What is Speed of Sound?

The speed of sound is the speed at which sound waves travel through a medium (like air, water, or solid).

• In air (at 20°C): ~343 m/s

• In water: ~1480 m/s

• In steel: ~5000 m/s

Sound travels faster in denser materials because molecules transfer energy more quickly.

How Speed of Sound Affects Human Hearing

Even though speed itself doesn’t change what we hear directly, it strongly affects how we perceive sound:

1. Time Delay (Localization)

• Your brain detects sound direction based on arrival time difference between ears.

• Faster speed = smaller delay differences → harder to localize in some environments.

2. Echo & Reverberation

• Sound reflecting from surfaces returns after a delay.

• Example:

  • 34.3 m distance → ~0.1 sec delay

• This affects:

  • Speech clarity (STI)

  • Room acoustics design

3. Temperature & Air Conditions

• Speed of sound changes with temperature:

  • Hot air → faster sound

  • Cold air → slower sound

• This affects:

  • Outdoor PA systems

  • Long-distance sound propagation

4. Phase & Alignment (Important for AV Engineers)

• In sound systems:

  • Delay mismatch = phase cancellation

• Example:

  • Subwoofer + speaker misalignment → loss of bass impact

Types of Sound Waves (Based on Speed & Frequency)

1. Subsonic (Infrasound)

• Frequency: < 20 Hz

• Below human hearing

• Examples:

  • Earthquakes

  • Elephants' communication

  • Large subwoofers (you feel it more than hear it)

Used in:

• Seismic monitoring

• Military detection

2. Sonic (Audible Sound)

• Frequency: 20 Hz – 20 kHz

• Human hearing range

• Core of:

  • Music

  • Speech

  • AV systems

3. Supersonic

• Speed: > Mach 1 (faster than sound)

• Creates shock waves

• Produces sonic boom

Example: Fighter jets

4. Hypersonic

• Speed: > Mach 5

• Extreme heat due to air compression

• Air becomes plasma around object

Used in:

• Advanced missiles

• Space re-entry vehicles

This is where it gets really interesting

Mach Number (Key Concept)

• Mach = Object speed / Speed of sound

• Mach 1 = Speed of sound (~343 m/s)

• Mach 2 = Twice speed of sound

Speed of Sound in AV System Design (Practical View)

In AV, we don’t just “know” the speed of sound—we use it to calculate timing, alignment, and coverage.

Base reference:

• Speed of sound ≈ 343 m/s

• Rule of thumb:

  • 1 meter ≈ 2.9 ms delay

1. Speaker Delay Alignment (MOST IMPORTANT)

Problem: Sound from different speakers reaches the listener at different times.

Example:

• Main speaker → 10 m away

• Delay speaker → 20 m away

Time difference:

• 10 m ÷ 343 ≈ 29 ms

Solution:

• Add 29 ms delay to the closer speaker

2. Subwoofer Alignment (Phase Control)

Problem:

If sub + top speakers are not time-aligned:

• Bass cancels out ❌

• Weak punch ❌

Why?

Because of wave interference (same physics as shock waves in aerospace).

Fix:

• Measure distance difference

• Apply delay:

  • Even 1–5 ms matters!

Result:

• Tight, punchy bass

• Proper summation at crossover

3. Large Venue / Video Wall Audio Sync

Problem:

• Audio arrives late compared to video

• Lip-sync issue

Example:

• Viewer at 30 m distance:

  • 30 ÷ 343 ≈ 87 ms delay

Without correction:

• Video first, audio later → unnatural experience

Fix:

• Add audio delay in DSP

• Or delay video feed

Result:

• Perfect lip sync

4. Psychoacoustics (Human Perception)

Speed of sound affects how humans perceive direction & clarity:

Haas Effect (Precedence Effect)

• If delay < 35 ms:

  • Brain fuses sounds → perceived as one

 Used in:

• Front-fill speakers

• Delay towers

Echo Threshold

• 50–80 ms:

  • Heard as distinct echo

Important for:

• Auditoriums

• Houses of worship

5. Environmental Impact (Outdoor AV)

Speed changes with temperature:

• 0°C → ~331 m/s

• 20°C → ~343 m/s

Difference = delay error

Real Impact:

• Long-distance PA systems shift timing

• Line array tuning changes

6. Direct Link to Rocket Science (Same Physics!)