5 or 10 cm? Choosing the thickness of an acoustic panel

Stillform panels come in two thicknesses: 5 and 10 cm. From the front they look the same; they differ in depth and in how far down the frequency range they reach. This guide explains in plain terms what that means and when each one makes sense.

Frequencies in brief

Sound is air vibrating at different frequencies, measured in hertz (Hz). Roughly:

• low frequencies, from 20 to about 250 Hz – bass, boom, a deep male voice,
• mid frequencies, from about 250 to 2000 Hz – most of the energy of speech, which decides how clear it is,
• high frequencies, above 2000 Hz – sibilants, rustles, the sparkle of instruments.

The lower the sound, the longer its wave. A 125 Hz wave is about 2.7 m long; a 1000 Hz wave about 34 cm. That’s why low frequencies are so hard to absorb.

Why thickness matters

A rock wool panel absorbs sound when air particles move through its fibres. Right next to a wall the air hardly moves; it moves fastest a quarter of a wavelength away from the wall. A thicker panel reaches further out from the wall, so it also catches longer waves – lower sounds.

Below are the indicative absorption coefficients for both thicknesses. A value of 1 means the panel absorbs almost all of the sound energy in that band.

The chart shows that from about 1000 Hz upwards both versions absorb practically the same. The difference starts below 500 Hz and is greatest in the lowest band, at 125 Hz, where a 10 cm panel absorbs more than twice as much as a 5 cm one. That’s where the choice is really made.

When 5 cm is enough

A 5 cm panel absorbs almost all the energy from about 500 Hz upwards – the range that holds most of the energy of speech. That’s enough when conversation and clarity are what matter:

• a home office and video calls,
• a living room, dining room or bedroom,
• a child’s room, a study or a meeting room.

In these rooms a 5 cm panel gives almost the same result as a 10 cm one, and it’s slimmer and lighter.

When to choose 10 cm

A 10 cm panel has two layers of wool and does noticeably better with lower frequencies, in the 125–250 Hz range. Choose it when:

• you record voice, especially a low voice close to the microphone,
• you’re setting up a home cinema or play music loud,
• the room is noticeably boomy, or the panel will hang in a corner or on a back wall,
• you want to cover less wall and still get a similar result.

The air gap

The panel hangs on a French cleat, so there are a few centimetres of air between it and the wall. Sound that has passed through the wool reflects off the wall and goes back through it a second time. That makes the panel behave at low frequencies a little as if it were thicker than it is. It applies to both versions.

Mixing thicknesses

You don’t have to choose one thickness for the whole room. A combination often works well: 10 cm where the most low-frequency energy builds up – on the back wall, near corners, behind you at the microphone – and 5 cm at the first reflection points on the side walls.

How it sounds in practice

In a room with 5 cm panels, voices become noticeably closer and cleaner, and the reverberation shorter. If the room tends to boom, though – with a deep male voice or bass-heavy music, say – some of that low end remains. 10 cm panels even out the sound over a wider range: a low voice stops sounding thicker than it should, and bass notes are tighter.

Depth, weight and looks

A 10 cm panel is twice as thick and heavier than a 5 cm panel of the same size, although both hang on the same French cleat. From the front they look identical; from the side, the 10 cm panel clearly stands further off the wall. In a hallway, or anywhere people brush past, 5 cm is more practical. In a home cinema or recording room, the depth rarely matters.

Examples

• Home office, 11 m², video calls: 5 cm.
• Open-plan living room with kitchen, conversation and TV: 5 cm, perhaps 10 cm on the wall behind the sofa.
• Voice-over corner or podcast: 10 cm.
• Home cinema: 10 cm, at least on the back wall and behind the speakers.
• Rehearsal or practice room: 10 cm.

A word on price

A 10 cm panel uses more material, so it costs more than a 5 cm panel of the same size. You can compare both in the configurator by changing only the thickness. If you’re unsure, it’s often better to spend the budget on more area of 5 cm panels in the right places than on a few 10 cm panels in random ones.

Common questions about thickness

Are two 5 cm panels stacked together the same as one 10 cm panel? Acoustically they’re close, but the panels are built into frames and covered in fabric, so they aren’t made to be combined like that. If you need absorption lower down, order 10 cm from the start.

Will a 10 cm panel make the room sound too dead? Not because of its thickness. How dead a room sounds depends mainly on the total panel area. A thicker panel simply absorbs a wider band, so the sound is more even.

Do I need 10 cm in a bedroom? Usually not. Bedrooms have plenty of fabric – the bed, bedding, curtains – and reverberation is rarely a problem. If you want a few panels behind the bed as a decorative feature, 5 cm is plenty.

In short

For conversation, work and everyday life in a living room, 5 cm is enough – it absorbs almost all the energy of speech and is slimmer and lighter. For voice recording, home cinemas, music and rooms that boom, choose 10 cm, which reaches further down. You can also combine both in one room: thicker panels where low frequencies build up, thinner ones at the first reflection points. If you’re still unsure, run your room through the calculator and compare the prices of both thicknesses in the configurator.