The impulse response IR is the heart of all of the loudspeaker data file formats. The IR describes how the loudspeaker responds to a perfect impulsive stimulus. It contains the time and frequency response of the loudspeaker. An IR must be be collected at a predetermined angular resolution. While almost any resolution is possible, our standard process uses 5-degree rotations between measurements.
Left - The Impulse Response Right - The Energy-Frequency Curve
The IR in its raw form is not very useful. It must be transformed into an Energy Frequency Curve EFC. The EFC's are processed into a data file that can be recongnized by room modeling programs. We provide data files in two formats:
EASE 4.x - EASE is a widely used acoustic prediction software platform (http://www.renkus-heinz.com/ease/index.html). ETC gathers the full impulse response of the loudspeaker at each measurement angle, which EASE imports and converts into its native file format. We perform the import, authorize the data, and provide you with the finished EASE data file. The EASE format is proprietary, so this data cannot be used by other acoustic prediction applications.
CLF - The Common Loudspeaker Format
CLF was developed to provide a common virtual specification sheet and file
format for loudspeaker data. The CLF is not an industry standard, but it
can be adapted to meet a standard when one is formalized. ETC is the first
testing facility to output data in the Common Loudspeaker Format. The free
CLF viewer (www.clfgroup.org)
application is a stand-alone utility that displays the CLF data. It also
includes details on how the data was collected, by whom, and the measurement
conditions.
The EASE and CLF formats assure that your loudspeaker data can be used by the vast majority of sound system designers in the field. ETC works closely with the developers of these software platforms to assure that the data is being gathered and presented correctly. Since we measure the entire impulse response, the data can be processed into future file formats without the need for re-measuring.
Each data package that we provide includes:
1. Loudspeaker Attenuation Balloons
This test measures the sound pressure level around the loudspeaker at 5-degree
intervals. The result is a "balloon" that describes the radiation
characteristics of the loudspeaker at 1/N-octave resolution.
2. Derived Electro-acoustic Metrics
Once the balloon data is measured, a number of useful benchmarks can be
derived from it. These include the Sensitivity, Directivity Factor Q, Directivity
Index DI, and others. Many designers use these scores to qualify the suitability
of a loudspeaker for a specific project.
3. Sensitivity
The sensitivity is measured with an applied voltage of 2.83Vrms. It is measured
at 8 meters and normalized to one meter. It is provided at 1/3-octave resolution
in the data packages, but we can provide it at any frequency resolution
upon request.
4. Impedance
The electrical impedance of the loudspeaker is provided 1/3-octave resolution
in the data packages. The CLF data also includes the average, minimum and
nomimal impedances derived from the impedance curve. Upon request we can
provide the impedance data at any frequency resolution, including the phase
vs. frequency graph.
5. Proprietary Drive Signals
If special drive signals are required for testing the loudspeaker (i.e.
crossovers or equalization) a high-resolution plot of these driving functions
are included in the CLF data file.
6. Maximum Input Power 
The test procedure includes an accelerated power test designed to determine
the maximum safe RMS voltage that can be applied to the loudspeaker. Details
of this test method are available from our Downloads page.
ETC can test your loudspeaker for maximum input power using a number of industry-standard methods. This is not part of the standard data packages. Please contact us for details regaring pricing.
7. DXF Wireframe
Many design applications allow the loudspeaker to be represented as a DXF
wireframe in the room model. Both the EASE and CLF data files include a
properly scaled wirefram as part of the loudspeaker data package.
In addition to loudspeaker testing, we continue to work through our sister company, Synergetic Audio Concepts, Inc. to provide the necessary training for system designers to use the data. Syn-Aud-Con provides training seminars on Sound System Design with emphasis on room acoustics and loudspeaker specifications. This popular seminar provides insights on how to use the data to do real-world sound system design and problem solving.
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