1. Does Filter-free class-D amplifier need the inductance of speaker to produce audio? Or IOW, if the speaker has the characteristic as a idea resistor, can Filter-free amplifier works well?
Yes, audio contents are still present in the square waves. Your
efficiency might hurt a little as Iidle is higher. There is no purely
2. If we need to pay attention to the inductance of speaker when we choose a speaker for Filter-free amplifier?
Not really, you might get slightly higher efficiency with higher
inductance, but I doubt you can see much improvement in efficiency
3. Is there any hearing difference when using speakers with different inductance?
Not with filterless Class D. If speaker L is higher, it will exhibit a
higher impedance at higher freq and might affect your audio a little at
It is more important to obtain the impedance response of the speaker
(i.e. Z vs freq) than to just look at a specific number like L.
4. Can I add an external inductor or ferrite bead to increase inductance of speaker in order to improve the performance.
Bad idea, anything extra that you add will introduce more loss and
distortion. You should only add extra components unless they serve a
specific function (eg. EMC, ESD, snubber).
Audio Applications Engineering Manager
Dallas, TX USA
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