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    PREVIOUS SCIENTIFIC APPROACHES TO LOUDSPEAKER AND ROOM EQUALISATION2006

    Some commercial room correction systems

    In 1991 B&W launched a room correction system called the B&W Digital
    Control Unit.
    Essentially it was based on the seventies Teledyne experimental
    system and to a large extent Colin Bean and Peter Craven’s earlier theoretical
    work (see above). A technical presentation can be found in Hi-Fi News &
    Record Review 1991 December.

    Marantz AX-1000, a combined room correction system and room simulation
    system, was accessible in 1992. An impressive piece of equipment for that time
    representing a power of 13.3 mips.

    TacT Audio introduced a room correction system in 1997 called RCS 2.2. The
    equipment only works together with a PC for calculating the equalisation
    filters, impulse response acquisition and real-time processing are both done
    independently. Splitting the measured impulses into three frequency bands,
    the RCS 2.2 uses different strategies for designing the correction filters. In the
    lowest frequency region, the correction resolution is 0.6 Hz, up to 1,500 Hz the
    resolution is 5 Hz, and above it is 300 Hz. Processing is powered by four Motorola
    DSP56002 processors. The RCS 2.2 was received with some excitement in
    the professional world, and although really expensive it has been reviewed
    (with good marks) in the home theatre / Hi-Fi literature. Many prejudges
    pointing towards digital Hi-Fi equipment was put to death, and the reviews
    reported on noticeable improvements in the subjective quality of reproduced
    sound. Later, TacT has launched simpler and cheaper versions producing almost
    the same subjective quality improvement.

    Roister Digital Audio has come up with a quite new set of digital room
    equalisers (1999), the Acoustics Compensators, having a processing capacity
    between 160 and 480 MIPS for the top-of-the-range model. That allows running
    two-channel FIR filters at 48 kHz with 768 up to 2336 filter coefficients.
    Input impulse responses must be supplied using external pieces of measuring
    equipment.

    Other recent pieces of room correction equipment are listed below. Also Philips
    launched a room equaliser in the early nineties (and a not too expensive set of
    active speakers in fact) - neither of those obtained much commercial success.

    SigTech AEC-1000/2000. Can handle 2,200 FIR filter taps in 48 kHz
    sampling and works adaptively, i.e. the correction filters are changed onthe-
    fly,

    Snell Acoustics RCS 1000. Room correction system with 1.5 Hz
    resolution,

    Behringer Ultracurve Pro 8024. A 1/3 octave equaliser that produces the
    band corrections automatically based on measurements.

    Why not more systems?
    Not many systems of the kind have emerged yet, and the world still waits for
    a simple, cheap, and completely automatic room correction system. Perhaps
    that is why the concept of room correction has not yet gained widespread popularity.
    Another explanation is that just ten years ago, digital Hi-Fi equipment
    was still approached with much scepticism (at least among purists).
    Perhaps still not completely vanished, the “fear-of-digital” has greatly reduced
    here at the beginning of the new century. Thus, a breakthrough for the digital
    room correction may be just around the corner.


    John N. Mourjopoulos: Digital Equalization of Room Acoustics,
    J. Audio Eng. Soc., Vol. 42, No. 11, 1994 November


    Signal-processing methods such as digital equalization can in theory achieve
    a reduction in acoustic reverberation. In practice, however, the realization of
    these methods is only partially successful for a number of objective and
    subjective (perceptual) reasons. Two of these problems, the dependence of the
    equalizer performance on the source and receiver positions and the requirement
    for extremely lengthy filters, are addressed. It is proposed that all-pole
    modelling of room responses can relax the equalizer filter length requirement,
    and the use of vector quantization can optimally classify such responses,
    obtained at different source and receiver positions. Such classification can be
    used as a spatial equalization library, achieving reduction in reverberation over
    a wide range of positions within an enclosure, as was confirmed by a number
    of tests.
    http://kurser.iha.dk/eit/eaku/litt/R...the%20Past.pdf

    http://kurser.iha.dk/eit/eaku/litt/
    Last edited by Vassilis; 05-01-2008 at 09:20 PM.

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