If you like bass, you need a:

Sub-Bass Quadratic Ramp Diffuser

  • Break up reflections

  • Reduce flutter + slapback

  • Avoid deadening the room

  • Reduce low energy buildup

What is a Diffuser?

An acoustic diffuser disperses sound reflections to improve a room’s acoustic qualities. Instead of returning as an echo, sound hitting a diffuser is reflected across a wide angled field over different time intervals, which helps reduce resonances and colouration. There are several types of diffuser, but this article focuses on a design known as a quadratic ramp diffuser, which is made up of parallel layers of material, arranged to form grooves or “wells” at highly specific variations in depth. The range of depth alters the phase of the reflected sound, which spreads and disperses sonic energy.

Big Bad Bass

Sound reflects. It bounces off walls, ceilings - basically everything in a room. Reflections cause acoustic problems. They change how things sound, making music reproduction less accurate, adding noise to and distorting microphone recordings and causing room modes.

To control reflections, we treat rooms with acoustic devices that absorb and/or disperse sound. The devices tend to be proportionate in size to the wavelength of the sound they deal with. Higher pitched sounds have shorter wavelengths, so the acoustic treatment is accordingly thin. Bass, on the other hand, is much harder to handle. The western scale note A2 has a frequency of 110 Hz, which means it has a wavelength of 3.12 metres.

How DId we Make One?

Low-end problems are some of the hardest to fix in any room, and ours was no exception — measurements revealed clear frequency build-ups in the rear ceiling corner, a classic spot for room modes to gather and muddy the bass. Rather than buy an off-the-shelf solution, we decided to design and build our own quadratic residue diffuser (QRD) for that exact corner.

The design followed the maths closely. A QRD works by creating reflective wells of carefully calculated depths, based on quadratic residue sequences, so that reflected sound is scattered evenly across time and angle rather than bouncing straight back. We kept the well bottoms flat — true to the QRD principle — since any curvature would smear the phase relationships the design depends on.

For our space, we built the diffuser as a ramp at a 20° angle with 50 cm deep wells, working out the geometry with simple trigonometry to get a horizontal run of roughly 1.37 metres — long enough to do its job, short enough to fit our 3.6 m room without dominating it. A small air gap behind the panel, lined with rockwool, adds extra absorption in the low-mids where the diffuser itself can't help.

The result is a corner that no longer fights us — reflections are scattered rather than slamming straight back at the listening position, and low-end decisions made in this room now hold up when they're played back on a proper club rig.