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BSWA Impedance Tubes



BSWA SW series Impedance Tubes can accurately measure sound absorption coefficients and impedance according to ISO or ASTM standards. They also support the sound transmission loss measurements based on the Transfer Function Method using four microphones.

BSWA offers complete set of Impedance Tube systems that include:

  • Tubes with built-in loudspeakers
  • Sample holders for absorption measurements
  • Extension tubes for transmission loss measurements
  • Microphones/cables
  • Microphone calibrator
  • DAQ hardware/amplifiers
  • Measurement software

Impedance Tubes

The SW series Impedance Tubes are specially designed not only to work with the cut samples, but also for direct use in the field. The small size and durable aluminum construction make it easy to be transported and used for estimating the properties of walls, ceilings, installed building materials, road surfaces, different ground surfaces, interiors of vehicles, etc.


BSWA 1/4’’ MPA416 microphones, which have excellent phase matches, are ideal for impedance applications. The microphones are directly connected to optional 2-channel MC3522 or 4-channel MC3242 data acquisition hardware using BNC-to-SMB cables. 

Data Acquisition Hardware/ Loudspeaker Amplifiers

The impedance tube systems are designed to be used with a 2-channel MC3522 or a 4-channel MC3242 data acquisition hardware cards. 

The 2-channel MC3522 is ideal for absorption measurement systems where only two microphones are necessary. The MC3522 has a built in amplifier used to power the loudspeakers of the test tubes. 

The 4-channel MC3242 is required for transmission loss measurements where 4 microphones are necessary. Unlike the MC3522, the MC3242 does not contain a built-in amplifier. As a result, a dedicated PA50 power amplifier is used to drive the loud speaker in the impedance tube.

Impedance Tube Models

Impedance Tube Models

Table below lists all the impedance tube models along with the minimum software and hardware requirements for absorption or tranmission loss testing.


Model Measurement Capability Frequency Range (Hz) Tube Diameter # of Microphones (MPA416) DAQ Hardware Speaker Amplifier Microphone Calibrator, Cables, Case Software
SW470 Absorption 1000-6100 30mm 2 2-Channel MC3522  Built in with MC3522 Included VA-LAB2
SW230 Absorption 125-3000 60mm 2 2-Channel MC3522 Built in with MC3522 Included VA-LAB2
SW260 Absorption 125-6100 30mm and 60mm 2 2-Channel MC3522 Built in with MC3522 Included VA-LAB2
SW420 Absorption 63-1600 100mm 2 2-Channel MC3522 Built in with MC3522 Included VA-LAB2
SW477 Absorption and Transmission Loss 1000-6100 30mm 4 4-Channel MC3242 PA50 Included VA-LAB4
SW433 Absorption and Transmission Loss 125-3000 60mm 4 4-Channel MC3242 PA50 Included VA-LAB4
SW466 Absorption and Transmission Loss 125-6100 30mm and 60mm 4 4-Channel MC3242 PA50 Included VA-LAB4
SW422 Absorption and Transmission Loss 63-1600 100mm 4 4-Channel MC3242 PA50 Included VA-LAB4
SW422 and SW477 Absorption and Transmission Loss 50-6100 30mm and 100mm 4 4-Channel MC3242 PA50 Included VA-LAB4


System diagram with a PA50 amplifier and MC3242 DAQ set-up for a transmission loss measurement 

System diagram with a MC3522 DAQ and built in amlifier set-up for absorption measurements



BSWA VA-Lab software includes the Impedance Tube Module (VALab IMP) which supports sound absorption and sound transmission measurement for BSWA SW series impedance tubes. The software works with BSWA MC3022, MC3522, MC3242 and MC3642 hardware for data acquisition and analysis. 
The software's ease of use allows the user to quickly choose between absorption and transmission loss measurement. 
All necessary parameters such as sample thickness and environmental conditions can be entered wihin a single window. 
Results from multiple tube dimensions can be combined to provide seamless results in a single frequency range. 
Reports can be quickly generated and exported into Excel using VA-LAB's report generator. 
Image below shows a window of the VA-LAB software used to set-up for absorption measurements

Image below shows a window of the VA-LAB software used to set-up for transmission loss measurements

Below Image shows a screen of the results of an absorpton test 

Below Image shows a screen of combined absorption results from multiple tubes

Below Image shows the report generator feature of VA-LAB

Measurement Capabilities

Measurement Capabilities

The VA-Lab IMP supports two methods to measure the absorption coefficients of material:
  • Method using Standing Wave Ratio (ISO10534-1)
  • Transfer Function Method (ISO10534-2, ASTM E1050, and ASTM E2611)

The SW series impedance tubes all use the Transfer Function Method for absorption and transmission loss testing. 
The Standing Wave Ratio Impedance Tube Method is a classic method for measuring acoustic characteristics of materials. Please contact us for more information if interested in such a system. 


Table below shows the measurement parameters available with each measurement standard:


Parameter ISO 10534-2 (Absorption) ASTM 1050 (Absorption) ISO (Standard Under Discussion, Transmission Loss) ASTM 2611 (Transmission Loss)
Absorption Coefficient x x   x
Reflection Coefficient x x   x
Impedance (Complex) x x   x
Admittance (Complex) x x    
Reflection Coefficient (Complex) x x    
1/n Octave Absoprtion Coefficient x x    
Transfer Function x      
Transmission Loss      x x
G11 Transfer Function     x  
G12 Transfer Function     x  
G13 Transfer Function     x  
G14 Transfer Function     x  
1/n Octave Transmission Loss     x x
Transmission Coefficient       x
Propagation Wave Number       x


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