6.1 Setting system limiters
You can use the RMS limiter in the DSP to set the system limiters.
About this task
We recommend that you set up the system gain structure with the amplifier channel volumes turned all the
way up if the volume setting is easily accessible by any user, such as via a front-panel knob that is not behind
a security panel. Disconnecting the loudspeakers from the amplifier during this process will most likely result
in conservative settings. You can connect the loudspeakers to the amplifier during this process if caution is
observed when increasing the stimulus level and confidence in the measuring setup is secured. In addition,
we recommend wearing hearing protection when setting up system limiters via the following procedure.
Caution: Loudspeaker damage as a result of exceeding the power handling specifications defined in
Dolby Speaker System 128 and system components specifications is not covered under the warranty.
Caution: Hearing damage can occur by prolonged exposure to excessive sound pressure level (SPL);
the loudspeaker is easily capable of generating SPL sufficient to cause permanent hearing damage to
performers, production crew, or audience members. Caution should be taken to avoid prolonged
exposure to SPL in excess of 90 dB.
It is recommended to set the system limiter for each amplifier channel individually. However, you may copy
the limiter settings to other channels if those channels share identical loudspeaker models, identical
amplifier models, and identical gain structure in the signal path (including any amplifier front-panel volume
controls).
Procedure
1. Connect a wide-bandwidth multimeter with averaging to the amplifier output.
A wide-bandwidth meter has a rated measuring bandwidth of at least 20 kHz with an averaging function
that is more than five seconds (very important for low-frequency outputs).
2. Access the RMS limiter setting in the DSP and set it to the maximum value, such that no limiting should
occur.
3. Set the attack and release times based on the high-pass filter (HPF), according to the recommended
digital signal processing settings for the respective loudspeaker being measured. If that data is not
available, we recommend these settings:
• HPF <30 Hz: attack 45 ms, release 720 ms
• HPF 30 Hz to 59 Hz: Attack 16 ms, release 256 ms
• HPF 60 Hz to 99 Hz: Attack 8 ms, release 128 ms
• HPF 100 Hz to 224 Hz: Attack 4 ms, release 65 ms
• HPF 225 Hz to 449 Hz: Attack 2 ms, release 32 ms
• HPF 450 Hz to 999 Hz: Attack 1 ms, release 16 ms
• HPF 1 kHz to 1.99 kHz: Attack 0.5 ms, release 8 ms
• HPF >2 kHz: attack 0.3 ms, release 4.8 ms
4. Mute all outputs into the system, except for the output you are setting.
5. Play low-level pink noise into the amplifier channel, and then confirm that the expected loudspeaker is
playing (if the loudspeaker is connected to the amplifier) and the multimeter is reading the voltage.
6. While monitoring the meter, slowly turn up the pink noise until the Vrms is at the published rating.
For low-frequency outputs, an average of at least five seconds at the same pink-noise level is required for
the reading to stabilize. Typically, some amplifier clipping will occur. However, if the amplifier clipping
light is almost solid, stop increasing the pink noise and leave it at a Vrms level below the published rating.
7. While pink noise is playing at the rated Vrms (or there is heavy amplifier clipping), turn down the
threshold on the root mean square (RMS) limiter block until the measured Vrms goes down slightly.
8. Turn up the stimulus gain, and then confirm that the Vrms does not increase beyond the rated Vrms. If it
does, turn down the limiter threshold again until the Vrms is not above the loudspeaker rating when the
stimulus is driven heavily.
System limiters
Dolby Speaker System 128 Owner's Manual
38
8800293 Issue 2
27 October 2021
