The inherent dependency upon frequency of the response of an electro-mechanical transducer is compensated over a wide frequency range by driving the transducer with a current source, the signal of which is modified to have a frequency characteristic which is the complement of the frequency characteristic of the mechanical response parameters of the transducer.
A compact subwoofer with exceptionally low distortion at 30 Hz and below is provided by a unique combination of system Q and an unconventional synthesized bandpass filter. The speaker has a system Q of 1.2 which is unusually high for a high quality, low distortion system. Nonetheless, a high Q with low distortion is made possible by the novel filter which has an oversized inductor and capacitor to provide a low-pass corner frequency nearly equal to the system resonant frequency. The result is a surprisingly broad, flat response at extremely low frequencies.
A method for processing the audio signal in a loudspeaker system prior to delivery to the loudspeaker and the apparatus for such processing is disclosed. Uniform acoustic output with respect to frequency at frequencies below the resonant frequency of the loudspeaker system is achieved by changing the strength of the signal at a constant rate in inverse proportion to audio signal frequencies from a frequency below the resonant frequency to a frequency at least one octave above the resonant frequency. A method and apparatus for limiting the audio signal to prevent distortion is also disclosed.
An arrangement for converting an electric signal into an acoustic signal (y/t) or vice versa, comprises an electroacoustic transducer (2) and means (3) for reducing distortion in the output signal of the arrangement, which distortion is caused by the electroacoustic or acoustoelectric conversion performed by the transducer. The means comprise a non-linear network (3', 3" or 3'" in FIGS. 3; 43', 43" or 43'" in FIG. 4). The non-linear network is arranged for reducing non-linear distortion by compensating for at least a second or higher order distortion component in the output signal of the arrangement. The network may comprise at least two parallel circuit branches (15a, 15b in FIG. 3; 47a, 47b in FIG. 4). At least one of the circuit branches (15b in FIG. 3; 47b in FIG. 4) compensates for non-linear distortion of the second or higher order.
An improved loudspeaker system is disclosed which includes a passive electrical network between the speaker input and the output of a speaker driver for reproducing bass frequencies. The loudspeaker uses a closed box system and obtains an extended low frequency response through the use of critical relationships in the passive electrical network including high order transfer functions.
A device for converting an electric signal into an acoustic signal, which comprises an electro-acoustic transducer unit (2) having a quality factor (Q) less than unity. The device further comprises an amplifier circuit (3) for driving the transducer unit. The amplifier circuit has a frequency-dependent gain characteristic (6) which increases towards the lower frequencies, starting from f.sub.2, in a frequency range between a first and a second frequency (f.sub.1 and f.sub.2), f.sub.1 being the resonant frequency of the transducer unit (2) and f.sub.2 being greater than f.sub.1. The efficiency can be increased if amplifier the circuit includes a special amplifier such as a switched amplifier, for example, a class-D amplifier, or an amplifier with a power supply that provides a DC voltage that depends on the drive level of the amplifier.
