The widespread acceptance of home audio in recent years has led many consumers to bypass learning the basic principles of sound reproduction and move straight to the business of selecting and purchasing a component system

The widespread acceptance of home audio in recent years has led many consumers to bypass learning the basic principles of sound reproduction and move straight to the business of selecting and purchasing a component system. While this may indicate a greater public awareness of the benefits of quality sound reproduction, it is important that the immediate concerns of products and prices do not obscure the more basic questions involved. Knowing about the history of high fidelity and some of the working principles behind sound reproduction will aid you in understanding discussions and product reviews found later.

The term "high fidelity" refers to the accurate reproduction of sound, sound reproduction with a high degree of faithfulness to the original sonic event. There are many techniques of measuring the fidelity of an audio component or an audio system. However, there is only one true standard for high fidelity sound reproduction: what the human ear and mind perceive as a natural and credible recreation of the live performance. And there is one term used by audio perfectionists to describe that characteristic: "musicality." That is, the ability of an audio component or system to sound like live music...not necessarily to sound "good" or to test well according to lab techniques, but recreate music as we perceive it in reality.

High fidelity saw its beginnings in the post-war years with the re-birth of the notion of "home entertainment,'' an industry that had been frozen by the wartime economy. Hi-fi enthusiasts at that time constituted a large circle of hobbyists, classed by many outsiders (along with short-wave radio hams and electronics experimenters) as another urban subculture based around material possessions and amateur tinkering. The business world was not greatly impressed by the hi-fi "bugs" either and the age of consumer audio had not yet arrived. Hi-fi enthusiasts who wanted superior reproduction were limited to the few quality components available through electronics supply houses (among them the noted General Electric VR pickup, the Brook amplifier and the Stevens Co-Spiral) and used equipment that could be begged from related professions: recording studios, radio stations, movie theaters. Or, hobbyists could build the equipment themselves - which many did.

In the fifties the popularization of 33-rpm long-playing records and the maturing of FM radio worked hand m hand with mounting affluence to rinse hi-fi from a hobby to a high-priced status item, manufactured by a few small firms. Soon after, hordes of manufacturers joined the rush to high fidelity with mass-market products that the general public was led to believe (and is still led to believe) were the equivalent of quality equipment.

The introduction of stereophonic sound in home audio at the close of the decade further broadened the hi-fi markets. The more gimmicky aspects of stereo attracted armies of new buyers who hadn't previously been "bitten by the hi-fi bug" and created space for greater and more diverse numbers of audio manufacturers. By the end of the sixties, the hi-fi industry was booming and home sound reproduction had become commonplace in America.

Recently, the hi-fi industry has begun a major campaign to revitalize and expand sales of audio equipment. As the hi-fi markets appeared to be reaching saturation levels at the opening of the seventies, the industry attempted to repeat the marketing success of stereo by introducing four-channel sound (a.k.a. “Quadraphonic”). It is uncertain whether design flaws, consumerism or lack of standardization is behind the public's indifference to the new four-channel equipment. It may be that the hi-fi industry is faced with a newer breed of audio consumers who are more wary and knowledgeable than the industry had supposed them to be.

Sound is a series of vibrations carried through some medium, generally air. There are four basic factors that distinguish one sound from another: (1) frequency, or rapidity of vibration; (2) volume, or intensity; (3) timbre, or sound quality; (4) duration, the length of time that a sound persists. The first two characteristics, frequency and loudness, are of more immediate importance in understanding sound and sound reproduction because they are the parameters most commonly employed in evaluating audio equipment.

The number of vibrations the sound contains in one second determines the frequency of a sound. This measurement is called "cycles per second" or "Hertz," or "cps" and "Hz" for short. Every musical note has a frequency or "pitch" by which it is characterized. The frequency of middle "C" is 262 Hz. The "A" that is normally used to tune an orchestra is 440 Hz. Notes that seem higher pitched have higher frequencies or rates of vibration.

Using these simple numbers to describe musical notes is actually a fudge because no musical note or natural sound is really made up of a single frequency. Actually, the basic or strongest vibration in any of the notes mentioned earlier is its "fundamental" frequency. Other frequencies, called "harmonics" or "overtones", accompany these basic frequencies and give them character or "quality."

