Bruel-Kjaer – 51.8 dB

Overview

Bruel & Kjaer 51.8 dB is a precision 1/4-inch condenser measurement microphone built for wide-bandwidth acoustic testing, covering a frequency range extending to 100 kHz. With a sensitivity of 4 mV/Pa, it is purpose-built for applications that demand response well beyond the audible range, including ultrasonic emission studies, transient impact events, and high-frequency structural acoustics where a standard audio-band microphone cannot capture the full signal content.

As the an experienced supply partner for Bruel & Kjaer, Seven Star LLC proudly supplies this 1/4-inch condenser microphone and its full range of compatible preamplifiers and measurement accessories to acoustic and vibration laboratories across Oman and the GCC. Every unit is sourced through Bruel & Kjaer’s trusted supply channel, giving research institutions and industrial test facilities genuine calibration traceability and full manufacturer support.

Operating Principle

The microphone uses condenser (capacitor) transduction: a thin, tensioned diaphragm forms one plate of a capacitor with a fixed backplate, and sound pressure fluctuations deflect the diaphragm, producing a proportional change in capacitance. This charge variation is converted into a voltage signal by a matched preamplifier, delivering an output that tracks the instantaneous sound pressure with very low distortion and a flat frequency response across the microphone’s rated bandwidth.

The compact 1/4-inch diaphragm diameter is what enables the extended 100 kHz upper frequency limit — smaller diaphragms have proportionally higher resonant frequencies, pushing the usable flat-response range further above the audible band than a larger 1/2-inch or 1-inch capsule can achieve. This makes the microphone especially well suited to capturing fast transients and ultrasonic content without the roll-off or resonance artifacts that would distort measurements taken with a lower-bandwidth instrument.

Engineering Design of the Bruel-Kjaer 51.8 dB Microphone

The Bruel-Kjaer 51.8 dB microphone is housed in a rugged stainless steel body that protects the precision diaphragm and backplate assembly from mechanical damage, moisture, and dust while preserving the acoustic transparency needed for accurate free-field or pressure-field measurement, depending on the calibration supplied. The capsule threads directly onto a matched Bruel & Kjaer preamplifier, forming a complete measurement chain that connects to standard data acquisition front ends via the preamplifier’s output cable.

Because the microphone is designed as an interchangeable cartridge, laboratories can swap capsules between preamplifiers to reconfigure a measurement chain for different frequency ranges or sensitivity requirements without re-cabling an entire test setup. This modularity, combined with the microphone’s stable long-term calibration characteristics, makes it a practical choice for facilities running multiple concurrent acoustic test programs.

Calibration and Measurement Chain Integration

A measurement microphone is only as trustworthy as the calibration behind it, and this 1/4-inch cartridge is intended to work as one element of a traceable acoustic measurement chain rather than as a standalone sensor. In routine practice the assembled cartridge and preamplifier are checked before and after each test session with a sound calibrator or pistonphone, which applies a known sound pressure level at a fixed reference frequency so the analyser input sensitivity can be trimmed to the actual, as-measured sensitivity of the capsule. Because condenser cartridges drift only slowly, this field check usually confirms rather than corrects — but it is the step that converts a raw voltage into a defensible decibel figure for a compliance report, a machinery acceptance test, or a warranty dispute.

Two further details matter whenever a 1/4-inch capsule is specified. The first is grid configuration: the protective grid forms part of the microphone acoustic design, and free-field cartridges are calibrated with the grid fitted, so removing it for a close-field measurement alters the high-frequency response and invalidates the supplied calibration curve. The second is the distinction between free-field, pressure-field, and random-incidence response — the same physical capsule is corrected differently for each, and applying the wrong correction introduces systematic error at precisely the high frequencies this microphone is bought for. The Seven Star LLC instrumentation team can confirm which response type and correction set apply to the unit supplied before it is committed to a test programme.

Handling and Environmental Considerations

Condenser measurement microphones are precision components. The diaphragm is only a few microns thick and is separated from the backplate by a comparably small air gap, so the protective grid should stay in place whenever the capsule is not actively being cleaned or calibrated, and the cartridge should be stored in its case with desiccant under humid coastal conditions. Moisture bridging the insulator between backplate and housing is the most common cause of noisy or unstable readings in Gulf environments, and it is almost always reversible when the capsule is dried gently rather than heated aggressively.

The cartridge is also vented so that slow barometric and altitude changes equalise across the diaphragm without statically deflecting it. That static-pressure equalisation vent is what sets the practical low-frequency limit of any condenser measurement microphone, and it is the reason such an instrument is specified for acoustic measurement rather than for true DC or static pressure work. For outdoor and open-plant surveys in Oman, a windscreen and a rain-and-wind protection kit are normally added to keep turbulent airflow off the diaphragm, since wind-induced pseudo-noise, not instrument noise, is the dominant error source in field acoustic surveys.

Key Features

This 1/4-inch condenser microphone brings together bandwidth, precision, and durability for demanding acoustic work.

• The microphone delivers a wide 0–100 kHz frequency range, extending measurement capability well into the ultrasonic band.
• A sensitivity of 4 mV/Pa provides a strong, low-noise signal suitable for both laboratory and field measurement conditions.
• Its rugged stainless steel housing protects the diaphragm assembly during transport, handling, and field deployment.
• The microphone is fully compatible with the broader family of Bruel & Kjaer preamplifiers and measurement systems.
• Its compact 1/4-inch diameter suits confined or space-limited measurement positions.
• The flat frequency response across the rated bandwidth minimizes measurement error from resonance or roll-off effects.
• Consistent, repeatable calibration supports both one-off acoustic surveys and long-term monitoring programs.

Industrial Applications

Across Oman’s industrial and research sectors, this microphone supports ultrasonic leak detection, high-frequency machinery noise analysis, and transient impact testing in facilities ranging from petrochemical plants to university acoustics laboratories. Its extended bandwidth is particularly valuable in district cooling and HVAC commissioning work, where ultrasonic emissions from valves, bearings, and compressors often carry early diagnostic information that audio-band instruments miss entirely.

Working closely with plant engineers in the region, Seven Star LLC distributes this microphone and its accessories to acoustic consultancies, university research departments, and industrial noise and vibration teams throughout Oman, Muscat, and the Sohar and Salalah economic zones, supporting both new test-bench builds and the replacement of aging measurement microphones on existing systems.

Technical Specifications

The table below summarizes the key specifications of the Bruel-Kjaer 51.8 dB condenser microphone.

Request a Quote for Bruel-Kjaer – 51.8 dB

Seven Star LLC invites acoustic engineers, research institutions, and industrial noise-testing teams across Oman and the GCC to submit a formal RFQ for the Bruel-Kjaer 51.8 dB condenser microphone. We supply on request with lead time confirmed at quotation, provide full technical datasheets on request, and our instrumentation division can help match this microphone to a compatible preamplifier for your specific measurement chain. With fast quotation turnaround and technical support, Seven Star LLC supplies calibration-traceable instruments on request, with manufacturer documentation and technical support for model selection.

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