Men in striped suits and straw hats, singing romantic, old-timey lyrics. This is a traditional barbershop quartet - what a Capella singing used to be like. A Capella has come to mean “without instrumentation," though it originally meant "choral style" in Italian.
It was a style that became popular in the 1930s and 40s. Though it’s gone through its ups and downs, a Capella is back in vogue today - more than 80 years later.