Läs US- patentet, Jocke:
http://www.mickandviv.com/pfm/US4008374.pdf
Här är ett litet urklipp:
"Conventional loudspeaker systems, for example, sealed box, infinite baffle, horn, electrostatic, bass re- flex, and transmission line systems all employ a loud- speaker or a membrane to produce frequencies includ- ing bass frequencies. The loudspeaker or membrane will normally have a much lower resonant frequency in free air than in an enclosure, for example, a bass driver may have a free air resonance at about 20 Hz but in an enclosure its resonance would occur at typically 25 - 35 Hz or higher. This raising of the loudspeaker reso- nance results in a peak in the loudspeaker system re- sponse curve resulting in "booming" and other undesir- able resonance effects within the audible spectrum.
Furthermore, in order to reproduce audible frequen- cies, and especially bass frequencies, most loudspeaker systems employ a fixed mass of air enclosed or re- stricted behind the driver. This means that the driver is constantly compressing and rarifying this restricted mass of air which has the effect of causing colouration and distortion in the sound produced. A bass reflex cabinet attempts to overcome this problem but the reflex action is found to only occur at around one fre- quency. This disadvantage is usually employed with a cabinet resonance to boost the bass response by the use of reflected anti-phase sound at a particular frequency in order that it emerges in phase. In common with other systems the response, especially the bass response, is neither as undistorted, uncoloured or as extensive as the original sound to be reproduced.
It is an object of the present invention to obviate or mitigate the disadvantages outlined above.
According to the present invention there is provided a bass unit for a loudspeaker system comprising a cas- ing, a first bass loudspeaker having front and rear faces, said first bass loudspeaker being so mounted in the casing that the front face of the said first bass loud- speaker faces outwardly of the casing, a second bass loudspeaker having front and rear faces, said second bass loudspeaker being mounted in the casing behind said first loudspeaker with its front face opposite the rear face of said first loudspeaker so as to define be- tween said first and second loudspeaker a chamber of
air, operating means for operating said first and second loudspeaker in phase such that the pressure of air in the chamber remains substantially constant, and sound absorbing means located in said chamber to absorb distortion components resulting from different re- sponse characteristics of said first and said second loudspeakers.
Further according to the present invention there is provided a bass unit for a loudspeaker system compris- ing a housing having a rear wall, a permanent magnet assembly mounted in said housing on said rear wail and having a central core, two sound radiating surfaces defining therebetween a chamber of air and each sound radiating surface being located around said central core, and operating means for independently driving said sound radiating surfaces in phase such that the pressure of air in the chamber remains substantially
constant, and sound absorbing means located in said chamber to absorb distortion components resulting from different response characteristics of said first and said second loudspeakers."
