Mute attached to brass instrument without change of pitch of sound

Abstract: A mute (10) attached to a brass instrument (11) has an inner surface shaped in such a manner that standing waves of represntative harmonic tones have respective final nodes (FN1 to FN4) therein close to final nodes of the standing waves generated without the mute, and the pitch of the sound is hardly changed between a performance with the mute and a performance without a mute.

Description: This invention relates to a mute available for a brass instrument and, more particularly, to a mute allowing a player to practice without a change of pitch of the sound. DESCRIPTION OF THE RELATED ART Conventionally, a mute is used for the variety of a musical expression. For example, a player temporally attaches the mute to a brass instrument so as to change the timbre of the brass instrument in the performance. Acoustic musical instruments usually generate loud sounds, and sometimes disturb the neighbors. This means that players need a soundproof chamber. However, if a mute is available for the acoustic musical instrument, the player can practice the acoustic musical instrument at home without complaint. Figure 1 illustrates a prior art mute available for a brass instrument, and the prior art mute is disclosed in Japanese Utility Model Publication of Unexamined Application No. 2-119697. The prior art mute 1 is attached to a brass instrument 2 such as a trumpet, and comprises a cylindrical case 1a and a flat head member 1b. The flat head member 1b closes one end of the cylindrical case 1a, and the inner space is open at the other end to the brass instrument 2. The prior art mute 1 further comprises an inner sound absorbing layer 1c laminated on the inner surface of the cylindrical case 1a and the inner surface of the bottom plate 1b, and a hole 1d is formed through the cylindrical case 1a and the sound absorbing layer 1c. The hole 1d allows the air to flow between the inner space and the outside of the mute 1. The prior art mute 1 further comprises a microphone 1e inserted into the inner space, and the microphone 1e is connected through wires 1f to a headphone 1g. The bell 2a of the brass instrument is inserted into the inner space of the cylindrical case 1a, and a player blows on the mouthpiece (not shown). The air column vibrates, and generates sound. The hole 1d allows the blow to escape therethrough. The sound is confined in the prior art mute 1, and is absorbed by the sound absorbing layer 1c. The sound merely leaks through the hole 1d. The microphone 1e picks up the sounds, and allows the player to hear the sounds through the headphone 1g. Another prior art mute 3 is illustrated in figure 2 of the drawings, and is inserted into a bell 4a of a brass instrument. The prior art mute 3 is fabricated from a flare tube member 3a of aluminum, a round head 3b also formed of aluminum and a sealing liner 3c of cork. The flare tube member 3a has a frusto-conical configuration, and the round head 3b is fixed to one end of the flare tube member 3a so as to form an inner space 3d open at the other end of the flare tube member 3a. A small hole 3e is formed in the flare tube member 3a, and conducts the inner space 3d to the outside of the mute 3. The sealing liner 3c is wound on the outer surface of the other end portion of the flare tube member 3a, and seals the air inside of the brass instrument and the prior art mute 3. When a player wants to practice the brass instrument with reduced sounds, he inserts the prior art mute 3 into the bell 4a of the brass instrument 4, and connects the inner space 3d to the inner space of the brass instrument 4. While he is blowing on the brass instrument, the air column vibrates so as to generate a sound, and the pitch of the sound is changed depending upon the length of the air column. The blow escapes through the small hole 3d only. The sound is confined in the inner space 3c of the prior art mute 3, and leaks through the small hole 3e only. Figure 3 illustrates yet another prior art mute 5 inserted into a bell 6a of the brass instrument 6. The prior art mute 5 is like the prior art mute 3, and comprises a flare tube member 5a, a round head 5b attached to one end or the flare tube member 5a and a sealing liner 5c attached to the outer surface of the other end portion of the flare tube member 5a. The flare tube member 5a and the round head 5b form an inner space 5d, and is connectable to the inner space of the brass instrument 6. The prior art mute 5 differs from the prior art mute 3 in a short tube member 5e inserted into an opening 5f formed in the round head 5b, and the inner space 5d is conducted through the short tube member 5e to the outside of the prior art mute 5. A player inserts the prior art mute 5 into the bell 6a of the brass instrument 6 before a performance, and blows on the mouthpiece (not shown) of the brass instrument 6. The air column vibrates so as to generate a sound. The blow escapes through the short tube member 5e. Although the prior art mute 5 slightly reduces the sounds, the timbre is widely changed, enabling the player to impart unique musical expression to the sounds. The prior art mutes 1, 3 and 5 encounter a problem in unstable intervals among the tones. In other words, even if a player exactly controls the blow on the mouthpiece and the length of the air column in accordance with a scale, the sounds reduced through the mutes 1, 3 and 5 are not on the scale. The unstable intervals are derived from the inner walls of the flat/round heads 1b/3b substantially perpendicular to the respective center axes CL1/CL2 of the brass instruments 2 and 4 for the prior art mutes 1 and 3. The substantially perpendicular inner walls can not reflect the sounds at good balance, and fluctuate the intervals. Especially, low pitch sounds tend to be higher. The unstable intervals of the prior