User manual AEA COLES 4038 STUDIO RIBBON MICROPHONE

[. . . ] Allen Avenue, Pasadena, CA 91104 Phone: (626) 798-9128 / Fax: (626) 798-2378 E-mail: stereoms@compuserve. com COLES 4038 STUDIO RIBBON MICROPHONE USERÕS GUIDE By Ron Streicher and Wes Dooley QUICK START I F YOU CAN'T WAIT TO USE YOUR NEW COLES 4038, PLEASE READ THESE PRECAUTIONS FIRST SO YOU DON'T ACCIDENTALLY TRASH YOUR NEW TOY. 1 . KEEP YOUR 4038 COVERED BY THE SUPPLIED PLASTIC BAG WHEN NOT ACTUALLY BEING USED. THIS KEEPS THE STRONG MAGNET INSIDE THE 4038 FROM ATTRACTING "TRAMP" IRON PARTICLES WHICH POLLUTE THE INSIDE OF THE MIC. THIS ALSO PROTECTS THE VERY THIN (. 6 micron) AND FAST ALUMINUM RIBBON INSIDE THE 4038 FROM BEING STRETCHED IF THE MIC CASE LID SNAPS SHUT OR IF THE MIC'S STAND IS MOVED TOO QUICKLY ACROSS THE STUDIO. [. . . ] When observing many sounds such as plucked strings, drums, brass, and voices on a scope or DAW waveform display, you may see that the signal goes positive higher above the zero line than negative below it (or vice versa). If you change the polarity (marked phase on most consoles) of these signals, it tends to sound as if you made an EQ change. However if you try to EQ back to the original sound, you never can get it back. Thus it is a good idea to watch polarity in microphones, cables, electronics and speakers. ). As the sound source moves from the central axis, the differential pressure Coles 4038 UserÕs Guide November, 1997 © Page 6 on the ribbon decreases, as will the electrical output. Thus it is easy to understand why a well designed bi-directional microphone has almost no output from sounds arriving from an angle of 90¡ off-axis: these sound waves strike the ribbon edgewise and exert equal pressure on both the front and rear surfaces of the diaphragm. The result is that there is no difference in the pressure exerted on the two surfaces of the ribbon; hence there is no motion, and no output signal is generated. The term velocity or pressure gradient is often used when describing ribbon microphones, because as noted above, as a sound wave passes the ribbon, minute differences in air pressure are created between the front and rear surfaces of this diaphragm. The classic ribbon microphones were the first to have a directional pattern, what we call a figure-of-eight or bidirectional polar response pattern. Earlier microphones were omnidirectional pressure microphones and responded only to the variations in the absolute air pressure of a sound wave without any particular regard to the sound's direction or distance of origin. Ribbon (velocity or pressure gradient) microphones have a well defined figure-of-eight directional pattern and their bass frequency response varies depending on whether the sound source is near or far. A near source will sound bass heavy compared with a far source. This bass boost proximity effect is characteristic of all directional mics. DESIGN OF THE COLES 4038 MICROPHONE ÒThe BBC-Marconi Type A microphone, believed to be the first of this type to be manufactured in Great Britain, was produced in 1934 É The performance of this microphone is still good, even by modern standards, but the instrument is bulky and there has long been a demand É for a smaller version giving an equal or better performance. Ó With these criteria as the goal, the engineering division of the BBC went about designing a new microphone to meet the growing demands of their FM radio and television production departments. The end result was the BBCÕs model PGS bi-directional ribbon microphone. Size and weight reductions were relatively easy to accomplish. But along the way, the additional problems of extended frequency response, ribbon fragility, and susceptibility to wind noise, were carefully addressed. The commercial realization of this microphone is the Coles 4038. The 4038 is first mentioned in print in December of 1955 in the excellent BBC monograph by D. The 4038 has a smooth response from 30 Hz to above 15 KHz, exhibiting an ideal 6 dB per octave roll-off at high frequencies. A symmetrical polar response in the vertical direction was achieved through the unique shape of the microphone housing which is designed to function as an acoustic lens. Its Coles 4038 UserÕs Guide November, 1997 © Page 7 standard electrical output impedance of 300 ohms remains nearly constant throughout the audio passband. Special attention was paid to reducing hum pickup through the use of a shielded toroidal output transformer and starquad style wiring around the ribbon itself. [. . . ] AEA shall be the sole determinant of what constitutes Òabuse. Ó (Exposure to rough handling, wind, excessive low frequency SPL, moisture or liquids, and microphone power such as phantom or "T" are some examples of abuse. ) Coles 4038 UserÕs Guide November, 1997 © Page 11 SPECIFICATIONS of the COLES 4038 P o l a r r e s p o n s e : Bi-directional (cosine, figure-of-eight) I m p e d a n c e : 300-ohm is standard; also 30-ohm by special order F r e q u e n c y r e s p o n s e : 30 Hz to 15, 000 Hz (see spec. sheet curve) S e n s i t i v i t y :-65dB re: 1 Volt/dyne/cm2 D i s t o r t i o n : Inversely related to frequency. Like most ribbon microphones the 4038 will handle very high SPL at high frequencies and is displacement limited at low frequencies. For example the 1% THD point at 110 Hz is 125 dB SPL while further down at 55 Hz this 1% point is reduced to 110 dB SPL. [. . . ]