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Branca Rayls 37X

Determination of acoustic impedance, Non-linear factor of precision fabrics for acoustical applications

ISO 9053:1991 [ Method A], ASTM C522, BS EN 29053:1993, ISO TC 43/SC 2

Overview

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Model:  
Acoustic impedance
Acoustic impedance + NLF
NLF

The apparel Branca Rayls 37X, designed by S.T.A. Branca Idealair and allows to generate Airflow Resistance-Testing Conditions, Laminar Flow-selection and Non Linear Factor expressed in MKS Rayls and CGS Acoustic Ohms suitable for precision fabrics for acoustical applications.

The original test area starts from 50 cm2 and reduction flanges of 20, 10, 5, 2, 1 cm2 are supplied together with the instrument (five couple of reduction flanges for upper/lower surfaces of test area), on request released with diameter certificate.

Branca Rayls 37X is equipped with an HMI panel operator as user interface that allows to set test parameters, test monitor, additional functions and evaluations at the end of each test.

Test procedures:

  • ACOUSTIC IMPEDANCE
    expressed in MKS Rayls or CGS Ohms (referred to 1 cm2), representing the result of pressure difference across the sample divided by the linear velocity of the airflow; MKS Rayls test procedure states to calculate the ratio between pressure drop (Pascals) and air velocity (meters per second) crossing the sample material.
    The airflow must be sufficiently low to obtain laminar, non turbulent airflow through the sample, in order to properly define the airflow resistance in a linear range.

    The output of the measure is the value of:

    • MKS Rayls = Pa*s/m


  • NON LINEAR FACTOR, which allows to check the behavior of the sample at a very high air velocity (turbulent air flow);
    The second test method is the measure of the NLF - Non Linear Factor.
    When turbulence happens, the measured airflow resistance is higher than in the linear range. This might lead to an undesired change of the acoustic performance of the final component .
    It is possible to measure this deviation by calculating the ratio between two measured values of specific airflow resistance, respectively at laminar and turbulent airflow (usually, at 0,2 m/s and 2 m/s airspeed).

    Examples of applications requiring NLF measures:
    • Acoustic devices - performance across narrow slots;
    • Acoustic devices - nonlinear performance at very high Sound Pressure Level;
    • Sound suppression panels working at high SPL;


  • AIR PERMEABILITY which pass perpendicularly across a sample under examination, under a determined pressure and time according to the norm Standard ISO 9237:97.
    The air permeability measure is mainly aligned to common Standards for Textiles (ISO 9237).
    It states to measure the airflow through the sample at assigned pressure drop (usually 200 Pa or 0,5WG = 127 Pa).
    This is not fully representative of the expected acoustic behavior, but it is a widely used measure for Textiles.

    For this reason the instrument has to be exclusively used:

    • with monofilament woven mesh for acoustic use;
    • 2) with other textile materials having thickness up to 3 mm;
    • 3) with power supplies listed in the instrument nameplate;
    • 4) with all lateral inspection panels closed;
    • 5) far from heat sources;
    • 6) with all safety devices on;

Specifications

Applications

APPLICATION FIELDS:

1) with monofilament woven mesh for acoustic use (SAATI materials);
2) with other textile materials having thickness up to 3 mm;
3) for acoustical applications;
4) for the determination of the LINEAR LAW (Laminar flow) and the NON-LINEAR LAW (Turbolent flow);

Photogallery
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