Formula Sound SENTRY MK2 Manuel de l'utilisateur - Page 7
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Setting The Permissible Volume Level continued
The actual sound pressure level (SPL) at which the unit operates can only be determined by
measuring the noise level using a calibrated sound pressure level meter and adjusting the unit
accordingly.
Alternatively the unit may be adjusted using trial and error but this should be used only as a
temporary measure or last resort. Measuring the sound level and setting to a limit agreed with the
local area official is the only recommended method.
An internal measuring microphone is fitted which will be suitable for most applications but should
the need arise an external microphone can be connected. The external microphone may be a
moving coil type, capacitor or electret. Microphone phantom power is provided and may be
selected as required. Select a microphone with the required frequency response and polar
response. (Please telephone our technical department if help is required).
NOTES:- If the unit is to be used in an entertainment venue to control a band or disco use a meter
with either a linear scale or 'C' weighting response.
The frequency response of the measuring circuit of the Sentry may be selected to be, Linear (Flat
response), 'C' (Conventional "C" scale) or Bass (LP filter @300Hz 12dB per octave slope.)
See Drg No 879
'A' weighting is a frequency response curve that resembles the human ear response. It is much
more sensitive in the mid 500Hz - 5kHz region. It is not recommended for entertainment venues
as it is less sensitive to the bass regions where most problems lie. An "A" weighting filter may be
fitted as a factory option if required.
SECURITY LABELS ARE PROVIDED. THESE SHOULD BE FITTED TO
COVER THE SCREW HEADS HOLDING THE REMOVABLE COVER IN
PLACE AND WILL REVEAL ANY UNAUTHORISED ATTEMPT TO CHANGE
THE THRESHOLDS
ALWAYS FIT SECURITY LABELS AFTER ADJUSTMENTS HAVE BEEN MADE.
EXTRA LABELS ARE AVAILABLE FROM FORMULA SOUND IF REQUIRED.
Remember that the acoustic characteristics of a venue will change depending on the number of
people in it. Our experience has shown that it is always advisable to take readings when the
venue is in use. It would be a wise precaution to allow in your costings for a site visit during
opening hours to take measurements and make final adjustments.
Security Loop
Provision to connect a security loop is provided. This may be required to detect open doors or
windows that would impair the sound proofing of a building, etc. Magnetically operated reed
switches of the type used in intruder alarms are most convenient for this application. If this facility
is not required a wire link must be connected to allow the Sentry to work normally. (see Drg No
879)
A front panel indicator shows if the security loop is opened.
Tampering
Correctly locating the unit out of reach is the best form of security.
If you find that you have problems with unauthorised persons tampering with the settings, security
screws are available to replace the cover screws, a special key is also supplied for the fitting
and removal of these screws. Contact FORMULA SOUND sales office for more details
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