HEYS INSTRUMENT, INC.
TECHNICAL BRIEF
Volume 1
Why Heys Chooses A Single Piezo Element Pickup?
By
Ka Wong
Copyright 1997 by Ka Wong
Why Heys Chooses A Single Piezo Element Pickup?
First let us look at the different types of pickups available and discuss the inherent advantages and disadvantages of each.
1. Piezo pickup
The theory behind the piezo element is quite simple. Excitation ( vibration from string movement ) will cause the piezo crystal to flex. The flex causes the molecular structure to move and energy is generated. This electrical energy given out by the crystal is the signal used to feed the amplifier. All piezo crystals work the same way. Some are more efficient at certain frequencies than others. Also tonal quality can vary depending on how the piezo is mounted in the bridge.
Single Piezo Pickup
This type has been use successfully by several manufactures(i.e. Barcus Berry, L.R. Baggs, fishman etc.)
Advantages:
Rich Overtones:
The piezo will pick up all fundamental and harmonic vibrations-both those created by the strings and those reflected by the body of the instrument.
High Dynamic Range:
Using a conventional bridge provides a stiff support for the string and little energy is lost between the string and piezo, even during hard play.
Flexible Bridge Profile:
Since most single piezo systems use a conventional bridge, the bridge profile can be easily tailored to accommodate different playing styles.
Correct Phasing:
In an acoustic instrument, the sound is generated by the string and mixed in the bridge, then the overall vibration is transmitted to the top of the violin. The bridge acts like an equalizer and a mixer at the same time, so by placing the one piezo at a strategic location the phase relationship between different frequencies can be faithfully duplicated, especially when playing double or triple stops.
Disadvantages:
Feedback:
It is ironic that an advantage can also be a disadvantage. When played at high volume, the body of an acoustic violin outfitted with a single piezo pickup will pickup acoustic energy( act like a microphone ) and cause feedback.
There are a number of ways to minimize of the feedback problem:
1. The use of electronics to notch out the feedback( disadvantage is more hardware)
2. Decouple the bridge from the body by using damping material under the bridge (disadvantage is dry tone, harsh sound )
3. Deaden the acoustic character of the violin by filling the hollow body with foam.( disadvantage- you won’t do it to a good violin.......period )
4. Build a solid body. ( disadvantage- the solid body, unlike the acoustic body, cannot be tuned with a sound post. If the solid body is not inherently tuned, the sound will be inconsistent.)
Optimal Piezo Placement:
The piezo must be placed at a point where it is at equal acoustic distance from each string( note: the acoustic distance is not merely the linear distance from the piezo to a string- it involves also the angle orientation of the piezo relative to the string and the properties of the material between the piezo and the string). The above conditions must me met in order for all strings to have even volume. The multi-element piezo pickup bridge is devised primarily for this reason.
Low Output:
Low output level will result if the piezo is placed too far away from the strings and/or in an area of the bridge which is too dense (dead) to transmit vibration to the piezo.
Multi-Piezo Pickup
This kind of pickup consists of at least one piezo element per string. Each element is devoted to pickup vibration from one particular string. This kind of pickup bridge system is usually setup in such a way that the piezo is decoupled from the adjacent string and the violin body. This is necessary to avoid phase cancellation (between piezo elements) and resulting inconsistent output level.
Advantages:
Even Output For Different Strings-Due to equal acoustic distance.
High Output-Due to the fact that the piezo can be placed very close to the string and receive maximum vibration.
No feedback from the violin body-Each piezo is decoupled( isolated ) from the violin body and all other strings. This set up negates the existence of the violin body so the designer can concentrate on the styling and not have to address the acoustic(nodal) issue of the violin. ( I have measured the piezo to pickup vibration from adjacent strings at -20db)
Disadvantages:
Lack Of Overtones (harmonics):
Since each string is decoupled from the violin body at -20db all the signal is generated solely by the string. Some pickups do have some very warm overtones which are generated by the piezo housing itself and not by the naturally resonating violin body.
