The UREI 539 Room Equalisation Filter Set is a professional active equalisation system designed specifically for room tuning and system alignment in fixed installations, sound reinforcement, broadcast, and critical monitoring environments. Released in 1986 as the successor to the highly regarded UREI Model 529, the UREI 539 introduced significant improvements in performance, flexibility, and noise characteristics while adding new features intended to simplify accurate room equalisation and long term system stability.
The UREI 539 is built around true L C derived filter networks, chosen for their low noise performance, high reliability, and predictable behaviour when multiple filters are used simultaneously. The unit provides 27 individual active band reject filters, each centred on standard ISO one third octave frequencies ranging from 40 Hz to 16 kHz. Each band offers continuously variable attenuation from 0 to 15 dB via vertical, stepless slide controls, allowing precise shaping of room response while maintaining a clear visual indication of the overall equalisation curve.
In addition to the graphic equalisation section, the UREI 539 includes independent high pass and low pass band limit filters to control low frequency rumble and high frequency roll off. The low cut filter is a twelve dB per octave Butterworth design, continuously adjustable from 20 Hz to 250 Hz. The high cut filter is also Butterworth, adjustable from 3.5 kHz to 20 kHz, with a selectable slope of either six dB or twelve dB per octave. These filters allow accurate control of band end contouring and the creation of controlled house curves in installed sound systems.
The active filter networks are minimum phase designs with optimised skirt characteristics, ensuring smooth combining action with minimal ripple and phase shift when multiple bands are attenuated. An adjustable front panel gain control provides up to 20 dB of gain to compensate for attenuation introduced by the filters and to establish maximum system gain before feedback. A front panel EQ In Out switch allows the entire equalisation network to be bypassed, restoring unity gain for direct comparison and system testing.
The UREI 539 offers balanced bridging differential inputs and floating, transformer isolated outputs, providing excellent noise rejection and compatibility with professional audio systems. Signal to noise ratio exceeds 110 dB at maximum output, and the unit is capable of delivering up to +24 dBm, ensuring wide dynamic range and clean operation in demanding environments. LED indicators provide clear visual feedback for power status and overload conditions, with signal levels monitored at both the input and output stages.
Power is supplied by an internal regulated power supply, selectable for operation on either 100 to 125 volt or 200 to 250 volt AC mains at 50 or 60 Hz. The UREI 539 is housed in a robust 19 inch rackmount chassis with a brushed clear anodised aluminium front panel and a cadmium plated steel chassis. An optional security cover was available to protect all front panel controls from accidental adjustment or tampering in permanent installations.
Features
- 27 band one third octave room equalisation system
- True L C derived active filter networks
- 0 to 15 dB attenuation per band
- ISO standard centre frequencies from 40 Hz to 16 kHz
- Independent adjustable low cut and high cut filters
- Selectable high frequency slope for band limiting
- Optimised minimum phase filter combining
- Front panel EQ bypass and gain adjustment
- Balanced input and transformer isolated output
- Optional security cover for fixed installations