Combination tones sit below the lower tone and vary greatly between listeners.

Evidence

These tones are always below the frequency of the lower pure tone and occur at integer multiples of the difference tone frequency below the lower tone. No listeners hear all and some hear none of these combination tones. The difference tone and the combination tones for n = 1 and n = 2, known as the “second-order difference tone” and the “third-order difference tone,” are those that are perceived most readily (e.g., Rasch and Plomp, 1982). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1578

Categorization

• DEFINE: Names and orders second- and third-order difference tones by perceptual salience.
• XREF: Cites Rasch and Plomp 1982 — a concrete research anchor into the psychoacoustics literature. — connects to: Combination tones exist below both source tones and vary in audibility; Two tones presented together generate an audible combination (difference) tone not physically present. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 773; Two simultaneous tones generate audible lower tones absent from the stimulus — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1571 (+4 more)

Broader Connections

• Combination tones exist below both source tones and vary in audibility #corroborates (1.00)
• Two tones presented together generate an audible combination (difference) tone not physically present. #expands (1.00) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 773
• Two simultaneous tones generate audible lower tones absent from the stimulus #expands (1.00) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1571
• Combination tones arise at a place well separated from both primaries. #corroborates (1.00) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1590
• A minority of listeners show quadratic distortion that depends non-ideally on level and phase. #expands (1.00) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1543
• Lower-order combination tones are perceived more readily than higher orders #complicates (0.90)
• Combination tones become audible only above roughly 70 dB primary level #complicates (0.80)