Low frequency Volume Source - Qlmf
The Qsources Qlmf low-mid frequency source is designed to produce a high level of volume displacement and simulate human body diffraction and ear directionality at low frequencies; 5 to 1,000 Hz. This source is typically used for transfer path analysis (TPA) of structure-borne or airborne noise and cabin vibro-acoustic modal analysis. Because most applications are for seat positions, the device is optimized for quick positioning on a seat with the acoustic center at ear location. This is in compliance with ISO 5128.
For linear vibro-acoustic systems, like a vehicle body, or aircraft cabin, the reciprocity principle is applicable. As a vehicle can be seen as a linear system in typical cases, the input and output of the system can be switched. This allows you to introduce acoustic energy at ear location and measure acceleration at many operational force input points, such as body interface locations for drive-line or turbine supports, wheel suspension, exhaust, hydraulic motors etc. This principle in combination with volume sources (like the Qlmf) often allows more accurate and much more efficient measurement for low frequency problem diagnosis or cabin/fuselage optimization and model comparison.
Features
Volume acceleration sound source for scaled frequency response functions
Driver and integrated sensor for a real time signal with long-time stable calibration
High sound pressure level in open and contained spaces
Specifically suitable for reciprocity based vibro-acoustic frequency response function measurements in aircraft, cars, trains, trucks, etc.
Provides a point sources at ear location and human body diffraction
Fast positioning on a seat
Measurement techniques
Transfer Path Analysis
Inverse source or load identification
(Vibro)Acoustic Experimental Modal Analysis
Statistical Energy Analysis and equivalent
Numerical model correlation and improvement
Main characteristics
Human upper body sized
Acoustic center located a ear location in sitting position ISO 5128
As a monopole, core frequency range 5-200 Hz*
Extended frequency range 5-1000 Hz**, with human body diffraction
Sound power 104 db Lw, non equalized white noise
Real time volume acceleration signal
Internal electric and thermal overload protection, with visual overload indicators
Availability
The Qlmf volume source is marketed in cooperation with Siemens under the Simcenter Qsources product line
*What is core frequency range for sound sources?
In the core frequency range a close approximation of omni-directionality and high output can be expected. Or in case of sources for ISO standard regulated requirements, like for building acoustics applications, the source will be well within the ISO requirements.
**What is extended frequency range for sound sources?
In enclosed spaces, a limited low frequency output from a source is not necessarily a limitation for measurement effectiveness or accuracy. Still in an open sound field, or very large enclosed space, the same source level may not generate sufficient sound pressure level at the lowest frequencies. Low frequency extension range is typically for smaller volume spaces like a car cabin, or an aircraft cabin.
The high frequency extended range of the Qlmf is not related to limited omni-directionality. The Qlmf source still is in close approximation of a monopole up to 1000 Hz in the specific situation of a monopole placed at the ear of a grown-up human. This is specifically useful for reciprocal measurements inside trains, aircraft, cars, tractors, control cabins etc. where normally a person is seated or standing and low-mid frequency problems are to be investigated.