Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/005—Details of transducers, loudspeakers or microphones using digitally weighted transducing elements

Definitions

• the invention relates to a method for converting digitized electrical signals generated according to pulse code modulation (PCM) using a scanning pulse with the frequency ft and containing sound information into sound waves using at least one electroacoustic transducer.
• PCM pulse code modulation
• the invention further relates to a circuit arrangement for performing this method.
• the object of the invention is to get rid of these restrictions and to use the advantages of digital technology also when converting the digitized signals into sound waves.
• the invention provides that the conversion of the digitized signals into sound waves takes place in the electroacoustic transducer itself. Calculations and tests show that this technique achieves an at least equally good and predominantly better sound quality with less equipment outlay than with previous conventional analog technology.
• a digital loudspeaker is to be understood as a loudspeaker to which the digitized signals are fed directly according to the invention.
• Speakers based on the electro-dynamic principle are the most frequently built types.
• Other types of transducers such as electrostatic, capacitive or the corona loudspeaker, have so far only been able to establish themselves in special fields, in particular as high-frequency radiators.
• the problem with all loudspeaker systems is that the entire frequency spectrum from 20 to 20,000 Hz should be radiated as linearly as possible. With this requirement cannot be met with a single loudspeaker chassis. For this reason, there are a number of combinations consisting of bass, mid and tweeter systems.
• the frequency ranges are divided by electrical switches on the individual sound transducers. By selecting suitable combinations and filter filters, very good combinations could be created.
• the efficiency that is to say the ratio of radiated acoustic energy to the electrical energy supplied, is only a few percent in all previously known systems.
• the non-linear distortions are about 3% at nominal load capacity (load that can be tolerated without permanent change in the loudspeaker properties, that is to say the destruction limit) for good loudspeakers. If you consider that the entire electronics in an audio system have distortion factor values of less than 0.1% and the connected boxes produce a few percent distortion, it is understandable that the "analog loudspeakers" must be replaced by other systems, so that natural music reproduction for humans is possible without compromise.
• the sampling frequency must be at least twice the highest frequency in the signal.
• the original signal must not contain a frequency higher than half the sampling frequency.
• Pulse code modulation is based on the sampling theorem and is used in digital audio technology. “Only the digitized amplitude values of an analog signal are transmitted and recorded on magnetic tape or pressed as information on a sound carrier, for example compact record. As long as the bit content (logical 0 or logical 1) can be evaluated during playback, the transmission remains uninterrupted. Another essential advantage of this technique is that only digital information needs to be dealt with during transmission or during playback. These functions are easy to integrate, and thanks to microelectronics, device prices are acceptable to a large audience.
• Digitized analog signals can be returned to their original form with digital-to-analog converters.
• An example of such a digitized analog signal is shown in FIG. 1.
• the sampled values are converted into an analog voltage by a digital-to-analog converter, and after filtering, the original signal is available again.
• the basic idea of the digital loudspeaker is based on the fact that the discrete amplitude values are emitted as small sound pulses in time with the sampling frequency by an electro-acoustic transducer. In other words, the digital information is only converted back when the sound is generated.
• the frequency spectrum of this method is shown in FIG. 2.
• the electro-acoustic transducer works on a fixed frequency. This frequency is the sampling frequency. If we apply the modulation to the transducer, the following frequencies are emitted:
• the digital speaker is based on the sampling theorem.
• the sampling theorem has been expanded to include sound reproduction. Experiments have shown that sound waves behave exactly like electrical signals.
• the fundamental meaning is that broadband electro-acoustic transducers are no longer required for sound reproduction, but only the sampling frequency of the analog signal has to be emitted with different intensities.
• the digital loudspeaker only emits the sampling frequency with different intensities. This frequency is in the ultrasound range and is, for example, 44.1 kHz in the digital record.
• the principle of the electro-acoustic transducer is of secondary importance. Rather, it is crucial that it is a narrowband system, that is, only the sampling frequency has to be emitted. Ceramic transducers or corona loudspeakers are suitable as sound transducers according to the ionization principle.
• a single electro-acoustic transducer converts the electrical energy into sound waves.
• the converter is driven as shown in FIG. 3.
• the amplitude values are emitted from the loudspeaker with different intensities.
• the digital-analog conversion takes place on the acoustic level. This is shown in FIG. 4.
• a resolution number of discrete amplitude levels
• six ten only electro-acoustic transducers are combined to form a loudspeaker system.
• the dimensions of the individual elements are chosen so that the radiated power corresponds to the binary value of the signal amplitude.
• the largest converter is able to radiate 50% of the total sound power. The second largest 25% etc.
• one or more electro-acoustic transducers are activated and the total sound power corresponds to the original amplitude of the analog signal.
• the complex digital-to-analog converter is no longer required.
• the power amplifier also works digitally, since only the individual sound converters, depending on the bit pattern, need to be activated. Problems with non-linear distortions in the output stage cannot occur at all, since everything takes place on the digital level up to the sound generation and the power amplifier actually only consists of sixteen switching transistors.
• the electro-acoustic transducers are chosen so that the resonance frequency of the scanning frequency is the same. On in this way a very high degree of efficiency is achieved.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Circuit For Audible Band Transducer (AREA)

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• 1984
  • 1984-12-22 DE DE19843447111 patent/DE3447111A1/de active Granted
• 1985
  • 1985-12-19 EP EP19860900064 patent/EP0205501A1/de not_active Withdrawn
  • 1985-12-19 WO PCT/DE1985/000532 patent/WO1986003927A1/de unknown

Non-Patent Citations (1)

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