Abstract:
A passive radiator baffle which mounts to the side opposite the beater drumhead membrane side of acoustic drums and is used by musicians to enhance the live acoustic sound of these drum percussion instruments by adding low-frequency punch to their performance. This low-frequency response is achieved by selecting the mass of an acoustically suspended piston to provide tuning the drum enclosure to a selected frequency.

Description:
This is a continuation-in-part of copending application Ser. No. 07/525,200, filed on May 18, 1990, now U.S. Pat. No. 5,095,796. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to musical instruments, particularly percussion instruments such as drums. 
     BACKGROUND OF THE INVENTION 
     In conventional drums such as a bass drum, the drum comprises a beater drumhead membrane mounted to the drum shell. The side of the drum opposite the beater drumhead may be open, or it may have another drumhead membrane, known as the carry, or resonating, head. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is a passive radiator baffle panel which mounts to the drum shell on the side opposite the beater drumhead membrane. The invention enhances the live acoustic sound of drum type percussion instruments by giving the low-frequency response an improved &#34;punch&#34;. This enhanced low-frequency response is achieved by replacing the resonating head with a rigid passive radiator piston having a mass and area selected to tune the drum baffle to the appropriate percentage of the free-air resonant frequency of the beater drumhead membrane in order to control the peak amplitude of the beater drumhead membrane and extend the low-frequency response of the acoustic drum. 
     The passive radiator baffle panel has the piston resiliently fastened to the side of the drum opposite the beater drumhead membrane. This resilient mounting may be achieved by a rim fastened to the drum which has an acoustically compliant rubber suspension to resiliently hold the piston in place. Alternatively, a rigid piston may be affixed to a standard drum membrane. The piston is preferably flat or curved, and most preferably concave. A microphone may be affixed to the baffle panel or the drum instrument. 
     Musical drum type percussion instruments require the use of the hands, drum sticks, or in the case of a bass drum, a foot pedal and beater to transfer the percussive force to the drum. This striking force is transferred to the beater membrane and then to the air inside the drum. The passive radiator baffle panel of the present invention acts as a sound control and tuning element which selectively controls the amount of sound being emitted from the drum due to the striking of the beater membrane. 
     The piston in the rigid baffle panel allows frequencies to be emitted from the drum shell in phase with the frequencies emitted from the front of the beater membrane. The piston controls the speed and radiation of the rear sound wave created by the beater drumhead membrane and which traverses the depth of the drum shell. The piston delays the rear sound wave slightly so that the rear sound wave is radiated in phase with the sound wave radiated from the front side of the beater drumhead membrane. 
     A passive radiator baffle panel of the invention mounted in a drum improves over an open-ended or double-headed drum because the peak amplitude at the resonant frequency of the beater drumhead membrane is reduced. The passive radiator baffle panel resists excessive vibration at resonance and properly loads the beater drumhead membrane with the pressurized internal volume of air. This insures that the drum will be tuned to the frequency for which the radiator is selected. This extends the bass response and reduces boominess associated with uncontrolled resonance, giving a smoother and more controlled acoustic drum sound. 
     If desired, a tuned port may also be provided in the piston or elsewhere in the baffle. A microphone is also preferably imbedded in the piston. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevation view of an embodiment of a passive radiator baffle panel. 
     FIG. 2 is a cross-section along the line &#34;2--2&#34; of the baffle panel of FIG. 1. 
     FIG. 3 is a front elevation view of the baffle panel of FIG. 1 mounted to the front of a bass drum. 
     FIG. 4 is a cross sectional view along the line &#34;4--4&#34; of FIG. 3, and shows the baffle panel mounted to the bass drum with the drum pedal and beater drumhead membrane in place. 
     FIG. 5 is a detail section of FIG. 4, and shows the mounting of the baffle panel to the drum shell. 
     FIG. 6 is an alternative embodiment of the invention showing a sized beater drumhead. 
     FIG. 7 is a detail view of a section of FIG. 6 showing the mounting of the beater membrane to the drum shell. 
     FIGS. 8 and 9 are alternative embodiments of the passive radiator baffle panel showing pistons having curved surfaces. 
     FIG. 10 is a schematic component layout for a microphone for a baffle panel. 
     FIG. 11a is a schematic circuit diagram for a microphone amplifier circuit for a baffle panel when phantom power is available to operate the microphone. 
     FIG. 11b is a schematic circuit diagram for a double microphone amplifier circuit for a baffle panel when phantom power is available to operate the microphone. 
     FIG. 11c is a schematic circuit diagram for a microphone amplifier circuit operating on battery power. 
