Mic of the Month - Shure 508 Stratoliner

Here is our first Microphone of the Month for 2015. This Shure Stratoliner looks like a Zeppelin airship or perhaps Flash Gordon's space ship. But is it a crystal, ribbon or dynamic microphone?

I had always thought that the Shure Stratoliner series were crystal microphones, and indeed the 708 model does have a crystal element. But although this 508C uses the same body, it is quite a different microphone inside.

This one says 'dynamic' on the label but it is really a rather strange ribbon microphone. Here is the business end of the mic with some kind of flat ribbon in place, possibly made from kitchen foil.

Once we remove the ribbon and clean the motor, we can see a series of slots right behind the ribbon. These make an acoustic cavity and help to control the directional pattern.

The motor design is quite basic, with two cylinder magnets behind the ribbon, covered in felt. The transformer is mounted behind the magnets.

This construction and slots behind the ribbon also do odd things to the frequency response. Here is the published response chart from the Shure 508a user manual:

Even the published chart is pretty bumpy, and it seems that Shure were willing to sacrifice fidelity for directionality. And the mic does sounds peaky - definitely one for the vintage / special effects shelf in your microphone locker.