AUDIBLE FREQUENCY RANGE.
The range of frequencies humans can hear is limited. Runs roughly from 20 Hz to 20 kHz. These limits vary depending on the person and his age. Sharks can hear ultra-low frequency and ultrasonic dog.
This range makes it not necessary that the speakers can play beyond those frequencies, and will not be audible, but usually it reproduce more frequencies to maintain a certain linearity and does not degrade the sound to reach ends of the band. Outside the audible spectrum
: • Above would
ultrasound (sound waves of frequencies above 20 kHz).
• Below, infrasound (Sound waves below 20 Hz).
The audible spectrum can be subdivided according to the tones:
1. Bass (low frequencies, corresponding to the first 4 octaves, ie from 16 Hz to 256 Hz).
2. Midrange (midrange octaves for fifth, sixth and seventh, that is, 256 Hz to 2 kHz).
3. Treble (high frequencies, corresponding to the last three octaves, that is, from 2 kHz to just over 16 kHz).
In the West, we divide the audio spectrum into 11 sections called octaves.
The eighth term is taken from a musical scale. The eighth is the interval between two sounds that have a frequency equal to 1:2 and up to eight notes of the musical scale. For example: if we start with a note like OJ, the full octave would be: DO-RE-MI-FA-SOL-LA-SI-DO. If the first OJ was tried in the second will be 440 Hz to 880 Hz
The maximum value of each octave frequency is twice the previous.
1. The first and second octave (more serious tones, 16 - 64 Hz). Not all people are able to perceive, depends on the sensitivity of the ear of every person.
2. The third and fourth octave (bass means, 64 - 250 Hz)
3. The Fifth, Sixth and Seventh Octave (halftones, 250 Hz - 2,000 Hz). Contain the fundamental tone and the first harmonic Most sound sources.
4. The eighth octave (treble, 2,000 Hz - 4,000 Hz). Includes the margin by which the human ear has greater sensitivity.
5. The ninth and eighteenth (high frequency tones, 4,000 to 16,000 Hz).
6. The eleventh octave (the higher tones of the audible spectrum above 16,000 Hz). Not all people are able to perceive, depends on the sensitivity of the ear of every person.
The octave can be divided into smaller values, for example, the middle eight (divide each octave into two) and the third octave (each interval of the octave is divided into three parts.)
addition, each octave is composed of 12 semitones determines what is known as high harmonic musical or height and determine the chromatic scale called sound. SOUND PRESSURE
or acoustic sound pressure is the product of the sound propagation. Particles traveling in the air taking advantage of the wave motion of sound waves generated by an alternating variation in static air pressure (small variations in atmospheric pressure. The atmospheric pressure is the pressure of air above the Earth's surface). The reason for these atmospheric pressure variations that occur areas where these particles are concentrated (concentration areas) and other areas are less saturated areas (rarefaction). Areas with the highest concentration of molecules have higher density and lower concentration areas have a lower density. When these waves are on their way to the ear pressure exerted on it is not equal for all wavelengths.
Thus the sound pressure is defined as the instantaneous pressure difference (when the sound wave reaches the ear) and static air pressure.
tolerable sound pressure is very small compared with atmospheric pressure. Sound pressure levels a thousand times less than atmospheric pressure will cause us pain and even risk hearing loss hearing.
SOUND POWER Sound power is the amount of energy (power) radiated by a particular source in the form of waves per unit time.
The sound power is determined by the amplitude of the wave itself, since the larger the wave amplitude, the greater the amount of energy (acoustic power) it generates.
The sound power is an intrinsic value of the source and not depend on the office where it is. It's like a light bulb, can have 100 w 100 w will always put it into our room or put in a huge ship its power is always the same. With the acoustic power occurs at the value does not change from being in a room a reverberant or dry. Unlike sound pressure if it varies according to several characteristics of the office where it is the source, distance etc.
loudness of perceived sound intensity, or property that causes it to capture as strong or as weak, is related to the intensity of the corresponding sound wave, also called sound pressure. The acoustic intensity is a quantity that gives an idea of \u200b\u200bthe amount of energy that is flowing through the middle as a result of wave propagation.
is defined as the energy passing through a unit area per second ready perpendicular to the direction of propagation. Equivalent to a power per unit area and expressed in W/m2. The intensity of a sound wave is proportional to the square of the frequency and the square of its amplitude and decreases with distance from the focus. SPEED OF SOUND
speed of sound in air
In this case the physical properties of air, pressure and humidity for example, are factors that affect speed.
For example, the higher the air temperature the greater the speed of propagation. The speed of sound in air increases 0.6 m / s for every 1 º C increase in temperature.
An approximate speed (in meters / second) can be calculated by the following empirical formula:
where the temperature in degrees Celsius (-273 Kelvin);
.
A more accurate expression, generally referred to as adiabatic sound speed is given by the following formula: Where
• R is the gas constant,
• m is the average molecular weight of air (R / m = 287 J / kgK for air),
• κ is the ratio of specific heats (κ = cp / cv being equal to 1.4 for air), and
• T is the absolute temperature in Kelvin.
In a standard atmosphere is considered that T is 293.15 K, giving a value of 343 m / s or 1,235 kilometers per hour. This formula means that sound transmission is lossless power in the middle, very close approximation to reality.
speed of sound in solids
In solids the speed of sound is given by:
where E is the Young's modulus and ρ is density. In this way we can calculate the speed of sound for steel is about 5,146 m / s.
speed of sound in water
The speed of sound in water is of interest to map the ocean floor. In saltwater, sound travels at approximately 1,500 m / s and in freshwater and 1.435 m / s. These speeds will vary due to pressure, depth, temperature, salinity and other factors.
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