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"Efficiency has no direct relationship to the quality of sound reproduction, and many lower efficiency speakers have excellent frequency response, low distortion, etc."

 

"Floor-standing, or tower speakers have been around for years and in many ways remain the standard against which all other speaker types are judged."

 

"A speaker will always change the original sound because realistically, there is no perfect speaker!"

 

"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."

 

Keep abreast of the latest news, information and reviews on loudspeaker design and technology.

 

"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?"

 

"If you are tempted to leave the decision to a friend or a trusted salesperson, remember this;nobody knows better than you what sounds good to you! Speaker preferences are personal, and you should make the selection. If you do leave it to a friend, you may end up owning what your friend likes and not what you like!"

 

"Choosing a speaker system merely on appearance or name brand recognition may be the worst mistake a consumer can make when they are evaluating new speakers."

Speaker enclosure - The name of a speaker enclosure is usually chosen to correspond with the configuration of the low frequency section. For example, “bass-reflex” and “acoustic suspension” refer to the construction of the low frequency cabinet. Cabinet design affects the mid and high frequency drivers as well, but its primary effect is on the lows.

If a woofer were placed out of doors, with no enclosure, it would exhibit very poor low frequency response because the cone would be “pushing” the air in front of it at the same time that it would be “pulling” the air from behind. The rarefield (a zone of lower air pressure, opposite of compressed or higher air pressure) sound wave from the rear of the cone would travel around to meet the compressed sound wave from the front of the cone, canceling the sound to a greater or lesser extent.

Infinite baffle - An “infinite baffle” enclosure is not really an enclosure, rather it is more like a wall of infinite height and breadth. The sound waves from the rear of the woofer cannot get around the front, thus solving the problem of rear-to-front-phase-cancellation. A closed or sealed box, with a woofer mounted in one face, effectively stops the sound radiated behind the cone from reaching the front, so it is called an infinite baffle enclosure. The drawback though is that because a driver moves as much air behind as it does in front, the box must be quite large (10 cubic feet or more) to prevent the mass of trapped air inside the box from acting like a spring, which can raise the effective resonance of the speaker. A moderate-sized enclosure of about 3 cubic feet, the low frequency response is somewhat more limited than that of a true infinite baffle.

Acoustic suspension - This type of speaker is a variety of infinite baffle box with a specially designed woofer. The woofer has a very low resonance that partially counteracts the resonance-raising characteristic of the sealed box. The acoustic suspension woofer must be capable of long, linear cone and voice coil excursions so it can produce solid bass output below the system resonance. Even smaller acoustic suspension enclosures (1 cubic foot or less) can exhibit good low frequency response.

Bass-reflex - A more popular design. The “bass reflex” design attempts to get more bass response by using an enclosure that controls rear-radiated sound waves. A port or vent distinguishes the bass reflex enclosure from a sealed box. The port extends low frequency response by lowering the speaker’s resonance (it makes it seem like a larger box). The sound energy from the rear of the driver can come through the port in phase with a sound from the front of the driver, thus improving the overall efficiency of the system.

Passive radiator - Passive radiator is a driver that is not powered (un-driven) similar to the low frequency driver (woofer), except it has no voice coil or magnet, and is used in conjunction with a woofer generating movement by being vibrated by the back pressure of the powered woofer. Passive radiators replace ports to achieve a similar effect; instead of being ported, the woofer enclosure is sealed and airtight. The powered woofer moves and creates pressure inside the cabinet, increasing pressure as it moves in and decreasing pressure as it moves out. The passive radiator is moved by these pressure changes being pushed out as the woofer moves in compressing the air inside the cabinet and being pulled in as the woofer cone moves out. The passive radiator allows the back force of the powered woofer to increase sound levels without using a port which results in tighter, lower bass.

Transmission line - This design uses a long tunnel within its cabinet internal structure by introducing internal partitioning that fold the line up and down the length of the cabinet. At the very end of the line there is a hole with specific size that vents directly into the room. The major benefit to this design is that the labyrinth braces the entire structure from beginning to end which helps eliminate cabinet coloration created by the effects of the outer walls of the cabinet flexing.

