# Trapezoidal shaped speaker cabinet



## qingcong (Jan 17, 2011)

Hello, I'm not really a woodworker by trade, but have done some general purpose woodworking/machining in my line of work. I'm going to build myself a guitar speaker cabinet, and to reduce standing waves my idea is to shape the cabinet like a trapezoid, see pic below. 

A guitar cabinet needs to be extremely structurally rigid for both sound purposes and practical usage - typically a 40-50 pound amp head sits on top of the cabinet. Most cabs are rectangular shaped and thus easy to join the sides, the trapezoid introduces some challenges. My question is, what are some joinery methods to ensure the strength of the joints of the sides?


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## qingcong (Jan 17, 2011)

My idea is to use a butt joint with angled bracings, see pic below.


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## qingcong (Jan 17, 2011)

I also thought about adding an additional reinforcement beam like this - 












I apologize for seemingly spamming my own thread.


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## woodnthings (Jan 24, 2009)

I think you've got it "nailed" Only one angle setting on the saw.
Your reinforcement panel may not work with the sound waves? I donno? Maybe on a sealed cabinet, not on a bass reflex if I recall.  bill


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## wmodavis (Dec 26, 2010)

*Standing Waves*

The real key to eliminating standing waves is to make the cabinet shorter. That way the waves will have to sit.
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Sorry Bad joke! :laughing:


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## qingcong (Jan 17, 2011)

woodnthings said:


> I think you've got it "nailed" Only one angle setting on the saw.
> Your reinforcement panel may not work with the sound waves? I donno? Maybe on a sealed cabinet, not on a bass reflex if I recall.  bill



Nah, the reinforcement wouldn't be a panel, just two beams on each side. I'm not terribly sure what affect the beams have on sound waves though. BTW, I'm building a ported guitar cab, the two little circles on the right are ports.


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## cabinetman (Jul 5, 2007)

Rabbet joints (glued/clamped) can be created with that shape. Add on interior cleats would not likely be needed.












 









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## woodnthings (Jan 24, 2009)

qingcong said:


> Nah, the reinforcement wouldn't be a panel, just two beams on each side. I'm not terribly sure what affect the beams have on sound waves though. BTW, I'm building a ported guitar cab, the two little circles on the right are ports.


Sound waves are nothing I have any knowledge of. Are you using "plans" or wingin' it? My only experience with speaker cabs was on some "ducted port" bass reflex types for a pair of 18" Electro Voice woofers. It must worked since I could rattle the entire house...all the ceiling lights. :laughing: The good 'ole days. They're in the attic now. Garage band anyone? :yes: bill


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## qingcong (Jan 17, 2011)

woodnthings said:


> Sound waves are nothing I have any knowledge of. Are you using "plans" or wingin' it? My only experience with speaker cabs was on some "ducted port" bass reflex types for a pair of 18" Electro Voice woofers. It must worked since I could rattle the entire house...all the ceiling lights. :laughing: The good 'ole days. They're in the attic now. Garage band anyone? :yes: bill



I'm doing my best to make it "designed", to optimize it for what I need. It's in the research stage right now. I'm not an acoustic engineer, I'm an electrical engineer, but I've worked for Altec Lansing before and have picked up a little bit on acoustics while there. Granted, these days Altec only makes dumb little ipod docks, so there wasn't too much to learn there.


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## qingcong (Jan 17, 2011)

cabinetman said:


> Rabbet joints (glued/clamped) can be created with that shape. Add on interior cleats would not likely be needed.
> 
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> 
> ...




So I guess a rabbit joint is inherently stronger than a butt joint? I guess it wouldn't hurt to add bracings in addition to the rabbit joint. How much more work is it to make a rabbit joint?

Note, I would not be doing the wood cutting. I'd have a professional cabinet maker cutting the wood for me, so I can do anything I want, but I don't want it to get too complicated cause it might start getting expensive.


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## JohnWP (Jan 18, 2011)

You can check out AVS Forums, they have an entire subsection on speaker building, and there are some very sharp people there. They could give you tips on the design and what might be needed/necessary.

John


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## Marv (Nov 30, 2008)

I've built a few speaker cabinets in my time 
http://s29.photobucket.com/albums/c258/MrMarv/?#!cpZZ1QQtppZZ20
and for guitar cabinets I typically use 12mm or 1/2" euro/baltic birch etc with simple butt joints brad nailed/clamped and bracing as seen below (for smaller cabinets I sometimes use dowels as bracing between the panels). This make for an extremely rigid and strong yet lightweight cabinet which is what my guitarist friends ask for (I may be doing a couple of new cabinets for a local band soon and can send pics of construction if you'd like)


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