"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."
"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."
"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!"
"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."
There are 5 basic parts to a driver; basket/frame, magnetic assembly, voice coil, suspension/surround system and diaphragm/dome/cone. Speaker basket provides a means to mount the driver in an enclosure. Some speaker baskets, particularly on high frequency drivers, may completely encase the back of the driver in order to acoustically “load” the unit, and to prevent interaction with sound pressure generated by other drivers in the same enclosure. Most low frequency driver baskets are of open construction, not only to reduce weight, but to allow the sound waves to radiate from the back of the cone into the enclosure. Regardless of the appearance or design of a basket, it must be rigid because it holds the driver’s parts in alignment; if the basket deforms in the least amount, audible distortion quickly develops. Basket deformation can lead to premature burn-out of the voice coil by allowing it to scrape against the magnetic assembly.
Magnetic assembly - The voice coil produces an alternating magnetic field which interacts with the fixed magnetic field of the magnetic assembly to produce movement of the cone. Strength of the magnetic field in the voice coil gap affects driver efficiency. Better drivers concentrate more “flux” in the voice coil gap with a magnetic “return circuit”. Circuit consists of steel or iron bottom plate and a “pole piece” that is attached to the magnet and serves to capture stray magnetic lines of force and to redirect them into the gap.
Voice coil - Conversion of electrical energy to mechanical motion depends on the voice coil. Audio (electric) current flows through the coil, and creates a changing magnetic field that interacts with the permanent magnet field in the voice coil gap, causing the coil and the cone, dome or diaphragm to which it is attached to move back and forth, creating the air motion which is sound. The most desirable coils are "edge-wound" with specially formed flat (squared) wire allowing a higher concentration of wire in the same area, increases the strength of the magnetic field, and therefore increases the driver’s efficiency. Copper coils and aluminum coils are common, but the choice of wire depends on the specific application. Copper has slightly lower power losses than aluminum wire, aluminum is lighter than copper, so the aluminum coil can move faster and may be more efficient and more accurate. Coil is wound on a paper, plastic resin, or metal form etc., and the form is suspended in the voice coil gap by the cone and spider assembly.
Suspension - In a woofer, the voice coil must move back and forth over a considerable distance. If the woofer is to have low distortion, the conversion of electrical energy to sound must be linear along the entire excursion. If the voice coil moves partially or completely out of the gap, it can cause distortion (non-linearity), and the stress may injure the driver. Similarly, the voice coil can hit the bottom of the gap causing distortion, and possible damage to the driver. The job of the suspension (also called surround) is to hold the voice coil in proper alignment as it moves through the gap, and to limit its excursion. The suspension may be stiff to limit travel at the extremes, or it may be loose. Loose loudspeaker suspension, relies on the air in a sealed enclosure to limit the cone motion, which is the origin of the term “acoustic suspension”. “Surround” is the part of the suspension that attaches the outermost edge of the cone or dome to the frame. “Spider” is the part of the suspension that attaches the voice coil form to the frame.
Cones, domes & diaphragms - Cone, dome or diaphragm, is the final link in the conversion of the electrical power to sound. A woofer cone must move as a whole and if the material is not stiff enough, the cone will begin to ripple and “break up”, especially at higher frequencies. Most cones are made of paper and sometimes the paper cone is “coated” to “tighten” low frequency response, although too much mass in the form of a coating will degrade transient and high frequency characteristics. Cone assembly made of heavy metal, for example, would be unlikely to deform, but the amplifier would waste most of its power simply overcoming the inertia of the cone. The mass of the cone assembly affects the resonance and efficiency of the driver so cones tend to be lightweight and sometimes the manufacturer adds ribs that strengthen the cone without adding much mass.
A few wide-range drivers intentionally utilize the tendency for the cone to break up at higher frequencies by adding a ring of softer material in the middle of the cone, which allows the cone to move in two segments; entire cone moves for lower frequencies, and just the inner portion moves for higher frequencies. Midrange and high frequency drivers may be constructed of special materials and in special shapes to provide the required stiffness with minimum mass, and to improve dispersion. Instead of a cone, the driver may use a hemispherical dome, or, in a compression driver, a gently curved diaphragm. Dome drivers exhibit some narrowing (“beaming”) at higher frequencies, but not a severe as that of conventional cone drivers. Compression drivers are meant to be used with horns, and the horns control the dispersion.
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