Proel PC260 - Manual (Page 26)

26
INFORMATION NOTE: Speaker protection setting
Replacing a professional speaker is an expensive cost and reducing this risk is good, so many users want to know how to set a limiter
properly for the speaker protection .
The PC260 processors, like other loudspeaker processors, can protect the speaker from excessive heating using the OUTPUT LIMITER
(though it is not possible to protect a speaker from every possible cause that occurs to damage it, such as over-excursion, very
unnatural sound signals or an erroneous cross-over filter setting) .
To protect a speaker from over heating you have to know some technical data:
1) The speaker power handling (P
AES
) measured with the AES2-1984 (r2003) standard (AES Recommended Practice - Specification of
loudspeaker components used in professional audio and sound reinforcement), usually it is indicated in the speaker technical data in
W
AES
. This standard is actually the best method to know the power handling capability of the speaker for a standard music program .
In case of a group of speaker connected to the same channel you have to consider the whole power handling .
2) The nominal impedance (z
NOM
) of the speaker and/or the resulting nominal impedance of the group of speaker connected at the
same amplifier channel (typically 4 or 8 ohm) .
3) Choose an amplifier that can drive this speaker with a nominal continuous power (P
AVG
or P
CONTINUOUS
or P
(EIA 1KHz THD<1%)
) higher than
the specified power handling of the speaker . Obviously this power must be delivered from the amplifier for the nominal impedance
specified . The power of the amplifier must be always higher than that of the speaker in order to avoid the signal clipping, an event
that can seriously damage or destroy a speaker
4) A typical professional amplifier has two operating modes that can be selected by a switch in the rear panel:
The first mode is at "nominal input sensitivity", which means that "full power is delivered when the input signal is XX dBu", typical
values being 0dBu or +4dBu .
The second mode is at "fixed gain", which means that the amplifier voltage gain is fixed at a specified value expressed in dB, typical
values being 26 or 32dB (GAIN) .
To simplify the calculations we consider only the second case with an amplifier with a fixed gain .
Calculate the limiter setting using the following equation:
As example we presume to have a speaker with the following data: P
AES
= 300 W Z
NOM
= 4 OHM
So we choose an amplifier capable of 500 W with a load of 4 ohm for channel with a fixed gain of: GAIN = 32 dB
Please note that in some cases you can obtain a negative result .
SOME TIPS
• To protect the high frequency drivers from dangerous feedbacks in live environments we suggest to set the limiter 3 dB under the
calculated value .
• In some speaker systems you can note that the low-mid frequencies are limited before the high-mid frequencies. This can be due
to the fact that the program reproduced is more rich in low frequencies (which usually have a higher energy contents) than in high
frequencies, so the LF limiter is activated before and more often than the HF limiter . In this cases, the system sound can become very
harsh and to restore a natural sound you'll need to set the HF driver limiter some dB under the calculated value (usually 3 - 6 dB) .
• Often using bridged amplifier you have to add 6 dB to your amplifier GAIN: see the amplifier manual.
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(𝑑𝑑𝑑𝑑𝑑𝑑)
= 20 × log
10
�
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0.775
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𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿
(𝑑𝑑𝑑𝑑𝑑𝑑)
= 20 × log
10
�
√300 × 4
0.775 � – 32 = +1 𝑑𝑑𝑑𝑑𝑑𝑑
𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿
(𝑑𝑑𝑑𝑑𝑑𝑑)
= 20 × log
10
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× 𝑍𝑍
𝑁𝑁𝑁𝑁𝑁𝑁
0.775
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𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿
(𝑑𝑑𝑑𝑑𝑑𝑑)
= 20 × log
10
�
√300 × 4
0.775 � – 32 = +1 𝑑𝑑𝑑𝑑𝑑𝑑