Party Science, Part 1: The Beats

Who doesn’t like to party, am I right? Going to your favorite concerts, dancing at clubs, or just chilling with friends, partying helps us all to relieve the stresses of daily life and maybe make a few lasting memories. Living in the time we do, we have the technology to throw some epic shindigs, and not to get preachy, but from the flashing lights to the music beats, a lot of what allows us to party in the way we do is realized through science. I want to take the next couple posts or so to talk about some of the basic aspects of party science. Today we’ll cover the beats.

What is sound anyway? In its basic form, sound is the perception of longitudinal waves propagating in the air around us. Take the drum for instance. A stereotypical drum consists of some sort of membrane adjacent to an echo chamber. When struck, the membrane implodes at the point of compression, but nearby surface immediately works to restore equilibrium by pulling up on the impact point while the impact point pulls the surrounding membrane down [1]. The result is a wave propagating across the membrane. What does this mean for the air around the drum membrane? when the membrane implodes, air under the membrane is put into pressure and triggers movement away from the drum surface, only to feel the opposite reaction when the membrane at that point fluctuates outward.

Fig. 1: Production of longitudinal waves in a drum (University of Leicester)

This air movement creates a series of propagating low- and high-pressure zones comprising the longitudinal sound waves that have communicated human culture for thousands of years. On string instruments, the concept is the same. When plucked, the string oscillates and sends those vibrations to the instrument belly, causing air fluctuations by the face of the string instrument, say, a guitar, to produce music that has colored many cultures with Spanish influence [2]. However, the way this effect is experienced differs with modern music like dubstep, electric, house or other computer-altered music types that don’t come from physical musical instruments per se. With this sort of music, the component properties of previously recorded sounds are altered with the help of computer software. For example, a gradual increase in sound frequency and tempo is the sensation often used to foreshadow a dubstep drop. How do you send these synthetic beats out to awaiting ears? The answer is with a speaker, what some would consider a crucial part of any party. The basic speaker consists of a membrane or cone attached to an electromagnetic coil (solenoid) next to a permanent magnet. When current is sent through the solenoid, a magnetic field is produce down the length of the coil oriented towards or away from the electromagnet at a given moment if the field is envisioned as a vector pointing down the coil center. As the current fluctuates, the membrane is moved towards and away from the magnet, creating sound waves. When worked in reverse, with sound waves generating current, the device is called a microphone. The single waveform current signal generated can then be broken down using Fourier analysis into component frequencies with corresponding amplitudes (aka that bar diagram widget that moves when your music plays). To generate music, the speaker current is controlled by programs that mathematically synthesize waveforms from music files and divvy up the responsibilities of producing a net sound effect between available speakers. In the end, if executed properly with a location that offers the right amount of acoustic bounce back, say in a closed room among friends or in the middle of Miami skyscrapers like in the video of Hardwell below, you’ve got the basis of a good time.

When you watch this video, think about how the sounds are being synthesized. Is wave frequency/amplitude being altered? Are the sounds natural or computer generated? Let me know your thoughts in the comments (and don’t feel obligated to watch the entire video, it’s long).