Harmonics are multiples of the fundamental frequency of a note. For instance, the harmonics of "A," which is 440 Hz, include 880 Hz, the second harmonic; 1320 Hz, the third harmonic; 1760 Hz, the fourth harmonic, and so on. An "overtone" is another name for a harmonic. Overtones are merely ordered differently. The first overtone is the second harmonic; the second is the third harmonic, etc. Because any harmonic (or overtone) is a multiple of the fundamental frequency, it is always in "tune" with the fundamental.

Related to the subject of frequency in sound and music is the topic of human hearing and its frequency range. The optimum range of human hearing is generally considered to extend from a low of 20 Hz to a high of 20,000 Hz, also written as 20 kilohertz or simply 20 kHz. High frequency hearing ability declines with age, more steeply for men than women. Nearly all young persons in good health can hear above 16 kHz. At age forty the average cutoff point is about 13 kHz. By sixty-six it has dropped to 11 kHz. Many older people cannot hear above 9 kHz.

Human hearing does not perceive sound intensity as it actually exists. Just as the eye has an iris which opens and closes to compensate for the amount of available light, the mind compensates for the enormous range of intensity from the slightest whisper to the loudest jet engine; a ratio of roughly a billion to one.

In order to measure volume levels in a way that more closely resembles our subjective impression of sound, a logarithmic scale has been developed that uses the "decibel" (abbreviated "dB" or "db") as a measure of sound intensity. The logarithmic scale indicates that every time the sound intensity is multiplied by a factor of 10 the decibel scale increases by 10. A sound intensity of 70 dB is ten times greater than 60 dB; 60 dB is ten times greater than 50 dB and so on. Therefore, the ratio of one billion to one that exists between the sound intensity of a whisper (which could be estimated at roughly 25 dB) and that of a jet engine (estimated at about 115 dB) would be measured as 90 dB. Clearly, the decibel figures are far more convenient to manipulate.

To assess the meaning of variations in volume on a decibel scale, note that 1 dB is the smallest perceptible change in volume. A 3-dB change is apparent even to the most uncritical listener. An increase or decrease of 10 dB is acknowledged to represent a subjective doubling or halving in volume. 10 dB louder is, seemingly, twice as loud, though it actually means a ten-fold increases in real - not perceived - sound intensity.

When the two criteria of frequency and dB level are applied to measure the accuracy of an audio component, the measurement is referred to as "frequency response." The frequency response of a component can be illustrated on a graph plotting the variation in dB level against the frequency, as shown below. Note that the 0-dB point does not refer to the absence of sound, but the output of the component at 1 kHz. This is a standard rating system. If the frequency response line ran straight across from one end of the 0 dB line to the other, the frequency response would be measurably (though not necessarily audibly) perfect. In audio terminology this is called "flat" or "linear" response.

Frequency response can also be expressed as a figure; e.g. the information in the above graph may be said to describe a component with a frequency response extending from 20 to 20,000 Hz with a maximum deviation of 2 dB. This may also be expressed as 20-20,000 Hz +-2 dB.

Frequency response is also discussed in more general descriptive terminology. One such term is "peak." A peak is a sharp rise in response occurring over a small range of frequencies. A sharp drop in response over a small range of frequencies is called a "trough" or a "hole in the response." Peaks in response are far more audible than troughs. A falling-off in response toward the high or low end of the frequency range is called a "roll-off." As a rule, peaks, holes and roll-offs are undesirable in that they represent deviations from flat or accurate response.

Variations in frequency response, peaks, troughs, roll-offs and more general risings and fallings in response tend to "color" reproduced sound in different ways. Terms for these colorations have been used among audio enthusiasts for numerous years. An exaggeration in very deep bass response (20-40 Hz) adds a "thunderous" quality to the sound. An increase in the lower highs (1,000-2,000 Hz) can render the sound "raucous" and "tinny." Weak response in the mid-bass region (40-80 Hz) causes reproduced sound to be "thin" and "cold." Imagery such as this will be used throughout this course to convey more precisely the sound quality of the frequency response of various components.

Distortion

Distortion, in its broadest sense, is anything adulterating the pure program material, the signal. "Ghosts" in a television picture are distortions. The "fuzzy" quality of poor radio reception is distortion. There are numerous types of distortion that can exist in audio. Distortion in a hi-fi system could be a cloudiness or veiled quality, to the sound, hardness, shrillness, grittiness or graininess (as in a photograph that has been enlarged too much), a lack of cohesiveness or a lack of focus.

