The Symbaline - An Active Wine Glass Instrument with a Liquid Sloshing Vibrato Mechanism Lior Arbel Yoav Y. Schechner Noam Amir Faculty of Architecture and Viterbi Faculty of Department of Town Planning Electrical Engineering Communication Disorders, Technion Technion Sackler Faculty of Medicine Israel Institute of Technology Israel Institute of Technology Tel-Aviv University Haifa, Israel Haifa, Israel Tel-Aviv, Israel [email protected] [email protected] [email protected] ABSTRACT musical instrument as an interface [2]. An overview of the The Symbaline is an active instrument comprised of several Symbaline is given in Section 2.1. This paper presents the partly-filled wine glasses excited by electromagnetic coils. development of a modulation mechanism for the Symbaline This work describes an electromechanical system for incor- based on existing studies of liquid sloshing in cylindrical porating frequency and amplitude modulation into the Sym- cups, as discussed in Section 3. Figure 1 shows a block baline's sound. A pendulum having a magnetic bob is sus- diagram of the mechanism. The mechanism consists of a pended inside the liquid in the wine glass. The pendulum is pendulum with a magnetic bob submerged inside the wa- put into oscillation by driving infra-sound signals through ter in a partly-filled wine glass. A low frequency signal the coil. The pendulum's movement causes the liquid in (∼ 3Hz) is sent to the Symbaline's electromagnetic coil, the glass to slosh back and forth. Simultaneously, wine glass placed in front of the pendulum, outside the glass. The in- sounds are produced by driving audio-range signals through duced magnetic field causes the pendulum to oscillate. The the coil, inducing vibrations in a small magnet attached to pendulum's movement creates a sloshing movement in the the glass's surface and exciting glass vibrations. As the liquid. An audio-range signal in the glass's pitch is sent glass vibrates, the sloshing liquid periodically changes the to the same coil, causing the wine glass itself to produce glass's resonance frequencies and dampens the glass, thus sounds via a small magnet attached to the glass's surface. modulating both wine glass pitch and sound intensity. The sloshing liquid both changes the glass resonance fre- quencies and dampens the glass vibrations, thus creating a modulation effect of both pitch and amplitude. Figure 2 Author Keywords shows the mechanism in mid-slosh position. Augmented, Electromechanical, Water, Wine glass, Modu- Sections 2-4 provide an overview of related works, modu- lation lation methods in musical instruments and liquid sloshing. The modulation mechanism is described in Section 5. Sec- CCS Concepts tion 6 describes a characterization experiment of the mod- ulation mechanism, where the glass was excited by input •Hardware ! Sound-based input / output; Electro- signals of different musical instruments, while being mod- mechanical devices; •Applied computing ! Sound and ulated by the mechanism. The complementary results are music computing; shown in Section 7. 1. INTRODUCTION 3Hz pure tone Pendulum Modulation effects are frequently used in both instrumen- Amplified oscillations Audio range Magnetic Modulated signals tal and vocal music. Modulation can affect a tone's pitch, instrument tone field glass sound amplitude, or both. Modulation production vary per instru- ment. In some instruments modulation effects may require external accessories or specific implementations such as an electric guitar's tremolo bar (Whammy bar) or involve large mechanical movements, such as Leslie speakers. While the terms vibrato and tremolo are used do describe different PC Amplifier Electromagnet Wine glass, Microphone modulation types [20], the precise definitions may vary be- (LM1876) Modulation mech. tween disciplines. Therefore, this paper uses the explicit Figure 1: Block diagram of the modulation mechanism and terms frequency modulation and amplitude modulation. experiment rig. The PC generates a low-frequency pure The Symbaline is an active wine glass instrument con- tone to activate the modulation mechanism and an audio- sisting of a set of partly-filled wine glasses actuated by an range tone sampled from a musical instrument to induce electromagnet. The Symbaline is played using an auxiliary glass vibrations. Both signals are amplified and routed to the electromagnet. The electromagnet generates a magnetic field. The audio range field excites wine glass vibrations and the low frequency field puts the pendulum into oscillations, causing water sloshing. Wine glass sounds modulated by Licensed under a Creative Commons Attribution sloshing are captured by the microphone. 4.0 International License (CC BY 4.0). Copyright remains with the author(s). NIME’19, June 3-6, 2019, Federal University of Rio Grande do Sul, Porto Alegre, Brazil. 