CCP X-Rugged Microphone Set GRAS 147EB 3.15-20kHz Class 2

Introduction

• 147EB is a free-field microphone optimized for wheelhouse brake noise testing in the automotive industry. It is designed to withstand the conditions in the wheelhouse during prolonged testing on public roads in all types of climate and weather. A rugged design that withstands shock and vibrations combined with a three-layer protection system for the diaphragm enables it to be used for realistic testing of brakes on proving grounds and public roads. The two protective grids and the customized windscreen are easily replaceable consumables. With the 147EB it is now no longer necessary to use sub-standard microphones and cumbersome customized protection for acoustic road testing of brakes – it is now possible to measure without compromising data quality using a high-quality IEC 61672 class 2 microphone.

Design

• Like other members of the GRAS family of microphones for automotive NVH testing, the 147EB is designed to perform optimally under the rough conditions encountered in automobile NVH testing. The most important design features to accomplish this are:

Effective protection

• The microphone-preamplifier assembly is effectively sealed against moisture and is IP67 rated. Special protective water and oil repellent coating adds further protection and makes it easy to clean. The microphone diaphragm is protected by two grids, a 1/2″ grid inside a 1″ grid. Each has a comprehensive multi-layer filtering system that ensures good protection against high-velocity particles and prevents dirt and dust from polluting the microphone. The filter in the 1/2″ grid is acoustically transparent. The filter in the 1″ grid is the same filter as that in the 1/2″ grid supplemented by a layer of foam. The influence of the 1″ grid can be compensated for with the transfer function that is included with the factory calibration. The calibration data and transfer function can be accessed online. Provided the filters are replaced at appropriate intervals this system ensures that the microphone will function properly even in very dirty conditions. The filter also protects the diaphragm against water splashes and oil mists.
• A customized windscreen is available. Even if turbulence is not a problem it must be used as the first layer of protection and thus protect the next layer of protection against early contamination.

Rugged

• The 147EB can withstand the effects of handling, including the occasional drop. A new design of the preamplifier and other internal parts makes it resilient to shock and vibrations.  It functions well under conditions with vibrations and g-forces from uneven road surfaces and other sudden directional shifts as encountered in real-life driving tests.
• Even though the microphone will be firmly attached to a vibrating structure and subjected to frequent directional shifts, this fact will not interfere significantly with the measurements.  If the effects of vibrations are considered to result in noise, it retains a very good signal-to-noise ratio even in vibration-rich conditions.
• The most vulnerable part of any condenser microphone is the diaphragm. In the 147EB a more robust type is used. It can be replaced during repair, keeping maintenance costs at a minimum.