The cocktail party effect

A guide for installers and expert planners in PA technology

Want to concentrate on a specific conversation in noisy surroundings? This often works surprisingly well. Your brain filters out the ambient noise and focuses on the selected voice. This psychoacoustic phenomenon is called the “cocktail party effect”. How can this effect be used in PA technology? Read on and find out what you as an installer or expert planner should know about this phenomenon.

This article focuses on:

The cocktail party effect: how the brain can “hear selectively"

The cocktail party effect describes the ability of the human ear to focus on a specific sound source in noisy surroundings. It also describes the brain's ability to focus on a specific sound source while keeping other sounds and voices in the background. This means that you not only hear the desired voice clearly, but also quickly switch between different sound sources. This is particularly useful if you suddenly hear your name in another conversation or need to pay attention to an important speech.

The name comes from situations in which many people are talking and music is also playing – of course it can happen just as well at a trade fair, a conference or in a ballroom.

The limits of the cocktail party effect

If the brain has the ability to react well to different sources of noise, why do we have to be familiar with this effect in PA technology? The challenge: not everyone has the ability to listen so selectively. And of course the effect has its limits. If the overall volume level at the party is too high, selective hearing becomes increasingly difficult.

Although the human brain is remarkably good at focusing on specific sounds, this ability also has its limitations. In surroundings with poor acoustics or too many competing noises, even the most focused ear can be overwhelmed. This is where PA technology comes into play.

Rooms with strong reverberation in particular have a low level of acoustic comfort in cocktail party situations: conversations may still be possible, but exhausting in the long run.

The “critical distance” for clear speech intelligibility is reduced in rooms with poor acoustics

The reverberation zone is the zone in the room in which the reflected sound level is higher than the direct sound. Imagine yourself and your conversational partners in the room as figures in a bubble. Within this bubble, you understand the words of your conversational partners well. The better the acoustical planning of the room, the larger is this “speech intelligibility bubble“. Outside of this bubble is the reverberation zone. The reverberation there is louder than the direct sound (of the conversation).

If the venue is not acoustically optimised (which is very common at high volume venues), the bubble for direct sound during conversations is very small and people have to move close to each other to have a conversation. The direct field zone and the reverberation zone define the "critical distance (CD)" - the distance at which a conversation is possible.

At trade fairs or cocktail parties, pay attention to whether individual groups stand very close to each other to converse – that is an indication of the acoustics being bad or the music being too loud.

Five recommendations for action for rooms with many sources of noise

1. Focus the sound

In large rooms or at events, it is often difficult to hear speech or music clearly – despite the cocktail party effect. Good PA technology can improve the acoustic quality by, for example, directing the music from the stage to only a specific area. For music that is intended to create a soundscape in the background, good PA sound projectors are an option.

2. Control the volume

With the right technology, you can control the volume so that it is pleasant and not overwhelming. This makes it easier to concentrate on conversations. Assume that you have 10 people speaking at a volume of 60 dB: each doubling of the number of people increases the volume by 3 dB. So with 20 people, it would be 63 dB, with 40 people 66 dB, with 80 people 69 dB and so on. There are now three options for the music:

As loud as the people: If you want the music to be as loud as the people, it should be at the same dB level. So, if there are 40 people in the room generating a volume of 66 dB, you should set the music to 66 dB.
Music in the foreground: If you want the music to be clearly audible but not overwhelming, the target value is 5-10 dB louder than the overall human volume.
Music as background: If you only want the music to play in the background, it would make sense to set it about 5-10 dB quieter than the overall human volume.

Remember that these values are just guidelines. Acoustics, sound decay and other factors can affect the actual perception.

3. Place speakers strategically

If you place the speakers well, you can direct the sound so that it quickly gets where you need it. This minimises deflections. In a conference room or exhibition hall with poor acoustics, the cocktail party effect becomes a problem. Use well-planned ceiling speakers with directed sound radiation exactly where people are likely to be: above seating areas, networking areas and other "natural" meeting points.

4. Analyse the acoustics in advance

Before you install a PA system, analyse the acoustics. This allows you to position the speakers optimally.

Listen: Listen to the music and conversations in different parts of the room. Does the clarity or volume change?
Clap test: A simple clap can tell you a lot about the reverberation in the room. Prolonged reverberation may mean that you should turn down the music to avoid drowning out conversations.
Sound level meter: You can measure the exact volume in the room using a sound level meter. This will give you a better understanding of the dB values of conversations and music.
Acoustics software: There is special software that can give you detailed information about the acoustics of your room. These tools can help you identify problem areas such as echoes or dead zones.

5. Think in different PA application scenarios

With multi-room amplifiers, you can individually adapt the PA application for different areas. In a restaurant, for example, you can set the music louder in the bar and quieter in the dining area. In restaurants and bars, the guests want to converse without being disturbed by the background music. Here, you can adjust wall-mounted speakers and multi-room amplifiers so that the music fades into the background, but is still present. The challenge in shopping centres is to make important announcements understandable. Here, you can use speakers with high speech intelligibility to improve acoustic comfort.

Conclusion

The cocktail party effect is more than just an interesting phenomenon. If you understand and use this effect, you can significantly improve acoustic comfort in noisy surroundings. This is how you take your projects to the next level.