reported
by: Mr. Jibby Jacob
Secretary (Term
1997/98)
On Thursday 16th April 1998 at
2.30 pm, 10 members and 21 guests of the AES Singapore Section gathered at
the Kallang theatre - Stadium Walk, Singapore. for a talk by Mr Eric Wong of
CCW Acoustics Pte. Ltd. Wong a Consulting Engineer and a founding member of
the Singapore Section and currently a committee member gave insightful tips
on how to avoid noise problems that are a bane of the installation sound
contractor.
With a 4 page handout distributed
to the audience, Wong lectured on the basic theory of balanced cabling and
equipment grounding in a sound system before proceeding to a demonstration
in the theatre. At the spacious Kallang theatre built in 1985 which seats an
audience of 1200 was used as the showcase installation to demonstrate how
noise problems were eliminated by good audio wiring practices. Wong then led
a tour round the facility to show how all equipment were grounded in a star
configuration using single ended shield termination.
|
Mr.Eric Wong
conducting an illustrated workshop session on 'How to avoid common noise
problems in sound system installation' on April 16, 1998 at the Kallang
Theatre" - photograph by Michael Teh |
Though all permanent connection
and cabling in the installation were balanced, Wong informed that many
travelling shows would bring in audio equipment that were consumer grade
with unbalanced inputs and outputs and professional balanced inputs and
outputs still created noise problems that are tedious to solve. As far as
possible Wong warned, audio systems should not share ground with other
services like dimmers, motor systems, most importantly the audio ground
cable goes directly to the earth rod.
He added, check the type balanced
connection and all audio cables should be encased in grounded metal conduit/
trouncing (which is also a shield). Another technique revealed by Wong was
to avoid running audio cables in parallel (at least one metro apart) with
electrical service cables. "Keep them perpendicular to each other if they
need to cross" Wong quipped to avoid picking up Electromagnetic or Radio
Frequency Interference (EMI /RFI). Kallang Theatre was selected as the venue
of this talk and demo, as it is plagued with radio frequency interference.
During the demonstration, Wong
then presented a few cable mock connections with the probe connected to PC
based narrow band low noise spectrum analyzer (connected to a video
projector) and to the theatre sound system. The participants can see and
hear the noise interference on the cables. He showed the different type of
connection and cable with different levels of noise interference. The most
dramatic display of the evening was the demonstration of the single ended
grounding on a balanced audio line.
|
Mr. Eric Wong
describing to the members of the audience the backstage equipment at the
Kallang Theatre sound control room -
photograph by Christopher Yap |
One end of the
cable is connected to a DAT player and the other end of the cable to a
line preamplifier both balanced input and output. The ground on the
shield is only on one end. The preamplifier power and earth is connected
on socket outlet and the DAT on another socket outlet, about 20 metres
away. In theory, this would have eliminate any ground loops, hence any
noise built up. The noise was not eliminated in this demo to the
surprise of the participants. Wong then "stuck" a line balancing
transformer on the output of the "balanced" DAT output and the noise was
eliminated, not a trace on the analyser. This concludes, that all
balanced connections does not necessary provide the noise rejection
required. Transformer balancing is still "king". |
2 hours later, over a cup of tea
and cakes Wong along with Mr R I Simon the technical officer of Kallang
theatre fielded the question and answers session from the audience.
Questions asked included the various noise problems faced in installations
and discussions to the problems. Feedback from the audience were positive
and for many this was their first exposure to "behind the curtain" look in
this prestigious theatre of Singapore.
Singapore Section would like to
thank Mr R I Simon, staff of National Arts Council and CCW Acoustics Pte.
Ltd. for their support in making this AES event a success.
|
Mr. Eric Wong
(centre, with AES plaque), posing with AES Singapore section members and
guests on the Kallang Theatre stage. |
|
