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Solid · Speed of sound

Speed of sound in acrylic (PMMA)

Sound travels through acrylic (PMMA) at 2,730 metres per second (9,828 km/h, 6,107 mph) – 8.0 times faster than in air. Conditions: bulk.

2,730 m/sSpeed of sound
9,828 km/hKilometres per hour
7.96×Compared with air
0.366 sTime to travel 1 km

Why sound moves at this speed

Solids are very stiff, so sound usually travels fastest through them. Speed rises with stiffness (elastic modulus) and falls with density.

Travel times and wavelengths

Over 100 m, sound in acrylic (PMMA) takes 36.6 ms; over a mile, 590 ms. At concert pitch A4 (440 Hz) the wavelength is 6.20 m, and at 1 kHz it is 2.73 m.

Acoustic impedance

Acoustic impedance (density × speed) is about 3,221,400 rayl (3.22 MRayl). Because it is so different from air's ~413 rayl, about 99.95% of sound energy is reflected at an air–acrylic (PMMA) boundary – which is why airborne sound hardly enters water or walls, and why ultrasound scans need gel.

Speed of sound in other materials

MaterialSpeedvs. air
Carbon dioxide267 m/s0.78×
Argon323 m/s0.94×
Oxygen326 m/s0.95×
Air at 0 °C331 m/s0.97×
Air343 m/s1.00×
Nitrogen349 m/s1.02×
Methane446 m/s1.30×
Cork500 m/s1.46×
Helium1,007 m/s2.94×
Ethanol1,162 m/s3.39×
Hydrogen1,310 m/s3.82×
Olive oil1,430 m/s4.17×
Mercury1,450 m/s4.23×
Fat tissue1,450 m/s4.23×
Fresh water1,481 m/s4.32×
Seawater1,500 m/s4.37×
Soft tissue (average)1,540 m/s4.49×
Blood1,570 m/s4.58×
Muscle1,580 m/s4.61×
Glycerol1,904 m/s5.55×
Lead2,160 m/s6.30×
Polystyrene2,350 m/s6.85×
Nylon2,600 m/s7.58×
Acrylic (PMMA)2,730 m/s7.96×
Gold3,240 m/s9.45×
Pine (along the grain)3,300 m/s9.62×
Tin3,320 m/s9.68×
Concrete3,600 m/s10.50×
Silver3,650 m/s10.64×
Oak (along the grain)3,850 m/s11.22×
Ice3,880 m/s11.31×
Bone (cortical)4,080 m/s11.90×
Zinc4,210 m/s12.27×
Brass4,400 m/s12.83×
Copper4,760 m/s13.88×
Tungsten5,220 m/s15.22×
Nickel5,600 m/s16.33×
Glass (Pyrex)5,640 m/s16.44×
Stainless steel5,790 m/s16.88×
Steel5,960 m/s17.38×
Granite6,000 m/s17.49×
Titanium6,070 m/s17.70×
Aluminium6,320 m/s18.43×
Diamond12,000 m/s34.99×
Beryllium12,890 m/s37.58×

Typical longitudinal (bulk) sound speeds at about 20 °C unless stated. Real values vary with composition, temperature, pressure and wave type; thin rods carry slower 'bar' waves.

Frequently asked questions

What is the speed of sound in acrylic (PMMA)?

2,730 m/s (bulk).

How long does sound take to travel 1 km through acrylic (PMMA)?

About 0.366 seconds.

Is sound faster in acrylic (PMMA) than in air?

Yes – 2,730 m/s versus 343 m/s in air at 20 °C.