Documentation sections

Room Acoustic Modes

POSThttps://rftools.io/api/py/v1/calculate

Slug room-modes. Calculate room axial modes using f = n·c/(2L). Find all standing wave frequencies, Schroeder frequency, and mode spacing for acoustic treatment and speaker placement.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of room-modes
Name	Unit	Range	Default	Description
lengthnumber	m	at least 0.5	5	Room Length
widthnumber	m	at least 0.5	3.5	Room Width
heightnumber	m	at least 0.5	2.5	Room Height
speedOfSoundnumber	m/s	300 … 360	343	343 m/s at 20°C
rt60number	s	0.05 … 5	0.4	Typical rooms 0.3–0.8 s
bandLownumber	Hz	at least 0	20	Where the band you care about starts: the bass a room's modes colour, from 20 Hz
bandHighnumber	Hz	at least 0	200	Where the band ends: about the Schroeder frequency, above which modes overlap

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of room-modes
Field	Unit	Description
flLengthheadline	Hz	Length Mode (1st)
flWidth	Hz	Width Mode (1st)
flHeight	Hz	Height Mode (1st)
schroeder	Hz	Schroeder Frequency
volume	m³	Room Volume
modesInBand	none	Axial, tangential and oblique modes (each mode number up to 40) inside the band: each a peak or a null to treat
modesNearBand	none	Modes outside the band whose half-power bandwidth reaches into it
modalBandwidth	Hz	Each mode's half-power bandwidth, 3·ln 10/(π·T₆₀), about 2.2/T₆₀: modes closer than this merge into one peak

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "room-modes",
    "inputs": {
      "length": 5,
      "width": 3.5,
      "height": 2.5,
      "speedOfSound": 343,
      "rt60": 0.4,
      "bandLow": 20,
      "bandHigh": 200
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("room-modes", {
    "length": 5,
    "width": 3.5,
    "height": 2.5,
    "speedOfSound": 343,
    "rt60": 0.4,
    "bandLow": 20,
    "bandHigh": 200,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "room-modes",
    "inputs": {
      "length": 5,
      "width": 3.5,
      "height": 2.5,
      "speedOfSound": 343,
      "rt60": 0.4,
      "bandLow": 20,
      "bandHigh": 200
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "room-modes",
	  "inputs": {
	    "length": 5,
	    "width": 3.5,
	    "height": 2.5,
	    "speedOfSound": 343,
	    "rt60": 0.4,
	    "bandLow": 20,
	    "bandHigh": 200
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "room-modes",
  "values": {
    "flLength": 34.3,
    "flWidth": 49,
    "flHeight": 68.6,
    "schroeder": 191.23657749350298,
    "volume": 43.75,
    "modesInBand": 57,
    "modesNearBand": 3,
    "modalBandwidth": 5.497016991595709
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:room-modes",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "length": {
          "min": 0.5,
          "max": null,
          "unit": "m"
        },
        "width": {
          "min": 0.5,
          "max": null,
          "unit": "m"
        },
        "height": {
          "min": 0.5,
          "max": null,
          "unit": "m"
        },
        "speedOfSound": {
          "min": 300,
          "max": 360,
          "unit": "m/s"
        },
        "rt60": {
          "min": 0.05,
          "max": 5,
          "unit": "s"
        },
        "bandLow": {
          "min": 0,
          "max": null,
          "unit": "Hz"
        },
        "bandHigh": {
          "min": 0,
          "max": null,
          "unit": "Hz"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "length": 5,
      "width": 3.5,
      "height": 2.5,
      "speedOfSound": 343,
      "rt60": 0.4,
      "bandLow": 20,
      "bandHigh": 200
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "length"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageRoom Acoustic Modes, at these values