Guitar Amplifier Cabinet Design -

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Guitar Amplifier Cabinet Design

So what should we think about when designing a guitar cabinet? Well it’s simple right - just a box with a hole?

That’s about right in fact. Amplifier cabinets do sound different to each other but their first job is to hold everything together and protect the delicate circuitry from years of abuse on the

Choose Your Material

The most popular material for guitar cabinets is wood, although other materials such as metals and plastics may be used. At barebones Guitar Amplification, all of our amplifiers have wooden cabinets so our next chose is the type of wood.

Solid wood may be used but finding large, flat panels of solid wood is tricky and expensive. Wood is a living thing and a piece which starts out flat may take on all sorts of twists and shapes once it dries.

The solution is to use plywood. Plywood is made up of thin sheets of solid wood glued together such that the grain of each layer lies at 90 degrees to the next. In this way it is much less likely (although not impossible) for the panel to warp. The result is an impressively flat sheet of wood measuring anything up to 8’x4’.

Catch the Buzz

Guitars produce music over a large frequency range from 82Hz to, say 4kHz. If any of these frequencies set off a vibration in the cabinet then the guitarist will lose patience pretty quickly, particularly if the vibration happens to coincide with the last note of their favourite solo! To avoid buzz and rattles, a quality plywood of good density and without air-holes must be used.

At barebones Guitar Amplification, our cabinets are manufactured using two grades of plywood, both 18mm (approx. ¾”) thick. The front panel, which holds the speaker, is made from high quality hardwood. This panel has a large influence on the overall sound, rather like the top panel of an acoustic guitar. The rest of the amplifier is made from a softer grade of plywood. Using hardwood for the entire amplifier would add a lot of weight (and cost) for not much gain in tone.

Stick it Together...

The next consideration is how to stick the cabinet together. At barebones Guitar Amplification we use solid wood struts to brace and join the cabinet panels

...And Cover It Up

Vinyl covering, such as Tolex or Levant is glued and stapled into place. The speaker cloth is attached to the front panel and decorative binding installed to add a little sparkle.
To protect you amp and provide a nice finishing touch, custom designed aluminium protectors are added to the corners.
All that remains is to add some feet or wheels, handles and a CNC machined rear protective panel to keep fingers away from the high voltage electronics whilst allowing sound to leave the rear of the cabinet – which brings us neatly on to -

Acoustic Design

So how about the acoustics?

Open-backed cabinets tend to have a more natural sound compared to closed-back cabinets. Almost as much sound will leave the back of a speaker as the front. If the cabinet is open at the rear then these extra sound waves will head off until reflected by the nearest wall. What you hear is the sound directly from the speaker plus these reflected sounds.
Although open-backed cabinets generally sound more natural, placement of your cabinet close to a wall or in the corner of a room may cause certain notes to boom and others to appear much quieter. If possible, place your cabinet away from solid surfaces and try to angle the cabinet a little so it is not square-on to the nearest wall.

Tune Up

Closed-back cabinets avoid these issues by deliberately blocking the sound leaving the rear of the cabinet. The speaker still produces the out-of-phase sound from the back but this is now reflected within the cabinet by the rear panel.
By careful design it is possible to 'tune' a closed-back cabinet so that it enhances certain frequencies. For example, a guitarist may use a lot of open-E tunings so the cabinet can be designed with peaks at 82Hz, 164Hz, etc. The down-side is that other frequencies will be cut so the sound may be less natural.

A tool used in some bass guitar cabinets and Hi-Fi speakers is to add a tuned port. These are tuned to give a big lift to the bass frequencies which can make cabinets some much 'larger' than they actually are.

Stack 'm Up

Using an extension cabinet or a multi-speaker cabinet gives a boost to your sound by simply moving more air (and looks great into the bargain!)
However, we do need to take a little care. Take a look at the following image.

This image shows the effect of placing multiple speakers on top of each other. Although the speakers are placed vertically on top of each other, the sound spreads out HORIZONTALLY and is in fact concentrated between the two speakers.

Now consider a 2x12" guitar cabinet. We may naturally assume that this wider speaker configuration will spread the sound out across the audience. But no, the sound is concentrated VERTICALLY between the two speakers. Some poor sucker standing directly in line with your rig is getting a neat boost from your guitar amp whilst those around are hearing much less. To make matters worse, the affect is strongest at the highest frequencies!

Ideally, a 2x12 should be designed with the speakers on top of each other. This makes the amp very cumbersome and not very pretty. A solution I’ve found works well is to use a 1x12” amplifier and place it on top of a 1x12” extension cabinet. This concentrates the sound in a horizontal pattern so all audience members get a good mix.

And Finally...

One final piece of advice is to tilt your cabinet up towards you when you are gigging. This is particularly important in smaller venues and when foldback is not available.
When standing close to your amp, most of the sound will pass through your legs - the audience will hear your amp louder than you! The guitar may be too loud for the audience (and the sound man) but the guitarist can't hear themselves. At barebones Guitar Amplification we are working on a tilt mechanism for our future amplifiers, but for now, make use of a guitar amp stand or try to raise your amplifier off of the ground.
Matt Green

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