Tutorials Articles
How is STI Measured?
STI (Speech Transmission Index) is measured using modulation transfer functions derived from impulse responses or STIPA test signals. Learn the full-band and STIPA methods per IEC 60268-16.
What Are Acoustic Baffles and Clouds?
Acoustic baffles and clouds are suspended absorbers that hang from ceilings to reduce reverberation in large spaces. Learn about vertical baffles, horizontal clouds, materials, and design strategies.
What Are Acoustic Ceiling Tiles?
Acoustic ceiling tiles absorb sound to reduce reverberation in offices, classrooms, and healthcare spaces. Learn about mineral fibre, fibreglass, and metal tile types, NRC ratings, and design.
What Are Acoustic Wall Panels?
Acoustic wall panels absorb mid and high-frequency sound to control reverberation and improve speech clarity. Learn about fabric-wrapped, foam, wood slat, and felt panel types.
What Are Bass Traps? (Corner Treatment Explained)
Bass traps absorb low-frequency sound energy that accumulates in room corners. Learn about porous, resonant, and membrane bass traps, placement strategies, and why they are essential.
What Are Acoustic Diffusers? (QRD, Skyline, Binary)
Acoustic diffusers scatter sound energy evenly across a room instead of absorbing it. Learn about QRD, Skyline, and binary diffuser types, how they work, and when to use them in acoustic design.
What Are Early Reflections? The First 50ms That Shape What You Hear
Early reflections are the first sound reflections arriving within 50-80ms of the direct sound. Learn how they affect clarity, spaciousness, and speech intelligibility in room acoustics.
What Are Green Acoustic Walls?
Green acoustic walls combine living plants with sound-absorbing substrates to reduce reverberation and improve indoor air quality. Learn how moss walls, living walls, and plant panels perform acoustically.
What Are Membrane Absorbers? (Panel, Drum, Plate)
Membrane absorbers are panels mounted over sealed air cavities that vibrate at a resonant frequency, absorbing low-frequency sound. Learn how panel absorbers, drum panels, and plate resonators work.
What Are Octave Bands? (125 Hz to 4000 Hz)
Octave bands divide the audible spectrum into standardised frequency ranges for acoustic analysis. Learn why 125-4000 Hz matters, how third-octave bands work, and how octave data drives design.
What Are Perforated Acoustic Panels?
Perforated acoustic panels use holes or slots in a rigid facing to allow sound through to an absorptive backing. Learn about perforation patterns, open area ratios, resonant absorption, and design.
What Are Porous Absorbers? (Mineral Wool, Foam, Fabric)
Porous absorbers are materials with interconnected air passages that convert sound energy to heat through viscous friction. Learn how mineral wool, foam, and fabric panels work and when to use them.
What Are Resonant Absorbers? (Helmholtz, Perforated)
Resonant absorbers use Helmholtz resonance or perforated/slotted panels to target specific frequency ranges. Learn how they work, how they differ from porous and membrane absorbers, and when to use them.
What Are Room Modes? (Axial, Tangential, Oblique)
Room modes are resonant frequencies where sound builds up between parallel surfaces. Learn axial, tangential, and oblique modes, how to calculate them, and how to control low-frequency problems.
What is a Decay Curve? (Measuring RT60)
A decay curve shows how sound energy decreases over time in a room. Learn how decay curves are generated, how RT60 is extracted from them, and why the Schroeder integration method is preferred.
What is a Decibel (dB)? The Logarithmic Scale Explained
A decibel (dB) is a logarithmic unit for expressing sound pressure level ratios. Learn why acoustics uses logarithms, how dB addition works, and what common dB values sound like.
What is a Sound Level Meter? The Essential Tool for Acoustic Measurement
A sound level meter (SLM) measures sound pressure level in decibels. Learn how SLMs work, the difference between Class 1 and Class 2, weighting curves, and when you need one for acoustic design.
What is Acoustic Calibration? Ensuring Measurement Accuracy
Acoustic calibration adjusts a measurement system to a known reference level. Learn why calibration matters, how calibrators work, IEC 60942 requirements, and field calibration procedures.
