Flexural oscillator
A flexural oscillator is a spring-mass system capable of harmonic oscillations , which in the simplest case consists of a rod . It is characteristic that the bending moment and mass distributed along the rod determine its natural frequency .
Flexural vibrators are either clamped on one side (examples see below), or freely or suspended in the vibration nodes ( zeroing of the amplitude ) of their basic frequency .
Physical basics
In addition to the basic frequency , flexural oscillators can also be excited in higher modes . The number of vibration nodes on the rod grows by at least one: with the flexural vibrator clamped on one side to at least two (clamping plus additional), with the freely suspended flexural vibrator to at least three (two suspension points plus additional).
By placing free flexural oscillators at the nodes of the fundamental oscillation (with homogeneous rods 22.4% of the total length of both ends), this is preferred for excitation (impact). This is important for the good sound of musical instruments and sound bodies, as it allows the harmonics - which are not harmonic tones to the fundamental - to be reduced.
The natural frequencies are inversely proportional to the square of the rod length.
Applications
Musical instruments and sound bodies
- clamped on one side:
- Clay comb from music boxes
- accordion
- Bar gong of the striking mechanism of clocks ( harmonics are also stimulated here)
- free ends on both sides:
- Marimba
- xylophone
- Metallophone
- Lyra (carillon)
- Doorbell
- Wind chimes
- Gong (in the broader sense). A padded mallet initially only stimulates low harmonics, which, however, also stimulate higher harmonics due to non-linear changes in shape as the period of oscillation increases .
Measuring instruments
- clamped on one side:
- Tongue rate monitor
- Atomic force microscope : the change in the natural frequency of a flexural oscillator when it approaches a solid surface is recorded
- Frequency references :
- free ends on both sides:
- Flexural oscillator (device) : the density determination of liquids and gases is traced back to the measurement of the natural frequency of a filled U-tube . The density is calculated from this.
- Acoustic piezoelectric signal generator (glued-on plate made of piezoceramic with pronounced natural flexural resonance ).
adjustment
If the detuning of the flexural vibrators is not the effect used, they must be adjusted or tuned .
Laser calibration is also used in some technical applications .
Material removal
By removing material (e.g. grinding ), the resonance frequency of the transducer can be increased or decreased, depending on the location of the spring action or mass prevailing on the transducer:
- the natural frequency increases when material is removed from the free ends and the mass is reduced
- the natural frequency decreases when material is removed in the area of elastic deformation on the surface (in the vicinity of the restraint or in the case of free suspension in the middle area).
Material application
Less often (for example with reed frequency meters) the mass is increased for adjustment (by applying solder or masses ).
Individual evidence
- ↑ Michael Kerscher: Xylophone and Bell - Vibration Modes of a Rod and a Bell ( Memento of the original from January 8, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , Page 8
- ↑ Michael Kerscher: Xylophone and Bell - Vibration Modes of a Rod and a Bell ( Memento of the original from January 8, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , Page 7
- ^ Neville H. Fletcher, Thomas Rossing: The Physics of Musical Instruments , page 63, equation (2.64)
