Organ resultant stops create the sensation of pitches below any note actually sounding

Evidence

The illusion produced by the combination of organ pipes to produce a sensation of pitch lower than any note actually sounding is also used in organ pedal resultant bass stops. These sound at 32′ (and very occasionally 64′), and their f0 values for bottom C are 16.25 Hz and 8.175 Hz, respectively. A resultant bass at 32′ pitch is formed by sounding together stops of 16′ and 102/3′, which form the second and third harmonics of the 32′ harmonic series (see Section 5.4). A 32′ stop perhaps labeled “acoustic bass” is a mutation stop of 102/3′, which when sounded with a 16′ rank produces a perceived pitch at 32′ (place theory of pitch perception from the second and third harmonics—see Chapter 3). A 64′ stop perhaps labeled “resultant bass” works similarly, sounding a 221/3′ rank with a 32′ rank. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1650

Categorization

• XREF: Connects to the place-theory pitch perception discussed in Chapter 3, and to the general principle of residue pitch / missing fundamental later in this chapter.
• DEFINE: Explains how resultant and acoustic bass stops work — combining 16’ and 10 2/3’ ranks to produce a perceived 32’ fundamental from harmonics alone.