Science of Rock Concerts
Sound At a Concert
Why Is There a Difference In What I Hear?
Anyone who has been to a concert can notice the difference in the music they hear live and what comes out of their iPod or stereo system. But why does this happen? Before this question can be answered we must take a look at the recording process then the conditions presented by a concert.
At a Recording Studio
Before we can know why the music we hear coming from our cds and iPods is different from what we hear at concerts we must first understand the circumstances under which the music was originally recorded. Most recording studios have three different types of rooms that all aid in the recording process. There is a live room, a control room, where the sound is recorded and manipulated and there are also one or more isolation booths. An isolation booth is a small, completely soundproof, room where vocals or individual pieces of music are recorded. All professional recording studios are built around desired room acoustics. They are soundproofed and all surfaces are covered in material that will absorb any extra sound and make sure the sound quality they are looking for is met. The professional studios go to extensive lengths to make sure the sound and music they produce is the best it can be. To see a video on soundproofing click here: http://www.youtube.com/watch?v=C2ReTr9Syqg&feature=fvw
At a Concert Venue
When looking at the conditions that are set up for the 'ideal' sound recording in comparison to many concert venues the difference is very vast. Where recording studios try to minimize the interference from outside noise concert venues seem to welcome it. The screaming crowd and the large room can affect the way the sound is heard. A lot of concert venues also have many hard surfaces that will, in a sense, reflect the sound waves and cause them to bounce around. When this happens it will change the way you hear the music, and the quality of the sound over all.
Other Reasons For Sound Distortion
At a concert the amplifiers can also cause a certain amount of disortion. Distortion from amplifiers can occur when the sound waves entering the amplifier aren't multiplied by the same factor, causing the wavelengths to no longer be linear. One of the most common types of distortion caused by amplifiers is called harmonic distortion. This happens when the amplifier clips the peaks of a sound wave. As a result harmonic frequencies are made that weren't there originally. There is also intermodulation distortion. This is when the original frequencies sum to create completely new sound waves. Distortion of this nature is very noticeable.
How Is Sound Quality Measured?
Sound quality is measured by the THD of the sound. THD means the total harmonic distortion. Most quality systems now have a less than 1% distortion rate, where some loud speakers can have up to 10%. Howevere these low bass frequencies are hard for the human ear to pick up.
Fun Facts
In 1877 Thomas Edison made the first recording of the human voice, it was of 'Mary Had a Little Lamb.'
