KCK true point source project

Good sound is one of the essential elements in any performance hall. It is extremely important for every member of the audience to hear as clearly and comprehensibly as possible, within the widest possible tonally balanced range. The comfort of the actors and musicians on stage is also significant. Their emotions conveyed from the stage to the audience are what fill the halls with people seeking experiences different from their daily lives.

To ensure this, stage technology and audio installation are crucial.

The venue is oval-shaped. The stage is surrounded by rows of seats on three sides at two levels: ground floor and balcony.

Particularly challenging was delivering sound to all seats and managing low frequencies. The hall doesn’t offer many possibilities for placing subwoofers and satellites since only the stage is available. Sound from randomly placed sources, which usually interfered visually due to their size, dispersed very unevenly in the hall. The solutions used so far did not meet expectations for even sound coverage of all seating areas. At NAW, we like such challenges. After a local inspection, an ambitious idea emerged, inspired by the specific geometry of the hall, which resembles a flattened sphere. We decided to build a system creating a truly point-source sound with specific directionality using FAVO AUDIO devices.

We used a system consisting of coaxial satellites FAVO VSC15 and VSC12 suspended in groups reaching specific seating zones and FAVO MBR118 basses in a suspended End-Fired arrangement. This setup aimed to minimize reflections from the walls and direct the maximum amount of sound emitted by the speakers precisely where the audience is.

The balcony was within the range of both the main sound system and a purposefully delayed zone.

Areas under the balcony, where significant low-frequency buildup always occurs, were supplemented with compact satellites FAVO C5F, creating a convenient workspace for the FOH operator. The entire system is controlled by FAVO NSP248 processors, with amplification provided by HD series amplifiers.

On January 31, 2020, we launched the system, which we simply called True Point Source. By placing sound sources above the stage and setting appropriate geometry for each, we achieved tonally balanced, even coverage for all seats.

Since 2020, everyone attending performances on the Small Stage at the Kielce Cultural Center will hear THE SAME GOOD SOUND, regardless of whether they are sitting in the front row, under the balcony, or on the upper floor. This is how we define our goal, expressed in the slogan “Only good sounds for everyone.” The audience in Kielce deserves top-quality entertainment, and the operators and actors deserve comfortable working conditions.

(Extended reading for those deeply interested in details. Reading time: 10 minutes)

Do you want to read further? Are you interested in acoustics and technicalities? Full respect to you!

THE IDEA

You’ve probably heard that low frequencies spread omnidirectionally and that the bass is heard almost equally from the front and the back of a subwoofer. Sound, however, has its source at a point, and this can be empirically measured. This certainly deserves a separate article – but today, please believe that for a package the size of MBR118, it is roughly 20 cm in front of the diaphragm.

Looking at the photos, you may have already noticed that the subwoofers are facing each other with their diaphragms. In the project visualization next to it, you will see two strangely shaped balls between them – these are representations of the acoustic sources – the starting points of the sound produced by the subs.

Facing the diaphragms towards each other created a single, coherent sound source from a pair of subs hanging on one horizontal beam. This point is our source – the beginning from which the sound will spread towards the listeners. But why two beams with two subwoofers (and thus two acoustic centers) suspended at different heights?

We don’t like it when sound reflects off hard surfaces (like walls and ceilings) because it returns to the listener, degrading the listening experience. Have you heard about room MODES? They cause specific frequencies to alternately amplify and attenuate. One solution to this problem is to ensure as little sound as possible reflects and returns to the listener, ruining the music experience. Controlling the directionality of the lowest frequencies is very difficult but possible. In short: the more subwoofers we have (and hence the appropriate amount of space), the easier it is.*

IMPLEMENTATION

For this installation, floor space (stage) was in short supply (not to mention the usual budget constraints of the investor). However, we had plenty of space in the air! We decided on a configuration of four basses in an End-Fired setup to transfer part of the energy emitted behind the axis of the acoustic centers towards the audience. As mentioned earlier, the hall’s geometry allowed us to place the sources in the space so that the sound reached all listeners coherently in the full frequency range. In the graphic above, one of the acoustic centers of the basses is labeled "SUB 0ms" – this is our starting point. All other sound sources are appropriately delayed so that the sound wave starting its journey from the 0ms point encounters full-range satellites along the way. This phenomenon is similar to what we observe when we throw a stone into water – concentrically spreading waves. The effect? Each seat has no more than a 4dB difference across the full range from 30Hz to 16kHz, whether on the ground floor or the balcony.

In the drawing next to it, you can see a simulation from the Ease Focus3 prediction program (which you get free with every FAVO AUDIO system). The boundary between the yellow and green color is the line of places with identical loudness for the 63Hz frequency (roughly the middle of the subwoofer range). All seats are covered to the best possible extent. Facing the diaphragms towards each other created a “corridor” through which sound can travel unobstructed (not having to bypass bass boxes) to the listeners, further enhancing quality.

Arrangement of measurement microphones

Multi-point measurements were carried out using calibrated IsemCon measurement microphones, a PC with a MOTU interface, and Smaart software. The microphones were placed in key locations within the audience area. A series of measurements were made with different microphone placements in the main audience, balcony, and side zones.

Comparison of the subwoofer range

The pink graph shows the measurement taken in the central point of the main audience. The orange graph shows the subwoofer range on the balcony, and the green graph shows the same range in the side stage zone. The subwoofers operate as designed by the project while showing significant buildup in the lowest part of the range on the balcony.

Comparison of the full range in different measurement locations

Three graphs focus on the full range again in the audience (green), balcony (red), and side zone (blue). Notice that the assumed 4dB differences are met for frequencies above 600Hz, while 6dB differences fluctuate between 100-600Hz, which we considered a satisfactory result.

SUMMARY

A well-executed project is the basis of a properly functioning sound installation. However, let’s not forget that theoretical assumptions and predictions based on predictive software calculations are just the first step. Proper implementation and final measurements are essential elements that provide the ultimate satisfaction with the project.

*Methods for directing sound were described in detail as early as the 1950s by Harry Olson in the book "Elements of Acoustical Engineering," but the tools enabling efficient implementation of his assumptions have only become available in recent decades. We recommend familiarizing yourself with this book to learn about other directional configurations such as Cardio or Gradient. Of course, you can also follow our articles, where we will certainly present information on this topic in an accessible form.