"You would not be losing much music program by purchasing less costly speakers whose frequency response falls off at the lowest and highest ends of the spectrum; as long as they are "flat" through the range of frequencies they do reproduce, the sound will be quite good...in some cases, indistinguishable from speakers with wider response. Compromise is a better way to save money than purchasing speakers that claim response from "20Hz to 30kHz", but give mediocre performance throughout the range they actually reproduce."
"The best way to evaluate a speaker is to listen to it but there are those of us who insist on thoroughly examining the specs and if you're going to read the specifications, make sure you know what they mean."
"Surrounds and spiders are kind of like shoes, they're not very flexible at first but with use, they become much more flexible and as the surrounds and spiders in your speakers become more flexible, your speakers will sound better."
"Before you rush out to begin frantic listening tests with a dozen of speaker systems, you might want to spend time preparing a few questions you might discuss with the audio consultant. What kind of amplifier or receiver will power the speakers? What is the maximum budget, and what budget is comfortable for me? Where are the speakers to be located, and what if anything, limits their placement? What kind of furniture, walls, and overall size describe the room?"
Crossover networks - Nearly all speaker systems (except the “one-way” speakers) use some type of frequency dividing network. Its purpose is to divide the audio spectrum into frequency ranges that complement each driver. If one driver is more sensitive than another, the frequency dividing network may also “pad” the more sensitive driver to smooth the speaker’s response. This network or crossover, as it is usually called, may be fairly complex made up of resistors, inductors, and capacitors (these are known as R-L-C networks where L stands for conductance). Some types of high frequency tweeters, such as the piezoelectric types, naturally reject low-frequency energy, but the lack of a crossover can be considered a shortcut that likely to produce uneven response and may lead to driver failure.
In conventional speaker systems, the crossover is located in the enclosure and this type of crossover is known as the high-level crossover because it electrically joins the output of the power amplifier (high-level audio) to the drivers. The high-level crossover does not require any power supply, so it is known as a passive crossover. Even the best high-level crossover "use up" some audio power, typically 1dB. Inferior crossovers can have insertion losses of several dB and a crossover with 3dB of loss uses up half the power of the amplifier, before that power reaches the drivers.
The crossover network, named for the fact that it crosses over frequencies to the proper driver, has connections to the binding posts on the rear of the speaker, so that the signal passes through the crossover network, and then to the speaker drivers. The property of sending low frequencies to the woofer is called "low pass", and the property of sending high frequencies to the tweeter is called "high pass". If you ever have a subwoofer, you may see these terms used. For example, in setting the low pass frequency that a subwoofer crosses over at, sending all signals below this frequency to the subwoofer amplifier, and the high pass frequency, above which, signals are sent back to the main speakers.
Crossovers slopes & frequencies - Crossover “point” of a speaker system is a center frequency in a range of frequencies where, as the frequency rises, the input to the lower frequency driver is gradually attenuated and the input to the higher frequency driver is gradually increased. "Crossover region" is the range of frequencies where both drivers are reproducing the same frequency. “Crossover point”, “crossover frequency” or “transition point” is the frequency where the output from two drivers is approximately equal. “Crossover point” may also be defined as the frequency where each driver is being fed 3dB less power than its full out-of-the-crossover-region power. Crossover frequencies are chosen to complement the drivers and to roughly split the frequency spectrum into equal energy portions.
In a 3-way system, the low-to-mid and mid-to-high frequency transitions usually occur somewhere around 800Hz and 5kHz. In a 2-way system the low-to-high frequency transition will usually occur between 1kHz and 2kHz. These crossover frequencies may vary considerably, depending on the system; the crossover frequency should not be considered an index of quality. Crossover “slope” is the rate at which the transition from one driver to the other takes place, and is usually expressed in dB per octave. Most common slope rates are 6dB/octave, 12dB/octave, 18dB octave, and 24dB octave. The steeper the slope (the larger the number), the more narrow the crossover region. Steep crossover slopes can be beneficial because they protect the drivers better, but the chances of phase distortion increase. Like so many other aspects of speaker design, crossover design involves trade-offs and in most cases, 12dB per octave is the best compromise.
