A hallmark of many people that I have met in the world of professional audio is the ability to get the show working quickly. Behind the scenes of most live audio and installation deployments are a set of compromises, sometimes small and sometimes not so small. This month’s article is a tale of such compromises.
When FRONT of HOUSE editor George Petersen approached me with the idea of writing about the use of nearfield monitors, I did not immediately jump at the topic. Early in my attempts at mixing, I used to stay buried in headphones, to the detriment of the audience. Once I stopped heavily using headphones, I was forced to develop the auditory muscles to become a better mixer. As a result, I generally discourage the regular use of headphones or supplemental monitoring to those who are learning the mixing craft.
Personal opinions aside, the live audio world is full of acoustically challenged locations where nearfield monitors are used to positive effect by mix professionals, either to supplement what they hear from the main P.A. or as a consequence of not being able to hear the main P.A. Especially in churches, there are countless sound booths, broadcast suites, mixing boards in/under balconies or other compromised mix locations. Such is the location we will walk through this month.
A Stopgap Measure
In one particular case, a house of worship client was putting off a major sanctuary renovation for several years until a new kids’ space was constructed. The plan was to increase purchasing leverage by upgrading the existing space at the same time as the new space was outfitted. The existing system was tired, the DSP was starting to experience memory glitches, and coverage of the tech balcony where FOH was located was less than ideal.
The goal was to make it to the next buildout in a fiscally responsible way, using the existing infrastructure. For starters, we were able to scavenge a DSP unit from an adjoining auditorium space as a consequence of re-tuning its system. Next, we replaced the HF diaphragms in the existing boxes to bring back some top-end sparkle. Finally, the boxes covering the floor seating were re-aimed to optimize coverage to those spaces. Then the system was re-tuned for the best overall floor response we could achieve.
The Tuning Process
Fig. 1 shows the result of the above as magnitude response displayed in SMAART. The green trace represents the average of a number of responses taken across the floor of the venue, and the yellow trace is the same collection of averages within the tech balcony. Note that subwoofers were turned on for the balcony (yellow) traces, but not for the floor (green) trace. Also note that these SMAART traces represent the average of multiple measurements, but there is almost no smoothing applied to the result.
Fig. 1 demonstrates a common theme in the pages of this column. Namely, that our comparatively small speaker boxes have good directivity at high frequencies, but that low and mid frequencies are not much controlled for directivity. In this case, sound above 3k Hz starts to roll-off in the balcony once the horn starts to provide pattern control.
From Fig. 1, it’s clear that coverage of the floor is workable, and both the low and midrange of the P.A. reaches the balcony — albeit not necessarily as smoothly as we would want. To help out the mixer person, we added a set of small powered nearfield monitors at the mixing position. The raw response of the nearfield monitors (purple) is compared to the balcony average (yellow) in Fig. 2.
For those readers not used to looking at SMAART, welcome to the messiness that is real-world measurement data. The peaks at 60 Hz and 180 Hz should be ignored, as these are from power supply leakage that made its way into the measurements. However, the two higher frequency dips are the result of very real reflections off the environment near the mixing desk.
Those dips from reflections are not something that can be tackled by equalization, and they would change in frequency and depth depending on the surroundings adjacent to the monitors. Such is an inherent limitation of using speakers in close proximity to reflective surfaces. These sort of dips are common when measuring nearfield speakers.
We now compare the raw nearfield response (purple) to that from the floor of the venue (green) in Fig. 3.
From Fig. 3, we can see the dips in the nearfield will be essentially filled in from spill provided by the main speakers. We can also see that the character of main floor response is more forward in the upper midrange, but less bright in the uppermost octave, than that of the nearfield monitors.
At this point, we applied a mixture of measurement and listening to decide on processing that brings the nearfield monitor response in alignment with the floor response. The before (purple) and after (pink) result for the nearfield monitors is shown in Fig. 4. The changes primarily shape the last octave and the upper midrange.
Next, we can overlay the floor average (green) with the final nearfield response (pink), as shown in Fig. 5. Getting the two traces from different loudspeaker systems to overlap perfectly would be an act of futility. Instead, we landed on a nearfield response that was judged similar in character to what was happening on the floor by all parties, keeping in mind the goal of helping any FOH mixers in the balcony do a better job of mixing for the people on the floor.
Once the equalization for both the floor and nearfields was in hand, the next step was to align the phase behavior between the main P.A. and the nearfields. Due to the reflections off the console, the alignment goal was to have 200 Hz to 1k Hz from the main central loudspeaker be as much in phase with the nearfield monitors as possible. This was so the main system would fill in any nearfield reflection dips with maximum coherency.
Achieving Balance
The final step was carefully balancing the level between the floor P.A. and the nearfield monitors. This was done by ear, with the goal of subtly focusing the sound field at the mixing desk, while avoiding a sense that the nearfield monitors completely replaced the sound from the main system. The net result was surprisingly pleasing within the confines of the project, and the system served its purpose until the new room was built.
The Wrap
While we have focused on a specific example, the point here is to demonstrate the application of modern measurement techniques to integrate a set of nearfield monitors with a larger P.A. system. By supplementing a poorly located mixing location, the nearfields help the client live to fight another day.
Creating a nearfield picture of what the P.A. is doing in a larger area required looking at the potential of cancellation from nearby surface reflections, along with matching the response of different loudspeaker systems and a (midrange-focused) approach to aligning two different zones of the P.A. system.
An essential part of the process is taking and using measurements and understanding how to interpret what the software is capturing. Here, we have barely cracked the scope of that topic. However, any aspect of the measurement should ultimately be correlated to physics principles about how loudspeakers behave. The more we grasp the physics, the more evident patterns in the measurements will become.
