Here’s a quick challenge: You want to make the most dramatic change possible in both the look and sound of a guitar rig, but can only change one item. What do you choose?
Hands up all those who said speaker cabinet? It may not have been the first thing that came to mind, but think about how much of the difference between a small combo, and that giant wall of Marshall stacks is really in speaker cabinets rather than the amps.
For manufacturers cost optimizing their products, cabinets and drivers are often the first targets for reduction. Compromises here will normally yield much greater savings than the electronics, enabling them to hit the required price point. Budget units can often conceal some really nice amps hidden behind crummy, low cost cabs and drivers. With a modest amount of effort, you can choose the right speaker drivers, get your own custom cabinet built for you, and assemble it yourself in an afternoon.
If you are using a tube head, then this should be quite straightforward. The purpose of separate heads after all, is to allow the use of different speaker cabinets. If you are using a combo, then you may have an extension speaker out on the back that permits connection of and additional cabinet. Some cabinet builders can also build new combo enclosures for your amp. If you are using a software based modeler, then you have a choice of using cabinet simulation software with a full range monitor, or turning these off and using a regular cabinet.
The first cabinet decisions are going to be the size of cabinet, and number and size of speakers. In general, a larger cabinet and more drivers is going to provide an increased Sound Pressure Level (SPL), in other words ‘louder’, and increased low frequency response.
If you are looking for a gut punching, pants leg flapping output like no other, then there really is no substitute for a big 4×12. Everyone should play through one of these at least once in their lives. It truly is an addictive experience. Alas, as with most addictions the trade-offs are numerous. A typical 412 is around 2.5 feet square, and a challenge for the trunk of most cars. At around 50lbs for just the empty cabinet they are not light either. With four vintage 30’s and some hardware such as casters, you are knocking on the door of 100lbs!
If you can live with a slightly reduced flap of the pants, then a 2×12 vertical or diagonal is a popular choice. These provide a good chunk of the look and feel of a 412 but in a smaller, lighter package. With the right choice of drivers, you can get something that still covers a wide range of amps, but comes in sub 50lbs fully loaded.
A 212 slanted diagonal is my personal favorite all round cabinet. A straight 412 is very directional: The high frequency tends to drop off quite significantly when you get off axis, so you’ll get a very different sound depending on where you are standing relative to the cab. A slanted diagonal cab does a better job of high frequency dispersion giving a more consistent frequency response over a wider area.
Side by side cabinets utilize two drivers in a low profile form factor that’s not too much bigger than a 1×12. This is a great configuration to give you the extra output of two drivers, while keeping the size manageable. Some 2×12 cabinets can be used in either horizontal or vertical configuration increasing the flexibility still further.
After choosing configuration, the next choice is going to be cabinet material. There are several suitable woods with the most common being Baltic birch ply and pine. The Baltic birch tree grows around the Baltic area of Northern Europe, hence its name. The ply has been used by European cabinet makers for many years and is known for it’s strength and stability. Typical ply wood is made from higher quality veneers on the outside and softer woods on the inside whereas Baltic birch ply uses the higher quality wood for every layer. The softer interior layers of standard ply also have areas of no wood at all called voids. Baltic birch ply is void free, so it’s 100% solid. It holds on to screws and inserts much better so it’s ideal for bolting oscillating speaker drivers to. Many good quality speaker cabinets are made entirely from Baltic birch including most of the classic British cabinets. Another suitable ply for speaker cabinets is Italian Poplar, which though not quite as strong, is generally lighter than Birch.
The traditional American Fender style cabinets are often made from solid pine. Pine is a little lighter, and being a little softer the pine cabinet can contribute more to the overall sound. Since the wood is less uniform than the Baltic birch, there can be differences from cab to to cab, and you have to be more careful matching the driver to avoid unwanted resonances. A good pine cab with appropriate speaker can give you that classic bright and lively American sound. Cabinets with pine shells and Baltic birch baffles can be a great choice. The Baffle is the front piece of wood that the speaker is bolted to. This way you get the strength and stability where it is needed most, and still some of that classic pine tone.
