Low Frequency Localisation Test: Sound Localization at Home
Overview
Low Frequency Localisation Test. Bass panned hard left or right and dropping in pitch with every trial — Low Frequency Localisation Test asks you to click Left or Right for where you think each tone is coming from. Click Start Test to work through 12 tones, then watch your accuracy in the results table collapse below about 80Hz — proof of exactly why subwoofer placement is so much more flexible than people assume. Run the tone generator online whenever you need a fresh signal — it works offline once loaded.
Close your eyes and a voice to your left is easy to place, but a deep rumble is not. A low frequency localisation test shows you exactly where that blind spot starts in your own audio setup: the critical frequency at which your brain stops hearing a tone as coming from one speaker and starts hearing it as coming from nowhere in particular. Your ears and your speakers decide the answer, and the test takes about five minutes.
Why Low Frequency Sound Localization Gets Harder Below 80 Hz
When a sound source sits off to one side, your brain compares what reaches each ear. That comparison drives sound localization across the whole hearing range, and it is a remarkably accurate skill: under good conditions listeners can judge direction to within a few degrees. Low pitches weaken both cues the brain depends on, so the frequency range below roughly 80 Hz is where your acoustic sense of direction fades. The sound pressure at both ears is nearly identical there, and the wave is so long that your head barely disturbs it. The room noise floor measurement online is a fast way to see a live number instead of guessing by ear.
Wavelength and the Critical Frequency
The wavelength of a tone is the speed of sound divided by its frequency:
$$\lambda = \frac{c}{f} = \frac{343\ \text{m/s}}{f}$$
At 40 Hz that is about 8.6 m, while your ears sit roughly 20 cm apart. The table shows how small your head becomes next to the wave, and how little phase offset it can create.
| Frequency | Wavelength | Ear spacing as share of wavelength | Maximum phase offset between ears |
|---|---|---|---|
| 200 Hz | 1.7 m | 11.7% | 42° |
| 80 Hz | 4.3 m | 4.7% | 17° |
| 40 Hz | 8.6 m | 2.3% | 8° |
| 31.5 Hz | 10.9 m | 1.8% | 7° |
Measured in dB or in degrees, the cue shrinks steadily as the pitch drops. Once it is smaller than your brain can resolve, the critical frequency has been crossed. For many listeners that happens near 80 Hz, although the exact value depends on the person and the room.
Interaural Time Differences and Interaural Phase Difference
Sound reaches the nearer ear first. These interaural time differences (ITDs) never exceed roughly 700 microseconds, and they matter most at low pitch. For a continuous tone the brain reads the ITD as an interaural phase difference: the two ears receive the same wave shifted by a tiny fraction of its cycle. Because the phase difference shrinks as the frequency falls, ITDs lose resolution toward the bottom of the scale. The inter-aural delay itself is still present, but it is too small to act on.
Interaural Level Differences and Head Shadow
Your head also casts an acoustic shadow, which produces interaural level differences (ILDs). A shadow forms only when the obstacle is comparable to half the wavelength, so ILDs work above about 800 Hz and vanish below it. Pitch matters for another reason too: spectral cues from the outer ear help with elevation, and they help people with monaural hearing, but they live at high frequencies and do nothing for bass. ILDs can exceed 30 dB at 11 kHz yet stay below 10 dB near 700 Hz, which is why ILDs fade long before the bass range. ITDs and spectral cues each cover a different slice of the spectrum, and the bottom slice is the thinnest for every cue.
How to Run the Low Frequency Localisation Test
Run the check with a sweep that glides downward until the direction disappears. The aim of this listener exercise is to note the frequency at which the apparent sound source localization collapses, and to confirm it with both channels. Listen with your head still, and keep your ears at the height of the speakers; a stimulus that pans even a few degrees is worth noticing, because that shift is the sign you are still localising. Run the dac and sound card quality test to see exactly what's working and what isn't.
Bass Sweep Test File Setup
A typical test file uses a bass sweep, a sweeping tone that starts near 200 Hz and slides down to 40 Hz while a voiceover announces the current frequency. Use one version that plays the sweep from the left speaker only and another for the right speaker. The voiceover plays from both, so it stays anchored in the centre as a reference. At first the tone clearly belongs to its speaker. As it descends, the position slides toward the middle. Write down the number the voice says at that moment, then repeat with the other channel.
Main Speakers and Your Audio Setup
Bypass the subwoofer first, so your main speakers carry the entire audio signal. Sit in the stereo sweet spot with the loudspeakers the same distance from you, and keep the amplifier tone controls flat. Your audio setup matters because small speakers stop producing the bass before the direction cue disappears, and then the sweep simply vanishes. In that case you have not measured your hearing, only the roll-off of the speakers. Remember to turn the volume to a comfortable level and avoid pushing it up to compensate: louder bass excites the room more, and the perception of direction then reflects the room instead of the signal.
