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Technical Library

Under this menu, you will find a listing of various technical documentation such as technical notes, application notes, handbooks, white papers and other technical information. Product information, manuals and the GRAS catalog continues to be found under the product specific pages. If you are missing a specific note or white paper, please do not hesitate to contact us.

Technical Notes   Aplication Notes   Handbooks   White Papers   Other Technical Information


147AX Positioning Guide, October 2020

Engine noise reduction (ENR) testing is usually performed under laboratory conditions using the reverse transfer path analysis (TPA) technique, where multiple microphones are placed inside the engine bay. This application note describes GRAS´ approach, using the same microphone positions across platforms. This facilitates gathering consistent data that can be reliably compared across every project for benchmarking. READ MORE >

Improved Measurement Procedures for Engine Noise Reduction with Advanced Microphones, May 2020

GRAS 147AX pressure microphones have been tested by Volvo Cars for transfer path analysis measurements in vehicles using the reverse transmission technique. Thanks to this microphone´s innovative form factor and mounting technique, the testing time has been dramatically reduced and the accuracy and repeatability of the measured results significantly increased. READ MORE >

High Resolution Testing with 45CC, March 2018

This technical note discusses how headphone geometry and even very small differences in positioning influence the repeatability and frequency response that can be obtained when testing at frequencies above 20 kHz (and up to 70kHz) when using GRAS 45CC test fixture fitted with 1/4" measurement microphones (GRAS 40BD/40BP). READ MORE >


Smart Speaker Acoustic Measurements, December 2021

Smart speakers are a relatively new class of consumer audio device with unique characteristics that make testing their audio performance difficult. In this application note, we provide an overview of smart speaker acoustic measurements with a focus on frequency response—the most important objective measurement of a device’s audio quality.  READ MORE >


The Importance of Measurement Microphone Venting, November 2021

Did you know that the small hole on your microphone serves a vital role in acquiring data? Proper microphone venting can mean the difference between good actionable data and data corrupted by pressure inequalities between the front and back of the microphone diaphragm. Our new application note explains how and why the vents work and why some microphones are front vented and others rear vented.  READ MORE >


How to Match a Measurement Microphone to a Sound Field, April 2021

Selecting the right measurement microphone for the environment is essential for obtaining accurate, actionable measurement data. Therefore, measurement microphones are designed for use in particular sound fields. Understanding the differences between the microphones can help in selecting the right micro¬phone and avoiding potential measurement errors. READ MORE >


Headphone Electroacoustic Measurements, November 2020

Due to the close coupling of earphones to the ears and the acoustic transmission paths involved, headphone measurements are complicated. Our 26-page application note discusses these challenges, headphones types, measurement standards, headphone acoustics, acoustic test fixtures required for measuring headphones, and the practical aspects of headphone measurements. Objective measurements are also discussed. READ MORE >


Loudspeaker Electroacoustic Measurements, November 2020

Compared to electronic audio test, measuring loudspeakers is complicated. First, to measure sound levels accurately requires precision measurement microphones and supporting electronics, which have a known, stable sensitivity and flat frequency response over the frequency range of interest. Measurements are further complicated by the interaction of the loudspeaker under test with the test environment. READ MORE >


147AX Microphone Vibration Sensitivity, April 2020

The design of the 147AX microphone has been optimized for mounting on surfaces and structures to measure the sound pressure in the surrounding air. But what happens when the microphone is mounted on a vibrating surface? This paper shows that, in most cases, 147AX can be safely mounted on vibrating structures without significant impact to the measurement results. READ MORE >

Engine Bay Measurements: Pressure vs Free-field Microphone, April 2020

Many users are still using free-field microphones for engine bay acoustic measurements. An engine bay is far from a free-field environment, which is why the use of a free-field microphone is not recommended for engine bay measurements. This application note uses a practical case to show the differences in results between using a free-field microphone and a pressure microphone for engine bay testing, and expands on why a pressure microphone is better suited for the application. READ MORE >

RA0357 Random-incidence Corrector for 146AE, May 2018

It is possible to alter the frequency response of a ½” free-field microphone so that accurate measurements in random-incidence (diffuse) sound fields are possible. This is done by using a random-incidence corrector like GRAS RA0122. Here we present the RA0357 random-incidence corrector, specifically designed to be used with the GRAS 146AE free-field microphone set. READ MORE >

Measurement of Impulsive Noise, April 2017

Measurement of short impulsive noise signals with broad frequency spectra in a free field requires the use of small transducers. The resulting measured peak value will depend on the frequency range and size of the transducer as well as the diffraction caused by the transducer. Furthermore, the phase response of the transducer together with the phase response of subsequent amplifiers and anti-aliasing filters will influence the results. READ MORE >

Periodic Verification of Measurement Microphones, April 2017

This application note describes the basics of measurement microphone calibration, including level calibration techniques to calculate the microphone´s sensitivity and frequency calibration using the electrostatic actuator method. It also describes setups for performing accurate calibrations in a reliable way. READ MORE >

Windscreens – Practical Guidelines for Acoustic Measurements in Situations with Windflow, May 2016

Even moderate airflow speeds may seriously affect the pressure measurements of microphones. Without wind protection, the wind-induced noise will dominate, and as a direct consequence the acoustic signals to be measured will be difficult to distinguish from the noise. This technical note analyzes the influence of wind noise in microphones of different sizes with and without a windscreen, the influence of the airflow orientation and the acoustic impact of mounting a windscreen on a microphone. READ MORE >

Acoustic Test Fixtures for Hearing Protectors, January 2015

GRAS 45CB test fixture is primarily designed in accordance with the ANSI S12.42 standard for objective testing of hearing protectors. This can be done thanks to its more than 60dB self-insertion loss. This application note describes how to use 45CB for hearing protector testing. READ MORE >


Measurements in Boundary Layers, January 2015

In this application note, we introduce surface, flush-mount and flush-mount turbulence screen measurement microphones and present the measurement results performed in the boundary layer of a wind tunnel. We compare and contrast the various approaches and highlight where one is better suited than the others are. READ MORE >


Microphone vs Pressure Sensor, September 2021

The purpose of this handbook is to help you understand the differences between measurement microphones and pressure sensors. When comparing pressure sensors with microphones, it is important to keep in mind that the comparison is made using pressure sensors designed for measuring dynamic pressure fluctuations rather than pressure sensors designed, for example, to monitor the fairly static oil pressure in a car. READ MORE >



On the Advantages of Using 1/4" Measurement Microphones to Reduce Uncertainty, September 2021

The effects of observation are often negligible, however, there are measurement scenarios where they are very apparent. This whitepaper addresses elements of size-dependent characteristics of measurement microphones, including how the size of an object in physical space can affect a measurement, and how microphone diaphragm reacts to incoming signals based on diaphragm size and angles of incidence. READ MORE >


Turbulence and Measuring in Boundary Layers without Affecting the Environment, May 2021

A new white paper examining measuring in boundary layers in flow without disrupting the measurement environment and new tools for acquiring valid, actionable data without damaging the item under test. READ MORE >


TEDS (Transducer Electronic Data Sheet)

Here we explore what is the technology call TEDS and what are the advantages of using it. READ MORE >