21. fevereiro 2022

How NTi Audio was making a difference at the Olympics

During the 2022 Winter Olympics in Beijing the spotlight was always on the athletes and their outstanding performances. People around the world were following the competitions with excitement via radio, television and the Internet. In addition to the sporting achievements, the spectators appreciated when the commentators' provided interesting, clearly understandable explanations.

At the various venues, for the spectators and particularly the athletes themselves, the loudspeaker announcements are an important source of information. At a top international event such as these Winter Olympics, the expectation is that this communication be easily understandable for everyone.

💡 In addition to the venue itself, the sound quality in the lounges, commentary room, control room, hallways and broadcast booths is considered.

Acoustics experts have relied on NTi Audio equipment since the start of the renovation and construction of event venues, such as the Water Cube.

 

So, from the start of construction to the completion of the project, acoustics consultants controlled every step of the process to ensure that all acoustic specifications were met and to achieve the best possible sound clarity. Subjective listening alone is not enough to judge the final quality here. Instead, objective measurement of the Speech Transmission Index STI is the scientifically-accepted method for evaluating announcement quality.

The GB/T 28049 standard Code for sound reinforcement system design of auditorium, gymnasiums and stadium sets clear requirements for the speech transmission index (STIPA for PA systems) in stadiums.

 

Firstly: Reverberation

Reverberation time is a key criterion for speech intelligibility. Many of us will have experienced live commentary or announcements in a highly reverberant indoor space.

The table demonstrates how, with increasing reverberation time, the speech transmission index decreases

 

The effect of reverberation time on intelligibility is also illustrated in the following two audio clips:

less reverberation    

more reverberation

 
The requirements for a sound reinforcement system result from the room volume and the reverberation time. A well planned and carefully measured sound reinforcement system can ensure a sufficiently high speech intelligibility for a room volume of 80000-160000 cubic meters and a reverberation time of 1.6-1.8 s.
 

💡 There is a distinction between stadiums and arenas, as an open stadium produces more like free-field conditions, while a closed arena produces more like a diffuse-field.

Measuring reverberation time in a large arena is no easy task. It requires not only a highly-accurate and easy-to-use instrument, but also a powerful sound source to fill the room with the test signal. This is where the DS3 Dodecahedron Loudspeaker comes in.

The lightweight DS3 dodecahedron speaker does the job

 

The measurement results are read directly on the XL2 Acoustics Analyzer and immediately identify those areas that do not meet the requirements. With no post-processing of data, the time needed is significantly reduced.

 

And then there is the noise

The louder the ambient noise, the lower the signal-to-noise ratio, and the less intelligible announcements are - so far so good. But noise from the spectators is not the only influencing factor. The acoustician therefore evaluates the venue when it is both empty and full.

When the arena is empty, there are no noisy spectators, but there are other sources, including ventilation, air conditioning and lighting, that generate noise. This is where noise curve measurements are required.

The GB/T 28049 standard specifies a maximum total sound level of NR35.

Noise curves are very easy to measure and can be read directly from the
XL2 Acoustic Analyzer, eliminating the need to cross-reference the frequency spectrum.

 

The question of how far ambient noise affects speech intelligibility has always been difficult to answer. Mainly because playing the test signal at the necessary level and making dozens of measurements in the middle of the spectators is not possible.

In response to this dilemma, NTi Audio has developed a creative feature to correct for the influence of ambient noise. The acoustician first measures the speech transmission index STIPA in an empty arena, and then overlays the result with the ambient noise level recorded when there are spectators present. In this way, the speech transmission index in the presence of spectators is obtained and the contradiction between the theoretical requirements and the actual measurement is resolved. 

An empty arena allows the consultants more work flexibility

 

Sound Pressure Level

It is difficult to hear whispers - experience suggests that the louder the sound, the better you hear. That's what scientists used to think, too. But people do tend to cover their ears when they hear very loud sounds. 

After years of research and experimentation, it was found that the best speech intelligibility
is achieved at a sound pressure level between 60 and 80 dBA.

 

Based on this finding, the international standard IEC 60268-16 on speech intelligibility indices has been refined over the years to correct for speech intelligibility indices at higher sound pressure levels.

Until 2003, the standard considered the STI value to be constant above a sound pressure level of 80 dBA.

 

STIPA measurement function with real-time sound pressure level display now supports ed5.0 standard  

 

And more

There are many more acoustic considerations in stadiums than those that have been mentioned in this article: Issues such as sound insulation and noise pollution during games must be considered in their entirety, because any omission could have undesirable negative consequences.

Thanks to the efforts of all those working behind the scenes and sophisticated measurement systems, we were ultimately able to enjoy many great events!

Picture by Maja Hitij/Getty Images