A low roar from a point outside the city reached the room.

The crowds in the street had been a low roar all morning, but now a different, more excited note rose from below.

A low roar began from somewhere behind them, building steadily in volume.

Outside there was a dull boom, followed at once by a low, steady roar.

The roar, constant and low, was almost like the sea.

Sure enough, the low roar of men's voices had grown louder.

Individual words sometimes emerged from the crowd's low roar.

The conversation was at a low roar, making individuals hard to hear.

A constant low roar made it hard to hear what was going on above.

Walking to the lab after lunch, Ramsey heard a low roar.