david@uwm.UUCP (David Robinson) (03/05/91)
The following article is from POSITIVE FEEDBACK, the newsletter of the Oregon Triode Society, and is Copyright 1991, all rights reserved. This article may be reposted or reprinted, as long as it is not resold, and as long as proper attribution of the source is made in full. Please keep this header in all copies made of this article. David W. Robinson Editor, POSITIVE FEEDBACK david@agora.rain.com ----------------------------------------------------------------------- THE ABSOLUTE TRUTH Bob Carver In my last column I touched on the importance of loudspeaker interconnect wire and the way in which the simple D.C. resistance of the loudspeaker wire interacts with the output impedance of the amplifier and loudspeaker impedance to cause a change in the performance of the system, and we saw that the resulting change could deliver a warmer bass, softer highs, bigger sound stage, deeper sound stage, a more forward mid-range or a tighter bass. In this column I'm going to continue that discussion, but broaden it to include the total and complete system. HOW TO MAKE YOUR STEREO SYSTEM SOUND BETTER WITHOUT SPENDING LOTS OF MONEY The first part of this process is to understand what is important and what is not important. Once we understand these concepts, we're in a much better position to modify the system to make changes that will improve it. What I'm going to say next is the most important thing we need to know about a hi-fi system: The total subjective sound (assuming low distortion) is related to only three things, and three things only. It's as simple as that. The first is the frequency response of the system. The second is the wave launch geometry of the system. The third is the room acoustics of the system. Every thing and anything that you can possibly think of that would change the quality of a system is a subset or special case of either frequency response, wave launch geometry, or room acoustics. The net frequency response of a system, as it pumps sound into a listening room, essentially determines the tonal qualities of the system: whether the bass is tight; whether the bass is warm; whether the mid-range is forward or recessed; and so on. The subjective qualities are almost totally determined by the net frequency response of the system. The frequency response of the system, as I mentioned in my last column, can also modify and change the apparent sound stage depth, the sound stage width, and the "airiness" of the sound stage. What do I mean by wave launch geometry? Wave launch geometry is a fancy way of saying dispersion, but it's more complicated because wave launch geometry also includes the notion of time delays in part of the musical spectrum versus another part of the spectrum. For example, imagine a small pulsating sphere perhaps the size of a marble radiating sound equally in all directions. That would be one particular wave launch geometry, or one particular kind of dispersion. Next, consider a long ribbon driver which launches sound forward and to the rear in a figure eight pattern with very little radiation out the sides and straight up or straight down. That's a different kind of radiation pattern, and it is called because we can see that, if this imaginary ribbon in this discussion were tilted back slightly, sound waves from the bottom of the ribbon would arrive at our ears sooner than sound waves emanating from the top, and a time delay is formed. That time delay is part of the wave launch geometry and adds a dimensional aspect--or spatial aspect--to the perceived sound stage generated by a ribbon. The same holds true for an electrostatic loudspeaker. So, a loudspeaker will sound boxy and closed in if it has a particular spectral energy distribution (that's a fancy way of saying frequency response) and a particular wave launch geometry. The particular wave launch geometry and tonal qualities of a box loudspeaker combine to make a box loudspeaker sound like--well, like a box. The particular wave launch geometry and spectral energy distribution of a large panel speaker combine to give a panel speaker--well, the sound of a dipole, or a panel speaker. Definitely unbox-like. This leads me to the third item of importance in what we hear when we listen to our system, and that is room acoustics. ROOM ACOUSTICS Room acoustics completely influence--totally influence--what we hear and what we make of our hi-fi system, but in a very unusual way. It works as follows: When the loudspeaker generates its first arrival sound, what we hear is the sound of the loudspeaker and the sound of the system. We could identify it whether it were in Room A, Room B or the great outdoors. We can identify a particular system (assuming familiarity) in much the same way that we can tell whether our brother or mother is speaker, regardless of the room acoustics--whether we are indoor, outdoors, in a gymnasium or an indoor swimming pool. The reason for this phenomenon is that the early arrivals are the arrivals that define for us the sonic signature of the reproducing instruments, whether they be vocal cords in a throat or loudspeakers in a hi-fi system. After the initial sound is processed by our brains, the reverberating and decaying sound field is processed, telling us a great deal about the environment that the music is taking place in. So the basic character of the system is not determined by the room acoustics, but the overall net effect is most definitely associated with the way the system and the room interact. Now, I know these three very simple notions may go against the grain of what you have been taught, and most certainly go against the grain of what you've been taught in the underground magazines. These notions may even go against the grain of your own experiences. That brings me to a final issue that's associated with how a hi-fi system sounds. Remember I mentioned three. There really is a fourth, and that is psychoacoustics. There are two sides to the psychoacoustics coin. On the one hand, we have the scientific use of psychoacoustics to provide the knowledge to build a believable, delicious, and lush sounding stereo system. That knowledge, for example, is embodied in a time delay system. It is embodied in the way particular loudspeakers are designed, and even in the acoustical treatment of listening rooms. The other side of the psychoacoustics coin is simply the "psycho" part of our minds at work; that is, our imagination at work in providing physically nonexistent clues and cues. The imagination side of our minds can easily and drastically modify or alter what we hear and how we hear it, even though there is no objective reality to any particular subjective sonic impression. Now, let me restate it: Taken together, there are now four things that define, completely, what we hear when we listen to our system. One is spectral energy distribution, which is a fancy way of saying frequency response. The second is wave launch geometry. The third, room acoustics. And the fourth, psychoacoustics. Taken together in a very special mix, these things--and these alone--provide