A vast majority of people like to listen to some form of audio. Be it in cars, homes, or theaters, audio is prevalent, and its applications are growing with the increasing use of portable devices. In all audio systems, important factors for a portable audio device are its design, size, cost, and quality. But listeners judge the performance of an audio device primarily on the basis of its capability to recreate the necessary audio frequencies.
The audio industry commonly refers to the frequency range that humans can hear and perceive as 20 Hz to 20,000 Hz. Although the average human can distinguish far less than this range, the ability depends on the age and health of the individual. For instance, with age, this range inevitably shrinks, with the loss being more pronounced at the higher frequencies.
Experts divide the perceptible audio spectrum into seven subsets. Starting with the sub-bass subset whose frequency ranges from 16 to 6 Hz, is the primary low range of musical instruments. Then comes the bass frequencies ranging from 60 to 250 Hz, and this is the normal speaking vocal range. Next is the lower mid-range of brass and wood instruments covering the range of 250 to 500 Hz. Mid-range frequencies follow next, covering 500 Hz to 2 kHz, where the higher end of fundamental frequencies of most musical instruments lies. The next range is the higher mid-range, covering 2 to 4 kHz, where the harmonics of most instruments are present. The next range is the presence ranging from 4 to 6 kHz, and this is where the harmonics of string instruments are. The last subset is the brilliance, ranging from 6 to 20 kHz, where the most whiles and whistles are present, and where the harmonics of most percussion instruments lie.
For visualizing and quantifying audio frequencies generate by most audio devices and electronic components, experts rely on frequency response graphs. These graphs are a plot of the sound pressure level at a specified distance plotted against frequency. For instance, a buzzer puts out an audible tone, which features a narrow frequency range on the response graph. On the other hand, audio speakers feature a wide frequency range coverage, as they must recreate sound and voice more faithfully.
A typical frequency response graph for electronic components generating sound depicts the sound pressure level or loudness on its Y-axis on a logarithmic scale, while the X-axis represents frequencies on a logarithmic scale. For electronic devices that sense audio input, such as microphones, the frequency response graph shows sensitivity as sound pressure level on the Y-axis on a logarithmic scale. Most of the frequency response graphs represent a constant power input to the device under measurement.
The frequency response graph is an important document for selecting electronic components for a specific application. For instance, it can differentiate whether a particular speaker will be a good performer for the entire audio frequency range, or it will be suitable for bass frequencies alone. Similarly, the frequency response graph for a microphone will characterize it as suitable for a concert or for instrumentation.