It has been a while since my old iPhone 11 had bad sound coming out from the speaker and the volume was way too low. Probably in all these years, I had all kinds of dirt and debris entered in the speaker place. The same thing with the microphone, it had muffled sound and I could barely hear my voice when recording, but I fixed it a couple of months ago with a cotton swab and some alcohol. The cotton swab hack did not work on the speaker though.
But do you want to know how I’ve cleaned/repaired it? Well, that’s very simple! With compressed air. I went to a self-wash car place and with a quarter I’ve used the compressed air thing to clean both of the speakers: the little ear one and the main speaker down.
Now the sound is super clean and loud like it was when I first got the phone. I’ve spent so much time with the speaker in that bad state that I forgot how it sounds like normal, so the first time the alarm went on I jumped out of the bed and did not know what’s that sound I am hearing.
So if you want to fix your muffled speaker, you can 100% use compressed air.