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● Acoustic Treatment
A completely bare, empty room will have undesirable acoustics. It will be very "echo-ey," with uneven bass. Acoustic room treatment is the application of various problem-solving materials attached to the room's surfaces and/or placed within the room. Some of these acoustic treatments may be specially constructed by your contractor, some may be bought premade, and some may be regular home furnishing chosen and placed for their acoustic properties.
Acoustic treatments affect the sound at any particular room boundary in one of three ways. They can:
- Absorb sound. Sound striking the surface is absorbed and not retransmitted to the room.
- Diffuse sound. Sound striking the surface bounces back into the room in all directions.
- Reflect sound. Sound striking the surface bounces back like a billiard ball striking a bumper (or a light ray shining on a mirror).
How a particular acoustic treatment affects sound will also vary with the audio frequencies involved (i.e. the pitches of the notes). For example, a thin acoustic treatment such as lightweight draperies may abort high frequencies, yet may allow midrange frequencies to be reflected by the wall behind the draperies.
Bass notes have much longer wavelengths. As the wavelength approaches the dimensions of the room, resonance becomes the dominate physical phenomenon governing the room's bass acoustics. Much larger, thicker absorption materials are needed to treat bass than are needed for high frequencies. The corners of the room will build up the most bass energy. In a rectangular "shoebox" shaped room, there will be eight tri-corners (four at the floor, four at the ceiling) where you will find the most bass energy building up under steady-state conditions. So it naturally follows that this is where you would usually first think to treat the room with bass trapping.
Another aspect of analyzing a room's acoustics is calculating the room's resonant frequencies. As we discussed above under Room Dimensions, we usually recommend that, when building a new room, you limit the shape of the room to a simple rectangular prism (shoebox-like shape). With this shape room, it is easier to predict the axial, tangential, and oblique modes than if the room is odd-shaped. However, if you already have an irregularly-shaped room, we can measure it's resonances with sophisticated computerized testing equipment such as a TEF (time, energy, frequency), MATT, or MLSSA ("Melissa") tests.
Above the bass region, room reverberation dominates the room's acoustics. An overly reverberant room (known as a "live" room) has unpleasant acoustics. It will be very hard to hear sounds distinctly. On the flip side, a completely non-reverberant ("dead") room, will cause an unpleasant "pressure on the ears" feeling, and will hinder the performance of a high quality audio system.
One particular type of reverberation is called "slap echo." If you clap your hands once sharply in a room with parallel bare walls, you will hear slap echo — a series of rapid distinct echoes. Because slap echo degrades music reproduction, it is one of the things that we seek to minimize when treating a room acoustically.
Tip: Most people are highly sensitive to the reverberation characteristics of a room. Even if you don't listen to music in a particular room, you may which to consider room acoustics in its construction. For example, a large, overly-live living room, family room, or dining room will not invite relaxed conversation.
Any listening room, whether for live music or reproduced sound, can be substantially improved with a comprehensive acoustic treatment design. We have used all sorts of approaches, many of which can be retrofitted to an existing room. So where do you start?
One method that we have used over and over with great success is to utilize ASC Tube Traps. Alan Goodwin was an early adopter of ASC Tube Traps way back in 1986. He has spent many man-days working with ASC tuning a number of rooms.
Art Noxon, the President and founder of Acoustic Sciences Corporation (ASC), has given a great deal of thought to how to design and manufacture modular acoustic treatments that can be fitted into a wide variety of room shapes. ASC has introduced many products which are used in both recording studios and in home listening environments around the world. There are a multitude of possibilities and combinations. We often use the following approach when we treat a room with ASC products:
- With a typical rectangular room, we usually start by treating the corners behind the speaker with bass traps. The mids and highs are also somewhat improved by treating these corners.
- Next, we treat the specular reflection points at the side walls. With a stereo (2-channel) system, there are two specular reflection points on each side wall.
- Depending upon the room's furnishing and window treatments, we would reduce the room's slap echo, particularly at the listening position and around the speakers.
- Returning to bass trapping, we would treat the corners behind the listening position, possibly with the same size bass traps as the corners behind the speakers, but possibly with a different size.
- Next, we may treat the middle of the wall behind the speakers to improve the imaging of most speaker systems.
- Last, we might address problems on the wall behind the listener and ceiling.
The methodology can be different however if there are particular acoustic anomalies that need to be specifically addressed first.
There are many other methods and approaches too. Another involves RPG. Back in 1983 Alan Goodwin attended a 3-day Syn-Aud-Con conference on recording studio acoustical design. The seminar included discussions on the acoustics of both the studio and of the control room. It was there that he first met Peter D'Antonio, founder and President of RPG. Peter has done considerable work on the acoustic design of recording studios. He created the famous RPG Diffuser, in recent years has added many other new products.
We have found that only through the experience of building and treating many, many rooms have we advanced our understanding of room acoustics. We have tried different approaches and refinements in the shape of the room, the construction techniques, and the interior acoustic treatment. Back in the early 80's, most of the high-end community was not particularly knowledgeable about room acoustics. Fortunately, recording studio designers were more aware of acoustic design techniques. So Alan Goodwin decided that the best way to learn about what was being done was to spend three full days in a room with most of the top designers in the world absorbing the concepts that they had been working on for many years.
Even though many people have expended a great deal of effort in designing and building studios, a surprising number of studio simply don't sound very good. There are several basic reasons why:
- Not everyone who designs recording studios does an equally good job.
- Some recording studios are designed to look good and function ergonomically, but not necessarily sound particularly good.
- Unfortunately even today in the new millenium, recording studios don't usually have playback systems in the control rooms which are as sonically neutral and linear as the best high end systems.
To get the best sound reproduction, Alan melded the best of what the professional world had to offer in terms of acoustic design with the best of what the high end world had to offer in terms of the most refined playback systems.
Please remember that this is just a brief introduction into a very complex field. We have applied many, many different approaches and products to rooms over the years. It would take a book-length manuscript to describe all that we have done.
If you are interested in improving your room's acoustics, we suggest that you make a scale drawing of your room from a birds-eye ("plan") view, with the furniture arrangement, window and door locations, and system placement sketched in. Also include a measurement of your ceiling height. If you wish to go one step further you can then "paint" your room with a series of overlapping photographs. Once we have your room information you are welcome to give us a call and we can discuss how to optimized your the acoustics of your particular room.