Low Dynamic Range:
Ideally the harder you play the stronger the signal should be. In the multi-piezo bridge the decoupling is done by putting separation slits in the bridge so the movement of each piezo is independent as possible. However, with these slits in the bridge the support for each string is greatly weakened. When played hard, the piezo housing will begin to flex beyond its operating range and much of the energy will be lost.( A good analogy would be fanning oneself with a piece of paper-the piece of paper at high speed will not mimick the movement of one's hand; it will make a lot of noise and not much air flow.). Hence the output of an isolated piezo housing will saturate at a certain level and cease to give the higher output that the player desires.
Incorrect Phasing:
In a conventional bridge the phase relationship of each string is handled in a way that produces classical sound. In a multi-piezo setup the bridge geometry is vastly different and the mixing of sound is not being done mechanically but by means of electrical connection. This can alter the character of the sound.
Non-Flexible Bridge Profile:
In most multi-piezo systems the bridge profile is predetermined which eliminates the possibility of accommodating different playing styles(i.e. classic vs. blue grass)
2. Magnetic Pickup
Basically magnetic pickups use the string as an inductor. When this inductor moves across the magnetic field an electrical energy is generated.
Advantages:
No Overall Feedback
The magnetic pickup will not pick up any acoustical content. It will only pick up string movement. This affords the builder freedom of instrument styling as with a muilt-piezo systems.
Disadvantages:
String to magnetic coil distance is extremely critical:
The following factors can be affected:
Non-Linear Gain:
Upon bowing, the distance from string to coil changes and the overall gain can be affected. When playing hard the increase in volume may be exaggerated. This would occur as the naturally greater string excursion(which produce more volume) couples with closer string to coil proximity(adding additional volume).
Non-Flexible Bridge Profile:
The bridge must be designed to insure even string to coil distance.
No overtones:
The electrical signal is solely generated by the string and the sound will resemble that of an electric guitar.
The Final Analysis
Heys has set out to make the best electric violin in the world.
Design Criteria:
1. Acoustic sound quality with all the good stuff like overtones and the flavor of wood.
2. No feedback at any playing volume
3. Ergonomic design. Items such as chin rest, shoulder rest and bridge profile can be outfitted in the same way as an acoustic violin-no need to adapt or get used to the instrument because it is a violin.
4. Use of conventional bridge. The conventional bridge plays a large part in determining the sound of the violin. The complex sound mixing that the bridge does has taken over 400 years to evolve and still there is no better way to mix sound.
5. No wires. The Heys violins were designed with wireless in mind. The acoustic violins have no wires and why should an electric! No belt pack and no extra wire to hang outside the body.
6. Structure & durability. Simply put “Bullet Proof”. Just play hard.
7. Looks. Absolutely dangerous. The design is so efficient, there is not a single gram of material was devoted for the sake of ornamentation. The Heys violin is definitely “built for speed”.
To make an electric violin that will make sound is easy-to make one which sounds like any other is just as easy. Some electric violin designers only concentrate on the styling of the instrument and pay little or no attention to the acoustic properties. To them the sound is solely dependent on the choice of pickup and it is quite a self fulfilling prophecy(refer to the above section on muti-piezo element and magnetic pickups). The multi-piezo pickup will sound the same regardless of violin geometry. The acoustic contribution is thrown out by the inherent nature of the pickup. To use a single piezo pickup causes more problems than it solves. But believing that the single piezo system produces the most natural acoustic sound, Heys chose to look into the problems and take action. In an electric violin there is no sound post to adjust. So Heys had to be very exacting in solving all the problems associated with the single element setup. We have invented a Patent Pending Equalizer TM Bridge to assure even gain throughout the entire tonal range of the instrument. The bridge allows for fine adjustment of the single piezo element to find its sweet spot(optimal acoustic placement point) see fig. 1. The adjustable feature works much like the sound post of the acoustic violin. The fine adjustment is extremely crucial, for different bridge profiles will affect the location of the sweet spot. To provide a sound with rich overtones, Heys took great care in designing the body to behave like that of an acoustic instrument. It even has an acoustic chamber to generate overtones and a rich wooden sound. The bodies were carefully dimensioned to strike the optimal balance for acoustic sound without the disadvantage of acoustical feed back.
The Verdict:
Heys has chosen to use a single piezo element pickup. It sounds great!
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