loudspeaker issue

hi newbie just looking for a bit of advise i have an iPhone 6 plus which is very quiet and tinny.I can hardly hear anything on youtube or playing music so decided today to take to shop and swap out the loud speaker when i returned to collect i was told it was the same he suggested swapping out the charging port which apparently the loud speaker attaches to so i agreed. an hour later phone still the same I've tried hard reset I've even dowloaded the firmware and reinstalled. If anyone could suggest anything else i could try i would be grateful as the shop is stumped as well. thank you in advance