Brüel & Kjær Type 4184 Weatherproof Microphone Unit

Product Data

The Brüel & Kjær Type 4184 is a weatherproof microphone unit designed for permanent, semi-permanent, or portable noise-monitoring systems. It is suitable for use in humid and corrosive atmospheres due to its stainless steel casing and built-in protection system against humidity. The unit complies with IEC 651 Type 1 and ANSI S 1.4-1983 Type 1 standards.

Its key attribute is its excellent omni-directional characteristics, providing high accuracy with fixed orientation and less dependency on operator expertise. The unit is fully rotational about its vertical axis without undesirable reflections from its casing affecting measurements.

The Type 4184 is based on a probe tube system, allowing the microphone cartridge to be installed within the unit's casing, providing rain protection according to IEC 529 IP44. Each unit is individually calibrated and supplied with a calibration chart detailing its frequency responses.

Uses

• Permanent noise-monitoring systems
• Semi-permanent noise-monitoring systems
• Portable noise-monitoring systems
• Noise measurements in most humid and corrosive atmospheres

Features

• Excellent omni-directional characteristics leading to high accuracy with fixed orientation and less dependency on operator expertise.
• Complies with IEC 651 Type 1 and ANSI S 1.4-1983 Type 1.
• Fulfils EMC Specifications.
• System noise level typically 25 dB(A).
• Lower limiting frequency of 4 Hz (–3 dB).
• Individually calibrated from 20 Hz to 20 kHz.
• Charge Injection Calibration facility.
• Built-in Test Sound Source (at 1 kHz).
• Low electrical output impedance.
• Can be used with most Brüel & Kjær measuring amplifiers and frequency analyzers.
• Rain protected according to IEC 529 IP44.

Description

The Weatherproof Microphone Unit Type 4184 consists of three main sections:

• Upper section: Windscreen with windscreen holder, probe tip, and probe tube.
• Middle section: Microphone, preamplifier, impedance matching tubes, circuit board (filter and cable driver), built-in test sound source, and its transmission tube. The impedance matching tube system comprises four tubes of specific lengths. The test sound source uses two miniature loudspeakers and a transmission tube that feeds the signal to a point below the mouth of the probe tube.
• Lower section: Dehumidifier system and a Brüel & Kjær 7-pin microphone plug.

Type 4184 can be fixed to a pole for permanent outdoor systems or to a tripod for semi-permanent or portable systems. An adapter for pole-mounting is included as an accessory. The unit's design ensures that the microphone is afforded rain protection according to Standard IEC 529 IP44.

Components and Functionality

Windscreen

The windscreen, made of specially prepared polyurethane foam, comprises two parts: the windscreen holder and the windscreen itself. The holder has three steel rods with spikes to prevent birds from perching. The windscreen and holder are essential for obtaining correct results.

Probe Tip

The probe tip provides excellent omni-directional characteristics for noise measurements and protects the probe from rain.

Probe Tube System

The probe tube is housed within the test sound source transmission tube. A removable protection tube and cap prevent damage during transportation. The protection tube also serves as a sound calibrator adaptor for use with the Pistonphone Type 4228.

Microphone

Type 4184 utilizes a measurement microphone cartridge similar to Type 4134, minimizing sensitivity variations with temperature changes.

Preamplifier

The preamplifier features an input stage and an output stage, providing a low output impedance and Charge Injection Calibration (CIC) for monitoring the complete measuring system.

Casing

The casing is made of stainless steel for corrosion protection. Its streamlined design minimizes reflections that could interfere with sound field measurements. It can be fitted to a tripod or pole using adaptors.

Dehumidifier

Two silica gel bags in the lower section dehumidify the unit. A humidity indicator paper shows when the silica gel needs replacement (typically every two years).

EMC Compliance

Type 4184 complies with EMC (electromagnetic compatibility) requirements specified in EN 50082–1 (residential, commercial, light industry) and EN 50082–2 (industrial environment). For full benefit, the microphone unit must be connected to an instrument that also complies with EMC requirements.

Calibration and Verification

Individual Factory Calibration

Each unit is individually calibrated and supplied with a calibration chart showing frequency responses.

Pistonphone Calibration

For accurate calibration of the complete system, the Pistonphone Type 4228 can be used. It produces a nominal sound pressure level of 124 dB at 250 Hz and fits directly onto the protection tube.

Charge Injection Calibration (CIC)

CIC is a patented technique for remote monitoring of the entire measurement set-up, including the microphone, preamplifier, and connecting cable. The attenuation of the return signal relative to the calibration signal is indicated on the calibration chart.

Built-in Test Sound Source

The test sound source consists of two miniature loudspeakers. The signal is fed to the probe tube via the transmission tube, which is vented for static-pressure equalization. This source allows monitoring of the probe tube system's function.

