JBL 660GTI - Manual (Page 5)

Anechoic Chambers: JBL’s anechoic chambers are expensive…but
worth the investment. The baffles on the walls of the chamber absorb
sound at all audible frequencies. In this setting, JBL engineers can
assess critical details of the speaker’s performance without the effects
of extraneous noise or reflected sound.
Environmental Test Lab: JBL’s environmental test lab includes machines
that subject speakers to hot and cold temperatures, humidity, ultraviolet
light and vibration. These tests are designed to simulate a lifetime of
abuse in the most adverse environmental conditions.
TESTING
At JBL, we spare no expense in testing loudspeakers. Prototype and production
samples are first tested for frequency-response range and uniformity in one of
our anechoic chambers using MLS and swept sine-wave analyzers. Sine-wave
analysis measures harmonic distortion, which is a critical element in determining
the sonic accuracy of the speaker. MLS, or maximum length sequence, analysis
compares the noise output from the analyzer to the output of the speaker to
determine the speaker’s impulse response, a measure of transient response
accuracy. The speaker’s impulse response measurement is then converted into
a high-resolution frequency-response measurement using a mathematical
operation called Fast Fourier Transform, or FFT. Real-Time Laser Vibrometry is
used to measure the structural behavior of the moving assembly. The Klippel
analyzer measures magnetic field symmetry during the speaker’s operation.
Careful analysis of all these measurements determines the location and causes
of unwanted resonance and distortion in the speaker’s output, enabling the
engineers to refine the speaker’s design to eliminate them.
Once the design is perfected, power handling is verified for production-grade
samples by subjecting them to filtered octaves of pink noise at rated power for
100 hours. That’s right, 100 hours. Finally, samples are tested for longevity in our
environmental test lab, according to the rigorous standards set by the automotive
industry. The last phase in our extensive testing involves the most critical
instruments in our possession – our ears. We listen…and listen…and listen.
Klippel Analyzer: This revolutionary analyzer developed by Klippel GmbH
separates the distortion generated by transducers into two categories:
distortions caused by the speaker’s motor and those caused by the
speaker’s suspension. By analyzing the symmetrical and linear nature of
the measured results, JBL engineers can formulate a cure for almost any
distortion caused by motor or suspension nonlinearity. Klippel analysis
provides accurate Thiele/Small parameter verification at virtually any
input power level.
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ENGLISH