Blown loudspeakers can mean several different things; either:
The coil is fried.
The cardboard cone is torn.
The edge ring has become brittle, and perished.
In the first case, when the coil is fried, you generally have to replace the entire driver. If the cone is torn, you can tape it back together, or carefully glue coffee filter paper over the tear. Not ideal, but will keep going. Edge rings differ depending on the type of speaker. Home hifi use rubber edge rings which perish due to age. These can be easily repaired with inexpensive parts, and some simple craftsmanship. You could try fabricate your own edge ring from cloth, but a proper rubber replacement part works best as it allows the speaker to flex, and travel better. Live audio equipment, PA speakers, combo amps etc tend to use speakers with corrugated cloth edge rings, and are therefore much more resilient, and durable, can stand up to changes in temperature, humidity, misuse, and the abuses of the road.