There are several measurement techniques commonly used to evaluate distortion, in audio components. One is "harmonic distortion." The harmonic distortion, or "THD" (total harmonic distortion) of a component is a measure of harmonics produced by that component which are not contained in the input signal. "Intermodulation distortion," or "IM," is a measure of the by-products of the interaction of two or more harmonically unrelated signals in that component.

As will be discussed in greater detail in the following chapter, measured distortion does not reveal the actual sound quality of a component. Many components show low distortion in tests but sound "unmusical" or unnatural to the ear. Alternately, many components test well and sound fine, too. Then, there are some components that show "substantial" IM and THD in the lab and nevertheless sound great. Still other components test poorly and sound just as bad. Distortion figures alone, derived from the current state of the testing art, simply do not constitute a definitive index to sound quality. Therefore, discussions of distortion and other aspects of fidelity in this article will reflect subjective impressions of components - not test results.

Noise is an unwanted addition to the program that is unrelated to its content. Hissing and humming in an audio component is noise. So is crackling and popping on a dusty record. The interference m radio reception can also be referred to as noise. This noise factor is measured as a ratio of signal (program material) to noise. The signal-to-noise ratio is commonly abbreviated as "S/N ratio" and is measured in decibels (dB). The higher the S/N ratio, the less the undesirable noise. A signal-to-noise ratio of 50 dB is minimal hi-fi. True high fidelity begins at around 60 dB, 70 dB being a fine figure. Above 70 dB lie the "perfectionist" S/N specifications.

Before the 1950's, virtually all sound reproduction equipment designed for home use produced only one channel of sound: one signal on tape, disc or radio, one amplifier and one speaker system. This type of reproduction is known as monophonic, monaural or single-channel reproduction. The sound you hear from a TV, an AM radio, or through a telephone is monophonic as there is only one signal or, more commonly, one channel of sound.

Stereophonic sound refers to the use of two (or more) separate channels of sound allowing us to utilize the capabilities of our binaural (two-eared) listening equipment. Stereo can "localize" (seemingly locate at a specific spot) instruments at one channel or the other. In addition, a well-made stereo recording will localize some instruments, usually solos or rhythm, at a center point between the two channels. (Such material is referred to as "center channel" information.) Some recordings localize instruments at other points between the two channels, although this is difficult and less common.

Actually, it is quite hard to discern the locations of individual performers at a live concert. Unless a listener is seated unusually close to the performers, all sound seems to emanate from a single, very large source, with various reflections and reverberations throughout the hall. It is only through the use of visual information that you distinguish the discrete locations of each performer.

Rather than duplicating the actual listening situation, most recording companies use stereo to offer a purely auditory image of the localization that we normally determine through sight, or a combination of sight and hearing. Therefore, commercial stereo is usually an attempt to reproduce sound as we perceive it, not simply as we hear it. Directionality in commercial stereo evokes the visual impression of a live performance, that of individual performers at discrete locations.

In addition, stereo has several other functions that may well be more important than directionality, but receive less discussion because they are subtler. First, stereophonic sound is instrumental in creating the illusion of the "single, very large source" and "various reflections and reverberations" described earlier. Even the finest monophonic audio system cannot provide a broad enough sonic image or sufficient reverberation or "ambience" (a feeling of the original recording environment) to capture the "size" and depth of a live performance. Stereo, with its sonic image spread across two channels, can more closely duplicate these effects.

The two stereo channels also divide the burden of providing and distributing sound output into a room and tend to separate the sources of the various sounds, allowing the listener to hear and identify voices and instruments more clearly. In this sense, stereo can be seen as a device for increasing sound output and sound "dispersion" and improving clarity and definition.

Every quality audio system is composed of "components," or parts, that serve specific functions. Record-playing equipment, tape machines and tuners are "source" components, which provide program material for an audio system. The amplifier controls the audio system and powers the speakers. Speakers and headphones are the components at the end of the audio chain; they turn electrical signals into audible sound.

The Amplifier

The amplifier is the heart of any audio system. It supplies the power to drive the speaker systems and provides the controls to vary the volume and tonal balance of the sound and to select the source program (choice of source components). The two functions of controlling and powering are separate and m better high fidelity systems they belong to two separate pieces of equipment referred to, respectively, as a "preamplifier" or "control amplifier" and a "power amplifier" or "basic amplifier." In most moderately priced systems these two components are combined into one unit called an "integrated amplifier" or, simply, an "amplifier." An integrated amplifier, a preamplifier and a power amplifier are shown below.

