"The room is the first thing we start with and the last thing we think about." [Unknown]
Welcome to the first in our Series of Articles on Acoustics. We strongly believe that room acoustics are fundamental to any good sound system. It's really astounding how good an average playback system can sound in a stellar room, and conversely, how badly a state-of-the-art mega dollar system will sound in a room with no positive acoustic values.
Throughout this series, we hope to educate and illustrate some of the fundamental points on room acoustics. This is by no means meant to be an intensive course on acoustics (which, by the way and for those who are interested, we recommend and encourage with a list of educational and training opportunities on our website). However, our Series here will give the reader some fundamentals and resources that may help in solving their own acoustical needs and problems. In this introductory article, we would like to accomplish a few goals:
The first will be to discuss many of the facts and myths that exist regarding acoustics. The second will be to give a very brief definition and description of some of the acoustical terms you may have heard. Lastly, we will discuss our intended direction in this series of articles.
Facts & Myths:
The world of audiophiles is full of snake oil and witch doctors with mystical powers. I have heard some strange and extreme claims yet must simultaneously admit that there are things which I have heard that I cannot physically explain. As a physicist however, being able to hear and mathematically prove it is far more comforting. Having said this, it is important to note that I do not dispel things that I have heard yet do not fully understand. I still look for the root or source to understand and explain why something works (or doesn't, for that matter). I have learned that when you can explain a complex concept to a six-year old, that's when you truly understand it yourself. With that preamble out of the way, let's examine some facts and myths in acoustics.
1. "It sounds bright - it could be my transport."
Okay, this could be fact at least 1% of the time. In truth, it could be anywhere in the signal path of the components and/or speakers. This illustrates the point that we can often hear the nature of the sonic degradation in our system but have absolutely no idea what the true root cause of the problem might be. With today's advanced state of technology, I doubt that in most cases the CD transport itself would be the main cause for a bright sound, yet this is a comment that I actually encountered. After discussing the situation, the owner still was convinced that he needed to upgrade his transport above all else.
The truth is that most equipment today is perfectly capable of performing nearly flat from 20kHz on down to whatever the low-frequency roll off of the speakers might be. If someone hears a bright, boomy, bloated sound or collapsed soundstage, with few exceptions it's the listening environment (the room) that's to blame. However, the myth insists that it must be the speakers, the amplifier or some other piece of hardware. No, wait - it's the cables.
2. "Room acoustics are ugly."
Well, this certainly can be true. And honestly, I can't blame people from steering away from room acoustics the way some of the devices on the market look. At least the preamp and other components can be reasonably well hidden to not make the living room into a studio. I think this is the biggest barrier to dealing objectively with acoustics: Appearance. If I had the perception that my living room had to look like foam central? Quite frankly, I wouldn't be interested either.
Alas, this statement is myth. Room acoustics can look like anything you want them to look - particularly if new construction is involved. In fact, with new construction, the acoustical treatment can be designed such as to stealthily integrate into the room, thereby saving money and creating an aesthetically pleasing atmosphere. Properly designed rooms can incorporate absorption, diffusion, traps and many other acoustical devices inside the walls, ceilings and even floors, using conventional finish materials such as glass and mirror, fabrics, carpet and wood. Looking at the room, invited guests would have no clue as to what went into it - except that it sounds far better than anything they've ever experienced before.
3. "This one specific acoustical device will bring your room to sonic perfection."
I actually received an e-mail stating this very thing. This is a myth. There are no magic bullets. After replying to the correspondent how this really didn't make sense; that, although there could be an improvement, perhaps even a very significant one in an otherwise entirely untreated room, achieving "sonic perfection" was really not possible - I received the response to "open your ears" by which, I guess, the sender implied "not your mind". As I've said, I don't dispel those items which I cannot explain - but this goes a little beyond even that. Room acoustics require a balance. Every room is different and every room needs different acoustical treatments to optimize it.
4. "Room acoustics are complex."
