.
HAVING DECIDED on what speakers you prefer, the next item on the agenda is correctly installing them.
This involves connecting them to the amplifier (or receiver) and finding the best location for each speaker system in your listening room. Some care is required for both chores.
The hookup involves running the proper wires to the speakers. The location problem is a bit more complex and logically divides itself into three main items (of which many listeners need concern them selves only with the first): best general positions for stereo; hints for "enhanced stereo"; and best gen eral positions for quadriphonic sound.
The Hookup
At the amplifier (or receiver) end, your main concern is in making a secure connection to whatever terminals are provided. By secure we mean making certain that the strands of wire of each lead are tightly wrapped around each other. Loose strands can make contact with an adjacent terminal to cause the output signal to become "short circuited." If you connect the wires by simply stripping off some insulation at the end, it's a good idea to "tin" the exposed strands after twisting them. Tinning means applying a little hot solder to the ends so that they stay together. You also can use "spade lugs"-these are small metal connectors that have a sleeve that fits over the exposed wire and a U shaped contact area. The usual size is No. 6. The sleeve should be crimped to the wire (tightened by pressure from a pliers) and, ideally, soldered too.
Note that the "press-to-connect" type of terminals used on many receivers will not readily accept spade lugs; these terminals are best used with leads that have been stripped and tinned.
Some high-powered amplifiers have "binding posts" that consist of round plastic nuts fitted over threaded metal pins. Often, a binding post can accept a variety of hookup techniques-stripped and tinned wire ends, or spade lugs, or exposed wire ends fitted with "banana plugs." A banana plug is an insulated connector that fits over a wire end and mates with the center opening of a binding post.
Whatever method you use, it's a good idea to "code" the various speaker leads to distinguish be tween signal and ground (or "common") leads on each channel. Use small plastic labels attached to the leads, or different colored snips of adhesive tape, etc.
------ Thickness of Wire for Speaker Hookup (in gauge no.)
---- This chart shows the smallest-diameter (thickness) wire to use in amplifier-to-speaker
connections to assure minimum signal loss. If in doubt, use the next thicker
wire (next lower gauge number).
What Size and Type of Wire?
At first glance, it may seem that the most attractive wire to use for connecting speakers would be the flat twinlead "ribbon" commonly used for FM and TV antenna lead-in. This wire will lie flat under carpets, and it can be easily tacked behind cabinets.
Actually, it is the worst wire to use for speaker hookups. It is too narrow in diameter or "gauge" for handling amplifier output signals, and in appreciable lengths it will reduce the total available signal.
The recommended wire to use for speaker hook ups is "zip cord" which is electrician's jargon for lamp-cord, the familiar twin conductor wiring with insulation wrapped around each lead. This wire comes in different thicknesses, designated by gauge numbers. The lower the gauge number, the thicker the wire. Ordinary lamp cord is of No. 18 gauge.
Thicker gauge versions come in No. 16, No. 14, etc.
The gauge to use depends on the length of wire needed to connect the speaker system to the amplifier. The greater this distance, the thicker the wire should be for optimum signal transfer and minimum loss en route. The accompanying chart can serve as a handy guide to this choice.
At the speakers themselves, observe the same care mentioned for the amplifier connections.
Avoid loose strands of wire. Connect all leads securely. Be sure that the pair of leads from a given amplifier channel do indeed go to the speaker sys tem intended to reproduce that channel. Do not confuse the ground lead from one channel with the signal lead of another channel.
A final point here has to do with phasing. When "in phase," speakers vibrate in step with one an other. That is to say, their diaphragms move in and out together. However, if the two leads connected to one speaker system are reversed with respect to the other pair of leads, the two speaker systems will be "out of phase." The low-frequency response will be degraded, and the stereo image-especially the center stereo information--will be ill-defined.
Sometimes soloists will seem to "wander" and in general you lose a sense of "firmness" in the stereo presentation.
To keep speaker systems in phase with each other when hooking them up, the wire-coding dodge mentioned earlier will help. Be consistent in how you connect the various leads. For instance, most zip cord has a slight "ridge" or molding, or sometimes a marking, along the insulation of one of its two leads. Decide that the lead with such identity is to be used for either "signal" or "ground" and then stick to that rule throughout.
If you are uncertain, after the hookup, about whether or not the speaker systems are in phase, lis ten to them playing a mono signal (switch the amplifier or receiver to mono mode). Stand in front of, and midway between, the two speaker systems. If you hear a well-defined sonic image but it is some what to one side, it could be that the channel balance is off; this should be corrected by the balance control on the amplifier or receiver. If, however, you can't tell where the sound is, chances are the speakers are out of phase. In that case, turn off the power, reverse the two leads going to either of the speaker systems, and repeat the test. The hookup that gives you the best-defined sonic image will be the correctly phased one.