The main driver is placed on the front face, heavily damped with absorbent acoustic material. This acoustic material or foam has to absorb all the upper bass frequencies and allow the lower frequencies to exit the vent at the other end of the line in phase with the main driver. Equilibrium must to be achieved between the length of line and the acoustic absorbency. That achieved, air density will increase by up to 30% making the 'effective' line length far greater than its physical length. This backpressure holds the main driver, huge frequency range is achieved, unwanted cone movement is reduced which lowers audible distortion. This lack of harmonic distortion in the low frequency creates excellent midrange clarity. The consistent air loading also facilitates full audible bandwidth at all listening levels allowing for extended periods of listening without the risk of fatigue. Transmission line speakers are capable of producing phenomenal low frequency extension even from a modest box.

Push-pull - Another variation is called "push pull" which uses two active drivers for the pushing and pulling. One driver is mounted inside the non-vented box facing outward, and another is mounted outside, facing inward, with the two drivers electrically connected out of phase so that when the cone of one is being driven outward, away from the magnet, the other is being pulled inward, towards the magnet, both being actively driven by the amplifier. But because they're electrically out of phase, and mechanically out of phase, they're acoustically in-phase. The primary benefit of this arrangement is that even ordered harmonic distortion from each driver is acoustically out of phase, due to the inverted mechanical orientation, and so cancels out, resulting in lower distortion. This design also benefits an increase in efficiency of roughly 3 dB due to the presence of a second driver working in tandem (assuming the drivers are fairly close to each other) and the two drivers have the potential for four times the output of a single driver.

Horns - A low frequency horn is a special type of enclosure. Instead of mounting the woofer flush on one face of the enclosure, the low frequency horn has a flared opening on one side of the woofer cone. The flared structure or “horn”, serves to acoustically couple the cone to a larger volume of air and this coupling is known as “loading”. Horns which are built out from the front of the woofer are known as “front-loaded” or "straight" horns, whereas horns built out behind the woofer are “rear-loaded horns”. The primary advantages of a horn are an increase in driver efficiency and more controlled dispersion; the primary disadvantage is their large size (for low frequency horns).

A low frequency horn is similar to a mid or high frequency horn, except the low frequency horn must be quite large in size due to the long wavelengths at low frequencies. One compromise is the “folded” horn, which is compact version of a full sized low frequency horn created by “folding” the horn back around itself. A further variation of the folded horn is an enclosure that uses the corner of a room to extend the effective size of the horn and it can develop very good low frequency response at high efficiency. Horns are often used for the mid and high frequency portions of a speaker system and since they are not required to reproduce large wavelengths, mid or high frequency horns can be much smaller. Again, some are straight, and others are folded and unlike low frequency horns, which use cone-type woofers. High frequency horns are not meant for use with cone-type midrange or tweeters; they are meant to be used with compression drivers.

Ribbon, Planar magnetic & Electrostatic - Some speakers do not use cones, they have thin foils suspended between magnets or metal sheets instead. With a ribbon speaker, the musical signal is applied to a foil ribbon, and the varying electrical charge placed upon it by the music causes it to be attracted or repelled by the magnets, moving air in doing so, and thus reproducing the sound. A variation on this consists of a foil attached to a large flat membrane, and it is the membrane which is suspended, such designs are called planar magnetic.

Electrostatic speakers, by comparison, have a plastic membrane, coated with something like powdered graphite, suspended between two perforated metal sheets. A positive voltage (several thousand volts) is connected to the membrane, and the musical signal, the voltage of which is increased by a transformer in the base of the speaker, is applied to the perforated sheets. The varying signal in the metal sheets attracts or repels the membrane, and the music is reproduced.

These ribbon, planar magnetic and electrostatic speakers reproduce midrange and upper frequencies with superb clarity, but are not very good at the low frequencies (below 100Hz) because of the lack of an enclosure to prevent the rear waves from canceling the front waves where the sound gets omni directional. Exceptions are very large panels, where the diaphragm itself provides a baffle to separate the front and rear bass waves. Therefore, they usually have standard cone type speakers in a separate cabinet at the base to serve as woofers, using a hybrid design. Ribbon speakers, planar magnetic and electrostatic speakers are dipolar in nature.

