Understanding sound in your room

Passive, powered and active speakers

A conventional passive bookshelf speaker uses an external power amplifier. Its crossover divides the amplified signal between drivers. A powered speaker has amplification built into the system; the label alone does not tell you how its crossover works.

In an active crossover design, the signal is divided before separate power amplifiers feed the drivers. Processing may be analogue or digital. Built-in amplification does not automatically mean automatic room correction. Check the exact model’s manual. Active crossover networks and their effect on combined driver radiation are treated in Linkwitz’s journal paper. [1]

For this planner, selecting a model supplies cabinet sizes and reference specifications. It does not load measured frequency response, directivity, amplifier headroom, crossover behavior or DSP settings. The powered/passive label does not change the acoustic equations.

Waves, reflections and quiet spots

Frequency describes cycles per second, in hertz (Hz). Wavelength is the distance between successive crests. Using the planner’s sound speed of 343 m/s, a 100 Hz wave is about 3.43 m long; a 1,000 Hz wave is about 34 cm long. These examples use wavelength = speed / frequency, not dimensions of a sound “beam.” [2]

When related waves arrive together, their pressures can reinforce or oppose each other. Reflections can therefore create peaks and dips, not just extra volume. Moving a speaker or seat changes those paths. The result depends on relative phase and amplitude. [2]

Room resonances involve repeated reflections between boundaries. Our first-reflection model does not reproduce the full resonant or reverberant field. The Allen–Berkley image-source paper [3] provides the foundation for mirrored paths; our implementation uses only direct paths and optional single bounces.

Real speakers also radiate differently with frequency and direction. Aiming and off-axis listening can change the sound. Our wave and response models assume omnidirectional sources; coverage’s optional beam shape is illustrative. Toole reviews the importance of loudspeaker radiation and room interactions. [4]

Why the maps can look different

Sound coverage: a level overview

Adds the energy of separate sound paths. It omits interference between paths, including a speaker and its own reflections. It is not a complete prediction of music in your room. With flat source gains and reflections off, the band maps can look identical.

Sound waves: a controlled interference example

Combines pressures, with travel delay and distance loss. Single-tone mode illustrates one frequency. Band mode assumes both speakers carry the same in-phase signal and averages energy across frequencies. Ordinary stereo recordings have varying left/right relationships.

Listener response: a seat-specific estimate

Shows the simplified model across frequency at your seat. It is not the measured response curve of your selected speaker.

Coverage’s Overall result weights frequency ranges by their octave span; wave bands use equal energy per Hz. Neither is a loudness rating or a particular song’s spectrum. Those different assumptions also help explain different readings.

0 dB here does not mean silence. The reference is one modeled source at 1 m. A positive value means higher than that reference, not a calibrated sound-pressure level. Red is not automatically better and blue is not automatically bad. Gray excludes points too close to a source for this model.

Calculated geometry, estimated sound

Distances, angles and cabinet clearances follow your inputs. Image calibration and real measurements determine their accuracy. Sound predictions are less certain: furniture, driver response, ports, diffraction, higher reflections and actual room measurements are missing.

Absorption settings describe energy removed from a reflection in this model. They are not a percentage reduction in perceived loudness or a soundproofing rating. Material presets are example assemblies: laminate is a hard-surface proxy; the ceiling uses drywall-on-studs data with paint unspecified. Values beyond the available frequency data hold the nearest endpoint. A single absorption value does not capture reflection phase or angle dependence. For the image-source method and boundary assumptions, see Allen and Berkley. [3] The material choices and extrapolation above are app assumptions, not validated room properties.

Recommendations search a limited set of placements for smoother modeled bass and left/right balance, while honoring enabled constraints. The score is our heuristic, not a scientifically validated preference score or proof of an optimal room layout.

A useful first experiment

1. Start with a practical, roughly symmetric layout. A 60° listening triangle is a reference starting point, not a rule for every home. Follow your speaker manual for orientation and clearance. The 60° reference appears in ITU-R BS.1116-3, Annex 1, §8.5.3. [5]
2. Save your layout. Hold the speaker spacing fixed and compare two practical seat locations, or hold the seat fixed and compare speaker locations.
3. Listen at a comparable volume with familiar recordings. Check nearby seats too; a very narrow modeled sweet spot may not be useful.
4. For stronger evidence, measure each speaker separately and both together with a calibrated measurement microphone and suitable software. Compare trends before making major changes.

Open the planner

Opened this from the planner? Close this guide tab to return to your unchanged workspace. The cited publications do not endorse or validate this app.

Scientific and educational references

Numbered citations identify published sources. Links provide access to the publication or its scholarly record. App behavior and audit findings are our own implementation descriptions, not claims of external validation.

1. S. H. Linkwitz, “Active Crossover Networks for Noncoincident Drivers,” Journal of the Audio Engineering Society, vol. 24, no. 1, pp. 2–8, 1976. AES publication record.
2. W. Moebs, S. J. Ling, and J. Sanny, University Physics, Volume 1. Houston, TX: OpenStax, Rice University, 2016, §§16.5, 17.1–17.5 (waves, sound, interference and normal modes). Textbook PDF. Numerical examples and diagram here are original.
3. J. B. Allen and D. A. Berkley, “Image method for efficiently simulating small-room acoustics,” Journal of the Acoustical Society of America, vol. 65, no. 4, pp. 943–950, 1979. DOI: 10.1121/1.382599. University-hosted paper.
4. F. E. Toole, “Loudspeakers and Rooms for Sound Reproduction—A Scientific Review,” Journal of the Audio Engineering Society, vol. 54, no. 6, pp. 451–476, 2006. AES publication record.
5. International Telecommunication Union, Methods for the subjective assessment of small impairments in audio systems, Recommendation ITU-R BS.1116-3, February 2015, Annex 1, §8.5.3 and Fig. 6 (two-channel listening arrangement). Standard PDF. A controlled listening-test reference, not a universal home-placement requirement.