Technical Information

Magnetic Transducers
DB Products line of miniature magnetic transducers offer the highest quality and reliability at a cost effective price. DB's extensive line of transducers include devices that are sealed for wave and wash processes, have side sound ports, and include a variety of different sizes to help meet all your design parameters.

APPLICATIONS:
Printer, telephone, timer, pager, cellular phone, electronic oven, electronic cash register, POS system, electronic typewriter, computer terminals, keyboard, copy machine, safety equipment for motor vehicles, portable and battery operated equipment.
*Note: All the transducers in this catalog require external circuitry to provide the drive signal to the transducer.

Signal Input Polarity
If the voltage signal input Vo-p is applied to our transducer with the polarity reversed, a sound will be generated but it will not always meet the catalog specifications for the sound pressure level.
This is because the reversed polarity input changes the magnetic force direction from "attract" to "repulse" or vice versa, which can cause the resonant frequency to deviate from its original point and produce variations in the sound pressure level.However, if the voltage signal input alternates from positive peak to negative peak (Vp-p), the reversed polarity will have no effect on the sound produced.

How frequency response characteristics are affected by changing the input of the amplitude.
Some Design engineers do not drive audio transducers at the rated voltage recommended by the manufacturer. In most cases this is due to the voltage available relative to the customer's specific application. DB's catalogues and data sheets shows the frequency characteristices with respect to the rated voltage. When different amplitudes are applied to a given transducer, the frequency characteristices change.
Generally, as the input voltage amplitude decreases below the rated voltage, the resonant frequency (fo) rises.

Conversely as the input voltage increases above the rated voltage, the resonant frequency (fo) falls.

The basic resonant frequency of a specific transducer is a fixed value relative to its acoustic design. As a result, at lower than rated voltage the frequency response band tends to narrow, and at higher voltage values the frequency band tends to be wider.
Consequently if the input voltage is too low, shifting the resonant frequency higher, the original rated frequency (i.e. 2,048Hz) may not fall within the frequency band. Thus the sound output will be well below the rated SPL.

Sound Pressure
The sound producing devices like our sound transducers are generally used in certain enclourse to have an appropriate resonance chamber in front of the sound producing device, it is possible to meet the requirements to a certain extent, for instance, to obtain an increased sound pressure, improved response in wider range of frequencies, or softened sound output. Design such resonator called “Helmholtz Resonator" according to the following equation:

Designing the resonator to have such dimensions that the resonant frequency (fv) of the resonance chamber may be? greater? than the resonant frequency (fo) of the sound producing device, improves the frequency? response in wider frequency range, increases the sound pressure and softens the sound output eliminating harmonic components.? (These effects may not be obtained if fv is lower than fo, or reduced if fv is excessively higher than fo.? For increasing the sound pressre only, it is recommended to set the fv two times as high as fo.)

To Allow to Respond to Wider Range of Frequency Input
Design>>
To broaden the frequency range to 2048~2700Hz, the resonator geometry is determined with an aim that the fv should be around 2700 Hz, slightly higher than the fundamental frequency of the transducer.?
The sound hole diameter oD is set to 1.5mm.? With those parameter set, the fv may be calculated as 2460Hz form the equation (I).
[Actual Measurement]??
Frequency Response..........as shown in Fig. 1
fv........................................2700Hz
As shown in Fig. 1, the frequency range may be broadened and a softer sound may be produced with the harmonic components considerably eliminated.

To Increase the SPL
Design>>
To increase the SPL at the findamental frequency of 2048Hz, the resonator geometryis determined with an aim that the fv should be around 4100Hz, almost twice as high as the fundamental frequency of the transducer.?
The sound hole dimeter oD is et to 3.3mm.? With those parameters set, the fv may be calculated as 4000Hz from the equation (I).
[Actual Measurement]??
Frequency Response..........as shown in Fig. 3
fv........................................4000Hz
As shown in Fig. 3, the SPL range may be considerably increased, while the sound may become sharper due to its secondary harmonic components increased.

Fig.1 Frequency response without additional resonator
Fig.2 Frequency response with resonator (Design I)
Fig.3 Frequency response with resonator (Design II)

MEASURING METHOD

REFLOW OVEN
TEMPERATURE PROFILE
Recommended Reflow Oven Temperature
Profile for Reflowable Transducers

Reference standard: EIAJ ED-4702
Infrared reflow oven
If you have any questions about the above temperature profile for infrared reflow oven, please feel feel to contact us.

Mechanical Buzzer
DB's electronic buzzer is a compact device capable o producing high sound pressure levels with minimum power consumption.? This is achieved by the use of a self-contained, feedback controlled, transistorized oscillator circuit, housed completely within the device.

