The Miata's stock seats have speakers in the headrest, however, the pair in our passenger seat were not sounding too healthy. They just kind of rattled. When I peeled back the upholstery (made easy with a zipper) it was clear why the sound wasn't very good. The speakers were completely shot.
I snipped the wires and pulled them out.
Here's what they look like outside the car. Weight savings: 10.5 oz