I don't think that the M40x needs any description since the M50x and the M40x are pretty popular. From what I saw when I searched for them on SD, the cheapest they have ever been was around 60 some dollars by adorama. I believe M40s have the same driver as the M50s, but I could be wrong. Either way, here is some info about them:
- Cutting-edge engineering and robust construction
- 40 mm drivers with rare earth magnets and copper-clad aluminum wire voice coils
- Circumaural design contours around the ears for excellent sound isolation in loud environments
- 90° swiveling earcups for easy, one-ear monitoring.NOTE: Kindly refer user manual before usage of the product.
- Professional-grade earpad and headband material delivers more durability and comfort. Removable cable