The study came about because the SP Technical Research Institute of Sweden had been asked to purchase four microphones of the same type from four different measurement microphone manufactures — Brüel & Kjær, BSWA, G.R.A.S. Sound and Vibration A/S, and PCB Piezotronics.
All the microphones had similar specifications and were all 0.5” Integrated Electronic Piezoelectric (IEPE) microphones with nominal 50-mV/Pa sensitivity. The microphones were purchased from their respective Swedish representatives without letting them know the purpose. The four Brüel & Kjær-type 4189-A-021 microphones were delivered in three working days, the four G.R.A.S.-type 46AE microphones were delivered in five working days, the four PCB-type 378B02 microphones were delivered in two working days, and the BSWA-type MPA201 microphones were delivered three weeks after being ordered.
The study measured the response of the microphones relative to the 250-Hz sensitivity. The study is approximately 40-pages and can be downloaded from the link provided by PCB Piezotronics at www.pcb.com/Linked_Documents/3P03218condensedreport.pdf