Joris Adelbert Maria Nieuwendijk

Hybrid loudspeaker system for converting digital signals to acoustic signals

In a loudspeaker system for converting an n-bit digitized electric signal (6) into an acoustic signal a plurality of sections (voice coils 14.1, 14.2, 14.3, 14.p) of a digital loudspeaker (1) are driven directly by the p most significant bits of the n-bit digitized electric signal (6). The loudspeaker (1) comprises at least one additional section (14.p+1). This (p+1)th voice coil receives a signal from a digital-to-analog converter (5), the input signal of the digital-to-analog converter comprising at least the n-p least significant bits (FIG. 2). In a different embodiment the digital-to-analog converter (5) receives all the n bits of the digitized electric signal as the input signal. At least the p sections (14.1 to 14.p) which correspond to the p most significant bits are provided with means (the resistances r) for producing a signal which is a measure of the sum of their instantaneous drive signals and for applying the said signal to a signal combination unit (32) arranged in the line (10) from the output of the digital-to-analog converter (5) to the (p+1)th section (R1). By means of this correction circuit the distortion in the loudspeaker system can be reduced substantially (FIG. 3b).

Loudspeaker system for converting a digitized electric signal into an acoustic signal

An electrodynamic transducer (1) for use in a loudspeaker system for converting an n-bit digitized electric signal (11) into an acoustic signal comprises n voice-coil devices (4.1, 4.2, . . . 4.n) which cooperate with a magnet system (3). The voice-coil devices each comprise a conductor whose length is the same for all the voice-coil devices. The areas of the perpendicular cross-sections of the conductors increase each time by a factor of two starting from the voice-coil device (4.n) corresponding to the least significant bit and going to voice-coil devices corresponding to consecutive more significant bits. The invention enables the transducer to be constructed in a simple manner if the transducer is a moving-coil loudspeaker or if it is a ribbon-type loudspeaker.

Synthetic Jet cooling using asymmetric acoustic dipoles

In two earlier papers [1, 2] the principles and experimental results have been discussed for a typical embodiment of synthetic jet cooling technology: an acoustic dipole cooler comprised of a standard loudspeaker in a housing provided with two pipes. The current paper shows experimental and numerical results for another type: the asymmetric dipole. Basically, this type consists of a loudspeaker with a minimal volume attached to it with one or more holes with or without pipes. Results for driving power and noise are presented for a number of actuators covering a large parameter space: frequency, pipe dimensions and driving voltage were varied over a large range. A relatively simple acoustic model extended to include separation losses matched the experimental results very well. The results indicate promising heat transfer performance with minimal noise combined with a large degree of freedom.