So, I know a lot of you were wondering about the speakers in the N97. Honestly, I don’t think they’re that bad… but they are a lot different than those found in the 5800. I was messing around tonight and noticed that basically the bass line was absent, almost entirely, from my tracks when I played them through the internal speakers.
Of course, the output is brilliant over headphones and I can’t really fault it at all for that. If I had to guess, I would say Nokia tuned these speakers much more for voice-calls and not for music.
The fidelity is very treble heavy and seems to boost any vocals. Here’s a short clip that shows side by side what the two phones sound like. Some caveats to this, first of all this was recorded by my E90 and the sound is not really faithful of the actual output, though the difference is still striking.
The microphone itself could not capture the entire bass-line in this song, though you’ll hear much more of the lows on the 5800 than the N97. In real life, the 5800 faithfully reproduces the song, (which can be found here) and all parts of the bass-line, including the sweeping “woo-woo” sound, are fully audible.
The N97 does not reproduce any of it and those are actually missing completely, leaving only the treble loop.
I do not think the speakers of the N97 are bad... They will not distort regardless of volume, but... they definitely do not have the fidelity of the 5800 Xpress music has.
Conclusion: Nokia N97's Loud Speaker sound quality is great with majorly Treble flow, but this sounds more natural. Whereas Nokia 5800 has little strong and hard Bass effect added to it for show off. If you are looking for better loudspeaker device ignoring all other features than Nokia 5800 is for you.

