# POUL PETERSEN

## Electronic design and prototype development.

##### Selecting the limiter threshold for a loudspeaker power limiter.
The two most common causes of loudspeaker damage are thermal overload and mechanical overload.
A power limiter can keep the power supplied to a loudspeaker within safe levels and thereby protect it from thermal overload. To protect a loudspeaker against mechanical overload, it must be driven only within the frequency range it is designed for.
To protect a loudspeaker from thermal overload, the limiter's threshold must be selected to match the loudspeaker's continuous power handling - normally half the power handling stated as continuous pink noise power handling - and the amplifier's voltage gain.

A JavaScript that calculates the limiter threshold is in Limiter threshold calculator for a loudspeaker power limiter.

Calculate the maximum allowable voltage across the loudspeaker:
 Variable Description Example VSP Maximum long term voltage across loudspeaker in dBu. The unit dBu is a voltage unit with 0.775 V reference. PSP The loudspeaker's long term RMS power handling in Watts. This is usually half its AES pink noise power handling. 300 W RSP The loudspeaker's nominal impedance in ohms. 8 ohms

Example:

Find the voltage gain of the amplifier used. Some manufacturers state this value in their data sheet.
Otherwise, the value can be calculated from the amplifier's nominal output power and its input sensitivity:

 Variable Description Example Av The amplifier's voltage gain in dB. PN The amplifier's nominal output power in Watts. 500 W RN Nominal load impedance for PN. 8 ohms VI Amplifier input sensitivity in volts. 1.5 V

Example:

Calculate required limiter threshold VTH:

Example:

This table shows the voltage for some typical speaker power ratings:
 Power 1 ohms 2 ohms 4 ohms 8 ohms 16 ohms 5 W 9.2 dBu 12.2 dBu 15.2 dBu 18.2 dBu 21.2 dBu 10 W 12.2 dBu 15.2 dBu 18.2 dBu 21.2 dBu 24.2 dBu 20 W 15.2 dBu 18.2 dBu 21.2 dBu 24.2 dBu 27.3 dBu 25 W 16.2 dBu 19.2 dBu 22.2 dBu 25.2 dBu 28.2 dBu 40 W 18.2 dBu 21.2 dBu 24.2 dBu 27.3 dBu 30.3 dBu 50 W 19.2 dBu 22.2 dBu 25.2 dBu 28.2 dBu 31.2 dBu 60 W 20.0 dBu 23.0 dBu 26.0 dBu 29.0 dBu 32.0 dBu 75 W 21.0 dBu 24.0 dBu 27.0 dBu 30.0 dBu 33.0 dBu 100 W 22.2 dBu 25.2 dBu 28.2 dBu 31.2 dBu 34.3 dBu 125 W 23.2 dBu 26.2 dBu 29.2 dBu 32.2 dBu 35.2 dBu 150 W 24.0 dBu 27.0 dBu 30.0 dBu 33.0 dBu 36.0 dBu 200 W 25.2 dBu 28.2 dBu 31.2 dBu 34.3 dBu 37.3 dBu 250 W 26.2 dBu 29.2 dBu 32.2 dBu 35.2 dBu 38.3 dBu 300 W 27.0 dBu 30.0 dBu 33.0 dBu 36.0 dBu 39.0 dBu 400 W 28.2 dBu 31.2 dBu 34.3 dBu 37.3 dBu 40.3 dBu 500 W 29.2 dBu 32.2 dBu 35.2 dBu 38.2 dBu 41.2 dBu 600 W 30.0 dBu 33.0 dBu 36.0 dBu 39.0 dBu 42.0 dBu 800 W 31.2 dBu 34.3 dBu 37.3 dBu 40.3 dBu 43.3 dBu 1000 W 32.2 dBu 35.2 dBu 38.3 dBu 41.2 dBu 44.3 dBu 1200 W 33.0 dBu 36.0 dBu 39.0 dBu 42.0 dBu 45.1 dBu 1500 W 34.0 dBu 37.0 dBu 40.0 dBu 43.0 dBu 46.0 dBu

These pages lists the voltage gain for different power amplifiers: AB International, Amcron (Crown), Carver, Cerwin Vega, Dynacord, Harrison, HH Electronics, JBL, NAD.

Poul Petersen, C/Faya 14, 35120 Arguineguín, Las Palmas, Spain.
Tel/Fax: (+34) 928 152 807, Skype: poul.petersen.gc.
http://www.poulpetersen.dk, E-mail: pp@poulpetersen.dk
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