Grampian DP1

This example is inscribed with the numbers "538" on the base of the cast capsule housing, which is presumably the serial number.

From a contemporary advertisement:

Here is a wide range fidelity moving coil type microphone which combines good sensitivity with a level response curve

Equally suitable for auditorium or outdoor work. Its use can confidently be advised for amateur as well as professional use. Housed in modern streamlined die cast alloy case of great strength and finished in hammered metallic lacquer with chromium plated grille. Delivery from stock. List price £8.8s.0d

• Weight 2lb.
• Frequency Response 60-9000 Hz.
• Output impedance 15 ohms.

From the Grampian DP1 specification sheet:

The new Grampian D.P.1. Microphone is a wide range high fidelity type particularly suitable for public address work, broadcasting and recording.

It is preferable to most other types for outdoor work due to its comparative immunity to wind noise, freedom from case shock noise and rigid Duralumin diaphragm which is unaffected by temperature and humidity changes.

Also suitable for Auditorium use when acoustic feedback conditions permit. The diaphragm and speech coil of aluminium wire, is very rigid and weighs only 560 milligrammes resulting in extreme sensitivity and good transient response. This, combined with the special acoustic chambers to eliminate resonances, produces a very level response curve.