I would guess that any decent speakerphone has to have some method of reducing feedback loops. I would also guess that modern, digital units would seek to achieve this my subtracting their speaker output signal from their microphone input signal. My third guess is that this method cannot be perfect in the real world because whatever method is used to perform the subtraction cannot possibly account for volume, tonality and time delay changes caused by the enviroment. I guess another method might be to just attenuate the overlap of frequency responce between the speakers and the mic, but imagine this technique can only get you so much improvement before you've lost the ability to hear what is spoken. Or maybe you could add some barely audible signature wave to the speaker output and then subtract any mic input that comes along with that signature wave? Hmmm, that one probably isn't practical. Anyway...
If my guesses are correct, I must conclude that all speakerphones have some small degree of feedback loop problems, and that their engineers just try to make their systems combat them as best they can, and perhaps HTC's engineers just didnt get things as close to right as they could have.
I must also imagine that having another loop on the other end of the call - as would be had if the other party is also on speakerphone, which is also imperfect - would compound the problem exponentially.
Sent from my SPH-D710 using Tapatalk 2