Understanding Different Bass Trapping | GIK Acoustics

Bass Trapping: The Low-Down on Low Frequency Absorbers

by Alexander Reynolds

There are many types of different bass trapping and low frequency treatments available for recording studios, control rooms, home theaters, and listening rooms alike. Whether you're looking at tuned traps, resonators, membrane absorbers, or porous absorption – most can be broken down into two categories: velocity based absorbers, and pressure based absorbers. The terms "velocity" and "pressure" don't describe their inner workings, but instead describe their optimum placement in a room. Pressure based treatments are most effective at areas of high sound pressure in the room, whereas velocity based treatments are most effective at areas of high particle velocity. This article is written to give you an idea on the differences of bass trapping, and how to use them to create the ultimate listening space catered to your preferences utilizing both.

Velocity Based Absorption

Velocity based absorbers are acoustic panels and bass traps based on porous, absorptive material. This includes but is not limited to: fiberglass, mineral wool, acoustic foam, and similar materials. For this reason, velocity based absorbers are commonly referred to as porous absorbers. Velocity based absorbers work, in short, by converting sound energy into heat, and then by absorbing and dissipating the heat. Porous absorbers typically absorb throughout most of the frequency spectrum, depending on their thickness. Even thin porous absorbers absorb quite even down to low-mid and bass frequencies. This wide absorbing nature of velocity based absorbers gives them their other name: broadband absorbers. So, whether someone is talking about broadband absorption, porous absorption, or velocity based absorption – they are referring to the same type of absorption.

Most of our product line consists of velocity based absorbers; the FlexRange® Acoustic Panel, FlexRange® Bass Trap Panel, TriTrap™ Corner Bass Trap, Soffit Corner Bass Trap, Screen Panel, and Acoustic Art Panel are all velocity based devices. Porous absorbers are commonly suggested as the "go-to" absorber for studios, home theaters, control rooms, and listening rooms alike for a multitude of reasons. Their broadband nature makes them suitable for any environment, and suitable for dealing with most acoustic problems. Porous absorbers can be used to combat room modes, standing waves, SBIR, comb-filter effects, flutter echo, as well as controlling reverb and stereo imaging in a room. Moreover, porous absorbers are relatively lightweight, so they can be placed easily in a room in many configurations. Though almost any useful thickness with porous absorbers will absorb high frequencies, thickness is necessary to reach lower down in frequency. This is why products like our Soffit Corner Bass Trap and FlexRange® Bass Trap Panel absorb low frequencies so well.

Bass Trapping: PRESSURE BASED ABSORPTION

Pressure based devices were created to deal with low frequency issues without using large amounts of floor space. There are many different types of pressure based devices, such as sealed panel absorbers, Helmholtz resonators, and membrane absorbers, among others. Pressure-based bass trapping is also commonly called tuned traps, sealed traps, resonant absorbers, or narrowband absorbers. Most pressure based absorbers are tuned to certain frequencies, typically in the 100 Hz and lower range. Design parameters, such as depth, mass, size of air cavities, type of dampening, sealing, and so on dictate the resonant frequency of the device. The panels strongly vibrate at their resonant frequency, which is then dampened internally. This means we can nail down very specific frequencies without dampening the rest of the frequency spectrum. In turn, we can dampen a resonance at 40 Hz easily, without sacrificing large amounts of floor real estate.

Tuned traps are narrowband, meaning that they work very efficiently over a small area in the frequency spectrum, in contrast to broadband traps that absorb throughout most of the whole spectrum. This allows bass trapping to tackle certain low frequency issues without needing to change around current treatment plans, and is why in most cases, pressure based absorbers are used to compliment velocity based absorption. Placement is also quite easy with pressure based devices, as they are designed to work in areas of high pressure in a room. All wall surfaces, including corners are areas of high pressure.

Pressure based absorbers also must be very carefully designed and crafted. If they are not built precisely, they can resonate at an unwanted frequency, and if not dampened or sealed correctly, can introduce bass resonance into the room, instead of absorbing it; or just fail altogether. Luckily, with the introduction of our Scopus Bass Traps, you won't have to worry about getting the numbers right – you instead get the pleasure of listening in a room with an accurate representation of the low end. We have designed three different tunings for our Scopus traps, covering the sub frequency spectrum. Our 100hz and 70hz Scopus Bass Traps are only four inches thick, yet absorb an impressive amount around 100 Hz and 70 Hz respectively. Our 40hz Scopus Bass Trap comes in at ten and a quarter inches thick, and will absorb all the way to 40 Hz and below. As the Scopus Bass Traps are two foot in length and width, they are lightweight and can be mounted onto a wall surface easily.

Bass Trapping: UTILIZATION