The radio tuner is one of several source components that provide program material for a high fidelity system. Tuners are available both as separate components and as integrated sections of "receivers." A receiver is a combination integrated amplifier (preamplifier plus power amplifier) and a tuner, both in the same enclosure. Some manufacturers have also integrated tuners with preamplifiers, but this has proven less popular.

The tuner used for serious listening in a quality audio system is an "FM" (Frequency Modulation) tuner. FM radio is a distinctly different entity from "AM" (Amplitude Modulation) radio, the band carried on small "transistor" radios and inexpensive clock radios. Whereas AM radio is broadcast on a constant frequency and varied in strength according to the audio signal, FM broadcast signals are of a constant frequency only when nothing is being transmitted. Audio impulses cause the signal to wobble back and forth across the center frequency. The repetition rate of the wobble determines the frequency of the audio signal and the extent of the wobble determines the volume. Static in radio reception is AM (Amplitude Modulation). Because FM radio is not concerned with amplitude modulation, it can provide practically noise-free program material.

The superior characteristics of FM radio have made it a standard program source in most audio systems. While AM tuners are included in many receivers (such as the one pictured here) and some component tuners, most audio buffs dismiss AM as an inadequate medium for high fidelity sound. For that reason the majority of AM tuners included in receivers are rather skimpy designs that provide only passable performance. There is a small number of companies that manufacture tuners or receivers with quality AM sections.

In addition to providing superior fidelity, much of FM broadcasting offers stereophonic sound. The FM stereo "multiplex" system is compatible with standard mono (single channel). FM tuners not equipped for multiplex merely receive a stereo FM broadcast as a mono signal. Since its introduction in the early sixties, the multiplex system has become standard on virtually all high fidelity FM tuners and receivers.

Record-playing equipment is another source component. More exactly, a set of components: a turntable, a tone arm, a cartridge and a stylus. The turntable is a device that rotates a disc at a constant, prescribed speed. The stylus, more commonly referred to as the "needle" (stylus is much preferred), is a tiny diamond mounted on an armature called the stylus "shank." The cartridge and stylus are both supported by the tone arm, the long rod mounted on a pivot at the far right-hand corner of theturntable. (The "tone arm" derives its name from the era of the acoustical phonograph, when the shape and construction of the arm determined the "tonal" quality of the sound.) All four components

As the turntable platter rotates a record, the stylus rides the record groove, moving in response to the undulations of the groove; undulations that constitute a physical representation of an audio signal. The movements of the stylus are transferred into the cartridge body where they are translated into a low-level electronic signal. This signal is then sent to the preamplifier for amplification and "equalization" (discussed later). Subsequently, the signal is sent to the power amp, amplified and ultimately conducted to the speaker systems.

The turntable, tone arm, cartridge and stylus are available in varying degrees of integration. In other words, you can purchase all the parts together in one package, or as two or three separate components (turntable, tone arm and cartridge/stylus - plus you can purchase additional styli for one cartridge, though cartridges are never sold without styli) that you select and match yourself. The most inexpensive record-playing equipment is typically available as "modules," where all the components are preassembled and sold as a single unit. More commonly, the turntable and tone arm are purchased as a single integrated component and the cartridge (with stylus) is bought as another single unit. Some of the more sophisticated and expensive turntables are supplied without arms and must be fitted with separate tone arms.

Record-playing equipment also comes in varying degrees of automation. The tone arm on a manual turntable must be operated by hand. It requires that you place the tone arm in the record groove at the beginning of a disc and remove it at the end. The tone arm of a semi-automatic turntable operates by push-button and returns by itself at the end of a disc. An automatic turntable will do this and change records without human assistance. Manuals and fully automatic turntables are far more common than semi-automatics, which have only recently been introduced.

The third source component is tape. There are three different tape formats and types of tape machines on the market: "reel-to-reel" (also known as "open-reel"), "cassette" and "cartridge." All three work on the same basic principle of tape recording: magnetizing particles of iron oxide impregnated on a strip of plastic tape.

Reel-to-reel recording is the most widespread and long-standing use of tape. All professional tape applications are reel-to-reel. Reel tape is available in various widths; 1/4 inch is the rule for consumer uses. Professional machines often use wider tape for studio recording.

