By focusing sound in a tight column, Acouspade™ is able to place sounds at any desired spatial location, making it possible to deliver acoustic information to the public precisely where it is needed.
Acouspade radiation patterns
Acouspade system specification
- Input voltage: 230V or 120V, 50/60 Hz
- Power supply: 24V/1A
Dimensions and weight
- Acouspade speaker dimension: 370 x 176 x 22 mm
- Acouspade speaker weight: 1100g
- Temperature: -20°C to 60°C (-4°F – 140°F)
- Humidity: 0 – 95% (non-condensing)
Ultrasonic and DSP processing
- Carrier frequency: cca. 40 kHz
- Modulation method: AM
- Input impedance: 60k Ohms
- Typical input signal: 160 mVrms
- Frequency response: 150 Hz to 17 kHz
- Max speaker output: 96 db @ 1kHz/1meter
- Audio input: 2x RCA
- Black, White, Grey
Acouspade frequency response
Directional audio – basic principle
Directional audio systems, also called Parametric Acoustic Arrays (PAA) have found their way into many practical audio applications in the last decade or so, due to their high directivity. Parametric acoustic arrays have come a long way since their introduction by Peter J. Westervelt in 1963. Due to their high directivity and almost nonexistent side lobes, many applications have been developed using PAA ranging from underwater applications, speech and music reproduction to medical applications. The two main challenges that each PAA system has to overcome are low conversion efficiency of the high frequency primary waves into secondary (audible) waves and the distortion of the desired (modulation) signal.
A parametric acoustic array is created by emitting an intense and highly directed ultrasonic beam consisting of a carrier wave and signal components introduced by one of the various modulation types. The carrier interacts with other spectral components of the ultrasonic beam due to the nonlinearity of air at high acoustic sound pressure levels (SPL) and generates new spectral components along the ultrasonic beam.
These secondary waves contain audible spectral components related to the difference between the carrier and side bands. The nonlinearity of air also generates higher inaudible frequencies which are quickly absorbed due to the high absorption coefficient at high frequencies. Thus the ultrasonic source creates a beam of ultrasound which acts as a virtual array of sound sources.
Ultrasonic sound waves in the air are usually generated by piezoelectric or electrostatic transducers. The mechanical construction of the piezoelectric ceramic transducer that is used in the Acouspade directional speaker is shown below. The active element is a thin disc made of Lead Zirconate Titanate (PZT) ceramics. The applied voltage causes the disc to expand and contract. The center of the PZT disc is thus displaced vertically up or down depending on the polarity of the voltage. The mechanical properties of the materials used as well as their physical dimensions determine the resonant frequency and bandwidth of the transducer.
These transducers can continuously transmit a SPL of about 120 dB at 40 kHz when driven by 10 VRMS. PZT transducers have a small bandwidth and can be driven with a maximum driving voltage of 20 VRMS, which generates up to 126 dB SPL.
The main functional units of the modulator/amplifier in an ultrasound-based directional sound system are:
− input amplifier and signal conditioner
− low distortion quadrature oscillator
− integrated multiplier with adder
− D-class power amplifier
Excerpt from the paper “Sources of Noise in Practical Implementations of Modulators/Amplifiers for Parametric Acoustic Arrays”, by authors: Matija Pirc and Andrej Levstek; Published at MIDEM 2014 – 50th International Conference on Microelectronics, Devices and Materials
Acouspade directional speaker
The Acouspade directional speaker is a result of several years of research and development in the field of non-linear directional audio systems. The speaker exhibits a highly directional sound-field distribution, creating a laser-like beam of audible sound, that can be directed precisely to the location where it is needed. The sound is of high-quality, with low noise and great frequency response, which includes authentic reproduction of bass notes and frequencies as low as 150 Hz. The speaker itself is easy to use – you only need to plug the audio output of your source device (such as portable music player, laptop, DVD-player etc.) to the speaker input and you are ready to go.
General information on the Acouspade directional audio system and it use-cases
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