Feedback, acoustics, improvisation,
industrial feedback, acoustic feedback
This paper deals with my fascination
for acoustic feedback. From an artistic point of view, I will
describe several types of feedback, and give descriptions, drawings
and images of works we made based upon these different types,
as well as links to videos and mp3s. Besides that, I want to express
my doubts, theories, and questions, as well as our motives and
enthusiasm for using this medium.
An introduction and
First let me introduce myself: Mario
van Horrik from the Netherlands. Together with my wife, Petra
Dubach, I work with the media movement and sound, mostly. Through
the years, we have presented sound/movement installations, performances
and concerts in museums, galleries, factory halls, mine buildings,
open air, concert halls, an abandoned synagogue, and other odd
places around the world.
Petra comes from a dance background,
I from the music. We are both in our early fifties and we feel
we've come a long way to where we are now. To be honest,
we are not sure where exactly this is and our work doesn't fit
the usual artistic disciplines or predicates any more. That happens
to people who get involved with feedback, as you will find out.
For me, everything started when I was a little boy, from a traditional
family in the southern part of the Netherlands. I was the youngest
of 11 children, and my 5 brothers and I slept in the attic of
the house. Since I was the youngest, I had to go to bed first,
and I always tried to stay awake until my older brothers would
come to bed. In so trying, I used to open the small attic window,
which I could reach from the end of the bed. If I stretched myself
a bit, I could just look outside, with the cold iron of the window
frame against my cheek. About a mile away from our house was the
railroad track, and the big mystery for me was that I sometimes
could hear a train, but couldn't see it; and sometimes I
could see the train, but not hear it.
When I was a bit older, I watched one of my brothers, a carpenter,
saw a piece of wood. I asked him if I could help, so he let me
saw a piece of wood. After a few minutes, I was exhausted, and
complained about it, when my brother told me: "You have to
let the saw do the work."
In the late 70's, when I was (still) a good looking, young guitar
player, who had given up the dream that some day I would be as
famous and as great a genius as Jimi Hendrix, I saw in a British
magazine a picture of the British composer and musician Steve
Beresford. In his hand, he held a guitar with clothespins clipped
on the strings. I was intrigued, and tried the pins on my guitar.
It sounded shitty, but soon I found myself playing on 3-stringed
guitars, prepared with sticks, beads, etc. Years later I met Steve,
and told him about the picture, and how it had inspired me. He
laughed and told me that the pins had been put on the strings
to make the picture look more interesting.
Types of feedback.
People may use feedback occasionally,
as a small part in a bigger whole, like guitar feedback in pop
music. That's not what this is about. We are using feedback as
a conceptual basis for our work. We are searching for the ‘bone'
of sound. We are not scientists, so our characterization of types
of feedback maybe not be accurate or complete; however it is based
on our practical experience. The types of feedback that I am acquainted
• Direct acoustic feedback:
direct contact between speaker and sound source (for instance
when you place your electric guitar against the speaker box).
• Indirect acoustic feedback:
the process that takes place through the air (microphone in front
• Industrial feedback: the
system of measuring and controlling, mostly performed by sensors,
and electric circuits.
• Improvisation: play acting
(controlling) and reacting (measuring) between 2 or more people
• Combinations of the above.
The simplest technique for creating
acoustic feedback is to put a mike in front of a speaker, and
turn up the volume of the amp to the point that the feedback will
build itself up. If you leave it like this, eventually your ears
and gear will be ruined. The frequency ‘picked' by the equipment
is determined by the quality and acoustic properties of the amp,
speaker, microphone, and the space. I don't know if a formula
exists that will make it possible to make calculations, but to
me it seems to be impossible.
Anyhow, the first conceptual acoustic
feedback-piece I know of is Pendulum Music (1968) by Steve Reich,
who used 3 microphones/amp/speaker-sets. The mikes hung from the
ceiling on different lengths of cable, and were swung. The tempo
varied because of the differences in cable-length, and passing
the speaker, a short feedback sound came from the speaker. The
piece ended when the sound was continuous, because the swinging
had died out. Other artists use feedback as a trigger: they have
a microphone or instrument making feedback, and load the sound
into an electric circuit, that itself may also be a feedback system.
They use filters and effects to shape the feedback sound into
material they can use further with computers, samplers, etc. They
are what I call the ‘in-betweens'; the method allows them
to keep control, and express their sonic ideas in structures under
their supervision; whereas Reich's concept is radical: the saw
does the work, so to speak.
