Timing is Everything
One of the most basic, yet often overlooked problem encountered when setting up a studio is locating and killing early reflections that cloud up your stereo imaging and create uneven frequency response problems. We are all aware that the sound we hear from our speakers is a blend of the direct sound from the monitors along with the sound that is reflected by the room and its contents. These reflections come from nearby walls and ceiling and also from the desk or equipment between the monitors and ourselves. If we don’t tame our early reflections, how can we accurately judge the ambience and imaging of our recorded sound? In typical live performance venue, a reasonable time delay difference between the direct sound from a performer and the first reflected sound from a wall or ceiling surface is about 20 milliseconds. Therefore, in order to accurately hear the recorded audio and it’s captured initial reflections, we need to eliminate or greatly reduce the level of any reflections in our studio which occur in the first 20 ms of a sound coming out of our speakers.
Studio design with this reflection free zone in mind is an implementation of a well-known studio design strategy called LEDE™ or live-end-dead-end design. Our goal is to create a reflection-free-zone in the front part of the room where we sit. The rear of the room produces late reflections that create a natural sense of space and while we don’t want that rear space to be out of control, the front space is our primary target for treatment. A few listening tests have been created to check your listening area for stereo image accuracy, including the LEDR™ test from Doug Jones and the Gold Stereo Set-up Disclistening tests from David Chesky of Chesky Records.
Hunting for the Reflections
Now we need to find these first reflection points. The simplest way to find the first reflections is to use a small mirror and the help of an assistant. Sit in the listening position while your assistant holds the mirror flat against a wall and slides it around until a reflection of the speaker can be seen in the mirror. Mark the wall with a piece of tape where the reflection occurred.
Repeat this on the opposite wall, ceiling and desk surfaces. We want to kill any first reflections that would reach your ear in 20 milliseconds or less. In practice, if your rear wall is at least 11 feet (3.5 meters) from your listening position, you don’t need to kill the reflections from the back wall. In most home studios and small production rooms, the ceiling and side walls are within 10 feet of your listening position, so those surfaces are the ones we want to treat. Keep in mind that we want to create a reasonably large sweet spot so that more than one person can sit in the listening position, so we want to kill reflections off a larger area than the exact point that we marked with the mirror.
Killing the Reflections
In professional studios, control room walls are angled in such a way that first reflections are directed away from the listening position, but most project studios are rectangular rooms, so sound absorbing acoustic panels must be placed at all the points of first reflection. These lightweight panels, which are hung like pictures, are usually made of 1” or 2” fiberglass insulation or mineral wool and are covered in decorative fabric. This article won’t get into details of the acoustic properties of these panels, but suffice to say that these panels, when mounted on or very close to a wall, will absorb most frequencies from about 800 Hz and up. These frequencies are the ones we need to control in order to maintain our stereo image and high frequency definition.
Many companies sell ready made, lightweight acoustic panels in sizes from 12” x 12” up to 2 feet by 4 feet which may be easily hung on a wall. These panels can be purchased from local music stores or may be built as an easy DIY project. Along with acoustic panels on the walls, an acoustic cloud may be hung above the listening position to reduce reflections from the ceiling.
Reflections from your desktop or console surface may be impractical to reduce, but you can listen for their effects simply by playing some familiar music and placing a blanket or quilt over your desk surface. Listen for changes in stereo imaging or high frequency response when the blanket is placed and then removed. Sometimes, simply moving your speakers further away from the listening position or raising their height may change the reflection angle enough to eliminate much of the desk reflections.
Creating a reflection free zone, along with proper speaker positioning will go a long way to creating an accurate listening environment for audio production and enjoyment. Once you have done your due diligence in these acoustic areas, applying correction from Sonarworks Reference 4 will further improve the sound of your monitors and perfect your listening space.