Speaker Feedback Instruments by Lesley Flanigan

Lesley Flanigan Speaker Feedback Instruments
Lesley Flanigan performing with her speaker feedback instruments at La Sala. © Lesley Flanigan

A beautiful example of combining acoustic feedback and musical instruments are the speaker feedback instruments by Lesley Flanigan.  What makes the technology of these instruments exceptional, is their use of so-called contact microphones (simple piezo-ceramic elements) instead of a microphone designed for picking up air pressure waves. These microphones  can easily amplify the mechanical vibrations of objects such as the sound board of a piano, an apple box, or a coffee cooker, without picking up the sonic vibrations of the air surrounding these objects. Or, simply speaking, when a contact microphone is connected to a table, and you are hitting the table and singing at the same time, the contact microphone will only amplify your voice.

In Lesley’s instruments though, these piezo-ceramic contact microphones are placed above the loudspeaker cone, without touching it. Surprisingly, they are in this case used for picking up air pressure vibrations. And indeed, feedback happens with this set-up because the air pressure waves emitted by the loudspeaker are strong enough to be picked up by the piezo-ceramic element and send back to the loudspeaker.  Due to their materiality the frequency response of these piezo-ceramic microphones will filter the sound quite heavily, and it is possible to create a very variable feedback sounds in just changing the distance between microphone and loudspeaker slightly. She discovered this set-up when trying out an amplifier:

I had built a small amplifying circuit, and to test it, I grabbed a couple items that happened to be on my table: a raw speaker cone for the output and a piezo element (basically, a microphone) for the input. The speaker and piezo were touching each other, and a very complex, tonal noise of feedback occurred (Lesley Flanagan in an interview by Tyler Miller).

contact microphone piezo ceramic speaker feedback
A piezo-ceramic element (often called contact microphone) is placed above the loudspeaker cone. © Lesley Flanigan

Since 2007 she has developed several of these speaker feedback instruments, and a speaker synth, which contains of five small different loudspeakers. Lesley told me, that she changes the set ups depending on what she feel works best for the show she is doing (or how far she needs to travel!), but definitely she has her favorites and tend to prefer playing with four at a time.

What inspired her, was that “The sounds of feedback they generated were so “real”—it was electronic sound that I could see and touch.” (Interview by Tyler Miller). It is especially this tactile element which becomes important in playing her instruments and developing her sounds. As can be seen from the video of the speaker synth both contact microphones and the membranes of the loudspeakers are touched to modify the feedback sounds. Each feedback circuit can be turned on and off, and a potentiometer next to the switch can be used for changing the feedback gain:

loudspeaker cones contact microphones
Several speaker feedback instruments made from very different loudspeaker cones taken out of old devices. © Lesley Flanigan

Her instruments are made from old loudspeakers. She is taking them out of devices, because she is interested in not finding a “perfect” loudspeaker but in the specific voice every loudspeaker has. When she heard these speaker feedback instruments “singing”, it felt just very natural for her to add her voice to them. In her performance set-up she literally shares her microphone with them, moving it from her mouth, to the speaker feedback instrument she wants to amplify through the PA system.

For me, it is a special process to collect their raw sounds with a microphone, and amplify them on a large scale. I love the moment when what was once a crusty little noise becomes a booming, warm bass swell of dense tonality. The sound itself never changed, but when amplified, its barely audible details are magnified, so we have the opportunity to hear it differently. By amplifying feedback tones, I’m trying to dig deeper and more introspectively into their sound (Lesley Flanagan in an interview by Rena Minegishi).

