muffler question

[Motortrend]

Chambered is like stock. Makes use of internal structure to (carefully? selectively?) cancel out certain frequencies. Basically adjust the sound. For OEM use it sacrifices a bit of performance to get a quieter, more relaxing drive.
This is in contrast to free flow mufflers that don't have much internal structure to get maximum airflow and thus performance, but with the sacrifice of possibly having a droning sound while driving.

Of course it is possible to implement a chambered muffler badly if the builder doesn't know what he's doing. For tuners they use chambered design to alter the sound (like reducing the frequency, getting rid of resonances) without trying to make it completely quiet.

Good written explanation here: Glasspack Vs. Chambered Vs. Straight Through Mufflers | RealTruck

Video demonstration:



Skipping straight to the video conclusion:

Yes, mostly for acoustics. Stock mufflers will have more chambers (quieter) while after market ones will have less chambers (slight performance improvement over stock but noisier).