Volume 1
A text-book of experimental psychology : with laboratory exercises / by Charles S. Myers.
- Charles Samuel Myers
- Date:
- 1911
Licence: Public Domain Mark
Credit: A text-book of experimental psychology : with laboratory exercises / by Charles S. Myers. Source: Wellcome Collection.
63/370 page 43
![A difference tone is heard with far more difficulty when its pitch lies between that of the primary tones. A simple calculation will show that if the primary tones bear a simple relation to one another (eg. I : 2, 2 : 3, 3:4), the various orders of difference tones (page 40) often coincide ; and it is under these circumstances that difference tones are best heard. The overtones of primary tones also yield combination tones with one another. Two or more combination tones and overtones may thus occur at the same moment, which are so closely similar in pitch that they fuse to produce a single beating intertone. Such beating intertones are formed even from pure (i.e. overtone-free) tones when consonant intervals are mistuned. For example, a tone will beat with its mistuned octave. If the first overtone be present, such beats are partly to be ascribed to the intertone formed be¬ tween the higher primary tone and the first overtone of the lower primary tone. But even when the latter overtone is removed by interference tubes, beats are still audible owing to the formation of a difference tone of nearly the same pitch as the lower primary tone. Difference tones may be heard when the primary tones are isolated and led separately to the two ears, or when one tone is led to the ear and another is communicated by a tuning-fork applied to the teeth or to the head. Under such circumstances, conduction of both primary tones to one and the same ear unquestionably takes place. The formation of the combination tones h 4- / and h — /, when a rigid body is simultaneously affected by vibrations of periods h and /, may be attributed to the periodic disturbances arising between h and /. We may thus regard combination tones as the result of mutual periodic disturbances in the generation of the primary tones.] Variation Tones.—Tones of like pitch and of like forma¬ tion are also produced when / is no longer a series of disturbing sound waves, but consists of a number of simple interruptions applied to h. Thus, if the tone hy issuing from a siren, be interrupted / times per second (by the closure of alternate groups of the holes in its rotating disc), the tones](https://iiif.wellcomecollection.org/image/b3135984x_0001_0063.jp2/full/800%2C/0/default.jpg)
