Newbie question re: "Proper" cabinet design

[Ken C]

Newbie question re: "Proper" cabinet design

I'm on my third project now, having started with the BR-1's, and another Dayton bookshelf model from PE.
But this 3rd project is a bit more complicated to me. I've decided to go cheap and build my own cabinets using the design's suggested cabinet dimensions. I noticed something that different about this cabinet compared to the others so I thought I'd ask my first question:

Lets say the exterior dimension (I forgot the exact numbers) are 14" X 9 X 10 (HXWXD), using 1/4" MDF, should the height of my baffles be the 14" with a width of 9", (14 X 9) or should I allow the top/bottom, and sides to go flush at the front face, effectively surrounding the baffles (ie: 12.5 X 7.5)???
Does it matter at all? If so why?
Thanks.

Ken C

 

[BillFitzmaurice]

I hopt that you don't use 1/4 MDF, but beyond that the preferred method is to surround the cabinet back with the top, bottom and sides and then have the front overlap those same pieces. That way if you don't veneer the joint lines are placed where they are least visible, assuming you're not going to the trouble of 45 degree mitres all around. That's not a bad option if your saw is precise enough to do the job and you have a bisquit joiner that makes a normally difficult assembly job quite easy.

 

[Ken C]

Geez what was I on? Yeah, of course 3/4 " MDF...unless I want some Walmart specials

I appreciate your reply. A follow up if I may...I have read that the front baffle should be 1" thick as it receives most of the stress from the woofer...would there be a big draw-back to using 3/4"?
1" MDF is aweful hard to find in my area....suppose I could glue two 1/2" pieces together?
Any comments?

 

[leadbelly]

This is more opinion than a "purist" answer. Don't bother with the thicker baffle. You are building budget speakers and are unlikely to hear the difference, plus the cabinets will be noticeably heavier. A 3/4" baffle will work nicely for you.

EDIT: I just realized you didn't describe the project in detail and so it may very well be a premium design.

If you have 3/4" material left over, double it up, but remember to chamfer the backside to unshroud the driver if necessary.

 

[Ken C]

No, I'm just going to try out the modes PeeCreek model at speakerbuilder.net.
Nothing too elaborate by any means. I'm glad you said 3/4" will be fine, that'll save some time and frustration.
What do most people do when they build their own cabinets as far as joints go? Butt, Rabbet, Mortis and Tennon, Lock Joint?

Any solid recommendations or does it matter? Assume bookshelf size speaker. Thanks.

 

[BillFitzmaurice]

3/4 is fine for baffles. So is 1/2" for that matter; my pro-sound boxes are all made of 1/2" plywood, but they are seriously cross-braced, with no unbraced panel spans greater than six inches. Cross-bracing pound for pound is some four times more effective than estra thickness for stability. and with weight a pro-sound concern crossbracing is worth the extra effort. For home use where wieght is less of a concern thicker panels are the easier route, but even with 3/4" MDF I wouldn't run an unbraced dimension greater than eight inches.

Sophisticated joinery is nice from a manufacturing point of view where CNCs do all the work for you, but for one-off home stuff simple butt joints are adequate as long as they are secured with screws no more than 5 inches apart. I've been using polyurethane based gun-applied construction adhesive now for 5 years; it works great, sands well, and expands into joints so that additional caulking is not required.