Passive vs active crossover - Passive crossover does not require electricity and does not use active circuitry to accomplish its task. Found in almost all speakers, they divide up the incoming signal and serve it to the various speaker drivers that make up the speaker. Passive crossovers are not adjustable beyond their factory-created settings making them somewhat less versatile than active crossovers using electronic circuitry to accomplish the crossover tasks. Passive crossovers use resistors, capacitors and inductors. Active crossover uses electronics supplied with a power source and acting on the sound to shift sound reproduction tasks from one speaker driver to another. Active crossovers are the most flexible types and compared to passive crossovers, which are fixed and use specified filters and capacitors. Active crossovers are adjustable and use electronic circuits to split up the frequency spectrum. These electronic circuits are often “cleaner” sounding than their passive counterparts. Most if not all powered subwoofers include active crossovers to split up the signal which they will reproduce from that which should be passed on to the other speakers.
Crossover quality - Active crossover network is not better in quality than a passive unit, or vice-versa, since these are variations of the same circuit, and are made to serve different purposes. Quality of any crossover, passive or active, depends on its components, its design, and its construction and you’ll probably have to find out about a given speaker’s crossover by asking the salesperson or reading the manufacturer’s literature. There are several criteria to use in evaluating a crossover; self-healing capacitors and low-loss, low-distortion inductors are desirable and resistors should have adequate power rating. To assure similar response from each speaker in a stereo pair, crossovers should be carefully matched as poorly matched crossovers will cause the stereo image to jump or to be unsteady. Better crossovers will meet all these criteria, and will introduce as little loss as possible, about 1dB (a 3dB loss would be a loss of 50% of the amplifier’s power). Inferior crossovers may introduce great power losses, may be more prone to “burn out”, and may not provide the smoothness of response that might otherwise be possible from drivers and enclosure.
Speaker drivers - Manufacturers often mount several different “drivers” in each enclosure. “Driver” is a term used to describe any component of the speaker that produces sound. In an attempt to maintain even dispersion, lower distortion and simpler driver construction, most speaker systems divide the frequency spectrum into two or three segments for reproduction by separate drivers which are optimized for each segment. These are known as “2-way” or “3-way” speaker systems. The frequency divisions are accomplished with crossover networks (frequency dividing networks) and are chosen so that the drivers cover approximately equal portions of the audio spectrum, by octaves. An octave is the interval between a given tone and its repetition eight tones above or below on the musical scale; a note which is an octave higher than another note is twice the frequency of the first note.
An enclosure with three or four drivers is not necessarily a 3 or 4-way speaker, since many manufacturers use several drivers to cover the same portion of the audio spectrum. Some speakers even have as many as eight or more identical drivers in one cabinet, each driver covering the full audio spectrum. A driver must move air at low frequencies to produce the same sound level as it would when producing mid or high frequencies. Thus, the bass driver is normally larger than the other drivers; the mid and high-frequency drivers are not required to move as much air, so they can be made smaller.
Small drivers actually offer an advantage with respect to dispersion pattern and crossover networks assign higher frequency sounds to smaller drivers so that wide dispersion can be maintained. Physical laws show that dispersion narrows as the wavelength of a sound approaches the diameter of the driver. Wavelength is the distance that the beginning of a sound wave travels by the time the next cycle vibration begins; the higher the frequency, the shorter the wavelength. This means that with a given size driver, as the frequency goes up, the dispersion narrows and by “crossing over” to a smaller driver, the wavelength becomes large with respect to the driver, so dispersion is wider than it would have been with the larger driver. Manufacturers sometimes use horn-type mid or high-frequency drivers to control dispersion to improve the efficiency. The horn is a funnel-like structure that flares out in front of the moving driver element. In larger speaker systems, horn-loaded drivers (cone type) may also reproduce the low frequency. While different types of drivers have characteristics separating them from each other, compression drivers with horns, cone drivers (with or without horns), and ribbon drivers all exhibit frequency response and dispersion which are related to driver size.
