A Speaker is actually a linear motor

That's right. Loudspeakers are really very simple devices from an operational standpoint. An amplifier generates electrical energy that alternates constantly from positive to negative in a pattern of waves that vary in size and frequency. The output from the amplifier is connected to the speaker at the Terminal Strip. There is a fine braided wire that carries the signal from the terminals to the conductors leading to the Voice Coil Assembly. These wires are extremely flexible, to enable the Cone to move back and forth without restriction or stress, and to do so without breaking these wires. The Voice coil itself is mounted on a rigid cylinder, to which it is firmly glued.
All the moving parts operate as a single unit, and are suspended by the surround, or outer edge of the cone at the front, and by the "Spider" at the rear. At it's natural resting point, the voice coil is centered within a narrow magnetic Field Gap. This gap constitutes the north and south poles of the Magnet Structure, whose energy is derived from a powerful permanent Magnet sandwiched between the two pole pieces. Essentially, the speaker operates by responding to positive and negative waves from the amplifier, passing through the voice coil, causing it to be moved back and forth by attraction to one pole of the magnet, and repulsion by the other. Since the voice coil is rigidly mounted to the cone, the resulting energy is transmitted to the cone producing a piston like motion that alternately compresses and evacuates the adjacent air, thus producing sound. If there is a high degree of conformity between the original recorded sound, and the sound produced from the speaker system as a whole, we then have high fidelity. If we do this for two channels of discrete sound information, we have stereo, and if there are four or more channels being activated, we have surround sound.

Things that make a difference in speaker quality

The operating principles that make a typical speaker work today are identical to those used one hundred years ago for the same purpose. The most obvious difference that might be noticed between those first speakers and common units today, is the replacement of the electrical field coil used to create the magnetic field in those early units, by a powerful, permanent (non-electrical) magnet made from highly refined metallurgical materials. Gauss density, which is a measure of the strength of magnets, is many times higher in modern alloys. The higher the gauss density, the greater the field strength. This is the force within the speaker motor that principally determines the amount of power from the amplifier that the speaker will be able to handle.
Another important factor used to assess power handling, is the weight of the magnet itself, which usually has a bearing on the amount of magnetic energy it can produce.
Important tip!
Among important things to remember when evaluating speakers, is to be sure to compare the right sorts of claims. Some manufacturers specify weight for the magnet only, while others weigh the entire magnet structure, which may be up to twice the weight of the magnet proper.
Another important parameter is the material of which the magnet is made. Newer speakers have magnets made of neodymium, strontium, and barium, among other technologically advanced metal composites. Older and cheaper units use alnico 5 and other less dense alloys that may have only one third or less of the magnetic potential of the newer composites.

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