art mute 5 are caused by the short tube member 5e. The short tube member 5e has a straight tube portion 5f inserted into the inner space 5d and a bell portion 5g open to the air. The straight tube portion 5f is constant in cross section, and the constant cross section changes the intervals. The present inventors measured sound pressures of harmonic tones generated by a brass instrument with and without the prior art mute 3. The sound pressures of the harmonic tones were plotted in figure 4. The broken lines BL1, BL2, BL3 and BL4 stand for the sound pressures of the second, fourth, sixth and eighth harmonic tones without the prior art mute 3, and real lines RL1, RL2, RL3 and RL4 represent the sound pressures of the harmonic tones with the prior art mute 3. The difference of the nodes is represented by dL. The standing waves BL1 to BL4 and RL1 to RL4 strongly affect an actual tone. All of the standing waves BL1 to BL4 representative of the harmonic tones have respective final nodes a1, a2, a3 and a4 in the neighborhood of the open end of the bell, and the final nodes a1 to a4 are substantially matched with one another. This feature contributes to the stability of the pitch of the sound. However, the standing waves RL1 to RL4 representative of the harmonic tones change the position of the final nodes b1, b2, b3 and b4 along dots-and-dash line DDL, and the final nodes b1 and b2 take place in the tube member inside of the bell. This results in undesirable wave components. For example, the wave component c1 of a quarter of the wavelength is produced from the standing wave RL1, and is radiated from the brass instrument. The variation of the nodes b1 to b4 is not constant over the tone range, and either harmonic tone strongly affects the fundamental pitch of the sound depending upon the note of the sound. The prior art mute 5 had the similar tendency as the prior art mute 3, and the unstable intervals are inherent in the prior art mutes 1, 3 and 5. The prior art mutes 1, 3 and 5 further have individual problems. The prior art mute 1 is expensive due to the attaching work on the sound absorbing layer 1c and the flare cylindrical member 1a together, and the sound absorbing layer 1c tends to be unsanitary due to water. Moreover, the small hole 1d imparts large resistance against the blow, and the player feels the blow unusual. The prior art mute 3 also gives large resistance against the blow due to the small hole 3e. On the other hand, the prior art mute 5 merely insufficiently reduces the sounds, because the prior art mute 5 aims at the change of the timbre. The resistance against the blow is not small. US 1 425 318 A relates to a mute which is adapted to be removably secured within a continuously and gradually enlarging bell of a musical instrument, such as a comet or trumpet. The mute comprises a body portion which is a bell-shaped tube substantially conforming in contour to the bell of the musical instrument, but of smaller size so that it may be readily mounted in the bell. The outer, larger diameter end of the tubular body portion is capped by a hemispherical end closure having its convexity outwardly exposed. The center of the closure is formed into a frusto-conical, re-entrant sound delivery tube which is greatest in diameter at its outer end and diminishes toward its inner end. The sound delivery tube and the end closure are coaxial with the body portion and also with the bell when the mute is in use. Further, US 2 574 591 A relates to a mute structure adapted to be placed in the bell of an air-column instrument for producing novel musical effects. US 1 409 860 A relates to a combination mute which may be used to produce a "jazz" effect with a brass musical instrument. This document was used as a basis for the preamble of claim 1. SUMMARY OF THE INVENTION It is therefore an important object of the present invention to provide a mute which sufficiently reduces sounds without change of the intervals. To accomplish the object, the present invention proposes to control reflection on an inner surface of a mute in such a manner as to match the distribution of sound pressures of harmonic tones with those of sound generated by a brass instrument without the mute. In accordance with the present invention, there is as set forth in claim1. Preferred embodiments of the invention may be gathered from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the mute according to the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which: Fig. 1 is a partially cut-away perspective view showing the prior art mute attached to the brass instrument; Fig. 2 is a partially cut-away side view showing another prior art mute attached to the brass instrument; Fig. 3 is a partially cut-away side view showing yet another prior art mute attached to the brass instrument; Fig. 4 is a graph showing sound pressures of harmonic tones with and without the prior art mute shown in figure 2; Fig. 5 is a partially cut-away side view showing the structure of a mute according to the present invention; Figure 6 is a graph showing sound pressures of harmonic tones with and without the mute shown in figure 5; Fig. 7 is a partially cut-away side view showing the structure of another mute according to the present invention; Fig. 8A is a partially cut-away plan view showing yet another mute according to the present invention; Fig. 8B is a partially cut-away side view showing the mute shown in figure 8A; Fig. 9 is a partially cut-away side view showing a sound isolating cover member incorporated in the mute shown in figures 8A and 8B; Fig. 10 is a diagram showing an electronic sound generating system connectable to a microphone incorporated in the mute shown in figure 9; Fig. 11 is a cross sectional side view showing still another mute according to the present invention; Fig. 12 is a cross sectional view taken along line A-A of figure 