What is Acoustic Foam?
Acoustic foam is an open-cell polyurethane or melamine foam used for sound absorption. Learn about wedge, pyramid, and flat foam types, their NRC ratings, limitations, and proper applications.
What is Acoustic Impedance?
Acoustic impedance is the ratio of sound pressure to particle velocity in a medium. Learn how impedance mismatch controls reflection and transmission, and why it matters for material selection.
What is Acoustic Plaster?
Acoustic plaster is a spray-applied or trowel-applied porous finish that absorbs sound while looking like a smooth seamless ceiling or wall. Learn how it works, its NRC performance, and applications.
What is Acoustic Privacy? Controlling Who Hears What
Acoustic privacy is the condition where speech cannot be understood by unintended listeners. Learn STC requirements, speech privacy classes, masking systems, and open-plan vs closed-office strategies.
What is Acoustic Zoning? Organising Spaces by Noise Sensitivity
Acoustic zoning groups building areas by noise sensitivity and output, separating loud from quiet functions. Learn zoning principles, buffer strategies, and how building codes require it.
What is Airborne Sound? How Noise Travels Through Air and Walls
Airborne sound is noise transmitted through the air that strikes a building partition, causing it to vibrate and radiate sound on the other side. Learn STC, Rw, mass law, and control strategies.
What is a Background Noise Survey?
A background noise survey measures ambient noise levels in octave bands to assess compliance with NC, NR, or RC criteria. Learn methodology, equipment, standards, and how results affect acoustic design.
How Does Carpet Affect Room Acoustics?
Carpet absorbs high-frequency sound and reduces impact noise in rooms. Learn how pile height, density, and underlay affect acoustic performance, NRC ratings, and when carpet helps or hinders design.
What is the Cocktail Party Effect? How Your Brain Filters Sound
The cocktail party effect is your brain's ability to focus on one voice amid many competing sounds. Learn the auditory science, how room acoustics help or hinder it, and design implications.
What is Critical Distance? Where Direct Sound Meets Reverberant Sound
Critical distance is the point where direct sound from a source equals the reverberant field. Learn the formula, why it determines speech clarity, and how to design rooms around it.
What is Acoustic Damping?
Acoustic damping is the dissipation of vibration energy within a material or structure, converting mechanical oscillation into heat. Learn how damping reduces resonance, improves TL, and controls noise.
What is Echo? (And How It Differs from Reverberation)
An echo is a distinct, delayed repetition of a sound caused by reflection from a distant surface. Learn the 50 ms threshold, how echoes form, and how acoustic design prevents them.
What is Frequency in Acoustics? (Hz Explained)
Frequency is the number of sound wave cycles per second, measured in Hertz (Hz). Learn how frequency determines pitch, why octave bands matter, and how acoustic design treats different frequencies.
What is HVAC Noise? Controlling Mechanical System Sound in Buildings
HVAC noise is unwanted sound from heating, ventilation, and air conditioning systems. Learn noise generation mechanisms, NC/NR criteria, duct attenuation, and practical control strategies.
What is Impact Sound? Footsteps, Drops, and Floor Noise Explained
Impact sound is noise generated by physical impacts on building surfaces, especially floors. Learn IIC, Ln,w, tapping machines, floating floors, and how to meet building code requirements.
What is an Impulse Response in Acoustics?
An impulse response captures a room's complete acoustic fingerprint — how it responds to a perfect instantaneous sound. Learn how IRs are measured, what they reveal, and how they drive room analysis.
What is Late Reverberation? The Diffuse Tail That Defines a Room
Late reverberation is the diffuse sound energy arriving after the first 50-80ms. Learn how it shapes perceived warmth, when it helps music, when it hurts speech, and how RT60 measures it.
What is the Lombard Effect? Why Noisy Rooms Get Even Noisier
The Lombard effect is the involuntary tendency to speak louder in noisy environments. Learn why it creates a vicious noise spiral, its acoustic impact, and how good room design breaks the cycle.
What is Mineral Wool? (Rockwool vs Glass Wool)
Mineral wool is the most widely used acoustic insulation material. Learn the differences between rockwool and glass wool, their absorption coefficients, density grades, and applications in acoustics.
