2012 LDS Conference Center Audio System Upgrade

Posted by: - on July 9, 2013

A major upgrade to the sound reinforcement system in the LDS Conference center was completed last december just in time for the Church’s Tabernacle Choir Christmas show, resulting in stellar audio quality for that production, as well as all events for years to come.

Brief History

The LDS Conference Center is located in downtown Salt Lake City and serves as the main meeting hall for conferences of the Church of Jesus Christ of Latter-Day Saints. It is also used for musical spectaculars that are sponsored by the LDS Church, most of which feature the famed Mormon Tabernacle Choir as well as other notable classical artists. The main auditorium seats over 21,000 parishioners. It is one of the largest, if not the largest, auditorium of its type in the world.

The building was completed in the year 2000 and included a sound system that was billed as “state-of-the-art”. The system was designed by a well-known national consultant and installed by an equally well-known national contractor, at a cost of nearly 3 million dollars. The design concept was tried and proven, having worked in so many other venues, and the installation was neatly done. However, at the first use of the room in April of 2000, the complaints about poor sound quality were abundant. These were mainly low volume in some areas and poor intelligibility in others. The consultant was called back in on several occasions to address the concerns, but after nearly a year of tweaking the problems were not improved and the owner was becoming frustrated. Several other engineers and consultants were then invited in to offer suggestions and solutions.

Meanwhile, to relieve the pressure of complaints, Poll Sound designers were asked to make suggestions on some temporary improvements. After a short study of the issues and some careful measurements, we concluded that the most severe problems were a result of violation of a few basic rules of solid sound system design. A new design concept was presented, a few changes were made to the original configuration, and a small amount of additional equipment was supplied on a rental basis. Just these changes were successful in cutting the complaints in half. The temporary improvements were, in fact, so successful that the building officials became very confident in our suggestions for a permanent fix. A short time later, graduate students from BYU acoustics department, led by their instructor Dr. Tim Leishman, completed an exhaustive study of the room acoustics. The information they provided was a clear confirmation that our design concept was the most feasible.

Building officials decided to implement the system fixes in stages, first addressing the most critical areas. To date we have completed six separate contracts for system improvements, the latest being in December of 2012. With each successive project, the quality went up and the complaints went down, culminating with the most recent project dropping the complaints to zero and earning praise from ecclesiastical leaders, building officials, and audience members.

One of the early problems was poor intelligibility in sections of the lower bowl, especially in the first several rows, off to the sides, and almost everywhere on the rostrum. Being that these areas are where the VIP’s sit, it was of utmost importance that the problems be immediately corrected. The issue was complex, involving both the direct sound sources that arrived from multiple locations, and room reflections. A temporary fix was implemented by turning off portions of the original system that were covering the lower bowl, hence reducing the sound arrivals from multiple points, and installing a new center cluster speaker system that would cover the entire area from one point.

Temporary Cluster Being Assembled and Tested

The cluster also contained elements that were down-firing, which served to “mask” late reflections coming in from the rear of the hall. At that point, nothing was done to actually reduce the room reflections but the masking did change the perception of the echo such that it was not as bothersome to the talker or listeners in that area. Again, this fix was supposed to be temporary but because it was successful, and as things sometimes go, it ended up being in place for over 10 years. The 2012 project was to finally engineer and install a system for the lower bowl that still accomplished the original goals of high intelligibility, but also offered higher quality and optimal gain-before-feedback.

Conference Center Main Hall with Temporary Cluster Installed

Since that initial cluster installation, a couple of the upgrade projects implemented changes to the system that did reduce the room reflections. This was done by changing the angles of the speakers that were covering the rear of the room, in the balcony and terrace, such that their reflection would not end back up in the front of the room. These modifications reduced the reflected energy some 12dB over the original system. However, through careful measurement we calculated that still more improvement could be made if we were to also redesign the lower bowl coverage such that less energy was being projected to the rear of the hall. The 2012 redesign of the cluster, therefore, also included changes to the way we covered the seats in the rear of the lower bowl.

It should be noted that in this venue there are separate sound systems for speech and music, although the speech system is used to augment the music system during musical presentations. It is, therefore, important that the speech system not only provide good intelligibility, but also that it provides high quality music reinforcement. The center cluster is part of the speech system.

