Microphone Techniques and Placement Flashcards

What is the 'free-field' vs. 'diffuse-field' equalization distinction for measurement microphones?

Answer: Free-field microphones are calibrated for direct sound from one direction; diffuse-field microphones are calibrated for a reverberant field with equal energy from all directions

Measurement microphones are equalized for specific acoustic conditions. Free-field mics are calibrated for sound arriving from a specific on-axis direction in an anechoic environment. Diffuse-field mics are calibrated for random incidence (reverberant room), compensating for the high-frequency boost that occurs with uniform random sound arrival.

When recording a string quartet, what is the primary advantage of using a 'Decca tree' microphone configuration?

Answer: It captures a natural, wide, and detailed stereo image of the ensemble with a center-fill microphone providing stability to the central image

The Decca tree uses three omnidirectional microphones in a T-shaped arrangement: a center mic flanked by left and right mics. It produces a wide, natural stereo image with a strong center fill, well suited to classical and orchestral recording in reverberant concert halls.

In film and broadcast production, what is a 'fishpole' boom and why is the microphone positioned above the actor rather than below?

Answer: A fishpole is a handheld pole holding a directional microphone above the scene; positioned above to stay out of the camera frame while keeping the mic close and capturing natural voice projection direction

A fishpole (or boom pole) is a lightweight telescoping pole allowing the boom operator to hold a directional (shotgun or supercardioid) microphone just out of camera frame over the actors. Positioning above captures natural voice direction and is preferred over below to avoid unnatural vocal coloration.

What is 'impedance matching' and why does it matter when connecting a microphone to a preamp?

Answer: Ensuring the output impedance of the microphone is significantly lower than the input impedance of the preamp so maximum voltage transfer occurs without loading the microphone

Proper impedance bridging requires the preamp's input impedance to be at least 5–10× the microphone's output impedance (typically ≥1500 Ω for a 150–300 Ω mic). Low input impedance loads the microphone, causing frequency response irregularities and loss of high-frequency content.

What technique is used to reduce ambient noise when recording a voice-over in an untreated room using a directional microphone?

Answer: Placing the microphone close to the talent and using the directional rejection of a cardioid or hypercardioid to minimize off-axis room reflections

Close microphone placement increases the direct-to-reverberant ratio, and using a directional polar pattern (cardioid/hypercardioid) rejects sound from the sides and rear where room reflections and ambient noise originate. This maximizes dialogue clarity in untreated spaces.

What does 'self-noise' specification (equivalent noise level) indicate about a condenser microphone?

Answer: The inherent electrical noise generated by the microphone's internal electronics, expressed in dBA; lower values indicate quieter microphones suited for quiet sources

Self-noise (equivalent noise level) is the level of electrical noise the microphone's internal electronics generate, expressed in dBA (A-weighted). A microphone with 5 dBA self-noise is very quiet and appropriate for recording soft sources (classical guitar, whispered vocals); 20 dBA would be audible on quiet recordings.