11 and showing the inside structure of the mute; Fig. 13 is a back view showing the mute; Fig. 14 is a partially cut-away side view showing a microphone unit incorporated in the mute; and Fig. 15 is a cross sectional side view showing a microphone forming a part of the microphone unit. DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment Referring first to figure 5 of the drawings, a mute 10 embodying the present invention is inserted into a trumpet 11. The mute 10 is formed of paper, wood, metal or synthetic resin, and defines an inner space 10a open at both ends thereof. The inner surface of the mute 10 is axially enlarged in diameter from the right end RE toward a middle point MDL, and is axially shrunk from the middle point MDL toward the left end LE. Therefore, the inner space 10a has the maximum diameter at the middle point MDL. If the maximum diameter is positions around a third of the length of the mute along the center axis CL4, the sound reduction characteristics are optimized for the trumpet 11. Two generally frusto-conical tube members 10b and 10c are assembled with one another at the middle point MDL. The generally frusto-conical tube member 10b may be fixed to the other generally frusto-conical tube member 10c. The inner surface 10d of the generally frusto-conical tube member 10b is outwardly warped, and, accordingly, the gradient is increased from the left end LE toward the middle point MDL. The generally frusto-conical tube member 10b has a turn-back portion 10e projecting into the inner space 10a, and the turn-back portion 10e has a frusto-conical configuration. The turn-back portion 10 is coaxial with the generally frusto-conical tube member 10b, and shares the center axis CL4 therewith. The inner diameter of the turn-back portion 10 is decreased from the left end LE to the leading end 10f thereof. When the mute 10 is snugly inserted into the bell 1a of the trumpet 11, the leading end 10f is positioned at a predetermined point. The predetermined point is farther from the left end LE than a first point where the maximum sound pressure takes place in the inner space 10a and closer to the left end LE than a second point where the final nodes of standing waves take place in the inner space 10a. Namely, the predetermined point takes place between the first point and the second point. The reason for the predetermined point is that, though the final nodes of the standing waves strongly affect the pitch of the sound, the final nodes of the harmonic tones differently take place as will be described hereinlater. The air passage at the leading end 10f is approximately equal in cross section to the air passage of the mouthpiece 11b of the trumpet 11. In general, if the air passage at the leading end 10f is wider than the air passage of the mouthpiece 11b, a player easily blows on the mouthpiece 11b, however, leakage sound is increased. On the other hand, if the air passage at the leading end 10f is narrower than the air passage of the mouthpiece, the leakage sound is decreased, however, the player is required to strongly blow on the mouthpiece 11b. Thus, there is a trade-off between the sound reduction capability and the playability. However, if the air passage at the leading end 10f is equal in cross section to the air passage of the mouthpiece 11b, the designer compromises the sound reduction capability with the playability. The standard mouthpiece 11b of a trumpet has the diameter of 4.2 millimeters at the minimum cross section, and the inner diameter at the leading end 10f is also regulated to 3.65 millimeters. On the other hand, the generally frusto-conical tube member 10c linearly increases the inner surface from the right end RE and changes the increment on the way to the middle point MDL. The gradient is firstly increased and, thereafter, decreased so as to form a convex outer surface. A sealing member 10g of cork is attached to the outer surface of the straight portion of the frusto-conical tube member 10c, and is effective against leakage air. The sealing member 10g effectively reduces the leakage sound, and does not allow the mute 10 to be unintentionally detached from the trumpet 11. The present inventors measured sound pressures of harmonics of a sound generated by the trumpet with and without the mute 10 according to the present invention. The sound pressures were plotted in figure 6. The dispersion of the sound pressure took place like a standing wave. Broken lines BL10, BL11, BL12 and BL13 represented the sound pressures of the second, fourth, sixth and eighth harmonic tones of the sound generated by the trumpet 11 without the mute 10, and solid lines RL10, RL11, RL12 and RL13 stood for the sound pressures of the second, fourth, sixth and eighth harmonic tones of the sound generated by the trumpet equipped with the mute 10 according to the present invention. The broken lines BL12 and BL13 were overlapped with the real lines RL12 and RL13, respectively. The maximum sound pressures took place at points MX1, MX2, MX3 and MX4, and the final nodes of the standing waves RL10 to RL13 were at points FN1, FN2, FN3 and FN4 in the inner space 10a. The leading end 10f was positioned between the points MX1 to MX4 and the points FN1 to FN4. The final nodes FN1 to FN4 are very close to the final nodes of the standing waves represented by the broken lines BL10 to BL13, and are adjacent to the opening end of the bell 11a. The small difference between the final nodes is derived from the configuration of the inner surface 10d. In detail, the inner surface 10d and the outer surface of the turn-back portion 10e define a taper reflecting surface, and the taper reflecting surface reflects the harmonic tones at different points. In other words, the harmonic tones have respective reflection points individually deviated along the center axis CL4. Even if the player changes the pitch