112 loud-speaking telephone receivers and other early sound reinforcement systems by Ralf Ehlert

early sound reinforcement system
An early example of a sound reinforcement system: 112 loud-speaking telephone horns in New York (picture source)

The picture above was made in 1919 during the Victory Liberty Loan and the lamp-like objects hanging above the crowd are so-called loud-speaking telephone receivers. The crowd had “the unusual sensation of having spoken messages come to them out of the air” (source: Electrical Review, May 31, 1919). These 112 loud-speaking telephone receivers with large horns—in other words loudspeakers—were amplifying the speeches and making them audible for apparently a crowd of 10.000 people (my experience with numbers in these kinds of descriptions is that they might be exaggerated, but on the pictures the crowd seems at least large).

loudspeaking telephone loudspeaker 1919
One of the loud-speaking telephone receivers used in what was called then a “Public Address Telephone System” (picture source).

This early use of outside sound amplification through loudspeakers is mentioned on the website www.medienstimmen.de. This site is focusing on early sound reinforcement systems and initiated by Ralf Gerhard Ehlert. It was a vary valuable resource for obtaining information during my research on early microphone and loudspeaker technology. For that reason I would like to dedicate a post to this website, since it might be helpful and inspiring for others too. Ralf developed this website as a part of a research project on the use of sound reinforcement systems for crowds during the first half of the twentieth century. A special focus was on the use of microphones and loudspeakers during by the National Sozialism (1933-1945), since the development of early sound reinforcement systems for crowds unfortunately is strongly related to this. Most of the articles are in German, but many links point to english sources and I think the lists are also very well understandable without any German knowledge.

The website provides resources, such as lists with microphone, amplifier and loudspeaker patents till 1950, a chronology of the use of sound reinforcement system during events and an extensive bibliography. There are many different loudspeakers to discover on the website, such as all kinds of horn loudspeakers:

Horn loudspeaker 1925
A Telefunken Lautsprecher (1925) for the Vox-Maschinen A.G. in Berlin combined headphones with a horn (picture source).
schallwand loudspeaker wall
The Schallwand (loudspeaker wall) invented by Peter Grassmann in 1936 (picture source).

Other inventions discussed by Ralf Ehlert are for example the transportable  Schallwand (sound wall) of 1936 by Peter Grassmann and the different Pilzlautsprecher (mushroom loudspeakers) which diffuse their sounds in many directions. These Pilzlautsprecher were very useful in sound reinforcement systems for very large crowds. By using many of these Pilzlautsprecher placed at regular distances a large crowd could hear the amplified sound without any of the echo problems a system with directional loudspeakers has. Some examples of these problems:

The sound is heard three times by the listener H on the left picture. The right way to position the loudspeaker is depicted on the right (picture source).
Doubling effect by two loudspeaker
Also in this loudspeaker set-up the sound is heard three times by the listener H on the left picture. The right way to place the loudspeakers is depicted on the right (picture source).
The use of so-called Pilzlautsprecher solves the problems caused by mono-directional loudspeakers (picture source).

I asked Ralf if he had a favourite among all those different patents listed on his site. He told me that he finds the Improvement in Magneto-Electric Apparatus by Ernst W. Siemens (US 149797 April 14 1974) very special, since it is describing already the modern electrodynamic loudspeaker, which is then “reinvented” again during the 1920s.

When reading the patent lists my eye felt on a patent of December 20, 1924, filed 9 days after the famous Rice and Kellogg patent (DRP 631724). Remarkably this patent (CH 113262) for a radiophonischer Lautsprecher (radiophonic loudspeaker) has been filed by a woman, not surprisingly the only one on this list. The invention itself is not very spectacular; it is a kind of double  moving iron loudspeaker, using two metal membranes. This system would become obsolete as soon as the electrodynamic system as described in the Rice and Kellog patent mentioned above was established as the common way to build loudspeakers. During my research for the book I did not have time to investigate any further, but during the last few days I tried to find out who Maria Schlatter Schrag was. My search has not yet ended, and it will probably take some more time to find out why this patent was filed by a woman. I am afraid though the reason might be much more mundane than I was hoping for. As far as I know now, she has been a servant and a cook, and not the polytechnical university student I was hoping for (Zurich university was open for women already from the 1860s onwards). Her husband Rudolf Schlatter was a radio technician though, and it might be him who invented the loudspeaker, and she just filed it for some practical reason.

