What are the speaker failures ?
How does a speaker work ?
The sound we hear is produced by the displacement of a conical membrane that vibrates the air, which causes the vibration of our eardrums.
To put the air in motion, the speaker uses a cone. At the back of this cone is glued a moving coil.
The cone is mainten perfectly in place by two flexible elements:
- The edge at the front of the membrane
- The spider at the back of the cone.
All of these moving parts are called "the moving crew"
The voice coil moves back and forth in a very narrow space called the gap without ever touching it. The gap is this space which delimits the two poles of the magnet.
In the air gap the space is only a few tenths of a millimeter. The space is narrow but the coil does not rub, if there is no friction, there is no wear.
If the loudspeaker is used within its limits, the voice coil lasts indefinitely.
A properly used speaker has an unlimited life.
The only two pieces that can wear are the edge and the spider.
The spider is built in an extremely resistant material, it is very rare that it needs to be changed. only the edge has an average life of fifteen years. After fifteen years we can change the edge to have another fifteen years and so on.
In normal use, the edge is the only part that wears on a loudspeaker.
The "edge" is the flexible edge of the cone.
The cone is usually made of cellulose fiber
The voice coil is the motor of the speaker.
Damage to the speaker edge
The edge and the spider are parts of the loudspeaker in great demand. They vibrate and deform several hundreds and even thousands of times per second!
At the rear, the spider is made of a very thick, very strong structure.
At the front the membrane is maintained by a suspension of polyethylene foam or synthetic rubber.
Speakers with foam edge have an average life of 15 years. Beyond the rim of the membrane disintegrates and falls into dust. This phenomenon occurs in the same way on unused speakers because it is a natural wear of the material.
This is not a serious breakdown, just change the edge for the speaker to leave for fifteen years and so on. This operation can be repeated to infinity.
It is inadvisable to operate a loudspeaker with a edge out of use because in this case the cone is no longer maintained at the front, it is no longer centered and the coil will wear while rubbing in the air gap.
In the photo on the left we see a 21.5 cm diameter SEAS 21F-B speaker whose edge has almost completely disappeared.
Do not believe that the speakers equipped with "rubber" suspensions, are therefore immune to this problem.
Some speakers are equipped with "rubber" suspensions that harden over time to the point that they eventually harden to the point of completely blocking the membrane. These suspensions become hard and brittle. They must be replaced.
Often a simple visual inspection can discern an damaged edge. On this speaker JBL it is very clear that it lacks pieces of edge. There is also a tear between the cone and the edge. Sometimes the edge is disintegrated even though it is not visible to the eye.
Edge wear test
A edge may look in good condition while it is no longer.
To find out if a edge is still good, try the following test. Pinch the edge between your fingers. It must be firm. If it is sticky or it is left between the fingers is that the edge is to change without waiting otherwise it can cause wear of the coil, which is more serious.
Damage to the voice coil
Although rarer, the damage on the mobile coils of the speakers is more serious.
If the edge of the loudspeakers can be compared to the tires of a car that naturally need to be replaced from time to time when they wear out, the voice coil associated with the magnet can be compared to the "motor" of the loudspeaker. speaker. It is the only active element of the loudspeaker, it is the coil that vibrates the membrane of which it is integral.
The voice coil consists of a cylindrical support which can be made of different materials, and a conductive wire wound around this cylindrical support. If the coil wire turns off the speaker becomes mute.
The coil does not cut itself. In normal use, they move back and forth in a very narrow space called the air gap, without ever touching it. There is therefore no wear since there is no friction.
The wear of the edge is one of the causes of friction of the voice coil in the gap. This audible friction is unpleasant. He recognizes himself easily.
Damage on voice coil
The symptoms are multiple:
- Speaker does not sound anymore
- The speaker makes a bad sound
- The cone is blocked, it does not move anymore
- The voice coil rubs in the gap
Voice coil test
To check if the speaker coil is rubbing in the gap, do the following test. Lay the speaker flat on a table. Press gently in the center.
The cone must move without friction
If you feel friction the coil is damaged.
Externally the speaker seems intact, yet it produces no sound. This is the classic symptom of a split voice coil.
There may be several reasons for the degradation of a voice coil, the friction of a edge out of state is one, but it is not the only one.
Other reasons are related to the abuse of speakers, and some are due to malfunction of the amplifier.
The use of Hi-Fi speakers to animate a party with friends is the first cause of death of a speaker. During the party the sound is gradually raised for several hours until the coil burns by excess heat accumulated in the speaker. It's classic.
The disassembly of the loudspeaker leaves no doubt about it, the coils of the voice coil detach and the copper wire is partially or completely burned and we smell a characteristic odor.
The use of a not powerful enough amplifier is another cause. A weak power amplifier pushed to its limit will generate unpleasant distortions for the ear and deadly for the speakers. Contrary to what we could logically believe, it is more likely to break a speaker with a low-power amp with a more powerful amp.
It is considered that the amplifier must have a power between 1 and 1.5 times the actual power of the speaker measured in watts Rms, and not in "Chinese watts". Take the example of a 50 watt Rms speaker, the recommended amp power is between 50 and 75 watts Rms.
The music is made up of strong passages and weak passages. The difference between strong passages and weak passages is called dynamics. Peaks of power that last only a few fractions of a second can reach or easily exceed 10 decibels, which is exactly 10 times the amp's rated power. A little powerful amp will turn this peak power peak distortion while a more powerful amp will be able to deliver this instantaneous power. Dynamics strongly contributes to the realism of sound reproduction.