Meeting Expectations

In the early days of concert sound, there wasn’t really an overriding need for a full and deep bottom end. To illustrate, let’s take a look at the two instruments most commonly found in the subs in traditional guitar-based rock music: kick drum and bass guitar.

If you stand next to an unamplified drum kit while it’s being played, you might notice that the kick drum isn’t actually that bass heavy. It moves a certain amount of air, and has the most bass of all the drums in the kit, but it doesn’t have that sound that “hits you in chest” like it does when standing in front of the PA at a gig. That sound is actually an artificial construction whereby the drum is close-miked with microphones that are tuned to bring out the bass frequencies – often in a disproportionate way.

The standard electric bass guitar has four strings that are tuned an octave down from the bottom four strings of the guitar. These oscillate at about 41, 55, 73 and 98 Hz, with the specific sound produced depending largely on the bass amp. (Very few bass amps are able to generate 41 Hz; in fact, most struggle to go below 80 Hz with sufficient level.)

Again we use techniques such as direct injection (DI) or close miking the bass amp cabinet to help bring out those lower frequencies.

The point I’m making is that routinely, we artificially enhance the bottom end of key instruments to create the sound we’ve come to desire and expect. This sound is the product of an evolutionary process pushed forward by a combination of production techniques, advances in amplifier and loudspeaker technology, and the expectations of the musicians and their audiences.

But why do we prefer a full and deep bass sound in our music? According to recent research by Laurel Trainor at the McMaster Institute for Music and The Mind in Ontario, Canada, our ears are much better at discerning subtle timing differences in low frequencies than high frequencies. The study suggests that this effect arises within the physiological mechanism of the ear and not in the perceptual center of the brain.

This tells us that we rely much more on the low-frequency content of music to help us lock into the rhythm, and further, it shows how important it is for live sound engineers to get the bottom end right, particularly for dance music.

There’s one more important factor that contributes to our enjoyment of low frequencies: they’re felt as much as heard. The sheer amount of air movement at low frequencies resonates in our chests and adds a visceral element to our enjoyment of the sound.

Much like that early Sensurround system, it helps put us “in” the sound and adds to our enjoyment of the music.