Patent Application
20140165821
1. Field of the Invention
The present invention provides an optical electro acoustic transducer for use in any acoustic string instrument, such as guitars, violins, string bass, cello, etc.
2. Description of the Prior Art
An acoustic guitar, one example of an acoustic string instrument, is a guitar that uses only an acoustic sound board. The air in this cavity resonates with the vibration modes of the string and at low frequencies, the volume of the sound generated increases or decreases depending on whether the air in the box is moving in phase or out of phase with the strings. The resonance interactions attenuate or amplify the sound at different frequencies, boosting or damping various harmonic tones.
No amplification actually occurs in this process, in the sense that no energy is externally added to increase the loudness of the sound (as would be the case with an electronic amplifier). All the energy is provided by the plucking of the string, the function of the entire acoustic system being to maximize intensity of sound.
An acoustic guitar can be amplified by using various types of pickups or microphones. The most common type of pickups used for acoustic guitar amplification are piezo and magnetic pickups. Piezo pickups are generally mounted under the bridge saddle of the acoustic guitar and can be plugged into a mixer or amplifier. Magnetic pickups are generally mounted in the sound hole of the acoustic guitar and are very similar to those found in electric guitars. An acoustic guitar with pickups for electrical amplification is known as an acoustic-electric guitar. New types of pickups have been introduced to try to amplify the full sound of these instruments, such as systems that include an internal microphone along with the body sensors or under the saddle pickups.
Most stringed instruments produce their sound through the application of energy to the strings, which sets them into vibratory motion. The strings alone, however, produce only a faint sound because they displace only a small volume of air as they vibrate. Consequently, the sound of the strings alone requires impedance matching to the surrounding air by transmitting their vibrations to a larger surface area capable of displacing larger volumes of air (and thus producing louder sounds). This calls for an arrangement that allows for the strings to vibrate freely, but also conducts those vibrations efficiently to the larger surface. A bridge is the customary means by which this is accomplished (a bridge is a device that supports the strings on a stringed instrument and transmits the vibration of those strings to some other structural component of the instrument in order to transfer the sound to the surrounding air).
Magnetic soundhole pickups exemplify the same functions as that of electric guitar pickups. Basically, they sense the movement of the strings of plain acoustic or acoustic electric guitars through a magnetic field.
Microphones are accurate transducers used to amplify both plain acoustic and acoustic electric guitars. They convert the sound produced by the guitar into electrical signals that are then picked up by amplifiers. In contrast with the magnetic soundhole pickups, microphones are more prone to feedback; as such, it is important that they are placed closely to the guitar, and that performers whose guitars have these transducers should have constrained motions. Despite the drawbacks of microphones, many musicians still prefer using these transducers because of their ability to pick up certain guitar sound characteristics such as high frequency and percussive sounds produced by tapping that cannot be picked up by other transducers.
Contact pickups are in direct contact with some specific parts of acoustic guitars. They pick up the motions taking place in the locations where they are installed and convert them into electrical signals that are then picked up by amplifiers. Almost all contact pickups use piezoelectric technology. Notable pickups that fall under this classification include the piezos, top pickups, and under-saddle pickups.
What is desired is to provide an acoustical transducer, or pickup, that has a more accurate reproduction to tonal quality of the instrument than provided by current piezo and magnetic pickups and more resistant to feedback than provided by microphones.
The present invention relates to a transducer device for use with any acoustic string instrument, the transducer device providing a more accurate reproduction to tonal quality to the instrument when compared to existing piezo and magnetic pickups and wherein feedback is significantly reduced when compared to microphone transducers. The acoustic instrument is fitted with a type of reed member that is positioned in the instrument either between the bridge and the body of the instrument or inside the body in such a fashion that the reed can vibrate freely in sync with the instrument. The instrument is also provided with a compact pickup unit attached thereunto in an arrangement comprised of cooperating optoelectronic devices including a LED and phototransistor which are mechanically isolated from the vibrations of the instrument and are positioned adjacent to the reed member. The reed interferes with, and when stationary, entirely obstructs, the path of a light beam generated by a light emitting device (LED) toward a light receiving device. In first embodiment of the invention, the frequency and intensity of the vibrations of the reed modulates the frequency and intensity of the light from the LED impinging on the receiving device to produce an electronic signal that corresponds to both the frequency of the note (or notes) played and to the tonal quality of the acoustic instrument on which the pickup is mounted. The associated circuitry of the receiving optoelectronic device is biased so that the output signal can be connected to any industry standard instrument amplifier or sound mixing board. The device of the present invention requires that the reed and at least one of the optoelectronic devices to be mechanically isolated from each other so that the reed modulates with the vibrations of the instrument and not by external vibrational forces.
In a second embodiment of the invention, the reed is stationary while a housing that encloses the LED and phototransistor is mounted to a flexure member, vibrations from the strings causing the flexure member to move in a manner so that at least a portion of the light beam generated by the LED is incident on the phototransistor. The level of impinging light is determined by the vibrations generated by the plucked strings.
For a better understanding of the present invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the accompanying drawing therein:
The present invention provides a system for converting the string vibrations from a musical instrument to a modulated electrical signal, the electrical signal being coupled to an amplifying device to provide an amplified sound that significantly improves tonal characteristics. Two embodiments of the system are described, the first for instruments having a bridge member and the second for instruments without a bridge member.
Referring to
A LED which has been successfully utilized is the Honeywell 800 nm device, model number SEP8705-002; a phototransistor successfully utilized is the Fairchild 880 nm peak device, model number QSD2030.
Optical housing 12 contains LED 24 (preferably an infrared LED although other light sources can be used) and phototransistor 22 is mounted to the interior of instrument 80. Phototransistor 22 is aligned with LED 24 such that the light beam generated by LED 24 is normally incident on the receptor surface of phototransistor 22. A flexible member, or reed, 82 is mounted to guitar 80 in a manner such that it can respond to the movement of the guitar strings (not shown) and positioned to intercept and block the light output 83 generated by LED 24 when the strings have not been plucked by a user. When plucked, the strings cause member 82 to vibrate such that the light output 82 from LED 24 incident on phototransistor 24. In essence, member 82 is biased to allow light beam 83 to strike phototransistor 24 such that a sine wave voltage signal is generated having a frequency and amplitude that corresponds to the acoustical sound generated when the guitar strings are plucked.
A 9 volt battery pack and circuit housing 86 is mounted to the interior of the instrument 80 and connected to LED 24 and phototransistor 22 via leads 90 and 92, respectively. The output signal from phototransistor 24 is connected to output jack 88 via lead 90.
The output signal from phototransistor 22 is a sine wave which is typically biased about 1 volt and having a maximum amplitude of 2 volts and a minimum value of zero volts.
The output from jack 88 is coupled to a conventional acoustic amplifier (not shown).
Member 82 is preferably fabricated from wood or other light weight material and can take various shapes, such as an elongated strip or a sphere. Member 82 must be capable of flexing and/or moving such that it can be positioned to allow beam 83 to strike photo transistor 24 when the strings are plucked by a user.
Note that the circular items 96 represent posts that support the guitar strings.
In operation, the instrument player engages a power on switch, not shown, to energize LED 24 and photo transistor 22 via the battery pack 95. As a player plucks the instrument strings, member 82 is caused to vibrate, allowing light beam 83 to be incident upon phototransistor 24 in a manner to produce a sine wave output. The frequency and amplitude of the sine wave depends upon the vibrations generated as the strings are being plucked, causing the output amplifier, in turn, to generate a sound which is proportional thereto.
While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its essential teachings.
