Brüel & Kjær Prepolarized Condenser Microphone Cartridges
Types 4129, 4155, and 4176
Introduction
Prepolarized Condenser Microphones Types 4129, 4155, and 4176 are high-quality, 1/2" diameter, free-field microphones that complement the existing range of externally polarized B&K Condenser Microphones for accurate and reliable sound measurements. They utilize a fixed charge-carrying polymer layer, eliminating the need for an external polarization voltage.
Advantages of dispensing with external polarization voltage include power and space savings in portable instruments, and improved reliability of the associated preamplifier in humid and polluted atmospheres. These factors make them suitable for field measurements, both outdoors and in industrial environments.
Features
Type 4129
- Free-field frequency response from 6.5 Hz to 8 kHz ±2 dB
- Dynamic range from 13.5 dB(A) noise floor to 142 dB (3% distortion limit)
Type 4155
- Free-field frequency response from 4 Hz to 16 kHz ±2 dB
- Dynamic range from 14.5 dB(A) noise floor to 146 dB (3% distortion limit)
Type 4176
- Free-field frequency response from 6.5 Hz to 12.5 kHz ±2 dB
- Dynamic range from 13.5 dB(A) noise floor to 142 dB (3% distortion limit)
Common Features
- Sensitivity: 50 mV/Pa (-26 dB re 1 V/Pa)
- No external polarization voltage required
- Artificially aged for long-term stability
- Very wide operating temperature range
- Low ambient temperature coefficient
- Well-defined operating characteristics
- Supplied with individual calibration chart
- Robust construction
- High resistance to humidity
Uses
In noise measurement systems:
- IEC 651, Type 1 (Types 4155 and 4176)
- IEC 651, Type 2 (Type 4129)
- ANSI S1.4-1983, Type 1 (Type 4176 with Random Incidence Corrector DZ 9566 supplied)
- ANSI S1.4-1983, Type 2 (Type 4129 with Random Incidence Corrector DZ 9566 supplied)
Type 4129 is used with Integrating Sound Level Meters Types 2225 and 2226.
Type 4155 is fitted to Precision Integrating Sound Level Meters Types 2230 and 2233, and Modular Precision Sound Level Meter Type 2231.
Type 4176 is primarily intended for use with Brüel & Kjær Precision Integrating Sound Level Meters Types 2221/22 and Precision Sound Level Meter Type 2232.
General Description - Construction
The microphones utilize a construction method that results in reliable transducers of high sensitivity and low temperature dependence. Cartridges are artificially aged at high temperatures for long-term stability. Static pressure equalization occurs via a vent at the rear, which determines the lower limiting frequency. Rear venting allows for the use of a Dehumidifier in humid environments.
Types 4129 and 4176 have a cartridge polarized by a fixed charge-carrying layer deposited on the backplate, resulting in a positively increasing output voltage for a positive sound pressure incident. The nickel diaphragm is coated with a thin polymer film for corrosion protection.
Type 4155 features a backplate and housing made of Monel for corrosion resistance. The diaphragm is pure nickel coated with quartz film. The insulator is silicone-treated synthetic sapphire for electrical insulation and dimensional stability.
All microphones are delivered with a removable protection grid containing a gauze filter to prevent dust and particle penetration.
For diffuse field conditions, a Random Incidence Corrector DZ 9566 is supplied, fitting over the normal protection grid.
Figure Descriptions:
- Figure 1: Illustration of various Brüel & Kjær sound level meters (Types 2232, 2225/26, 2221/22, 2230/33) and filter sets (Types 1624, 1625, 1627).
- Figure 2: Photographs of 1/2" Microphones Types 4129, 4176, and the Random Incidence Corrector DZ 9566.
- Figure 3: Photograph of 1/2" Microphone Type 4155 with its protection grid removed, showing the flat diaphragm flush with the housing.
- Figure 4: A sectional view illustrating the internal construction of a Prepolarized Condenser Microphone Type 4155, detailing the backplate, charge-carrying layer, diaphragm, protection grid, output terminal, and pressure equalization vent.
- Figure 5: Diagram of a rear-vented microphone cartridge.
- Figure 6: Photographs showing various microphone and preamplifier combinations: Type 4129 on Preamplifier Type 2639; Type 4155 on Preamplifier Type 2639; Type 4155 fitted with Dehumidifier UA 0308 on Preamplifier Type 2639; and Type 4176 on Preamplifier Type 2639.
Preamplifiers
The microphones are designed for use with preamplifiers, such as the 1/2" Preamplifier Type 2639, which acts as an impedance converter. Type 2639 is a low-noise preamplifier powered by a 120 V DC supply, typically via connection to Brüel & Kjær measuring amplifiers and analyzers.
When using prepolarized microphones with systems designed for externally polarized microphones, it is essential to ground the polarization voltage connection on the preamplifier.
