Patent Application
20090091431
The object of the present invention is a gong, more particularly a gong used in a striking mechanism (or striking works) of a horological movement such as those used in watches having minute repeaters, small and grand strikes, and alarms.
In a general way, the mechanisms that produce the sound emission function in a striking mechanism must realize the four sub-functions of excitation, frequency selection, structure-borne vibratory transmission, and acoustic radiation. In known striking mechanisms, excitation is realized by one or several hammers and their actuating systems where these hammers hit one or several gongs fastened inside the watch by way of a heel. The gong (or gongs) realizes the frequency selection function by vibrating at a range of frequencies among which the audible ones will tune the emitted sound to a certain perceived pitch level. The vibratory transmission function is realized by materials selection, geometries, and by the design of the interfaces between the gong or gongs, their heels, and the element of the watch movement or case to which the heel or heels are fastened. Finally, the acoustic radiation function is realized by the part or parts of the watch case, generally the back or crystal, which convert the parietal vibrations to the ambient air as audible acoustic pressures.
It is the aim of the present invention, to improve the quality of the sound emitted by a striking mechanism, more precisely, the perceived pitch selectivity, richness, amplitude, and, in the case of two or several gongs, the inter-gongs tone homogeneity. To this end, the present invention aims to improve the gong or gongs used in a striking mechanism, and also at improving the transmission of the vibrations of said gong to its heel.
The object of the present invention is a gong comprising the characteristics listed in claim 1.
The annexed drawing illustrates in a schematic and exemplary way several embodiments of a gong according to the invention.
It is a particular aim of the present invention to realize a gong with harmonic components, or non-integer multiples in given pre-defined ratios, in a frequency range of interest such that the sound emitted by this gong is subjectively very well defined, generally perceived as the same sound by different users or persons, and, in the case of two or several gongs, with high level inter-gongs tuning.
In prior art gongs, the so-called harmonics of the fundamental frequency, that are located within the range of useful audible frequencies, are partial, rather than integral, multiples of the fundamental frequency (these are hereinafter referred as “partials”). For this reason, the sound emitted by such prior art gongs is generally not a harmonic sound. As a result, the individual sound pitch of a given gong is not perceived in identical fashion by all people, and, when two or more gongs strike successively, imprecise tuning is subjectively felt.
The aim of the present invention is to realize, in a frequency range of interest, a gong with pre-defined ratio components, or, identically, in the case of integer ratios, with strictly harmonic components, such that the overall pitch of the sound (i.e., the amplitude and phase composition of these components) is preferably within a margin of typically 5 cents of the desired partial or integer ratio of the fundamental targeted pitch tone vibration frequency of the gong (depending the materials and geometrical contingencies there are typically about live to ten of these in the frequency range of interest). As will be appreciated by those skilled in the art, a cent is a unit of pitch where one equal tempered semitone equals 100 cents and one octave equals 1200 cents.
The present inventors have determined that in order to provide a gong with such determined components in the frequency range of interest, it is highly advantageous for the size of the gong's cross-section to vary along at least an end section of the gong's longitudinal axis (i.e., along its length). The “size” of the cross section refers to the area of the cross-section at any particular point along the gong's length.
By varying the size of the cross-section of the gong along all or part of the gong's longitudinal axis including at least an end section, and in particular with the size of the gong's cross-section preferably increasing in the direction toward the free end of the gong, it is possible to create a family of audibly dominant partials or harmonics, and thus to obtain a strictly tonally controlled sound. The specific nature or degree of the variation in the dimensions (including possibly its shape) of the gong's cross section over its length can be optimised for a desired audible tone, at a given pitch, by employing standard dynamic finite-element simulation software tools to calculate the vibrational behavior of a gong with given geometry, materials and mounting conditions, Such a tool can then be used to iteratively vary one or more parameters (e.g., diameter, length, width) of the gong's cross-section. Subsequently, a gong having the desired geometry can be manufactured by means of standard machining.
In accordance with a first embodiment,
In a variant of this embodiment, the size of the cross-section may also vary over the first section a. The cross-section of such a gong may be circular (as illustrated in
In each of the above embodiments, one can define β as the ratio of the size of the cross section at the free end of the gong to the size of the cross-section at the point on the going where the variable cross-section size begins (i.e., the beginning of the end section). In a preferred embodiment, the size ratio β is at least equal to 2, and in a more preferred embodiment β is at least equal to 4; however it will be appreciated that β is by no means necessarily an integer and this ratio will vary depending on the specifics of the acoustic application. In addition, the rate of increase of cross-sectional size along the longitudinal axis (or the end section) of a gong may be constant (as shown in
In the above described embodiments, the shape of the gong's cross section remains the same, however in other embodiments, the gong's cross-section may additionally change its shape along the gong's longitudinal axis x-x, for instance by passing from a circular to an elliptical section or conversely.
As a further embodiment, illustrated in
In accordance with the invention, the specific dimensions given to the gong's cross-section along its longitudinal x-x axis are chosen to vary in such a way so as to induce a family of frequency components that are in desired ratios or harmony with each other within the audible frequency range of interest. As indicated above, in a preferred embodiment, these variations in the gong's cross-section can be designed and optimised so that the emitted sound (which consists of several different frequency components—generally about from five to ten) meets strict acoustic quality parameters, preferably that each of the partials is within 5 cents of the desired ratio or integral multiple of a fundamental pitch frequency, while the overall frequency of the sound resulting from an amplitude and phase summation of these partials is a frequency having a value within 5 cents of the frequency of the desired sound (i.e., the perceived pitch frequency of the gong).
As noted above, by selecting a desired perceived pitch frequency and applying the teachings of the present invention, one of ordinary skill in the art using a standard finite-element calculation tool can readily arrive at a specific gong design that meets such required acoustic quality parameters (such as those just mentioned above). For example, a gong with the profile illustrated in
In accordance with other variants, the size of the gong's cross-section may rise in the direction of its free end towards the heel onto which it is mounted; however an increase in the direction towards the free end of the gong is strongly preferred.
Finally, all variants of the gong according to the invention may be fabricated integrally with the heel T (
