‘Auto IIR‘ is not used in this example (filter adjustments are applied manually). Auto IIR is available in FIR Designer v4.2 & above. Learn more about using Auto IIR for automatic EQ generation.
Room Tuning with IIR Filters | CASE STUDY
Room tuning using IIR filters commonly involves taking live, continuous measurements while adjusting processor settings. Alternatively, it can be an iterative process of measuring and filter adjustment. FIR Designer’s ‘IIR Filters’ capability (with branded IIR filter emulation) is a powerful and convenient tool for room tuning, automating much of the iterative process & vastly reducing the time that it takes to achieve an optimally tuned system.
This case study provides a walk-through using FIR Designer to tune a system using only IIRs.
For processors not solely limited to IIR filters (i.e. processors with user-accessible FIR settings), FIR Designer takes room tuning to another level with it’s ability to create arbitrary-phase filters that perform room EQ, phase-correction and loudspeaker magnitude & phase matching.
Background
An Australian church recently completed a major building renovation that included significant upgrades to some elements of the audio and visual systems.
To minimize costs, certain existing elements of the audio – including the FOH loudspeakers – were retained, resulting in a combination of old & new equipment.
Physical changes to the main auditorium required repositioning the four existing main FOH loudspeakers into two clusters; each providing coverage to half the room. Seats roughly in the centre-line of the room would experience some overlapping coverage and some stereo effect.
A new four channel QSC PLD4.3 was installed to drive the four (12″+horn) loudspeakers individually.
Room Layout & Coverage
The following EASE diagrams and simulations show the room dimensions, loudspeaker cluster locations and right-side coverage. (The left-side coverage is mirror of the right-side.) The room is 21 m (68.9 ft) wide and 11.7 m (38.4 ft) deep. The two loudspeaker clusters were hung approximately above the front corners of the stage and with the underside of the loudspeakers approximately 4.1 m (13.4 ft) above the floor. Initial loudspeaker aiming was determined in EASE and adjusted on site.
IIR filter sets for the amplifier DSP were created with FIR Designer using averages of loudspeaker measurements taken throughout the seating area.
Room Measurements
The left and right halves of the room were measured separately. In each half, both loudspeakers in the cluster were on. Twelve transfer-function measurements – using Rational Acoustics Smaart® v8 – were taken in various seating locations in each half, at approximately 1.2 m (4 ft) above the ground.
See a list of loudspeaker measurement file formats & brands supported by FIR Designer