QindW Miniature Sound Source

Qsources QindW is a Wind tunnel reference sound source. A custom miniature sound source part of Infra-Qsources built for TU Delft Aeroacoustics & Wind Energy Research Group.

QindW is a custom miniature sound source with very low diffraction and excellent omni-directionality. A narrow and long design allows minimal impact on the flow and minimal feedback from the flow on the source output.

With a diameter of 22 mm and a length of 120 mm the disturbance is minimal and much smaller than any other sound source. The frequency range with a long-time stable relation between
drive voltage and emitted sound power is 500 – 6300 Hz. The set includes a powering cable with source protection electronics. The sound source can be driven with any signal from random noise to sine sweeps to music signals and can be calibrated for the sound power under different signal settings in an anechoic chamber.

Product Characteristics:

Frequency range: 500-6300Hz.

Length: 120mm.

Diameter: 22mm.

Sound pressure level: 65dB at 1meter in free field (white noise, 500-6300Hz.)

Sound power level: 76dB Lw (white noise, 500-6300kHz.)

Amplifier requirement: 100 Watt RMS to 4 Ohm or more

Low Turbulence Tunnel experiment

The experiment using QindW took place in the Low Turbulence Tunnel (LTT) at TU Delft. The wind tunnel campaign was part of the NWO-TTW THAMES project (grant 15215): Towards High-Reynolds Airfoil self-noise MEasurementS.

The goal of the project is to understand how to improve noise measurements in closed wind tunnels, with particular application to wind turbine blade noise studies. The test section used in the closed wind tunnel has been modified for better aeroacoustic measurements. In order to improve noise measurements inside the test section, lining materials have been applied at the wall.

The goal of the wind tunnel campaign was to study how the different lining materials improve the noise measurements: by reducing sound reflections inside the test section, and by reducing reverberation inside the tunnel circuit.

The lining materials included:

  • wedged melamine side panels, covered by Kevlar
  • flat melamine foam panels on the floor and ceiling

The microphone array was mounted behind a Kevlar panel, so that it records less noise from the boundary layer of the tunnel (i.e. noise originated from pressure fluctuations in the flow).

Improved aeroacoustic measurements

The test has lead to significant improvements of noise measurements in closed wind tunnels using Qsources’ QindW source to generate noise in-situ, placing it in the center of the test section to study the effect of reflections. The Sound source incorporates two long stroke electrodynamic actuators. The test set-up included flow-off and flow-on measurements.

QindW is a customized product part of the Infra-Qsources range of high quality sound sources. The Infra-Qsources range includes solutions for efficient on-site acoustic testing in buildings, rooms and infrastructure.

Where the QindW is a custom product built by Qsources for TU Delft, another miniature sound source named Q-IND, is available under the Simcenter Qsources range. Specific for the Simcenter Qsources Q-IND are the sensors for a real-time volume displacement signal up to 2000Hz. This is the source strength descriptor which is practically independent from the acoustic environment, providing a basis for reciprocity and modal analysis testing.

The Simcenter Qsources Miniature Volume Source can be used for Airborne Source Quantification (ASQ), Transfer Path Analysis (TPA) as well as Vibro-Acoustic Modal Analysis (EMA). Its miniature size allows accurate acoustic transfer function measurements around intake and exhaust nozzles for airborne source quantification techniques. The FRFs are acquired without the influence of the volume of a large low mid frequency source. Its size makes it ideal to excite structures from inside, like white goods and consumer electronics.
Besides ASQ, the source can be used for scaled modal analysis using the internal volume displacement sensor as reference.”


The campaign took place thanks to two PhD candidates: Mr. Hugo Bento and Mr. Colin VanDercreek and was supervised by Prof. Dr. Mirjam Snellen, Dr. Daniele Ragni and Dr. Francesco Avallone.

For further inquiries related to this aeroacoustics project. Please contact:

Hugo Bento
Aeroacoustics/Wind Energy Research Group
Building 62 – Room 6.08
Delft University of Technology