Drawmer SL22 Sound Level Limiter - Manual (Page 5)

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1 - SAFEGUARD YOUR HEARING
As the SL22 offers the ability to calibrate and control the level of the dedicated headphone output in just the same
way as the speaker outputs it can be used to prevent hearing damage to anyone wearing headphones on a regular
basis - DJ’s, sound engineers in recording studio’s, students listening to audio via various media. As well as the
dedicated headphone output the SL22 has additional connectors on the rear that can be used for remote data
logging of its operation, or to operate external indicator’s, such as signals on the wall.
2 - CONFORM TO REGULATIONS
As well as protecting the equipment the precise calibration and volume controlling of the SL22 allows venues, such
as clubs, theatres, pubs, schools, universities etc. to conform to Local Authority Noise Regulations.
The concept and development of the original Speaker Protector was encouraged by Drawmer distributors and
installers dissatisfied with other protection systems currently available (these often take the form of a crude switch,
either turning off the power or disconnecting the speakers, both of which are ’disruptive’ in any event), and the SL22
has taken these ideas and developed them still further. The SL22 offers the same protection, but also is more
responsive and versatile. The controls are only accessible by those holding the supplied tamper-proof screwdriver,
and the rear panel XLR’s can be ‘locked away’ using the optional tamper-proof bracket - making tampering with the
volume levels extremely difficult. In addition, the SL22 has the facility to be controlled remotely, meaning that a
manager can attenuate or mute the volume as required, or it can be connected directly to a fire alarm, reducing the
volume automatically during a fire and allowing the alarm to be heard more clearly.
3 - PROTECT YOUR SPEAKERS
Whether in a large arena with a p.a. system and multiple speakers, or smaller venues such as bars and theatres,
there are few things more annoying and troublesome than blowing a speaker cone or amplifier electronics. There
are several possible causes for the sound pressure level to rise: it could be caused by sudden spikes and pops in the
system; it may be that the amplifier is too powerful or the speakers have too low a rating and increasing the volume
overloads the speakers; sudden clipping in the audio signal chain causing a sine wave; in a venue an over enthusiastic
DJ may just turn up every knob to get the gig as load as possible: whatever the reason, unlike standard compressor/
limiters, the SL22 has been specifically designed to transparently catch those unwanted SPL’s and protect your
gear. Not only will it save money by reducing the cost of speaker repairs, but also reduce ’call-out’ costs of sound
system service/repair engineers, lower sound system ’down time’ and the consequential loss of venue income, as
well as the reputation of the venue.
allowed to perform. If the SL22 receives increased signal levels, the transparent ’protection’ circuitry is activated
which maintains the specified system volume level without degradation in sound quality. With the security plate
replaced a security label can be placed across (supplied) to provide further security and show evidence of tampering
with the settings. In addition, on the right side of the panel three LED indicators complement the simple setup with
simple and ‘at a glance’ monitoring.
To the rear the difference between the SL22 and the SP2120 is just as apparent. In its development we liaised with
and were approached by local authority commissioners, installation specialists and venue owners who all advised
and recommended attributes to suit their own specific requirements, the result being the addition many more versatile
features that so many other sound level limiters lack. As well as the standard input and output XLRs (that can be
securely locked using the optional tamperproof bracket) the SL22 also features a limited headphone output, that
works in the same manner as the XLR’s, plus the ability to be controlled externally via a fire alarm or operator, and
also connections to allow data logging of the SL22’s operation, or external visual indication via a light on a wall, for
example.
Development of the SL22 and Noise at Work
The development of the SL22 has been undertaken in conjunction with a multi-national media company needing
to conform to Noise At Work Legislation and protect the hearing of the DJ’s in their radio studios. During testing
they had become very disillusioned by the current products on offer, finding that they were either so crude that
they didn’t really work, or, at best, the attenuation could be heard and was intrusive. Many products were tried,
and a few experiments, and concluded that the SP2120 was the most transparent product on the market, it just
required a few adaptations to fully suit their requirements - the SL22 is the result of this development.