Microphone/Preamplifier Assembly Response
The overall response of the microphone/preamplifier assembly is influenced by the preamplifier's input capacitance, extension cables, and the preamplifier's own attenuation. This combined response is determined by adding the open-circuit response of the microphone to the preamplifier's response.
Cartridge Response
General
The cartridges offer wide dynamic and frequency ranges, high sensitivity, and stability. Each microphone is supplied with an individual calibration chart, and Type 4155 includes individual frequency response curves.
Dynamic Range
Dynamic range is defined by the microphone's inherent noise and preamplifier noise at the lower pressure limit, and by distortion at the upper limit (typically 3%). Below 1 kHz, preamplifier noise is dominant; above 1 kHz, cartridge noise dominates. Noise spectra are shown in Figure 7, and distortion characteristics in Figure 8. Dynamic ranges for combinations are shown in Figure 9.
Free-Field Corrections
Free-field corrections account for sound pressure changes due to diffraction around the microphone. These become significant at higher frequencies where the wavelength is comparable to the microphone's dimensions. Figure 10 provides free-field correction curves for various angles of incidence and the random response.
Frequency Response
The microphones are designed as free-field microphones, with damping adjusted so that when the 0° incidence free-field correction is added to the pressure response, the resulting free-field response is frequency-independent to the highest possible frequency. Typical 0° incidence free-field and random incidence responses are shown in Figure 11 for Types 4129 and 4176, and Figure 12 for Type 4155.
Figure Descriptions:
- Figure 7: 1/3 octave noise spectra for Types 4129, 4155, and 4176 using Preamplifier Type 2619 (note: Type 2619 has been replaced by Type 2639). Includes estimated noise spectra for cartridges alone.
- Figure 8: Distortion characteristics (2nd and 3rd harmonic) of the microphones at high sound pressure levels.
- Figure 9: Dynamic ranges of the Microphone/Preamplifier combinations, showing upper limits for 3% and 10% distortion, and typical lower limits for various bandwidths.
- Figure 10: Free-field correction curves for Microphone 4155 and Microphones 4129 and 4176, shown for various angles of incidence (0°, 30°, 60°, 90°, 120°, 150°, 180°) and random incidence.
- Figure 11: Typical frequency response curves for Types 4129 and 4176, showing both free-field (0° incidence) and random field responses.
- Figure 12: Individual calibration chart for Type 4155, including summarized response characteristics and frequency response data.
Long Term Stability
Temperature Effects
Microphone sensitivity changes slowly over time due to diaphragm tension relaxation (increasing sensitivity) and loss of charge from the electret material (decreasing sensitivity). These effects are temperature-dependent. Long-term stability is estimated at approximately 1 dB over 400 years at 20°C, achieved through artificial aging.
Humidity Effects
High humidity can cause a slow, permanent loss of sensitivity due to charge loss, minimized by artificial aging in a humid environment. Long-term stability in humid environments is also shown in Figure 13.
Figure Descriptions:
- Figure 13: Graph showing the relative stability of the microphones, illustrating the effects of humidity (90% RH) and temperature on the charge-carrying element and diaphragm.
Short Term (Environmental Stability)
Temperature Effects
Ambient temperature variations cause reversible changes in sensitivity due to differential expansion of microphone components. The frequency response also changes with temperature due to thermal expansion and changes in air viscosity affecting damping.
Humidity Effects
Type 4155 exhibits a reversible, short-term sensitivity change dependent on humidity, attributed to moisture absorption by the protective quartz coating on the diaphragm.
Figure Descriptions:
- Figure 14: Graph illustrating the typical effect of temperature on the sensitivity of Microphone Type 4155, showing reversible changes.
- Figure 15: Graph showing the effect of temperature on the pressure response of Type 4155.
- Figure 16: Graph illustrating the short-term reversible effect of humidity on Type 4155.
Use with Other B&K Instruments and Accessories
Various instruments and accessories are available for optimal utilization of the microphones. Further details are available in Brüel & Kjær publications.
Calibration Equipment
The Pistonphone Type 4220 (124 dB at 250 Hz) and Sound Level Calibrator Type 4230 (94 dB at 1000 Hz) are used for accurate calibration of sound measuring systems.
Accessories
Accessories include Windscreens (UA 0570, UA 0237, UA 0459), Nose Cone (UA 0386), Turbulence Screen (UA 0436), Dehumidifier (UA 0308), Preamplifier (Type 2639), and various Power Supplies (Types 2804, 2807, 2810) and Multiplexers (Type 2811).
Figure Descriptions:
- Figure 17: Photographs of the Pistonphone Type 4220 and Sound Level Calibrator Type 4230.
- Figure 18: Photographs of various Microphone Accessories: Windscreens (UA 0570, UA 0237, UA 0459), Nose Cone (UA 0386), and Turbulence Screen (UA 0436).
- Figure 19: Photograph of the Dehumidifier UA 0308.