What is an NC Rating?
NC (Noise Criteria) is an octave-band rating system for background noise in buildings. Learn how NC curves work, how to read them, target values by room type, and how NC relates to NR and RC.
What is Noise Path Analysis? Tracing Sound from Source to Receiver
Noise path analysis identifies every route sound takes from a source to a receiver — direct, flanking, airborne, and structure-borne. Learn the method, ISO 12354, and how it drives cost-effective fixes.
What is Noise? (Wanted vs Unwanted Sound)
Noise is unwanted sound that interferes with communication, concentration, or comfort. Learn how noise is measured, classified, and controlled in building acoustic design.
What is an NR Rating?
NR (Noise Rating) is the European octave-band system for specifying acceptable background noise in buildings. Learn how NR curves work, how they compare to NC, and NR targets by room type.
What is an RC Rating?
RC (Room Criteria) is an enhanced noise rating system that evaluates both level and spectral quality of background noise. Learn how RC curves, spectral balance, and quality descriptors work per ASHRAE.
What is Acoustic Resonance?
Acoustic resonance is the amplification of sound at specific frequencies determined by the physical dimensions of a space or object. Learn about room modes, Helmholtz resonance, and standing waves.
What is Reverberation? (vs Echo vs Delay)
Reverberation is the persistence of sound in a room after the source stops, caused by thousands of overlapping reflections. Learn how it differs from echo and delay, and why it shapes every room.
What is the Schroeder Integration Method?
The Schroeder integration method converts a noisy impulse response into a smooth energy decay curve for reliable RT60 measurement. Learn the math, history, and practical application of this technique.
What is Sound Absorption?
Sound absorption is the conversion of acoustic energy into heat when sound strikes a surface. Learn how absorption coefficients work, why they matter for room acoustics, and how to use them in design.
What is Sound Diffraction?
Sound diffraction is the bending of sound waves around obstacles and through openings. Learn how diffraction affects noise barriers, room acoustics, and building design.
What is Sound Diffusion?
Sound diffusion scatters reflected sound energy evenly across a space. Learn how diffusers work, the difference between diffusion and absorption, and when to use each in acoustic design.
What is Sound Insulation Testing? Verifying As-Built Acoustic Performance
Sound insulation testing measures the actual airborne and impact noise reduction between rooms after construction. Learn ISO 16283, field test procedures, pass/fail criteria, and common pitfalls.
What is Sound Pressure? (Pa and dB)
Sound pressure is the local variation in air pressure caused by a sound wave, measured in Pascals (Pa) and expressed in decibels (dB SPL). Learn how sound pressure relates to loudness and acoustic design.
What is Sound Reflection?
Sound reflection occurs when sound waves bounce off a surface. Learn how reflection creates reverberation, flutter echoes, and standing waves — and how to control it in room design.
What is Sound Refraction?
Sound refraction is the bending of sound waves as they pass through regions of different temperature, wind speed, or density. Learn how refraction affects outdoor and indoor acoustics.
What is Speech Intelligibility? The Science of Being Understood
Speech intelligibility measures how well listeners understand spoken words in a space. Learn about STI, STIPA, the factors that affect it, and the standards that define acceptable levels.
What is Spray Cellulose Insulation for Acoustics?
Spray cellulose is a recycled-paper fibre insulation sprayed onto ceilings and walls for sound absorption. Learn how it works, its NRC performance, sustainability benefits, and acoustic applications.
What is Structure-Borne Sound? When Buildings Conduct Noise
Structure-borne sound travels through building elements as vibration before radiating as airborne noise. Learn transmission mechanisms, measurement methods, and isolation strategies.
What is Transmission Loss (TL)?
Transmission loss is the reduction in sound energy as it passes through a building element like a wall, floor, or window. Learn how TL is measured, what STC and Rw mean, and how mass law works.
What is Sound Wavelength?
Sound wavelength is the physical distance between consecutive pressure peaks in a sound wave. Learn how wavelength relates to frequency, why it determines acoustic behaviour, and its role in design.