Description of some
pieces, according to types of feedback:
(Direct feedback). Concert piece.
In 1988, we conceived the
piece Het Vogelbekkenstuk. The piece is a statement about
movement and sound.
There are 2 identical instruments;
each consisting of 2 hinged wooden beams, with a string
and spring stretched between the 2 ends of the beams,
(Figure 1). The strings have a piezo-pick-up, and the
amp/speaker stands on the lying beam. With the volume
turned up loud enough, the system will produce direct
acoustic feedback (the acoustic feedback takes place because
there is a direct contact between the instrument and the
Each player holds one instrument, and tries to stand
as still as possible. We didn't succeed in remaining still,
but this is something that can't be seen, it is only heard.
We look static, but whalelike, gliding sounds come from
Sometimes, for a short while the sounds are stable and
fixed, but then something changes again, interferes, etc.
Originally, I made the instruments so that the strings
would be plucked, but during the soundcheck of a concert,
on a hollow stage, the instruments started to give us
feedback. It took quite some time to get rid of it.....So
you see, strange coincidences can happen, and in this
case (as is in most) my brother was right: we did let
the saw do the work.
Figure 1 (above):
Het Vogelbekkenstuk. Photo:Wim Janssen. Performed
at Stedelijk Museum, Amsterdam.
Below: Sound sample of Het Vogelbekkenstuk
A completely different type of feedback,
maybe unfamiliar to most artists, (although it is a part of everyday
life) is industrial feedback. I was first told about it in 1991by
professor Zweitse Houkes from the Technical University of Enschede
in the Netherlands. He explained to me that industrial feedback
is a system of measuring and steering (or controlling) to create
certain results. For instance your central heating system: if
you want your living room to be 20 degrees Celsius (68F), you
set your control to20C. If it is colder, the heater will start
heating until it is 21C (69.8F). Then it stops, and starts again
when it is 18C (64.4F). Temperature is measured, heater switched
on or off: simple.
In industry, feedback is used to
have very precise control over processes: to have pieces of wood
sawn in the exact format and shape needed; to have parts of trains
interlock precisely, and to produce as many clothespins a day
as possible. So, I wondered if I could make a feedback system
that would be useless (art), and especially unpredictable in what
it produced and when. I didn't want it to be precise and exact,
but to find the widest limits possible.
I was lucky, and got an invitation
to do a show in Art in General in New York City, as well as a
residency at Harvestwork's Studio Pass in 1994. Besides that,
several Dutch institutions were so kind to spend a great amount
of money on my new work to be shown at Art in General: DioN.Y.sus'
Scales. The basis of this installation was a performance called
‘the Boxing-ring' that Petra and Iperformed several times.
|The basic construction is 4 strings tensed
vertically from floor to ceiling, with piezo pick-ups mounted
on the strings, and a metal ring at hip height. Ropes stretched
horizontally between the rings make the instrument look like
a boxing-ring. On cross-strings a steel and an aluminum stave
were attached to it. I would play the instrument from the
outside with sticks, a bow, my voice and an electric razor,
while Petra performed inside the ring; pulling the ropes,
hitting them, leaning against them, etc. and, in this way,
tuning the sounds and adding sounds. So the Boxing ring was
automated. Four motors, mounted on the floor, pulling and
releasing ropes extended the basic form (see video). We employed
weighing scales (the type with a spring and hook, used to
weigh sacks of potatoes) with a sliding potentiometer (like
the volume controls from a mixing board) attached to it, to
measure the pulling force and translate it into voltage. The
piezo-pickups were used as vibration sensors as well. Henk
Goossens and Erik van de Poel, two enthusiastic Electrical
Engineering students of Eindhoven Technical University designed
and built me the fantastic piece of equipment that allowed
me to input all the pulling and vibration measurements. These
were used to steer the output volumes to the 4 amp/speaker
combinations. Volumes increased or decreased according to
a more or less pulling force or vibration on a string, with
a possibility to shut down the volume-output from 4 seconds
to 4 minutes, using peak-level measurements from other sources.