Next up is to select the speaker driver. Most of the major guitar speaker driver manufacturers provide extensive details on their websites of the characteristics of their various drivers, and suitability for certain types of cabinets and the tones they are aimed at. Take the time to read through these. Mounting holes are sort of a standard. In most cases a 12” driver from vendor A and a 12” driver from vendor B can be exchanged and the mounting holes in the cab match up, but it’s not absolute, so check the specs that will be published by the vendor.
Drivers can be front or rear loaded, which means the driver is put in through the baffle and bolted either through the front of the cabinet or the rear respectively. You should check both the cabinet and the speaker driver specs to see which orientation they require. Some cabinets and speakers will support both in which case you can choose which you like best. Otherwise you should make sure they are compatible. For example, if your cabinet is rear load only, and your speaker is front load only, then they won’t work together without modification.
Drivers will have impedance and power handling ratings. Guitar speakers are most commonly 4, 8, or 16 ohm impedance. These figures are per driver and will change when using multiple
drivers depending on how they are wired. Speaker manufacturer Eminence publish some great technical resources on the different ways to wire together multiple drivers, and how this impacts total impedance. Check them out at www.eminence.com. Check to make sure that the total impedance of all drivers wired together the way you have chosen is supported by your amplifier. Mismatched impedance can cause improper operation and in some cases serious damage to either drivers, amp or both.
Power handling for guitar speakers is usually from around 20W at the low end to around 200W at the high end. These figures are per driver and will change accordingly when using multiple drivers. Matching speaker power handling to amp output depends to a large extent on what your personal requirements are. In general, if the effect of speaker break-up is part of your required tone, then you should aim for the low side of the power handling. It’s OK in most cases, and sometimes desirable to use lower rated drivers with higher rated amps, as long as appropriate precautions are taken. For example, if you are looking for some speaker break-up at lower volumes, using a 30W rated speaker driver with a 50W rated amp is appropriate because the driver is going to begin to breakup long before you hit maximum volume. If you pound away with a bunch of high gain pedals at full volume with the amp cranked to the max at a stadium gig, then you do risk damaging the speaker driver, but if you are running the amp at lower volumes then you’ll likely remain well within the driver specs and get towards your desired tone at the same time. Vice versa if you want to make sure that your speaker tone remains clean and does not break up at all, then you can over rate the driver. Using a 100W or 150W speaker with a 50W amp could be suitable in this case.
There’s only so much you can determine from specs, and eventually you are going to have to start putting speakers in cabs and trying them out to see how they sound to you. Don’t be too surprised if you have to have a two or three goes at it to find something you really like. Start by following the speaker drivers recommended cabinet configurations, and going with something that’s a known quantity such as 30W British style drivers in a birch 412, or American style drivers in a 2×12 pine, and you’ll be relatively safe. Later on you can start experimenting by trying unconventional combinations like American style drivers in British style cabs. You can even mix different drivers within the same cab. For example putting low frequency optimized drivers at the bottom of a cab and higher frequency optimized ones at the top can help give a more hi-fi like tone.
For wiring up, your speaker cabinet builder may offer pre-assembled wiring harnesses so you you can just plug in and play without any soldering or crimping required. If you are au-fait with these techniques and have the right tools, you can do your own wiring. Remember that for both internal connections and when connecting the finished cabinet to the amp, the wires carry power amp level outputs so you must use suitable gauge speaker wire. Don’t use a guitar cable to connect your 200W tube head to your 412! If you are not comfortable with basic electrical wiring, then you should have a qualified person do it for you.
Most of all, experiment. There are a few basic rules such as the mechanical and electrical ones described earlier, but other than that try different stuff out and see what you like. As long as it’s put together safely, if it sounds good, then it is good!