Soundproofing vs Acoustic Treatment — What's the Difference? | AcousPlan
The most common misconception in acoustics explained: soundproofing (STC, insulation) vs acoustic treatment (NRC, absorption). What each does, when you need which, with real examples.
How Much Acoustic Treatment? — Area Calculation from RT60 Target
Work backwards from a 0.6 s RT60 target to find how much acoustic treatment a 150 m³ meeting room needs. Three treatment options compared: ceiling tiles, wall panels, baffles.
How to Calculate RT60 for an Open-Plan Office — Full Worked Example
Step-by-step Sabine RT60 calculation for a 300 m² open-plan office. Every surface area, absorption coefficient, and octave-band sum shown — from bare slab to treated space.
How to Calculate STI for a Classroom — IEC 60268-16 Step-by-Step
Full STI calculation for a 200 m³ classroom. Derive RT60 via Sabine, then compute speech transmission index using the modulation transfer function method per IEC 60268-16:2020.
Ceiling Absorption Calculation: Octave-Band RT60 Prediction for 3 Ceiling Types
Same 200 m³ room, three ceiling systems: 15mm mineral fibre, 25mm perforated metal with backing, and 50mm exposed mineral wool. Full Sabine RT60 for each at 125–4000 Hz.
Concert Hall RT60 Design: 1,800-Seat Auditorium Worked Example
Design an 1,800-seat concert hall for RT60 2.0 s (occupied). Full octave-band Sabine calculation, audience absorption, occupied vs unoccupied comparison, and EDT estimation.
Impact Noise Floor Build-Up: ΔLw Improvement Calculation — ISO 717-2
Start with bare 150mm concrete slab (L'nT,w 78 dB). Add resilient mat, screed, and carpet step by step. Calculate ΔLw at each stage per ISO 717-2 with full IIC ratings.
NC Curve Calculation from Octave-Band Measurements — Step-by-Step
Determine the NC rating from a set of octave-band background noise measurements. Step-by-step tangent curve method, controlling frequency identification, and RC Mark II comparison.
Facade Noise Break-In Calculation: External Noise to Internal Level — ISO 12354-3
70 dBA road traffic at facade: calculate internal noise through composite wall, window, and ventilator using ISO 12354-3. Area-weighted Rw and BS 8233 compliance check.
Outdoor Noise Propagation Calculation: ISO 9613-2 Step-by-Step Example
Industrial source at 200m: calculate receiver level using ISO 9613-2. Geometrical divergence, atmospheric absorption, ground effect, and barrier attenuation — full octave-band worked example.
Lab STC to Field FSTC: How to Predict Real-World Sound Insulation Performance
Take a lab STC 55 partition and predict field FSTC accounting for flanking paths: floor, ceiling plenum, ductwork, and outlets. Full ISO 15712 worked example.
Restaurant Acoustic Treatment Calculation — From 2.1 s RT60 to Comfortable Dining
250 m² restaurant with 4 m ceilings and RT60 = 2.1 s. Calculate the absorption deficit and design a treatment scheme to reach 0.8 s — with full octave-band before/after comparison.
Sabine vs Eyring: Same Room, Different Answers — Worked Comparison
Calculate RT60 with both Sabine and Eyring equations for the same recording studio. See exactly where the results diverge, why, and when the 28% difference matters for design decisions.
Sound Masking System Design: Spectrum, Level, and Coverage Calculation
Design a sound masking system for a 500 m² open office from scratch: masking spectrum, required level, speaker spacing, and before/after Articulation Index.
Composite STC Calculation: Wall + Door + Window — Full Worked Example
Calculate composite STC for an office wall with a door and window. See how an STC 28 door drags down an STC 55 wall — with full area-weighted transmission loss at every 1/3 octave band.
WELL v2 Feature 74 Compliance: Full Acoustic Calculation for a 3-Storey Office
Full WELL v2 Feature 74 compliance check for a 3-storey office: Sound Mapping (L01), STC requirements (L03), Background Noise (L05), and RT60 (L07) with detailed calculations.
