In many auditoria, the seating and audience form the main absorption in the room, and consequently being able to correctly measure and predict the absorption coefficient of these surfaces is very important. The wrong estimation of seating absorption has been blamed for acoustic problems in many halls. Salford University developed a method for testing theatre seating which is now used commercial.
The aim of measuring the random incidence absorption of a small sample of seats in a reverberation chamber is to predict the absorption that a large area of the same seats will exhibit when installed in an auditorium. There are problems, however, in that the small sample of chairs in the reverberation chamber (say 24) is unrepresentative of a large block of seating because the edge effect is overemphasised in the reverberation chamber measurements.
The Kath and Kuhl method involves placing the seating in the corner of the reverberation chamber in rows with their intended row spacing, and the exposed edges obscured with barriers. The concept is to separately measure three absorption coefficients by carrying out measurements with and without barriers:
For an infinite array with no edges with side and front barriers in place;
For the front edges with the side barrier only in place, and
For the side edges with the front barrier only in place.
This then allows the absorption of the array, front and sides to be found, and a proper prediction of the absorption of any size array.
The test technique has been used extensively over the past few years to test provide information for the design several new or refurbished theatres and concert halls such as the Royal Albert Hall and Royal Festival Hall.