of the sound, the harmonic tones of the new sound find respective reflecting points on the taper reflecting surface, and the harmonic tones also concentrate the final nodes around the open end of the bell 11a. Thus, the harmonic tones do not widely change the final nodes FN1 to FN4, and the final nodes FN1 to FN4 are close to the final nodes of the harmonic tones generated by the brass instrument without the mute 10. These final nodes FN1 to FN4 enhance the stability of the pitch of the sound and the intervals of the tones of the sounds. The inner surface 10d is outwardly warped, and the inner surface of the frusto-conical tube member 10c inwardly warped. This surface configuration is conducive to not only the stability of the intervals but also the sound reduction, the balance of the loudness between the sounds and a stable playability in comparison with the prior art mutes is shown in figures 2 and 3. The turn-back portion 10e defines an inner space increasing the cross section from the leading end 10f toward the left end open to the air. This feature enhances the stability of the air flow passing therethrough, and provides comfortable resistance of blow to the player. Even if the player changes the blow in crescendo, the sound does not fluctuate. The leading end 10f is positioned between the final nodes FN1 to FN4 and the points MX1 to MX4 of the maximum sound pressure, and the brass instrument 11 with the mute 10 not only stably generates sounds over the scale but also achieves large sound reduction. The leading end 10f is adjusted to a point MIN where the minimum sound pressure due to representative harmonic tones takes place, and the adjustment maximizes the sound reduction. The point of the maximum sound pressure MX1/MX2/MX3/MX4 and the point of the minimum sound pressure are variable depending upon the harmonic tones which are taken into account. The representative harmonic tones are defined as "harmonic tones which give the unique timbre to the brass instrument". The eighth harmonic tone to the twelfth harmonic tone are the representative harmonic tones of the trumpet. The trumpet has the point of the minimum sound pressure at 30 millimeters from the left end of the mute 10 open to the air. Second Embodiment Turning to figure 7 of the drawings, another mute 20 embodying the present invention largely also comprises two frusto-conical tube members 20a and 20b assembled together, and is inserted into a bell 21a of a brass instrument 21. A small frusto-conical tube member 20c projects from the left end of the frusto-conical tube member 20a into an inner space 20d defined in the mute 20 as similar to the mute 10. The frusto-conical tube members 20a and 20b have respective straight inner surfaces 20e and 20f, and the other features are similar to those of the first embodiment. The frusto-conical tube members 20a and 20b with the straight inner surfaces 20e and 20f are easily manufactured, and decrease the production cost of the mute 20. The taper inner space between the large and small frusto-conical tube members 20a and 20c achieves the stable sounds and a good sound reduction. Third Embodiment Figures 8A and 8B illustrate yet another mute 30 embodying the present invention used for a brass instrument 31. The mute 30 is designed on the basis of the mute 10, and the same references as those in figure 5 are labeled with corresponding components parts of the mute 30 without detailed description for the same of simplicity. The mute 30 further comprises a sound insulating cover member 30a attached to the generally frusto-conical tube members 10b and 10c and a built-in microphone 30b accommodated in the inner space 10a. As will be better seen in figure 9, the sound insulating cover member 31 is shaped in a cup-like configuration, and is formed of synthetic resin or metal. In detail, the sound insulating cover member 31 has a bottom wall 30c and a side wall 30d merged with the bottom wall 30c. The side wall 30d is inserted into a groove formed in the generally frusto-conical tube member 10b so as to attach the sound insulating cover member 30a thereto. The side wall 30d is partially cut away at intervals so as to form vent holes 30e. The frusto-conical tube member 10b and the sound isolating cover member 30a attached thereto form an inner space 30, and a gap takes place between the bottom wall 30c and the left end of the frusto-conical tube member 10b. As a result, the inner space 30f is connected through the gap and the inner space of the turn-back portion 10e to the inner space 10a. The air is blown through the narrow gap between the sound insulating cover member 30c and the frusto-conical tube member 10b, and expands in the wider inner space 30f. The sound carried on the air is decayed, and the narrow gap and the wide inner space 30f serves as a muffler like that of a car. The vent holes 30e are open to the air, and the inner space 30f is conducted through the vent holes 30e to the air. The vent holes 30e do not provide resistance against the blow larger than the resistance of the brass instrument 31. When a player generates low-pitch sound, the amount of air to be blown is increased, and the designer takes the variation of the blow into account in the design work on the vent holes 30e. In this instance, the sound insulating cover member 30a has six vent holes 30e angularly spaced at 60 degrees around the periphery of the side wall 30d. Each of the vent holes 30e is elongated hole of 3 millimeters in width, and the total opening area of the vent holes 30e is twice to eighth times larger than the opening at the leading end 10f. It is preferable for the vent holes 30e to be four times to six times wider than the opening at the leading end 10f. A jack 30g is embedded into the frusto-conical tube member 10c adjacent to the middle point MDL, and is connected through wires 30h to the microphone 