Types of speaker drivers - Speaker drivers can be categorized in two ways, with regard to the frequency range they are meant to reproduce, and with regard to their physical design. Speaker drivers meant to reproduce bass frequencies are known as "woofers". Speaker drivers meant to reproduce the middle frequencies are known as "midrange drivers". Speaker drivers meant to reproduce the treble frequencies are known as "tweeters". 2-way speaker systems have at least one woofer and one tweeter. 3-way speaker systems have at least one woofer, midrange and tweeter. 4-way speaker systems may divide the mid-range into two segments for coverage by different drivers. Some speaker systems utilize additional drivers called "subwoofers" for the extreme bass region and "super tweeters" for extreme treble region.
low-frequency driver is also commonly called a “woofer” and it
covers the frequency range of “bass” tones - low vocals and instruments.
limit of the woofer is partly determined by the cabinet configuration, and
generally falls in the range between 30Hz and 100Hz. The
woofer’s high frequency limit usually falls somewhere between 600Hz
and 800Hz in a
3-way system, or between 1,000Hz and 2,000Hz in a 2- way system. Actual limit for a given woofer is determined by the diameter and mass of the cone, and by the slope and transition of the crossover network.
Midrange drivers - Midrange frequencies are important to most vocals and instruments, and the uppermost frequency response of the mid-range driver begins to reproduce some of the “sibilant” range (breath sounds in vocals, etc). “Midrange” may be defined roughly by 500Hz (lower limit) and 5,000Hz (upper limit) and the midrange driver covers most of the midrange frequencies, from the upper limits of the woofer’s response, to the lower limits of the tweeter.
Tweeters - In a 3-way speaker, the tweeter covers those frequencies above the limit of the midrange driver, and up to 20,000Hz or higher. In 2-way speakers, where there is no midrange driver, the tweeter also covers the upper midrange (while the woofer cover the lower midrange). Upper harmonics of instruments, cymbal sounds and sibilants are reproduced by the tweeter.
Full-range drivers - Full-range single driver speakers attempt to cover the entire audible frequency spectrum using only one driver unit, removing the need for an electronic crossover network, which is well known for being hard to design without introducing colorations to the sound. In practice, how well a single driver speaker delivers depends both on the driver and the speaker cabinet design. Several types of “full-range” or “wide-range” drivers are available and the simplest being the “coaxial” driver which consists of a woofer with a smaller “whizzer cone” in the center. The “whizzer” cone is fixed to the larger cone and driven by the same voice coil, but allows the overall response to reach higher frequencies with wider dispersion. Some full-range designs share one magnetic assembly but use separate tweeter and woofer sections with their own voice coils. One such design employs a compression driver mounted behind the woofer cone, with a throat (emerging from the center of the magnet) terminated by a small horn.
Electrostatic drivers - The "electrostatic" drivers cover mid or high frequencies, and sometimes both while a few designs even attempt to reproduce bass frequencies, though results are questionable. The electrostatic driver is constructed of two preforated plates which are charged with high voltage at opposite polarities and a diaphragm between the plates is driven by a conventional power amplifier and audio signals (voltages) applied to the diaphragm cause it be alternately attracted to one plate and then the other, moving air to create sound. Excursion of an electrostatic diaphragm is limited, and therefore its low frequency output is limited. The electrostatic drivers also require a polarizing voltage; some units must be plugged into the wall, others require a special amplifier with built-in power supply, while others rectify a portion of the audio energy fed to the driver to polarize the plates. Unless they are very large in size, electrostatic drivers have limited sound output but they have many advantages in that they may image better and create a more open and expanded soundstage than conventional cone speakers.
Courtesy of HowStuffWorks
Compression drivers - Very high efficiencies can be obtained with compression driver. Compression drivers operate like cone drivers, except that the diaphragm is usually metal, and it must be loaded by a lens or a mid or high frequency horn. Properly designed horns and lenses have controlled, if not wide, dispersion. Major disadvantages of compresion driver systems are their size, cost, and sometimes limited dispersion.
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