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JBL LSR6300 Series Technical Note page 4

Studio monitors
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Figure 8. LF, MF, and HF contributions in
LSR6332 system.
Figure 9. HF 0 dB/-1 dB option in LSR6332.
Wide-Band Distortion:
Plots of second and third harmonic distortion
components at nominal listening levels of 96 dB and
102 dB SPL, measured at a distance of 1 meter, are
shown in Figure 10. The distortion plots in these
graphs have been raised 20 dB for ease in reading. At
A, the distortion components above 100 Hz are −40 dB
relative to the fundamental, while at B the same
components are about −35 dB relative to the
fundamental. This is remarkable performance for any
loudspeaker when you consider that peak program
levels in a surround sound environment with the
loudspeakers at an average distance of 2 meters from
the listeners would be in the range of 100 dB SPL.
This would correspond to a per-loudspeaker reference
level of about 100 dB SPL at 1 meter.
Port Turbulence:
At low frequencies in the region of port tuning, many
LF systems exhibit what is called port compression , a
tendency for turbulence to develop in the port and
cause both noise and distortion. Contouring of the port
terminations, both inside and outside the enclosure,
can reduce this tendency considerably. JBL uses a
proprietary Linear Dynamics Aperture port, whose
cross-section contour is shown in Figure 11. The effect
of this port, as compared to a straight port, is shown in
Figure 12. The difference between the LSR6332 port
and the normal straight port design can be clearly
seen, reaching a difference of 4.4 dB at a power input
of 400 watts. Note that for the LSR6332 system there
4
Figure 10. Second and third harmonic distortion in
LSR6332, 96 dB and 102 dB SPL at 1 meter.
Figure 11. Linear Dynamics Aperture port contour
as used in the LSR6300 Series.
is about 0.5 dB compression at 10 watts input,
gradually increasing to 2 dB for 100 watts input. For
the straight port the compression at 10 watts is 1.5 dB,
increasing to 4.5 dB at 100 watts.
Power Compression:
Power compression results from heating of the voice
coil, which causes an increase in voice coil resistance.
The result of this is a loss of overall electromechanical
coupling in the driver and a loss of output. Power
compression is normally shown by scaling and
superimposing curves run at different values of input
power. If there were no power compression at all, then
the response curves would lie directly one atop the
other. Figure 13 shows the power compression in the
LSR6332 system at power inputs of 10, 30, and 100
watts. The curves have been normalized so that the
flat curve at 0 dB represents the response measured

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