In these short fragments of her performances, you can recognise well how the sound of a speaker feedback instrument is amplified as soon as the microphone is approaching it:

As Lesley told me, also this bigger amplification system becomes a part of her instrumental set-up:  “I use a PA for amplification, but often like moving back and forth between the large PA amplified sound and the ‘acoustic’ sound of the feedback instruments without any amplification.” During her performances, she develops different layers of feedback and voice, using a looping pedal for sampling sounds. Whereas they are carefully prepared and rehearsed, and she clearly knows her instruments very well, she is always also reacting on what happens at each specific moment: “I knew which speakers to work with and how to play each one to bring out elements of tonality, noise and rhythm I wanted to hear. The sampling and layering of their sounds were intentionally obvious, methodical and dense. But with all that said, I could have never predicted the exact sounds that would come out of the process. Many variables effect the feedback I work with, so no matter how much control I have planned, improvisation is always at the forefront” (Lesley Flanigan in an interview by Marc Weidenbaum).



Fifty years of loudspeakers and ping pong balls

Some objects seem particularly suitable to be used for preparing loudspeakers. The lightness and characteristic sound of ping pong balls might be a reason, why they have been favourable objects for this. Comparing several of these set-ups reveals that—fortunately!—using a similar technology can still result in completely different works.

Loudspeakers ping pong balls
Leser 1 by Manfred Mohr and Jochen Gerz. The loudspeakers and ping pong balls are covered by a large transparent plastic bag. Polyester tube, 19 loudspeakers,  printed transparent plastic bag, 19 moving ping pong balls, electric motor, 180 cm x 45 cm, 1967 Source: www.emohr.com/collab-exp/col_mohr-gerz.html © Manfred Mohr and Jochen Herz

As far as I know, the first work using ping pong balls in combination with loudspeakers is Leser 1 (1967) by Manfred Mohr, who created the audio sculpture, and Jochen Gerz, who wrote the text for this installation. This  tower contains 19 loudspeakers, each prepared with a single ping pong ball and was exhibited for the first time in 1968 in Paris. The audience can press a foot pedal to turn the installation on for a minute. Three different frequencies are then played through the loudspeakers and causing the ping pong balls to move away from the loudspeaker membranes and hit the plastic bag (see also the scheme at the end of this post). The ping pong balls are alternating between striking the plastic bag and the loudspeaker membrane and the combination of 19 ping pong balls making this movement produces a noisy sound. Together with the text printed on the big plastic bag and a random letter printed on each ping pong ball the whole installation seems to make an attempt to speak. The text itself seems also to be related to the movement of the ping pong balls: the big letters in the middle read: “Auf Flüchtlinge wird [ge]schossen”, which could be translated as “shoot the people fleeing”. Manfred Mohr explained me, that this text refers to the fact that at that time the East German police had the order to shoot the people fleeing to West Germany.

In Music for Pure Waves, Bass Drums and Acoustic Pendulums (1980) Alvin Lucier uses four bass drums and places them in front of four loudspeakers. A low sinus sweep is played through these loudspeakers and the membranes of the bass drums start to vibrate, according to their resonance to the frequency of the sinus wave. In front of each drum a ping pong ball is hanging from the ceiling, just touching the drum head. The vibrations of the skin push the ping pong ball away from the drum. Depending of the moment of hitting the drum, when the ball falls back, as well as the direction and amount of vibrations of the drum head, the ping pong ball will be pushed away next time with more or less force. Although the set-up seems to be four times the same, the results of the small differences in material of bass drum, loudspeaker and ping pong ball can be clearly perceived in the movement of the ping pong balls and the resulting sound. The shape of the ping pong balls reminds me of the head of a drum stick, and these drums seem mysteriously “played” by the ping pong balls.

Christian Skjødt uses 16 loudspeakers and an equal amount of ping pong balls in Inclinations (2016). Here again each loudspeaker with ping pong ball combination creates its own rhythm, but due to the ping pong balls moving in upwards direction they fall down much faster than in Lucier’s set-up. This causes a constantly changing, soft and noisy rumbling. Christian is not using any other material such as a plastic bag or drums. Since the frequencies played through the loudspeakers are too low for humans to be heard, all sound is produced by the collisions of ping pong balls and loudspeaker membranes. The minimal visual quality of this installation underlines the focus on these sonic events.

loudspeakers ping pong balls
The three different relationships between ping pong balls and loudspeakers, from left to right: In Leser 1 the ping pong ball hits the loudspeaker and the transparent plastic bag. In Music for Music for Pure Waves, Bass Drums and Acoustic Pendulums the loudspeaker just hits the drums. In Inclinations the ping pong ball is placed directly on the loudspeaker.