The piezo-pickups also delivered variable voltage for the
4 motors on the floor, with a protection that changed poles
when the pulling force was reaching a limit; and to change
poles as well through a peak-level measurement on one of the
strings, for example. And it had the same possibilities for
several smaller motors, such as a motor driven bow; a ‘rattler,'
a propeller, etc, to play the instrument. This electronic
device gave me the opportunity to connect whatever with whatever;
and the result was amazing.
There was a seemingly uncontrolled
and uncontrollable moving, silent, screaming, resting, breathing,
grim, grinding, growling beast; completely unpredictable, because
too many things happened at once. Most fascinating for me was
the discrepancy between the electronics and the material: sometimes
a string was pulled out of reach of the motor that was supposed
to play it; sudden movements made metals swing out of reach of
its player-motor, etc. The whole system pulled its own leg.
And so you see...hearing a train
and not seeing it (or the other way around) is peanuts compared
to the things you may cause yourself once you're an adult.
Another type of feedback we have
come across is similar to the industrial feedback, but is performed
by people. In that sense, every piece of improvisation is a performance
of this type of feedback; that is, if it is performed by at least
2 persons simultaneously. The purpose is, of course, to make music
together; and because you can't tell what your music partner will
do, you have to be very alert. Sometimes you 'work together',
and sometimes you try to get your partner to 'follow' or change
what he or she is doing. So you might call it mental, aural or
physical feedback. I conceived the piece Flexitar in 1988, first
as a solo piece. The setup is like this:
A long string is woven through the
3 strings of a guitar and it ends in a piece of elastic cord that
is attached to a fixed object, like a wall. At the point where
the long string (minimum length 3 meters) is connected to the
cord, a piezo pickup is clipped on the string with a clothespin
(!). When playing the guitar strings, something weird happens:
somehow the transversal vibrations of the guitar strings are being
transformed into longitudinal vibrations in the long string. This
means, that you don't need much tension on the long string to
make it sound.
By using the elasticity of the cord,
I have some freedom to move a little bit (maybe one meter, depending
on the length of the elastic cord), and in that way I can 'tune'
the long string. Sometimes, when playing one guitar string, up
to five layers of sound frequencies occur from the long string,
ranging from very low to very high. When 'tuning', this changes:
the low frequencies have a tendency to change slowly, sometimes
they disappear; sometimes they slowly glide into another higher
or lower, more or less for some time 'fixed' pitch.
The highest frequencies change very
fast, already when I shift my weight from one leg to the other.
|Figure 2 (above): Flexitar.
Drawing by Mario van Horrik.
Below: Sound Sample of Flexitar.
When we play the piece together, the construction is like this:
guitar-long string-elastic cord- long string- guitar. (Figure
2). Then, the process becomes more complex of course. Partly,
in the space the sounds of the 2 long strings interfere, merge;
and because neither of us can stand completely still while playing,
the sounds change all the time. The aim is to make a sound piece
that is interesting in its development, with climaxes, changes,
The problem is that one of us may
not understand what the other's intentions are. So, when one of
us likes to continue what we were doing, the other may wish to
introduce some change. When this is a big change, then it's obvious,
and there's not much the other one can do to prevent it. With
small changes, some kind of struggle between us is often the result.
In fact, we place ourselves in a difficult situation, because
the sounds are not really pitched, and they also change rapidly.
And if Ishift my weight to my other leg, it not only changes my
sounds, but also those of Petra; and she may not like that, and
may try to recreate what happened before, etc.
To be quite honest, we are lucky
to have such a stable relationship, because sometimes our domestic
disagreements are the major subject of a performance of Flexitar.
You, the listener don't have a clue, of course, and thank God.....But
the thing is, that if you place yourself in an ‘uncertain'
circumstance, you need another way of communicating (feedback)
and the more often you do this, the more sensitive you think you
are for it.
But that's the nice thing about
feedback, isn't it? Nothing is certain.
Interference. (Direct feedback).
Installation and performance.
This is a sound installation conceived
in 2001, using direct feedback. But the feedback is being
disturbed by itself. From the ceiling 3 copperplates,
dimensions 1x2 meters and 3mm
thick, hang, each on two strings, one with a piezo-pickup
(Figure 3). Against each plate
stands a Fender Sidekick 30 speaker/amp. The volume is
turned up to the point that the acoustic feedback occurs.
The pickup is positioned so that a low-pitched, sonorous
sound comes from the speaker. The sound builds up, until
the plates start ‘shaking'; causing them to move
away from the speaker, fall back, etc. In this way, higher
pitches are added to the drones. Elements like draft,
and movements of people influence the sounds as well.
