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GLOBAL LIMITER-CONTROLLER LD500 (OUT OF PRODUCTION)

This model achieved a simple product adapted to the needs of authorities and leisure business owners, as it is respectful with the laws without damaging the commercial activity. After several years we stopped its production and have increased performance with the new model EQlimit.

The limiting core is a sophisticated circuit that controls the audio signal that feeds the power amplifiers. The regulation is made by means of VCAs (Voltage Controlled Amplifiers) that vary their gain as a function of a signal measured by a microphone located in the hall that measures the real sound pressure level (SPL) and is shown on a remote digital display, calibrated in dB with "A" weighting. Or, alternatively, by means of the audio program signal, leaving the microphone only for level indication and alarm generation.

The control signal is compared with levels programmed and measured at its display. In case of limitation, even if the input signal or power amplifiers where far increased, the level in the house will not exceed the prefixed threshold. The limiter's action is signalled with a series of LEDs marked with 5, 10, 15 and 20 dB. Though it does not signal above these quantities, the device will keep on limiting even if the signal is increased more than 60dB. When the input signal exceeds a level near the maximum, the limiter signals, by means of a LED called AUDIO, to advice of possible signal distortion.

The limiting circuit is one of the important advantages of this device, because its design imposes a maximum level but without abrupt music fading, attaining a high quality in the listening even with high attenuation levels. This avoids the trend of many users to manipulate when the effects of the limiter alter the music quality. Also it remembers the last attenuation level when the input signal is interrupted, in such a way that when the input signal is back there are no abrupt high levels as happens with other similar devices that produce high peak levels as they adapt again to the needed attenuation level.

It has a global gain adjust for both channels, by means of which we can proportionate the sound system's maximum level to the real level required, avoiding the need to reduce that difference by means only of active limitation. This ensures a maximum sound level without the limiter limiting normally.

The alarm functionality, if the maximum SPL is exceeded continuously, makes the device mute the sound output during an adjustable "punish" time, if we desire so. This situation is signalled in the remote display by means of a LED marked ALARM and a LED marked MUTE. This alarm generates a level alarm event recorded in non-volatile memory together with its date, time and SPL that produces such alarm, for later inspection by the competent authority.

For security against manipulation, it has a detecting circuit that generates a manipulation alarm if the microphone is disconnected, displaced and/or covered with isolating materials in an attempt to alter its measures, registering the moment in which this change in efficiency appears in the system.

All these adjustments are only possible by means of control software, SCL, that requires a license leased to the user and a password for the limiter, which avoids unauthorised manipulation. For more security against manipulation, the rear panel connections and the microphone, all have protecting sealable lids.

The remote display is housed in a separate enclosure in order to install it at an appropriate location, making possible to provide permanent information about the limiter's action to the user of the system.

The mains input connectors and cables comply with security standards and are of the normalized type IEC, with several international organizations' approvals, and have earth connection. The device has protecting fuse accessible from the outside. All this in order to comply with the "Low Voltage" directives. At the same time the design and materials used make the device comply with the European directive for electromagnetic compatibility.

As an ideal complement for its installation and adjusting, the device has a pink noise generator for initial manual calibration. This allows to make the adjustments and measures in a more comfortable and reliable manner.