Understanding Sound Principles and Audio Amplifiers

Sound Fundamentals

Sound: A variation of air pressure, caused by a sound source, perceivable by the human ear.

Sound Features

• Speed of Propagation: How fast sound travels through a medium.
• Wavelength: The distance sound travels during one complete vibration cycle.
• Intensity: Determines the perceived loudness (scale of strong and weak sounds).

Acoustic Quantification

• Hearing Threshold: The minimum acoustic pressure level that causes an auditory sensation.
• Pain Threshold: The maximum sound pressure level the human ear can withstand without experiencing pain (typically around 120 dB).
• The Decibel (dB): A logarithmic unit measuring sound intensity, tailored to the non-linear perception of the human ear.

Sound Qualities

• Absorption & Reflection: When a sound wave hits an object, some energy is absorbed by the object, and the rest is reflected.
• Diffraction: The ability of sound waves to bend around obstacles.
• Refraction: The change in direction of sound waves as they pass from one medium to another.
• Echo & Reverberation: If reflected sound reaches the ear after 0.1 seconds from the original sound, it's perceived as an echo. If it arrives before 0.1 seconds, it contributes to reverberation.

Audio Amplifiers Explained

Amplifier: A crucial component in electro-acoustic systems. Amplifiers boost audio signals, enabling background music in large spaces and driving speakers with sufficient power. They must provide both voltage gain and power gain.

Amplifier Features

• Power Delivered: The continuous power an amplifier can deliver to the speaker output.
• Distortion: Undesired alteration of the audio signal. Two main types:
  • Linear (Frequency) Distortion: Difference in amplitude relationships between the input and output signals across frequencies.
  • Non-linear (Harmonic) Distortion: Introduction of harmonics (multiples of the original frequencies) not present in the input signal.

Input Characteristics

Amplifiers typically handle two main input level types:

• Low-Level Inputs: Typically 0.1 mV to 10 mV (e.g., microphones, phono cartridges/turntables).
• Line-Level Inputs: Typically 100 mV to 800 mV (e.g., CD players, tuners, video sources, DACs).

Output Characteristics

Amplifier outputs are commonly designed for:

• Constant Impedance Outputs: Designed to match specific speaker impedances (common values: 2, 4, 6, 8, 16 Ohms).
• Constant Voltage Outputs: Used in distributed audio systems (common values: 25V, 50V, 70V, 100V).

Amplifier Controls

• Volume Controls: Adjust the overall loudness. Can include input level trims and master volume controls for speaker output.
• Tone Controls: Allow adjustment of the amplifier's frequency response (e.g., bass and treble controls).