bill, would there be any performance or durability issues if I use the pine, ~3.5mm 3ply plywood that I have now, for backs and HF chamber? I´m doing full sides, so the backs wont be subjected to any external loads, just the acoustic loads. I´m guessing it will be alright? They will be Kappalite 3012HO loaded
And grilles for the horn openings, so no external loads on the HF chamber either.

Thanks!

I don't see a problem with pine, other than it has a prominent grain that's hard to hide.

Our government take very much of all money we make

And they spend it on foolish things like universal health care and education. What a waste. You'd think with all that money they'd be able to afford to go fight a war every now and then.

Thanks Bill, you just made my day alot easier:) i can get more 4mm pine ön my local woodstore at a good price, next door from my workplace so:)

I,ll have to paint them some extra;) it was no problem on my titans, but those i painted with 4component gelcoat, left over from my boatbuilding project.


Yeah, I know, real foolish stuff:p but the problem is all cheating basterd politicians that waste money on stuff that actually are foolish and immoral... And I'm not sure our school and healthcare are all that much better than the rest of say europe that have lower taxes and such..
I dont really mind paying 31% income tax, but when you then have to pay tax on the taxes more or less, it starts to feel like you much more then 50% tax all in all.. not to speak of running a company:p

But, atleast we dont go to war, officialy that is..

Political rant over, now I'm of to make more sawdust:)

Robin_Larsson wrote:the problem is all cheating basterd politicians that waste money on stuff that actually are foolish and immoral.

Over here that's considered business as usual.

Bill Fitzmaurice wrote:

Robin_Larsson wrote:the problem is all cheating basterd politicians that waste money on stuff that actually are foolish and immoral.

Over here that's considered business as usual.

Don't think you're alone Bill, probably universal. Lying was also omitted.

Good news about the reasoning for specifying BB or italian poplar.
So I can use any 3mm ply, cool...

Would be great to see pics of the molds/jigs you've made

bitSmasher wrote:Would be great to see pics of the molds/jigs you've made

Sure, I´ll take some pics of them later today, I´m just gonna eat and take a few hours in the workshop, gonna try to post some build pics also, we´ve made some progress:)

//Robin

I'm sorry i havent posted any pictures yet, but I have atleast taken some:p more importantly,I've made some progress:) put in the the last braces, the big ones, today, tomorrow we'll put in the backhalves and msybe even the sides, then its "just" the compressionhorn and its chamber left, and finish and all:p

I'm on my phone now, couldn't post the pics, so I'll try to do it tomorrow:p

So, the HF chamber and horn are almost done now, gonna put on the sheats today, and start with the inner parts of the compression horn.

I shall try to post pics soon...

I got to think about driver burn in/break in, couldnt find anything in the plans, and the search function on the forum really only gave me few threads concerning burn in of sub drivers. But I´m guessing my 3012HO´s need a burn in also? 30hz at 10V for 12 hours, is that good for those also, or should it be at a higher frequency or something?
And also, does my compression drivers also need a burn in? If not, why not, if so, what would a good frequency and voltage be? I imagine that it should be atleast above 1kz? The driver I have are Beyma CD10fe. Good for a 1.2 kHz crossover.

Thanks guys

And I say it again, the DR´s are fun to build even if they are timecomsuming, been at them for 2 weeks now, a few hours each day, but soon its just the finishing and such left But I admit, there was a few frustrating moments with the bent backhalves and their supports;) It ended well though.

//Robin

Robin_Larsson wrote:
I got to think about driver burn in/break in, couldnt find anything in the plans, and the search function on the forum really only gave me few threads concerning burn in of sub drivers. But I´m guessing my 3012HO´s need a burn in also? 30hz at 10V for 12 hours, is that good for those also?

//Robin

I would think so, wouldn't hurt.

Tom Smit wrote:

Robin_Larsson wrote:
I got to think about driver burn in/break in, couldnt find anything in the plans, and the search function on the forum really only gave me few threads concerning burn in of sub drivers. But I´m guessing my 3012HO´s need a burn in also? 30hz at 10V for 12 hours, is that good for those also?

//Robin

I would think so, wouldn't hurt.

Yes and more than that, it's necessary. Among other things the process allows you to verify the drivers specs and 100% function prior to install.

Drey Chennells wrote:

Tom Smit wrote:

Robin_Larsson wrote:
I got to think about driver burn in/break in, couldnt find anything in the plans, and the search function on the forum really only gave me few threads concerning burn in of sub drivers. But I´m guessing my 3012HO´s need a burn in also? 30hz at 10V for 12 hours, is that good for those also?

//Robin

I would think so, wouldn't hurt.

Yes and more than that, it's necessary. Among other things the process allows you to verify the drivers specs and 100% function prior to install.

I thought it would be something like that, thanks guys! Is the exact frequency very important? 30hz is good, not to low for the 3012HO´s? I mean, its lower than they are designed to play, isnt it? Shouldnt be a problem since its only at 10V I guess?
Whats the best, a constant frequency of say 30hz, or a sweep from 0 or 10 up to 30 or more?

What about the compressiondrivers? 30hz must be way to low for them, no? I believe they are speced to run down to 700hz, 1.2khz recommended crossover. Anyone ever burn in their CD´s, and how?

I´ll get the burn in started today on 3012HO´s then, 12 hours or so? would it be beneficial to go for longer than that, 24 hours or more? In the link that Bill provides in the Look here first section, they talk about burn in needing to be much longer than 10-12 hours, more than 40 I think, but the only number I´ve seen here on the forum is 10-12 hours. I´m guessing that after 12 hours one gets diminishing returns?