Maria Schlatter Schrag radiophonischer lautsprecher loudspeaker 1924
The patent for a radiophonischer Lautsprecher by Maria Schlatter Schrag, 1924.

Transduction and Acoustic Radiator by Kristen Roos

Acoustic Radiator prepared speakers electromagnetic spectrum
Acoustic Radiator by Kristen Roos. © Kristen Roos

Not only is Kristen Roos working with the frequency range audible for human beings, but also many other frequencies and vibrational phenomena are of high importance in his work. He makes different parts of the electromagnetic spectrum perceivable for human beings and often vibrations are translated from one form of appearance to another. Kristen’s work investigates what we would perceive if we had an organ similar to a radio frequency receiver. It connects us to the unseen and unheard world of all these frequencies surrounding us in everyday life. Many of these frequencies are part of the electromagnetic spectrum which  includes for example not only light but also micro-waves, X-rays and radio waves. The frequencies of this electromagnetic radiation are often very high, in the realm of terahertz or even more. By translating these frequencies into different media Kristen makes them audible, and loudspeakers play a central role in this sonification process. His installation Acoustic Radiator (2016) gives us a bewitching impression:

At the core of this installation is a WiFi router. WiFi routers periodically transmit so-called beacon frames to report the presence of a wireless network to possible receivers of that network. This is similar to how a lighthouse is sending out its light signals. The signals sent by this WiFi router are in the 2.4 GHz range. A radio frequency receiver is used to pick up these frequencies. With the help of a modular synthesizer (with a clock divider, VCA’s and ADSR’s) and audio amplifiers the signal of the router is transformed into an electric current, which is sent to three loudspeakers and a subwoofer. Another loudspeaker is placed on the table next to the WiFi router and connected directly to the RF receiver. Asking him about the function of this fourth loudspeaker, Kristen answered me that this allows the visitor to see the movements of the mechanism which is the same as the speakers that vibrate the radiators and door.

Kristen Roos Acoustic Radiator
Overview of the set-up for Acoustic Radiator.

The three other loudspeakers are also prepared with a small metal rod, attached to their dust cap (the centre part of their diaphragm). On top of the rod a piece of felt is placed. These prepared loudspeakers are placed in the space, two touching a radiator, the third one placed against a door.  Kristen made this video to explain this translation process from electromagnetic waves radiated by the WiFi routers to audible waves radiated by the loudspeakers:

The loudspeakers in this installation are used as a kind of automised percussion players, since they hit objects such as a door and radiators. But this hitting is done not by a single hit but with many vibrations, causing the radiators and door to vibrate much more variable than it would when just hit once. As Kristen explained me he decided not to use common tactile transducers (which he used for example in his work Ghost Station) but instead developed his own prepared loudspeakers. He had several reasons for this. First of all, the installation consists of all kinds of misused equipment, and therefore a misused loudspeaker seemed to be more at place than a properly used tactile transducer. Also, the making of the sound becomes clearly visible to the audience by the vibrating metal rod. Furthermore, and perhaps most significant, the sound can be more precise and subtle, since the felt-covered metal rod is able to transmit the vibrations on to a very specific small spot of the radiators and door.

prepared speaker metal rod
A loudspeaker prepared with a metal rod and felt is placed next to a radiator. © Kristen Roos
prepared loudspeaker
The third loudspeaker prepared with a metal rod and felt is placed next to a door. © Kristen Roos