The two other tape formats, cartridge and cassette, are closed tape packages. Unlike open-reel tape, which must be threaded by hand, cartridges and cassettes are merely slipped m and out of cartridge and cassette tape machines. Although all three tape formats work on the same principle, cartridges, cassettes and open-reel tape are all totally incompatible with one another.

Cartridge tape is 1/4 inch in width, just as consumer open-reel is, but the tape in a cartridge does not travel from one enclosed reel to another. Rather, the tape is a single spool winding back inside itself as it is played, the layers of tape slipping against one another. Because of this arrangement, tape cartridges can be somewhat irregular in speed and cannot be rapidly "fast-forwarded" or run in reverse. Also, it is difficult to record on cartridges because they allow for no more than ten minutes of recording time without interruption. As such, cartridges have been limited to the "home entertainment" and car-tape markets and have never made serious inroads into high fidelity.

At first the cassette may seem similar to the cartridge in that both are small plastic packages. However, instead of a single spool of tape, the cassette is actually a miniature (1/8 inch wide) "reel-to-reel" set-up encased in a container. Because the tape cassette does not have the inherent design problems of the cartridge, it has been able to evolve into a high fidelity medium that can compete with home-type open-reel in most aspects of performance.

Cartridges, cassettes and reel-to-reel tape machines are available as "tape decks," which means they have no internal power amplifiers or speakers and are designed as source components for an audio system to work in conjunction with component amplifiers and speakers. "Tape recorders" are distinguished from decks in that they do have built-in power amplifiers and speakers for playing independently of an audio system. Tape recorders, may also be connected to a separate audio system, in which case they function as tape decks. All of the tape machines discussed in this article are tape decks, built for use as components in an audio system.

Most tape machines have provisions for making tape recordings, either electronically (that is, from an FM tuner or a turntable) or through microphones, for "live" recording. Tape decks, designed only for playing back pre-recorded tapes and not for recording, are referred to as "playback decks." Most cartridge machines are playback decks.

The speaker, also referred to as the "Loudspeaker" is the final component in an audio system. It is the device that translates electrical signals into audible sound, either in headphones designed for personal listening or, more generally, in speaker systems, which can fill an entire room or hall with sound.

There are basically two types of loudspeaker mechanisms in common use. Several others are available and many more have been tried experimentally, but these two are the only types employed in the speaker systems and headphones recommended in this article. These two types of mechanisms are called "dynamic" and "electrostatic."

The dynamic loudspeaker is far more common than the electrostatic. Nearly all speakers designed for non-hi-fi applications use a dynamic mechanism, for example: radios, phonographs, television sets, movie theaters and outdoor sound systems. However, the dynamic loudspeaker is also used in some of the finest speaker systems.

A dynamic loudspeaker employs a magnet, a "voice coil," (moving in response to the electrical information) and a moveable cone (sometimes attached to a solid horn), to increase the volume of the sound.

Each of these loudspeakers has limitations that make it impractical as a full-frequency-range reproducer without augmentation. The cone speaker cannot produce bass frequencies at more than minimal volumes because the compression of air occurring at the front of the speaker tends to be "cancelled" by the rarefaction of air at the rear. Thehorn speaker produces almost no bass at all. Although it may seem that a horn merely "fans out sound," in truth, a horn must be designed according to various acoustical laws. Among other things, these laws demand that the horn be increased in Size as the bass cutoff (the frequency at which bass can no longer be reproduced) is lowered. In order to produce bass down to 20 or 30 Hz, the lowest reaches of human hearing, a horn must be larger than most living rooms. Both of these problems, in cones and horns, have been at least partially overcome through various enclosure designs and certain compromises.

The problem of canceling in cone speakers is traditionally overcome by mounting the speaker inside a cabinet (baffle) large enough to act as an "infinite" space in which the "backwave" of the speaker can be absorbed and canceling cannot occur. The problem with the classical "infinite baffle" design is that it must be very large. If it is made too small the air inside the baffle (cabinet) tends to act as a cushion and raises the "resonance" of the speaker, i.e. the frequency at which theloudspeaker will naturally vibrate. Because loudspeaker response drops off rapidly below the resonant frequency, a speaker system with a high resonant frequency is incapable of producing deep bass.

