Gp Acoustics International Limited

Christopher Spear

Jack Anthony Oclee-Brown

Mark Alexander Dodd

A loudspeaker comprising two acoustic diaphragms mounted to face in axially-opposed directions, two voice coils each having an axis and an axial length and being configured to reciprocate along its axis to drive one of the diaphragms, the axes being substantially parallel and both axes passing through both diaphragms, and at least one magnet forming part of a chassis assembly configured to provide two axially-extending gaps, one for each of the voice coils to reciprocate within, wherein the at least one magnet and the chassis assembly are adapted so that magnetic flux flows across the gaps in opposite directions, and wherein when in use the diaphragms are at their predetermined maximum negative excursions the voice coils overlap in the axial direction by between 10% and 90% of their average axial length, and wherein when in use the diaphragms are in a relaxed position, between their maximum negative and positive excursions, the voice coils do not overlap in the axial direction.

Loudpseakers

Sound emanating from the high-frequency diaphragm of a coaxial speaker will diffract into the annular gap between the tweeter unit and the midrange cone. This results in response irregularities. We therefore disclose a loudspeaker, comprising first and second drivers located substantially coaxially with the first driver located centrally and the second driver located concentrically around the first driver, the loudspeaker being bounded at its radially outer side for at least part of its extent by the voice coil former of the second driver and including a spacing between the outermost extent of the first driver and the innermost extent of the second driver thus defining an annular space, the annular space containing a sound-absorbent material. By placing the sound-absorbing material in the annular space, the resonances within this space are damped, thus alleviating their effect. The annular space can have a lower resonant frequency that is below the passband of the first driver. Essentially, instead of minimising the effect of the annular gap by reducing its size and seeking to seal its outer opening, we propose to enlarge the space so that the fundamental resonant frequency it exhibits drops out of the passband of the high-frequency driver and hence out of the frequency range of interest. This both prevents the fundamental frequency of the cavity from being excited, and also allows sufficient room within the space to accommodate a sound-absorbent material to absorb these undesirable resonances.

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Maidstone, United Kingdom

Christopher Spear