I'm wondering if it's just my phone or all 6s Plus models but I've noticed quite a big difference in speaker quality between my 6s Plus and my old iPhone 6. I then compared it with a normal 6 Plus and a normal size 6s - they all sounded better. The only phone I haven't been able to compare it to yet is another 6s plus. I think I need to take this back to Apple, unless everyone else has the same issue?