Subwoofers - Subwoofers are designed to reproduce only the lowest frequencies in the music or movie sound track. The woofer drivers typically range from 8" up to 18" in diameter and most have built-in power amplifiers, and a few are just the driver in the enclosure (passive subwoofer) where you will need a separate power amplifier to use them. Most subwoofers design follows the 3 traditional types of enclosure design discussed earlier; bass-reflex, passive radiator and push-pull. Other types of subwoofer designs are bandpass and transmission line systems. There are 10 octaves in the range of human hearing. Each octave doubles the frequency; octave 1 is 20 Hz - 40 Hz, octave 2 is 40 Hz - 80 Hz, octave 3 is 80 Hz - 160 Hz, and so on, up to 20 kHz. Subwoofers reproduce the lowest 2 octaves, or 20 - 80Hz or slightly higher. You will need a subwoofer if your speakers are not capable of producing the sub-frequencies especially in surround sound setup.

In-wall speakers - In-wall speakers form a special sub-section of enclosures since they typically use the wall itself as an enclosure. Some in-wall designs utilize a complete sealed or ported enclosure that is built into the wall, but most feature only a baffle and drivers. The speaker is mounted in the wall between studs with the baffle fixed flush with the wall's surface and most in-wall speakers are fairly small in size, similar to a bookshelf speaker with similar sonic characteristics and a general lack of low bass extension. In-wall speakers are a special form of speaker intended for custom installation and their primary benefit is that in-walls do not take up any space in a room and can be hidden in various locations. In-wall speakers may be placed in the ceiling, floor or anywhere across a flat wall surface and they are particularly well suited to whole-house audio systems where they are used to provide background music in multiple rooms without the need for regular speakers and their associated equipment. Most in-wall speakers use the wall cavity as their enclosure; they are attached by special screws in the baffle to the drywall (or other wall surface), to a nearby stud, or to a special frame attached to the studs.

Generally, in-wall speakers do not perform as well as their out-of-wall counterparts as the wall structure does not provide a solid, resonant-free enclosure as can be had with traditional enclosure designs. The speakers also tend to suffer from diffraction as sound waves moving to the sides of the speaker are reflected off the wall surface. The wall surface itself also tends to vibrate with the speaker muddying the sound, especially in the low bass ranges. Placement of in-wall speakers is highly flexible since they can be inserted into almost any wall cavity but in-wall speakers are often not placed for optimal listening quality. The speakers may be placed near ceilings, in corners, in the ceiling, but most of those positions place the speakers too far above or below ear level. Therefore, in-wall speakers are better for background music or surround channel and not for critical listening. Subwoofers may be used to supplement the bass capabilities of in-wall speakers, and there are in fact subwoofers designed to be installed as in-wall speakers themselves.


Bipolar vs dipolar - The direction that the speakers radiate their sound depends on how the drivers are lined up in the enclosure. If the speaker has all drivers in the front, and radiates sound primarily forward, it is called a "front" or "direct" radiating speaker. If there are some drivers on the back, and those drivers are in phase with the front drivers, it is called a "bipolar" radiator. The bipolar design pushes out more bass and is the design used for main speakers. If there is substantial output from the rear of the speaker, and it is out of phase with the output from the front of the speaker, either due to out of phase drivers, or simply because the output is from the rear of the same speaker of the front, such as the case of Ribbon, Magnetic planar or Electrostatic panels, it is a "dipolar" radiator. This technique produces a more diffuse sound and is used for surround speakers.

Active speakers - Active speakers use drivers powered by their own internal amplifiers and differs from a traditional speaker in that they do not need an outside source of amplification. A common example of an active speaker is a powered subwoofer. When using an active speaker, an interconnect cable is connected to an input terminal on the speaker which feeds a low level signal directly from the preamplifier to the speaker's built in amplifier(s) instead of using speaker wire and the associated high level, amplified signal. When properly designed, an active speaker benefits from amplifiers designed to work specifically with its drivers and their specific characteristics. This may allow higher quality output or more efficient powering of the speakers, if the built-in amplifiers are of high quality and are properly matched to the speakers that is. However, active speakers take away some degree of choice, as one cannot choose an amplifier separate of the speakers or upgrade the amplifier at a later time. Active speaker systems are commonly used in studios and production houses.

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