Patent Publication Number: US-7214871-B2

Title: Transmitter for sound recording of an electric signal from an acoustic drum

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a transmitter for reception of an electric signal from an acoustic drum. The transmitter comprises a vibration-sensitive body, which is designed in such a way that it lies on the drumhead, whose undulation it can acquire and record. 
   It is well known to arrange transmitters or microphones on the body of an instrument in order to receive an electric signal which can be used for the activation of synthesizers or for the conversion of MIDI information (Musical Instrument Digital Interface). 
   Known transmitters for acoustic drums comprise as a rule a piezoelectric ceramic body, which is attached to the drumhead with a double-sided adhesive tape. The ceramic body exhibits a relatively slight thickness and in general a circular base area. The transmitters usually used acquire waves of the drumhead regardless of their direction. This triggers problems, among other things because rolls on the drumhead in the middle of the drum emit a weak signal amplitude, while rolls near the edge of the drum result in a strong signal amplitude. This is a genuine source of false signals from the transmitter and was the object of electronic corrections in the subsequent amplification circuit. Certainly it was possible in this way to eliminate a great part of the false signals; however this was dependent on the transmitter sensitivity and on the frequency range of the generated signal. 
   To prevent the transmitter body from being struck by the drumstick, the body is arranged in great proximity to the edge of the drum. Up until now this has also produced the shortest possible wiring to the required plug and socket device, which up to now has been provided in the form of a separated unit underneath the edge of the drum. 
   By means of shaping of the transmitter body area and by means of its decentralized positioning on the drumhead the transmitter reacts sensitively to all the different undulations as the result of a roll on the drumhead. Such a transmitter is also especially sensitive to decentralized rolls and the undulations generated therewith on the drumhead. A transmitter in oblong shape for a drum is well known from WO 90/03639. 
   A further transmitter is well known from EP 0 542 706B1. The vibration-sensitive device of that transmitter is oblong in shape. The longitudinal axis of the vibration-sensitive device points towards the middle of the drumhead. 
   Such a transmitter has the following drawback: 
   The sound level which a drumstick roll carries out on the drum depends on the location at which the drumstick strikes the drumhead. The sound level is higher, the closer the drumroll is to the edge area of the drumhead. This can be extraordinarily unpleasant and impair the playback of compositions. 
   SUMMARY OF THE INVENTION 
   The object of the invention is thus to specify a transmitter of the type initially described, which is designed in such a way that the sound level is not influenced by the location at which the drumstick strikes the drumhead. 
   In the process, the inventor has proceeded from the lessen teachings of EP 0 542 706B1. Instead of designing the vibration-sensitive device to be oblong, as specified in the aforementioned patent, the inventor selects a completely different shape for this device. Said device is namely of a shape that does not permit the detection of any orientation, and in any event is not “long stretched out”. The vibration-sensitive device is designed in such a way that it acquires waves in a prescribed wavelength range. 
   The shape of a sector of a circle has proven to be particularly favorable. In the process the arc of the circle in expedient fashion has the same radius of curvature as the drumhead, so that it can be placed at the border of the drumhead and is snugly fitting. One could also say that the device has the shape of a wedge of pie. The aperture angle of the segment can amount to 90°. Deviations to the top or the bottom are possible. An angle of 70 or 80°, or even of 100 or 110° is conceivable. 
   Other configurations also come into consideration, for example an essentially circular configuration. In this case the device should have a projection, which points to the center of the drumhead. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
     The invention is explained in detail with the aid of the drawings. The figures show the following: 
       FIG. 1  is a perspective view of an acoustic drum with an attached transmitter as per the present invention; 
       FIG. 2  is a perspective view of a transmitter as per  FIG. 1 , showed in non-attached state, and 
       FIG. 3  is an embodiment of the vibration-sensitive body of the transmitter. 
       FIGS. 4   a ,  4   b ,  4   c ,  4   d ,  4   e  show variants of vibration-sensitive bodies in a plan view. 
   

