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Old 7th November 2011, 09:15 PM   #1
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Default Parts Express knock-down trapezoid cabinets

I stared building my Parts Express knock-down (ship flat) trapezoidal PA cabinets. I hope to post up some pics as it preogresses.

The #1 screwdriver bits don't last.

At every screw, the clearance hole thru the first piece of wood is already drilled, but there in no deeper pilot body hole. I assembled all the cabinets and wrapped some bungees around them to hold them temporarily. Then I used a 1/16" drill bit to drill to almost the depth to match the length of the screws.

That was too tight and the screws tended to strip at the small phillips head.

So I'm going to be conservative and just go to 5/64.

I'm also going to add some internal braces.

Once the screws were in and glue was drying I also blasted in a few hundred small nearly-headliess brad-type nails (nail-stick) with an air-nailer. Can't hurt.
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Old 9th November 2011, 03:42 AM   #2
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What are you putting in them?
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Old 9th November 2011, 03:49 AM   #3
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Next time try a #2 phillips( did you use drywall screws?) I find when I put boxes together to glue th panels and then put a few brad nails in( at an angle) , then that will give you time to do some screwin'
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Old 14th November 2011, 09:34 PM   #4
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The kit comes with screws, and a LOT of extras.

The #2 bits don't fit the small-head screws at all. I went from a 1/16 to a 5/64 to a 3/32 bit and drilled a little deeper. Now I can get by with 1 or 2 bits per cabinet instead of 4 or 5.
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Old 14th November 2011, 09:40 PM   #5
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What I learned:
- pre-drill deep with a 1/8 or just smaller bit.
- use tons of glue and wipe up the excess later.
- I used a small finish nailer too. I put 3 more nails between every 2 screws. Then at every joint where the screws went one way, I also put nails the other way to lock it.
- the glue is what really matters.
- a better grade of plywood would make a huge improvement.
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Old 14th November 2011, 09:47 PM   #6
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Quote:
Originally Posted by Top Shelf View Post
What are you putting in them?
I'm putting 4 12" drivers in each cabinet, clamshell-isobaric with 2 magnets sticking into the cabinets and 2 magnets sticking out. I am concerned that they are going to be very front-heavy. I may need to glue on an additional top and bottom board just to make sure they don't fall on their faces.

Since the cabinets come with the front baffle board pre-cut for one off-center 15" driver, I enlarged that opening like a big figure-8 and will install some t-nuts and a thin rubber foam seal and just use it as something to bolt a new baffle board onto.

So now I need to buy some 1-inch MDF to make new baffle boards out of.
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Old 28th November 2011, 11:06 PM   #7
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The 1" MDF is wonderful to work with. Not strong, but so consistent and predictable, and easy to shape and sand.

Nearing completion. I'll take pictures next weekend when I start working on it again. I added an additional layer of plywood on the inside of the top and bottom. That way I don't have to worry about steel plates for spring-loaded handles leaking or weakening the area.

I'm also adding a large center brace divider panel to tie the front and back and tie the two sides. There's two holes, so that I can insert T-nuts and long screws to the removable front bafle board.

I tried to use my electric plane to trim the front cabinet edge nearly flush with the removable front baffle board. The plywood exploded when the cutter hit, and delaminated expecially badly at every corner when the blades ripped off the last laminations. Not good, quite a mess but salvageable.

What do you think I should use as gasket material for mounting the front baffle board? I'd think a wide but thin rubber or foam weatherstrip might be perfect.

The rear jack plates are rather large. In each speaker I installed: two 4-contact Neutrik connectors. In other words, each of the four speakers in each cabinet can be connected to independently from the external connectors.

There's 2 more holes, meant for 1/4 inch jacks, but I don't think I'll mount any 1/4" jacks.

But I was contemplating perhaps 8 oversized binding posts, so that each speaker can be connected to independently.

Or, I was considering installing 2 center-off DPDT switches to connect each driver in a clamshelled pair in series or parallel, then another center-off DPDT switch to connect the two clamshelled pairs in series or parallel. Then one more center-off DPDT for normal or reverse polarity.

I'd need to find some 40-amp toggle switches, or settle for whatever I can find.

Or I could still add other jacks and/or binding posts.

What do you think of the switches? I'd want some hefty high-current toggle switches that don't rattle. Personally, I love the convenience of a polarity switch, which really makes comparisons fast and easy. Especially since there doesn't seem to be any standard for the 4-connecter Neutrik connectors.

And if I connected just one set of wires, the switches would give me:

2@ 6-ohm clamshelled drivers in parallel for 3 ohms, with both clamshelled pairs also in parallel: 1.5 ohm

2@ 6-ohm clamshelled drivers in series for 12 ohms, with both clamshelled pairs in parallel: 6 ohms (not preferred)

2@ 6-ohm clamshelled drivers in parallel for 3 ohms, with both clamshelled pairs in series: 6 ohms (preferred)

2@ 6-ohm clamshelled drivers in series for 12 ohms, with both clamshelled pairs in series: 24 ohms
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Old 5th December 2011, 05:22 PM   #8
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what kind of setting will the speakers be used in and what frequency range ?
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Old 5th December 2011, 05:50 PM   #9
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Since I did so little math before-hand, and didn't pay much attention to the spacing between isobaric drivers, I need to build them then do a lot of critical listening before I'm really sure how I'll run them. I just know my little scan-speak mid-bass drivers are too small to make loud enough low bass.

Mostly in my home theater crossed over somewhere about below 300 hz with a lot of EQ, but occasionally (rarely) they will travel out for small medium-volume PA crossed over around 800. Eventually I plan to make more, using different drivers. I might even play some bass guitar thru them.

They have ply cones, and I'm hoping the isobaric cones couple well, and that you don't hear the back cone thru the front one. I have had some disappointing isobaric experiments and some encouraging ones. In two more weekends I will know what it means for them to "sound twice as big" LOL.
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Old 5th December 2011, 07:59 PM   #10
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Did you consider going direct radiating with the 12's for twice as much SD? You could stll get the benefits of harmonic reduction with an enclosure like a Push/Pull Slot Loaded but retain all the driver area, only you don't get the reduced vb/vas like a clamshell isobaric. I can't load a handrawn picture of this setup in a trap box, and it would all depend on availible room in the box. But its an effective usage of drivers.
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