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Guitar Loudspeaker Cabinet Design.

Posted on 2004-04-28
Medium Priority
Last Modified: 2007-12-19
For transport reasons I need a new, smaller speaker cabinet so I thought I would go for building a 2x12 cab with a pair of 50 watt celestions or something inside.
Are there any good or bad design features to consider?
I was thinking of a good solid rectangular plywood box with handles, but I have heard of baffles and ‘breather’ holes, dimensional requirements such as a height to depth ratio and all sorts of complications.  Does it really make much difference, as long as I join the red one to the red one and the black to the black? A decent sound and maximum whoomph from the front are all that’s required.
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LVL 11

Expert Comment

ID: 10938370
Hi RobinD,

You could ... but I wouldn't recommend it. Designing a speaker cabinet is an art and you have to follow a few rules or the sound of the systems won't be right. There are books and plans available that will help you build your own speaker. Go to a site like partsexpress ( http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=29) and check out what they offer. Take a look at their book section, too.

LVL 17
ID: 10939792
That's the sort of complication I was trying to avoid.
I took a look at the glossary which seemed very comprehensive and full of things that I'd never heard of 'traditionally any volume roughly 5 times the Vas of the driver is considered infinite. Woofers to be used in infinite baffle situations must have a high Qts, giving them adequate damping in a free-air situation'.

I am using an old marshall 4x12 at the moment and when you take the back off it's really no more than a very solidly built box - no internal baffles, no crossover units, just 4 big speakers bolted (not screwed) to the front.
I think that my main concern is whether the actual physical dimensions of the cabinet play an important part in the sound - your link suggests the golden ratio, but I wonder how much of this is because it just looks better - I want it to fit neatly in a car.
I'm not looking for hi-fi, just portability and something to kick a bit of noise out.
(Speaker prices are a bit scary on that site, I have found elsewhere some 50w celestions with a web price of about £35 (50$ ?) )
LVL 22

Expert Comment

ID: 10943509

Robin>  There are some real easy methods to get you what you want.  While Griesh's post is accurate it is sufficient to say that that as long as the width is twice as wide as the speaker and the depth is 3 times as deep as the speaker you are in pretty good shape.

Or if you are going to use the "golden ratio"

.62 : 1 : 1.62

That is, everything should be in this ratio for optimal resonance and minimal wave collisions.

Let's suppose you have an 8 inch diameter sub woofer(round).

your box should be approx. 9 inches wide, 5.5 inches deep and 14.5 inches tall.  

This will give you a decent sound (not muffled, and not tinny).  

This will not be perfect, but few people could tell the difference anyway.

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LVL 22

Accepted Solution

_TAD_ earned 1200 total points
ID: 10943522

simple construction with reference to the golden ratio and why its improtant
LVL 17
ID: 10947401

Thanks, that link has almost exactly the level of simplicity I was looking for.

It seems to mention the important points without having to draw graphs of fequency responses etc.

It mentions 'tonal colouration', and as this is for a guitar a bit of the right sort of tonal colouration may be a positive thing - as long as it's not too nasal.

I'm going to have to start now by measuring the space in the car, calculating the golden ratio and then working out what size cones I can fit - or buy another car.

Cheap, stable and solid with protective stuff on the outside is what I am aiming for.
LVL 22

Expert Comment

ID: 10948817

Good Luck!!

If you think about it, come back and post your success.

I'm interested in hearing what the final design is like.
LVL 17
ID: 10949338
I'll try to do that.

It'll probably look like a box with inset handles (I like the ones on my marshal).
Toying with the idea of tilting one of the speakers a-la-marshall slope so I can hear what I am playing without drowning everything else out, but I still want to put the amp on the top (you have to stand your beer on something), and it's still got to fit in the available space in the car. Some experimentation with cardboard boxes is likely.
I'd like to use 3/4 - 1 inch plywood for the construction and your link even suggests what grade of wood to use!
 Looking at Celestion vintage 30's [http://www.leisure-lynx.com/products/full_info.asp?id=766] for the drivers as the price is about right and if you can believe the write-up they ought to sound pretty good.
It does worry some small venues when you turn up struggling through the door with a 4x12 'we don't want you to be too loud', but the sound is so much better than my little practice amp.

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