I googled for that monitor now and I found some not so positive reviews about the sound system. In this review, one of the cons is the speaker system:
http://www.epinions.com/reviews/Hewlett_Packard_w1907_Black_Silver_Monitor

In this other review, it's written:
http://www.pcworld.com/reviews/product/30783/review/w1907.html

"This 19-inch wide-screen has built-in speakers, located in the back of the monitor. They are adequate for operating system warnings and other beeps and pops from software applications. But for multimedia sounds, results are mixed. Audio in movies is sufficiently audible, but whispered dialogue is barely discernible to the ear. MP3 playback, on the other hand, is loud enough to hear."

I did speak in a low volume, so maybe there's indeed an incompatibility between the way I speak and your sound system. :-(
I have to speak louder next time. :-)