all of the components of the sound field that we hear. What is not important in this is the particular kind of wire that's used. What is not important is the particular kind of capacitors that are used in building the equipment. What is not important are things like magic bricks. What is not important is green ink. There are so many things that are not important that are fun to do--and as long as they're fun and not harmful, by all means put on magic bricks, put lots of green ink on your CDs--but don't lose track of what really makes a system sound better. It's not those magic things. To make a system sound better we need to experiment with the right things--because the magic bricks and green ink will yield fruit only in the fourth dimension, one-half of the psychoacoustics equation: In our imaginations. Now I'm going to tell you how to change and modify each of the four variables to really make your system sound better. This process can be lots and lots of fun. The first thing to do is do all the magical things you may think are important. Go to the junk yard or an old TV shop and get an old transformer, cut all the wires off and stick it on top of your amplifier. Take some green ink and put it on your CDs. You could even try Armorall-- just be careful not to get too much on because it might clog up the CD player works. Go to the store and buy some really thick speaker interconnecting cable--not expensive, just thick and beefy. Hook all that up to your system. Do all of those things and then sit back and listen. After you've listened for a while, it's time to start the improvement process. Now, think. First item: spectral energy distribution. That is, the net frequency response of the system. So, how are you going to change that to make it sound better? Well, the way to do that is to use an equalizer or to change the impedance of the wire you're using or to turn any frequency trim controls your loudspeaker might have up or down. But the question remains: how do you do it in an organized way that will result in a better sounding system, with freater depth, better ambience retrieval, more articulation, better separation of instruments throughout the sound stage and sweeter, more believable highs? The details of the interactions are so complex that there's no simple direct way to do it. Let me suggest an indirect way the works quite well. First, elevate your speakers off the floor by at least a foot and a half. Move them away from the back walls and from the side walls--at least a meter to a meter and a half from the back wall, and at least half a metter to a meter from the side wall. That's the first step. Sit back and listen for a while. Next step, with the help of a friend, line your speakers up so that you're sitting precisely, exactly between them. Use a non-stretching tape measure and have a friend hold it in such a way that the top bottm corner, the right corner of the opposite side speaker and each corner of the loudspeaker is exactly the same distance to the denter of your breastbone. To the centimeter. What this will do is to allow all the timing cues and phase information that are inherent in the signal source to be accurately delivered to your ear- brain system. This should result in a system that's able to make a sound stage that will extend beyond the confines of the loudspeaker. The sound stage should be much deeper now than it was before--unless you had the speakers already set up like this, of course. Listen to it for a while until you are able to hear the depth in the sound stage and sound field and are able to hear sound events that extend off to the left and to the right of the loudspeaker so that the sound stage is a large arc. So much for that. It takes some time to learn how to hear these effects if you haven't been exposed to them before. Takes several hours. The next thing to do is to borrow, buy or obtain by hook or crook a pair of Stax Pro Electrostatic headphones. The purpose of this next exercise is to put on your program material and listen to the headphones. You will find that the Stax headphones have a beautiful tonal balance and a very lush sound stage. Of course, being headphone derived, it will all be inside your head. The object at this point is to adjust the frequency response of your total system so that it matches as closely as possible the frequency response--that is, the frequency balance--of the Stax headphones. Do this with a graphic equalizer. The adjustments that you make will be very small ones. Those sliders will be displaced from their center position by typically plus or minus less than one-helf inch. Very small adjustments. This process takes a lot of time, but it's a lot of fun. It will take hours and hours to get it just right. Incidentally, the Stax headphones are quite flat. This must be done by ear; it cannot be done by instrumentation because the instruments aren't sensitive enough. Also our two ears hear things differently than a microphone hears things simply because our two ears operate into a brain, and the microphone does not. By and by, after you "home in" on this by meticulously adjusting the graphic equalizer, you should be able to take the headphones off, listen to the system, put the headphones on, listen to the headphones, and when you rapidly remove and replace the headphones from your head, you should hear very little timbre change, spectral energy distribution change or frequency response change. At this point, you should have an interplay of tonal balance (that is, frequency response), room acoustics and wave launch geometry that will provide a beautiful, three-dimensional and believable sound stage. It will also provide the ability to float a human voice in three dimensional space behind and slightly above the loudspeakers. There's a lot more to do, but that will wait until my next column. In my next column I'll describe how to modify the room acoustics and the wave launch geometry and make those modifications change the way your system sounds. Most importantly--and this is so important--understand in your mind clearly the relationships that exist between what you hear and what you change in the system. EXACTLY, what does wave launch geometry do in particular to change the way a system sounds? EXACTLY, what does the frequency response do and precisely how do room acoustics influence what we hear? It's important to scientifically understand all of these things, and the nicest way to understand them is to engage yourself in a two-fold process. On one hand, have a practical or theoretical understanding of the sort taught here, in articles or in books, and on the other hand, to actually physically do it yourself and enjoy the process. Those two approaches in combination will yield the most dramatic results that you can possibly achieve in making your system sound better. The best part of this is that it doesn't depend on musical capacitors; it doesn't depend on the expenditure of tons of money. Go for the magical mystery tour but do it for fun--and remember, don't confuse magic with science. Until next time, this is Bob Carver signing off.