The Acoustic Design Process: From Brief to Handover in 8 Stages
A complete guide to the acoustic design process across all 8 project stages — from initial brief and simulation, through specification writing, construction review, and post-occupancy measurement.
The Decibel Scale Explained for Architects — Why 3 dB Doubles the Sound Power
The decibel scale is logarithmic, not linear. Learn why 3 dB doubles sound power, why 10 dB feels twice as loud, and how to read acoustic specifications without getting confused by the math.
What Is Acoustic Diffusion? — Scattering Sound Without Absorbing It
Acoustic diffusion scatters sound energy in many directions instead of creating strong reflections. Learn how diffusers work, the QRD design, and when to use diffusion instead of absorption.
What Is Clarity (C80) and Definition (D50)? — Room Acoustic Parameters Explained
C80 and D50 measure how clearly individual notes and syllables stand out in a room. Learn what these ISO 3382 parameters mean, how they're calculated, and what values suit music versus speech.
What Is Flanking Transmission? — Why Your Wall's STC Rating Doesn't Matter
Flanking transmission is sound that bypasses a partition by travelling through connected structure — floors, ceilings, ducts, or walls — and it routinely cuts field STC by 10 points or more. Here is how to find and stop it.
What Is Impact Insulation Class (IIC)? — Floor Noise Rating Explained
IIC rates how well a floor-ceiling assembly reduces footstep and impact noise. Learn what the number means, how it is tested, and why IIC often matters more than STC in multi-storey buildings.
What Is Noise Criteria (NC)? — Background Noise Rating for Buildings
NC curves rate background noise across octave bands to reflect how human hearing perceives HVAC and mechanical noise. Learn what NC numbers mean, how they are measured, and what targets apply to your building type.
What Is Sound Masking? — How Adding Noise Creates Privacy
Sound masking adds engineered background noise to make speech unintelligible at a distance, creating acoustic privacy without physical barriers. Learn how it works, where it is used, and how to specify it correctly.
What Is Sound Transmission Class (STC)? — A Plain-English Guide
STC is a single-number rating for how well a wall, floor, or door blocks airborne sound. Learn what the number means, how it is measured, and why a higher STC is not always enough.
Architectural Acoustic Design: The Student Guide (With Free Calculation Tools)
Written for architecture and engineering students, this guide covers sound behaviour, absorption, reflection, diffusion, the Sabine and Eyring equations derived from first principles, common assignment types, and a fully worked lecture theatre design example using free tools.
Acoustic Treatment vs Soundproofing: Why Most People Get This Wrong
The definitive explanation of the difference between acoustic treatment (controlling sound within a room) and soundproofing (blocking sound between rooms). Covers the mass law, decoupling, the 1% rule, STC vs NRC, and when you need each approach — with cost comparisons and worked examples.
Building Acoustics vs Room Acoustics: What's the Difference?
Building acoustics blocks sound between rooms using mass and decoupling (STC/Rw). Room acoustics controls sound within a room using absorption (RT60/C80). Here is when you need each, how they interact, and the standards that govern them.
How Do Acoustic Panels Work? The Physics of Sound Absorption
Acoustic panels absorb sound by converting kinetic energy into heat through viscous friction in porous materials, membrane vibration, or Helmholtz resonance. Learn the physics behind all three absorber types, why panel thickness determines low-frequency performance, and how mounting position changes everything.
How to Acoustically Treat a Home Studio for Under £500 (Step-by-Step)
A complete home studio acoustic treatment guide for under £500. Priority order: ceiling cloud first, bass traps second, side wall panels third. Exact product specifications, placement guide, and before/after RT60 calculation.
NC Curves Explained: Understanding NC-25, NC-35, NC-45 Background Noise Ratings
A comprehensive guide to Noise Criteria (NC) curves: how they work, how to determine an NC rating, target values for every room type, and the differences between NC, NR, and RC rating methods. Includes ASHRAE recommended levels and step-by-step calculation examples.
