Collaborative Tapped horn project

[Don Snyder]

A few years ago, one of Danley's guys said they only used air driven ring-shank nails and TiteBond. Of course, that requires careful cutting or CAD-CAM so there are no gaps. Many of the guys who built LabHorns used West System Epoxy, which is hard stuff to work with. All this was with 13 layer ply, so it might not apply to MDF and OSB.

If the joints are close and clean, TiteBond II is stronger than Ply, OSB, or MDF. When manufacturing these materials, the factory uses a small amount of mould release, to keep the sheets from sticking in the press. This is a wax, which can compromise the bond, no matter what glue you use. A little sandpaper can clean any wax or oil from the glue-line.

The acoustic loads can't be more than a pound per square foot, so if you break your cabinet, it'll be when it falls off the truck.

[steve71]

Thanks for the glue suggestion guys. I've used titebond wood glue with MDF before with excellent results and I'll use it for everything but the "lid". I'd feel better with something that will fill any gaps just in case.

The other idea I had was to line the top of the box and baffles with speaker gasket and screw the lid on.. screws every 8 inches or so. That way I can gain access to the horn if I need to add any additional bracing or hunt down a rattling bit of wire etc? Any reason why this wouldn't work?

Something about sealing up $260 worth of ply without testing it first is a little scary.

[just a guy]

Foam gaskets work, but are not cheap when you need that much, maybe $20 worth or more to seal a big box.

For testing, you can even lay it open end down on the carpet without sealing it at all. It will sound considerably different than it would with a sealed panel, but it's a quick and easy way to test for rattles.

On one project, I "glued" the "lid" with silicone so I could remove it later. I was able to later remove the "lid" but not without considerable damage to the wood (cheap mdf) from prying and such. I wouldn't recommend trying silicone for this purpose. I am fairly confident though, that silicone could be used instead of glue in a pinch, although I can't imagine in being in THAT much of a rush.

[littlemike]

Something about sealing up $260 worth of ply without testing it first is a little scary.

Wow - $260???

These must be HUGE huge cabinets!

What sort of ply are you using?

$260 would buy me 8 sheets of the cheap ply I have been using for the prototyping and testing, or 15 sheets of the heavy duty OSB I plan to use for the next round of subs.

I've had generally good results using the thin closed-cell foam weatherstripping tape on access flanges. From experience, I can say that this approach works best when the flange sealing surface is wide and flat, which often compromises the appearance of the final product. Experience (mostly bad) has taught me to include removable access panels to allow for driver replacement in enclosures where the drivers are hidden, I have had to use them (or wished that they were there) after letting the magic smoke out.

[steve71]

Originally posted by just a guy
Foam gaskets work, but are not cheap when you need that much, maybe $20 worth or more to seal a big box.

For testing, you can even lay it open end down on the carpet without sealing it at all. It will sound considerably different than it would with a sealed panel, but it's a quick and easy way to test for rattles.

Thanks for the open end down on the carpet tip. Unfortunately my home was built is 1890 and has "undulating" wood floors! If I'm determined enough I might be able to find a flat area large enough and lay down a rug .

I'd need about 737cm (24ft) of gasket which I have left over from a 50ft roll. This stuff should do the job at a reasonable cost, no?
http://www.partsexpress.com/pe/showd...number=260-542

Originally posted by littlemike


Wow - $260???

These must be HUGE huge cabinets!

What sort of ply are you using?

$260 would buy me 8 sheets of the cheap ply I have been using for the prototyping and testing, or 15 sheets of the heavy duty OSB I plan to use for the next round of subs.

I've had generally good results using the thin closed-cell foam weatherstripping tape on access flanges. From experience, I can say that this approach works best when the flange sealing surface is wide and flat, which often compromises the appearance of the final product. Experience (mostly bad) has taught me to include removable access panels to allow for driver replacement in enclosures where the drivers are hidden, I have had to use them (or wished that they were there) after letting the magic smoke out.

The box is a double folded TH which is about 133(w)x 82(d) x 50(h). which will take two 4x8ft and one 5x5ft sheet of (void free) BB to build. I bought the ply today and the total cost was a little less than expected - $215.

I really should make a proto out of OSB, but I don't have the time to make two boxes. Most DIY'er here seem pretty satisfied their horns are close to what HR predicted, hopefully mine will be no different... otherwise it'll make a great coffee table, right?

[littlemike]

... otherwise it'll make a great coffee table, right?

That or a lovely bonfire....

....once the meaningful bits are pulled out.

As I said in an earlier post -

If you model things realistically and build what you model accurately, what you build should behave as your model predicts. If reality does not agree with your model, check your assumptions first, check your measurements second.

[steve71]

Originally posted by littlemike


That or a lovely bonfire....

For $215 I'd expect fireworks.

And one last question.

Does the driver need to be flush mounted with the front (inside face) of the baffle? Since it's a doubled folded horn, it's a lot easier to just mount the driver on the back of the baffle, but does this offset S2 by the thickness of the ply (18mm)?

[littlemike]

Mount it the easy way.

I've mounted drivers both ways, does not seem to make much difference, though one direction is usually much easier.

I doubt that the 18 mm is that critical. S2 and S4 would not really change that much - the driver hole only adds a small amount of area to S2. If you're really worried - glue/nail the cutout piece opposite the driver - that should mitigate all but the saw or router kerf.

Just make absolutely sure that the mounting hole is clean, the surface is smooth, and the gasket seals well (some well-known high-quality drivers have gaskets with gaps in them that cause leaks).

Oh - and be sure that your t-nuts are installed pointing in the right direction. (not a fun thing to find out...)

[steve71]

Thanks for all the Advice Mike! I got all the panels (minus any bracing) cut yesterday, so today I should be able to start to put the thing together.

[Don Snyder]

Hi Steve,

How about some info ... we've been waiting for two weeks now!