ISOBARIC BASS

摘要

A lot of rot was talked about isobaric bass loading when it made headlines through its use in the Linn Isobarik loudspeaker. Putting one bass driver behind another, with a small, sealed enclosure between them, does not eliminate the speaker's bass resonance and subsequent roll-off, nor - a bit more reasonably - does it lower the front driver's resonance frequency to its free-air value. This should be obvious from the fact that the rear driver has a bass roll-off that prevents it maintaining constant pressure within the coupling chamber, as the isobaric name implies. In fact what happens when two identical drivers are connected acoustically in series and electrically in parallel is that they produce a composite driver with twice the moving mass and half the suspension compliance, which lowers the free-air resonance by half an octave and allows greater bass extension to be achieved from a given cabinet volume.