Background

Background information – ideal reverberation times

It is a proven fact that a too long low frequency reverberation, is what makes a hall unsuitable for amplified electronic music such as pop and rock. Here is a video with an auditive analogy of what a too long reverberation time at low frequencies sounds like within the genre. I am sure you will recall the sound …

The first minute explains why sound gets more muddy further away from the orchestra/loudspeakers.

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When a room does not absorb sound waves they are left to bounce around between surfaces for a long time. That equals a long reverberation. The time it takes for the sound to die out is called the reverberation time. So room acoustics is indeed happening in the time domain.

Longer reverberation also means louder reverberation. And that may, in turn, make the original sound unintelligeble. We know this from for instance churches: the message of the priest becomes hard to understand. Same for music with a lot of rhythm and syncopation of a staccato, percussive nature: the intelligibility of the music becomes low since one sound keeps going at a loud level while the next one starts. The loud, reverberant sound of the first impulse masks the next. On the other hand: choir or legato-types music sounds great with a long reverb.

Most contemporary music is rhythmically active and loud at lower frequencies. Many rooms have a long reverberation in the 63, and 125 Hz octave band but not in the 250 Hz band or above. This is due to the nature of many dedicated acoustically absorptive materials on the market. Try to notice how a female speaker might be easier to understand than a male speaker … Many (other) musical instruments  also stretch down in at least the 125 Hz band: bass, guitars, keyboards, drums …

Mid- and high frequencies are absorbed by audience and the air. The lows are not. And a higher Q-factor of the loud speakers at these higher frequencies ensures that high frequency reverberation is rarely causing trouble at amplified concerts. Actually, this is favorable for everybody at the concert to feel enveloped in sound and for the musicians to be able to express dynamics.

At very low frequencies, the 63 Hz band and below, our threshold of hearing is quite high. Therefore, a sound decay here ‘disappears’ faster than at higher frequencies. In fact, the reverberation time here can be a little longer than in the 125 Hz band without being disturbing.