HomeMy WebLinkAboutItem 8.2 ModifyChamberMicrophones
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CITY OF DUBLIN
AGENDA STATEMENT
CITY COUNCIL MEETING DATE: May 22,1995
~,...,{Modification of Council Chamber Microphones
VJF ,Prepared by: Paul S. Rankin, Assistant City Manager)
1. /. Microphone "Window of Acceptance"
2. / Catalog Description of Proposed Lavaliere Microphone
RECOMMENDATION,~~i;!t~: Authorize Staff to proceed with the modifications as outlined.
SUBJECT
EXHIBITS ATTACHED
FINANCIAL STATEMENT: Estimated Cost For 11 New Microphones is $2,640. Estimated cost of
manufacturing new connection and installation is $2,360. Funds are
available in the current year Building Management Budget.
DESCRIPTION As part of the annual Goals and Objectives, the City Council had
requested that Staff evaluate potential modifications to the Council Chamber audio system. The intent was
to provide a better amplification without requiring each speaker to look straight into their microphone.
During deliberations it is not uncommon for the seated Staff positions or City Councilmembers to address
individuals seated to their right or left.
System Configuration
The original system had the pyramid microphones mounted on the desk top and there was not a lighted
mute switch. In 1990, the City contracted with Coast Business Communications, Inc. (CBC) to modify the
system to raise the microphones and install the lighted mute switch. The current system is manufactured by
Shure and is from their Automatic Microphone System (AMS) line of products. The AMS system is
designed to solve problems typically encountered with a multiple microphone installation. All of the
microphones are "direction-sensitive" and are designed to turn on only when they are addressed within a
120 degree window.(See Exhibit 1) When the system is operated in the automatic mode, and more than one
microphone is used simultaneously, the gain level on the amplifier will automatically adjust. This feature
helps to avoid feedback and other distortion.
Proposed Changes
Staff contacted the CBC who is familiar with this system as well as has experience with Council Chamber
audio systems. The Contractor concurred with Staff. analysis that a "lavaliere" style microphone would be
the best way to assure the speaker remained within the "Window of Acceptance". The curved layout of the
Council Chamber dais, and the frequent occurrence where persons speak to individuals to the side, would
make it difficult for any other style to improve the amplification. Attached as Exhibit 2 is a catalog
description of the proposed microphone. This is still part of the Shure AMS line. Since the microphone
would be worn by the speaker it should capture their voice without regard to the direction they are facing.
In order to install the new microphones the Contractor has proposed to install an audio jack, which will
automatically disengage the pedestal microphones when the "lavaliere" microphone is plugged in. The
lighted mute button would continue to operate in the same manner as the current system. In addition to this
work, Staff has requested that the Contractor tune the system and provide a brief on-site overview of the
operation of the system for appropriate maintenance and City Staff.
Staff has also requested an estimate to modify one of the wall mounted microphone jacks to an audio output
jack. The purpose of this modification would be to allow Community Television a direct access point to the
audio system. The exact mechanics of this change have not been fully detailed. However, Staff has
discussed the conceptual operation with CTV and the Contractor and it appears that it is a feasible option.
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The purchase of the 11 new "lavaliere" microphones is estimated at $2,640. The manufacturing of the
switches, installation, system tuning, and CTV modification is anticipated not to exceed $2,360. This results
in a total project cost not to exceed $5,000. Staff has identified that funds are available in the Building
Management Department Budget and the modifications could be completed prior to June 30, 1995. Staff
would request City Council authorization to authorize Coast Business Communications, Inc. to proceed
with the modifications as outlined in this report.
ITEMNO.-8.Z
COPIES TO:
CITY CLERK
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BASIC SETUP: THE MICROPHONES
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WHAT TO DO
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6. In general, place the talker within the front acceptance
angla of the microphone.
7A. If the chairs are 3 feet or less from each other, use
one microphone between eech pair of seats.
78. If chairs are more than 3 feet from each other, use one
microphone per seat.
8. Remove any objects immediately behind the
microphones that may reflect sound.
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AMS22
MICROPHONE II
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AMS24
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HOW TO DO IT
6. Sound sources outside the shaded acceptance angle
will not tum on the microphone. See diagrams 6A
through 60.