30b. The microphone 30b is located at the point M (see figure 6) where the effective standing waves are terminated, and the point M is close to the right end of the mute 30 in this instance. The jack 30g is either male or female type. Low-order harmonic tones put nodes around the point M, and high-order harmonic tones put anti-nodes around the point M. For this reason, the volume and the timbre are constant over the scale. The mute 30 achieves the stability of the pitch as similar to the first embodiment, and the sound insulating cover member 30a further improves the sound reduction. In fact, when a player blows on the mouthpiece (not shown) of the brass instrument 31, he only hears vent noise. The inner space 30f eliminates high frequency components from the vent noise, and the vent noise is small. The vent holes 30e are open along the boundary between the frusto-conical tube members 10b and 10c, and are hardly noticed. Therefore, the external appearance of the mute 30 is attractive. The player can confirm the sounds through the microphone 30b and enjoy an ensemble performance together with other electronic musical instrument without acoustic sounds. The microphone 30b is coupled to a sound processing system 40 shown in figure 10. A mixing/amplification unit with a digital reverb and a module with a reverb are incorporated in the sound processing system 40. The mutes 30 are respectively attached to a trumpet 41, a trombone 42 and a horn, and the microphones 30b in the mutes 30 are coupled through wirings 43 and 44 to input terminals MIC of the sound processing system 40. Head-phones 45 and 46 are respectively connected to output terminals PHONE of the sound processing system 40. The sound processing system 40 further has auxiliary input terminals AUX assigned to a compact disk unit CD, a silent piano 47b, a mic-mixing unit 47c for a singer, a sequencer 47d, a digital metronome 47e and a television set 47f and auxiliary output terminals LINE assigned to an effecter 48a, a tuner 48b, a MIDI (Musical Instruments Digital Interface) converter 48c, a tone generator module 48d, an amplifier/speaker 48e and a tape recorder 48f. The effecter 48a is connected to a speaker system 49a, and the MIDI converter 48c is coupled to MIDI musical instruments 49b and a personal computer 49c. The personal computer 49c is further coupled to the tone generator module 48d. The sound processing system 40 allows a player to enjoy an ensemble as follows. While the compact disk unit 47a or the television unit 47f is reproducing music, the player blows on either trumpet 41 or trombone 42, and imparts a suitable reverb to the sound generated by the brass instrument. The player or listeners hear the ensemble through the headphones 45 and 46, or records it through the tape recorder 48f. While the silent piano 47b or the mic-mixing unit 47c is reproducing music recorded on a floppy disk 49d or 49e, the player blows on the brass instrument 41 or 42, and hears electronic sounds through the headphone 45 or 46. Using the digital metronome 47e and the tuner 48b, the player can practice a music. The metronome 47e gives a tempo through the headphone 45 or 46, and guides the player. The sound processing system 40 imparts a suitable reverb to the sounds generated by the brass instrument 41 or 42, and the player conforms the sounds through the headphone 45 or 46 and the indication of the tuner 48b. While the player is blowing on the brass instrument 41 or 42, the effecter 48a changes the timbre of the brass instrument 41 or 42 to an arbitrary timbre, and the speaker system 49a reproduces the performance through the selected timbre. While the player is blowing on the brass instrument 41 or 42, the MIDI converter 48c changes the music data signal representative of a series of sounds into a series of MIDI data codes, and the tone generator module 48d and the amplifier/speaker 48e reproduces the sounds through another timbre such as, for example, a piano or a synthesizer. If the MIDI data codes are supplied to the personal computer unit 49a together with MIDI codes for other parts, the personal computer unit 49c prepares a complete score. If the modules are multiplied, sounds of the brass instrument 41 or 42 are recorded without an undesirable influence of other musical instrument in a narrow room. Moreover, reverb is imparted to the sounds without a special recording studio. The personal computer 49a evaluates a performance through comparison between the sounds generated by the brass instrument and the sounds of a standard performance. If the auxiliary output terminal LINE is suitably connected to the auxiliary input terminal AUX, players respectively blow on the brass instruments 41 and 42, and hear the ensemble through the headphones 45 and 46. If a transmitter is incorporated in the sound processing system 40, the music data representative of the sounds are transferred to a receiver at a long-distance place. Fourth Embodiment Figures 11 to 13 illustrate still another mute 40 embodying the present invention. The mute 40 is designed on the basis of the mute 30, and for this reason, references designating parts of the mute 30 are labeled with the corresponding components parts of the mute 40 without detailed description. The mute 40 differs from the mute 30 as follows. First, a seal layer 40a of synthetic resin is wound on the felt side portion of the frusto-conical tube member 10c instead of the cork layer 10g. Silicon rubber is available, for the seal layer 40a. A plurality of grooves 40b are formed on the outer surface of the seal layer 40a like a ripple, and enhances friction between the seal layer 40a and the bell of a brass instrument (not shown). Second, a frusto-conical tube member 40c is thicker than the generally frusto-conical tube member 10b. Namely, the thickness t1 is larger than the thickness t2, and is equal to or