#acoustics

Building-acoustics soundproofing maths as an API, computed locally and deterministically. The mass-law endpoint computes the sound-transmission loss of a single partition from its surface mass density and the frequency using the field-incidence mass law, TL = 20·log10(m·f) − 47 dB — transmission loss rises about 6 dB for every doubling of mass or of frequency — and also gives the normal-incidence value. The composite endpoint combines the transmission losses of several elements that make up one wall, such as a heavy wall with a window or a door, by area-weighting their transmission coefficients, TL = −10·log10(Σ(Ai·τi)/ΣAi) — which shows how the weakest element, like a small gap or a thin window, dominates and wrecks an otherwise good wall. The transmission endpoint computes the received sound level on the far side of a partition, the source level minus the transmission loss, with an optional room-to-room correction that adds 10·log10(partition area / receiving-room absorption). Surface density is in kg/m², frequency in Hz, levels and transmission losses in dB and areas in m². Everything is computed locally and deterministically, so it is instant and private. Ideal for architecture, building-acoustics, studio-design, HVAC-noise and construction app developers, partition and noise-control tools, and acoustics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is sound insulation; for room reverberation use a reverberation API and for sound pressure level a sound-level API.

api.oanor.com/soundproof-api

Helmholtz-resonator acoustics as an API, computed locally and deterministically. The frequency endpoint computes the resonant frequency of a Helmholtz resonator — a cavity with a neck, like a bottle or a ported speaker box — from the neck area (or diameter), the neck length and the cavity volume, f = (c/2π)·√(A/(V·L_eff)), adding the acoustic end correction (about 0.85·radius for a flanged end and 0.61·radius for a free end) so a short or open neck resonates lower than its physical length suggests. The design endpoint inverts the relation, V = A·c²/(L_eff·ω²), to give the cavity volume needed to tune a resonator or a muffler chamber to a target frequency. The port-tuning endpoint sizes a bass-reflex (vented loudspeaker) box port in practical audio units — from the box volume in litres and the port diameter in centimetres it gives the tuning frequency for a given port length, or the port length required for a target tuning frequency, using the 0.732·diameter end correction. Core endpoints use SI units; the speed of sound defaults to 343 m/s. Everything is computed locally and deterministically, so it is instant and private. Ideal for audio, loudspeaker-design, musical-instrument, muffler and acoustic-treatment app developers, bass-reflex and resonator tools, and acoustics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is Helmholtz resonance; for room reverberation use a reverberation API and for standing waves on strings and in pipes a standing-wave API.

api.oanor.com/helmholtz-api

Room-acoustics reverberation-time maths as an API, computed locally and deterministically. The sabine endpoint computes the reverberation time of a room — the RT60, the time for the sound to decay by 60 dB — from the Sabine formula RT60 = 0.161·V/A, where V is the room volume and A the total absorption in metric sabins; you can give the absorption directly, or as a surface area times an average absorption coefficient, and it also solves the absorption you would need to hit a target reverberation time. The eyring endpoint uses the Eyring-Norris formula RT60 = 0.161·V/(−S·ln(1−ᾱ)), which is more accurate than Sabine for absorbent rooms with a high average coefficient, and reports both for comparison. The absorption endpoint builds the absorption budget from a list of surfaces, each with its area and absorption coefficient, returning the total and average absorption and the resulting Sabine RT60, plus the extra absorption needed to reach a target. Everything is computed locally and deterministically, so it is instant and private. Ideal for acoustic-design, studio, classroom and home-theatre tools, room-treatment planning and building-acoustics apps, and audio-engineering education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is room reverberation time; for decibel conversion and combining sound levels use a sound-level API.

api.oanor.com/reverb-api

Standing-wave and resonance maths for strings and air columns as an API, computed locally and deterministically. The string endpoint models a string fixed at both ends: from its length and the wave speed — given directly or as the tension and the linear mass density (which you can supply directly, or have computed from a mass and length, or from a wire diameter and material density) — it returns the wave speed v = √(T/μ), the fundamental frequency f₁ = v/(2L) and the harmonic series f_n = n·f₁, each with its wavelength and node and antinode count; it can also solve the tension needed to tune the string to a target fundamental. The pipe endpoint does the same for an air column: an open pipe (both ends open) resonates at all harmonics f_n = n·v/(2L) while a closed (stopped) pipe resonates only at the odd harmonics f_n = (2n−1)·v/(4L), with the speed of sound given directly or worked out from the air temperature, v = 331.3·√(1 + θ/273.15). The harmonics endpoint generates the harmonic series from a fundamental frequency, or from a wave speed and a length, for a string, an open pipe or a closed pipe. Everything is computed locally and deterministically, so it is instant and private. Ideal for musical-instrument and luthier tools, acoustics and audio apps, organ-pipe and wind-instrument design, and physics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is mechanical standing waves and resonance; for note-to-frequency music theory use a music-note API and for electromagnetic wavelength λ = c/f use a wavelength API.

api.oanor.com/standingwave-api

Doppler-effect maths as an API, computed locally and deterministically. The sound endpoint computes the acoustic Doppler shift, f' = f·(v + vo) / (v − vs), where v is the speed of sound (given directly, derived from an air temperature, or the default 343 m/s at 20 °C), vs is the source velocity and vo the observer velocity, with positive velocities meaning approaching: it returns the observed frequency and the frequency shift, and refuses a supersonic source. The light endpoint computes the relativistic Doppler effect for light, f' = f·√((1+β)/(1−β)), from a velocity in metres per second or as a fraction of the speed of light and a direction (approaching blue-shifts, receding red-shifts), returning the frequency and wavelength factor, the observed frequency or wavelength, and the redshift z. The radial-velocity endpoint reverses it: from a measured redshift, or an observed and rest wavelength, it recovers the radial velocity with the exact relativistic relation and the simple v ≈ z·c estimate. Frequencies are in hertz, wavelengths in nanometres, velocities in metres per second. Everything is computed locally and deterministically, so it is instant and private. Ideal for physics and astronomy education, radar, sonar and lidar tools, audio and acoustics apps, and spectroscopy and redshift calculators. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is the Doppler effect; for sound levels and decibels use an acoustics API.

api.oanor.com/doppler-api

Acoustics and decibel maths as an API. The decibel endpoint converts between a linear ratio and decibels, in either the power convention (10·log₁₀) or the amplitude/pressure convention (20·log₁₀), in both directions. The combine endpoint adds sound levels the way real (incoherent) sources combine — by energy summation, so two equal 80 dB sources give 83 dB, not 160 — and can also subtract a known source from a measured total. The distance endpoint applies the inverse-square law to a point source in a free field (−6 dB per doubling of distance) to find the level at a new distance. The wavelength endpoint converts between frequency and wavelength for sound, deriving the speed of sound from the air temperature (or a value you provide). Everything is computed locally and deterministically, so it is instant and private. Ideal for audio engineering and live sound, room and architectural acoustics, noise assessment and environmental monitoring, and physics teaching. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 5 endpoints. This is acoustics maths; for electrical circuits use an Ohm's-law API and for general unit conversion use a unit API.

api.oanor.com/soundlevel-api