crown I-Tech HD LevelMAX Limiter Suite User Manual

I-Tech HD LevelMAX™ Limiter Suite

The I-Tech HD LevelMAX™ Limiter Suite features three types of limiting:

 Peak
 RMS
 Transducer Thermal

And two modes of operation:

 Auto
 Advanced

The standard I-Tech HD LevelMAX Limiter panel (Advanced Mode) is shown below:

LevelMAX has been designed to limit accurately to the specified voltage thresholds. The
addition of a thermal limiter allows thresholds for the faster-acting RMS and peak limiters to be
set higher, providing more output and maintaining dynamic range before the onset of limiting,
while protecting the long term integrity of the transducers.

In Auto or Advanced modes, turning on the LevelMAX Limiter Suite will enable all three
limiters: Peak, RMS and Thermal.

The three LevelMAX limiter types and operating modes are outlined in the following sections.

VRMS*2Vpk 

1.0 LevelMAX Peak Limiter

LevelMAX Peak limiting instantaneously limits the output voltage to not exceed the defined
peak threshold voltage.

1.1 Peak Limiter Threshold (Vpk)

In Auto mode, the peak limiter threshold value is automatically determined from the defined
RMS threshold and the low pass frequency defined in the XOVER block. For a low pass
frequency less than 100 Hz, the RMS to peak threshold ratio is 6 dB. From 100 Hz to 400 Hz,
the RMS to peak ratio increases from 6 dB to 9 dB. Above 400 Hz, the ratio remains at 9 dB.

For Advanced mode, the peak limiter threshold can be set by the user.

1.2 Peak Limiter Attack (sec)

The peak limiter attack time is instantaneous and cannot be modified. The output voltage is
limited to the value defined by the peak limiter threshold (see 1.1).

1.3 Peak Limiter Release (sec)

In Auto mode, the peak limiter release time is determined by the high pass frequency defined in
the XOVER block.

For Advanced mode, the peak limiter release time can be set by the user.

1.4 Peak Limiter Look-Ahead

Peak Limiter Look-Ahead inserts a delay into the peak limiter signal path in order to ‘look’ at the
input signal and anticipate when the peak threshold will be exceeded. If it detects that the
threshold will be exceeded, the signal is gradually reduced prior to reaching the threshold, while
still limiting to the correct peak voltage. This approach eliminates a sharp signal discontinuity
which, in turn, could create audible distortion.

The peak limiter look-ahead value is 0.5 ms. This value was determined to be subjectively
acceptable for most frequency ranges while not adversely compromising overall latency. Overall
latency remains constant regardless of whether the LevelMAX Limiter suite is enabled (ON) or
bypassed (OFF).

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2.0 LevelMAX RMS Limiter

LevelMAX RMS limiting accurately limits the output signal to the specified RMS threshold
voltage.

2.1 RMS Threshold (V

The RMS Threshold should be set by the user to correspond to the short term (2 hour) power
handling of the transducer or system.

Refer to the appropriate JBL Specification Sheet, Technical Manual or Product Manual for two
hour power ratings. To calculate the RMS Threshold in V

where AES Power (Wrms, 2 hour) is the free air component power rating.

If minimum impedance data is unavailable, use nominal impedance. If 2 hour AES power ratings
are unavailable, use 2 hour IEC power ratings. For most applications, it is recommended to
operate LevelMAX limiters in Auto mode so that peak thresholds are automatically calculated
based on the RMS threshold and selected LP frequency (see 1.1).

2.2 RMS Attack Time

RMS

)

, use the following equation:

RMS

The RMS attack time is set automatically in Auto or Advanced modes and is based on the peak
limiter release time. The RMS attack time has been designed to smoothly transition from peak to
RMS limiting while minimizing audible limiter anomalies.

2.3 RMS Release Time

For Auto mode, the RMS release time is determined based on the high pass frequency that is
defined in the XOVER block.

For Advanced mode, the RMS release time can be set by the user.

2.4 RMS Detector Time

The RMS Detector Time is determined based on the high and low pass frequencies defined in the
XOVER block and is not user-adjustable.