World-renowned sound reinforcement expert Dr Wolfgang Ahnert has been responsible for developing the acoustic design aspects of some of the world's most iconic buildings, including Abu Dhabi's Grand Mosque and the recently refurbished Berlin Olympic Stadium. Here, he talks to S&S about the challenges of his role at the forefront of acoustic design.
Your company Acoustic Design Ahnert (ADA) recently established its Middle East headquarters in Doha, Qatar. What sort of business do you hope to secure now ADA has a permanent presence in the region?
We want to work on special projects throughout the GCC. We also recently opened a satellite office in Dubai which will help us snare additional business in the UAE. Many hotels in Dubai suffer from terrible acoustics, particularly those with grand lobbies and ballrooms. One property - which will remain nameless - has had to close 15 first-floor rooms to guests because of the noise from a nightclub located on the ground floor.
We want to work with clients to resolve these kinds of issues.
In recent years, you have developed a reputation as a leading expert in acoustic design for places of worship, particularly mosques. How did you become interested in the field?
I'd been working with a young man from Saudi Arabia called Wasim Al Fahdi, who was completing his PhD in Germany which focused on speech intelligibility in mosques. Subsequently, I became very interested in the subject myself. The majority of mosques suffer from poor acoustics which affects sound clarity, particularly from PA systems. No one has really worked to develop solutions in this area, so it's really pioneering research we're involved in.
What are the main issues from an acoustic design perspective?
The fundamental issue relates to interior design. The interior of a typical mosque has very few sound absorption areas and many reflective surfaces.
The sound systems that are primarily employed in many of these mosques are not specifically designed for public address applications.
Most mosques are equipped with undersized speakers for economic and aesthetic reasons, and they're positioned in reverberant environments meaning they often work against each other.
Another consideration is the carpet. Most mosques have a carpet, but it's not always the right type to make any difference to the acoustics.
Do you believe that architects need to take greater responsibility to address these issues?
Well, architects need to learn that not all mosques are the same, in terms of their interior design requirements.
They must be encouraged to consider acoustic optimisation from the initial design stages.
Every architect understands the interplay of light, but as acoustic designers we are at a disadvantage because we cannot provide a visual representation of sound patterns. By the time these buildings are constructed it's often too late to address acoustic issues.
What can be done to improve this situation?
In the case of constructing a new mosque, a lot can be done to improve the acoustics. You can incorporate sound absorption panels in the initial design.
The carpet is potentially the biggest absorption panel available. Very often you'll find that a carpet is laid out on a marble floor providing very good high frequency response, but people's voices do not reach this frequency. This means typical speech patterns are affected by a very long reverberation time at low frequencies, depending on the type of carpet employed.
To resolve this, we suggest the carpet should have an underlay and boast a denser pile to ensure it is capable of low frequency absorption.
If it's too expensive to replace the carpet, we suggest the installation of high-mounted directional loudspeakers such as very slim, computer-controlled line arrays. We have recommended this type of installation at the Grand Mosque in Abu Dhabi.
Is this because of issues with the carpet that's being laid in the Grand Mosque?
Well, it's a compromise solution. The carpet that is being laid down in the mosque is the world's largest and we recommended an underlay be installed but this was rejected. So instead, the developers have agreed to lay a special concrete material beneath the carpet that has certain sound absorption characteristics.
The computer-controlled line arrays provide the main benefits. They can operate on reduced power or be individually controlled depending on how many worshippers are in the mosque at a given time.
What other projects of this kind do you have in the pipeline?
We are currently pitching to be involved in the development of the largest mosque outside those in Mecca and Medina in Qatar. We have also worked on similar large-scale projects in Yemen, Oman and Malaysia, which has provided our team with a great degree of experience.
You have also earned a formidable reputation for your work in the area of stadium design.
It's a professional and personal passion of mine. I was directly involved in designing the sound reinforcement system for the Berlin Olympic Stadium, which hosted the 2006 FIFA World Cup final. ADA is also currently negotiating to develop a stadium in Singapore, and we're working on three stadiums in South Africa that will be used during the 2010 World Cup.
Locally, we're involved in the development of Dubai Sports City. We have submitted acoustic design plans for the three main stadiums in the precinct in conjunction with German architect GMP.
We have had to revisit the acoustic plan for the largest of the three stadiums following the developer's decision to raise seating capacity from 25,000 to 60,000. Obviously, the larger the stadium the more loudspeakers required, but the more speakers you install the harder it is to ensure speech intelligibility, if the proper acoustic design is not implemented.
We are also involved in the development of the new Dubai Airport terminal. The public address and sound reinforcement systems are being supplied by a contractor, but they have been having problems with the environmental acoustics so they contacted us to develop an acoustic design for the terminal. They've reported significant issues relating to reverberation, which we're working to address.
How has technology changed the way you work?
In the past, we would have to build scale models using miniature loudspeakers and microphones to work on identifying the appropriate frequencies.
Nowadays, this process is performed virtually using software, which has cut back development times remarkably.
I started using a computer towards the end of the 1960s but it proved a very cumbersome experience working with punch cards. It was only in the mid-1980s that we began to employ technology that forms the basis of what we use today.
Simulation programmes have become fairly standard tools for acoustic design.
My other company (Software Design Ahnert - SDA) has developed Electronic and Acoustic System Evaluation and Response Analysis (EASERA) technology, which is a comprehensive software package for acoustic and electronic measurement.
At the moment we're working on a special version of this software that will allow us to use 'normal' signals to apply to music or speech recordings to generate impulse responses of four to eight seconds.
It's a very technically challenging process, but ultimately one that could prove a major breakthrough in terms of acoustic design, if we are successful.
• Berlin Olympic Stadium, Germany (1999-2004).
• Beijing National Stadium, China (2003).
• Berlin Central Station, Germany (2006).
• House of Music, Great Hall, Moscow, Russia (2001).
• Dubai Sports City stadiums (2004 -).
• President's Mosque, San'a, Yemen (2004).
• Grand Mosque, Abu Dhabi, UAE (2003 -).
• Dubai International Airport, UAE (2005 -).
• Doha International Airport, Qatar (2005 -).