Best Positions for Stereo
A very general rule is to locate each speaker system so that it becomes the end of an equilateral triangle with respect to the main listening area. This rule can be violated to some degree, of course, but there are limits. If the speakers are too close together, you will lose some of the stereo effect. If the speakers are too far apart, you will hear exaggerated channel separation or "Ping-pong" sound.
In an average rectangular room, you can enjoy stereo whether the speakers are placed against the long wall or the short wall. But note that generally the speakers will provide stronger bass and smoother highs when they "work" into a long dimension-this way there is less chance for standing waves and excessive "bounce" to develop in the re produced sound.
To a great extent, the recent design trend to "omni-directionality" in speakers helps the distribution of sound with somewhat less critical attention to exact placement in a variety of rooms. If you use such speakers, make sure that you place them to take advantage of their dispersion pattern; the instructions for positioning them found in the owner's manual should be followed carefully.
The closer to an adjacent surface (floor, wall, or ceiling) you install any speaker, the more apparent bass it will furnish. In some rooms, however, trying to get more bass this way can prove frustrating.
You may find, for instance, that the speaker is ex citing room resonances that are falsifying the bass, making it sound too heavy. If so, move the speaker away from the wall, etc., and settle for less, but cleaner-sounding, bass. The major exception to this advice is, of course, a corner-horn system which depends on adjacent walls to serve as extensions of its own horn structure. Such a system must be placed in a corner.
Any speaker, ideally, should be located in a relatively "live" portion of a room and look out at an acoustically softer portion. Not recommended, for instance, is placing speakers near heavy draperies.
Place the speakers as far away as possible from draperies.
The speaker system, for each channel, should ideally look into the same kind of acoustic environment: symmetry here is the keynote. A setup, for instance, in which one speaker faces a large un draped window and the other a long corridor will be difficult to balance for stereo. Chances are one speaker in such an installation will always sound a little (or a lot) different than the other. The trouble is not that the manufacturer couldn't make two identical models; it's that you have loaded them to the room in utterly different ways. And, of course, you would not place a speaker behind a large item of furnishing any more than you'd block an air conditioner with an overstuffed chair.
Most rooms, with a normal complement of furniture, carpeting, window hangings, bookshelves, and so on, do turn out--acoustically speaking--to be within a broad average range between "dead" and "live," or over-absorbent of sound and over reverberant respectively. However, if the room is predominantly "live" or "echoey," you can add up holstered furniture, heavier draperies, or carpeting to tame it down. Sometimes ceiling tiles help (especially in a playroom that has been carved out of a basement or part of a garage), but use these care fully. They deaden the sound quite a bit and if used excessively they will muffle the highs and un balance the best of speaker systems. For this reason they are not recommended for use in a normal living room in which you also want to enjoy good stereo.
The most difficult shape of room for good sound is the one with dimensions approaching a cube (length, width, and ceiling height all the same or nearly the same). Deliberately offsetting these equal dimensions can help-floor-to-ceiling built-in shelves along one wall or heavy draperies at one end might do the trick. If all else fails and the room sounds boomy no matter what, you might try one dodge that has been reported as being effective. If there is a sofa in this room, get a sheet of 1/2-inch or thicker plywood that is just a bit shorter than the sofa and not quite as high as its back. Tack a layer of fiber glass to one side of the plywood, and then position it behind the sofa. It won't show, and it may help "flatten" the room's response.
Getting Into Stereo and Room Acoustics
The acoustical character of your listening room has a definite effect on how any speakers will sound in that room. What follows is a detailed guide to this often difficult relationship.
A prerequisite to evaluating the sound of stereo is a rudimentary knowledge of the frequency spectrum. It is divided into three segments. The bass ex tends from the deepest audible tones (about 20 Hz) to about 200 Hz (roughly, three notes below middle C). The midrange extends from here to about 3,000 Hz, which is just below the top range of the highest musical instruments, the piccolo and the organ.
The highs extend from this point to the highest audible fundamental sounds (just below 20,000 Hz) and for at least an octave above to about 40,000 Hz.
This last segment is a most important one since it contains the overtones. Every musical tone consists of a fundamental tone that is the one we are conscious of and a series of overtones that sound so softly that they cannot be distinguished as such but instill a unique timbre to the sound. It is only through the particular loudness pattern of the over tones that we are able to distinguish an oboe from a flute, for example.
In order to evaluate your stereo system, you must be able to distinguish the three segments of the frequency spectrum by ear. First, the bass. Very low bass (below 60 Hz) is felt more than heard. Try to remember the last time you heard an organ in a church or concert hall. Do you remember the awe some feeling of low bass tones of the organ, which seem to shake the very foundations of the building? Do you remember feeling the vibrations, particularly in your stomach? If not, try to become conscious of the rumble while riding on a subway or standing in a subway station while a train is approaching. Such rumble is quite similar to very low musical tones insofar as frequency is concerned.