This is fact. Room acoustics are extremely complex, but not beyond understanding. This is the other area which, I believe, creates a barrier for people considering entering the jungle of acoustics. The worst thing anyone can do is of course to ignore the issue. For starters, take some very basic measurements, listen and then try to correlate the two. You might be amazed at how it accelerates your path to good -- or at the very least, reasonable -- acoustics.
So many believe "it's the transport" or "the cables" and go out to buy new ones only to discover that a new problem issue surfaces. If only the acoustic basics were right -- and we're not talking about a studio-engineered listening room -- these changes would be so much more meaningful and occurring in a proper context. Otherwise it's very much like fretting over correct spelling while your grammar is so bad as to prevent anyone from reading what you had to say in the first place.
There are two possible routes to approach room acoustics. You can take some time to educate yourself (there's an incredible amount of information on the web and in a few really well-written books), make modest changes along the way and achieve the desired acoustical goals; or you can hire a professional to do the design and engineering for you. The first will take longer but could be more rewarding for many. I've always believed that "audio nirvana" is a road, not a destination. I have enjoyed changes in my own system a little at a time. Not everyone is like that - or perhaps they want to enjoy the changes focussing solely on their equipment. In that case, hiring an engineering consultancy group may make more sense.
5. "We would like to know what your questions are."
We have a basic outline of what will transpire throughout this Series but will likely adapt our topics to include questions and comments from our readers. Please write to us or the Editor of this publication on topics you would like to see discussed.
What follows are several basic definitions of terms that we will likely discuss in more detail throughout these articles. As we will advance into more complex concepts, we want to start off slowly and build a good foundation for understanding.
Ambient Sound: See Indirect Sound
Diffuse Sound: This is non-correlated sound. Unlike reflected sound, diffuse sound no longer carries the coherency of a reflected sound because different wavelengths of sound exit (and scatter) at different angles of reflection. While the maintained energy of diffuse sound may be as much as reflected (not absorbed) sound, it no longer carries the coherency of reflected sound.
Direct Sound: This is the sound that arrives at the listener's ear directly from the speakers and is distinct and different from indirect, reflected or ambient sound.
Frequency Response: In our context, we will refer to the frequency response as the normal response for human hearing, namely 20Hz to 20kHz.
Indirect Sound: For our purposes, indirect, ambient and diffuse sound have the same meaning. This is the sound that arrives at the listener by some path other than directly from the speakers. It can be reflected, diffused or partially absorbed sound. In an anechoic chamber, indirect sound doesn't exist. These chambers are designed to eliminate all reflections of sound.
Reflected Sound: This is sound that has struck at least one surface and is for the most part neither absorbed nor diffused.
Reverberant Sound: This is another form of indirect sound. Reverberant sound has struck more than one reflection point and maintains some energy and -- for the most part -- coherency, though at lower levels, this may be difficult to detect.
Reverberation Time: This is the time it takes for in-room sound to decay to inaudibility. Most commonly, we use the term RT-60, meaning the time it takes for a direct sound to decay by 60dB. RT-30 and RT-90 are also used depending on the size of venue and purpose. The issues of RT measurements in small environments will be discussed in a later article.
Total Sound: This is the sum of both direct and indirect (reflected) sound.
Octave: An octave is a measurement used in music and refers to a doubling of frequency. For example, 20Hz to 40Hz spans one bass octave as does 10,000Hz to 20,000Hz in the treble.
Pink Noise: Pink noise has equivalent energy per 1/3 octave bands. On a linear frequency scale, it thus appears that there is less energy in the higher as compared to lower frequencies. Pink noise is commonly used for most test measurements.
White Noise: White noise has equivalent energy per frequency. On a linear frequency scale, it thus appears linear. White noise is commonly not used in acoustical measurements.
Here are the topics we plan to cover in upcoming installments:
We hope you will join us in about 1 month for our next article on Frequency Response and RT-60 and how they affect our listening rooms and listening experience. [Due to my vacation, the next article will likely be slightly delayed to appear no sooner than mid-March. However, our friends at Positive Feedback On-Line should have it as soon as they receive their raw copy from Rives Audio - Ed.]