Reading Your Localization Test Result
The frequency at which the sweep leaves its speaker is your personal threshold. Between 80 and 100 Hz is common. If your threshold is far lower, you are likely benefiting from a quiet room and well-matched speakers; if it is higher, reflections or speaker limits are probably masking the cue. Repeat the low frequency test from a second seat and compare. A consistent result is more trustworthy than a single lucky one.
What Sound Localization Results Mean for Pure Tones
Researchers have measured how well people judge direction with pure tones and with pink noise in controlled listening sessions. In one experiment with 18 participants, changes of about 10 degrees could be detected reliably for pink noise from 31.5 Hz, but for pure tones only from about 63 Hz. The experiment used two-alternative trials: the listener hears two sound events and says whether the direction changed, so guessing shows up as chance-level scores. The difference is that noise carries energy across several bands, giving the brain extra material to compare. So a test with a single tone is the harder case, as every experiment comparing the two sound types has found, and a music track with plenty of bass harmonics will feel easier than the sweep suggests. A low frequency sound localization test using a sweep therefore gives you a conservative threshold, which is exactly what you want when planning a crossover.
Subwoofer Imaging and Crossover Frequency
The threshold you found is the number to use when you set up a subwoofer. A crossover frequency below the critical frequency means the subwoofer only plays what your ears cannot place, so its position in the corner of the room stays invisible. Set the crossover above it and listeners can hear bass coming out of the box. Good subwoofer imaging is the result of choosing the crossover below your threshold; if your subwoofer cannot go that low, move it or add a second unit. Treat the crossover as a measured setting rather than a guess, since the right number belongs to your own room and speakers.
Stereo Imaging With a Subwoofer
Without a subwoofer, small speakers stop before the critical frequency, so the sweep fades out while it still points to one side. Adding the unit fills in the missing octave, but any content it reproduces above your threshold is perceived at the unit, which damages stereo imaging. Use the sweep result to decide between these options:
- Crossover below your threshold: imaging stays intact.
- Crossover above your threshold: bass drifts toward the unit and the image narrows.
- Speakers that stop above your threshold: bass cannot be placed, so the unit must cover it.
Spatial Hearing Research on Low-Frequency Sound Sources
Textbook spatial hearing claims that humans cannot place low-frequency sound sources below a certain pitch, yet newer work finds directional judgement down to the lowest audible tones. Recent studies of auditory localisation and low-frequency sound source localisation in an echo-free chamber found that listeners could separate directions in the left half of the horizontal plane, not merely tell left from right. Psychoacoustic research suggests the apparent contradiction comes from the listening room, which brings us to the next point about hearing in real rooms.
Standing Waves and Room Resonances in an Anechoic Room
In an anechoic room there are almost no reflections, and results are cleaner. In a normal living room, standing waves and room resonances create pressure peaks and nulls that change which direction a tone seems to come from. Even in a lab with minor resonances, some frequencies produced a significant shift in judged direction. If your own sweep jumps around at certain pitches, suspect the room before you suspect your ears.
Azimuth and Binaural Cues
Researchers describe the left-right plane as the azimuth, measured in degrees around your head, and the binaural cues are the differences between your two ears. Clinical tests use narrow-band noise and low pass filtered noise to separate ITD-driven judgement from ILD-driven judgement: a low-pass signal contains only the frequencies that ITDs can serve, so it isolates the time cue.
Directional Hearing, Headphones and Hearing Loss in a Low Frequency Test
To get a valid result from the sweep you need two working ears, because directional hearing depends on both. If you have hearing loss in one ear, temporary or permanent, the sweep and binaural demonstrations will not behave as described. Headphones add their own problem: headphones that process or delay the signal, particularly wireless bluetooth headphones, can distort the timing cues that ITDs rely on, and some laptop sound hardware cuts corners as well. Test with wired headphones or a pair of loudspeakers, and rule out a blocked ear before you worry about the result. A cochlear implant recipient will usually need a clinical assessment, since consumer sweeps cannot measure that kind of hearing.
Clinical Sound Source Localization Tests
Clinics extend the idea with several loudspeakers placed in an arc and ask the patient to point to the one that played. In azimuth testing a stimulus such as narrow noise plays from a random speaker several times, and the error between the pointed and true speaker is summarised as a root-mean-square value. Two-speaker versions create a sound localization test of level cues alone by varying the loudness between the pair. These measure localisation ability in a way a home sweep cannot, and they illustrate how to localize sound in practice: present a sound, collect a response, then compare it with the truth. For bass, the home low frequency localisation test remains the practical choice, because it answers one concrete question about your own system.