greater than 2 millimeters. The frusto-conical tube member 40c thicker than 2 millimeters makes low-pitch sounds stable, and effective against noise due to edge-tone phenomenon. Third, the frusto-conical tube member 40c has an inner surface 40d shaped by rotating a trapezoid defined by angle AG. The angle AG ranges from 5 degrees to 15 degrees, and the player feels the blow through the inner surface 40d natural. If the angle AG is less than 5 degrees, the player feels the resistance of the frusto-conical tube member 40c heavy. On the other hand, if the angle AG is greater than 15 degrees, the air flow is disturbed, and the player feels the blow unstable. In case of a trumpet, it is preferable to adjust the angle AG to 7 degrees. Fourth, the microphone 30b is integrated into a microphone unit 40e together with the wires 30h. In detail, the microphone 30b is inserted into a tube-shaped microphone holder 40f (see figures 14 and 15), and is open to the inner space of the brass instrument (not shown). A thin sheet of synthetic resin such as polyester is provided between the inner surface of the tube-shaped microphone holder 40f and the microphone 30b, and the microphone 30b is fixed to the inner surface of the microphone holder 40f by means of adhesion compound. The thin sheet changes the frequency characteristics of the microphone 30b, and causes the sound processing unit 40 to generate sounds close to the acoustic sounds of the brass instrument. The microphone holder 40f is fixed to a ring-shaped bracket member 40h. Arms 40i are connected to the ring-shaped bracket member 50h, and are angularly spaced from one another. The arms 40i are held in contact with the inner surface of the generally frusto-conical tube member 10c, and maintain a relative position between the generally frusto-conical tube member 10c and the microphone holder 40f and, accordingly, the microphone 30b. The microphone unit 40e further includes a jack holder 40j, and the jack 30g is retained by the jack holder 40j in such a manner as to be exposed to the outside. The jack holder 40j is placed in the inner space 10a with the maximum diameter, and is fixed to the generally frusto-conical tube member 10c. The projecting portion of the jack 30g is threaded, and a lock nut (not shown) is meshed with the threaded projecting portion so as not to fall a plug (not shown) from the jack 30g. The microphone unit 40e further includes a wire case 40k connected between the jack holder 40j and the microphone holder 40f. The wires 30h extend inside of the wire case 40k along the center axis of the mute 40 CL5, and connect the microphone 30b to the jack 30g. Thus, the microphone 30b is integrated into the microphone unit 40e, and the microphone unit 40e is easily assembled with the frusto-conical tube member 10c. This results in reduction of production cost. Moreover, the microphone holder 40h, the wire case 40k and the jack holder 40j maintain the relative positions among the microphone 30b, the wires 30h and the jack 30g, and, for this reason, prevent an electric signal propagated through the wires 30h from noise due to undesirable physical vibrations on these components. As will be appreciated from the foregoing description, the inner space of the mute according to the present invention is shaped in such a manner that the standing waves of the representative harmonic tones have the final nodes close to those of the standing waves generated without the mute, and the intervals among the notes do not fluctuate. The leading end of the frusto-conical tube member is located at a position where the minimum sound pressure due to standing waves of representative harmonic tones featuring the brass instrument takes place, and enhances the sound reduction. Moreover, the frusto-conical tube member 10e, 20c or 40c projects into the inner space, and the player does not feel the blow unnatural. The inner surface of the frusto-conical tube members 10b/10c or the variation of the gradient enhances the balance of the intervals. The frusto-conical tube member with the angle between 5 degrees and 15 degrees makes the player feel the blow natural, and the thickness not less than 2 millimeters enhances the stability of the low-pitch tones. The built-in microphone allows a player to practice the brass instrument without disturbance to the neighbors. If the microphone is placed at the terminated position of the standing waves of the representative harmonic tones in the bell, the microphone picks up the sounds without change of timbre.and loudness. If the sound insulating cover member is further attached, the acoustic sounds are eliminated by the sound insulating cover member perfectly. The inner space between the sound isolating cover member and the frusto-conical tube member is two to eigh times wider in cross section than the inner space of the inwardly projecting frusto-conical tube member, and the sound insulating cover member does not increase the resistance against the blow. Relation Between Principle of the Invention and Embodiment When a player blows on a brass instrument, an acoustic wave is generated, and is partially radiated from the inner space of the brass instrument to the outside. The acoustic wave is partially reflected around the outlet end of the brass instrument due to a difference in acoustic impedance between the inner space and the outer space, and is backwardly propagated toward the inlet end. Thus, a reverse acoustic wave is created through the reflection. The reverse acoustic wave interferes with the acoustic wave, and, as a result, a standing wave takes place inside of the brass instrument. Even though the acoustic wave is reflected around the outlet end of the brass instrument, the acoustic wave in part is radiated from the outlet end. For example, a trumpet radiates the vibrational energy of the standing wave at only 1 or less than 