Most speaker manufacturers have pretty solid Web sites loaded with info on how their different models are voiced, so start there. You can also seek out info on your favorite players’ rigs and see which speakers they load their cabs with, although other factors (such as amp, signal path, etc.) will color the sound you’re digging. Local players and guitar-oriented forums can provide excellent references, as well.
Once you zero in on a few options, you should consider the speaker magnet. There are various kinds of magnets for different applications, but, for guitarists, it usually boils down to alnico or ceramic. Alnico (aluminum-nickel-cobalt) magnets have a lot of allure for blues and roots players, because as you play louder, the voice coil’s own magnetic field begins to temporarily demagnetize the alnico structure, resulting in decreased speaker movement, but also smooth compression and sweet sustain. Ceramic (strontium ferrite) magnets are far less susceptible to compression and demagnetization, so, at high volumes, the speaker simply goes as far as it can, and then breaks up with a hard, bright crunch that’s perfect for edgy rock or metal.
A speaker’s power rating is another critical factor, as you’ll definitely need the speaker to handle the power your amp is pouring into it. As a rule of thumb, if your amp is rated at 60 watts, you shouldn’t use a speaker that’s rated at less than 60 watts. While cool sonic things can occur when speakers are pushed hard—as in a 30-watt Vox AC30 equipped with two 15-watt Celestion Blues—it’s probably wise to use a speaker (or combination of speakers) that can handle about twice the rated power of your amp.
You’ll also need to consider impedance. For example, if the speaker in that 60-watt amp was rated at 4 ohms, then you shouldn’t replace it with anything that puts a load of less than 4 ohms on your amp’s output circuit. Less is a deceiving term, however, because when you lower the impedance, you’re actually increasing the current sent from the amp. Now, it’s one thing to blow up a speaker, but going below the impedance rating can fry the output transformer in a tube amp, or all the output transistors in a solid-state amp. Figuring total impedance for multiple speaker arrays involves Ohm’s Law and some relatively simple math (all of which can be explored in detail on the Web), but here are some common configurations:
• Two 4-ohm speakers wired in series provide a total impedance of 8 ohms.
• Two 8-ohm speakers wired in parallel provide a total impedance of 4 ohms.
• Four 16-ohm speakers wired in series/parallel yield a total impedance of 16 ohms.
What the heck is series, parallel, and series-parallel wiring? Glad you asked. Read on.
Of course, the easiest way to replace two or more speakers in a cabinet is to rewire them exactly the way they were before you started futzing around. Take a digital photo for reference. If you want a little science behind the practical, however, here’s some knowledge.
In many cases where two speakers are involved, the pair were likely wired in parallel—meaning all the positive terminals of each speaker are connected to the positive (tip) side of the speaker jack, and all of the negative terminals are connected to the negative (ring) side of the jack (Fig. 1). An advantage of this wiring scheme is that if one speaker blows, the remaining speaker (or speakers) will continue to get current and produce sound. In addition, as more speakers are connected, the impedance load on the amp decreases, which results in more acoustic output.
In a series configuration with two speakers, the positive terminal of one speaker is connected to the positive (tip) side of the speaker jack, the negative terminal of the second speaker is connected to the negative (ring) side of the jack, and remaining positive and negative terminals on both speakers are connected together (Fig. 2). In series connections, the more speakers used, the higher the impedance, which results in a lower acoustical output.
A series/parallel wiring scheme allows you to use additional speakers to increase volume, while maintaining a total impedance that’s compatible with the amplifier (usually between 2 and 16 ohms). In a typical four-speaker setup, a single wire from the positive (tip) side of the speaker jack runs to the positive terminals of speakers A and C. Next, the negative terminals of Speakers A and C are wired to the positive terminals of Speakers B and D. Finally, a loop is created by running a single wire from the negative (ring) side of the jack and splitting it between the negative terminals of Speakers B and D (Fig. 3).
Lay your amp or cab facedown (so you can easily lift the speaker in and out), unbolt the speaker from the cabinet, and get ready to detach that sucker and prep a home for your new speaker. Depending on the brand and type of speaker, it may have slide-on, pushbutton, or solder-style connections that need to be detached. For slide-ons, grab the female connector on each speaker wire and carefully work it off. Pushbuttons are easy—just depress the button with one hand, and pull the wire out with the other.
To unsolder a wire from a speaker terminal, hold onto the insulated part with one hand, and apply the soldering iron with the other hand just long enough to slowly pull the wire off. Make sure you wear goggles (hot solder can splatter), and keep the window open (you’re working with a lead-based product). Now, check out the photos for help on soldering your new connections.