For transmitting the low frequencies a subwoofer is hidden under a pile of out of use radiators. These radiators “radiate” the sonic vibrations of the subwoofer, because they will start to vibrate according to the low frequencies produced by the subwoofer.  It is through these combination of loudspeakers—the speaker connected to the RF receiver, the three placed close to radiators and door and the subwoofer—that the signal of the WiFi router is materialised into sound. The title of the installation itself is of course a reference to the old radiators used, but at the same time an acoustic radiator is also another name for a loudspeaker.

subwoofer radiator
A subwoofer is hidden under a pile of radiators. © Kristen Roos

The direct translation from imperceptible frequencies around the audience becomes even more clear by the involvement of their own personal devices radiating electromagnetic frequencies. Entering the room, they can connect their mobile phone to the WiFi router. This will result in some glitches in the sound of the installation happening due to the establishment of a new connection between router and mobile phone.

Transduction by Kristen Roos.
Transduction by Kristen Roos and Dorion Berg. © Kristen Roos & Dorion Berg

In Transduction (2001), an installation developed together with Dorion Berg vibrations are once more the point of departure. Eight towers with each a dismantled monitor, a reversed drum skin filled with water and a loudspeaker are presented in the gallery space. The original electric signal is produced by a drum machine—a Yamaha RX7—with eight different outputs. Each of the loudspeaker–drum skin–monitor towers is connected to one of these outputs of the drum machine. This electric signal is translated into two different forms of presentation: in a visual form on the monitor and as audible vibrations of a loudspeaker membrane. The loudspeaker membrane vibrations are transduced into another waveform, namely water waves. The loudspeaker membrane is connected to the reverse drum skin filled with water by a thin fishing line. In this manner, the vibrations of the speaker are picked up by the drum skin and will gently move the water in a wave pattern specific to the vibration frequency. Since the drum skin is placed directly above the monitor, the water waves break the light of the monitor. In this way the different representations of the same signal are meeting again, leaving a mysterious impression of their hidden electrical origins .

transduction dorion roos loudspeaker water drum skin
Each of the eight towers contains a loudspeaker, a monitor and in between a drum skin filled with water. © Kristen Roos and Dorion Berg.
loudspeaker water drum skin
The same electric signal is sent both to the loudspeaker and the monitor.

Loudspeakeroperas by Huba de Graaff

Huba de Graaff's opera Lautsprecher Arnolt
Several of the loudspeaker sculptures used in Huba de Graaff’s opera Lautsprecher Arnolt. © Huba de Graaff

In her opera Lautsprecher Arnolt (2004) Huba de Graaff decided to have most roles played by loudspeakers. Only the main character—the writer Arnolt Bronnen (1895-1959)—is played by a human actor, Marien Jongewaard. Arnolt himself is literally a  “loud speaker”, screaming and provoking the kinetic loudspeaker sculptures. Arnolt often changes his policitical orientation, depending of what seemed to be the most advantageous at that time, similar to how loudspeakers can reproduce all kinds of sounds and do not have to choose one direction. The loudspeaker sculptures in their turn are all humanised. They are constructed by Bart Visser and can often move and play the characters of, for example, Bertolt Brecht (a very long thin and vibrating loudspeaker), Joseph Goebbels (a long column of loudspeakers, which can grow higher and shorter)  and Arnolt Bronnen’s wife Olga Förster-Prowe (two loudspeakers in the form of a bra). The piece is set during the first half of the twentieth century. During that time the loudspeaker was developed and became suitable for mass communication and soon after used in Nazi Germany for dissemination of their propaganda.

