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.
Bass Trapping: VELOCITY BASED ABSORPTION
Velocity based absorbers are acoustic panels and bass traps based on porous, absorptive material. This includes but is not limited to: rock mineral wool, 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 GIK 242 Acoustic Panel, GIK 244 Bass Trap, GIK Monster Bass Trap, GIK Tri-Trap, GIK Soffit Trap, GIK Screen Panel, and GIK ArtPanel 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 GIK Soffit Trap and GIK Monster Bass Trap 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 GIK Scopus Tuned 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 T100 and T70 Scopus Tuned Traps are only four inches thick, yet absorb an impressive amount around 100 Hz and 70 Hz respectively. Our T40 Scopus Tuned Trap comes in at ten and a quarter inches thick, and will absorb all the way to 40 Hz and below. As the Scopus Tuned Traps are two foot in length and width, they are lightweight and can be mounted onto a wall surface easily.
Bass Trapping: UTILIZATION
Broadband absorbers can be used to gain more depth, a better stereo image, flutter-free reverb, and a clearer bass response free of resonances. Our GIK Room Kits offer great options at an attractive price, and feature our broadband line of treatments. As all rooms are different from each other, they all have different problems in the low end. Broadband treatment assures that all of our customers have sufficient means to deal with acoustic issues in their room. If there are any lingering problems in the low end after broadband treatments, pressure based devices will be a great addition to clear up muddiness, and will help to deliver true bass from your system.
Some also simply prefer a more “live” room – that is, more reverberant – and in this case, pressure based devices can be used to clear up bass problems in the room without absorbing mid and high frequencies. A more “live” room can deal with mid and high frequency issues with sparing use of broadband treatments, as well as the use of diffusors such as our GIK GridFusor/GIK VersiFusor, our GIK QRD Diffusor or our Q7d Diffusors to deliver healthy, diffuse reverb back to your listening position.
At GIK Acoustics, we are happy to be able to bring solutions for any room, meeting any of our customer’s needs and preferences at an unbeatable price. You can complete our Acoustic Advice form for personalized recommendations for your room!