Acoustic feedback, also known as the Larsen effect, is a phenomenon that was first discovered by Danish physicist Søren Absalon Larsen (1871-1957). Acoustic feedback occurs when a “resonant frequency” is captured by a microphone, it is then emitted from an amplified loudspeaker, and then picked up and projected by the same microphone and loudspeaker, creating a cycle of continuous amplification that often results in a high-pitched ringing. Resonant frequencies are those that are most easily excited within an acoustic environment, and are influenced by the dimensions, material, and electrical components within the feedback loop.
Acoustic feedback is often the product of a mistake – when a microphone is too loud, or it is inadvertently pointed towards, or placed too close to, a loudspeaker – so it looms over any musical setting that involves high volumes and the miking of acoustic instruments. Despite the risks, musicians have nonetheless been fascinated with this “fundamental sound of electronic music.”1 Hugh Davies (1943-2005) was a British composer and musical instrument inventor who was inspired by such mistakes while he was rehearsing with Stockhausen for a performance of Mikrophonie I.2 Davies channeled these experiences into his 1968 work, Quintet (Alstrabal...). I was unable to procure a digital copy of this score and there are no physical copies in Canada, so I will be relying on secondary sources for this examination, including van Eck’s analysis and articles by Hugh Davies scholar, Dr. James Mooney.
Figure 3‑4: Stage plot for Quintet.3
According to Mooney, Quintet is written for “5 performers, 5 microphones, sine/square-wave generator, 4-channel switching unit, potentiometers, amplifiers, and 6 loudspeakers.”4 The premise of the piece centres around microphonists producing feedback that is influenced by a mixing board. In Quintet, as in Mikrophonie I, performers move their microphones according to instructions in the score. Unlike the highly detailed score of Mikrophonie I, Davies directs performers in a general fashion, such as “move the microphone slowly in different directions, producing increasingly wider pitch intervals.”5 These generalized instructions are needed to accommodate acoustic feedback pitches that will differ with every performance, depending on the room, audience, and more. While any through-composed piece involving human players will vary between performances, the complete pitch indeterminacy of Davies’ Quintet places it in the category of “process music.” Process music is an approach to composition whereby the composer dictates the actions that the musician must carry out, as opposed to the sounds that must be produced. This approach is especially suited to works that explore acoustic feedback and other indeterminate musical processes, such as Cartridge Music (1960) by John Cage (1912-1992), Pendulum Music (1968) by Steve Reich (b.1936), Bird and Person Dyning (1975) by Alvin Lucier (1931-2021), and Spiral (1968) by Stockhausen.
Like Mikrophonie I, the microphonic instrumentarium of Quintet also includes a mixing console. Quintet’s stage plot (fig. 3-4) depicts four microphonists surrounding the performance space with a fifth in the audience itself. This fifth performer “also operates other electronic equipment so as to alter the characteristics of the feedback sounds, in a ‘solo’ that happens around four-and-a-half minutes into the piece.”6 Part of this “other electronic equipment,” what I refer to as the mixing board, is a sine/square wave generator that is used in the following way:
If the sound generated by an electronic sine/square wave generator is projected via the loudspeaker at the same time as it is producing acoustic feedback, then the generator sounds and the feedback sounds will interact with each other. The effect is similar in principle to ring-modulation – i.e. it is as though the feedback sounds are being ring-modulated with the generator sounds – except that the modulation occurs without the use of a ring modulator circuit.7
In addition to the wave generator, the mixing console of Quintet is comprised of two loudspeakers, a 4-channel switching unit, as well as the necessary potentiometers (volume faders) and amplifiers. Continuing her focus on the microphone, van Eck omits this piece’s mixing console in her discussion. Considering how easily the sonic characteristics of Quintet could be interpreted as deriving only from the visible interactions of the microphonists, such an oversight hampers a full understanding of the work. While the mixing board’s instrumental nature is not made explicit through easily identifiable performance gestures, it nevertheless plays a vital role in the piece. Without any acoustic sound sources, Quintet achieves a more convincing version of Stockhausen’s Mikrophonie concept: the primary sounds are those resulting of the microphone and the loudspeaker interacting, rather than the microphone amplifying and shaping the sound of another instrument. Regardless of the virtuosity of the microphone movements in Mikrophonie I, they could be perceived as “only” supporting the sound of the tam-tam. Moreover, without any traditional instrument in Quintet, there is no question as to the instrumental nature of the microphone-loudspeaker relationship.
In the latter years of the 1960s, when Davies composed this seminal avant-garde work, popular artists were also exploring the expressive capabilities of feedback. As described earlier, acoustic feedback is typically the product of a system involving a microphone and loudspeaker, but it can also occur when the microphone is replaced with another sound capturing medium, such as the “pickup” on an electric guitar. The British pop group The Beatles may have been the first well-known band to use feedback between a pickup and loudspeaker in their recording I Feel Fine, but it was electric guitar virtuoso James Marshall Hendrix, better known as Jimi Hendrix (1942-1970), who brought feedback into mainstream rock‘n’roll performance practice.