BS in Materials Engineering
Materials Engineering Department
Ribbons of 4 μm thin 99.1% pure aluminum foil were cut and corrugated to replace the stock ribbon in an Apex 205 ribbon microphone. Prior to corrugation, half of the ribbons were sandwiched between two KimWipes and two pieces of cardstock then hammered to impart strain hardening. Each ribbon was placed into the microphone capsule and the frequency response of each ribbon was measured. A 10 second sine sweep from 20-20,000 Hz was played through a KRK Rokit 5 speaker and recorded through a ribbon microphone placed 6 inches away from the speaker cone. The signal generated by the ribbon microphone was recorded through a Presonus Firepod, and the software FuzzMeasure 3 was used to analyze the sonic characteristics of the microphone when outfitted with different ribbons. The stock ribbon demonstrated a level frequency response the mid range frequencies from about 85-500 Hz, which is often desirable, followed by an exponential decrease in the high frequencies starting at approximately 500 Hz. In contrast, ribbons prepared for this investigation showed a loss in mid-range fidelity, with a 10 dB drop just after 90 Hz. The same exponential decay in the high frequencies was observed in all the ribbons tested. No large differences were observed between the hammered and non-hammered ribbons; as such, cold working the ribbon does not greatly affect the acoustic performance of a ribbon microphone. However, minor high frequency attenuation was observed in the hammered ribbon that could be caused by increased dislocation density, either by dislocations creating strain fields that cause phase interference with phonons, or by dislocations impeding electron flow.