Marien Jongewaard next to the column loudspeaker Joseph Goebbels, in its shortest form.
Marien Jongewaard next to the loudspeaker column Joseph Goebbels, in its shortest form. © Huba de Graaff
Speaker opera Goebbels
The loudspeaker column Joseph Goebbels can increase in length (compare it’s length with the picture above). © Huba de Graaff

As Huba explains in her text about loudspeakers and sound systems, she considers the loudspeaker as the real instrument of electronic music. For this reason it is essential for her that loudspeakers become moving objects on stage. In this way a physical connection between sound and movement is created and the speakers become a sound source which is moving when it is sounding (similar to instrumentalists playing their instrument). A typical example of such moving loudspeakers are the so-called AATs, an abbreviation of Addressable Audio Transducers. These are rotating loudspeakers derived from Leslie loudspeaker cabinets produced by Yamaha. Huba transformed them in such a way that their movements are controllable by MIDI. Here they speak in German on loudspeakers as instruments:

Except the often historic voice recordings and some texts by the director of the piece Erik-Ward Geerlings,  most of the sounds diffused through the loudspeakers are sounds which can not exist without loudspeakers: sine waves, all kinds of other synthesised sounds, hammond organ, electric guitar, but also the characteristic mostly unwished hum of sound amplification systems and of course acoustic feedback.

Huba de Graaff composed several other works with loudspeakers, one of them is the opera Hephaistos (1997), for 40 loudspeakers, robotspeakers, computercontrolled moving loudspeakers, three singers and computers. Also in this opera the loudspeakers are part of the scenery, as for example the singers are wearing loudspeaker heads.

loudspeaker hats Huba de Graaff
The two actresses in Huba de Graaff’s opera Hephaistos are wearing loudspeaker hats. © Huba de Graaff.

An earlier piece is Corenicken (1990). Although not called opera, this is again a large scale work, using many different sound sources and performed by Huba on violin and a percussion player. The audience is surrounded by all kinds of loudspeakers and also visual media such as small televisions. Huba herself wears her “Japon Fuzz”, a tin dress containing electronic equipment, so it can create “fuzzy” and feedback sounds in response to her movements. The piezo disks attached to the dress (see the second picture of the dress) pick up the sound of the dress. As soon as Huba approaches a loudspeaker, her amplified tin dress feedbacks with the loudspeaker:

Huba de Graaff loudspeaker dress
The “japon fuzz”, a tin dress with electronic equipment to create “fuzzy” and feedback sounds. © Huba de Graaff
dress with speakers
A close up of the Japon Fuzz, using piezo disks to pick up sound. © Huba de Graaff

There are also two rotating loudspeakers (similar to the AATs mentioned above) on stage and an enormous amount of piezo ceramic elements is hanging above the audience. Together they form three grids, containing each 256 piezo disks (a total of 768!). Huba developed a computer software to control pulse-trains send to these disks, resulting in moving soundscapes. Every piezo disk is prepared with a piece of thick aluminium foil, so it diffuses its sound louder. Wonderful clouds of small sounds are moving above the audience:

Huba de Graaff Piezo grids 768 piezo ceramic elements
Setting up for Huba de Graaff’s Corenicken: the audience is placed around the stage. Three grids containing 768 piezo disks prepared with aluminium foil are hanging above the audience. © Huba de Graaff

Huba considers stereophonic sound as used in hifi-systems for the living room or in concert hall amplification as a strange and flat reproduction of reality. Sound loses its depth and perspective when reproduced by such systems. A common P.A. system (a public address system used for sound amplification in all kinds of situations, such as concert halls, theatres, and stadiums) creates a distance between the audience and the creators. In works such as Corenicken Huba is looking for a what she calls an I.A. system (individual address), as opposed to the common P.A. system. Every audience member is surrounded in a different way by loudspeakers. And indeed each of her imaginative loudspeaker sculptures diffuses its sound in an individual way.

Huba is currently working on a new piece for the AAT loudspeakers, which will be premiered soon. I’ll keep you posted.

Points of Contact by Erfan Abdi

Erfan Abdi in the bird cage, performing Points of Contact at STEIM.
Erfan Abdi in the bird cage, performing Points of Contact at STEIM. © Erfan Abdi

Big eyes as contact microphones, a bird cage as a loudspeaker, and two double spring objects of which again one functions as a loudspeaker and the other as a loudspeaker: this is the inventive set-up Erfan Abdi uses for his performance Points of Contact (2017). Erfan himself seems to be a bird, placed in the cage to perform for us, gently trying to break out by touching the bars with his metal eyes.