The upper bass region from about 60 Hz to 200 Hz imparts to music a richness and roundness of sound. If accentuated, however, this region can cause the sound to become woofy and thick, with an over-resonance :hat seems to spread itself throughout a room annoyingly.
How do you distinguish midrange and highs? Listen to the sound of a very small radio or tele vision set. Its little speaker and limited electronics will be unable to reproduce any bass to speak of or any highs beyond 5,000 Hz. What remains is practically all midrange--a sound lacking the warmth of the upper bass, the virility of the lower bass, and the sparkling, crisp, and lifelike sound of the highs.
A system lacking highs will produce a dull, lack luster sound with little realism. To judge the reproduction of highs, pick one of the recordings recommended at the end of this article and listen to instruments such as the cymbal, bells, or triangle. Do they appear with realistic sparkle and brightness, or do they sound dull? Also listen to a recommended spoken-word recording and see if the natural sibilance of speech is being reproduced. Over-brilliance is easily spotted by excessive sibilance.
It should be apparent by now that frequency response and sound quality are interrelated. Any deviation in frequency response (an increase or de crease) in any portion of the frequency spectrum will (in a predictable way) affect the quality of sound.
A perfect stereo system does not exist. Each sys tem produces inherent deviations which impart a specific coloration to everything played through the system. Each component will contribute some degree of frequency distortion. The shortcomings of components must be accepted, but we can learn how to choose the best components for a particular acoustic environment. This brings us to the truly final component in the chain-the room. A stereo system does not exist in a vacuum. Although it has a specific and measurable frequency response, it will change color like a chameleon from room to room. The same applies to the sound of your voice, a particular symphony orchestra playing in different concert halls, or any sound source. The in fluence of the acoustic environment is enormous.
The shape (rectangular, square, irregular), the dimensions, the placement of furniture, the nature of the materials present in the room, all affect the sound. Furthermore, the chain of electronic components (carefully matched to each other) must also match the final component-an acoustic one.
In order to experiment with room acoustics, we must learn to recognize deficiencies in the frequency spectrum, resonances, sonic "holes," and relative dryness or reverberance in the various parts of the spectrum.
We have described how to recognize bass, mid range, and highs, and we will next discuss room reverberation and resonances. But before we do, let us touch on what I like to call the "musical relativity theory." It answers in very simple terms the basic questions of how much bass, how much mid range, how much treble, and how much reverberation is the correct amount. It's all relative.
No two conductors balance the low, middle, and high instruments of the orchestra exactly alike. Not everyone prefers the same concert hall or the same stereo system. The balance of the three frequency ranges and amount of reverberation are matters of personal taste. There are no absolutes. However, gross deviations from the way music is written to sound are simply incorrect and not to be tolerated.
If the sound is so bright that the bass is hardly audible, you will hear the music poorly balanced. The same is true for the reverse condition-over powering bass and insufficient treble, and so forth.
If there is an excess of reverberation, the music loses clarity-you cannot hear fast-moving notes clearly.
The relativity theory also works in this respect:
When manipulating or adjusting the frequency spectrum by means of tone controls or speaker placement, you can never gain anything without losing something. For example, increasing bass doesn't merely have the effect of increasing bass but also of decreasing treble (in a relative way).
This can be best understood graphically. A relatively well-balanced sound spectrum would be de scribed as having a flat frequency curve. Increasing bass would cause the curve to deviate (Fig. 1). Since the ear (the brain) does not have exact auditory memory for sound, it does not recognize that the second sound spectrum contains the same amount of treble (in an absolute way) as the first one. It now simply hears an imbalance of treble vs. bass-more bass than treble, less treble than bass. This is musical relativity.
INCREASED BASS FLAT RESPONSE
Fig. 1
Personal preferences regarding the frequency spectrum should be judiciously exercised within the range dictated by musical considerations. It is important to learn how to control room acoustics and equipment to achieve your wishes. Perhaps you prefer a bigger-than-life sound. Perhaps you are more of a purist who wants to hear the natural sound of an orchestra in a concert hall as he re members it. On the other hand, you might prefer a more powerful bass, or a more brilliant treble than you would ever hear at a live concert, or more reverberation than in your favorite hall. There are some effects we are sure you will not like, however: boomy or woofy bass, annoying resonances, sonic "holes" produced by standing waves, screechy, hissy highs, a bottomless sound lacking warmth, a hollow sound lacking midrange, a lackluster sound deficient in highs, an indistinct, inarticulate sound caused by excessive echo, or a small, dry sound caused by insufficient reverberation.
Let us start our experiments with the intention of getting the most out of our present equipment with out changing any components or switching to an other room, but considering the possibility of changing speaker placement, altering the acoustics by simple maneuvering of furniture, and adding or removing rugs and drapes.
