Reading and interpreting technical specifications for loudspeakers can be painful at times. There are often so many specifications, graphs and plots it can be difficult to determine even simple things like what colors the loudspeakers come in (hint: they’re usually white, black or sometimes gray for outdoor loudspeakers). All specifications are important to varying degrees, but comparing multiple models from different manufacturers can quickly become time-consuming and exhausting. Here are a few attributes to focus on initially to see if the loudspeakers are a good fit for your project.
Speech Intelligibility and STI
In houses of worship, speech intelligibility is essential for loudspeaker selection. Clear, comprehensible audio ensures the congregation can fully engage and connect with the message. However, you’ll never find intelligibility listed on a data sheet; speech intelligibility is not itself a loudspeaker specification but rather a product of how the loudspeaker system interacts with the room. Maximizing speech intelligibility is done by choosing the correct loudspeakers at the design phase, so understanding loudspeaker specifications can help users make the most informed choices possible.
Simply put, speech intelligibility is the percentage of speech a listener can understand. Intelligibility is affected by the volume level and quality of the speech signal, the type and level of background noise, room reverberation and more. Speech intelligibility uses the Sound Transmission Index (STI) to predict — not measure — the likelihood of syllables, words and sentences being comprehended using the selected loudspeakers in the room under typical conditions. STI is based on a scale from 0 (bad) to 1 (excellent), and an STI of at least 0.6 throughout the seating area is recommended for houses of worship. For native speakers, this equates to roughly 75% of syllables being understood, 90% of words understood and 95% of sentences understood. A rule of thumb for excellent intelligibility is usually a signal-to-noise ratio (SNR) of 12 dB, meaning the signal should be roughly four times louder than the noise floor.
Loudspeaker directivity (aka “dispersion pattern”) is the extent to which loudspeakers focus the sound in a particular direction (typically towards the listener) instead of broadcasting it in all directions around the room. A rule of thumb is the greater the directivity, the better the potential intelligibility. Loudspeaker directivity also varies with frequency: dispersion patterns tend to be wider at low frequencies and tighter at higher frequencies. Directivity control devices, like horns or waveguides, work to generate constant directivity (a dispersion pattern that does not change with frequency). Constant directivity devices are very important because they allow the designer to be confident that they are covering the areas they need to more effectively. Other technologies like beam steering allow the integrator to create directivity patterns perfectly suited to the room, delivering excellent coverage in the audience areas while avoiding reflective surfaces. Ultimately, directivity tells you where the sound will go once you put a speaker in a room, and if the loudspeaker’s directivity doesn’t meet the project’s needs, the results will be inadequate.
Sound Pressure Level (SPL)
One of the first attributes many people gravitate towards is “How loud is the loudspeaker?” Louder is often better, but evaluating loudness alone can paint an incomplete picture of a loudspeaker’s performance. The loudspeaker’s sensitivity and power handling are typically more important than the loudspeaker’s raw output capability. Sensitivity is a rating that describes how much SPL a loudspeaker will produce for a given input voltage. Power handling will tell you how much power a loudspeaker can take before overheating (AES/RMS ratings) or suffering physical damage (peak ratings). Knowing a loudspeaker’s sensitivity and power handling will allow a system designer to put together a system that is not only loud enough but also will meet the dynamic range requirements of the application. Dynamic range is a comparative measurement of the peak and average (RMS) levels of a loudspeaker system’s output, and different applications require different levels of dynamic range. For example, a contemporary rock’n’roll church with a full praise band has very different mix requirements than a traditional church that only deals with spoken word.
Another consideration regarding SPL specifications is that manufacturers often use different measurement qualifications. Therefore, pay close attention to footnotes denoting signal type, crest factor and loading conditions. You want to ensure you’re comparing apples to apples, so knowing how manufacturers rate their products will help you compare various options more accurately.
Most modern loudspeakers sound pretty good “out of the box,” but even so, frequency response remains an important specification to consider; however, the importance depends on the application. Human hearing spans a range of 20 Hz up to 20 kHz, with the average adult hearing up to around 15-17 kHz. The bandwidth of human speech is typically about 85-150 Hz at the lowest, up to about 10 kHz and beyond at the highest, with frequencies between 400 and 8 kHz being the most important for speech intelligibility. With that in mind, system designers will focus on a relatively narrow frequency range when designing an audio system for a traditional house of worship with only spoken word for program material. However, a project for a modern contemporary worship space would have much broader requirements for frequency reproduction, with the main loudspeakers being as close to full range as possible and likely supplemented by subwoofers for low-frequency reproduction.
The size of the loudspeakers plays a role in their acoustic performance and ability to add or subtract from the room’s environment. The larger the physical cabinet size, the more air it can push. For example, subwoofers generally have large amounts of loudspeaker cone movement (excursion), which moves large amounts of air to create low-frequency sound. Also, since loudspeaker placement in the room can directly contribute to speech intelligibility, you’ll need to know if the loudspeakers can fit in the proposed locations. Another possible issue with the loudspeakers is whether they’ll visually detract (or distract) from the room’s environment. If they’re large or the color clashes with the surroundings, different form factors (such as replacing flown arrays with beam-steered loudspeakers) or custom paint jobs may need to be considered to ensure minimal architectural intrusion and maintain the space’s worship atmosphere.
The Value of Acoustic Modeling
Once the initial slate of loudspeakers has been chosen, acoustic modeling is an excellent method for comparing how each loudspeaker affects the space and the optimal placement. Acoustic modeling or simulation lets consultants and integrators understand the current acoustics of a space and how the placement of loudspeakers and other factors affect the room’s acoustics with a high degree of accuracy, all from the safety of their computers. Popular software packages like EASE have an extensive library of loudspeakers from various manufacturers that allow for accurate models that closely map to actual values measured in the room after the loudspeakers have been installed. This acoustic modeling helps verify the accuracy of the loudspeaker specifications and builds peace of mind in your selection.
There are plenty of other specifications to consider when selecting the best loudspeaker for an installation, so don’t fall into the trap of thinking only the entries highlighted above are important. They’ll help you navigate the plethora of loudspeaker offerings available and dial in on a few models. Then you can go through the remaining attributes for IP ratings, certifications, accessories and more to recommend the best choice for your installation.
Loudspeakers play a critical role in creating truly immersive worship experiences for a congregation. Investing the time to research different loudspeaker offerings and even arranging listening demos will go a long way toward ensuring every worshiper receives the best sound possible.
About the author
Brandon Heinz is a Project Manager for Renkus-Heinz. Renkus-Heinz has sound solutions for a wide range of applications from performing arts venues, transportation hubs and houses of worship to educational, corporate and governmental facilities. For more information, please visit www.renkus-heinz.com.