- Figure 20: Photographs of Power Supplies (Types 2804, 2807, 2810) and the Eight Channel Multiplexer Type 2811.
- Figure 21: Diagram illustrating the correct connection for using Prepolarized Condenser Microphone Cartridges with a preamplifier, showing grounding of the polarization voltage pin.
- Figure 22: View of the standard Brüel & Kjær seven-pin plug fitted to Preamplifier Type 2639.
- Figure 23: Circuit board of Microphone Power Supply Type 2810.
Specifications: Types 4129, 4155, 4176
Types 4129 and 4176
| Open Circuit Sensitivity at 250 Hz | 50 mV/Pa (-26 ±2 dB re 1 V/Pa) |
| Frequency Response (0° Incidence Free-Field) | Type 4129: 6.5 Hz to 8 kHz (±2 dB), IEC 651, Type 2 Type 4176: 6.5 Hz to 12.5 kHz (±2 dB), IEC 651, Type 1 |
| Frequency Response (Random) | Type 4129: ANSI S1.4-1983, Type 2 (with DZ 9566) Type 4176: ANSI S1.4-1983, Type 1 (with DZ 9566) |
| Lower Limiting Frequency (-3 dB) | 0.5 to 5 Hz |
| Pressure Equalization Time Constant | 0.32 to 0.032 s (Back vented) |
| Diaphragm Resonance Frequency (90° Phase Shift) | 12.5 kHz |
| Capacitance at 250 Hz | 12.5 pF |
| Thermal Noise | 1.1 µPa/√Hz (A-weighted: 13.5 dB, Lin.: 14.5 dB) |
| Upper Limit of Dynamic Range | 142 dB (3% distortion limit) |
| Safety Limit | 156 dB (peak) |
| Equivalent Air Volume | 50 mm³ |
| Operating Temperature Range | Up to +100 °C (+212 °F) Up to +70 °C (+158 °F) with DZ 9566 |
| Ambient Temperature Coefficient | -0.004 dB/°C (mean -10 °C to +50 °C) |
| Long Term Stability at 20 °C | >250 years/dB |
| Influence of Static Pressure | -0.002 dB/mbar |
| Influence of 1 m/s² Axial Vibration | Typically 60 dB equivalent SPL |
| Influence of 80 A/m, 50 Hz Magnetic Field | Typically 30 dB equivalent SPL |
| Influence of Humidity | <0.1 dB (no condensation) |
| Dimensions | Overall Diameter with Protection Grid: 13.2 mm Cartridge Housing Diameter: 12.7 mm Height: 14.9 mm Diameter with Corrector DZ 9566: 14.35 mm Height with Corrector DZ 9566: 16.7 mm |
| Accessories Included | Random Incidence Corrector DZ 9566 |
| Accessories Available | Preamplifier Type 2639, Sound Level Calibrator Type 4230, Pistonphone Type 4220, Dehumidifier UA 0308, Windscreens (UA 0237, UA 0459), etc. |
Type 4155
| Open Circuit Sensitivity at 250 Hz | 50 mV/Pa (-26 ±2 dB re 1 V/Pa) |
| Frequency Response (0° Incidence Free-Field) | 4 Hz to 16 kHz (±2 dB), IEC 651, Type 1 |
| Lower Limiting Frequency (-3 dB) | 1 to 3 Hz |
| Pressure Equalization Time Constant | 0.16 to 0.053 s (Back vented) |
| Diaphragm Resonance Frequency (90° Phase Shift) | 14 kHz |
| Capacitance at 250 Hz | 15 pF |
| Thermal Noise | 1.2 µPa/√Hz (A-weighted: 14.5 dB, Lin.: 15.5 dB) |
| Upper Limit of Dynamic Range | 146 dB (3% distortion limit) |
| Safety Limit | 160 dB (peak) |
| Equivalent Air Volume | 40 mm³ |
| Operating Temperature Range | Up to +150 °C (+302 °F) |
| Ambient Temperature Coefficient | -0.006 dB/°C (mean -10 °C to +50 °C) |
| Long Term Stability at 20 °C | >400 years/dB |
| Influence of Static Pressure | -0.001 dB/mbar |
| Influence of 1 m/s² Axial Vibration | Typically 60 dB equivalent SPL |
| Influence of 80 A/m, 50 Hz Magnetic Field | Typically 30 dB equivalent SPL |
| Influence of Humidity | 0.004 dB/%RH |
| Dimensions | Diameter with Protection Grid: 13.2 mm Cartridge Housing Diameter: 12.7 mm Height with Protection Grid: 17.3 mm Height without Protection Grid: 16.2 mm |
| Accessories Available | Preamplifier Type 2639, Sound Level Calibrator Type 4230, Pistonphone Type 4220, Dehumidifier UA 0308, Turbulence Screen UA 0436, Nose Cone UA 0386, Windscreen UA 0570, Windscreens (UA 0237, UA 0459), etc. |
