Acoustic head shadow creates a better ear with higher SNR in everyday listening

Evidence

Acoustically, the entire head (and shoulders) makes part of the external ear. The distance between the two ears, located at opposite sides of the head, causes an arrival time difference of the sound wavefront that depends on the angle of incidence. A difference in sound level appears at high frequencies due to shadowing by the head to the side that is opposite to the sound source. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 726 (#expands, via linked claim)

In the case of a hearing aid, it is generally assumed that the listener’s head is pointing in the direction of the sound of interest. In this way, a directional microphone selectively represents sounds to the front of the listener more than sounds to the side or the back of the listener. Assessment of directional microphones includes measurements of speech recognition thresholds (SRTs) in the laboratory, which has demonstrated great success in improving the perception of speech in noise. In some cases improvements in the SNR of over 7 dB have been observed (e. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1735 (#expands, via linked claim)

Whether a sound is reflected or diffracted is determined by its wavelength and the size of the object encountered. The smaller the ratio between wavelength and object size, the greater the reflected sound energy. The wavelength of sound (l) is determined by the frequency of sound and the speed of sound, l =c/f, where c is the speed of sound and f is the frequency of sound in Hz. The speed of sound is roughly a constant, and is approximately 340 m/s. Thus, we observe that the wavelength of sound is inversely proportional to its frequency: Low-frequency sounds have long wavelengths and high-frequency sounds have short wavelengths. Thus, high-frequency sounds are more likely to reflect from objects whereas low-frequency sounds are more likely to diffract around objects. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1450 (#expands, via linked claim)

Categorization

• XREF: connects to: Head shadowing gives roughly 6 dB interaural amplitude difference near 1.85 kHz; A meaningful speech-in-noise benefit requires at least 6 dB of SNR improvement; Head shadow attenuates sound arriving at the far ear unless the source is centered — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1454 (+6 more)

Broader Connections

• Head shading creates interaural level differences used for sound localization #expands (0.85) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 726
• High-frequency sounds reflect off the head while low-frequency sounds diffract around it #expands (0.80) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1450
• Head-related pressure reflections and binaural hearing boost sensitivity by about 6-12 dB #corroborates (0.80) — David Howard, Jamie Angus, coustics and Psychoacoustics, 634
• Directional hearing-aid microphones improve speech-in-noise SNR by over 7 dB. #expands (0.80) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1735
• Binaural squelch adds 3 to 5 dB by using the poorer ear’s signal #expands (0.75)