The power of the amplifier is less than the power of the speaker, the distortion is serious, is broken. Change a power amplifier than the speaker power, the volume do not open too large, the distortion is a little smaller, there is no broken sound.
The speaker is old, the speaker may have cracks, there is broken sound. Repair the cracks and there will be no broken sound.
If the volume is not big, it is also broken sound, may be the speaker has been bad --- press the center of the speaker with a finger, feel the friction inside the speaker (good speaker inside the friction is not felt), it is the speaker voice coil has been bad, and need to be repaired.