 Hot on the heels
of the Esplanade: Theatres on the Bay’s grand opening on the Oct 11th, the
AES Singapore Section organized an on-location full day seminar focusing
on the S$600 million facility’s audio signal path, from microphone to
speakers. Attended by 60 AES members, audio professionals and enthusiasts,
the audience included AES members who flew to Singapore from Hong Kong and
Malaysia to attend the seminar. The full day program was divided into
four sessions covering the mixers, microphones, processing equipment and
speakers. The presenter for each session gave a 2-hour presentation followed
by a Q&A.
First up was Tony Waldron (technical manager) and
Mark Ray (sales manager) of Cadac. Tony started his
presentation by bringing to our attention a very important factor in the
pursuit of audio fidelity, grounding. He stressed that a surprising
proportion of audio equipment on the market are not properly grounded
against Electro Magnetic Interferences (EMI) present in our atmosphere.
These interferences manifest themselves as clicks, hums and buzz. Part of
the reason for this negligence is because 30 years ago, before the dawn of
the wireless age, most cable systems were designed to withstand only low
frequency interferences such as those from the AC mains and dimmer circuits
in lighting equipment. Times have since changed. Today, the atmosphere is
saturated with radio frequencies going into the gigahertz range. He then
went on to explain what are the differences between the input safety ground,
the sub-system ground and the electronic circuit ground. These 3 grounds
should ideally be 0V. Unfortunately, this is impossible to achieve in
practice because all materials have an electrical resistance no matter how
small it is. The best we can do is to design a proper grounding structure to
minimize EMI. Tony then gave a detailed explanation of the three grounding
techniques that are independent ground return, star ground return and meshed
ground return. A practical shielded wiring system that minimizes EMI was
presented in detail. In summary, he said double shielded cable should be
used for non EMC compliant equipment. It is also necessary to minimize loop
areas and know where the return current flows.
 The second
presenter for the day was Rick Shen (assistant director, product management) from
Sennheiser Electronics Asia. He presented some valuable and practical
advice on the correct usage of wireless microphones in a multi-microphone
environment. He started by explaining how pre-emphasis and de-emphasis are
applied to Sennheiser wireless microphones in the transmission and receiving
stages. Next, he gave us an insight to how improper usage can lead to
reduced transmission and receiving range. For example, the user should avoid
holding the antenna end of a wireless microphone as this reduces the power
of the received signal. This was followed by a discussion on how
intermodulation between nearby frequencies can lead to signal distortion in
a multi-microphone environment. When two wireless microphones are working on
transmission and receiving frequencies that are very close to each other,
intermodulation will generate a lot of unwanted harmonics that will degrade
the quality of the received audio. The solution to this is to select
frequencies that are inter-modulation free for the wireless microphones.
Apart from avoiding intermodulation, the choice and usage of antennas are
equally important for high quality replication of the audio signal. A
discussion of the different types of antennas and their correct usage in
different scenarios followed. Rick then presented a detailed description of
signal loss and compensation with boosters. The session ended with an
insight of how the “Squelch” setting on Sennheiser wireless microphones
should be set to filter out unwanted RF frequencies.
After lunch, acoustic drapes lined the sides of the huge
concert hall at the push of a button. This reduced the reverberation time
from 4.0 to about 1.2 seconds. The first speaker to present in this new
acoustic environment was Matthew Packer from Electronics and
Engineering Pte. Ltd. Matthew's presentation was on BSS Audio 's
Soundweb and Crown Audio's IQ system used in the Esplanade. Soundweb is the
underlying framework that provides networked DSP to the various venues in
the Esplanade. The Soundweb Network has a latency of 20.833 micro-seconds
per node. Such low transport latency is of paramount importance in
situations where acoustic and amplified sounds co-exist. Matthew continued
by giving the audience some important specifications of the Soundweb
installation such as the data rate, frame size, bit-depth and bandwidth. A
distributed DSP system allows for remote monitoring of audio quality. Not to
mention the savings in cables for networked DSP installation. Soundweb is
used in the 4 main venues of the Esplanade. They are the concert hall, the
theatre and the two recital studios. Next on Matthew's presentation is the
IQ system by Crown audio used in the Esplanade. IQ system is a flexible and
easy to operate system which employs computer technology for monitoring and
controlling a distributed audio system. It allows the audio engineer to
remotely monitor and tweak audio parameters such as input attenuator levels
and audio I/O levels. It can also be used for load supervision as well as
loudspeaker management from within the amplifier. Matthew rounded off his
presentation with a brief overview of another prominent audio networking
technology by Peak Audio called Cobranet. This technology uses TCP/IP over a
Fast Ethernet network.
The final presenter for the seminar was Ralf Zuleeg,
application support engineer of d&b audiotechnik. Ralf’s talk
revolved around the speaker installations used in the Esplanade. True to d&b’s
philosophy of user education, Ralf begin his presentation with a run through
of the basics in acoustics and sound reinforcement. After laying down some
foundations such as the definition of sound, wavelength and frequency, he
elaborated on the propagation of sound in different atmospheric conditions.
He refreshed our knowledge in acoustics by highlighting the effects of
damping, reflection, refraction, diffraction and absorption on sound waves.
Next, he touched on the topic of reinforcing a performance by using multiple
loud speakers in various configurations. It was interesting to learn how the
angle, orientation and number of the loud speakers can affect the coherence,
phasing and audience coverage of the reinforced performance. Ralf went on to
the all important topic of level distribution over the audience area. In
sound reinforcement, it is always good to minimize the level drop over
distance so that the aural experience of the audience in front of the stage
will not be too different from those sitting at the back. A detailed
explanation of how this can be achieved by proper installation of the loud
speakers was given. Next, he spoke on the various speaker arrays used in the
impressive concert hall of the Esplanade.
The seminar concluded with a live demonstration of the
loudspeakers in the concert hall. Several audio recordings of different
genres were played over the sound system that left the audience spellbound.
The evening closed with an optional dinner buffet at Pan Pacific Hotel where
the guests mingled and exchanged their ideas and passions for audio
technology. |
