The acoustical quality of an auditorium is a subjective impression and even now, after years of research, is difficult to relate to any one simple objective measure. Historically, reverberation time has been adopted as the measure of a hall's acoustic and is still arguably one of the most important single parameters. It is a considerable task to design a concert hall to exhibit the chosen reverberation time and London's Royal Festival Hall is one example where, despite careful design, insufficient low‐frequency reverberation resulted. Traditional remedies were discounted on economic grounds and the electronic solution known as “assisted resonance” was conceived. This overcame the lack of warmth by employing multiple channel, frequency selective positive feedback via the normal modes of vibration of the auditorium, thereby increasing the reverberation time. Since this prototype installation, the “assisted resonance” concept has been applied to another ten halls of a variety of types, and the approach can now be considered well proven by example. During this time the elements of the system have been developed considerably, including the recent introduction of sophisticated signal processing equipment. This not only enhances the management of the basic process of reverberation magnification but also brings closer the ability to control and optimize other acoustic parameters which contribute to listening enjoyment.

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