   DETAILED DESCRIPTION 
     FIG. 1  represents an acoustic drum  1  with a transmitter  2  attached to it. The transmitter  2  comprises a holder  3  with a hook  4 , which takes hold of the edge  5  of the border  6  of the drum  1 . The holder  3  is attached with a screw  7 , which is fastened to the border  6 . The transmitter  2  comprises a vibration-sensitive body  8  ( FIGS. 2 and 3 ), which is borne by a spring device  9 , which presses the body  8  against the head  10  of the drum  1 . 
     FIG. 2  represents the embodiment of the body  8  of the invention, as it is currently preferred. The holder  3  exhibits a reversed L-shape, which creates a housing-like cover  11 , which protrudes from above and chiefly in a plane running parallel to the drum head  10  ( FIG. 1 ). At the surface of the cover  11 , which is directed toward the drum head  10 , the vibration-sensitive body  8  is borne by the spring device  9  as shown in  FIG. 3 . In the preferred embodiment the device  9  consists of a piece  12 , preferably made of hard rubber, which is adhered to the inner surface of the cover  11 , which for its part carries a cushion  13 , which is preferably made of artificial foam, to which the surface of the downward pointing vibration-sensitive body  8  is attached. The attachment takes place preferably by means of adhesion. 
   The vibration-sensitive body  8  is connected to the electrical conductors  15  at its base, said conductors leading to the inside of the holder  3  down to a plug and socket device  16  at the end of the foot  17  of the holder  3 . 
   The cover  11  and the foot  17  of the holder  3  form the hook  4 , whose shape is adapted to the shape of the edge  5  of the border  6  of the drum  1 . By means of this hook  4  and the screw  7  the holder  3  is firmly attached to the drum  1 , causing the vibration-sensitive body  8  to fit securely to the drum head  10 . 
   One can also recognize the shape of the vibration-sensitive body  8  from  FIGS. 2 and 3 . The body is a sector of a circle in the plan view. It exhibits a tip  8 . 1 . The angle α to the tip amounts in the present case to somewhat less than 90°. The following are possible: 60, 70, 80, 90, 100, 110, 120, 130, 140° with intermediate values. 
   The chord of the sector is in the preferred case somewhat the same length as each of the two lateral edges of the segment. The tip  8 . 1  of the sector can also be rounded off or even cut. 
   The vibration-sensitive body  8  is made of a piezoelectric ceramic material, piezoelectric synthetic material or the like. 
     FIG. 4   a  shows one possible embodiment of a vibration-sensitive body  8  of the invention. 
   The body  8  as per  FIG. 4   a  is at least approximately circular. It exhibits a wart-like projection  8 . 2 . The projection could also be designed as a tip. 
   In the case of the embodiment as per  FIG. 4   b  the body  8  is designed in the shape of a hatchet. The peripheral edge  8 . 3  of the body  8  is circular. It has the same radius of curvature as the drumhead itself. However, deviations from this are also possible. The lateral edges  8 . 4  and  8 . 5  are concave in design. Between the two lateral edges  8 . 4  and  8 . 5  a wart-like projection  8 . 2  is formed. Here again, a tip could be here instead of the wart-like projection  8 . 2 . 
   The embodiment as per  FIG. 4   c  corresponds to the embodiment as per  FIGS. 2 and 3 . One recognizes a tip  8 . 1  as well as the two lateral edges  8 . 4 ,  8 . 5  and the peripheral edge  8 . 3 . 
   In the case of the embodiment as per  FIG. 4   d  the vibration-sensitive body  8  has at least approximately the shape of an ellipse. Said ellipse in turn exhibits a wart-like projection  8 . 2 , which is directed toward the center of the drumhead, which is not shown here. The opposing side of the ellipse has a radius of curvature, which approximates the radius of curvature of the drumhead. 
   In the case of the embodiment as per  FIG. 4   e  the vibration-sensitive body  8  has the shape of a rectangle with rounded off corners. Here again the wart-like projection  8 . 2  is present. 
   In all of the cases the wart-like projection could also exhibit a tip, which in mounted state points toward the center of the drumhead. 
   The basic idea in the case of all of the embodiments shown here  4   a  through  4   e  consists in the fact that the vibration-sensitive body  8  in mounted state viewed in radial direction of the drumhead exhibits a smaller or equally large or at the most essentially larger extension than the dimension running vertically or in the peripheral direction of the drumhead.