Relative dryness or liveness of your listening room
The materials present in a room and the placement of the furniture greatly affect the acoustics. The liveness or dryness of a room (in the three frequency ranges) is our primary concern. What, exactly, do we mean by liveness or dryness? Let's find out. Go to that room in your apartment or house which is most amply filled with rugs, heavy drapes, and stuffed furniture. Make believe you are Ezio Pinza and belt out Some Enchanted Evening, making sure to listen to the quality of your voice.
Do it several times until you really hear your own voice as a listener would. Now proceed to your bathroom and sing the same song. What a difference! Your voice now sounds bigger, more resonant, effortless, and round. (Don't get any delusions; everyone's voice sounds great in a bathroom.) Needless to say, your bathroom is relatively live, and the other room relatively dry. Your bathroom reflects more sound than it absorbs, and the other room absorbs more sound than it reflects.
The reflection of sound causes reverberation or echo. While necessary and important to the sound source, echo in excess becomes very annoying.
Should you place your stereo in a completely empty room, the sound would bounce around with such liveness and resonance that much of the detail of the recorded sound would be swallowed up (un less the room happens to be covered with acoustic tile or other sound-absorbing materials). In the other extreme, a room loaded with sound-absorbing items such as heavy curtains, thick rugs, stuffed furniture, and with little or no empty wall space, will cause the identical stereo system to sound small, lackluster, and with unnatural dryness.
Now that you have carried out the first part of this experiment, repeat it in your listening room. If your voice sounds small and unpleasant, you have a rather dry room. If it sounds resonant and pleas ing, you probably have a good listening room.
Should it sound somewhat the same as in your bathroom, you have an over-reverberant room which will obscure details of the music. But the real test is a full-frequency orchestral record. Play some music that has notes in rapid succession to see whether one note is blurred into another. Don't, however, base your judgment on one record alone-you cannot take for granted that each and every record is recorded with the utmost clarity. Be sure to select passages in the three frequency ranges. Your room might very well be adequately reverberant in one range and deficient or over abundant in another. For this test I recommend Barta's Concerto for Orchestra, with the New York Philharmonic conducted by Pierre Boulez (Columbia M 32132). Special arrangements were written for each section of the orchestra so that the full capabilities of the instrumentalists and the complete ranges of all the instruments could be displayed. Another excellent way to check your sound is to use an organ recording.
Evaluating the room's reverberation, resonances, and nulls In evaluating the reverberant qualities of your room, you will have to take into consideration the phenomenon of standing waves.
Briefly, a standing wave is produced by a sound wave whose length is twice that of any room dimension, which causes that wave to be reinforced via re flections. These standing waves or resonance frequencies exist for each dimension of a room. They also form at all multiples of these fundamental resonances. Each room, therefore, will produce resonances at many frequencies depending on its dimensions. These resonances are beneficial if they are evenly spaced throughout the frequency spectrum and of uniform intensity. By intensifying sound they decrease the amount of acoustic power needed. However, when there are one or more isolated resonances of great intensity, the effect is quite annoying and interferes with listening enjoyment. These are easily spotted. They seem to pervade the whole room rather than merely emanating from the speakers. Standing waves also produce pressure nulls in the room where the particular frequency is somewhat cancelled out.
The quickest way of finding the resonances of your room is to use a frequency test record which contains a sweep tone. Such a tone "sweeps" all the frequencies from around 20 Hz to 20,000 Hz. Resonances will be quite obvious, and since most sweep tones contain marker signals for every 100 Hz, you will be able to note the approximate frequency of the resonances.
Fig 2
Fig 3
Fig. 4
Fig. 5
There are two ways to deal with annoying resonances. One way is to increase room absorption, the other to move the speakers to a location where they will not stimulate a particular standing wave.
Play the sweep tone and listen for the offending resonance along the wall at which the speakers are placed. You should be able to find a spot where the resonance is minimal. This will generally be about halfway up the wall and perhaps one third to a quarter in from the corners. The absorption technique decreases the intensity of the standing waves and assures a more even spread of sound pressure throughout the room. At the same time, the aver age loudness of the music decreases and the sound deadens considerably. Resonance-damping below 100 Hz is difficult to well-nigh impossible for practical purposes. Above this frequency, damping can be accomplished by the use of rugs, upholstered chairs and sofas, and soft drapes.
It can be seen that the control of reverberation and resonances is interrelated. Ample reverberation is usually more pleasant, but increases any tendency toward resonances that exist in the room.
Speaker placement in relation to bass, separation, and shape of room Bass response in a room is strongest when speakers are placed in corners on the floor (or up against the ceiling). In this case, the walls help propagate the low-frequency waves. Bass can be minimized by taking the speakers off the floor or moving them away from corners, of course.
Since liveness means more reflection, it also means less separation. By separation we mean the preservation of the two stereo channels as distinct sound sources emanating from two distinct locations. If there is a great deal of reflection, the two channels become somewhat homogenized before reaching the ears of the listener and lose some of their identity. In a very live room, the speakers should be placed further apart. Conversely, in a very dry room the speakers should be placed closer together in order to prevent a "hole-in-the-middle" effect: a lack of blending between the two channels which prevents the synthesizing of the many "ghost channels" that should fill the space between the speakers.
