Your old speaker may be missing, damaged, or just plain tired. This new speaker is the closes size to the original.. slightly smaller in diameter. But the magnet is significantly larger, and it is 8 ohms like the original.
Old speaker tends to distort? This new one is much stronger.
You will have to unsolder the wires and resolder them to the new speaker, which takes soldering skills. You will also make four new holes to mount the speaker, hardware included.
Hint: when you insert the screws from the bottom, use tape to hold them in while you run the nuts on the top side.