What you should know about room acoustics
This section will give you a basic knowledge of Room Acoustics and key terminology to help you understand and communicate how our product line affects Room Acoustics.
Ideal room design and acoustic performance objectives:
The purpose and objective of any room that is primarily used for listening or recording is to experience or capture the acoustic energyin its purest form. That means experience sound that is free from distortion or interference. There is a complex interaction that occurs between the room, the loudspeaker, or performer, and listener that can cause "acoustic distortion". Acoustic distortion is as real and as important as electronic distortion. Acoustic distortions affect how the listener "feels and perceives" the sound. This can occur by altering the frequency response or timbre which also affects the imaging and spatial impression.
The perceived frequency response in a room is produced by the free-field loudspeaker response, the room dimensions, the acoustic coupling of the listener/loudspeaker to the modal pressure variations, the speaker-boundary interference between the direct sound and adjacent reflections, the internal contents of the room, the acoustical nature of the boundary surfaces and surface treatment and the hearing capability of the listener. Therefore, all rooms impart their own audio signature rather than having a flat frequency response.
Because of the particular size of a room and the placement of the loudspeakers or performers in the room, certain room modes are created. These "room modes" are comprised of standing waves of high and low pressure points in the room. It is because of these unwanted imbalances that you can move around in a room and hear a completely different timbre or range of frequencies. So what the listener hears can vary greatly from different locations in the room. By utilizing both absorption and diffusion devices effectively, these imbalances can be eliminated.
Sound absorbing materials remove acoustic energy and convert it to heat. In an effort to get rooms to have good acoustic characteristics designers and engineers typically "deaden" the rooms by absorbing the acoustical energy. The better alternative is to manage the acoustical energy to create a cleaner, livelier acoustic environment. Ideal acoustic environments have a comfortable "feel" to them with clear and clean sonic imagery. They react to the entire audio spectrum evenly and uniformly. Virtually, every room adds distortion to the sounds created. A properly constructed and treated room will not.
Acoustic distortions affect how we "feel and perceive" sound. These distortions alter the frequency response or timbre of a sound. They also have a negative affect on imaging and spatial impression. Frequency response or timbre refers to the perception of the harmonic content of the music. Imaging refers to the size of the sonic images of voices and instruments. (I.e. their apparent width, height and depth along with their apparent location in the stereo or surround field). Spatial impression is the feeling of the environment, the sense of immersion into the sonic event that listeners are experiencing.
Techniques to get a room to perform well:
- Room Geometry - The room geometry and setup in the room should be as symmetrical as possible. (There are preferred room ratios if one has the luxury to start from scratch, h -1, d -1.62, w -2.24) This provides good imagery. Rooms that are domed, round rooms, rooms with concave surfaces and cubical rooms are all very difficult to obtain good acoustic performance. This is because these types of shapes cause focal points and lines to form. This causes an unbalanced response in the room.
- 2. Speaker Placement - The speakers should be moved around in the generally designed position until the bass response is heard at its maximum. This is the most efficient coupling between the room and the speakers. The speakers should be turned on axis toward the listening position.
- Minimize reflection - Minimize the first order reflections from the walls, ceiling and floor between the loudspeakers and the listening position using absorption and diffusion. Consider the effects of furniture and objects in the room. To understand where to put diffusion and/or absorption is to locate the first order reflections as they relate to the primary listening position. These can easily be found by using a mirror placed at all of the boundary surfaces and see if you can see the loudspeakers.
This will be a first order reflection point.
Since most of the troublesome sound waves are quite large, an appreciably larger area than the mirror must be treated. As a general rule of thumb, the more diffusion that can be used as a treatment option the more "lively " and fuller the room will feel. Absorption can then be added to set the overall volume characteristics of the room and reverb time.
For listening and performing rooms a more diffuse field will provide a big listening environment. For critical mix rooms a more absorptive front end of the room will provide a more exacting positioning environment but not as pleasant of an overall experience of just listening. In the mix room diffusion will start on the sidewalls parallel to, or just slightly back of the listening position, and of course on the rear walls ceiling and corners.
- Control reflections - Place diffusion on rear wall, ceiling/wall corners and ceiling/wall/wall corners to control reflections. The amount of diffusion needed will vary, depending on room conditions and desired level of linearity, or flatness.
- Reduce low frequency problems - Backfill diffusion panels with sound absorbing material to control and reduce low frequency modal problems. If considerable low frequency problems persist membrane absorbers can be added behind the diffusion panels. A good way to tell if you solved the room's modal problems is to play a bass note in a nice slow glissando. If the room is working properly they decay will be uniform, if the room needs more diffusion the note will pulse or appear slightly louder and softer as it decays.
- Measure reverb time, Adjust - Measure the room reverb time and frequency response at several listening positions using an electronic room analyzing program. Readjust room acoustic treatments and speaker locations if necessary to achieve desired room performance. Add absorption as needed.