The Perfect Partner
Guest writer Dan Coggins explains how speaker choice, and efficiency thereof, can affect your sound – and your hearing
It might be a matter of personal preference and taste, but there can be no denying how profound an effect the combination of amp and speaker have on one another. In last issue’s article, I pointed out that in some designs the speaker affects the amp’s behaviour more than others – and that it is, to a lesser or greater degree, a synergistic relationship. In other words, some speakers and amps go together sonically like peaches and cream, while other combinations, frankly, sound awful. Guitar amps rarely sound good into full-range PA speakers, for example. It’s really a matter of experimentation, especially if you have any misgivings about the overall tone of your rig.
While it’s important to look at the construction and materials when selecting a speaker, here we’ll explain some other factors that give specific brands and types their distinct voices, much like a particular and somewhat extreme fixed EQ setting.
Think about PA systems and keyboard amps and they have historically used fullrange, almost hi-fi speakers. Guitar amps, however (and, to a lesser extent over time, bass amps), tend to use lower-bandwidth speakers. If we consider the classic valve amps that are still popular today, we can see that Vox and Marshall used Celestion, for example, and in the States, Fender and Gibson amps often used Jensen.These were
Alnico units in the 60s, moving to ceramicmagnet variations into the 70s.What most of these speakers have in common is a limited bandwidth that rolls off in the upper midrange around 4kHz to 5kHz, and a self-resonance around 75Hz, along with a non-linear response across the audible frequencies in between.
Alnico- (and more recently neodymium-) magnet speakers are among the most efficient, whereas some ceramic-magnet speakers can have lower efficiency and might sound half as loud as their more efficient counterparts. This means that ceramic-magnet speakers are a better choice for amps with ‘watts to burn’, unless
you want to use them deliberately to‘waste’ power and get distorted tones at lower sound-pressure levels.
For maximum headroom (for pedal platforms or ‘king of kleen’ sounds, for example), pairing very efficient loudspeakers with a decently high-powered amp is the answer. Consider the stellar combination of the 1970s 135-watt Fender Twin Reverb model when fitted out with a pair of super-efficient JBL D120F speakers. For distortion, lowerwattage or master volume amps (perhaps with power soaks/attenuators) are another opposite approach.
As anyone who has used a power soak, as well as ear plugs for that matter, will have noticed, the original sound and attenuated sound are noticeably unalike tonally. Why could this be, you ask? In short, this is due to the Fletcher-Munson loudness curves that characterise the human hearing frequency response at differing soundpressure levels. A quick internet search of the above hyphenated moniker will reveal a diagram that shows a range of wavy lines demonstrating how the frequency response of our hearing mechanism approaches being ‘flat’ only at relatively high sound-pressure levels; at lower levels there is a tendency to emphasise the midrange over the bass and treble frequencies. This is believed to be a historic evolutionary mechanism by which our ancestors needed to hear voices and sounds of predators first and foremost – at night, possibly from a distance, for survival. This is why passing partygoers’ voices in the night might wake you up from your slumber. When listening to music, the loudness control on your hi-fi sound system artificially boosts the bass and treble frequencies relative to the midrange to compensate for this discrepancy at lower volumes.
Further things to consider are the positioning of loudspeakers and cabinets relative to the floor space, whether to select closed-back or open-back (the latter has less bass; those frequencies cancel out somewhat from front-to-back), and whether or not series- or parallel-wired will affect the resulting tonal response. The diameter of the speaker also determines its frequency response and it is worth hearing a 10-, 12and 15-inch driver, preferably of the same type, to hear the relative differences. Broadly speaking, the 10s will have a more ‘vocal; midrange sound with less low and high frequencies, the 15s will likely have a relatively scooped midrange because of their extended bass and treble response, and 12-inch driver usually represents a good balance and compromise between the two extremes.
Finally, hearing loss. The tendency to hear increasingly fewer high frequencies, tinnitus and masking are all casualties of either age and/or the rock ’n’ roll lifestyle – though the health and safety considerations of present times have probably mitigated this to an extent (good luck cranking up your 4x12 cabinets anywhere nowadays!). Exposure time and sound pressure levels are the co-factors for hearing damage: the bottom line is to either play loudly and briefly, or play quietly for longer. Hearing protection is optional but recommended!
“For maximum headroom, pairing very efficient loudspeakers with a decently high‑powered amp is the answer”