Short answer: there isn’t a brick-wall cutoff below which low frequency source direction cannot be detected. At low frequencies the ear uses inter-aural time differences (ITDs) carried by the temporal fine structure to tell left from right; this mechanism works best below ~1–1.5 kHz and then fades out as phase-locking fails.

How low can humans hear “where the bass is”?

• Pure tones: In tightly controlled tests with real loudspeakers in an anechoic room, listeners could reliably tell a change in direction as small as 10° for tones ≥ ~63.5 Hz; at 40–50 Hz the same task generally fell to chance even with large source separations. (Quantitatively, the measured ITD needed for reliable discrimination—the MAITD—was ~158 µs at 63.5 Hz; at 40–50 Hz performance did not reach criterion.)
• Low-frequency noise (narrow-band): When the stimulus had some bandwidth (1/3-octave “pink” noise bands), the same study found reliable 10° discrimination down to ~31.5 Hz (MAITD about 60–77 µs). Bandwidth gives the brain extra envelope and cross-frequency comparison cues that aren’t available in a single steady sine wave.
• Why “bass is non-directional” is only partly true: Below ~1 kHz the head creates little level shadow, so level cues (ILDs) contribute little; localization relies on microsecond-scale ITDs in fine structure (and in envelopes for wider-band or transient sounds). Sensitivity to fine-structure ITD is excellent at a few hundred hertz (JNDs tens of µs) but collapses above ~1–1.4 kHz, which is why low frequencies are the most informative for azimuth—just not when the stimulus is a long, very narrowband tone.
• Rooms make it harder: Strong room modes at very low frequencies scramble binaural cues; experiments show these standing waves degrade low-bass directional perception even when the ear could do it in anechoic conditions.

Bottom line

• With pure, steady tones, robust left/right localization typically emerges around ~60–70 Hz; below that it quickly becomes unreliable without other cues.
• With low-frequency noise or real-world bass (some bandwidth, onsets, harmonics), listeners can perceive direction well below 60 Hz—down to ~30 Hz under good conditions.

Design implication: the oft-quoted 80 Hz subwoofer crossover is a practical engineering convention to minimize leakage of directional cues from the sub (and from the room), not a psychoacoustic limit of the ear. The ear can use low-frequency ITDs; whether you actually hear direction depends on stimulus bandwidth/temporal structure, level, and the room.

Here are audio-psychoacoustics definitions if these terms are unfamiliar:

• JND (Just-Noticeable Difference)
  The smallest change in a stimulus a listener can reliably detect under a set criterion (often ~75% correct in a 2-alternative forced-choice task). You can have a JND for level (dB), frequency (Hz), time/ITD (µs), etc.
• ILD (Interaural Level Difference)
  The difference in sound level (in dB) arriving at the two ears. ILDs arise mainly from the head’s acoustic shadowand are a primary cue for left-right localization—especially at high frequencies where the head blocks sound more strongly.
• Level shadow (Head shadow / Acoustic shadow)
  The frequency-dependent reduction in sound level on the far side of an object (e.g., your head) relative to the source side. Shadowing is weak when wavelength ≫ object size (low frequencies) and strong when wavelength ≪ object size (high frequencies). It’s the physical cause behind large ILDs.
• (Temporal) Fine Structure
  The rapid, cycle-by-cycle oscillations of a sound within an auditory filter band—the “carrier” variations that track instantaneous phase. This contrasts with the envelope, which is the slower change in amplitude. The auditory system can use fine-structure timing (via neural phase-locking) to extract microsecond-scale ITD cues at low frequencies.

• Azimuth (in spatial hearing) is the horizontal angle of a sound source around the listener.

0° is straight ahead (nose).

±90° is directly left/right.

±180° (or 180°) is straight behind.

Azimuth is measured in the horizontal plane (separate from elevation, which is up/down). Note: sign convention varies by field—some define + to the right, others to the left.