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The Role of Loudspeaker Diameter in the Relentless Pursuit of Tone

These days, guitar speakers are available in a range of sizes from two or three inches, right up to 15". Smaller speakers are great for bedroom blasters and practice amps, where reduced output at low frequencies can minimize sound spillage between rooms and keep the neighbors sweet. If you’re like most, though, chances are you’ll be using 12" speakers for much of your recording and live work. But with an ever-increasing range of quality 10" speakers, and even some interesting 15" speakers available, one has to ask the question, “What role does speaker size play in the ‘relentless pursuit of tone?”

Inside the Mind of the Speaker Designer
Practically all of a guitar speaker’s constituent parts contribute in some way to its sonic signature. Chief among them are voice coil, magnet assembly and cone [but also influential are the suspension, surround, dustcap, cone treatments, etc.]. Each of these factors interacts with the others, together contributing to overall tone. These interactions, though in some cases very complex, are governed by certain principles of physics, in particular:

Output level [a.k.a. sensitivity] is determined by how efficiently the speaker converts electrical energy into movement of air.

Sound dispersion is controlled by the directional nature of high frequency sound and the tendency of certain cone shapes to focus the output signal in different ways.

This laser doppler image indicates vibration modes within the body of the cone.

For guitar speakers in particular, vibration “modes” within the body of the cone add much of the harmonic complexity and coloration that significantly contributes to great tone.

The speaker designer uses their expertise to find the right mix of all of these factors to hit a given “tone target.” Now, imagine we want to use a small speaker with a thin and light cone. There would be more intense vibration modes within this type of cone [compared to a cone of greater thickness, which would be more resistant to these vibrations], resulting in a richer, more harmonically complex tonality. However, use the same cone thickness with a larger diameter speaker and that cone might lack sufficient stiffness to withstand the proposed power handling, and could buckle under the force of the moving voice coil.

In this situation there would need to be some “trade-off” between tonality and power handling, requiring the designer to make both musical and technical choices to reach a desirable and workable solution. An experienced speaker designer will have the capability to identify the “right” choices to make in these situations, and use the opportunity to create a completely new sounding speaker.

What This Means For Tone
So, we see that attributes like size, harmonic complexity, power handling and high-note dispersion are clearly linked in the design process. Over time, the 12" speaker has come to be regarded as having the best balance of these attributes. However, 10" and 15" speakers can offer some alternative, interesting and even exotic flavors!

Good sounding 10" speakers can deliver a fast, punchy sound at wider listening angles with reduced “boom” on small stages. They can offer increased portability, reduced cost and the ability to push your amp into overdrive at reasonable levels without having drumsticks aimed at the back of your head. A well-designed 15" speaker can move more air so you can gig those wonderful little valve amps. The vocal range can be creamier, with extended low end and lots of detail and harmonic complexity, giving surprising richness to some otherwise scratchy-sounding guitar and amp combinations.

Which Size is For You?
It’s becoming more widely understood that changing speakers has a greater impact on tone than swapping guitar, pickup, or even amplifier. So ask yourself, why just one size of speaker? As players, all we need to do is select the right one according to situation, application … and desire.

Try this:
For the recording or practice session, why not try a small amp through a sweet, wellbalanced 10"?

At your big break support gig on the city hall stage, how about a wall of 4x12s?

Need to add some beef to your retro “plasticaster”? Break out a 1x15 cabinet.

What’s more, just as boutique amp makers have mixed different models to increase harmonic detail, you might even try and take this a step further by mixing 10", 12" and even 15" speakers to create that unique signature sound. But that’s another column.

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