9 Figure 3: The Symbaline, tuned to a full octave, showing the wine glasses and electromagnets. The Symbaline is played by an amplified external musical instrument (not shown). Figure 2: The modulation mechanism in mid oscillation. sounds. In addition, modulation sometimes occurs due to The pendulum is excited by the electromagnet, placed left arbitrarily occurring warble - an amplitude modulation ef- of the glass. The water is sloshing to the right, lowering the fect caused by mild glass asymmetry. The asymmetry causes wine glass's pitch. a frequency difference between the components of a mode doublet [19], adding a beating effect to the glass tone. Both modulation methods are limited in capabilities, raising the 2. RELATED WORK need for the modulation mechanism described in this work. 2.1 The Symbaline 2.2 Musical Modulation Mechanisms The Symbaline, shown in Figure 3, [2] is an active instru- Modulation methods and mechanisms vary per instrument. ment consisting of a set of partly-filled wine glasses. Each In string instruments, the vibrating string's length is peri- wine glass is actuated by an electromagnet, exciting a small odically changed by a rocking motion of the string-stopping magnet attached to the glass's surface. The electromag- finger. In wind instruments and singing, modulation is pro- netic actuation method is inspired by earlier augmented in- duced by periodically changing the air flow, the mouth piece struments such as the Magnetic Resonator Piano [10], the pressure or similar techniques [11]. Electromagnetically Sustained Rhodes Piano [21] and the Some electric guitars are equipped with a dedicated mod- EMvibe [4]. These instruments use electromagnets to ex- ulation mechanism; a non-fixed bridge is rocked back and cite and augment sounds produced by strings, tines and forth using a controlling lever to alter the vibrating string's bars. length and tension [13]. The Floyd Rose bridge is a specific The Symbaline is played by using an auxiliary musical modulation mechanism for the electric guitar, capable of instrument as an interface. This instrument, such as a clas- generating extreme pitch modulations [17]. A Leslie speaker sical guitar or a MIDI keyboard, produces an analog sig- is a device, originally intended to be used with the Ham- nal. The signal is sampled by an audio interface and pro- mond organ, in which the sound produced by a loudspeaker cessed with various audio effects and filters on a PC. The is directed through a rotating wooden drum or horn. The processed signal is then converted back to an analog sig- sound source's periodical movement away and towards the nal, split, amplified, and sent to the electromagnets. The listener produces both amplitude and frequency modula- electromagnets generate magnetic fields which vibrate the tion [14]. Similar principles of sound modulation by sound magnets attached to the glasses, thus producing wine glass source rotations are found in the Corrugaphone (Whirley sounds. tube) [12] and the Bullroarer [16]. The vibraphone is a per- The Symbaline's sound is created by two distinct sources: cussion instrument resembling a marimba with tubular res- 1) The wine glasses' radiated sounds; 2) The input instru- onators. The vibraphone is equipped with a unique mech- ment's original sound, radiated by the input instrument anism: electrically rotating discs are placed at the top of itself or by an additional speaker. The glass sounds are the resonators, changing the bar-resonator coupling, thus characterized by the input signal's properties: decay and creating amplitude modulation [5]. attack times, volume envelope and spectral content can all A simple method exists for wine glass modulation: the be modified to an extent by using different input signals, tilt modulation method. A partly filled wine glass is fixed in instruments and effects. The Symbaline is based on earlier a tilted position, letting water extend to the lowered side. prototypes which implement wine glass-string coupling by The glass is played by rubbing the rim in circular motions. strictly mechanical means [1]. As the nodes and anti-nodes revolve around the glass, the The previous Symbaline's implementation enables mod- contribution of the 'higher' water level at one side of the ulation by input signal processing. However, this imple- glass fluctuates, resulting in frequency modulation [15]. As mentation is limited in effect as input signals outside the the Symbaline's wine glass excitation points are fixed, this glasses' resonance frequencies tend to produce dim and quiet method is inapplicable. 10 2.3 Liquids in Musical Instruments Musical instruments utilize the flowing and wobbling prop- erties of liquids in various manners. The waterphone con- sists of an enclosed steel bowl with protruding rods. Water wobbling inside the bowl create a mostly arbitrary change of resonance frequencies, modulating the sounds produced by the bowed rods or struck bowl [22]. The hydraulophones are a family of instrument, all consisting of water jets spout- ing out of a series of holes in a large pipe. The player blocks the holes, redirecting the jets towards sound produc- (a) t = 0. (b) t = T=4. (c) t = T=2. ing mechanisms such as perforated disks or shafts [7].