7 A. Place each.microphona a foot and a half from the table
edge, halMay between the two seats,
78. Place each microphone a foot and a half from the table
edge, directly in front of the talker
8. The grille of en AMS26 [probe) or AMS24 [gooseneck]
microphone should be at least 8 inches above any table-
top. [The A26X Extension Tube inserted between the
swivel adf,lpter and desk stand will raise the AMS26 en
additional 3".) Remove objects behind AMS22 micro-
phones. .
EXHIBIT 1-
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MODEL AMS28
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LAVALlEA MICROPHONE FOR SHURE AUiOMATIC MICROPHONE SYSTEM
rhe Model AMS28 Condenser Microphone Is design.
ed for use only with the Shure Automatic Mlorophone
System (AMS). a unique and highly efficient method of
turning microphones on only when and If they are need.
ed. When used with Shure AMS mixers such as th~~
AM$4000 and AMSaOOO, this microphone provides ex.
cellent performance, versatility and ease of use In multi.
microphone Installations such as oonferenoe tooms,
legislatures, churohes, courtrooms, broadcast studios,
and panel discussions. The AMS28 Is a lavaller unit.
designed for chest.worn operation, and supplied With a
matching lavaller assembly.
Unlike conventional microphones, the AMS26 con
talns electronic: circuitry and a novel transducer con.
figuration to make It compatible with Shure AMS mix.
ers. Note that the AMS28 should not be conneoted to
standard phantom- (simplex.) or non-phantom.powefsd
microphone Inputs; It will not function properlY.
AMS microphones, In conjunction with the lifJ!:Icial
circuitry in the AM$ mIxers, uniquely discriminate be-
tween desired sounds that originate within their 120"
front acceptance angle and all other sounds. Sounds
from the front of a microphone are detected and caU$O
It to be gated on. transmitting 115 signal to the mixer Oul.
put. Sounds outside the acceptance angle will not galu .
the microphone on, When an AMS28 Is gated on. it
operates like a unidirectional (cardioid) microphone,
Each AMS microphone operates completely ill.
dependently In analyzing Its own sound field and
deoldlng whether or not a sound source Is within the
front acceptance angle.
The microphone connector Is a standard tlHue-pin
professional audio type (XLR). Under most clr.
cumstances, lengths of 150 meters (500 ft) Ot more of
gOOd.quallty two.conduotor shielded microphone cable
oan be used as an extension between AMS
microphones and AMS mixer Inputs. Note that the same
conductor must be wired to the same numbered. pin at
both endS of the cable to enSll(e proper functioning of
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the units. The shield must be connected to pin 1 at both
ends of the cable. Good practice dictates that
microphone and extension oables be grounded only to
Itle AMS mIxer chassis.
Features
. Microphone only turns on for weare('s speech and
nol for other talkers
. Low vibration and hum sensitivity
. Unidirectional design minImizes background noise
. Wide frequency response, especially tailored for
voice clarity
. A(:oustlcally optimized for lavalier operation
. Extremely flexible long.llfe cable
. l.ow handling and clothing noise
INSTAllATION
The lavaller assembly provided with the AMS28 Is
llesigned to keep the microphone fl(mly In plaoe durIng
use. The microphone, clip a.nd cord can be engaged ad.
jU$ted and removed quickly and easily. I
WII!) the AM$2S held by the rubber ring ot the lavaller
f:l$s(~mbly, place the lavaller oord around the user's neck
and secure the free end of the oord In the slot at the side
of the assembly (see Figure 1). Fasten the clip to the
\J5~r's shirt or blouse, and pull the oord through the slot
until the stack Is taken up. If desired. the ollp can be
rotated for left or right fastening, or It can be removed
by turning It to the vertical position and pulling straight
out. Adjust the cord length so that the AMS28 Is 200 to
250 mm (8 to 10 In.) belOW the user's mouth. IMPOR.
TANT: For proper operation, the AMS28 must be at
least 76 mm (3 In,) from any solid surface (table top or
Eldge).
ro rfllTlQve thE!! microphone, first disengage the clip.
With the microphone In one hand, pull the end of ihe
cord with the other hand to remove It from the lavaller
(l:,;sernbly slot; a qulok. steady movement will release It
Elasily.
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LAVALIER ASSEMBLY
FIGU RE 1
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