Instruction Manual

GRAS RA4800 Adapter for Sensitivity Verification of Flush and Surface Microphones

Document Identifier: LI0275 | Date: 15 June 2022

Revision History

Revision	Date	Description
1	2 November 2020	First edition
2	15 June 2022	Update Correction table with 40PS-1 values

Copyright Notice

Website: www.grasacoustics.com

GRAS Sound & Vibration holds the copyright for all technical documentation made available. The content is subject to change without notice, and GRAS Sound & Vibration is not liable for errors or inaccuracies.

Trademarks

Product names mentioned are trademarks or registered trademarks of their respective companies and are hereby acknowledged.

Introduction

The RA4800 is an adapter designed for in situ verification of flush and surface microphones. It allows for quick and convenient verification of the measurement setup's integrity without needing to dismount the microphone from its structure. The RA4800 is typically used with a sound calibrator, such as the GRAS 42AG Multifunction Sound Calibrator.

Description

The adapter features three main characteristics:

It includes a 1" stud/collar for compatibility with any GRAS calibrator designed for 1" adapters.
It incorporates a soft cushion, similar to those found on circum-aural headphones, which creates a closed cavity over the microphone for calibration.
It is equipped with four spacers that, when the cushion is depressed, ensure a well-defined cavity that remains consistent across calibrations.

Diagram Description: The diagram illustrates the GRAS RA4800 adapter. The 'Top view' shows a circular component with a central opening. The 'Side view' displays the adapter's structure, including a 1-inch collar and a soft cushion with integrated spacers. A third image shows the adapter fitted around a microphone, resembling a headset, ready for calibration.

Procedure

Before performing verification, ensure the microphone is properly connected and powered on.

Diagram Description: The diagram depicts the GRAS 42AG sound calibrator in use. The left image shows the calibrator unit with its display indicating 'dB', 'Hz', and 'Met'. The right image shows the calibrator, with the RA4800 adapter attached (implied), positioned over a microphone on a test setup, ready for verification.

Once the calibrator is turned on and placed over the microphone, maintain its position until the reading on the analyzer stabilizes. For detailed operation of the calibrator, refer to the GRAS 42AG manual.

Correction values

The following table provides correction values for different microphone models at specific frequencies:

Microphone Model	250 Hz	1 kHz	Accuracy
40LA	-0.6 dB	-2.1 dB	±0.2 dB
40LS	-0.6 dB	-2.1 dB	±0.2 dB
40PS-1	0.03 dB	1.43 dB	±0.29 dB^*, ±0.44 dB^†
48LA	-0.8 dB	-3.0 dB	±0.2 dB
48LX-1	-0.8 dB	-3.0 dB	±0.2 dB
48LX-4	-0.8 dB	-3.0 dB	±0.2 dB
48LX-8	-0.8 dB	-3.0 dB	±0.2 dB

^* Correction at 250 Hz

^† Correction at 1 kHz

Warranty, Service and Repair

GRAS products are manufactured using high-quality components and branded parts, ensuring long-term stability and robustness. The warranty does not cover damage resulting from negligent use, incorrect power supply, or improper connection to equipment.

For further information on warranty and repair services, visit grasacoustics.com/repair-center.

Conformance Information:

Manufactured to conform with CE marking directive: 93/68/EEC
WEEE directive: 2002/96/EC
RoHS directive: 2002/95/EC

GRAS Sound & Vibration is committed to continuous product improvement. Specifications and accessories are subject to change.