An N-wave is a type of sound wave that is characterized by a sudden, sharp rise in pressure followed by a gradual, exponential decay. N-waves are often generated by supersonic aircraft or explosions.

Here's why they don't need a medium:

* Sound waves are pressure waves: They are created by vibrations that travel through a medium (like air, water, or solids) by causing the molecules within that medium to bump into each other.

* Electromagnetic radiation: N-waves, specifically those from supersonic aircraft, fall under the category of electromagnetic radiation. Electromagnetic radiation is a form of energy that can travel through a vacuum (like space). It doesn't require a medium to propagate.

So, while sound waves in general need a medium to travel, N-waves, as a form of electromagnetic radiation, can travel through a vacuum.