He is a bit mutton, so you should speak louder.
mutton
idiom Slang
Cockney rhyming slang · East London
named after Mutt and Jeff , two early 20th century comic strip characters
Origin
via Mutt and Jeff → deaf
My grandfather is getting quite mutton in his old age, so we often have to repeat ourselves during dinner.
The elderly man sat quietly in the corner, appearing somewhat mutton as the lively conversation of the party flowed around him without his participation.