The rise at 3kHz is from the tweeter dial being a bit high, but it is likely dialed up a bit. The 800 Hz dip may also be from the dial being a bit low.
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"From its inception, the 4311 monitor carried the designation "Control Monitor," while all other models have carried the designation "Studio Monitor." Even when later refined in the mid 1980's as the 4312, it retained the same forward voicing and low-frequency characteristics of its predecessors.
Thus, JBL has maintained a distinction between Studio Monitors and Control Monitors."
Control Monitors have been designed with the following characteristics as most important:
A. Rising mid-range response.
B. Low-frequency response relatively undamped for rising response in free-standing positions.
C. Extended high frequency response.
Studio Monitors were designed with the following performance characteristics:
A. Flat axial response, with extended bandwidth beyond 20 kHz and optimum low-frequency performance in freestanding position.
B. Smooth power response.
C. Smooth phase (time domain) response.