Impedance tube material absorption and sound insulation test system was widely used to test the acoustic characteristics of materials in all walks of life, such as sound absorption coefficient, reflection coefficient, acoustic impedance, acoustic admittance and so on. In architectural acoustic design, designers needed to know the acoustic characteristics of various materials in order to calculate the indoor reverberation time. In the design of automobile interior trim, engineers calculated the effect of interior noise reduction according to the acoustic characteristics of vehicle interior materials, and improved the interior acoustic comfort by optimizing the weight, volume and acoustic performance. In the field of aerospace, it was necessary to select more appropriate alloy materials and cabin seat materials through material acoustic performance test. In the research industry of new materials and composites, it was necessary to test the acoustic properties of products with different molecular structures or different raw material ratios.

The produced impedance tube test system was designed according to the national standard GB / t18696.2-2002 《measurement of sound absorption coefficient and acoustic impedance in impedance tube part 2: transfer function method》 and iso10534-2:1998. This paper explained the solution of SKC material absorption and sound insulation test through two parts: test system introduction and test case sharing.

Part A --- introduction to SKC impedance tube test system

The whole system was composed of impedance tube, high-precision phase matching microphone, data collector, power amplifier and test software. Compared with the standing wave ratio method of standing wave tube, it had the characteristics of short test time, continuous spectrum and good repeatability. In particular, it could greatly improve the efficiency of comparative experiment in material research.

The system construction diagram is as follows:

System composition and instrument introduction:

a. Impedance tube:

The whole set of impedance tube was made of high-strength hard aluminum alloy.

It could ensure the stability of pipe diameter and cavity to the greatest extent.

Impedance tube had a variety of pipe diameters and microphone spacing, and its measurement frequency range was large.

Only a small sample was needed to complete the material absorption and sound insulation test.

The system was easy to install and disassemble, and the size of the rear cavity was adjustable.

b. Microphone SKC MP40:

The microphone used in the impedance tube test system was the high-precision 1/4-inch microphone mp40 independently developed and produced by SKC.

The microphone phase was strictly matched and the lower limit frequency was low（ 2 for sound absorption test and 4 for sound insulation test).

The specific parameters of MP40 were as follows:

c. Four channel data collector Q421

Q421 data collector had four channels input and two channels output, and the frequency and amplitude of the output signal could be set freely within the specified range.

Specific parameters were as follows:

d. Power amplifier PA50

SKC power amplifier PA50 had output DC detection, on-off and overload protection devices. The specific parameters were as follows:

e. Test software - SoundExpress

The main interface of the software was shown in the figure below, mainly including:

1.Project Management

2.Hardware Setup

3.Calibration

It could test sound pressure level, sound intensity, sound power, material sound absorption / sound insulation test.

Software features: the test software had good stability, strong portability and simple operation.

Part B - Test Case Sharing

Case 1 -- sound absorption sample test of interior trim parts in a complete vehicle factory.

Three groups of test samples: 10mm thick sound-absorbing cotton.

Test requirements: test the sound absorption coefficient of three groups of test pieces at 800hz-6300hz.

Sound absorption test solution using SKC materials.

The curve of sound absorption coefficient was as follows:

The sound absorption coefficient data of three groups of samples were as follows:

The test results met customer requirements.

Case 2 -- Test of sound insulation / absorption coefficient of composite samples in a university.

Sample (large): diameter: 99.96mm, thickness: 2.8mm

Sample (small): diameter: 28.90mm, thickness: 2.8mm

Test solution for sound absorption and insulation using SKC materials.

The sound insulation curve and 1/3 octave band data were as follows:

Test solution for sound absorption and insulation using SKC materials.

The sound absorption coefficient curve and 1/3 octave band data were as follows:

SKC impedance tube material absorption and sound insulation test system could be used in construction industry, automobile interior, polymer material research, new material design, composite material development, universities, scientific research institutes, various research institutions and other industries, such as wall, ceiling, automobile interior trim, felt, carbon fiber materials, multi-body composites, honeycomb aluminum Acoustic absorption and sound insulation test should be conducted for porous materials.

"Sincere, Knowledgable, Creative" was SKC's tenet of providing services to customers. SKC was committed to the integrated service of acoustic vibration industry.