The most common type of speaker is a cone speaker. This speaker has a diaphragm made out of a cone of a fairly stiff material, such as paper, polypropylene, carbon fiber, or aluminum, although other more exotic materials have been used. The diaphagm moves back and forth, pushing air out into the room, generating the sounds you hear.
The best material for a speaker cone is something that has low mass, good stiffness, and good damping properties. The low mass improves the speakers efficiency, meaning less power is needed to drive the speaker. If the material is not stiff enough, it won't generate clean sounds, especially at higher frequencies and higher volumes. And if there's not enough damping, the speaker will have a characteristic "ringing" sound.
Interestingly, paper is a good speaker material, because it has all of the properties needed. However, paper has the disadvantage of not handling moisture well (including changes in humidity). Polypropylene is used often in in outdoor or high moisture applications. Aluminum and other metal cones are light and stiff, but often don't have sufficient damping properties, and can sound too "bright". Fiberglass, Kevlar and Carbon Fiber have good properties, but can increase the cost of the speakers. So if you're interested in good speakers, and willing to pay a little more, we often recommend these materials.
The best material for a speaker cone is something that has low mass, good stiffness, and good damping properties. The low mass improves the speakers efficiency, meaning less power is needed to drive the speaker. If the material is not stiff enough, it won't generate clean sounds, especially at higher frequencies and higher volumes. And if there's not enough damping, the speaker will have a characteristic "ringing" sound.
Interestingly, paper is a good speaker material, because it has all of the properties needed. However, paper has the disadvantage of not handling moisture well (including changes in humidity). Polypropylene is used often in in outdoor or high moisture applications. Aluminum and other metal cones are light and stiff, but often don't have sufficient damping properties, and can sound too "bright". Fiberglass, Kevlar and Carbon Fiber have good properties, but can increase the cost of the speakers. So if you're interested in good speakers, and willing to pay a little more, we often recommend these materials.
The mechanism that moves the cone back and forth is a large magnet and an electromagnet. These two work together to vibrate the cone, compressing and decompressing the air, and generating sound waves. Note that the speaker generates sound in both directions. Since the reverse direction is exactly opposite the forward direction (180 degrees out of phase), care must be taken to ensure the reverse sound doesn't cancel out the forward sound!
In order to provide a stiff frame for the magnets to drive against, the speaker has a "spider", which is a stiff cage. Many spiders are made from a stiff plastic, while others are made of aluminum or another metal. At one time, spiders were made of Bakelite, but plastic and aluminum are much more durable. Plastic is light and inexpensive, but can distort under high load (high volume).
Speakers also have a flexible surround which binds the cone to the frame. This surround also keeps the sound generated by the reverse direction of the cone from coming around to the front and canceling the sound generated by the forward direction. In many older speakers, the surrounds have degraded to the point where this happens, and the speakers need to be repaired or replaced.
I'll talk more about speaker types and speaker design in future Blog postings, so stay tuned!
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