Capacitive Loading and Frequency Response

The capacitive load of extension cables affects the frequency response and upper distortion limit. Figure 4 illustrates the influence on the high-frequency cutoff at different load capacitances. Figure 5 shows the sound pressure level at which 3% distortion occurs for various cable lengths and frequencies.

Extension Cables

Table 1 lists available extension cables (AO 0027, AO 0028, AO 0029) with their lengths and capacitances.

Examples of Use

A typical application is in the Noise-monitoring Terminal Type 3543. When used in portable noise-monitoring systems, the Type 4184's excellent omni-directional characteristics reduce dependency on operator expertise for measurement accuracy.

Specifications

Pressure Response

• In accordance with IEC 651 Type 1 and ANSI S 1.4-1983 Type 1.
• 250 Hz: ±0 dB (ref.)
• 20 Hz to 5 kHz: +1 dB
• 20 Hz to 8 kHz: +1 dB, -2 dB
• 4 Hz to 10 kHz: +1 dB, -3 dB
• 4 Hz to 12.5 kHz: +1 dB, -4 dB
• 4 Hz to 16 kHz: +1 dB, -5 dB

Sensitivity (250 Hz, 200 V Pol. V.)

• 12.5 mV/Pa nom. or -38 dB ±0.3 dB

Dynamic Range

• Upper Limit (THD <3% at 100 Hz): 140 dB SPL (200 V Pol. V.)
• Upper Limit (THD <3% at 100 Hz): 157 dB SPL (28 V Pol. V.)

Safety Limit

• 174 dB

System Noise Level

• <27 dB (A)
• <33 dB (Lin. 22.5 Hz to 22.5 kHz)

Acoustical Probe Tube Impedance

• 5x10⁶ Ns/m⁵

Electrical Output Impedance

• From preamplifier: <50 Ω

Output Current

• > 1.5 mA

Test Source (1 kHz)

• SPL (20°C (68°F)): 92 dB ±4 dB (individually ±1.5dB)
• SPL (-10 to +50°C (14 to 122°F)): SPL (20 °C (68 °F)) ±3 dB

Environmental

• Humidity Range: <100% RH. Maximum humidity at 40 °C (104 °F) is 90% RH.
• Humidity Influence (at 250 Hz, 20°C (68°F)): <0.1 dB
• Temperature Range for ±0.5 dB (250 Hz): -10 to +50°C (14°F to 122°F)
• Ambient Temperature Coefficient (250 Hz): -0.005 dB/°C (in the range -10°C to +50°C)
• Ambient Pressure Coefficient (250 Hz, 101.3 kPa): -0.006 dB/kPa

Vibration Sensitivity (<60 Hz)

• Max. 74 dB SPL for 1 ms 2 or 0.1 Pa/ms⁻²

Magnetic Sensitivity

• Typically 34 dB SPL, max. 40 dB SPL at 50 Hz and 80 A/m (worst direction)

Dehumidifier

Contains replaceable silica gel with a visible indicator.

Dimensions and Weight

• Probe Diameter (at microphone slit): 7.5 mm (0.3")
• Probe Length (from cone): 94.0 mm (3.7")
• Housing Diameter: 50.0 mm (2")
• Total Visible Length (pole mounted): 622.0 mm (24.8")
• Weight (excluding tripod mounting adaptor): 2.1 kg (4.6 lbs)
• Tripod-Mounting Thread: 3/8"-16 UNC or 1/4"-16 UNC

Pole Adaptor Thread

• G 1½" (ISO 228/1)

Compliance with Standards

• Safety: CE mark indicates compliance with EMC Directive, EN 61010-1 and IEC 1010-1.
• EMC Emission: EN 50081-1, EN 50081-2, CISPR 22, FCC Rules Part 15.
• EMC Immunity: EN 50082-1, EN 50082-2.
• Temperature: IEC 68-2-1 & IEC 68-2-2 (Operating: -40 to +50°C, Storage: -40 to +70°C). IEC 68-2-14 (Change of Temperature).
• Humidity: IEC 68-2-3 (Damp Heat: 90% RH at 40°C).
• Mechanical: IEC 68-2-6 (Vibration), IEC 68-2-27 (Shock), IEC 68-2-29 (Bump).
• Reliability: MIL-HDBK 217F, GB (Part-stress): MTBF >200000 hours.
• Enclosure: IEC 529 (1989): Protection provided by enclosures: IP 44.

Ordering Information

Optional Accessories

• Type 5935: Microphone Power Supply
• Type 4228: Pistonphone
• Microphone Preamplifier Extension Cables:
• AO 0027: Brüel & Kjær Microphone Extension Cable, (3 m)
• AO 0028: Similar to AO 0027 but double screen, (10 m)
• AO 0029: Similar to AO 0028, (30 m)

Contact Information

Brüel & Kjær

HEADQUARTERS: DK-2850 Nærum Denmark Telephone: +4545800500 Fax: +4545801405. http://www.bksv.com e-mail: info@bksv.com

Local representatives and service organisations worldwide.