After I finished this post on loudspeakers and ping pong balls, Ricardo Arias brought the piece PingRoll (1997) by Manuel Rocha Iturbide to my attention:

And João Ricardo mentioned Kugel-Percussion (2006) by Peter Vogel to me:

loudspeaker ping pong ball
Kugel-Percussion by Peter Vogel, with one ping pong ball and one loudspeaker © Peter Vogel


Hemispherical loudspeakers for laptop orchestras


hemispherical loudspeaker
A hemispherical loudspeaker as currently used by the Princeton Laptop Orchestra. © Scott Smallwood, Lawrence McIntyre, Dan Trueman, and Perry Cook

With the rise of laptops in music in the 1990s, and more and more musicians using laptops on stage, it did not take long before the first laptop orchestra was founded. Nowadays there are many of them and there is even an International Association of Laptop Orchestras. They are often associated with universities and open not only for music majors, but for all students who want to make music with computers and delve deeper into making music with new technology.

Taking inspiration from the traditional orchestra, one of the aims is to make every laptop diffusing its sound similar to how acoustical instruments do this. To achieve this, every member of the orchestra gets their own loudspeaker and in this way their sound is diffused from one spot in space, similar to how a violin or a trumpet does this. It also makes it easier for the musician to distinguish their own sound from that of the others, and thus have a hierarchical relationship to your own sound in relation to that of others, similar to what is the case in traditional orchestra playing.

Dan Trueman and Perry Cook founded the first laptop orchestra in 2005, calling it the  Princeton Laptop Orchestra (or just PLOrk). To amplify the sound of each player through an individual loudspeaker they used hemispherical loudspeakers designed to diffuse sound from one point into all directions. The history of these hemispherical loudspeakers starts twenty years ago with Dan being unsatisfied with a guitar loudspeaker for his electric violin and looking a more appropriate loudspeaker set-up in the form of a spherical speaker in 1997.

spherical loudspeaker
The first spherical loudspeaker used by Dan Trueman to amplify his electric violin. © Dan Trueman

This was developed further into an instrument called  BoSSA (short for the Bowed Sensor Speaker Array). This instrument  “includes elements of both the violin’s physical performance interface and its spatial filtering audio diffusor, yet eliminates both the resonating body and the strings” as Dan and Perry described. Besides sensors to control the instrument and software to process the sound, this instrument contains a spherical loudspeaker for sound diffusion.

Bossa Dan Trueman
Dan Trueman plays the BoSSA, using a spherical loudspeaker to diffuse the sound. © Dan Trueman

By the time PLOrk was founded, these experiments had evolved in several kinds of hemispherical and spherical loudspeakers. Nowadays they are constructed in such a way that each member just needs two elements to perform in the laptop orchestra: his or her laptop and a hemispherical loudspeaker (with built-in audio interface and six channel amplifier).

PLOrk Princeton Laptop Orchestra
A typical rehearsal of the Princeton Laptop Orchestra: each student’s laptop is connected to a hemispherical loudspeaker, or to a “hemi” as the orchestra members calls them. This is a picture from 2006, and as you can see, the amplifiers were not integrated in the loudspeaker cabinets yet. © Dan Trueman

As Jeff Snyder, current co-director of PLOrk, explained to me why the hemispherical and not the spherical loudspeakers are used for the orchestra. After playing around with both hemispherical and spherical speakers, the hemispherical seemed the most practical, since they can just be placed on the floor, next to the player (and they cost half of the money of a spherical loudspeaker, of course). The acoustical difference between hemisphere and sphere was not very relevant for this kind of application. The loudspeakers nowadays use six loudspeakers but are connected to a mono signal, so each speaker diffuses the same audio signal. Also, to add some power to low frequencies, the “hemis” are placed on a subwoofer.

