Right now, I miss my electronic drum kit. People ask me why I would choose an electronic one over a sparkly array of loud toms and cymbals. They are certainly fun to clang about on. The standard answer is about space. The student room where I live is too small to house my pride and joy. In fact, for the last eighteen months, I have had no opportunity to grasp those sticks, place my headphones on, crank the volume up, and bolster my brain’s coordination function. But that’s another story. In the meantime, tapping on the desk while listening to my iPod will have to suffice. I felt the void during orientation week when the level of the anticipation, about the coming year, was matched by the intensity of the music in the streets around my accommodation. Given a decent stereo, the distance that the sound of the bass and bass drum travels, on a balmy summer’s evening, is quite sizeable. Even with the windows closed.
And it got me wondering…
Why is it always the doof, doof, doof of the neighbour’s bass drum that we hear at 2am?
Well, let’s begin with the basics of sound. Sound is energy. It’s a particularly wonderful form of energy (just like chocolate). The drum skin vibrates, when it is struck by the beater, moving molecules of air back and forth, creating an audible sound wave. The harder the strike force, the greater the intensity. This is what gives us the volume measured in decibels (dB).
Just like a slinky, the air is first compressed, then extended back to its start point. The length of time it takes to complete one cycle, of compression, extension and back to compression is its wavelength.
Frequency is the number of cycles the wave completes in one second and is measured by the Standard International (SI) unit called Hertz (Hz). Slower waves take longer to complete that cycle so they’re called low frequency waves. Those are the ones you can feel in your chest at the nightclub and in the bass drum to form our low doof, doof, doof. Rapid vibrations create a high pitch – you can hear the Brian Wilson’s vocal chords vibrating very rapidly in the song!
Now back to the neighbour’s missing high frequency sounds. There are two parts to this. Firstly, in higher frequencies, the molecules are moving faster so more energy is lost to friction, reducing the intensity, and the sound simply fades away. Secondly, higher frequencies are better reflected from obstacles such as walls or car doors whereas lower frequencies can pass through more easily. Smooth, densely packed walls will reflect more easily but those with pores, hairs, or other surface-area-enhancing opportunities to lose energy, create great sound absorbers. This, and the small room size, goes a long way towards explaining why some people insist they sound better when they sing in the shower – particularly sopranos.
Now I have another reason for having an electronic drum kit. I can bang away quite happily knowing that no-one else can hear me. Even at 2am.
For more on drumming see this TED talk by Clayton Cameron “How I fell in Love with the drums”.