Speaker Now (Or Forever Hold Your Peace)
By Brian Fox
Sun, 1 May 2011

BP0511_techbench3_nr1The cutaway cross-section view reveals a speaker’s hidden components.


“I DON’T KNOW—ASK MY TECH.” IT’S a response I’ve gotten in more BASS PLAYER interviews than I care to admit when the conversation has turned to the technical aspects of bass gear. Fair enough—I know my earliest motivation for playing had absolutely nothing to do with things like damping factor, the Fletcher-Munson effect, or any other kind of highfalutin tech terms. But allow me to enumerate a few facts for those of us who can’t afford to hire gear geeks to think for us:

1. There’s more to being a bass player than playing bass.
2. Gear can be expensive, and when it breaks or doesn’t work right, it sucks.
3. Learning some general principles of electronics and acoustics will result in your playing better, sounding smarter, and looking hotter.

Okay, so m aybe I’m getting a little carried away. But bumping up basic knowledge of how your gear works will go a long way in making yourself a more well-rounded bass player. For now, let’s take a closer look at one of the most crucial components in sound production for amplified bass: speakers.


First of all, what exactly is sound? Sound is “mechanical radiant energy transmitted by longitudinal pressure waves in a material medium (as air),” according to the good folks at Merriam-Webster. In bass amplification, the loudspeaker, or driver, is the key agent in converting an amplifier’s radiant energy into airborne pressure waves. It does this through the process of excursion, the back-and-forth motion of a speaker’s cone (or diaphragm), driven by the electromagnetic interaction of a speaker’s movable voice coil with a fixed magnet [see Fig. 1].

BP0511_techbench2_nr1Fig. 2



From Alexander Graham Bell’s first patented telephone loudspeaker in 1876 through the moving-coil speakers of Magnavox in 1917 and the high-tech drivers of the modern day, the materials used to fabricate loudspeakers have changed quite a bit. In the early days of amplification, drivers typically featured paper cones and magnets made of alnico, a composite of aluminum, nickel, and cobalt. As the cost of alnico shot skyward in the ’60s, speaker magnets were made increasingly of ceramic ferrite. Nowadays, a number of manufacturers have begun to favor lightweight neodymium as a magnet material, a choice that cuts the net weight of a 10" driver roughly in half. While some players are suspicious of neodymium drivers, claiming they introduce an unwelcome spike in the midrange frequencies, many others are quick to go neo on the grounds of weight alone.


In the diaphragm department, Larry Hartke flipped the speaker world on its conehead when he built his first aluminum-cone driver for bassist Jaco Pastorius in the early ’80s. Hartke’s reputation grew through the ’80s and ’90s on the merits of the aluminum driver’s fast, snappy response. Hartke Systems recently re-upped the ante with the release of its HyDrive hybrid cones made of both paper and aluminum [Fig. 2]. Alternative materials ranging from hemp to Kevlar have also begun to gain some traction in the cone field.

BP0511_techbench1_nrFig. 3



From the booty-full bite of Phil Jones’s 5" Piranha speakers [Fig. 3] to the bowel-battering “brown sound” of the AccuGroove Whappo Grande’s 21" super-sub [Fig. 4], drivers come in sizes big and small. While it’s true an 18" speaker is capable of moving more air than a 10" driver by virtue of its speaker cone’s greater surface area, the calculation gets more complicated when you begin to factor in the design of the cabinet itself and the number of speakers within.


Power handling and impedance—the resistance presented in a circuit containing alternating current (AC)—is where things can get a bit harder for the average Joe to grok. A popular analogy to help illustrate the way electrical current flows is to imagine the circuit as a garden hose, where the current is the flow of water through the hose, voltage is the water pressure as it exits the nozzle, and impedance is the nozzle (or thumb) controlling the flow of current.

The mathematical equation used to determine the relationship between current, voltage, and impedance is known as Ohm’s law, which states: current (measured in amperes) equals voltage (in volts) divided by impedance (in ohms). To calculate impedance, you can simply switch around the equation to read: impedance equals voltage divided by current.

When it comes to speakers and amps, if a speaker or combination of speakers puts up too much resistance, the potential energy from the amplifier won’t be efficiently translated into sound. But perhaps a larger problem is when a group of speakers offers too little resistance, forcing the amplifier to pump out more current that it should, ultimately frying it.

The calculation of impedance is pretty straightforward when you’re dealing with a single speaker—say, a 15" rated at 4Ω. Paired with a Markbass F 500 head, which puts out 500 watts at 4Ω, you’re in good shape. If you add an identical 1x15 cab to the mix, you effectively double the load to the amplifier by halving the speakers’ impedance 2Ω. While some heads can operate safely at 2Ω, others can’t. This is where the calculation of total impedance (or load) becomes really important.

We’ll dig deeper into the subject of impedance in a future column. In the meantime, take a second to familiarize yourself with all the specs listed on your heads and cabinets. Hopefully all the numbers and calculations don’t make your head explode, and with any luck, you can use those numbers and calculations to keep your head from exploding. In the meantime, play well, study hard, and look sharp!





















 Fig. 4


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