An auditorium has organ pipes at the front and at the rear of the hall. Two identical pipes, one at the front and one at the back, have fundamental frequencies of 271.0 Hz at 20.0°C. During a performance, the organ pipes at the back of the hall are at 26.4°C, while those at the front are still at 20.0°C. What is the beat frequency when the two pipes sound simultaneously?