Everything You Always Wanted to Know About Acoustics:
(Impress the girls when you can explain how your cochlea works)

Music is an artistic method of vibrating air. How fast, how much, and
when the air is vibrated, determines what we will ultimately hear as
sound. The science of this process is called acoustics.

When a speaker (or anything else that has the ability to vibrate)
moves forward, the air molecules in front of the cone are compressed,
causing the molecules to run into each other moving them all forward.
This continues to happen until the speaker moves in the other
direction, which causes a rarefaction (or thinning) of the air that
was just compressed. This is the basic concept of how sound waves are
produced.

**WAVES**

A Sound wave can be described by two basic characteristics, the speed
of the vibration (Frequency), and the extent of the vibration
(Amplitude).

When a speaker moves forward, backward and back to its original
position, this is called a cycle. Frequency is determined as to the
number of cycles per second. It is labeled Hertz (Hz) after an early
scientist in the field of acoustics. Diagram 1 is a graphical
representation of a sound wave. The top half of the curve is where
pressure increases, the bottom half is the decreasing of the pressure.

Diagram 1 - The Soundwave

It has been determined that sound travels through air at sea level at
a speed of 1128 feet per second. The wavelength is the distance a
sound travels in one cycle. This distance can be determined by
dividing 1128 by frequency. With this formula we determine that a 20
Hz note is 56.4 feet long. On the other hand a 20kHz (20,000 Hz) is
.056 feet which is about 5/8 of an inch. Understanding this
relationship between distance and soundwaves will be important in
understanding how we hear, and therefore how to properly set up a
sound system.

Yet another description of the soundwave is phase. Phase refers to the
pressure change of the soundwave at a certain time and place. Once
again, refer to diagram 1, and see how the first part of the curve is
above the zero line. This is known as positive phase (increase of
pressure). When the curve is below the zero line, it is known as
negative phase (decrease of pressure). When Two or more waves combine
the combination can be referred to as being in phase or out of phase.
In phase means that the soundwaves are combining to form a wave that
is larger than either of the two. When the waves are out of phase,
meaning the phase of one wave is positive and the other is negative,
they will subtract from each other, therefore reducing the pressure
level. Soundwaves are constantly interacting with one another and
creating what is known as a complex wave. All musical instruments
create complex sound waves. The instruments combine waves to create
the sound that makes them unique.

Octaves and Harmonics

An octave is a doubling or halving of frequency. One octave up from
100 Hz is 200 Hz, where one octave down from 100 Hz is 50 Hz. A
harmonic is a doubling (2nd harmonic), tripling (3rd harmonic),
quadrupling (4th Harmonic... etc) of a fundamental frequency. Musical
instruments (with the exception of synthesizers) do not create pure
tones. The fundamental (main frequency) is combined with its harmonics
at various levels to create the sonic signature of that instrument.

**SPL**

Our ears have a tremendous ability to evaluate sounds that range from
very soft to very loud. The decibel (dB), named after Alexander Graham
Bell, is a method of describing acoustic pressure, without having to
deal with the billion-fold range of sound pressures to which our ears
are sensitive. A Bel is the difference in loudness produced by a ten
fold increase in power.

A decibel is 1/10th of a Bel. A doubling of sound pressure level (SPL)
is a 10 dB increase, where a halving of SPL is a

 

very nice find....ROE has so much great stuff

 

I just post these up when im bored out of my mind lol.


Very helpful info tho. Helps everyone to learn