Acoustics is the science of the production, transmission and effect of sound. Cinema halls, lecture halls and auditoriums are designed in such a way that speeches or music programmes can be heard clearly by the audience. While designing such buildings it is always taken into account that no echo is produced. Do you know how the buildings with good acoustical quality are designed? Architectural acoustics is now an integral part of modern architecture.
While designing such buildings it is kept in mind that the sound of the speaker is neither too loud nor too low so that it is clearly audible to everyone in the hall. Normally some materials such as plaster reflect the sound. Other materials, such as carpets, clothing, draperies and human bodies absorb sound. Thus in an auditorium a perfect balance has to be maintained by placing these things in such a way that the reflection and absorption of the sound is evenly spread.
Two properties of sound help the builders a great deal in designing the buildings of good acoustical qualities. These properties are echo and reverberation. An echo is a sound that has been reflected from a surface. Substances which reflect sound produce strong echoes. In an auditorium, we hear the sound from two sources: directly from the speaker, and from a surface. It has travelled farther than the direct sound. This means that it reaches our ears after the direct sound. In a properly designed room, the echo and direct sound are heard almost at the same time, thus ensuring that there’s no disturbance and the sound heard is clear and distinct. But in a poorly designed room, the time gap between the two is quite long and as a result sound is not heard clearly.
A reverberation is defined as a close group of echoes i.e. echoes and re-echoes. Each successive echo is quieter than the previous one. One can minimize echoes and reverberations by building rooms with sound absorbent materials. But then the sound in such a room would have a dead quality. A certain amount of reverberation is also required for good quality of sound. In general, the reverberations should last for 1 to 2.5 seconds. This is called the reverberation time.
Another difficulty encountered while designing an auditorium is the volume of sound. People sitting at the back of the auditorium should be able to hear as clearly as those in front. For this purpose sometimes sound has to be amplified by loudspeakers. Often this is not a very satisfactory arrangement as loudspeakers do not reproduce sound very accurately.
In designing good sound quality rooms, we must consider pitch or frequency also. Sounds with different pitches can be reflected from surfaces in different degrees. Resonance also must be avoided. Due to resonance one particular frequency sounds much louder than the others. The frequency of sound waves makes sound high or low. If the high frequencies are loud, we hear shrill sounds, and if the low frequencies are too loud, we hear dull sounds.
Ancient Greeks were the first people to build their theatres with good sound qualities. They placed their audience on steep hillsides where sound could travel to them directly. These theatres were called amphitheatres. The speaker’s stage was parallel to the first row of seats at the bottom. And thus every member of the audience could see and hear well. The Hollywood Bowl in California is a modern-day amphitheatre. Modern hi-fidelity equipments can reproduce sound with life-like clarity.