1 percent. The remaining energy is partially consumed in the friction between the vibrative column of air and the inner surface of the brass instrument, and is partially converted to heat. In order to mute an acoustic sound generated by a brass instrument, it is a basic concept to reduce the vibrational energy of the standing wave radiated from the outlet end. High frequency components are much liable to be radiated. One of the approaches to reduce the vibrational energy radiated from the outlet end is to decrease the area of the outlet end of the brass instrument. However, if the area of the outlet end is too narrow, the blow can not escape from the inner space, and the player feels not comfortable. For this reason, it is necessary to design a vent at least equal in area to the minimum cross section of the air passage in the mouthpiece. When the prior art mute is attached to the flare or the bell of a brass instrument, the pitch of sound is increased by a semitone. This is because of the fact that the prior art mute changes the boundary condition of the resonance from an open end to a closed end. Even if the prior art mute has a vent, the vent is too narrow to serve as the open end, and the boundary condition is assumed to be the closed end. The change of the boundary condition results in that the vibrative column of air is prolonged by a quarter wavelength of each frequency component of the standing wave. The additional quarter wavelength is conventionally not taken into account, and the prior art mute suffers from the increase of the pitch of sound. It is necessary to provide a counter measurement against the change of the boundary condition. The present inventor noticed that if the reflection surface of a mute was deviated by a quarter wavelength, the standing wave generated in the brass instrument equipped with the mute was matched with the standing wave generated in the brass instrument without the mute. The standing wave generated in a brass instrument without the mute and the standing wave generated in the brass instrument with a mute are hereinbelow referred to as "original standing wave" and "modified standing wave", respectively. When the quarter wavelength is canceled by a prolonged vibrative column of air, a regulated standing wave takes place inside of the brass instrument. In order to match the original standing wave with the corrected standing wave, the present inventors provided a regulative portion to a mute between the outlet end of a brass instrument and the reflection surface of the acoustic wave. The regulative portion is implemented by the frusto-conical tube member such as 10c, and the frusto-conical tube member 10c theoretically changes the reflection surface from the outlet end of the bell portion 11a to the middle point MDL. As a result, the vibrative column of air is prolonged by the quarter wavelength. It is natural for the regulative portion to be increased in cross section toward the reflection surface like the bell portion of a brass instrument so as to exactly prolong the vibrative column of air. In other words, it is theoretically desirable for the regulative portion to have a horn configuration, the cross section of which is gradually increased toward the reflection surface like the bell of the brass instrument. The present inventor evaluated various configurations, and concluded that an exponential horn configuration was appropriate. However, the exponential horn configuration was required to be modified as similar to the horn configuration of the bell portion, and partially bulged out. The modified exponential horn configuration enhances the balance of tones on the scale. If the acoustic wave was constituted by a single frequency component, the regulative portion would eliminate the undesirable increase of pitch. However, various frequency components form the actual acoustic wave, and a vertical reflection surface is not always appropriate to all of the frequency components. In fact, a vertical reflection surface optimum to a fundamental frequency component is not appropriate to higher harmonic frequency components. For this reason, the reflection surface is modified so as to disperse the reflecting points of the frequency components. The dispersion of the reflecting points is expected to achieve the resonance of vibrative columns of air different in length. The present inventors form the reflecting surface with a continuously oblique surface projecting from the regulative portion. The cross section defined by the continuously oblique surface is decreased by spacing from the regulative portion. The continuously oblique surface is, by way of example, formed by the inner surface 10d of the tube member 10b and the inner surface of the turn-back portion. It is desirable for the continuously oblique surface to have an inverted exponential horn configuration, and the cross section is exponentially decreased toward the open end to the outside. In the first embodiment, the leading end 10f forms the open end. The turn-back portion shortens the total length of the oblique reflection surface. The present inventors confirmed that the inner surface of the turn-back portion did not deteriorate the wave-reflecting characteristics, the stability of the tones, player's impression on the blow and the tone quality of the low-pitch tones. The low-pitch tones are rather improved. High-pitch tones are stimulative. If the dispersion of sound pressure of a high-pitch tone is deviated toward a low pressure position, the high-pitch tones are comfortable for a listener. Although particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the present invention as defined in the appended claims. For example, the brass instrument may be a French horn, a trombone or a tuba, and the inner configuration of the mute is tailored in consideration of the representative harmonic tones.

