Rated 4.9 (120 reviews)
The Sentry MK2 is the cut-off noise limiter most UK environmental health officers already know, and the one written into a lot of premises licence conditions. A microphone measures the sound level in the room; a bar display shows staff and the DJ how close they are to the limit, a warning lights just before it, and if the level stays over the limit the Sentry trips a contactor and removes mains power from the music system until someone resets it. It works with any PA, band or DJ rig because it controls the power, not the audio signal, and every adjustment sits behind a sealed cover so the level the EHO signs off is the level that stays.
2 levels
Thresholds · Switchable
10 LED
Display · -20 to +3 dB
4 weightings
Lin · C · A · Bass
Fire alarm
Interface · Built in
Contactor not includedThe Sentry MK2 is the monitoring and display unit. It needs a contactor to switch the mains: the Formula Sound 071 32A contactor (single ring) is the matching part, or it can drive your own mains-coil contactor up to 60 VA, or use its isolated relay contacts. Installation should be carried out by a qualified electrician to BS 7671, and the Sentry itself must be powered from a supply the contactor does not control.
Features
Cuts mains to the sound system via a contactor when the limit is exceeded for a set time
Two independent threshold levels, e.g. a lower limit after 11pm or when doors or windows are open
Level 2 selected by switch, time switch or door/window reed contacts, with a front-panel LED
Linear, C, A or Bass weighting, so low-frequency complaints can be targeted directly
10-segment display from -20 dB to +3 dB, with WARNING and OVER LIMIT stages
Fire alarm interface: voltage applied, voltage removed, contacts closing or opening
Security loop trips the unit if broken, for tamper switches or equipment racks
Microphone tamper circuit detects a covered or disconnected mic
Adjustments under a screwed cover sealed with non-reusable security labels
External microphone input with selectable phantom power for a remote measuring mic
Remote LED outputs and remote reset input for the 074K or 074P reset boxes
Mains output (60 VA) for a warning lamp in the room
Specifications
| Type | Cut-off sound level limiter (mains disconnect) |
| Threshold range | 85 to 125 dB (Formula Sound product page), two levels |
| Trip delay | Adjustable, factory set around 20 seconds |
| Weighting | Linear, C, A or Bass (jumper selected) |
| Display | 10 LED segments: -20, -10, -7, -5, -3, -1, 0, +1, WARNING +2, OVER LIMIT +3 dB |
| Trip outputs | Low-voltage drive for 071 contactor (12 to 18 V DC, under 100 mA); switched mains up to 60 VA; isolated relay contacts (NO, NC on request) |
| Inputs | External mic (dynamic, capacitor or electret, phantom selectable); fire alarm; security loop; level 2 select; remote reset |
| Remote outputs | Mic tamper, level 2, warning and reset required LEDs; slave display terminals |
| Reset | Manual, local or remote; powers up in the tripped state |
| Power | 240 V AC approx. 1 A, or 120 V approx. 2 A (internally selectable) |
| Enclosure | Polycarbonate, grey with clear hinged cover, wall mounted |
| Dimensions (W x H x D) | 320 (incl. hinges) x 261 x 120 mm |
| In the box | Sentry MK2 unit, security labels. Contactor not included |
| Part number | 073 |
