Build Your Own Guitar Cab

Want to build your own guitar speaker cab? Here's some useful information...

September 16, 2011

A 1x12 combo
As guitar speakers are different, so their cabinets are different. The box design is acoustically less critical than that for hi-fi or PA systems, but proper construction is essential.

Primarily, the cabinet is a convenient way of housing the speaker, so it should be solidly built to ensure no joint vibration (unpleasant buzzing), and be strong enough to withstand hard use. After all guitar speakers are quite heavy and amplifiers that sit on top of guitar cabs are even heavier.

Guitar cabs aren't built to provide bass extension like a PA box might, but they do perform an "acoustic" function. If the driver were used without any cabinet at all, the sound coming from the rear of the unit would cancel out some of the sound coming from the front, thereby reducing the amount of bass heard. Enclosing the the speaker inside a cabinet reduces this effect resulting in a truer bass performance that is neither enhanced nor attenuated.

For illustrative purposes, a basic design for a 2x10 or 1x12 open back cabinet is shown here. To build a cabinet like this we would recommended the use of 15mm plywood with number 10 screws positioned no more than 150mm (6") apart.

Panel joints can be simple butt-joints, screwed and glued, with reinforcing battens (you can use more sophisticated joints if your woodworking skills are up to it!) Whatever joint type you use, it is important that the whole thing is both airtight and secure.

The drivers can be mounted to the front or the back of the baffle. Front mounting makes a very simple job of dropping the speaker in or out of the cabinet. In either case it's preferable to use mounting bolts and T-nuts to fix the driver to the baffle.

There is a wide range of speaker cabinet accessories available from specialist suppliers. Fitted carefully so as not to weaken the box or create air leaks; wheels, handles, grilles and corners all add to convenience and durability.

In summary: 
  • Plywood or real wood construction is preferable 
  • Strong, rigid construction means no buzzes or rattles 
  • Size is not critical 
  • Ensure the speaker is adequately mounted and protected 
  • Avoid air leaks if using sealed box construction 

CAUTION 
We do not advise mixing different impedances of driver within the same cabinet. This can lead to uneven power sharing between speakers, causing one speaker to be overdriven and damaged, while the other is underdriven. 

THIELE SMALL PARAMETERS 
Thiele Small parameters are useful for controlling the low frequency response of sealed or ported cabinet systems by changing the cabinet internal volume, and port dimensions. However they are of severely limited use when designing a guitar speaker cabinet. 
  • Electric guitar speakers do not reproduce 'low' frequencies (the low E string of a lead guitar has a fundamental of 82Hz) and so the frequencies at which Thiele Small parameters have significance are mostly below the operating range. 
  • Also, the parameters are measured at very small signal levels. Guitar speakers become non linear at very low levels compared to other types of speaker, greatly reducing the significance of Thiele Small parameters in actual speaker use. Using the Thiele Small parameters of a typical guitar speaker, you will find that halving or doubling the cabinet size makes minimal difference to the response. 
  • They have no relevance to open back cabinets. 
  • Guitar speakers are not recommended for use in ported cabinets (as the increase in cone excursion below the tuning frequency can cause the thin paper edge of the cone to tear). 
FINAL NOTE
The cabinet size, shape and construction are of far higher significance than the internal volume. Cabinet design using Thiele Small parameters ignores these most fundamental aspects. Important factors include the material you make the cabinet from, the panel sizes and shapes, how they are joined, how the cabinet is finished, the mounting of the speaker, etc. These, not Thiele Small parameters are the critical factors in the design and ultimately the sound of a guitar speaker cabinet.
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