Bass trap or acoustic panel? When you need which

If you are looking at acoustic panels, sooner or later you will come across bass traps. They sound serious and studio-like, so it is easy to assume you cannot do without them. The truth is simpler: in most homes panels are enough, and bass traps solve one specific problem. This guide will help you tell whether you have it.

Two different problems in a room

Reverberation is sound that keeps circling the room for a moment after the source stops, bouncing off the walls. You hear it in speech: voices sound as if they were in a bathroom, and conversation at the table turns into a din. It is mostly mid and high frequencies, and 5 and 10 cm panels deal with them very well.

Booming bass is a different thing altogether. Low sounds have wavelengths of several metres – a 100 Hz wave is about 3.4 m long. In a room they bounce between parallel walls and form what are called standing waves, or room modes. In some places the bass adds up and booms; in others it almost disappears. Some bass notes sound loud and long, others weak. You hear this mostly in music, films and recordings of low voices, and much less in ordinary conversation.

What a bass trap is

A bass trap is simply a very thick absorber placed where the bass is strongest. Ours has 15 cm of stone wool in three layers – half as much again as a 10 cm panel. It has the same frame, fabric and mounting options as our panels, so it looks like them, only deeper.

Thickness matters because a porous material absorbs best where the air moves fastest – a quarter of a wavelength away from the wall. For high frequencies that is a few centimetres; for 100 Hz it is more than 80 cm. No panel is that thick, but every extra centimetre of wool, and every centimetre of air gap behind it, moves the absorption lower. That is why a 15 cm trap, spaced off the wall or standing in a corner, reaches noticeably lower than a panel.

Why corners

In a rectangular room every standing wave has its pressure maximum at the walls, and the strongest in the corners, where two or three surfaces meet. An absorber works most efficiently there, because it sits where the bass has the most energy.

The best spots are vertical corners, floor to ceiling – especially those behind the speakers and behind where you sit. A 60 × 180 cm trap can stand in such a corner on feet. Smaller sizes can hang in a corner or where the wall meets the ceiling. Standing diagonally across a corner, a trap has a large pocket of air behind it, which helps further with the lowest notes.

When panels are enough

You do not need bass traps if what you want is:

• a clear voice on video calls and in a home office,
• calmer conversation in the living room and at the table,
• less echo in an empty, newly furnished flat,
• a more pleasant sound in a bedroom or a child's room.

In these rooms the problem is reverberation in the speech range, and 5 cm panels – or 10 cm if you want to reach a little lower – solve it completely. How many you need is covered in how many acoustic panels do I need.

When to add bass traps

Bass traps make sense when:

• you listen to music on good speakers or with a subwoofer and the bass sounds uneven – some notes boom, others are barely there,
• the bass sounds completely different in different parts of the room, for example booming on the sofa and vanishing half a metre away,
• you are setting up a home cinema and want effects to have shape rather than blur into a hum,
• you record a low voice or instruments and the recordings sound muddy despite the panels,
• the room is small and has a lot of parallel, smooth walls.

A simple test: play a track with a clear, steady bass line and walk around the room. If the loudness of the bass changes noticeably and some notes ring on longer than others, bass traps will help.

How many traps and where to start

Start with two traps in the corners behind the speakers or the TV. That usually makes the biggest difference. Put the next two in the rear corners, behind the listening position. In a small cinema or listening room, all four vertical corners is a good target. Combine the traps with panels at the first reflection points – the panels sharpen dialogue and stereo imaging, the traps tidy up the bass.

Choose the size to suit the room: 60 × 180 cm uses the full height of a corner, 60 × 120 cm fits above furniture, and 60 × 60 cm works where the wall meets the ceiling. You will find every size and price on the bass traps page.

What a bass trap will not do

To be honest: the lowest bass, below roughly 80 Hz, has waves so long that no absorber of sensible thickness will remove it completely. A 15 cm trap clearly smooths the bass and shortens how long it rings, but strong resonances in a small room may remain audible.

Two things help for free, and are worth doing before you buy or alongside:

• where you sit – avoid the exact middle of the room and the spot right against the back wall, where room modes are strongest; moving the sofa by 30–50 cm is often enough,
• where the speakers and subwoofer go – pulling the speakers away from the wall and moving the subwoofer can change the bass more than any absorber.

If the bass booms badly or you do not know where to start, send us photos and the dimensions of your room – with our free advice we will suggest how many traps and panels you need and where to put them.

Summary

• 5–10 cm panel – shortens reverberation in the speech range; enough for an office, living room, bedroom and most homes.
• 15 cm bass trap – absorbs lower, goes in the corners; for music, home cinema and recording when the bass booms or is uneven.
• Best together – panels at the first reflection points, traps in the corners.