Sujet Commentaires sur le test : Test des moniteurs AIAIAI UNIT-4

Without a subwoofer, the Squeezebox Boom goes from a -3 dB response at 50 Hz (at low volume settings) to about 85 Hz (at high volume settings), all the way to 20 kHz.

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By modeling the low-frequency response mathematically, we can create an inverse filter that compensates for the speaker roll-off, and then we can put a new low frequency roll-off at whatever frequency is desired. Of course, the tradeoff is that as the bass response extends lower, it’s necessary to drive much more power into the speakers at low frequency, risking distortion. At low volumes, this can be done very effectively without excessive distortion. Of course, as the volume goes up, the excess boost at low frequencies causes either the ower amplifier or the loudspeaker itself to go beyond its linear region, causing significant distortion, system shut down, or even physical damage to the speakers.

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In general, it would not be wise to implement the green digital filter of Figure 11 without any other filtering, since it would quickly over-drive the speakers and power amplifiers. This 32 dB boost at 20 Hz corresponds to more than 1000 times more energy at 20 Hz than at 200 Hz. This is not reasonable for any but the lowest listening level. To make matters orse at low listening levels, an additional signal boost is needed at low frequencies to compensate for the loss of sensitivity to low frequencies at low SPL levels.

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The true beauty of the Squeezebox Boom architecture is that we can dynamically and silently switch among any of the filters as volume settings and/or signal strength changes. Currently, we implement a sliding cutoff frequency based on volume setting.