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How rooms work, and how they are designed.

24 short chapters on the physics behind every acoustic decision and every home theatre system — written plainly, with an animated schematic for each, and a section for integrators and architects with the numbers, standards and what to specify.

Where a figure is a published reference value, its source is linked. The schematics illustrate the principle — they are not measurement data, and nothing here is a Science of Sound measurement or a claim about a project.

Planning a room? Start hereBook a site measurement
01How rooms behave4 chapters02Treatment5 chapters03Isolation4 chapters04Home theatre systems6 chapters05Measurement1 chapters06By space4 chapters

01

How rooms behave

What sound does between leaving a loudspeaker and reaching an ear.

direct · early reflections · reverberationdirectearlytailimpulse responsetime →Start hereHow sound behaves in a roomDirect sound, reflections, reverberation and resonance — the four things a room adds to every loudspeaker.6 minplasterBare wallreturns almost all of itabsorberTreated wallreturns a faint remainderFundamentalsReflections and first reflection pointsWhy a bare wall smears the image, what a treated wall does instead, and how to find the spots that matter.7 minnode · almost nothing at this noteloud herequiet herewallwallfirst axial mode — pressure swings between the walls, zero in the middleFundamentalsRoom modes and room dimensionsWhy some bass notes boom and others vanish depending on where you sit — and why the room’s proportions are decided before anything else.8 min−60 dB0dBRT60 · treateduntreated →level after the source stops · time →FundamentalsRT60 and reverberation timeThe one number everyone quotes, what it actually measures, and the target ranges different rooms are designed to.7 min

02

Treatment

Absorption, diffusion, bass control and the materials that do it.

25 mm1252505001k2k4kabsorption by band50 mm1252505001k2k4kabsorption by band100 mm1252505001k2k4kabsorption by bandrepresentative values for fibrous panels on a wall · not a product testTreatmentAbsorption and NRCHow porous absorbers work, what an NRC rating does and doesn’t tell you, and why thickness beats area.7 minFlat wallone strong reflectionDiffusermany weak reflections, spread in time and angleTreatmentDiffusionScattering sound instead of absorbing it — what diffusers do, where they belong, and where they are a waste of money.6 minRoom in plan · pressure across the floor at one low modecorner trap · dampedsubnodal line · near-zero pressurepeakpeakpeakdarker = more pressure · every corner is a peaka corner trap sits on the peak; mid-wall it would sit near a null and do far lessTreatmentBass traps and low-frequency controlWhy bass is the hardest part of any room, what a bass trap actually is, and why the corners matter.7 min1252505001k2k4klongshortunder-treatedover-treated, thinbalancedreverberation time by frequency band — the shape matters more than any single numberTreatmentOver-treating and under-treating a roomThe two ways a treated room goes wrong — dead and boomy, or live and smeared — and what balance sounds like.6 minLight and porous · absorbswave goes in, most of it never comes backHeavy and airtight · blockswave bounces off, little passes throughnothing light blocks sound; nothing heavy absorbs much of itTreatmentAcoustic materials: what is used and whyThe materials behind treatment and isolation — what each one does, what it doesn’t, and how to tell a real acoustic product from a decorative one.8 min

03

Isolation

Keeping sound in, keeping noise out, and why that is a different job.

Single leafwall vibrates, re-radiatesDouble leaf, damped cavitycavity is a poor connection · little passessame source level on the left of each; arrow length ≈ what gets throughIsolationSound isolation vs acoustic treatmentTwo different jobs that get one name. Treatment changes how a room sounds inside. Isolation stops sound crossing the wall — and it is built from mass, separation and sealing, not panels.8 minceiling voidslabducttheatrebedroomwall: blockedover the walldoor gapslabsection · the wall is only one of five paths between these two roomsIsolationDoors, windows and flanking pathsThe wall is rarely the weak point. The door, the window, the slab, the ceiling void and the duct are — and sound finds whichever is easiest.7 minceiling voidslabducttheatrebedroomwall: blockedover the walldoor gapslabsection · the wall is only one of five paths between these two roomsIsolationQuiet rooms: air-conditioning, equipment and background noiseHow quiet a theatre, studio or meeting room should be, how that is specified with NC curves, and how air-conditioning, ducts and equipment racks are kept from spoiling it.8 minSingle leafwall vibrates, re-radiatesDouble leaf, damped cavitycavity is a poor connection · little passessame source level on the left of each; arrow length ≈ what gets throughIsolationConstruction details for sound isolationFor builders and contractors: how brick, block and drywall perform, how decoupled walls, ceilings and floors are built, and the site mistakes that quietly undo them.10 min

04

Home theatre systems

Screen, seating, loudspeakers, subwoofers and calibration — the system designed around the room.