Deriving Sabine's and Eyring's Reverberation Time Formulas from First Principles
Step-by-step mathematical derivation of Sabine's T60 = 0.161V/A and Eyring's T60 = -0.161V/(S·ln(1-ᾱ)) from the diffuse field energy balance. With worked examples showing why Sabine fails at high absorption and when Eyring is the better choice.
Speech Privacy Index (SPI): How to Measure and Achieve Acoustic Privacy
A technical guide to the Speech Privacy Index (SPI) per ASTM E1130: how it relates to STI and AI, the three elements that determine privacy, privacy classification thresholds, and practical design strategies for offices, healthcare, and open plan environments.
What Is a Sabin? The Acoustic Absorption Unit Explained
A sabin is the unit of sound absorption equivalent to 1 square foot of perfectly absorptive surface. Learn how sabins relate to absorption coefficients, how to calculate total room absorption in sabins, and why thinking in sabins instead of alpha values prevents acoustic design failures.
The Acoustic Design Process: From Brief to Handover in 8 Steps
Acoustic design follows a structured 8-step process: establish criteria, model the room, calculate the baseline, identify deficiencies, specify treatment, verify compliance, document, and measure post-construction. Here is each step explained with the specific deliverables and ISO references.
A Practical Guide to Acoustic Materials: Foam, Mineral Wool, Wood, and Everything In Between
Acoustic materials fall into three categories: absorbers, reflectors, and diffusers. Each type works differently at different frequencies. Here is a practical guide to selecting the right material for your room — with NRC values, octave-band data, cost ranges, and fire ratings for every major product type.
How to Measure Room Acoustics: Equipment, Methods, and What the Numbers Mean
Measuring room acoustics requires a sound source, a microphone, and analysis software — but the method you choose determines whether your results are valid. Here is a practical guide to acoustic measurement: from balloon pops to dodecahedron speakers, from smartphone apps to ISO 3382-compliant equipment.
Noise Criteria Explained: NR, NC, and RC Curves — Which One Does Your Project Need?
NR (Noise Rating), NC (Noise Criteria), and RC (Room Criteria) all rate background noise levels in buildings — but they use different curves, different frequency ranges, and are required by different standards. Here is how each system works, when to use which, and the specific values your HVAC engineer needs to hit.
Room Acoustics Fundamentals: How Sound Behaves Inside a Room
Sound in a room does not simply travel from source to listener. It reflects off every surface, arrives at the listener hundreds of times with different delays, and creates a complex acoustic signature. Here are the fundamentals of room acoustics — from direct sound to late reflections to standing waves.
Understanding Octave Band Analysis: Why Single-Number Ratings Hide the Truth About Your Room
A single RT60 value or NRC rating averages across frequencies and hides critical problems. Octave band analysis breaks sound into 6 frequency ranges — revealing that your room might pass at 500Hz and catastrophically fail at 125Hz. Here is how octave bands work and why every acoustic assessment should use them.
Understanding Sound Insulation: STC, Rw, and Why Walls Don't Block All Frequencies Equally
STC (Sound Transmission Class) and Rw (Weighted Sound Reduction Index) both rate how well a wall blocks sound — but they use different standards, different frequency ranges, and can give different results for the same wall. Here is what each rating means, how they are measured, and which one applies to your project.
What Is NRC (Noise Reduction Coefficient) — The Number on Every Acoustic Panel Datasheet
NRC is a single number rating from 0.00 to 1.00 that describes how much sound a material absorbs. But NRC hides critical information about low-frequency performance. Here is what NRC means, how it is calculated, and why you need octave-band data for any serious acoustic design.
What Is RT60 — And Why It Determines Whether Your Room Sounds Good or Terrible
RT60 is the time it takes for sound to decay by 60dB after a source stops. Too long and speech blurs. Too short and rooms feel dead. Here is what RT60 means, why it matters for every room type, and the optimal targets that acoustic standards have established over 100 years of research.
What Is STI (Speech Transmission Index) — Can People Actually Understand Speech in Your Room?
STI measures how much a room degrades speech from source to listener, on a scale from 0 (unintelligible) to 1 (perfect). An STI below 0.50 means one in four words is lost. Here is how STI works, what scores you need, and why reverberation time alone is not enough.