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jam4jaudio

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Reply with quote  #1 

I get a lot a emails asking about speaker cabinet corners.
For example:
     What's the difference between the two leg, and the three leg corners?
     And why do some corners have a "lip" on them while others don't?
     What is meant by the "radius"?

The emails that I hate the most are "I bought these corners and they don't fit". Hopefully this tutorial will help prevent that from happening!
    

     We'll start by looking at some typical "amp" corners. Shown here are the Penn/Elcom amp corners which are fairly common on speaker cabinets and guitar amps. These are steel and come in either black or nickel. From left to right we have the wrap around style, the three leg style and the non-wrap style.  

    The first thing you'll want to note is that these corners have a rounded edge which must be matched up to a rounded edge on the cabinet. The edges of the speaker cabinet are most commonly rounded over with a router during cabinet construction, and the radius on the cabinet edge must match the radius of the corners. (most common egde radius for speaker cabinets is 1/2").
    Important note!! The thickness of your covering material affects the overall radius of the finished cabinet edge! Tolex is fairly thin so it won't affect the radius much, but if you're using something thicker like speaker carpet, you'll want to take this into account. The finished radius of the corner will increase by the thickness of the covering material. Speaker carpet is typically about 1/8" thick so you'll want the raw cabinet rounded with a 3/8" radius (if using corners with 1/2" radius).   

Here's a line drawing of the Penn C1823 corner.

You can see here how the corner is radiused (they spec it at 15/32", but they are designed for cabinets with 1/2" radius).

Here's the wrap around corner installed on a cabinet. Typical use for this style corner would be on the rear of a cabinet with a removable back, as shown here.
Here's a view of the same corner, looking at the wrap around lip. You can see here why these must be used with 3/4" wood.

    This is a picture of the 3 leg style of corner. The proper application would be on a cabinet where three panels come flush together.    

    Shown here on the rear of a cabinet with non-removable back. Each leg of the corner extends out over it's respective panel (top, side, and rear of the cabinet).

And last, here's the 2 leg non-wrap corner. Since the corner has no wrap around or third leg, it can be used in place of either of the other style corners, but since this style corner is only held in place by two screws it is prone to getting knocked loose from the edge of the cabinet, so I would only use it when you can't use one of the other corners. For example, in place of the wrap around style when the cabinet is constructed out of thicker or thinner material.

So, now let's look at some other corners which are commonly used in cabinet construction.

    Here we have a plastic stacking corner. These are more often found on cabinets which are covered in cabinet carpet -like PA speaker cabinets, Rack cases and sometimes Bass Guitar cabinets. These are called stacking corners because the chevron tread will interlock when stacking like size cabinets on top of each other.
    Most of these types of corners have a fairly tight 1/4in radius so they can generally be used on non radiused edges that are covered in carpet.
    Hint: the best plastic stacking corners are made by Penn Fabrication. These are made of thicker flexible plastic, and are not prone to breakage like the hard, brittle corners made by others companies. They're available in two sizes -large (C1568) and small (C1567).

     Stacking corners are also available in steel. These have a dimple for stacking instead of the treaded design.

      This corner is made by Penn Fabrication (part #C1335), and is available in black or zinc.

     These are designed for cabinets with 1/2" radius (3/8" if using cabinet carpet).  
Here's one of the few corners available for cabinets with zero edge radius. These are most commonly used on rack cabinets or utility boxes.

And then of course there are a myriad of specialty corners available.

    The ones shown here are for trapezoid shaped PA speaker cabinets. These are most often sold in sets of eight because each corner is designed to fit on a particular corner of the speaker cabinet (R. front, L. front, R. rear, L. rear, etc).
     The real trick with these is that not only do you need to have the correct radius on the edges, but you must match the angles of the cabinet to the angle of the corners.    
     new information added 6/12/08 

    This style of corner is made of plastic with a niced textured finish. These will be similar to what you might find on many contemporary guitar amps and speaker cabinets. Note that the four front corners are radiused on all three edges, but the back corners are designed for cabinets where the back edge is not radiused, similar to the Marshall configuration (see the pictures that follow). Like the steel amp corners, these are for cabinets with a 1/2" edge radius.

    Please note that while these may look similar to a Marshall corner, these will not fit Marshall cabinets. Marshall cabinets have a much larger radius!

Here's a view of the front corner.

Here's a view of the rear corners. Note how the back edge of the cabinet has a non-radiused egde.

Here's a similar corner in chrome plastic. Please note that, while the chrome might look nice, the chrome plating requires that the corners be made of a harder, brittle plastic so these should only be used for cabinets that won't be seeing a lot of wear and tear.

 Marshall corners:
   Here's a set of original Marshall corners. The large radius pretty much limits them to direct Marshall replacement. Most DIY speaker builders will not have the tooling to recreate the large corner radius required for these corners to fit properly.  

So are you more confused now than ever? Hopefully not.
     I think the important thing is to know what parts you're going to use and how they are going to fit before building your cabinet. Don't build a cabinet with weird angles or edge radiuses and then try to find hardware to fit as an afterthought. You'll find it a lot easier if you design the cabinet to accept commonly available hardware.  
 
    

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micstew

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Reply with quote  #2 
Hey, real nice website and great photos.  I've got a corner problem I hope you can help with.
I've made some cabinets (amp head and speaker cabs) from the finest 3/4" plywood available at my local Lowes hardware store.  Only of course as it turns out it's not quiiite 3/4", it's actually thinner by a about a 16th.  In any case, I tolex'd the cabinets and bought a pile of standard 2-hole corners with the little lips on them.  But now that I'm down to the final assembly I find that they are not even close.  They're nearly 1/8" too wide (that is, the cabinet material would need to be 1/8" thicker).  Then I bought a bunch more corners without lips but the faces on those corners are only 1/2", thereby not quite covering the not quite perfect tolex seams in the corners.  I have a Carvin MTS combo with 2-hole, no lip corners and the faces on those corners are at least 5/8" and would cover the tolex seam better but I cannot find more corners like these ANYWHERE.  I've got a call in to Carvin to try to get the name of their supplier but they are discontinuing the MTS series so I'm not too hopeful there and, well, sob sob, etc etc...  Any ideas would be GREATLY appreciated.  Thanks in advance...
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jam4jaudio

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Reply with quote  #3 

Most of the corners shown on this tutorial come from Penn Fabrication (http://www.pennfabrication.com) and are available in 1" (part #c1829) or 3/4" (part #c1819). It sounds like you must have gotten the thicker c1829 corners. As for the non-wrap around corners -I don't know where you could find some with a wider edge. 

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bcgilliam

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Reply with quote  #4 
jam4jaudio, This post on the corners needed for amps, cabs, etc are most helpful and useful. Thank you for this post, and a very nice JOB!

I do want to ask however, and this is probably silly, but can you put up a post showing the techniques of installing speaker carpet? I recently built a pedalboard and installed the carpet I purchased from you using 3m Super 77 spray adhesive and was wondering how you installed it on the edges of the plywood? Mine doubled on the overlap of the edges. I now see what your talking about when you say the speaker carpet takes up 1/8" on every side, as I had to recut my braces for the pedalboard and had to cut off Appr. 1/4" and cut some of the carpet off of the edges because I had overlaped it twice. Anyway, I really appreciate these post you are putting up to help people like me. This is however the first time I have started making Pro audio equipment and will be doing it for a long time to come. I will be purchasing from you and have you added as one of my favorite stores! Thanks again and Keep up the GOOD WORK!
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