1) Just old age where the paper cone starts to get brittle and the outer corrugated ring just tears. The same applies to speakers that have a foam or rubber surround where, after time, the material perishes.

2) Being heavily overdriven to the point that the cone is driven past its compliance and distorts the cone as the photographs below show. In some cases the cone can totally split. If your speaker is in this state then the failure is user error. Most probably if it has been used for vocals and the microphone has been too close to the lips or someone has tapped the microphone to check the system is working.

3) Speech coil failure. This is where the winding has experienced dc voltage as a result of amplifier failure, although serious overload can cause the same problem. You will very often see this with hf and mid-range speakers. In this case it is essential for the amplifier to be thoroughly checked . Any dc offset greater than 40mV is suspect and needs looking into.

The photo above shows the components that are replaced. It consists of the cone, speech-coil and suspension assembly, a dust cone which stops dust and debris getting into the magnet assembly and an outer gasket ring that is glued to the circumference for it to bolt up to a baffle. All speakers today use a Ceramic Magnet. Back in the 1950’s as these magnets did not exist, this was made of an electro-magnet and acted as the choke in the DC rectification stages. If the magnet has been dislodged through impact or shock and the clearance is not symmetrical, then the speaker is a write-off. We will put more examples up from time to time as they come through the workshop.  

The speaker above after it has been totally rebuilt.