Concert speakers turn electrical signals into moving air, creating pressure waves that your ears and body can detect. A big stage system uses different speakers for different frequency ranges so the music stays loud, clear, and powerful. Subwoofers handle the lowest notes, midrange drivers carry much of the voice and instruments, and tweeters reproduce high details like cymbals.
Understanding the physics helps explain why concerts can sound huge without becoming a muddy wall of noise.
A speaker cone moves back and forth, compressing and rarefying the air to match the waveform of the music. Low frequencies require larger cone motion and move more air, which is why bass can be felt in your chest as vibrations. Line array speakers stack many drivers vertically so their waves combine in a controlled pattern that projects sound far into the crowd while reducing spill upward and downward.
Sound level is measured in decibels on a logarithmic scale, so small number changes can mean large changes in acoustic intensity.
Key Facts
- Sound speed in air at room temperature is about v = 343 m/s.
- Wave relationship: v = fλ, where v is wave speed, f is frequency, and λ is wavelength.
- Subwoofer range is roughly 20 Hz to 80 Hz, producing long wavelengths and strong physical vibration.
- Midrange speakers often cover about 80 Hz to 2,000 Hz, including much of vocals, guitars, and keyboards.
- Tweeters often cover about 2,000 Hz to 20,000 Hz, adding brightness, detail, and sharp transients.
- Sound level in decibels: β = 10 log10(I/I0), so a 10 dB increase means 10 times the sound intensity.
Vocabulary
- Sound pressure wave
- A repeating pattern of air compressions and rarefactions that carries sound energy away from a vibrating source.
- Frequency
- The number of wave cycles per second, measured in hertz, that determines the pitch of a sound.
- Wavelength
- The distance between matching points on a wave, such as one compression to the next compression.
- Line array
- A vertical stack of speakers designed so their sound waves combine to control the direction and coverage of the sound.
- Decibel
- A logarithmic unit used to compare sound intensity or sound pressure level.
Common Mistakes to Avoid
- Treating decibels as a normal linear scale is wrong because decibels are logarithmic. A 10 dB increase represents 10 times the intensity, not 10 extra units of sound.
- Assuming bigger speakers always mean higher pitch is wrong because large drivers are usually better for low frequencies. Bass requires moving a large volume of air, while high frequencies use smaller, lighter drivers.
- Forgetting to use consistent units in v = fλ is wrong because frequency must be in hertz and wavelength in meters to get speed in meters per second. Mixing centimeters and meters gives incorrect wavelengths or speeds.
- Thinking a line array only makes sound louder is incomplete because its main advantage is directional control. The spacing and timing of the drivers help steer sound toward the audience and reduce unwanted reflections.
Practice Questions
- 1 A subwoofer plays a 50 Hz bass note. Using v = 343 m/s, calculate the wavelength of the sound in air.
- 2 A concert sound level increases from 90 dB to 100 dB. By what factor does the sound intensity increase?
- 3 Explain why a concert system uses separate subwoofers, midrange drivers, and tweeters instead of one speaker driver for all sounds.