     FIGS. 12-1 and 12-2 are a table of design parameters for passive radiator baffle panels for drum type percussion instruments in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1-12, a passive radiator baffle panel 10 in accordance with one embodiment of the invention is shown. 
     Baffle panel 10 is adapted to mount in a drum instrument having a drum shell and a beater membrane. Baffle panel 10 has a rigid circular outer rim 12 which is sufficiently thick, and made of sufficiently stiff materials so as to resist flexural movement. This rigidity minimizes undesirable resonances. 
     Rim 12 is mounted to a drum shell edge 14 of a drum instrument opposite the beater membrane 16 of the drum instrument using baffle panel clips 18 which are secured to the drum by a drumhead rim 20 and tension rod brackets 22. 
     Rim 12 has in its inner circumference a resilient rubber acoustic suspension ring 24. Suspension ring 24 retains piston 26 to rim 12, yet is sufficiently resilient to permit the necessary degree and speed of travel to permit piston 26 to generate sound waves upon energy input to the drum from the beater membrane 16. Suspension ring may be affixed to the rim 12 and piston 26 by gluing and/or by mechanical fasteners. 
     Piston 26 is a rigid panel and is sufficiently thick and stiff to resist flexural movement. Piston 26 has a mass selected to provide a tuned sound output from the drum instrument wherein sound waves created by an impact against the beater membrane are radiated by piston 26 in phase with and additively with sound waves radiated from the beater membrane 16, so that the peak amplitude of the resonant frequency of the beater membrane 16 is reduced. The drum instrument is thereby provided with an extended low frequency response. Piston 26 may have a mass selected to give a tuned sound output from the drum at the resonant frequency of the beater membrane 16 or it may have an area selected to give a tuned sound output from the drum at a frequency other than the resonant frequency of the beater membrane 16. 
     In the preferred embodiment, piston 26 is generally circular, however if desired, the piston 26 may be non-circular, so long as piston 26 is of the selected mass. 
     Typically, the baffle panel 10 will be sized and will have a circular perimeter to match the drum to which it is mounted. However, other shapes can be adopted as necessary to match a drum shape. For example, triangular, hexagonal, rectangular or other shapes might be used. Where the baffle panel 10 is circular, it will have an outer circular edge and the piston 26 will be contained, preferably concentrically, within the outer circular edge. 
     The mass of piston 26 is preferably selected using the design parameters set out in the Table of FIG. 12. FIG. 12 shows the necessary mass and area for a piston 26 to tune drums of a variety of sizes to a variety of selected frequencies. For example, FIG. 12 shows various bass drum, floor tom, and mounted tom drum sizes and corresponding piston masses needed to tune the drums to selected frequencies ranging from about 50 hertz (bass drum) up to about 140 hertz (tom drum). The selected frequencies of about 50, 60, 70, 80, 90, 100, 110, 120, 130 or 140 hertz shown in FIG. 12 reflect typical desirable frequencies for a drum. 
     If desired, a tuned port may also be provided in the piston as set forth in my application Ser. No. 07/525,200. 
     In one preferred embodiment, acoustic compliance is improved where the piston has a larger surface area than the beater membrane. Referring now to FIGS. 6 and 7, a reduced diameter beater membrane 30 is shown. Reduced membrane 30 is adapted to fit in a standard bass drum and permits use of a piston with an area nearly equal to the maximum area of a face of the drum shell. Preferably the surface area of piston 26 is about twice the surface area of reduced diameter beater membrane 30. 
     In an alternative embodiment, the piston 26 is mounted directly by adhesives or by mechanical fasteners to a conventional resonating head. In this case, the piston 26 could be a rigid plastic panel. The piston 26 may be a laminate, and might have two mating pieces with the membrane sandwiched between them. In this case the membrane and piston will be mounted on the drum in a conventional manner. A tuned port may also be provided. 
     Referring now to FIGS. 8 and 9, two curved pistons are shown. In FIG. 8, piston 32 is concave. In FIG. 9, piston 34 is convex. The concave piston 32 is preferred. 
     Referring now to FIGS. 10 and 11, a circuit layout for a microphone for amplification of a drum instrument incorporating a passive radiator baffle panel 10 is shown. 
     In FIG. 10, a microphone capsule is imbedded in the drum, preferably in piston 26. The microphone capsule is resistant to shocks and impacts. An amplifier circuit for the microphone capsule is shown in FIG. 11. This gives a microphone output suited for further amplification in a conventional concert sound system. 
     The present invention provides a unique percussion product with a tunable percussion output. The invention is not limited to the description above but includes such variations and equivalents known in the art.