Petra performed a piece several times, in which she gradually
increased her tempo while walking around the plates. It
ended with her sudden stop, and the plates swinging, hitting
the amps, etc, until they gradually came to rest, and
the feedback could build up again. In fact, it's quite
paradoxical: the feedback is disturbed by movement (wind).
Haven't I noticed
this before sometime?
Figure 3: Interference. Photos by Petra Dubach. At Mine
Building, Waterschei Belgium.
The Chaotic Drumming Machine. (Industrial feedback).
Concert piece and installation.
Very recently, when I was working
with the steering machine that was built for DioN.Y.sus' Scales,
I had an amplified string played by a little motor with a rope
at the axel, like a propeller. The machine was set so that the
motor got just enough voltage to make it turn. If it would hit
the string, the vibrations of the string would increase the voltage
fed to the motor. So, I expected the voltage to build up to the
max, like in a normal feedback, and in no time the motor to be
hitting the string full speed. First it did, but when I limited
the maximum voltage and decreased the gain for the motor a bit,
something strange happened: the motor ran at a certain speed,
for some time, accelerated, slowed down, stayed stable for a short
while, slowed down, etc.
Figures 4 and 5: Chaotic Drumming Machine. Drawings by Mario
It had become a random voltage motor (Scheme: Figures 4 and 5).
I have no explanation for it; maybe one of you scientific wizards
can explain it? Anyhow, later I used this circuit like this: five
strings of different length (between 15 and 25 centimeters), material
(such as phosphor bronze, piano wire, copper) and thickness, are
clamped in between two metal bars. The bars have one pickup. The
propeller motor (this time with a double elastic cord as a propeller)
hits the ends of the strings. The motor is mounted on a table
microphone stand. It is an amazing drumming machine: it has some
kind of chaotic basic beat that alters the tempo all the time.
Besides that, the strings get hit at fast tempo, but most of the
time ‘dance' away from the motor's reach; plus the elastic
cord makes strange, irregular movements while playing the strings.
It sounds very, very irregular and virtuoso, yet with some ‘steadiness'
in it. I'm planning to use it as an installation, but also in
concerts, changing the position of the motor. Let the (electric)
saw do the work......
Figure 6 and 7: Donar's Chariot. Photo by Mario van
Horrik. At Islip Art Museum, Islip, Long Island.
(Combined direct acoustic feedback and industrial feedback).
This sound installation was conceived in 1991. In a space,
2 steel cables are horizontally stretched between 2 walls.
A stripped children's carriage is resting on the steel cables.
Attached to its frame is a long string, ending in a long elastic
cord, that is attached to the wall. A piezo pickup is put
on the long string, near the place where it meets the elastic
cord. An amp/speaker combination hangs under the carriage,
as a counterweight (Figure 6 and 7). The speaker voltage is
fed into a voltage-amplifier that feeds a permanent magnet
motor that is mounted on the carriage. The motor pulls a rope
stretched between the two walls. What happens is this: the
volume of the amp is set, so that the installation produces
direct acoustic feedback. And because the speaker is 'fed',
the motor will pull the rope, and the
carriage will drive over the steel cables. Because it moves,
the tension on the string/elastic cord construction changes,
and the feedback sounds change pitch, so it builds up again,
and so on. Sometimes the produced sound is so loud, that the
system pulls itself through these 'dead points.' When the
carriage reaches a point near to one of the walls, a switch
changes the poles of the motor, so it will drive backwards,
Slow Motion (Indirect feedback). Performance
Conceived in 2006. For us
this is a wondrous piece, because the indirect feedback
sounds and the process of controlling them are combined
in the same system, in this case: instrument. The basic
setup is an acoustic guitar with a guitar pickup on a
stand. At some distance, an amp/speaker combination is
placed on the floor. The guitar may have 3-5 strings.
A stick of wood or metal is woven through the strings.
The result is a combination of the qualities of the space,
the position in the space of the guitar and the amp/speaker
combination, the distance and position of amp and guitar,
the tuning of the guitar strings, and the position of
So you can imagine that there is no such thing as an ‘ideal'
setup, but there will always be some kind of result, and decisions
will be made, eventually....... When the volume is turned up loud
enough, one of the guitar strings will start to resonate; the
stick resonates with it, and will cause the other strings to vibrate
as well. In the same time, this will prevent the system to run
wild, because it would take too much ‘energy.' This means
that sometimes the system will build itself up, and die out, builds
up, etc. It produces cycles that may last several seconds, and
they are quite complex and unstable. Sometimes, the stick will
‘walk' a bit, so the cycles become part of a longer cycle.