Should it be impossible or undesirable (for extramusical reasons) to control the dryness or liveness of the room, you might follow the suggestions for speaker placement shown in Figs. 2 and 3.
Note that when placing speakers widely apart in a live room, more clarity is sometimes obtained by angling the speakers inward for more direct sound.
Otherwise one may be out of range of the dispersion of the tweeters which operate at a narrower angle than midrange or woofers (Fig. 4). Conversely, more reflected sound can be obtained in a dry room by angling speakers outward (Fig. 5).
At times a center-channel speaker is desirable.
For example, if you have a long but narrow room and want to place the speakers against the long wall, the wide separation between speakers would make a center speaker desirable (Fig. 6). The arrangement at the right is probably more satisfactory. There is increased listening area and more direct and intense sound due to the angling of the speakers. L-shaped rooms can be handled as shown in Fig. 7.
Fig. 6
Fig. 7
Speaker placement in relation to highs
The distance between speakers and their position relative to each other (angled or not) affects the dispersion of the highs. Tweeters have a much narrower angle of dispersion than midrange or bass speakers. The positioning of the speakers must assure adequate highs from both speakers. Map out the general area which is to be used for listening and then check to see whether every spot in that area receives adequate highs from each speaker. Angling speakers in or moving them closer together will pull more highs into the listening area.
The use of tone controls
When all experimentation regarding furnishings and speaker placement has been completed, further adjustments can be made through the use of tone controls. Because tone controls are designed to make rather gentle changes over a major portion of the frequency spectrum, they have limited efficacy.
For example, most bass controls affect the response up to 500 or even 1,000 Hz and they should really be called "bass/midrange" controls. Solving any real problems due to room acoustics via tone controls is doubtful. They can somewhat compensate for deficiencies in speakers or amplifiers.
Again, experimentation is necessary.
How to upgrade components and match them to your room
Do you have enough power? This depends on three factors: the acoustic character of your room, the efficiency of your speakers, and the loudness with which you like to listen. More power is needed for a large room, an acoustically dead room, less efficient speakers, and for loud listening levels. Less power is needed for a smaller room, an acoustically live one, more efficient speakers, and for lower-volume listening levels.
Which speaker/amplifier combination is best for a particular room? If your room has a tendency toward low-frequency resonances, you would be wise to invest in a good transistor amplifier with a high damping factor. This kind of amplifier delivers a tight bass signal free of resonances. (Resonances can be produced by amplifiers and speakers, as well as by rooms-these are electronic rather than acoustic resonances.) You should also buy a speaker that minimizes bass resonances. Any acoustic suspension speaker should do the trick, but there are also excellent speakers operating on other principles that offer a tight, clean bass.
The efficiency of the speaker, the desired loud ness, and the liveness of the room determine amplifier power needed. Your sensitivity to distortion will also play a role. If you are more sensitive to distortion, you will need more amplifier power. The transients caused by a percussive piano, a cymbal crash, or a xylophone demand sudden quantities of power. If there is no reserve, the result is distortion.
The purchasing of speakers is particularly tricky since they will never sound the same in your home as they sound in the dealer's showroom. The only safe way is to buy speakers with an exchange privilege and a trial period of a day or two during which you can find out how well they sound in your particular room.
As to cartridges in relation to your room, you should be aware of the fact that they have tendencies toward resonances in various parts of the spectrum. Most commonly, they produce a resonance in the area of 8,000 to 12,000 Hz. If your room tends to be dull, you need not worry about such resonance unless it is really excessive. The ability of the cartridge to reproduce bass cleanly or with moderate resonance again should be taken into account in relation to your room resonances in this part of the spectrum.
Choosing a room
Since the effects of materials and furnishings have already been discussed, we need only consider the dimensions and shapes of rooms. These have a great bearing on the pattern of standing waves that the room will produce. Ideally speaking, no single dimension of the room should be less than ten feet, no dimension should be a multiple of any other, and no two surfaces should be parallel. The worst possible case is a perfect cube.
Since ideal conditions will seldom be met, keep in mind the following principles. Small rooms cannot reproduce low bass adequately since the length of the waves of very low notes will be greater than any dimension of the room. For example, the first note of Also Sprach Zarathustra, a low C, is 32 Hz, with a wave length of thirty-five feet. A 40-Hz tone has a wavelength of about twenty-eight feet. Since music generally does not go deeper than 32 Hz, a thirty five-foot room is all you will ever need. Bass reproduction decreases as the dimensions decrease. A small room, such as an 8 x 10 x 12 is unable to do justice to bass below 100 Hz, for example.
