Directiva r1.2 design and build

[Alan J]

My hand is healed enough to resume working but I have some things to do before there will be substantive progress: Remake my router table to be flatter and with a more readily adjusted fence, and assuming I stick with lock miters for the corners build a sled to cut them with more control and safety.

 

[Okankav]

is there any update?

 

[Alan J]

Regrettably, not just yet, due to one distraction after another, plus a great vacation, that's held up the workshop re-do. Over the next few weeks we have a grandchild babysitting stint, a big deal wedding, and my wife's getting a brand new hip. I'm actually hoping that while I'm home and on call for her recovery I can be getting some things done!

 

[Okankav]

Hİ Alan, is there any update?

 

[Alan J]

Soon, I hope! My hand is pretty well healed (I think that the therapist will send me on my way this week), my new and better workbench is complete, and my new router table is in place.

I need to make a cabinet material choice, informed by both acoustic properties and desired finish (and, OK, practicality). The plan is for the baffles to be the natural cherry probably with a simple Danish oil finish, and the boxes a charcoal color.

I spent this morning looking at Richlite (mentioned in @Rick Sykora's new thread on damping materials and have samples in my cart. But right now I'm most likely to go with 18 mm plywood either stained or painted, or MDF.

 

[Okankav]

hi alan, what will be crossover point in the last case? I remembered you worked with lr4 around 2,2 khz. Is there any change in this area?

 

[Joe BKNY]

Soon, I hope! My hand is pretty well healed (I think that the therapist will send me on my way this week), my new and better workbench is complete, and my new router table is in place.

I need to make a cabinet material choice, informed by both acoustic properties and desired finish (and, OK, practicality). The plan is for the baffles to be the natural cherry probably with a simple Danish oil finish, and the boxes a charcoal color.

I spent this morning looking at Richlite (mentioned in @Rick Sykora's new thread on damping materials and have samples in my cart. But right now I'm most likely to go with 18 mm plywood either stained or painted, or MDF.

Glad to hear your hand is doing much better. It wasn’t intentional, but you did the forum a service by reminding us to be careful!

 

[Alan J]

hi alan, what will be crossover point in the last case? I remembered you worked with lr4 around 2,2 khz. Is there any change in this area?

Right. We were thrilled by listening tests with LR4 around 2100-2200 Hz. This was with a DSP crossover, limiting myself to functions that are in theory available with passive components (not that it will be fully practical to replicate).

[EDIT] With that said, I'll be open to changes when I zero in on a passive crossover. I'm wary of going too high, at least not without ensuring that any higher frequency stuff from the Purifi is well managed. But crossovers that look best in simulation have consistently been in the 2000-2400 range and I'm likely to land somewhere in the lower half of that range.

 

[Alan J]

It wasn’t intentional, but you did the forum a service by reminding us to be careful!

In that spirit, a few pics:

New sled for passing vertical panels through the router (the tall piece of MDF there only for illustration):

A test lock miter joint (almost dialed in) done with the sled, along with stock guides for the piece that goes through flat:

In both cases, the setup makes it hard to get one's hand near the bit, and it's conducive to standing alongside the workpiece, not behind it. I also have proper dust collection now.

 

[Alan J]

Plywood for the enclosures is in hand! After a lot of searching and ruminating, and some testing of finishes, I chose Columbia Forest Products' 18 mm Europly plywood. The product is marketed as a substitute for Baltic birch. It has 13 birch plies plus thin face and back veneers of the chosen species. They import the core from Poland, then apply face and back veneers. At $108 for a 2x8' half sheet, it was more expensive than the full sheet price for BB but BB is still coming from Russia and I wanted to avoid it. In addition, test samples of our likely finishes on birch didn't look good. We were happy, in contrast, with finishes on Columbia's less expensive maple-faced plywood, samples of which cut without splintering of the face veneer.

It was easy enough to measure the elastic modulus: Support the sheet at both ends, place a weight at the center supported by a narrow board, and measure the displacement. Elastic modulus in the face grain direction measured at 9.7 GPa, which is a bit higher than published values for BB. Density is 85 lb per 4x8 sheet (722 Kg/m^3), compared with around 675 Kg/m^3 for BB.

 

[Alan J]

I'm occupied by other things over the next 2+ weeks, so a quick update...

Cutting of enclosure panels is finished. Lock miters are tedious to set up and require sub-millimeter precision especially if using a lock miter on the rear panel.

Both the black cherry baffles and the Europly enclosure parts are at 6% moisture content. From there, the plywood parts would not be expected to move much. In conditioned space, the baffles would be expected to grow a mm or so horizontally, or several mm if ever stored in un-conditioned space. Baffle mounting will keep the baffles centered on the enclosure while allowing for a few mm of movement on each side. Accordingly, the enclosures are about 0.5 mm smaller than the baffles all around, and there will be a thin spacer (stay tuned for details) so that the break between enclosure and baffle looks natural.

Coming up next: Purifi mounting to allow for some movement while providing a good seal (and perhaps some isolation in the process), as well as detailing mounting of the baffles to the enclosures.

 

[terryforsythe]

Beautiful wood work!!!