You are here: Know-how / Measurements / Nonlinear Distortion / Air leakage noise

Air leakage noise

Characteristics:

KLIPPEL R&D System KLIPPEL QC System

Absolute envelope of modulated noise MOD

LD (Leak Detection)

Relative envelope of modulated noise RMOD


LD (Leak Detection)

Peak value of random distortion RAND

TRF

QC Standard,

LD (Leak Detection)

Peak value of deterministic distortion DET

TRF

QC Standard,

LD (Leak Detection)

Crest factor of deterministic distortion CREST

TRF

QC Standard,

LD (Leak Detection), 

LOC (Leak Localization)

Inter-channel delay time


QC Local

Incident angle

QC Local

Mechanical loss factor Qms

QC Standard,

MSC

Port resonance frequency fp

MSC

Quality factor representing box leakage

MSC

The air passing a leakage at the dust cap or in the enclosure generates turbulent noise which is audible and which is perceived as a loudspeaker defect. Conventional spectral analysis shows broad-band noise which is very similar to the measurement noise generated by the microphone or production noise. Averaging will not increase the sensitivity of the measurement because air leakage noise is as random as the disturbances. However, time domain analysis reveals a deterministic envelope of the air leakage noise which is modulated by the sound pressure. Using a sinusoidal excitation signal of known frequency, the envelope can be calculated. Increasing the measurement time corresponds with an averaging of the deterministic envelope and will increase the sensitivity of the measurement beyond the human ear. The demodulation technique combined with a microphone array allows to detect the position of the noise source.

KLIPPEL R&D SYSTEM (development)

Module

Comment

Transfer Function Module (TRF Pro)

TRF PRO may only be used for detecting the air noise by exploiting the intensity of the higher-order harmonics. A separation between Rub & Buzz and air leakage noise is not possible.

KLIPPEL QC SYSTEM (end-of-line testing)

Module

Comment

QC Standard: SPL Task; SPL+IMP Task
System Task

The normal SPL measurement task is the simplest way for detecting significant air leakage noise. Particular symptoms of air leakage are not detected and cannot be used for diagnostics.

Air Leakage detection Task

(preview)

The leakage detection task uses only one microphone for detecting the air noise by the sensitive demodulation technique. Here, only the intensity of the modulation can be used to detect the position of the source approximately. The 2nd microphone may be located in the far field for detecting production noise.

Motor Suspension Task (MSC)

MSC measures the mechanical quality factors of the drive unit Qms and of the vented box system.

Air leakage localization task

(preview)

This task performs a two-channel demodulation and correlation analysis between two microphone signals provided by the air leakage tracer or by microphones in a fixed installation selected in pairs by a multiplexer. The direction of the noise source is displayed on the LED display of the air leakage tracer. Further measurements with the handy tool guide the user to the precise location of the signal source. For a fixed installation of microphones, the inter-channel time delay is the basis for calculating the sound source by triangulation methods.

QC Standard: IMP Task; SPL+IMP Task

IMP measures the mechanical quality factor Qms which indicates a leaky dust cap.

 

Example:

 

The figure above shows the air leakage tracer localizing the position of the air leakage source and a buzzing screen. The angles of incident are calculated by a novel demodulation technique using two microphones or a microphone array. The color, intensity and pulsing frequency of the LED display give detailed diagnostic information about the cause of the defect.
The figure above shows the air leakage tracer localizing the position of the air leakage source and a buzzing screen. The angles of incident are calculated by a novel demodulation technique using two microphones or a microphone array. The color, intensity

Templates of KLIPPEL products

Name of the Template

Application

TRF rub+buzz w/o Golden Unit

Rub & Buzz detection without "Golden Unit" according Application Note AN 22

TRF rub+buzz with Golden Unit

Rub & Buzz detection with "Golden Unit" according Application Note AN 23

Diagnost. RUB&BUZZ Sp1

Batch of Rub & Buzz tests with increased voltage (applied to high power devices)

Diagnost. RUB & BUZZ Sp2

Batch of Rub & Buzz tests with increased voltage (applied to low power devices)

TRF Crest Harmonics (x,f)

Crest factor harmonic distortion versus displacement to find Rub & Buzz and other loudspeaker defects

TRF Peak harmonics, time domain

Peak value of higher-order harmonics in time domain for Rub & Buzz analysis

Diagnost. MIDRANGE Sp1

Comprehensive testing of midrange drivers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1

Diagnost. SUBWOOFER (Sp1)

Comprehensive testing of subwoofers with a resonance 10 Hz < fs < 70 Hz using standard current sensor 1

Diagnostics MICROSPEAKER Sp2

Comprehensive testing of microspeakers with a resonance 100 Hz < fs < 2 kHz using sensitive current sensor 2

Diagnostics TWEETER (Sp2)

Comprehensive testing of tweeters with a resonance 100 Hz < fs < 2 kHz using sensitive current sensor 2

Diagnostics VENTED BOX SP1

Comprehensive testing of vented box systems using standard current sensor 1

Diagnostics WOOFER (Sp1)

Comprehensive testing of subwoofers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1

LPM Microspeaker T/S (SP2)

Linear parameters of microspeakers using sensitive current sensor 2

LPM Subwoofer T/S (Sp1)

Linear parameters of subwoofers using standard current sensor 1

LPM Subwoofer T/S (Sp2)

Linear parameters of subwoofers using sensitive current sensor 2

LPM Tweeter T/S (SP2)

Linear parameters of tweeters using sensitive current sensor 2

LPM Woofer T/S (Sp1)

Linear parameters of woofers using standard current sensor 1

LPM Woofer T/S (Sp2)

Linear parameters of woofers using sensitive current sensor 2

LSI Woofer+Box Nonl. P Sp1

Nonlinear parameters of woofers operated in free air, sealed or vented enclosure with a resonance frequency fs < 300 Hz at standard current sensor Sp1

Diagnostics WOOFER Sp1,2

Comprehensive testing of subwoofers with a resonance 30 Hz < fs < 200 Hz using current sensor 1 and 2

Standards:

  • IEC Standard IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
  • AES2-1984 AES Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement


Papers and Preprints:

W. Klippel, Tutorial “Loudspeaker Nonlinearities - Causes, Parameters, Symptoms,” J. of Audio Eng. Soc. 54, No. 10, pp. 907-939 (2006 Oct.).

W. Klippel, U. Seidel, “Measurement of Impulsive Distortion, Rub and Buzz and other Disturbances,” presented at the 114th Convention of the Audio Eng. Soc., 2003 March 22–25, Amsterdam, The Netherlands, Preprint 5734.