Goodwin's High End

 

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 pre-made, and some may be regular home furnishing chosen and placed for their various 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 at particular frequencies and not retransmitted to the room.
  • Diffuse sound: Sound striking the surface bounces back into the room in many different directions.
  • Reflect sound: Higher frequencies of sound striking a 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 absorb certain high frequencies, yet may allow midrange frequencies to be reflected by the wall behind the draperies.

Bass notes have much longer wavelengthsand the lower the bass note the longer the wavelength. As the wavelength approaches the dimensions of the room, resonances become the dominate physical phenomena governing the room's bass acoustics. Much larger, thicker absorption materials are needed to treat bass than are needed for high frequencies. Other approaches to bass treatment include utilizing Helmholtz resonators. 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 have your room measured with sophisticated computerized testing equipment.

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 very 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 still may wish to consider room acoustics in its construction. For example, a large, overly-live (meaning way too reverberant) 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 any 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 both in 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 now well-known RPG Quadratic Diffuser. And over the years RPG has added many other new acoustical treatments.

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 1980'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 great.
  • Unfortunately even today in the new millennium, 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.

Another aspect to designing room acoustics is the look of the room after everything is completed. Some people who have a dedicated listening room and/or home theater are fine with having their room look like a recording studio. However others may wish to have their room look like a normal room. In the latter case we employ special acoustical fabric which can be stretched over ceilings, wall, or portions thereof. If you would like to see a sampling of the vast array of patterns and colors that are available you can see some links here, here, here, and here.

Please remember that this is just a brief introduction into a very complex field. It is often said that room acoustics is both an art and a science. Certainly 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 optimize the acoustics of your particular room.


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