The sounds during the performance are created by different combinations of the same set-up: both amplification as well as feedback through the contact microphones and tactile transducers are used. By using additional long springs the different elements can be connected to each other. To give an example of one of the many possibilities for doing all kinds of physical signal processing with this set-up: a signal of the big eyes contact microphones is sounding through the bird cage transducer, and since both are touching each other a feedback loop occurs (1 in the scheme below). The bird cage is also connected with a spring (2) to the double springs with a contact microphone (3). This is amplified through the transducer attached to two double springs (4). This is fed back again to the double springs with a contact microphone (5) by connecting the springs with the help of again an additional spring. The sound of all contact microphones is also amplified by the two main loudspeakers in the hall (the PA system) (6).

transducer exciter contact mike microphone Erfan Abdi
Set-up scheme for Points of Contact by Erfan Abdi, see the description above for a detailed explanation.

What makes this set-up so versatile for producing all kinds of different sounds, is that the two feedback loops can both be combined, influence each other but also broken up again (the first feedback loop are the contact microphone eyes and bird cage transducer, and the second the springs contact microphone and springs transducer). Take away, for example, the spring in between the two double springs—(5) in the scheme above—and the double springs become a spring reverb for the sound produced by the bird cage feedback. The whole set-up is constructed in search for fragility and inaccuracy in response to the feedback signal. For this reason, the two contact microphone springs have been chosen by Erfan because their frequency response is slightly different: this results in a modulating feedback sound instead of a feedback on one constant pitch.

The two contact microphone eyes
The two contact microphones are enlarged by small metal plates so they can touch several bars of the bird cage at once. © Erfan Abdi

For the same reason the contact microphones eyes are made by simple piezo disks placed on round metal plates: this gives the possibility to touch the bird cage at two or three bars. As Erfan explained me, when there is just one point of contact between the contact microphone eye and a bird cage bar the feedback tends to be especially strong on the fundamental frequency of the pitch. But as soon as you touch two or three of the bird cage bars, more partials are added to the sound. And by using two contact microphone eyes they also start to modulate each other. The placement of the contact microphone below the  two springs is again aiming for a richer and less stable sound: instead of having just a single point of contact, the whole disk is touching as much as possible of the surface of both springs.

The contact microphone beneath the springs. © Erfan Abdi
The contact microphone beneath the springs. © Erfan Abdi
The contact microphone beneath the springs. exciter body shaker
The tactile transducer underneath the two other springs. © Erfan Abdi
The tactile transducer bird cage exciter body shaker
The tactile transducer attached to the bird cage. © Erfan Abdi

Erfan uses the music software Reason to do some processing of the feedback. Basically it provides a compressor, a delay line and an amplitude follower. The amplitude follower is used for modulating the delay time, so as soon as one frequency gets too loud, the delay is changed, and the frequency of the feedback will also change. The connections between the different parts of the set-up—which contact microphone is connected to which transducer etcetera—is controlled live by Erfan with a small MIDI controller.

During the performance Erfan is sitting in the cage, an intriguing image for a music performance. The movements of his head towards the thin cage bars seem to underline the scenery of a bird locked in against his will. But it is with the resulting sounds that this bird seems to be able to leave the cage: the variety of sounds not only enlarge the musical possibilities of this set-up, but also give the impression that the music can sonically fly away from the cage. The bird might seem to be locked in visually but sonically it is free to come and go.

Below you can view some short fragments of Erfan Abdi performing Points of Contact at STEIM in Amsterdam, and listening to a recording of a performance excerpt. And if you are close to The Hague: Erfan performs a new version of this piece tomorrow (Thursday 10th of October) at Ephémère at Studio LOOS.