Two alternatives to the infinite baffle have largely supplanted it in mass-market speaker design. One is the "bass reflex" cabinet. The bass reflex cabinet makes use of the "back-wave" by routing it around to a port at the face of the speaker cabinet. In a properly designed bass reflex the specific distance that the "back-wave" must travel before it reaches the port causes it to arrive too late to cancel the "front-wave" but just in time to joint it and reinforce the total bass output of the speaker system. Aside from allowing a cabinet to be a smaller size, the bass reflex principle also increases the efficiency (relative ability to turn electricity into sound) of the speaker system.

The second remedy for the large size of the infinite baffle was an extension of its own basic design, called "acoustic suspension." As discussed earlier, if an infinite baffle is made too small the air inside acts as a be designed according to various acoustical laws. Among other things, these laws demand that the horn be increased in Size as the bass cutoff (the frequency at which bass can no longer be reproduced) is lowered. In order to produce bass down to 20 or 30 Hz, the lowest reaches of human hearing, a horn must be larger than most living rooms. Both of these problems, in cones and horns, have been at least partially overcome through various enclosure designs and certain compromises.

The second remedy for the large size of the infinite baffle was an extension of its own basic design, called "acoustic suspension." As discussed earlier, if an infinite baffle is made too small the air inside acts as a cushion and rinses the resonance of the speaker. Acoustic Research (AR) was the first audio manufacturer to realize that this effect could be used to good advantage. Instead of using a regular speaker cone, AR designed a very floppy one with an extremely low resonance. By mounting the loudspeaker in a small baffle, the volume of air held within raised the resonance sufficiently to cause the speaker to simulate the function of a standard cone in a larger baffle. The only drawback to "acoustic suspension" is poor efficiency.

Neither the bass reflex nor the acoustic suspension principle has actually won out as the design of choice. At one time acoustic suspension was employed in virtually every mass-market speaker system introduced and seemed destined to take over the speaker market entirely. However, at present, acoustic suspension appears to have lost ground and bass reflex speakers and other speakers employing more esoteric enclosure designs (tuned pipes, transmission line and free-space mounting) now comprise a large share of the current home-type speaker systems.

Attempts to make the horn speaker acceptable as a full-range reproducer have met with limited commercial success, although a full-range horn is quite workable, theoretically. As mentioned earlier, a horn speaker must be increased in size as the bass cutoff is lowered. The vast space and materials required to construct a full-range horn system are prohibitive and only a small number have been built.

Accordingly, there have been two compromises in the use of horns. One has been to employ them solely for middle and high frequency ranges where the necessary horns are still of a manageable size. The Klipsch "Cornwall" and Klipsch "Heresy" speaker systems use horns in these ranges.

The second compromise has been to fold the horn around itself, much like a French horn, to conserve space. This is referred to as a "folded horn." Those designed to work out of a corner, using the walls as extensions of the horn, are called "corner horns." Both folded horns and corner horns are among the most efficient speakers available.

The folded horn had its heyday as a home-type speaker system in the postwar period and the fifties. Today, only a handful of manufacturers offer full-range horn speakers for anything but PA or theater uses. One notable manufacturer who still advocates the use of horns in home-type loudspeakers is Paul Klipsch.

Few wide-range speaker systems utilize only one loudspeaker to cover the entire range of frequencies. Virtually every speaker system described in this article (though not every headphone) employs an electronic device called a "crossover" to distribute different frequency ranges to various loudspeakers within the speaker system.

The loudspeaker that covers the bass range, the "woofer," is the largest loudspeaker, m terms of cone diameter, in any speaker system. The loudspeaker used to cover the high frequencies, the "tweeter," is the smallest of the loudspeakers in any speaker system. (However, a horn tweeter can sometimes be bigger than a cone woofer, as is the case in the Altec-Lansing "Voice of the Theater" speaker system.) A third loudspeaker, called a "midrange" is employed in some speaker systems to cover the middle frequencies. In addition to the mid-range, a few speaker systems also contain a mid-bass driver or a "super-tweeter" for extreme highs or multiples of woofers, midranges and tweeters. Yet it should be understood that the number of loudspeakers employed in a speaker system is not necessarily an index to quality. Ten bad tweeters do not sound better than a single good one.

Another type of loudspeaker, which was popular in the early days of hi-fi, is the "co-axial" design. In a co-axial loudspeaker the tweeter is mounted on the same chassis as the woofer, within the circumference of the woofer cone. While largely a dated approach, quality co-axials are still produced by. such manufacturers as Tannoy, Hartley and Altec-Lansing.