There are two kinds of speakers, high impedance and low.
The electrical signal is sent through the speaker by a current that travels from one end to another inside it which creates an electromagnetic field around its surface with sound waves radiating outwards in all directions.
When there’s too much volume for the small diameter pipe or when you put your finger into the water flow then more pressure builds up at either side until something gives way such as bursting pipes or ear drums respectively.
A lower impedance speaker allows more electricity which means it can handle louder volumes without distorting due to excessive power being delivered than higher resistance models because they require less voltage so if I was looking for my first set of really good hi-fi speakers I would want them be 4 ohms rather.