All that said, we may be able to hear system frequency response, but our hearing is much more sensitive to peaks in response than dips.
We can’t delineate what is direct sound arriving from the loudspeaker and what the room is adding to the direct sound.
We can hear the effects of phase on frequency and transients, but we can’t hear absolute phase.
We can’t identify the differences in phase at a given frequency just by listening.
We also can’t determine small time arrival differences (
<40-50 ms), only their effect on frequency response and localization perception.
Yet all of these things have a significant impact on multiway loudspeaker performance, both frequency and polar response.
They all have an impact on closely spaced arrays of multi-way loudspeakers. They all have an impact on the relationship between main and delayed loudspeaker systems.
Virtually all of the systems we deal with include one or more of these conditions. This is why the successful optimization of most any sound reinforcement system must include the use of both of your well rested, well cared-for ears and the educated and proper use of a good, high resolution, 3D (that's magnitude, frequency, and time) measurement system.
Real-time analyzers (RTAs) can only show you the sum of all energy arriving at the microphone. It can't show you arrivals, direct vs. reflected sound, phase shifts, etc. -- all things that give you clues as to what can and cannot be equalized, and maybe more importantly, what might be done physically to fix response anomalies. The best equalization fix might be to adjust the loudspeaker array rather than a filter.
So you might say "I run a touring live sound rig and don't have time to do all this measuring and tweaking!" Granted, it can take hours, even days to properly measure and optimize a complex loudspeaker system. But this does not mean the process can't be applied to touring systems as well.
Much of the time-consuming part of measurement can be performed in the shop leaving the final touches to be done at the gig. How is this possible?
Because proper system optimization involves three basic steps.
1. DIRECT RESPONSE
This is where you make corrections for anomalies inherent to the loudspeaker, set crossovers, transducer alignment, etc. These corrections are independent of the room where the loudspeaker is located and are probably easier accomplished in the shop or rehearsal hall.
You want to maximize the direct sound from the loudspeakers while minimizing reflected sound and noise. You also want quality time to focus on the process rather than trying to squeeze this in between load in and sound check.
Get it done in the shop and you don’t have to do it again unless there is a significant change in the loudspeaker system. This is also the place to perform flat phase tuning.
The proper use of a high-resolution measurement system is critical to completing the first step. Certainly you will want to perform listening tests as you progress to ensure you are getting the system response you want/need, but measurement will help you get there far better than listening alone.