Air Leak Detection (ALD) & Stethoscope (ALS)
Optional Modules for KLIPPEL QC Framework
Features and Benefits
- Detect small air leaks and other defects
- Ambient noise immune (auto repeat)
- Simple setup
- End-of-line application (ALD - integrates in test sequence)
- Off-line diagnostics (ALS)
- Localize and auralize defects
The Air Leak Detection (ALD) module applies special audio signal processing to isolate pulsating flow noise generated by air leakage in loudspeaker drivers and enclosures as well as ports and in orifices. Limits can be applied to the resulting absolute and relative distortion levels in order to qualify and quantify air leakage and many other defects (rubbing, buzzing, loose particles). This technology can be applied as an automatic end-of-line test which seamlessly integrates in the test sequence with single tone excitation or as part of the standard chirp measurement (QC SPL - Sound Pressure).
Sharing the same processing kernel, the Air Leak Stethoscope (ALS) is a powerful off-line diagnostics tool to auralize and locate defects interactively.
- Low frequency drive units (woofer)
- Active and passive subwoofers units (closed, vented, band pass)
- Active or wireless mobile speakers (Bluetooth®)
- HiFi peakers and studio monitors
- Automobile audio system
- Smart speakers
- Outdoor speakers
- Active mufflers
Comprehensive Active System Test
The picture shows a typical end-of-line test setup for active speaker systems such as a multimedia, Hi-Fi or portable speakers using KLIPPEL Analyzer 3 equipped with Laser Card and XLR Card. The main test microphone is located in the front for testing typical parameters such as frequency response, THD, Rub&Buzz distortion etc. using SPL – Sound Pressure Task. In order to detect loose joints, enclosure defects or irregular port noise, leakage testing can be integrated simply, directly into the sweep test by activating the ALD option in the SPL Task without adding any extra test time.
To make sure that also rear defects and leakage problems are detected reliably, another test microphone may be placed at the back of the speaker for an additional ALD test step. Up to four microphones can be used for a single shot test. During the complete test sequence, the ambient microphone outside the test chamber detects ambient noise disturbance reliably and triggers the auto-repeat mechanism for single test steps, if necessary.
Inspection of Professional Speaker
The incoming goods inspection in a rental company for professional audio products (PA speakers, stage monitors…) is crucial to identify damage due to ageing or misuse. The ALS is a powerful tool to identify and localize such defects easily. Using noise insulated headphones the operator can test the equipment at critical playback levels with maximal sensitivity while protecting the ears.
Mircophone Array for Large Subwoofer
Detecting air leaks in large speaker systems with only one microphone suffers from acoustical shadowing of the high frequency leak noise. Locating multiple microphones around the device under test overcomes this problem and the complete surface can be covered for optimal leaks detection.
Sequential Test (Production Analyzer + Mic Multiplexer)
The Production Analyzer provides only two simultaneous input channels; therefore, a sequential measurement is required if multiple test microphones are used. In this example, four test microphones are switched by a multiplexer. An additional microphone outside of the test chamber monitors ambient noise in parallel. The test chamber ensures a low average acoustical noise floor for maximal measurement sensitivity.
Simultaneous Test (KA3 with Input Signal Sharing)
Using the KA3 hardware, a high number of input channels can be measured simultaneously using signal data sharing feature. The QC software currently supports measuring with four acoustical microphones at the same time. In case ambient noise is measured (recommended), three other microphone channels are available that may be connected to the Laser Card (IEPE microphones) or the XLR Card (48V microphones or IEPE using XLR-BNC adaptor). The stimulus signal is played back only once by the source ALD task which is recording all input signals. The receiver tasks only process the microphone signals recorded by the source tasks in order to generate the test results and verdicts for all microphones.
Gluing errors in drivers are likely to cause air leakage in the surround or the dust cap that may only be audible in the final application when the driver is mounted in a closed or vented enclosure. Such leaks may not be detected under free air conditions due to the lag of air pressure caused by the acoustical short-circuit at low frequencies. Measuring the driver in an adequately small test box provides the required in-box pressure at low frequencies to stimulate even very small driver leaks. Additionally, the test box offers ambient noise attenuation to go for maximal sensitivity in leak detection and driver testing.
Literature and Papers
Measurement of Turbulent Air Noise Distortion in Loudspeaker Systems
Germany: 102009033614; USA: 8,401,823B2; China: ZL201010228820.8