The 2012 Upgrade

With the design goal clear, we began research into equipment that would satisfy the design criteria as well as provide the highest possible audio quality. Many brands were considered, but L-Acoustics was the decisive winner. They were chosen for the following reasons:

  • They manufacture equipment that meets the unusual design criteria

  • Their design and modeling software is very precise, insuring the accuracy of the design, and accuracy of the end product

  • Their design and modeling software is very precise, insuring the accuracy of the design, and accuracy of the end product

  • They are very well known and accepted in the entertainment industry giving visiting artists confidence that the audio quality will be the very best

  • Parts of the choir reinforcement system were already L-Acoustics. Having this new system also L-Acoustics insured audio consistency for all the sound reinforcement

  • Having worked with L-Acoustics previously, the venue sound system technicians were confident and comfortable with the product

The new lower bowl design uses both a center cluster and a delay ring. The center cluster is really not a cluster, but rather is 3 separate line arrays strategically spaced, oriented, and shaded to avoid comb filtering between them. Each array consists of 10 L-Acoustics KARA array module. They are designed and aimed to cover only back to the main isle, which is about 2/3 of the way back from the stage. By limiting their coverage to this point, we avoid slap-back from the rear of the hall. Low frequencies are supplied by 2 cardioid sub arrays, each consisting of 3 L-Acoustics SB18 sub boxes are hung between the KARA arrays. The rear of the lower bowl is covered from a delay ring that consists of 7 arrays of 4 L-Acoustics KIVA modules. Two more 4 element KIVA arrays were installed over the extreme rear corners because of the distance from the cluster. There were also 2 additional KIVA arrays installed over the rostrum area that provide both front fill and masking of any remaining rear-of-room reflection.

KARA array prepared and ready to positionLooking down at the center array and both sub arraysRear view of KARA array wired and ready for installation

One of the delay ring KIVA arraysView of the main arrays also showing a front-fill KIVA arrayDelay ring, a rear fill array and the main arrays in the distance

Power for the new speaker components is supplied by 14 - L-Acoustics LA8 and LA4 amplifier/controllers. The DSP within the amplifier provides the proper optimization filters and insures that harmful signals do not reach the loudspeakers. BSS London processors are inserted prior to the amplifiers to provide further processing and routing capabilities. The existing console, a Yamaha PM1D, was retained. Since all of these components are digital, it was decided that the signal path should be kept entirely digital instead of doing several analog-to-digital and digital-to-analog conversions. The digital platform used was AES/EBU, which is very robust and has a great track record. Clock for the entire system normally originates at the console, but this can be changed if a high quality digital source is used.

Once the installation was complete the projected entered the balancing and tuning phase. This was a daunting task. Not only did the new equipment require alignment, but it is interfacing with the existing system that covers the balcony and terrace, the existing choir reinforcement system, the existing rostrum monitor system, and the LARES (artificial reverberation) system. Just in the balcony and terrace there are over 400 loudspeakers, each with their own amplifier and DSP point. These were previously aligned to the old temporary cluster, but now that the new arrays were in place it was necessary to completely realign each one of them. The task is complicated because the delay rings are not symmetrical in relation to the main arrays so each device in the ring is a different distance from the main. Further, one of the elements in obtaining consistent audio quality and forward imaging is to insure that the frequency response characteristics of the delayed speakers closely match the main arrays. This meant that a complete re-tuning was required. Likewise, the choir reinforcement system and rostrum monitor system were re-aligned and re-tuned. Also added was the ability for the operator to have both a speech mode and a music mode for the new system. The basic difference is that when in speech mode, the system is aligned with the podium. In music mode, the new system is aligned with the choir reinforcement system. Through highly cooperative and synergistic teamwork between our technicians and the Conference Center staff, balancing and tuning was completed in about 1-1/2 days. We used multiple measurement platforms including SysTune, EASERA, RoomCapture, TEF, Smaart, and NTI. Much more detail on tuning, balancing, and alignment will be the focus of future articles on this sound system.

The End Result

It is always difficult to assign a measure for the success of a sound system. This is because much of it is subjective judgment. There are some measures, however, that can be considered objective and therefore quantifiable. Two such measures of this system were intelligibility and gain-before-feedback.

STI-PA measurements taken at 50 points in the hall yielded an average of .69, with the worst being .66 and the best .76. In STI measure, that rates between very good and excellent intelligibility. The measurements were substantiated by actual listening tests by staff and volunteers. There was not a single listener who didn’t confirm very clear, concise, and intelligible speech.

The gain-before-feedback improvement of the system was also astounding. With one particular weak talker, we measured a 17dB improvement in gain. That is significant! This was of especially good news to the operators who had been struggling with feedback for the past 10 years.

In terms of subjective quality, this system hits a home run. After the first production, comments of praise poured in from the golden-ear mix engineers, to the musicians, to the clergy, to the staff and volunteers that have worked in the building the past 10 years, to the common parishioner.

Below: Stage Area, with the Mormon Tabernacle Choir and the Orchestra at Temple Square, during the 2012 Christmas Program

2012 LDS Conference Center Audio System Upgrade

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