Here you can see the concentrically corrugated spider attached to the apex of the speaker cone.

Impedance: As a general rule, in order to operate properly and avoid risk of damage to itself and/or your amp, a speaker should have an impedance rating that matches your amp’s output-impedance rating (the number printed next to the speaker jack, usually 4, 8, or 16 ohms, sometimes 2 ohms for bass amps)—although there are some somewhat complicated exceptions beyond the scope of this introductory article. That said, keep in mind that wiring two or more speakers together changes the impedance load on the amp itself: For example, two 8-ohm speakers wired in parallel will create a 4-ohm load, and two 8-ohm speakers wired in series become a 16-ohm load.

Power rating: A speaker’s power-handling ability is measured in watts, and it’s a specification that’s often misunderstood or misinterpreted. The rating indicates the wattage a speaker can endure when tested—not with a guitar signal, but with a standard pink-noise signal called EIA 426A—before experiencing mechanical failure though overheating or breakage of one or more of its components. When amplifying a guitar signal, a speaker pushed to the upper limits of its power rating will not necessarily sound good—but it won’t mechanically fail unless that limit is exceeded. In addition, if one speaker’s wattage rating is higher than another’s, that doesn’t necessarily indicate it will be louder. A speaker’s volume capacity is indicated by its efficiency rating: a measure of the speaker’s loudness with a given input signal. However, this is yet another rabbit hole beyond the scope of our basic discussion. For our intents here, the loudness of any given amp and speaker configuration is determined by a number of factors, including the type, efficiency, and wattage of your amp’s power section—which is, after all, what’s driving the speaker.

One myth commonly heard by Lucas at Eminence concerns the relationship between wattage rating and “breakup”—i.e., overdrive or distortion. “Everyone thinks that if you have a high-power speaker, it won’t break up, or that a low-rated speaker will break up too much. That may be true in many cases, but power ratings and breakup are not directly related.” Many factors determine when and how a speaker’s sound will break up. And driving a speaker until it distorts will sound better for some speakers than others. For this reason, most manufacturers proffer layman’s-terms descriptions of a speaker’s general sound to supplement the electrical specifications.

While speakers of different makes and builds have varying efficiency ratings, on the whole, traditional speaker designs of the sort discussed here are dismally inefficient: The ratio of “power out” over “power in” is less than 5 percent. Speakers produce heat more than they produce sound.

Cone design: Perhaps the most influential factor in speaker breakup is the thickness and density of the cone material. Since the beginning of speaker history, paper has been the primary material used for cones. A cone made from a lighter, thinner paper will break up more readily than a cone made from heavier, denser paper. The choice of material has other implications as well. For example, a more flexible paper will be better at conveying low frequencies, while a stiffer paper is typically more suitable for treble frequencies.

TIDBIT: While speakers of difference makes and builds have varying efficiency ratings, on the whole, traditional speaker designs of the sort discussed here are dismally inefficient—the ratio of "power out" over "power in" is less than five percent. Speakers produce heat more than they produce sound.

When speaker shopping, you may notice that some speakers feature cones that are smooth, while others are ribbed. Ribbed cones started appearing in the late 1940s and early 1950s as a way to gain the advantages of stiffer cone paper without adding mass, which would have an effect on tone. It was a simple solution to accommodate loud playing while avoiding distortion. Because of this, all else being equal, a smooth cone will distort more readily than a ribbed one.

The spider: Looking at a speaker assembly, you may be inclined to think the spider (the concentrically corrugated part that holds the voice coil in place and allows it to move freely) isn’t designed to influence the tone. But spiders can be made stiffer or looser in order to affect upper-midrange response from around 800 to 1,000 Hz.

The surround: Yes, even the part of the speaker that connects the outer rim of the cone to the “hoop” of the speaker’s metal frame affects tones, mostly in the higher range. Generally, stiffer surrounds are more conducive to emitting treble frequencies. Common surround materials include corrugated cloth or paper. Also, while the surround’s design is intended to allow free movement of the cone, the surround itself may have a resonant frequency, increasing or decreasing specific frequencies and affecting tone. In some cases, an unwanted “edge yowl” can occur when the energy from the surround’s resonation transfers back to the cone.

Embarking on the Adventure
Shopping for the perfect speaker isn’t easy—it’s certainly more complicated than buying, say, a new instrument or amp. However, as with guitars and pickup swapping, many times the right replacement speaker can make that final bit of difference between liking an amp and finding it absolutely indispensible. In some cases, the right speaker swap can even make you fall in love with an amp you didn’t like at all and were considering hocking.

The ideal approach to speaker shopping has many facets: researching your favorite players’ go-to speakers, reading reviews and forum posts from players who seem to have gear and musical tastes similar to your own, consulting with trusted and experienced players who get what you’re going for, listening to sound samples, watching demo videos, and, of course, confirming that the technical specifications of speakers in the narrowed field comport with your amp. In the end, though, your ears are always going to be the final judge. You’ll never know for sure if you like a speaker unless you audition it in person, using your own guitar, amp, and pedals, and spending a reasonable amount of time playing at the sorts of volumes you normally play at.

Given the breadth of offerings on the market, chances are you won’t get to audition most of the speakers that could be a good match for you. But keep in mind that doing your homework and then making a leap-of-faith purchase has just as much potential to transform your sound as a new pedal—and a new speaker is often easier to incorporate into your signal chain than figuring out where to insert a new stompbox on a crowded board. The other good news is that, just as with pedals, there are so many great guitar and bass speakers to choose from that there is no single “right choice”—there are likely several speakers that would be a wonderful match for your needs.

On the other hand, going gong shopping would be much easier.