Also, it happens that the system finds a balance, and the sound
seems to be stable, and doesn't change. But then (and this happens
in all circumstances), as soon as I change my physical position
in the space, these sounds change as well. It may be, that one
layer of the sound will be more emphasized then before; it may
be that cycles become longer or shorter; it may be that the sound
becomes louder or softer, or that silences during cycles become
longer or shorter; it may be that unstable cycles change into
stable sounds; it may be that the sound color changes. Mostly
we work with a setup of 2 string instruments, each with its own
amp/speaker. This complicates the result enormously, because the
sounds of both systems interfere with one another, and cause even
more unpredictable changes and processes. Also, in our experience,
this seems to increase the influence of a person slowly moving
in the space upon the resulting sound. The body in the space 'disturbs'
the complex of standing waves; small movements can cause remarkable
differences. In addition, we have experienced that the system
needs some time to 'react' to these movements and so Petra usually
moves around with very slow movements; that also explains the
title of the piece.
When we present the work as an installation,
the public will cause some of the changes in the sound when moving
through the space.
Many artists, who use acoustic feedback
as a concept for their work, describe the influence of movement
and space on its functioning. Draft, wind, doors and windows opening
or closing, people passing by, the positioning of people, objects
in the space, changes in their position, materials of the space
and the architectural forms and dimensions of the space, the positioning
of the speakers, etc,etc. You might call these pieces "Gesamtkunstwerke."
The complexity is enormous, because of all the influences mentioned
above. It may sound foolish and naive, but sometimes I think that
a feedback piece is the expression of theories like quantum physics,
or (how appropriate) the string theory; of which I understand
nothing of course, but still.......
(don't laugh; I'm only an artist
who was already fooled by Steve Beresford and his clothespins).
What I'm really trying to say here, is that the phenomenon is
so fascinating and complex, that the ‘normal' musical ‘rules‘,
or any other rule is not applicable. The best way to deal with
acoustic feedback is to expect nothing; gradually you may become
like me (or some Zen-figure) who spends more time listening to
the wonders of a system that changes all by itself and all the
time in a very subtle way, than may be good for him. You turn
into a loner, endlessly turning his head (like a slow-motion head
banger) to hear the most minimal differences.
Now you might think that us, feedbackfreaks
are weirdos who hear things nobody else can hear; maybe we are
weirdos, but everybody can hear the differences that occur. Maybe
it needs some training and getting used to listening to it, but
eventually you'll see (no:hear).
Yes, feedback is THE drug. And so,
it's not only a Gesamtkunstwerk, but it also becomes a lifestyle.
Because the feedback feeds back
on the way I think and act. Take for instance my attitude: a ‘normal'
musician or composer likes to be in control of what he or she
plays or composes. I used to be like that. But gradually it seems
to become more appropriate and interesting to find out ‘what
the materials and systems themselves have to say.' This means
that my goals have instead become questions; control has become
To take it even a bit further: it
seems like I'm no longer ‘mastering' the process of experimentation;
there is a feedback from the results back to me; they seem to
give me new directions that I can follow up.
A few months ago, I was preparing
for a performance of the Slow Motion piece. I had spent several
hours in our studio working with a setup of a guitar and a laud
(Portuguese lute-alike), tuning the instruments, positioning the
amp/speakers, listening, walking around slowly, smoking one cigarette
after another, with the instruments feedbacking all the time.
Then I decided to go to the kitchen to make tea, and when I reached
the door to step out of the studio, it became quiet....... I was
amazed, and slowly turned around. The sound built up again.....
There are a few possible explanations
for what happened. Although very, very unlikely, it could be possible
that the instruments were silently laughing at me: "This
old fool thinks that after 30 years he knows something!! Let's
teach him a lesson." Of course, I never believed in this
ridiculous theory. The following explanation of course is far
more appropriate: when you work together, you also develop a relationship.
The guitar and laud were of course sad that I left, and they were
afraid that I would never come back. It was a misunderstanding,
we talked it over, and we agreed that it would never happen again.