Help me finish my polystyrene cab build

[neal sanger]

Joe, there is a sign making store near me about 10 miles down route 1. I'll have to pop in and see what they have and what they'd sell me.

 

[Blues Bass 2]

What about just rolling on Duratex to stiffen it up . I know it isn't as sturdy as Line X but it might help .

 

[alexclaber]

True, but that process should have been attempted before constructing the box I reckon. But then it would have stuffed his finger jointing maths. And made a lot more mess in his parents' basement.

It's a terrible way to make a cab if you want it to sound good and last for more than a few weeks but I was just pointing out that laminating a layer that could be stiff due to its Young's Modulus but is bendy due to its Second Moment of Area, to the outsides of a thick panel, can add a lot of stiffness by manipulating the Second Moment of Area. Just like an I-beam girder or a honeycomb aluminium panel.

 

[Downunderwonder]

It's a terrible way to make a cab if you want it to sound good and last for more than a few weeks but I was just pointing out that laminating a layer that could be stiff due to its Young's Modulus but is bendy due to its Second Moment of Area, to the outsides of a thick panel, can add a lot of stiffness by manipulating the Second Moment of Area. Just like an I-beam girder or a honeycomb aluminium panel.

Yep.

 

[JimChjones]

Easy to spend a hell of a lot of money on coating materials, and then find that the underlying foam is so soft that it bangs to bits anyway. I'm not sure its going to be money well spent. Better to save the cash for a second prototype if the results justify. I could talk a lot about skins, choice of core material etc etc for a second one.

If its not going on the road find an offcut of ply or something to sit on top of it as a shelf to save it from the more obvious insults and just be careful. The odd dent or ten isn't going to make a lot of difference.

 

[neal sanger]

If you recall, I'm doing this for fun.

 

[neal sanger]

Porting has been added. I messed with winisd a bunch, but I was unsure how the porting would behave (someone suggested the flexion of the cabinet foam would lead to an effectively larger acoustic volume). I just cut a 12" length of schedule 40 PVC in half with my table saw. I used several different programs to calculate the tuning frequency and it came back between 32-39.9hz ( I couldn't figure out how to control the volume of bracing each program assumed as it was all free and some of it crappy oftware). I got a port velocity of ~13 with a hypothetical 150w signal around the tuning frequency having used two ports to cut it down. It all seems ok enough to me.

 

[neal sanger]

I mounted the ports by cutting out 6" squares of foam and cutting out a traced diameter from a section of schedule 40 4" pipe. I let stopped one side of the holes and glued them for about 2 days so the glue partially set up around the pipes and shimmed them with bits of the 2" foam core- as the had a uniform thickness congruent with the depth of the back panel.

For the holes in the cabinet, I cut them much more tightly to tolerance to friction fit the pipe while it was drying.

I slathered up the mounting faces of the 6" squares with glue and put them into the bottom of the box as shown above. Since the glue had only cured a few days, I was then able to push and pull the pipe out to be perfectly flush with the outside of the box. I set it up on some risers to dry. It will probably be 2 weeks before this glue up sets.

 

[neal sanger]

Here is a close up of the porting glue job.

 

[neal sanger]

I also glued a the front panel to the baffle backboard and pressed it with some heavy things. This will also be drying for the next two weeks. The last step will be cutting the finger joints and gluing the top panel (followed by a probably 3-4 week cure time).

 

[dbase]

I'm thinking, wrap the whole thing with Duct tape so it wont fly apart.

 

[Fat Freddy]

I'm thinking, wrap the whole thing with Duct tape so it wont fly apart.

Yeah.....Camo duct tape so that nobody can see it to steal it....

 

[dbase]

Yeah.....Camo duct tape so that nobody can see it to steal it....

Or that shiny stuff that looks like chrome

 

[Fat Freddy]

Or that shiny stuff that looks like chrome

Mmmmm......Shiiiiinyyyyy....drool

 

[Rick James]

It's a terrible way to make a cab if you want it to sound good and last for more than a few weeks

+1. Sometimes things aren't done a certain way because no one ever thought of it before, sometimes they're not done a certain way because it just doesn't work. This just won't work.

 

[JoeWPgh]

+1. Sometimes things aren't done a certain way because no one ever thought of it before, sometimes they're not done a certain way because it just doesn't work. This just won't work.

There's no reason it won't work, provided you use the right adhesive, and don't move it around very much

 

[neal sanger]

Im not going to duct tape it. That's a dumb idea

 

[Fat Freddy]

Im not going to duct tape it. That's a dumb idea

What a rude young fellow you are.....

Makes me sad.....

 

[agedhorse]

Im not going to duct tape it. That's a dumb idea

Perhaps you are taking this whole thing a bit too seriously? You might want to open yourself up to the little bit of the humor that's being offered.

 

[Mike Arnopol]

as I said---I built around 75 cabs that were fiberglass over polystyrene foam. They're all out there 4 years later. I know it's for fun, but if both sides aren't laminated with fiberglass---the enclosure will essentially eat all of your low end. The fiberglass ones sound great. I stopped making them because of extreme sensitivity to even a small amount of fiberglass dust.