Decibel (dB)Logarithmic unit of sound intensityA-weighted decibel (dBA)Adjusted to human ear perception; most used in regulationsB-weighted decibel (dBB)For medium levels (~70 phons); rarely used todayC-weighted decibel (dBC)Nearly flat across the spectrum; for detecting low frequencyD-weighted decibel (dBD)Specific to aircraft noiseZ-weighted decibel (dBZ)Unweighted, flat response (also called "linear")dBHL (Hearing Level)Referenced to hearing threshold; used in audiometryPhonUnit of subjective loudnessSoneUnit of loudness; 1 sone = tone of 1000 Hz at 40 dBRw (weighted sound reduction index)Overall parameter of how much noise an element blocks (dB)C (spectrum adaptation term)Correction for medium/high frequency noise (voices, appliances)Ctr (spectrum adaptation term for traffic)Correction for low frequency (traffic, aircraft, music)Rw(C;Ctr)Full notation; e.g.: 37(-4;-9) dB → Rw=37, Rw+C=33, Rw+Ctr=28RASimplified index: RA = Rw + C (for interior noise)RA,trTraffic-adapted index: RA,tr = Rw + Ctr (the most relevant for urban facades)DnT,AAirborne sound insulation measured in situ between roomsD2m,nT,AtrFacade sound insulation (measured at 2 m); key parameter of DB-HRL'nT,wImpact noise level (in situ); lower value = better insulationSTC (Sound Transmission Class)North American system equivalent to Rw (STC values ~3-4 dB higher)Frequency (Hz)Oscillations per second; determines pitch (low/high)Human audible spectrum20 Hz to 20,000 HzLow frequencyBass sounds (traffic, machinery)High frequencyTreble sounds (voices, alarms)Critical frequency (coincidence frequency)Acoustic weak point where the panel transmits more noiseResonance frequency (f0)Natural vibration frequency of the systemOctaveInterval where the frequency doublesThird octaveSubdivision used for spectral analysis and Rw calculationSound attenuationReduction of sound level when passing through an elementCoincidence effectThe bending wave of the panel matches the sound wave; drop in insulationMass effectGreater mass = greater acoustic insulationMass-spring-mass effectPrinciple of double glazing: two masses separated by a cavityAsymmetry principleGlass panes of different thickness prevent simultaneous resonanceMass lawDoubling the mass increases insulation by 6 dBAirborne noisePropagates through the air (voices, music, traffic)Impact noise (structural)From direct contact or impact (footsteps, vibrations)Flanking noiseTransmitted through adjacent elements (side walls, floor, ceiling)Pink noiseReference in measurements; drops 3 dB per octaveWhite noiseSame intensity at all frequenciesTraffic noisePredominance of low frequencies; spectrum to which Ctr refersContinuous noiseFluctuates less than 5 dB(A) per minuteImpulsive noiseFluctuations greater than 5 dB in less than one secondLd (daytime noise index)Daytime equivalent level (07:00-19:00); determines DB-HR requirementsLe (evening noise index)Evening period (19:00-23:00)Ln (night-time noise index)Night-time period (23:00-07:00)LdenOverall 24h indicator penalising evening (+5 dB) and night-time (+10 dB) noiseLAeq,TA-weighted equivalent continuous level during period TStrategic Noise Map (SNM)EU mandatory mapping with Lden and Ln levelsAcoustic sensitivity areaZone with maximum levels according to land useHearing threshold0 dB (20 micropascals)Pain threshold140 dBHearing damageProlonged exposure to > 85 dBAEqual-loudness contours (Fletcher-Munson)Curves of equal loudness; the ear is most sensitive between 1,000-4,000 HzReverberationPersistence of sound due to multiple reflectionsReverberation time (T60)Time for sound to decay by 60 dBSpeech intelligibilityPercentage of speech correctly perceiveddBC-dBA differentialIndicates low frequency predominance (>10 dB = structural transmission)D2m,nT,Atr according to LdFrom ≥30 dBA (Ld<60) to ≥47 dBA (Ld≥75) in bedroomsDnT,A between dwellings≥50 dBAL'nT,w between dwellings (impact)≤65 dBBuilding services noise≤30 dBA in bedrooms/living rooms, ≤35 dBA in kitchens/bathroomsWHO recommendation for bedroom at nightMaximum 30 dBAWHO recommendation for outdoor trafficDay: max 53 dBA / Night: max 45 dBA