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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.
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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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)(Impedance Minimum)hour2,(PowerAES)(ThresholdRMS ohmsxWrmsVrms
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.
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)(Impedance Nominal)hour100,(Power)(ThresholdThermal ohmsxWrmsVrms
3.0 LevelMAX Transducer Thermal Limiter
LevelMAX Transducer Thermal limiting is designed to protect transducers from long term
thermal damage by gradually adjusting the RMS threshold until the target long term thermal
threshold voltage has been reached. The thermal limiter functions only when the RMS limiter is
enabled and when the thermal voltage threshold is lower than the RMS threshold. On the main
limiter panel, the thermal protection LED turns on once the thermal limiter is 0.75 dB into limit.
3.1. Thermal Voltage (V
The thermal voltage threshold should be set to correspond to the long term (100 hour) power
handling of the transducer or system.
Refer to the appropriate JBL Specification Sheet, Technical Manual or Product Manual for 100
hour power ratings. To calculate the Thermal Voltage Threshold in V
equation:
where Power (Wrms, 100 hour) is the 100 hour power rating.
If 100 hour power handling data is unavailable, set 100 hour power rating ≈ 0.8 x 2 hour power
rating.
3.2 Thermal Response Time (s)
RMS
)
, use the following
RMS
The thermal response time is the amount of time the average RMS signal is above the thermal
threshold voltage before limiting begins. Once the threshold has been exceeded for the amount of
time defined by the thermal response time, the RMS threshold is lowered until the target thermal
voltage has been reached. The thermal response time is not the time it takes to reach the target
voltage, although the longer the thermal response time, the longer it takes to reach the target
voltage. It is also dependent on the amount of gain reduction and the ratio between RMS and
thermal thresholds.
Thermal response time is transducer-dependent and should be based on the initial temperature
rise of the transducer voice coil to protect it from thermal overload.
If detailed transducer data is unavailable, the Thermal Response Time should be left at the
default value of 10 sec.
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PEAK RMS Thermal
Threshold (V) Release (s) Threshold (Vrms) Release (s) Voltage Response Time (s)
4887 / 4887A
MID / HI 79 0.0164 28 0.0739 24 8
LOW 130 0.0998 77 0.3132 70 8
4888
HIGH 113 0.0045 40 0.0388 28 9
MID 160 0.024 57 0.0894 46 8
LOW 200 0.1812 77 0.5521 65 7
4889 / 4889-1
HIGH 169 0.0048 60 0.04 42 9
MID 220 0.0335 78 0.111 65 8
LOW 195 0.1995 74 0.605 60 7
4881A
SUB 218 0.224 110 0.6754 84.9 8
4882
SUB 157 0.216 79 0.6523 65.9 7
4880
SUB 157 0.2327 79 0.7003 70 6
4880A
SUB 218 0.2419 110 0.7265 84.9 8
4.0 LevelMAX Parameters for I-Tech HD VerTec V4 device files
For I-Tech HD VerTec V4 device files, LevelMAX parameters are based on the automatic
calculation of the values outlined in the previous sections and are set to Manual (JBL OEM
Factory Locked) mode to reduce the potential for accidental modification of key parameters.
Thermal limiter response times were determined by measuring the initial temperature rise for
each transducer. Taking 63% of the time taken to the projected temperature rise to 200ºC was
used to determine the ‘time constant’ of the voice coil. The value entered into the thermal time
constant was ½ of that value for smoothest transition from RMS to thermal limiting. HF units
were set to a slightly longer thermal time constant, due to their initial low operating temperature,
while their long term voltage needs to be limited to the 100 hour threshold.
LevelMAX parameters for I-Tech HD VerTec V4 are summarized as follows:
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Parameter
Auto
Advanced
Visible in Main
Panel
Peak Enable
Peak Threshold
Peak Attack
Peak Release
RMS Enable
RMS Threshold
RMS Attack
RMS Release
RMS Detector Time
Thermal Enable
Thermal Threshold
Thermal Attack
Thermal Slope (Kp & Ki)
Look-Ahead
Parameter
Auto
Increment
Peak Threshold (See
below)
1-400V
1V
Peak Release
0.1ms-10s
1ms
RMS Threshold
1-200V
1V
RMS Attack
0-10s
n/a
RMS Release
0-10s
1ms
RMS Detector Time
1ms-1s
n/a
Thermal Threshold
1-200V
0.1V
Thermal Attack
1-600s
1s
Thermal Slope (Kp & Ki)
0-10
n/a
look-ahead
0-10ms
n/a
Model
Auto
Advanced
I-Tech HD 5000
201.2
400
I-Tech HD 9000
217.6
400
I-Tech HD 12000
233.4
400
Appendix A: Table of parameters modified by each mode with LevelMAX Limiter Suite enabled
SV Value Range
Auto Peak max for each model (online).
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Appendix B: LevelMAX Limiter panel in Auto and Advanced, offline and
online.
Offline:
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Online:
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