Understanding Speaker Cabinet Designs
September 23, 2008 by Charlie
Ask a group of guitarists what their favorite instrument, amplifiers and effects are, and each one will surely ramble on for hours about his gear of choice. Ask that same group about their favorite speakers and cabinets, however, and many of them will likely respond with a simple “I dunno.” The sad truth is that even though cabinets and speakers play major roles in shaping the tone of a guitar sound, they are often overlooked by players.
The overall sound of a cabinet is the result of all the components that go into building it and how they’re put together. Once you acquire the knowledge of what goes into building speakers and cabinets, you’ll start to understand exactly what you like and dislike about different cabinets. In this lesson, I’m going to focus on defining the components and materials that go into building speakers and cabinets as they relate to the sound they produce. My hope is that at the end of the two lessons, you will be well informed and on your way to identifying what you preferences are and what speakers and cabinets complement your playing the best.
With very few exceptions, cabinets are made out of wood. Plied birch wood is far and away the most common choice, though some cabs are made from particle board or a combination of the two. Sonically, birch is great because it strikes a very desirable balance; it’s rigid enough to produce punch and definition while being soft enough to sound warm but not floppy. Remember that the cabinet acts as a resonator for the speakers just as the wood of a guitar acts as a resonator for the vibrations of the strings. Birch is also super durable and is well suited to withstand the vibrations, abuse and travel that a cabinet is likely to endure.
The average wall thickness of a 4×12, 2×12 and 1×12 cabinets is ¾-inch, though some combos have been made from one-inch thick wood. A one-inch wall will be more rigid and will produce a tighter, darker and more blunt sound; a ½-inch wall will usually accentuate high frequencies.
Another factor to consider is whether the cabinet has an open back or a closed back. Open back cabinets generally don’t produce as much low end because the back pressure created by the speakers has a lot of room to escape. With a closed back enclosure, the back pressure has a much harder time escaping the cabinet which, in turn, creates a more significant low end resonance. In some closed back and front loaded (where the speakers are mounted on the front of the baffle board) cabinet designs, you will see holes in the front or back of the cabinets. Those holes are known as ports and are intended to let some of the back pressure escape to allow for desirable frequency response.
An interesting characteristic I discovered about closed back cabinets is that you can change the sound of the cabinet by loosening and tightening the screws that hold the back board on. By loosening (or removing) some of the screws, you can “tune” the cabinet to be soft and floppy. If you want clarity and defined punch, use all the screws and tighten them up. It’s similar to the way drums are tuned—just think of the back board as the drum skin and the rest of the cabinet as the drum.
Another thing that I’ve found to affect the sound of a cabinet is the vinyl covering and the glue that holds it onto the cabinet. The glue and the vinyl slightly muffle the higher frequencies, in most cases in a desirable way. I first discovered this when I decided I wanted one of my 4x12s to have bare wood finish and proceeded to rip off all the vinyl. After the vinyl had been stripped I noticed a difference in sound.
The age of the cabinet and amount of time it’s been played also affect the sound. An old cabinet with years of use and heavy gigging will, in time, soften up and lose it’s stiffness-sometimes too much for desirable results. The sound of a cabinet is also affected by what surface it’s sitting on. I’d much rather have my amp sitting on a wood floor than carpet or concrete. Wood interacting with wood will only extend the resonance of an amp as opposed to carpet or concrete which have a little or no resonating abilities. For the same reason, I also recommend resting cabinets on rubber feet or nothing at all, as opposed to leaving the wheels on all the time.