By space
How studio acoustics work
Control rooms and live rooms: the tightest tolerances of any small room, because the decisions made in them travel with the recording.
8 min read5 sourcesChapter 24 of 24
Schematic
A control room in plan. Symmetry about the centre line, monitors flush in the front wall or placed to push boundary interference above the bass, a reflection-free zone around the mix position, deep trapping at the rear and in every corner, and a diffusive rear wall to keep the room from feeling dead.
Animated illustration of the principle. Not measured data.
A studio control room has to tell the truth. Whatever the room adds, the engineer will unconsciously correct for in the mix, and that correction goes out into the world with the record. So the control room is designed to add as little as possible, with the shortest reverberation and the flattest response of any room type. The live room next door is designed to the opposite end — to add a chosen character.
The control room
Two principles do most of the work. Symmetry: the left and right sides of the room must present the same reflections to the mix position, or the stereo image is skewed before anything is mixed. And the reflection-free zone: the surfaces around the monitors are angled or absorbed so that no early reflection reaches the engineer’s ears within the first several milliseconds — what arrives is the direct sound, then the room, cleanly separated.
Monitors are flush-mounted in the front wall wherever the design allows. It removes the front-wall boundary cancellation, adds the wall’s baffle to the low frequencies, and takes the largest single variable out of the room. Free-standing monitors are placed to push that cancellation above the bass and are measured to confirm it.
The bass, again
Control rooms are small and their modal problems are severe; a room that has not controlled its bass will produce mixes that are thin in one room and boomy in the next. The rear wall usually carries the deepest trapping in the building — sometimes the entire rear wall is absorber a metre deep behind a slatted or diffusive face. Corners are trapped floor to ceiling. Published guidance puts control-room reverberation around 0.2–0.4 s, and it is the evenness of that figure across the bass that separates a good room from a merely quiet one.
A control room is the one place where “too dead” is rarely the complaint. The risk is the opposite: a room that looks treated and still has a 40 Hz mode ringing for half a second.
The live room
The live room is designed to sound like something — a chosen amount of reverberation, a chosen character, often variable: hard floor and a soft ceiling, a reflective end and an absorbent end, movable panels that turn a bright room warm. Isolation from the control room is a hard requirement, and the window between them is built as two panes of dissimilar thickness, angled, with a deep sealed gap.
Isolation both ways
A studio must keep its own sound in — drums at two in the morning — and keep the city out, to a lower noise floor than any other room type. That means the full toolkit: floated floors, room-within-a-room walls on isolated frames, isolated ceilings, and mechanical services designed for near-silence. The structural questions are asked first, because a studio in the wrong part of a building cannot be rescued by the fit-out.
For integrators and architectsThe numbers, the standards, and what to specify
- Targets
- Control room RT60 between 0.2 and 0.4 s averaged from 200 Hz to 4 kHz, following EBU Tech 3276 / ITU-R BS.1116: Tm = 0.25 × (V / 100 m³)^⅓ s — about 0.25 s for a 100 m³ room. Low bands held close to mid; noise floor as a low NC / NR curve; frequency response at the mix position within a stated tolerance after room correction.
- Geometry
- Reflection-free zone by angled front walls and ceiling soffit, or by absorption where geometry is fixed; strict left–right symmetry in surfaces, not just furniture.
- Monitors
- Flush-mount where possible with a sealed, damped soffit; otherwise position to move SBIR above the crossover to the subwoofer and confirm by measurement.
- Low frequency
- Deep porous trapping at rear and corners; membrane or Helmholtz devices against measured modes; multiple subwoofers where the layout allows.
- Isolation
- Room-within-a-room construction with independent inner leaves, floating floor, isolated ceiling; control-room window as dissimilar laminated panes with a wide gap; all services on resilient mounts.
What to write into the brief
- A structural and flanking review before the studio’s location is fixed; control-room geometry drawn for symmetry and reflection-free zone; verification measurements at the mix position before the room is signed off.
Sources
- 01EBU Tech 3276 — Listening conditions for the assessment of sound programme materialControl-room RT: Tm = 0.25 (V/100)^⅓ s, 0.2–0.4 s.
- 02ITU-R BS.1116-3 — Methods for the subjective assessment of small impairments in audio systemsSame reverberation formula for critical listening rooms.
- 03Bonello, “A new criterion for the distribution of normal room modes”, JAES 29, 1981
- 04Sepmeyer, “Computed frequency and angular distribution of the normal modes of vibration in rectangular rooms”, JASA 37(3), 1965Source of the 1 : 1.14 : 1.39, 1 : 1.28 : 1.54 and 1 : 1.60 : 2.33 ratios.
- 05Warnock, NRC Canada Building Digest CBD-239 — Factors affecting sound transmission lossMass law, double-leaf walls and coincidence, from Canada’s National Research Council.
External links open in a new tab. Figures quoted in this chapter are taken from these sources; a Science of Sound measurement is only ever presented as one, with its file, date and instrument.
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