Since there are very few rooms with ten-foot ceilings and thirty-five-foot lengths, let us discuss the possibilities for conventional rooms with eight-foot ceilings. Height, width, and length ratios have been worked out for small, average, and large rooms.
Ratio
Small Room dimensions ratio
Average Room dimensions
Large Room
ratio dimensions
height 1 8' 1 8' 1 8'
width 1.25 10' 1.6 12' 9" 1.25 10'
length 1.6 12' 9" 2.5 20' 3.2 25' 7"
If you are lucky enough to have a ten-foot ceiling, look for the dimensions 10' x 12' 6" x 32'. Stay away from the dimension of 17' 6" since this will emphasize any inherent 60-Hz hum.
As for the shape of your listening room, an irregularly shaped room is sometimes better. Don't be afraid to try it.
In conclusion
Experimentation, involving time and effort, is the only way to arrive at good reproduction of recordings at home. But do not expect to hear music at home with the same realism as in the concert hall. Recording, not unlike film-making, bears only an oblique relationship to reality. Both media can and do surpass realism. Learn to appreciate the medium of recording. You will hear sounds that you have never heard before and subtleties of balance unheard of in the concert halls.
You will feel the excitement of controlling the sound yourself via experimentation and the up grading of your equipment.
How Many Speakers for Stereo?
One widely proposed and often-tried solution to the problems of room acoustics vis-à-vis good stereo sound is the use-in the same room-of more than the two speaker systems nominally required.
Only two channels are reproduced, but they are beefed up by auxiliary speakers. In general there are two methods of doing this. One is to use a "center fill" speaker. The other is to use "flankers." The center-fill speaker reproduces a combined left-channel and right-channel signal ("A plus B").
It helps fill a sonic "hole in the middle" between widely spaced left- and right-channel speakers and thereby creates more of a "wall of sound" effect.
The flankers are simply additional speakers paralleled to the regular left- and right-channel speakers. They help spread the sound when the original pair are too closely spaced. Again, they help create a wall-of-sound effect and--if they are located along the sides--they can also add a lifelike ambience to the reproduction. Sometimes this effect, on ordinary stereo, gets surprisingly close to quadriphonic sound.
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MEANS OF CONTROLLING ROOM REVERBERATION AND RESONANCES
To Increase Reverberation Create more reflective surfaces. (Only hard surfaces of glass, wood, plaster, etc., reflect sound efficiently.) Remove absorptive surfaces.
To Decrease Reverberation
Create more absorptive surfaces. Remove reflective surfaces.
Try these various steps one at a time and keep checking the sound of your stereo with a full frequency musical composition such as Also Sprach Zarathustra by Richard Strauss. (The opening note is around 32 Hz.)
1) Remove a couple of small scatter rugs, exposing the hard floor.
2) Open drapes, exposing the glass surfaces of the windows.
3) Close doors, thereby creating additional wood surfaces.
4) Remove unnecessary furniture to ex pose more wall and floor space.
5) Remove any tapestry or ornamental cloth from walls.
6) Substitute contemporary furniture featuring wood, glass, plastics, for stuffed chairs and couches.
7) Use ornamental objects with hard surfaces-vases, sculpture, glass framed pictures.
8) Remove all rugs, if necessary.
1) Place scatter rugs on floor. For damping at low frequencies of about 100 1-z upwards, it is necessary to use heavy carpeting with padding.
2) Install heavy, soft drapes and close them. (About half as effective as heavy carpeting with padding.)
3) Open doors and windows (effective Gown to about 350 Hz for average-size doors).
4) Use upholstered chairs and sofas (quite effective down to low frequencies).
5) Add tapestries, oriental rugs, or cloth to one wall, preferably opposite to speakers (this will affect the midrange and highs).
6) Install thick, wall-to-wall carpeting.
7) Install acoustic tile on ceiling (effective for highs and midrange--little effect below 1,000 Hz).
8) Place a room-divider-bookcase with a burlap-covered Celotex back some where near the center of the room.
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Details on these advanced hookups are given elsewhere in this book. But briefly, here are some relevant pointers.
The extra speakers for such installations need not be as fine performers as the two main units they will not, after all, be carrying the main burden of program reproduction, only lending a helping hand. In any case, before launching into this kind of sonic adventure, check your equipment (receiver or amplifier) to make sure it can handle the added load. Some sets are not recommended for simultaneously driving more than one speaker system per channel. Others are--and in fact many late models actually provide the connecting terminals for extra speakers, as well as a front-panel switch that lets you turn them on or off at will. This arrangement not only permits you to experiment with multi-sound-source techniques, it also makes it very convenient to run extension speakers for stereo in another room. Indeed, why shouldn't someone pre paring a gourmet dinner in the kitchen be able to hear Glenn Gould as well as you, sprawled out in the living room? To use extension speakers in another room, or additional speakers in the same room, the amplifier must have enough power to drive them all and enough stability to withstand the different loading conditions of extra speakers. If you're in doubt, or if your owner's manual makes no mention of this, query your dealer or the manufacturer.
