These generated notes have a separate tonal quality to the notes above them and are in reverse phase. The resonator generates an artificial bass to represent the lowest notes. The ported box becomes a Helmholtz resonator (enclosed volume of air with aperture) similar to wind instruments. Ported Box The trend for boxes to be small makes the port a forced compromise. Some systems designed this way work well but often sound un-musical.
Amplifier power requirement can be approx 300 Watts for domestic application. These speakers already have heavy cones and therefore inefficient. If the speaker-box system resonance is 60Hz and the system is required to be flat down to 30Hz, then the amplifier will have to put out 16 times more power at 30Hz to compensate. Many sub-bass amplifiers have special equalization (EQ) to boost amplifier power, compensating for the decrease in efficiency below resonance. Efficiency and therefore frequency response rolls off at -12dB/octave (1/16th the power for each octave decrease below system resonance).
Below system resonance the cone excursion is kept constant by the box. Below system resonance the cone cannot increase excursion at 4 times the distance for each octave decrease as previously explained. The fundamental resonance of these speaker-box systems can be as high as 50-100Hz. Many use 10-12in speakers in very small boxes, approx 1-2 cubic ft or 30-60 litres. Sub-woofer EQ There is a large market for active sub-woofers especially for home cinema and vehicles.
0 kommentar(er)
