I suppose you mean this issue ?
http://talk.maemo.org/showthread.php?t=91325

Joerg commented that
"we're gonna use same class-d amp, we will get some proper simple HPF in place, and we use similar but not original speakers"

HPF = High-Pass Filter.

The reason for changing the speakers in Neo900 is that the N900 original doesn't seem to be easy to find. The replacement speakers are likely to have different characteristics (different impedance), but a class D amplifier is largely tolerant to this.

Hope this helps.

- Werner