Cabinet Handbook

This handbook covers all the major kinds of cab types you’re likely to want to try and build. Anything from horn-loaded subwoofers to 4×12 guitar cabs, along with advice on dimensions, fixings materials and construction.

There are useful sections on porting and crossover design including some basic scientific theory to help you make the right choices for your application.

For more advice on choosing PA speakers, click here.

For more advice on choosing guitar speakers, click here.

Speaker Wiring Configurations

Replacing a speaker or speakers in your cab can be a really cost-effective way of significantly upgrading your tone. If you’re thinking of swapping out speakers yourself, then you’ve come to the right place! It needn’t be a difficult operation, but it’s important to be aware of how the speakers are connected up, as well as some of the implications of wiring up multiple speakers together. Before you get to re-loading your cab.. take a moment to read through the important background information below and get ready to take a step closer to great tone!

Single Speaker

The most basic cabinet configuration is a single speaker.

1 x 8 ohm Speaker = 8 ohm load
1×16 ohm speaker = 16 ohm load

Two Speakers

Remember:
1. Match impedances (ohms) – all speakers in the same box should have the same impedance.

2. Power handling – as a rule of thumb, when mixing speaker types in a two speaker cabinet, maximum power handling is 2 x the lowest rated speaker (e.g. for 30-watt & 60-watt speakers, max power handling = 2×30-watt = 60-watt)

There are two ways you can wire a two speaker cabinet.

 

Series: 2 x 4 Ohm Speaker = 8 Ohm Load;

2 X 8 Ohm Speaker = 16 Ohm Load;

2 X 16 Ohm Speaker = 32 Ohm Load

 

Or, in Parallel: 2 X 4 Ohm Speaker = 2 Ohm Load;

2 X 8 Ohm Speaker = 4 Ohm Load;

2 X 16 Ohm Speaker = 8 Ohm Load

Four Speakers

Remember:
1. Match impedances (ohms) – all speakers in the same box should have the same impedance

2. Power handling – as a rule of thumb, when mixing speakers in a four speaker cabinet, maximum power is 4 x the lowest rated speaker (e.g. for 2×30-watt & 2×60-watt speakers, max power handling = 4×30-watt = 120-watt)

There are two ways you can wire a 4×12 (or 4×10 for that matter), the main one is Series/Parallel: 4 X 8 Ohm Speaker = 8 Ohm Load; 4 X 16 Ohm Speaker = 16 Ohm Load

Power Handling: All you need to know!

Different speaker manufacturers use differing methods to determine power handling. At Celestion, every speaker is rigorously power/longevity tested using an in-house developed noise source. From this test, we find out how much power the speaker is capable of using and how much will destroy the speaker outright. By skilful analysis of the test data, we calculate a suitable power-handling figure.

The value chosen is low enough so there’s little or no risk of damage, but highenough for the speaker to fulfil the application it was designed for. It is NOT an absolute limit above which you must never go, more like a “speed limit” You can exceed the limit if you want, but it’s not recommended and if you do, theremay be trouble ahead…Generally, you can safely run a 60-watt Celestion speaker at 60 watts and it’ll keep going all day long.* Connect it up to 100 watts and it might work for anhour or more before it incinerates. “Over-power” any speaker and it’ll workfine for a while; just don’t bank on it lasting.

(* Extreme use can break a speaker at lower-than-rated power levels. Forexample a sustained drop-tuned Metalcore pummelling through vintage-typespeakers would almost certainly cause damage.)

Power Handling for Combined Speakers

If you mix different speakers with different power ratings in the same cabinet, it’s important to be aware of the combined power handling of the cabinet itself. Unfortunately it’s not quite as simple as adding together the two power handling values.

As a rule of thumb, the cabinet power handling should be calculated as a multiple of the lowest rated speaker. For example in a 2×12 containing a 60-watt speaker and a 30-watt speaker, overall cabinet power handling is 2×30-watt = 60-watt. In a 4×12 containing 2×60-watt speakers and 2×30-watt speakers, overall cabinet power handling is 4×30-watt = 120-watt.

Build Your Own Guitar Cab

Want to build your own guitar speaker cab? Here’s some useful information…
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 2×10 or 1×12 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
CautionWe 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.