Setting Accurate Limiter Thresholds - PROEL DSO26 User Manual

DSO26 User Manual

Setting Accurate Limiter Thresholds

The limiters built into the DSO26 are intended to be used for for loudspeaker driver
protection, as opposed to amplifier protection. All modern professional power amplifiers
designed for live sound use have their own limiters which are tailored to protecting the
amplifier from clipping.
The following section describes how to set up the DSO26's limiters to provide exceptional
protection against driver overheating, and cone over-excursion.
Most speaker systems are given a power rating in Watts RMS. This is the maximum
continuous power that the system will handle and often appears very conservative. In
reality, as music program is far from continuous in nature, the peak power of the system is
much higher – up to ten times the continuous figure. Any limiter, which is to protect the
driver from damage, must be able to fulfil the following tasks.
Have an attack time which is calculated to allow transients through but keep the RMS level
below the speaker manufacturers specification;
Have a release time which is sufficiently long to avoid the limiter itself modulating the
program ;
Be intelligent enough to adjust the envelope of the limiter according to the frequency
content of the program material.
The DSO26's limiters are capable of performing all these tasks. The only parameter which
the user must set manually is the threshold, and it is crucial that this is done correctly.
Consider the table below.
dB
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
Using this table it is a straightforward procedure to work out the required setting of the
limiter thresholds for the system. Follow the steps described overleaf.
First, check the RMS power rating of the speaker system, and its impedance.
Look up this value in the table above, using the closest value below the rated power of the
speaker system. Note the corresponding 'dB' value.
Check the gain of your amplifier, which needs to be in 'dB'.
Ratio Vrms
Pwr 8 Ω Pwr 4 Ω
177.83 137.74 2371.71 4743.42
158.49 122.77 1883.91 3767.83
141.25 109.41 1496.45 2992.89
125.89 97.52 1188.67 2377.34
112.20 86.91 944.19
100.00 77.46 750.00
89.13 69.04 595.75
79.43 61.53 473.22
70.79 54.84 375.89
63.10 48.87 298.58
56.23 43.56 237.17
50.12 38.82 188.39
44.67 34.60 149.64
39.81 30.84 118.87
35.48 27.48 94.42
31.62 24.49 75.00
Pwr 2 Ω
9486.83
7535.66
5985.79
4754.68
1888.39 3776.78
1500.00 3000.00
1191.49 2382.98
946.44 1892.87
751.78 1503.56
597.16 1194.32
474.34 948.68
376.78 753.57
299.29 598.58
237.73 475.47
188.84 377.68
150.00 300.00
35