The Audio-Technica Model AT 4071a condenser shotgun microphone
The Audio-Technica AT 4071a is a transformerless, externally polarized line plus gradient condenser microphone. It has been specially created to meet the critical long-distance pickup demands of broadcasting, film/TV sound, professional recording and theater sound reinforcement.
The AT 4071a features a broadband, linear on-axis frequency response, with maximum rejection of sounds from both the sides and the rear of the microphone. Rear polar lobing, common in shotgun microphones, has been greatly reduced and the off-axis response remains highly uniform. The resultant lack of sound coloration on- and off-axis makes the AT 4071a particularly useful for miking dynamic action in film/TV audio as well as in “spot” miking techniques in the music studio or theater.
The effective working distance of a directional microphone is determined in great part by its polar pattern and the uniformity of its off-axis response. These factors help determine the signal-to-ambient noise ratio. Of course, the electronic signal-to-noise ratio also affects the usable miking distance. This distance may be less than desired if the overall system signal-to-noise ratio is poor due to low microphone sensitivity or noisy electronics. The AT 4071a provides extremely high output and a noise floor that is hardly measurable, much less audible. It may be used with confidence in distant miking applications and even under the stringent demands of modern digital recording systems.
The AT 4071a balanced output is direct-coupled. This results in a clean output signal, especially under high-output conditions. The microphone is totally free of the distortion associated with conventional transformer-coupled outputs.
The AT 4071a sets new standards in small size and light weight. Overall length is 15.55" and it weighs just 5.5 oz. The AT 4071a adds practically no noticeable weight to the end of a fish pole or the top of a minicam. Through the use of an advanced, proprietary Audio-Technica design, the interference tube of the AT 4071a provides a narrow acceptance angle that would require a tube 50 percent longer using conventional technology.
Another unique Audio-Technica engineering innovation in the AT 4071a provides two additional benefits. An ordinary line microphone has its capsule positioned immediately at the rear of the interference tube. Audio-Technica engineers, however, have located the capsule entirely within the tube. Both the diaphragm and the side ports are exposed to the same acoustic environment.
One significant result of this unique capsule positioning is that the AT 4071a is less sensitive to noise caused by wind turbulence or the “encounter” noise of panning action. The second benefit is a marked reduction in proximity effect. Recordings made at varying distances remain more consistent in response, making both production and editing quicker, easier and less costly.
The AT 4071a is also exceptionally resistant to mechanical or handling noise, thanks to careful control of structural resonances and the low mass of the condenser diaphragm. An integral second-order 150 Hz hi-pass filter may be selected to “roll-off” the low-frequency response, thereby attenuating unwanted low-frequency ambient noise such as from traffic or air-handling systems. The switch is recessed to prevent accidental activation. The AT 4071a is built from the inside out to withstand the rigorous conditions of field use. Construction-grade aluminum alloy is used in the forming of the dual-concentric cylindrical interference tube. Major component parts are machined with exacting precision and assembled in a nested technique that eliminates damage from inertial shift. The AT 4071a will operate in conjunction with any remote “phantom” or “simplex” power source supplying from 11 volts to 52 volts DC. This voltage not only powers the microphone’s impedance converter, but also is stepped-up to a higher voltage internally to polarize the condenser element.
Unique Interference Tube Design
The ability to control low-frequency directivity in conventional “shotgun” microphones is limited by the length of their interference tubes—the longer the tube, the more directional the microphone and the lower the frequencies over which the tube still exercises control. Below the effective cut-off frequency of the interference tube, line microphones depend on the directional capabilities of the microphone capsule mounted at the rear of the tube. Audio-Technica has pioneered a unique approach to interference tube design in the AT 4071a. The sideporting system of the new Audio-Technica interference tube incorporates two acoustically damped slots combined with an extremely narrow longitudinal side port. The latter acoustical aperture is terminated in a series of miniature membranes, arranged in an acoustic taper. Pressure changes in the narrow side port cause these membranes to reradiate a specific band of frequencies into the tube. The taper is calculated to allow the lowest frequencies of the band passed to enter the tube at the farthest point from the condenser element and the higher frequencies of the band passed to enter close to the element. Low-frequency sound waves arriving from off-axis see this path into the interference tube as a series inductance and resistance. This L/R combination causes an increase in phase shift at frequencies below the normal tube cut-off. The result is directionality equal to conventional line microphones with interference tubes 1.5 times the length of that on the AT 4071a.
Text quoted from the Audio-Technica AT 4071a technical notes.