Operation Principle and Construction
All models are low frequency devices (300 ~ 500HZ) which utilize an oscillating hammer to resonate a membrance.? The Hammer is controlled by an electromagnetic assembly (Fig.1).
Fig.2 shows a typical circuit diagram utilized within each buzzer; the frequency of the oscillator circuit is approximately 1,000HZ, while the natural frequency of the hammer is 400HZ.? When the current flows through the coil, L1 and the hammer begin to vibrate, another coil, L2 detects its vibration, providing feedback to a transistor so that the oscillator becomes synchronized with the vibrating hammer.

Soldering
The miniature electro-magnetic transducer by DB Products Ltd.? should not be exposed to extremely high temperature for prolonged period of time.? As excessive heat will degrade the sealing performance of the unit, soldering should be conducted as quickly as possible.
Recommended Temperature and Time for Soldering?
Wave Soldering (Noryl, PBT, PPS)
256oC…….within 3 seconds?
350oC…….within? 1 seconds

Washing :

Washable Type Transducers
Along with other electronic components, these transducers may be washed with cleaning solvents after the soldering process.
Non- Washable Type Transducers
Most cleaning solvents will be damaging to these transducers,? wave soldering & washing should be prohibited.

Flux Removing Solvents
In the view of the recent requirement for total elemination of ozone-depleting chemicals, we have decided to recommend our customers to use deionized water for their cleaning process at the conditions given below, instead of "CFC" that was conventionally used.
Cleaning solvent….. Deionized Water
Solvent Temperature….. 55 oC± 5o

Sound Pressure and Distance
As there are differences in the meausring distances when manufacturers make the measurement of sound pressure, the following formula is recommended for calculation on occasions when a buzzer itself is tested or compared with a planned finished product.
However, as far as the calculated value is concerned, it is theretical one and therefore subject to change, depending upon circumstances and conditions.

The formula is: B=A+20 log (La/Lb)---A :Sound Pressure Value at distance La Ex.When the distance is doubled---B : Sound Pressure Value at distance Lb B=A+20 log (la/Lb)=A+20 log (1/2) =A - 6.02 i.e. the sound pressure is apt to be reduced by 6.02 dB. The table below is to shape up relations between the measuring distance variation and the sound pressure variation for reference.

Tone
The tone output, generated by buzzers, is essential in product design.? A recommended way of selecting a desired tone is by listening to the different tones produced by the different buzzer.? Additionaly, FFT analysis is usable for visual tone selection method.? The sound is not an oscillation of a single frequency, but as a collected body of individual frequencies.? The analysis is to diagnose the ratio of constituent frequencies.? The following is a sample analysis of our typical buzzers.

Sound Element:
Element with Feedback Tab:
This type of element has a tab form on the ceramic part. It used as the feedback function in a simple oscillation circuit , it will create a back voltage , or back EMF. to the internal circuit .? Thus,? the element operates automatically at the natural resonant frequency of the element and the? loudness sound can be obtained.

Edge Mounting (External Drive Usage)
To fix the edge of the element to the supporting ring of the case.? SPL depends on input frequency.? However, considerable sound pressure can be obtained covering a wide frequency range around the resonant frequency.

Nodal Mounting (Self Drive Usage )
To fix the nodal diameter of the element to the supporting ring of the case.?? Loud sound pressure can be obtained at the resonant frequency.? The SPL will drastically drop when the frequency is not at resonant point.? This is the high efficient type of mounting for feedback type element???

Mounting Method for Sound Element
EDGE MOUNTING
NODAL MOUNTING

Piezo Transducers
DB Products line of Wide Range Piezo Transducers offer the signalling and alarming transducer at a cost effective price.? DB extensive line of transducers include devices that are sealed for washing, have different mounting type include, Flange mount, PCB mount, panel mount, plate mount and SMD mount.

Operation Principles
Piezoelectric Ceramic buzzer element have a simple structure in which piezoceramic element is gluded to vibration plate.? When alternating voltage is applied to piezoceramic element, the element expands or shrinks diametrically.? This utilized to make vibration plate bend to generate sounds.
The acoustic generating method can be roughly divided into self-drive oscillation method and external drive oscillation method. The former shows the lowest impedance on the acoustic generator, and produces the sound by the positive feedback oscillation circuit to make resonance.? Thereby, big sound pressure can be obtained by a simple circuit.? While the latter selects an optional frequency and makes sound by the nonstable multivibrator, and it is used for the case having the oscillation circuit.