Engineering / design / construction of produced mufflers / tips for F6B didn't change its technology at all .

All excitement for "expected differences" in sound between 13/14' models , compared to the 15' are related to the external pipe's plating . Chrome is a metal , which transfers heat and sound in different ratio then ceramic paint .

A radiant heat is insulated from the thermal barrier / coating , which in these differences , play the role of an absorbent for the Sound Spectrum, called "Sound Board". Acoustical properties of different "insulators" create final effectiveness , which one might looking for .

So , following Sound Transmission Class (STC) and Impact Insulation Class (IIC), it produce slightly different , maybe deeper / throatier sound and doesn't have anything to do with expected performance , but could be an answer for few.