Archives of Acoustics, 33, 4(S), pp. 59–64, 2008

Ironless Lowfrequency Loudspeaker Working Under its Resonance Frequency

Benoit MERIT
LAUM, CNRS, Université du Maine

Guy LEMARQUAND
LAUM, CNRS, Université du Maine


A soon achieved low frequency loudspeaker (10 Hz to 100 Hz) is described. To suppress
the non-linearities and the drawbacks due to the motor, its structure is totally ironless. The
large flat diaphragm and the high force factor of the loudspeaker lead to its high efficiency.
Efforts have been made for reducing the non-linearities of the loudspeaker for a more accurate
sound reproduction. Especially we have developed a motor totally made of permanent magnets,
which create a uniform induction across the entire intended displacement of the coil. The
motor linearity and the high force factor of the loudspeaker make it possible to work under its
resonance frequency. This functioning needs the use of a DSP to raise the 12 dB/octave slope
of the pressure response of the loudspeaker under its resonance frequency and to protect the
moving pieces from large displacements. Results presented here are to be completed as soon
as the loudspeaker will be achieved.
Keywords: flat diaphragm, ironless motor, under resonance frequency functioning
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