Something Old, Something New ...

[dougzilla]

Originally posted by jcdahl

How much fill did you use?
How is the granite top attached?
What material is the grill made of?

I used as much fiberglass as I could fit, just leaving room for the components, basically. Probably less than 15% free air space.

Gravity suffices for the granite--it weighs about 30 lbs.

The grille is PE's black grille cloth stretched over a plywood frame. It attaches with small magnets imbedded in the frame and the baffle board at the corners. The magnets are PE parts also.

Cheers,
Doug

[dougzilla]

Originally posted by jtgyn
[B

Please excuse my woodworking ignorance.. but how is the box held together again ?

[/B]

I guess I forgot to mention the GLUE. I use Franklin's Titebond II on almost all my projects. If you need a longer assembly time, you could consider Resorcinol types. Urethanes or epoxys would be pretty expensive. Whatever you are comfortable with, of course. None of the joints are under much stress, so the properties you want are easy application, decent open joint time (say 5 minutes), some void filling capability, and easy cleanup.

Cheers,

[dougzilla]

Originally posted by boputnam



I'm not confident of it's provenance, as there is so much shipping of slab these days. And, neither the texture nor composition is common to the Sierra batholith (although it could be a localized intrusion into said batholith), but I suspect it's age may be materially younger than 100Ma, perhaps something of the 34Ma or 65Ma cluster (if from North America...).

Bo,

I got the stone from an importer's yard. He mainly deals in Italian marbles, but said this was "Baltic." He doesn't speak much English, think he is Croatian. Maybe some of the European lads on the Forum recognize it?

I know the Sierra is relatively young granite at 65 Ma and figured this was probably older. I think the age contributes significantly to the sound, don't you?

I'll PM you about the paint.

Best,
Doug

[boputnam]

The Sierra is quite complicated - it does have younger bits, where late-stage plutons have intruded and been incorporated within it, but I think overall it's median age is older...

Way OT, and from the Internet: The main mass of the Sierra Nevada batholith is an irregular, ellipsoidal mass nearly 650 km long and 100 km wide, has an irregular northern and eastern boundary marked by isolated plutons, local faults, unconformities, and intrusive contacts. The rocks of the batholith range in age from about 220 to 75 m.y.

And, I think of it as more leucocratic - lighter colored, and dull grayish (but much of it tends toward granodiorite) - without those nice pink feldspars. I'll have to go Baltic and see for myself!

[Audiobeer]

Outstanding job! Excellent workmanship. Lot's of time but great therapy right!

[jtgyn]

G'Day Doug,
Thanks, How did you cut the "lock miter joints" ? Is there some router bits to do this ?

Thanks & Regards Scott


For others woodworking challenged like me ...

lock miter joints
http://www.americanfurnituredsgn.com...%20joionts.htm

dado slot & overlap rabbetted
http://www.garageman.com/info/strong_back.cfm

[dougzilla]

Originally posted by jtgyn
How did you cut the "lock miter joints" ? Is there some router bits to do this ?

Right, they're done with a special router bit, mounted with your router upside down in a router table. Here's a link to my favorite supplier of CMT bits and the bit itself.
Carbide.com

Although these bits are expensive, they are wonderful for speaker and other box construction, because they pretty much guarantee that your corners will glue up at right angles. Hooray, no more parallelograms! Lock miters are extremely strong joints, eliminating need for screws, corner blocks, etc. and they are absolutely airtight.

The only downside is that your setup must be perfect, with a high fence on the table at a precise right angle to the base, the router exactly perpendicular to the table in both axes. and the bit height and fence depth set so as to place the cut exactly in the middle of the work piece.

The technique is that you run one box side through laying flat on the table with outside face up, and then, without repositioning the bit, run its adjoining side positioned against the fence with the outside face away from the fence. A clamping jig to hold the vertical cut piece against the fence is nice but not absolutely necessary.

When used with MDF, this technique can produce a joint so tight that the glue line at the outside corner is invisible. Your speaker cabinet looks like it's just cast out of one continuous piece of material.

Good luck,

[mikebake]

How is that plate amp performing?

[dougzilla]

Mike,

Fine as far as I can tell. It's a bit susceptible to external fields (e.g. lamp dimmer circuits), as there is no internal case shielding. Other than that, it's low noise and undistorted at the listening levels I prefer. I haven't tried to equalize everything yet, but from basic room acoustics point of view, the amp is the least of my issues.

The box, being really airtight, means lower efficiency, but I would guess I am at least 10 db down from the amp's clipping levels even at really loud volumes (things-begin-to-walk-off-shelves levels). The gain control is less than half way up. I know the speaker can take more than this amp can deliver but it just isn't worth it for me to upsize to wattage that I'll never use.

I was actually a little concerned about speaker heat build-up because the box is so well insulated, but the speaker frame acts like a big heat sink for the voice coil/magnet structure and the internal air, and dumps its ergs to the outside air around the rim. (That is, the rim gets warm during extended loud usage.) The amp has generous cast cooling fins for the output transistors, no worries there.

Best,