The use of extra speakers, by the way, is a big reason for some enthusiasts' preferring-despite the undisputed excellence of today's combination units-completely separate preamp and power amplifier, or that type of combination amplifier which permits you to "go into" the circuit, so to speak, be tween its preamp and power amp sections. With such equipment, you can bridge the preamp output (connect it to more than one load simultaneously) so that it feeds not only the stereo basic that is driving your two regular speakers, but also drives a separate amplifier which in turn is driving its own speaker or speakers. This elaborate setup is costly and takes up more installation space, but it side steps all possible problems or amplifier power and loading, and it does provide an optimum match for additional speakers.
Some separate "deluxe" preamps make it easy-...
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Fig. 9
Fig. 8
Fig. 10
Fig. 11
Fig. 12
Fig. 13 "Standard" four-speaker arrangement (Fig. 8) is ideal but may not be feasible in many rooms. "A" designates maximum quadriphonic effect area. "B" area emphasizes up front stereo effect, provides less prominent signal information from rear speakers. "C" area lessens normal stereo effect, emphasizes rear-channel signals.
In room similarly shaped to that shown in Fig. 9, this speaker arrangement may prove very useful. Listening area "A" provides maximum surround-sound effect and may be preferred for some new pop albums recorded with primary signals on all four channels. "B" area provides less obvious rear-channel information but affords very spacious ambient effect you may prefer for more traditional music.
Least satisfactory arrangement (Fig. 10) is to place the rear speakers a good deal closer together than the front speakers. This reduces effective quadriphonic area to "A" but still permits fairly large area "B" for enhanced ambience on traditionally recorded material. If latter effect is all you want, it can be achieved by using the simple Dynaco Quadaptor hookup which permits driving rear speakers without the need for additional amplifier.
In room (Fig. 11) where main (front) speakers are on long wall to provide very broad stereo "front," placing the rear speakers too close together (a typical plan may be to flank the sofa with them) limits the maximum quadriphonic area to "A." Listening from the sofa this way may not provide the best four-channel sound unless level control for rear speakers is carefully adjusted.
In room similarly shaped (Fig. 12) rear speakers may be placed farther apart than front speakers. This optimizes area "A" for quadriphonic effect, while area "B" tends to emphasize rear-channel information. Again, this can be corrected by using level or balance controls on quadraphonic adapter or amplifier.
Again (Fig. 13), in room in which main speakers are on long wall, rear speakers may De added along side walls. This will enlarge quadriphonic area to "A" as shown, while "B" area continues to emphasize original up-front stereo effect.
Fig. 14; Fig. 15
L-shaped rooms present special problems. If original stereo (front) speakers are on short wall (Fig. 14), rear speakers may be added asymmetrically to produce good quadriphonic effect in area "A." More experimentation is called for with this type of room than with rooms that are rectangular in shape.
In L-shaped room in which main speakers are on long wall (Fig. 15), rear speakers may be added, probably asymmetrically. Note that in both diagrams one of the added (rear) speakers will get bass reinforcement due to proximity to corner. Other rear speaker will produce less bass. In both instances, adjustment of level and or tone controls may be required to get optimum balance for good quadriphonic effect.
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...they come with dual sets of signal outputs for each channel, which can drive two separate stereo basic amplifiers (or one stereo basic and another stereo control amplifier) at once. The output of your main speakers is controlled by the volume control on the system's preamp. The level of the added speakers can be controlled by input level adjustments on that second basic amplifier, or by the volume control on the second control amplifier. If no signal-level controls for the added channels are present, it would be wise to use speaker "pads" (external level controls) in the lines feeding the extra speakers.
The point is, you want those extra speakers to beef up the stereo spread, but not to overwhelm your main speakers. Level controls will enable you to get just the right shading of volume relative to all the speakers. This way you can balance everything precisely to suit different kinds of program material, the acoustics of the room, and your own listening tastes.
Special Setups for Quadriphonic Systems
Most of the diagrams offered so far by the sound industry to show how the four speakers of a quadriphonic system are to be placed follow a common pattern. The four speakers are located so as to form the corners of a rectangle and they are designated as LF (left front), RF (right front), LB (left back), and RB (right back). This placement also has been widely (though not exclusively) used at shows and demonstrations. It is not, however, the only arrangement possible. And in some instances it may not even be the most desirable, nor conducive to optimum results. We are in truth only on the threshold of four-channel sound, and much re mains to be learned. The possible variables-in recording technique, speaker placement vis-à-vis room acoustics, and so on-seem more numerous for quadriphonic than for conventional (two-channel) stereo.
