Class D Audio amplifiers aren't so great after all?

http://www.irf.com/technical-info/appnotes/an-1071.pdf

The above web doc on page 12 shows how “bus pumping” is unavoidable with half-bridge class D audio amplifiers. The Gain of a class D amp is proportional to the bus voltage, so therefore bus pumping is not good.
Why does anybody ever do a half bridge class D when a full-bridge class D avoids the problem, for the mere price of two more FETs.?

Also, Page 13 shows how class D amplifiers have a big EMC problem…..a class D amplifier suffers from high noise due to the top fet turning on when the bottom fet is reverse recovering its diode (and vice versa). Is there any way to avoid this in a class D amplifier?

Audio Designs have historically considered the dampening factor or ratio of load impedance to source impedance over the signal bandwidth. At low frequencies the source impedance is limited by the sum of all source ESR + storage capacitance divided by the feedback gain. At low f, the load impedance tends towards the sum of all ESR's ( speaker, wiring). In this case , the ripple current passes thru both source and load and if the capacitance of the supply is sufficiently large, the voltage ripple becomes the ratio of source to load impedance. Feedback is used to lower the source impedance and where feedback is taken affects this dampening factor (DF) as well as phase margin, (PM) if reactive affects the phase of feedback. If one considers the ESR of the bass speaker coil is a small fraction of 8 Ohms and a typical dampening DF ranges for quality designs ranges from 100 to 1000, the cost vs power losses is a significant tradeoff.

Thus the cost of a full vs half bridge must weigh these factors which ends up being THD and Ploss vs cost.

The cost vs complexity vs THD and P.out levels will determine if it is a trival cost. Essentially there are 2 stages SMPS regulation. THe source supply voltage and the signal voltage. For the same P.out, a full bridge (FB) can reduce the supply voltage required in half while doubling the signal voltage, while dioubling the supply current and expected losses and halfing the signal driver current and losses for the same MOSFETs. Generally a full bridge also doubles the switch losses, but a lower Vds rating tends to also lower RdsOn at the same cost to a lesser extent so overall it is not quite 2x. So it becomes a tradeoff between power loss, dampening factor, cost and output power, which in high volume may not be a trivial optimization. The back EMF from the speaker coil and series choke both must be considered for source ripple or so called pumping from the dynamic signal load at low f.

Considering a buck regulator efficiency tends to increase with higher Pout design criteria and 90~95% with a good design is far greater than any linear design at 50~65%, Class D is pretty good, but not perfect, so other classes were created ( eg Class E,F,G...) to improve performance in these key areas ( $, THD, efficiency.) but gain margin is also a consideration with choices for feedback ( voltage, current, before/after filter).

The Full bridge has a this advantage of back EMF cancellation but you also have the choice of reducing source impedance optimizing the duty factor, d.f. of the deadband time and commutation period, which raises the source impedance slightly by (1/1-d.f) This required deadband commutation for an active bridge is open to prevent shootthru currents for some X microseconds and a full bridge will have 2 deadtimes per cycle or twice the potential ripple that must be attenuated at high f.

At any frequency, lowering ripple, Ploss and THD, ultimately becomes a goal to raise the dampening factor over the measured bandwidth.

A half-bridge class-D amplifier is cheap junk like some cheap class-B amplifiers. There are some excellent class-D or class-AB amplifiers available but they ain't cheap.

Bus pumping can be, and is, cured by adding other power circuits to keep the rails balanced, we did one for Fusion car audio amps...

Faster fets minimise the reverse recovery problem

Fusion car audio?? I have some Fusion two-way 6x9 car speakers that are 18 years old and still sound pretty good. They have very heavy magnets, firm polypropylene woofer cones and nice dome tweeters. I use them for surround sound rear speakers in my family room.