Yeah, I know that emulator... there's also another project for a ZX Spectrum emulator made with Flash 9 here: http://www.jorin.com/shed/zx-spectrum-48k-games/
Both the C64 and the Spectrum emulators doesn't have sound, because it's actually impossible to implement custom sounds with Flash 9 and Actionscript 3.

if you want to have a look at a good java spectrum emulator embedded in a good website also check out: WWW (DOT) ZXSPECTRUM (DOT) NET (I'm not writing the url because it contains many commercial games that can be played within the website)