Nonetheless, even at this stage in the game, it seems apparent that a few ground rules can be suggested. In general--and ideally--the speakers (in any sound system, mono, stereo, or quadriphonic) should be placed: 1), to take advantage of the acoustical characteristics of a particular room with respect to the speakers' own response and dispersion characteristics; while 2), at the same time affording a suitable presentation of the program material being reproduced (for stereo, that is, the speakers must be separated by about the same distance from the listening area); and 3), also fitting in with the room's general seating and decor plan.
Let's call this the "A B C" of speaker placement: A for acoustics, B for balance, and C for comfort. It is a big order and is far easier to state than to achieve in many homes. I know of no formula or simplified procedure that you can follow to accomplish this threefold ideal. In the vast majority of installations (my own included) the placement of speakers must be a compromise between these three criteria. Inevitably, one factor wins out over the others. From an acoustical standpoint (i.e., the reason you bought the equipment in the first place), the least desirable factor to allow to outweigh the others is the one dealing with room decor. More often than I care to recount, I have seen and heard stereo systems that were installed primarily from a "how it looks" standpoint rather than from a "how it sounds" standpoint.
For instance, I've seen expensive and very fine speaker systems that produced little clean, full bass: They were incorrectly baffled to get them to fit into an impossibly small space, or--if correctly housed--were placed in the wrong parts of the room. I've seen others that had perfectly good tweeters but were producing inadequate highs:
They were radiating at, and being blocked by, an overstuffed chair. And so on.
Obviously these considerations become more demanding the more speakers you have. If you are seriously into stereo, you probably have worked out reasonably good locations for your two speaker systems. But now along comes quadriphonics with two more speakers that are, according to the prevailing trend, supposed to be placed at the opposite end of the room and symmetrically with respect to the original pair.
If you start with a bare room, you may have a fighting chance of accomplishing this arrangement.
But if you are adding rear speakers to an existing stereo setup, or if you are putting an entirely new four-channel system into a room that already is furnished and being lived in, you could and probably will run into some hairy problems vis-à-vis that perfect rectangle pattern for locating the four speakers. I mean you might just not want to take down part of a book-and-storage wall to make room for two more speakers. Or you might not care to shift your favorite paintings or posters that hap pen to be lined up on the wall with respect to the "correct" speaker location. Or, you might have a sofa against this wall, which is a dandy spot from which to listen to stereo from the two speakers at the opposite end of the room, but which might not be so great for four-channel sound with the "rear" speakers at your elbows.
Some new four-channel installations I've learned about tackle the problem of locating the rear speakers by installing them relatively high up on a wall, even at the juncture of wall and ceiling. Fine, as long as the owner can manage that sort of decor gymnastics (either himself or by hiring someone to do it), and as long as the speakers-once positioned up there-really sound good. I suppose getting two people up on ladders, holding the speakers in the approximate proposed locations, and playing some four-channel material may be the only practical way to judge whether this type of setup really will work-in your room.
What I'm getting at is not that four-channel set ups are "impossible." On the contrary, they are very possible-but not necessarily in the formal rectangle pattern that has been so far almost universally proposed. In fact, once you get away from rigid adherence to that pattern you find that you can set up four speakers that produce the quadriphonic effect and also satisfy, at least to some degree the "A B C" requirements I mentioned above.
Four-channel setups have emphasized the "B" aspect. Of course, you should try to get the speakers as well balanced in terms of relative distances as possible. But even with speakers placed markedly out of a rectangular pattern, surround sound is still possible-those balance and level controls on your amplifier or receiver are not only for the program material, but for relative differences between the speakers. If, for instance, you have to place the left-back speaker farther away from your listening spot than the right-back speaker, a judicious use of one or two control knobs often will compensate for the discrepancy.
There's another point that bears on this subject, and it has to do with the nature of the quadriphonic program you're playing. Unless the recording was made deliberately to put the listener inside a "circle of sound" (which implies equal or "primary" sounds coming at you from all directions), you can get very satisfying quadriphonic characteristics (a sense of living ambience, a greater "dimension" in the reproduced sound, offstage effects, and so on) without having to stick to that rigid rectangular arrangement for the four speakers.
What exact arrangement you should use depends of course on those other three criteria listed earlier. For instance, if your speakers seem a bit shy on the highs, you will not want to locate them too far below the level of your ears when you're in your favorite listening chair. Nor will you want to place them so that other things in the room block the tweeter. If your speakers sound a bit bass-shy, you will probably want to move them closer to two large adjacent surfaces (floor and corner wall, for in stance) to reinforce the low frequencies. The ac companying diagrams suggest some of the general plans possible. Use them as guides, modifying them to suit your own needs and tastes and room situation. With a little experimentation and effort you probably will come up with a four-channel arrangement that works for you.
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(High Fidelity, 1976)
Also see:
OMINIDIRECTIONAL SPEAKERS: PRO and CON -- Just what are they and how good are they?
BUYER'S GUIDE TO SPEAKER SYSTEMS--A complete listing of available models from various manufacturers giving important design and performance features, sizes, prices.