screenriserclearancerear row → bottom of image, clearing the head in frontfront row → top of image: the angle the neck has to makeθplan · viewing anglesection · screen height, riser and sightlines are designed togetherHome theatre systemsScreen size, seating and sightlinesHow big the screen should be for the seats, how far back each row sits, how high the risers go, and what an acoustically transparent screen does to the sound.9 minfront L/R ±22–30°side surrounds ±90–110°rear surrounds ±135–150°centre 0° · on the screen axisoverhead pairs~45° elevation (30–55°)reference seatplan · angles from the reference seat (ITU-R BS.775 / BS.2051, format makers’ guides)Home theatre systemsSurround and immersive speaker layoutsWhere each loudspeaker goes in 5.1, 7.1 and immersive layouts such as 7.1.4 — the angles, the heights, and how the layout adapts to more than one row.9 minddirectvia the front wall · arrives laternotch at c / 4dfrequency →Home theatre systemsSpeaker placement and the roomWhy the distance from a loudspeaker to the wall behind it changes the bass, and how placement is the cheapest acoustic treatment there is.7 minplasterBare wallreturns almost all of itabsorberTreated wallreturns a faint remainderHome theatre systemsChoosing loudspeakers for a roomWhat actually distinguishes a good loudspeaker — directivity, matching and output — and how to check one will play loud enough for the room.8 minnode · almost nothing at this noteloud herequiet herewallwallfirst axial mode — pressure swings between the walls, zero in the middleHome theatre systemsSubwoofers and bass managementWhy one subwoofer gives every seat different bass, how several subwoofers fix it, and how bass management, crossovers and the LFE channel actually work.8 minSine sweep played into the room20 Hz20 kHz→ recorded at the seat, deconvolved → impulse responsedirectreflectionsreverberant tail · modal ringingHome theatre systemsCalibrating a home theatreWhat calibration sets — levels, distances, crossovers, subwoofer alignment and equalisation — the reference levels it works to, and what room correction can’t fix.8 min

05

Measurement

What a room measurement shows, and what to ask for.

Sine sweep played into the room20 Hz20 kHz→ recorded at the seat, deconvolved → impulse responsedirectreflectionsreverberant tail · modal ringingMeasurementHow a room is measuredWhat a microphone and a sweep can tell you about a room, which graphs matter, and why a room isn’t finished until it has been measured.7 min

06

By space

How the same physics is applied in four different kinds of room.

acoustically transparent screentreatedside wallsubsreardiffuserplan · shell, screen, fronts, subs, surrounds, treatment, traps, diffusionBy spaceHow a home theatre is designedHow the physics is applied in a dedicated cinema room: isolation first, then layout, then bass, then reflections — in that order.8 minceiling reflectors angled to the rear seatsstageraked seatingabsorbedrear wallsection · early reflections carry the stage to the back rowsBy spaceHow auditorium acoustics workLarge rooms where the room is part of the instrument: shaping reflections to carry sound to every seat, and setting reverberation for speech, music, or both.8 minglassdisplayabsorbent ceiling raft above the tableACnoiseplan · the microphone hears the ceiling, glass and AC before it hears youBy spaceHow conference room acoustics workRooms built for speech, increasingly heard through a microphone by someone who isn’t there — and why glass, ceilings and air-conditioning decide how they sound.7 minreflection-free zoneplan · symmetric splayed walls, flush monitors, deep rear trappingBy spaceHow studio acoustics workControl rooms and live rooms: the tightest tolerances of any small room, because the decisions made in them travel with the recording.8 min

Start here

A reading path for your role.

The same physics, read in a different order. Each chapter has a drawer marked “For integrators and architects” with the figures, the standards and what to write into a specification.

Homeowners planning a theatre

What a good room needs, in the order decisions are made — so you can brief any designer, including us.

  1. 01How sound behaves in a room
  2. 02Sound isolation vs acoustic treatment
  3. 03How a home theatre is designed
  4. 04Screen size, seating and sightlines
  5. 05Surround and immersive speaker layouts
  6. 06Subwoofers and bass management
  7. 07Calibrating a home theatre
How we work on a project →

AV integrators

The room side of the system: layout geometry, loudspeaker behaviour in rooms, bass across seats and calibration limits.

  1. 01Surround and immersive speaker layouts
  2. 02Speaker placement and the room
  3. 03Choosing loudspeakers for a room
  4. 04Subwoofers and bass management
  5. 05Calibrating a home theatre
  6. 06Reflections and first reflection points
  7. 07Quiet rooms: air-conditioning, equipment and background noise
Working with us as your acoustic partner →

Architects and interior designers

The decisions that are yours to make early — proportions, ceiling heights, finishes, services — and what treatment needs from the interior.

  1. 01How a home theatre is designed
  2. 02Screen size, seating and sightlines
  3. 03Room modes and room dimensions
  4. 04RT60 and reverberation time
  5. 05Acoustic materials: what is used and why
  6. 06Sound isolation vs acoustic treatment
  7. 07Quiet rooms: air-conditioning, equipment and background noise
For professionals →

Builders and contractors

How isolation is actually built, the performance of common Indian walls, and the site details that make or break it.

  1. 01Sound isolation vs acoustic treatment
  2. 02Construction details for sound isolation
  3. 03Doors, windows and flanking paths
  4. 04Quiet rooms: air-conditioning, equipment and background noise
  5. 05Acoustic materials: what is used and why

The chapters cite 168 sources between them — standards, research papers, textbooks and manufacturers’ published test data. If you find a figure that doesn’t match its source, tell us; we would rather correct it than defend it.

If you are planning a room

Start with How sound behaves in a room, then the chapter for your space. That is enough to have a good conversation with any acoustician — including us.

If you are an integrator or architect

Every chapter has a drawer marked For integrators and architects with the figures, the standards and what to write into a specification. The chapter on measurement says what to ask for as evidence.

If something here is wrong

The chapters cite 168 sources between them. If you find a figure that doesn’t match its source, tell us — we would rather correct it than defend it.

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