hemispherical loudspeaker on subwoofer
A “hemi” placed on a subwoofer. In between you see the audio interface attached to the bottom of the hemispherical loudspeaker. © Jeff Snyder

Dan Trueman and Perry Cook on founding the Princeton Laptop Orchestra:

A detailed construction guide has been written by Scott Smallwood, Lawrence McIntyre, Dan Trueman, and Perry Cook, in case you are interested in building one yourself. Other laptop orchestras use slightly different ones, as can be seen from the manual for building loudspeakers for SLOrk (the Stanford Laptop Orchestra). These are still based on IKEA salad bowls, as some of the earlier Princeton versions did as well.

hemispherical speaker
Mounting the loudspeakers in the hemispherical speaker construction. © Scott Smallwood, Lawrence McIntyre, Dan Trueman, and Perry Cook.

During the piece Twilight by Ge Wang—a former PLOrk member, and founder of SLOrk—the members of the Stanford Laptop Orchestra (SLOrk) control their laptops with sensors, and each of them is amplified by a typical SLOrk loudspeaker:

If you want to hear PLOrk live, your next chance is on May 3, 2017. The Princeton Laptop Orchestra (PLOrk), directed by Jeff Snyder and Jason Treuting, presents their spring concert, featuring guest artists HPrizm and Iarla O’Lionaird. Taplin Auditorium, Princeton University, Princeton, NJ.

Doppelbelichtung by Carola Bauckholt

Carola Bauckholt has written several pieces in which the imitation of bird sounds plays an important role. Examples are Lichtung (2011) for string quartet and Zugvögel (2011/2012) for five wind instruments. In her piece Doppelbelichtung (2016) for the first time these “photographic imitations”—as Carola calls them—are confronted with real recordings of singing birds. This piece is for violin and 12 loudspeakers, among them several “violin loudspeakers”: by placing tactile transducers on violins and hanging them in the concert hall, sounds are transmitted through the corpuses of violins.

A tactile transducer violin ceiling
A tactile transducer attached to a violin, hanging from the ceiling. © Carola Bauckholt

Carola brought both worlds of violins and birds together in this composition and both have to be transformed to be able to approach each other. To imitate the bird songs, it is necessary that the violinist listens very carefully to the birds and searches for appropriate playing techniques to be able to imitate the birds as good as possible. But also the birds have to move closer to the violin:  their songs are slowed down, resulting in lower and slower songs. Both bird and violin sounds are notated very precisely in the score:

score Doppelbelichtung Carola Bauckholt
A fragment of the score of Doppelbelichtung by Carola Bauckholt. All bird names as well as the speed change of the recording are notated. © Carola Bauckholt

The twelve audio tracks of transformed bird recordings are played through twelve loudspeakers. Two of these loudspeakers are normal PA loudspeakers. Four of them are small loudspeakers placed in the audience, another small one is used as a monitor for the violinist. Most remarkable are the five “violin loudspeakers”, as mentioned above these violins have tactile transducers attached to them and the audio is sounding through the violin.

set-up violin loudspeakers Carola Bauckholt Doppelbelichtung
An overview of the set-up for Doppelbelichtung with the five violin loudspeakers (violin loudspeaker 5 is playing Specht sounds, which is a woodpecker). © Michael Acker, SWR Experimentalstudio
Violin loudspeakers Carola Bauckholt
The set-up in the concert hall, with the hanging violins, the PA loudspeakers on stage behind the violinist Karin Hellqvist and the small loudspeakers (the metallic objects next to Karin Hellqvist belong to another piece). © Carola Bauckholt

Double exposure—the english translation of the title Doppelbelichtung—is the technique of taking two pictures on one frame of film. In this piece every sound seems to be a sonic double exposure of a violin and a bird: the violin is imitating the bird sounds, which are in turn modified to resemble the violin. By transmitting these sounds through tactile transducers attached to violin corpuses hanging in the air every bird recording acquires spectral characteristics of a violin. The piece is a thoughtful conversation between these new creatures.

Doppelbelichtung has been performed by Karin Hellqvist and the SWR Experimental Studio: