Ronald Aarts

Aarts and his collaborators at Philips have been involved in the development, improvement, and hardware implementation of bass enhancement/restoration systems exploiting the natural psycho-acoustic phenomenon known as the "missing fundamental".[9][10] Small loudspeakers are in general not capable of reproducing low-frequency notes, but by exploiting auditory illusions one can use either the virtual pitch phenomenon to shift the low frequencies to a higher frequency band where the loudspeakers are capable, this is sometimes referred to as Ultra Bass;[11] or, one can map the very low frequency to one single frequency where the loudspeaker is designed for high efficiency, this is sometimes referred to as Bary Bass.[12] On the other hand, if the loudspeaker is capable of radiating low frequencies, but if they are not present in the music, those frequencies can be derived from the music using a bandwidth extension scheme, this is sometimes referred to as Infra Bass.[13] Finally, the audio quality, especially from high Q low-frequency sound transducers, can be improved by attenuating decay parts of bass signals thereby reducing sustain or ringing for bass notes, this is sometimes referred to as punchy bass.[14]

Aarts and his coworkers at Philips have also been involved in the design and applications of loudspeaker radiation. An extended version of the Zernike polynomials, known as ENZ,[15] was applied to solve forward and inverse problems in acoustic radiation of a flexible circular piston surrounded by a rigid infinite plane (baffle) and of a flexible spherical cap on a rigid sphere, showing that the latter is quite similar to that of a real loudspeaker.[16] The use of several loudspeakers arranged in an array allows special radiation characteristics. For example, one can increase the sweet spot area during stereophonic listening by making use of interaural time differences, this system was called position-independent stereo.[17] Another application is to direct the sound to a listener without disturbing others, this is known as personal sound. Yet another application is to use quadratic phase arrays to design loudspeaker arrays that radiate just like a single loudspeaker.[18] For loudspeaker radiation calculations the Struve function is often needed, simple approximations have been derived for this.

On small TVs and portable audio equipment, the speakers are close together. With special signal processing, so-called phantom or virtual sources can be made so that the sound seems to be generated far outside the loudspeakers. This principle has been applied by Philips to many TV and audio sets, under the commercial name 'Incredible sound'.[19] The director Spike Lee made a commercial for this in 1996, which was set on Wall Street in NYC.[20]

A small loudspeaker in a special housing can generate synthetic jets that offer advantages over a fan, such as higher efficiency, greater design freedom, and less noise and wear.[21] Experiments have shown that for small surfaces up to approximately 40 cm², the synthetic jets cool better and make less noise than a fan.

Monitoring of, e.g., epilepsy, sleep, and heart problems such as atrial fibrillation; and vital signs such as blood pressure, heart rate, and respiratory rate, can be performed without hindering the patient using a photoplethysmogram (PPG). A PPG sensor can easily be built into a bracelet such as a sports watch, preferably extended with accelerometers.[22]