Claims: A mute attached to a bell portion of a brass instrument (11; 21; 31), comprising: a case member including a first inner surface defining a first inner space (10a; 20d) having a first end connected to an air passage of said brass instrument and a second end open to the outside, the cross section of said first inner space (10a; 20d) increasing from said first end to a middle point (MDL) and decreasing from said middle point to said second end; and a tube member (10e; 20c; 40c) connected at one end thereof to said second end of said case member, and projecting into said first inner space, wherein said mute offers a reflection surface for standing waves produced through a blowing at said middle point (MDL) so that standing waves are produced, characterized in that an additional reflecting surface comprises a continuously oblique surface projecting from a regulative portion between the outlet end of the brass instrument and the reflection surface of the acoustic wave, said regulative portion being implemented by a frusto-conical tube member (10c) so that said standing waves are substantially the same as standing waves to be produced in said brass instrument without said mute. The mute as set forth in claim 1, in which a leading end (10f) of said tube member (10; 20c) is located at a position where the minimum sound pressure due to standing waves representative of predetermined harmonic tones featuring said brass instrument takes place. The mute as set forth in claim 2, in which said brass instrument is a trumpet, and said predetermined harmonic tones are the eighth harmonic tone to the twelfth harmonic tones. The mute as set forth in claim 1, in which an increment of said cross section is constant from said first end to a first certain point on the way to said middle point (MDL), and increases from said first certain point to a second certain point on the way to said middle point (MDL) and decreases from said second certain point to said middle point (MDL). a decrement of said cross section decreasing from said middle point (MDL) to said second end. The mute as set forth in claim 1, in which an increment of said cross section is constant from said first end to said middle point, and a decrement of said cross section is constant from said middle point to said second end. The mute as set forth in claim 1, in which a leading end of said tube member (10e; 20c) is farther from said second end than first points in said first inner space (10a; 20d) and closer to said second end than second points in said first inner space (10a; 20d), the maximum sound pressures of harmonic tones of a sound generated by said brass instrument attached to said mute (10; 20; 30; 40) taking place at said first points, final nodes (FN1 to FN4) of standing waves respectively representative of dispersions of sound pressures of said harmonic tones taking place at said second points. The mute as set forth in claim 1, further comprising a sound insulating cover member (30a) partially covering an outer surface of said case member so as to define a third inner space (30f) contiguous to a second inner space through a gap formed between a third inner surface of said sound insulating cover member and an outer surface of said case member, said third inner space being open through an air vent (30e) to the outside of said mute (30; 40). The mute as set forth in claim 7, in which said third inner space has a cross section larger in area than said gap. The mute as set forth in claim 7, in which said third inner space has a cross section larger in area than said gap, and said air vent (30e) is twice to eighth times larger in area than said cross section of said second inner space. The mute as set forth in claim 1 or 7, further comprising a microphone (30b) accommodated in said first inner space (10a) so as to pick up sounds generated by said brass instrument. The mute as set forth in claim 10, in which said microphone is connected through wires (30h) to a jack (30g), and said microphone, said wires and said jack are integrated into a microphone unit (40e) accommodated in said mute.

Inventors: HAMANAGA SHINJI, MATSUKUMA YOSHIHIKO, HAMANAGA, SHINJI, MATSUKUMA, YOSHIHIKO, Hamanaga, Shinji, c/o Yamaha Corporation, Matsukuma, Yoshihiko, c/o Yamaha Corporation
Applicants: YAMAHA CORP, YAMAHA CORPORATION
Application year: 1995
Main classification: G10D9
IPC codes: G10D7, G10D9