Acoustics is actually the branch of physics that relates to the study of sound. It also refers to the quality of the sound environment.

The acoustical characteristics of a venue for the live performance of music or drama are an important part of the audience experience. For music performance, the room becomes part of the instrument, helping define the character of the musical sound that the audience hears. Whether it is a symphony hall, or an intimate chamber music venue, careful attention to detail in the acoustical design ensures that the audience can hear every subtle nuance of the performance, and feel like part of the live experience. A drama theatre has a different, but no less critical need for acoustical design. The theatre must be able to deliver all the subtle nature of a stage whisper to every seat, and do so with all the variables of sets, curtains, lighting and props.

To understand stage sound properly, you need some knowledge of the science of 'acoustics so that you can work out what equipment you will need and what that equipment does to the sound.

First of all, sound is merely vibrating air. Of course, vibrations can occur at different speeds: the faster the vibration, the higher-pitched the sound. We count the number of times a sound vibrates in one second and call this the frequency of the sound. Frequency is measured in Hertz. Frequencies are usually divided into high (above 10kHz), mid-range, and low (below 100Hz).

High frequencies are directional: that is, they tend to move in the direction in which the source is pointed. If a loudspeaker is pushing out high frequencies you hear the sound best in front of the speaker, less well to either side, and poorly, if at all, behind.

Low frequencies, however, are omni-directional: that is, they tend to spread equally in all directions. So if you are listening to a rock group, you will hear the bass guitar almost as well if you are behind the speaker as you would if you were in front.

This can cause problems, in particular feedback.  What happens here is that sound from a speaker is picked up by a microphone and fed back through the system, producing that awful shriek or howl which we have all heard at one time or another.  Often reducing the bass response of the amplifier will help get rid of the problem.

A decibel is not a unit in itself, like a volt or watt or Herz, but a comparison between two levels.  Usually we use it in reference to sound pressure level (SPL), the level of sound.  0dB is defined as the smallest sound the ear can hear at a frequency of 1000Hz (1kHz).  Because decibels, like our ears, work on a logarithmic rather than a linear scale (and I won't even try to explain that!), an increase of 3dB means a doubling of the sound.  If one sound is 100 times louder than another, we can say it has a ratio of 100:1 or 102:1.  We could also say it is 20dB louder.  Thus if the ratio of sound A to sound B is 1000:1 (or 103:1), we can say it is 30dB louder.  You will find that the gain, equaliser and fader controls on mixers are calibrated in decibels.  The "normal" position will be marked as 0dB and increases marked with a plus sign (+6dB) and decreases with a minus (-6dB).

To complicate matters - and they're rarely simple in sound! – at the input stage, the above is true, but when we refer to the output, when sound pressure is doubled, it increases by 6dB! You don't really have to remember all this: just as most people know the difference between a 60W bulb and a 100W but would be pushed to tell you exactly what a Watt is, so we can treat the decibel as a measure of the difference between two sounds without knowing exactly what a dB is.

When recording sound it is a lot easier to contrl the environment. You can find or create the perfect acoustics, you can set up the level of each input just how you want it and you have the benefit of being able to manipulate the audio once it is recorded.

In a live setting you have to do your best to set up the system well t the beginning and ensure that thorough sound checks are conducted but you are faced with many aspects that could change and you must be able to adjust on the fly. You also do not have the benefit of 'doing another take' or manipulating the sound after it has been recorded. Audiences however, enjoy the concept of live music and gives them an experience that they do not have with recorded music.

Activity

As a small group, discuss the pros and cons of both live music and recroded music. Create an argument as to which one is 'better' and debate your argument with the rest of the class.

If we can talk about acoustics in terms of the sound waves bouncing off of the walls within a space what happens when you are outside?

The first consideration in your audio design is to determine where you want the audio and how loud it needs to play. Will it be used as foreground sound, for parties or announcements, or as background music to enhance the space’s ambiance? Decide if you need to contain sound in a specific area, like a pool or exhibit or if general background sound is needed for a large area like walking paths at a theme park or an outdoor mall. Area of coverage will vastly differ between products.

Next, determine how many zones are needed. Is this a central system or a zone from an indoor audio system as you would design for an outdoor patio at a restaurant?

You also need to consider the speaker selection as this is one of the most important aspects and will be based on your clients’ needs. Outdoor speakers fall into three main categories: omni directional, direct radiators and line arrays. They all serve a different need outdoors. Omni directional speakers offer 360° coverage and work well in situations where you need sound everywhere. They will cover as much area as two direct radiating speakers. Direct radiators (or directional speakers) work well if you want to contain the sound to a specific area and line arrays are great choices if you need to project sound out over longer distances. Line arrays are made for long throw and will send sound out to 40’ with little level drop where a direct radiating speaker will lose too much level over that distance to be heard clearly. Line arrays levels typically drop at half the amount as direct radiators – 6 dB versus -3 dB with doubling of distance. 

Make sure that you have considered how you are going to protect your speaker from the weather.

Activity

Discuss with the person next to you some considerations needed for a performance that is outside.