Tuning & Optimizing Large-Scale Concert Sound Systems

Step 8 – Optimizing the System: Balancing and Aligning All Support Sections to the Mains

The goal of the final system optimizing process is that when the engineer is running the show he can be absolutely confident that what the vast majority of the audience is hearing in all other areas of the venue is matched as closely as possible in terms of tonality and balance to what he is hearing at the mix position from the mains.

After all the sections of the full system are individually “tonally” matched to the mains the next step is to get the “imaging” between them and all the support systems correct.

There are a couple of methods that will work well but the more exact one is of course to place the measurement microphone at a central overlapping area between the two systems and perform a time delay measurement for each system separately then add an offset time delay difference to the support system. For the front fill system, the reference microphone should be moved to a position where the best imaging will be between the mains and the fills (i.e., slightly off center at approximately the fourth seat row). Unfortunately this exact method is totally unusable outdoors with any wind present and takes time, which at most show setups, is not always available.

A really quick method that can be used very reliably under all conditions for all elements of the total system (especially the delay systems) is to create a “click track” on a CD disc or other playable media. This can be made easily by tapping a coin edge onto a selected metal surface multiple times and then EQing (i.e., eliminating any low frequencies) and looping it using music editing software to create a long (30 minutes) continuous series of very short, sharp, high-frequency transient “clicks” that when played through the system make it remarkably easy to align almost any pair of sound sources by timing one source to another until only one distinct click is heard without any doubling/time offset effects present. This method assumes of course that when you are setting this timing (“imaging”) you are listening within the central overlapping area of the two systems where you want the imaging to be at it’s best for the audience.

Once the imaging between all the sections of the full system are done the next step is to time and balance the levels of all the support systems relative to the mains.

Unmute but turn down all the master levels for each of the support systems, leaving only the main left and right system on and set to the normal operating level. With a favorite music track playing at a moderate level walk to an ideal position between the mains and the first support system you want to optimize say one of the side support systems. Using a wireless tablet or with an assistant on a radio at the FOH control area slowly turn up the master level of the section of the support system until it is perfectly balanced against the main system. Once you feel that the balance is very close walk back and forth through the whole area while muting and unmuting the support system to get a feeling of what the that support system is doing relative to the mains system. Correct the level (and maybe even the offset timing!) of the support system as necessary. The aim is to get the balance to be as seamless as possible.

Repeat this process for all the other support sections of the total system until each and every section of the sound system is tuned, timed and balanced relative to the left and right mains system. For front fill systems, adjusting the timing carefully by decreasing the offset time slightly and adjusting the level can “pull” the imaging down closer to the stage for the audience in the front. For delay systems always remember to adjust the timing/level for the “Haas Effect” to get the correct imaging back to the mains.

This optimization process is a little complicated but, if done correctly, will not only balance the levels between all the various system sections as they relate to the L/R mains but also create perfect sound imaging BETWEEN those various elements for the audience members that happen to be situated in areas where they can hear overlapping sections of the full system.

Up until this stage we (should) have had all the sub bass systems muted for all of the tuning and optimizing steps (except for the subs/mains phase alignment operation!) which ensures that the main system together with all the various support systems will sound as even and balanced as possible for the majority of the audience areas without the influence of the Sub Bass systems which may be more efficient in certain areas of the audience areas and ruin our perspective of the low frequency balance of the total system.

When setting up the level balance between the low frequency elements of the sound system and the Sub Bass systems it is vital that the Sub Bass systems should always be set only ever as an “extension” of the main system low frequency sections and not as a separate (louder!) entity. If dramatic amounts of low-frequency “sub” energy is required for certain types of music it should be added within the “mix” on the console so it translates to any live recordings, broadcast feeds etc.

Unmute but turn down the master level for the Sub Bass system and while playing a favorite track on the full system slowly bring up the Subs master level until the Subs become a true low-end “extension” (only) of the existing system low frequencies. Mute and unmute the subs to check what they are actually adding to the low frequencies and to check if the room is handling all that extra low frequency extension. If the room is not then keep the subs down in level as they may be making the overall system low-frequency clarity worse rather than better in a difficult venue!

Step 9 – Optimizing the System: The Final Tuning and Voicing of the System

Once all of the previous steps have been finished and with the full system now unmuted, put pink noise into the system a last time and then voice the full system a final time to carefully “touch up” any minor tuning anomalies required to correct for the effects of the total system summation and interaction. Keep any of these final adjustments to a minimum otherwise all of the previous tuning work will be lost. The final optimization process is the key to great, consistent sounding shows in any venue with any type of system.

While the soundcheck or show is actually running with a really good system tune (in an acoustically stable venue!) you should see a pretty flat line on the FFT system. If the line is constantly high in the high end then the system tune is too bright – too low in the high end the tune is too dull same for the mids same for the lows although the lows below 100Hz may be very inaccurate (always too high!) due to room decay etc. so use your ears to decide if the low end is translating the low end of the mix from the console.

With this FFT setup remember you are only looking for an average of a flat line response. Don’t keep changing things based on one song which may have many peaks and dips based on that song’s particular texture – wait and check two or three different sounding songs and if something is constantly sitting out then adjust it slightly. Leaving this FFT measurement setup fully connected and with the measurement microphone next to the mixing console during the soundcheck and the show you can continuously see on the FFT display if the sound system is (on average) correctly reproducing what is coming out of the mixing console – the “mix!

**A LAST WORD OF CAUTION! – TO REAP THE FULL BENEFITS OF THIS TUNING METHOD AND REALLY HEAR THE DIFFERENCE IT MAKES, DO NOT JUST CARRY OVER YOUR OLD MIXES/SNAPSHOTS/FILES FROM PREVIOUS SHOWS AS THEY WILL INEVITABLY HAVE EXCESSIVE AMOUNTS OF CHANNEL EQ/PROCESSING FROM EARLIER INACCURATE SYSTEM TUNINGS (PLUS THE “CREEP” FACTOR!). AFTER USING THIS NEW TUNING METHOD, YOU CAN CERTAINLY LOAD UP YOUR OLD SHOW FILE BUT IT IS VITAL YOU THEN PUT ALL OF YOUR CONSOLE CHANNEL EQs BACK TO FLAT AND BUILD A NEW SHOW FROM THERE. AS YOU BUILD THAT NEW SHOW I THINK YOU WILL BE AMAZED AT HOW MUCH CHANNEL EQ YOU DON’T NEED AS YOU ARE NOW HEARING THE REAL SOUND OF ALL YOUR MICROPHONES!