Anatomy of a loudspeaker
Your typical dynamic loudspeaker consists of several parts:
- A diaphragm to move the air (typically shaped as a dome or cone)
- A voice coil wound around a voice coil former (typically plastic, metal, or paper) to exert force on the cone
- A magnet and pole structure to provide a magnetic field for the voice coil to act against
- A suspension to keep the voice coil centered in the magnetic gap and returns the cone to a centered "rest" position
- A basket (or chassis) to hold everything together
The Basket
The basket holds the whole driver together. It is a rigid structure that keeps the voice coil aligned in the magnetic gap and gives you some way to mount the driver. Ideally, the basket will not resonate in the working frequency range of the driver.
The Suspension
Your typical driver's suspension is comprised of two parts - the surround and the spider. The suspension provides three critical functions:
- It centers the voice coil and cone throughout their excursion
- It applies a restoring force on the coil/cone directed toward the rest position of the coil
- It provides some mechanical damping
The spider is typically a pleated ring that is attached between the voice coil former and basket. It provides most of the stiffness of the suspension and locates the voice coil in the magnetic gap. The spider is usually made of a woven fabric. There are two main types of spiders: progressive and linear. Progressive spiders are designed to exert a linear restoring force (that is, a force proportional to excursion) - see
[Hooke's law]. The pleats in progressive spiders are large on the outside and gradually get smaller toward the voice coil former. Linear spiders exert a non-linear restoring force with excursion in that the force increases faster than the excursion. This is helpful to prevent over-excursion which can damage a driver but may increase distortion within the linear region of excursion. The pleats from the center to the circumference of a linear spider are all the same size.
The surround is attached between the outer edge of the cone and the basket. In addition to applying a small restoring force, the surround contributes much of the mechanical damping of the driver. It is usually made of a material like rubber or foam, but some drivers use pleated cloth surrounds as well. Different surround materials have different characteristics which are useful to a speaker designer.
The Cone
The cone is the part of the loudspeaker that alternately compresses and rarefies the air according to the signal fed to it; this is how sound is created. The ideal cone in a multi-driver speaker acts as a rigid non-resonant unit throughout the operating frequency range of the speaker. The cone attaches to the voice coil former and the surround. For subwoofers the cone is fairly mundane, but its design becomes increasingly important at higher frequencies.
A dust cap is often glued over the center of the cone to keep dust out of the magnetic gap. Sometimes (like in Seas woofers) in lieu of a dust cap there is a "phase plug" which is a bullet-shaped piece that protrudes from the center of the cone where the dustcap would be and is used to aid the response and dispersion characteristics at high frequencies. The "phase plug" can also aid in thermal dissipation, if made out of a thermally conductive material like aluminum or copper.
Though now part of common parlance, the phase plug should be called the center cap, because phase plugs were originally used in compression drivers to correct the phase of the sound produced by the diaphragm so that cancellation would not occur.
The Magnet Structure
The magnet structure in your typical speaker consists of three parts:
- The magnet itself
- The top plate
- The t-yoke (comprised of the pole piece and back plate)
The magnet provides the flux in the gap that the voice coil acts against to move the cone. Many older drivers used an electromagnet called a "field coil" to provide the magnetic field; the introduction of cheaper and more reliable permanent magnets has eliminated this from modern drivers.
The combination of the top plate and the t-yoke concentrates the magnetic field in the "gap" that the voice coil moves in. The t-yoke is often vented to allow forced air circulation on long-throw drivers for cooling the voice coil.
The Voice Coil
The voice coil consists of some fine wire wound around a tube called a former. The wire is usually copper or aluminum and the former material is usually Kapton (a high performance plastic, whose trademark is registered by DuPont
?) or aluminum. The voice coil is connected to your speaker leads by tinsel leads; these are thin, flexible wires meant to withstand constant movement. In non-woofer drivers, the tinsel leads typically rest between the cone and the spider, supported only by their two ends (where they attach to the voice coil and the driver terminals). However, in drivers with higher excursion, the tinsel leads are sometimes woven into the spider to eliminate a destructive phenomenon called "tinsel lead slap", where the leads slap against the cone.
Electric current applied to the voice coil exerts a force on the cone due to the interaction between the magnetic field produced by the current flowing through the voice coil and the field that exists in the voice coil gap. This force causes a movement of the diaphragm, which follows the input signal, giving us the sound we want.
=Will Finish Later=
