Installed systemsSound reinforcementAcoustic design

Selecting and placing microphones in installed systems

Capture enough direct sound first, then address loudspeaker feedback, room reverberation, and background noise.

By · DADAO Acoustics Lab · DADAO AUDIO7 min read
Diagram of microphone, loudspeaker, and audience coverage relationships in a meeting space.

Contents

What this article covers

5 chapters · About 7 minutes

Chapter01

System

Set audience-area goals before choosing equipment

An installed reinforcement system must deliver intelligible speech to every seat, keep the sound natural and the noise floor acceptable, and avoid operating at the feedback threshold. The problem is rarely one device. Talker-to-microphone distance, room reflections, gain structure, loudspeaker coverage, and operating practice all interact.[1][6] Define intelligibility, coverage, and level targets before laying out microphones and loudspeakers.

Chapter02

Acoustics

There is no universal pass value for RT60 or background noise

RT60 is the time required for sound energy to decay by 60 dB. As it increases, reverberation from one syllable is more likely to mask the next. DPA treats roughly 2 s as an experience-based boundary beyond which speech reinforcement becomes difficult, but 0.6–1.2 s is not a universal target for every project.[1] Classrooms, meeting rooms, courtrooms, and performance spaces differ in volume and purpose, so their reverberation and background-noise criteria also differ.[7] If the room uses 30–50 kHz ultrasonic sensors, check whether they trigger microphones, automatic gain control, or other nonlinear stages.[1]

Room acoustics: use determines targets 01 · Use case Purpose and volume Seats, content, occupancy Reinforced or natural 02 · Acoustics Measure RT60 by band Log HVAC + ambient noise Check ultrasound + vibration 03 · Validate Measure STI + SPL by seat Retest occupied, normal noise Use the relevant standard No single RT60 limit fits meeting rooms, classrooms, courts, and performance venues
Figure 1 · Room-acoustics inspection sequence; set target values according to use, volume, and the applicable standard.
Chapter03

Selection

Sensitivity is not pickup distance

Sensitivity states how much voltage a microphone produces at a given sound pressure; it does not mean the microphone can “reach farther.” Distant pickup also depends on self-noise, maximum SPL, directivity, critical distance, and gain before feedback.[1] Do not confuse distance factor (DSF) with directivity index (DI): an ideal cardioid has a DSF of about 1.73 and a DI of about 4.8 dB, while a supercardioid is about 1.93 and 5.7 dB.[2] With a lavalier on the chest, level and the 2–4 kHz region also change with position and body shadowing, so listen on site.[1]

What a specification states, and what it cannot state alone Parameter What it states What it cannot state alone Sensitivity Output at a given SPL “Pickup distance” Pattern / DI Relative response by angle Final room feedback margin Self-noise Microphone noise floor Total on-site SNR Maximum SPL Level at specified distortion Clarity at low SPL Distance also depends on working and critical distance, noise, loudspeaker position, and gain structure
Figure 2 · Evaluate output, direction, noise, and level handling separately; no single number determines working distance.
Chapter04

Placement

Shorten the working distance before relying on algorithms

Keep the microphone as close to the talker and as far from loudspeakers as practical. Aim the least-sensitive direction of a directional microphone toward the main feedback path. When a ceiling loudspeaker sits near the microphone, its zone can be reduced or disabled, but first confirm that this does not leave a coverage gap in the audience area. When several microphones capture the same source, begin with the 3:1 rule: space adjacent microphones at least three times the distance from each microphone to its intended source, then listen and measure for comb filtering.[3][4] Treat structural vibration from desks, floors, and ceilings with resilient isolators rated for the actual load.

Chapter05

Calibration

More open microphones leave less potential feedback margin

During commissioning, check channel polarity before setting input gain and feedback safety margin. Polarity errors can cause cancellation when correlated signals are summed; every doubling of open-microphone count typically reduces potential gain before feedback by about 3 dB.[5][6] Automatic mixers can attenuate idle channels through gating, priority, or gain sharing, but different algorithms do not share a universal “0 to −3 dB” guarantee. Finally, under normal occupied and background-noise conditions, measure sound pressure and STI at multiple seats. Follow IEC 60268-16 for STI measurement instead of substituting a single recording or hand clap.[8]

Relative change when the number of open microphones doubles NOM 1 2 4 8 Relative PAG 0 dB −3 dB −6 dB −9 dB Approximation: ΔPAG ≈ −10 log₁₀(NOM) This is a relative PAG change, not the system’s remaining total margin Automixing can attenuate idle channels; results depend on algorithm, threshold, and routing
Figure 3 · Each doubling of NOM reduces potential gain before feedback by about 3 dB; this is a relative change, not the system’s total margin.

References

Sources

Standards, technical documents, and official manufacturer pages checked for this revision.

  1. 1
    10 Points on Microphones in Installed Systems

    DPA Microphones · Accessed 2026-08-09

  2. 2
    How to Specify the Directivity of a Shotgun Mic

    DPA Microphones · Accessed 2026-08-09

  3. 3
    What Is Close Miking? Why Use It?

    DPA Microphones · Accessed 2026-08-09

  4. 4
  5. 5
  6. 6
    Sound System Design Reference Manual

    Shure · Accessed 2026-08-09

  7. 7
    ANSI/ASA S12.60 Part 1: Acoustical Performance Criteria for Schools

    American National Standards Institute · Accessed 2026-08-09

  8. 8
    IEC 60268-16:2020: Objective rating of speech intelligibility by speech transmission index

    International Electrotechnical Commission · Accessed 2026-08-09

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