MEETING THE DEMAND FOR CEILING MICS IN THE ENTERPRISE
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WHITE PAPER
MEETING THE DEMAND FOR CEILING MICS
IN THE ENTERPRISE
5 BEST PRACTICES
This white paper will help you overcome potential issues with ceiling mics and
give you tips for delivering high-performance ceiling mic solutions in corporate
installations. The five best practices described in this paper will help you:
1. Develop an acoustical model to determine mic placement
2. Minimize ceiling noise impact
3. Configure mic settings for DSP/mixer
4. Create zones when voice lift is requested
5. Test system to ensure quality
1
WHITE PAPER: MEETING THE DEMAND FOR CEILING MICS IN THE ENTERPRISE
When the IT team at a F100 energy solutions manufacturer was tasked with
outfitting a new training room with AV equipment, they had a number of spe-
cific requirements. The room needed to support multiple configurations with
two divider walls. Tables in the room are stored in racks and are arranged
based on room use. This level of flexibility precludes tabletop mics as a solu-
tion and makes limited cabling a must. The VP of training, who signed off on
the budget, specifically requested minimal footprint of all AV equipment to
maintain the aesthetics of the room.
Multipurpose room applications and a growing preference among customers are making
ceiling mic installations more common in the corporate enterprise. The benefits to customers
are clear, but for integrators who have limited experience working with ceiling mics, respond-
ing to this demand can raise concerns. Will you be able to produce professional quality
audio? Is a ceiling mic a good fit for the room environment? Will the voices of participants
seated around the perimeter of the room be picked up? And what about ceiling noise?
THE DEMAND FOR CEILING MICS
Customers like ceiling microphones for a variety of reasons — no cables on the table, no
drilling holes in tables, a more aesthetically pleasing design, and freedom to move around
the room. Integrators, on the other hand, aren’t as enthusiastic. Ceiling mics have historically
been fraught with challenges due to their close proximity to loudspeakers and HVAC systems
and their distance from the person talking.
While the general rule of “the closer the microphone is to the talker, the better it will sound”
remains true, you can produce high-quality audio with ceiling microphones. Many techno-
logical advancements and improvements in mic design now make it possible for ceiling mic
quality to be as good, if not better, than tabletop mics in many environments.
The distance from the table gives ceiling mics an advantage in that they won’t pick up as
much intermittent table noises like paper shuffling and pen tapping. What’s more, the ceil-
ing tile surrounding the mic enhances low-frequency response, making voices sound more
natural than tabletop mics.
Still, to avoid issues such as poor intelligibility, feedback and echo, it is important to follow
best practices for ceiling mic installations. Doing so enables you to not only produce the best
quality sound possible when customers request ceiling mics, but also allows you to recom-
mend ceiling mics without hesitation when they provide a better solution for your customers.
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WHITE PAPER: MEETING THE DEMAND FOR CEILING MICS IN THE ENTERPRISE
BEST PRACTICES FOR CEILING MIC INSTALLATIONS
1. DEVELOP AN ACOUSTICAL MODEL
The best method to ensure ceiling mics will perform well in a room is to create an acousti-
cal model. An acoustical model is based on room dimensions, materials, application, and
acoustics. It will help you determine whether ceiling mics are appropriate for the room, the
number of mics needed, and where they should be placed to deliver the desired coverage.
Consider room acoustics
Room acoustics have the most impact on the success of a ceiling mic project. Room acoustics
are impacted by hard surfaces such as glass or brick walls, concrete floors, or hard ceilings.
These surfaces reflect audio and cause reverberation, which can reduce intelligibility, making
it difficult to understand meeting participants.
To ensure the space is appropriate for ceiling microphones, measure the reverberation pe-
riod. You can do this by using a calculation that determines if speech sounds reverberant due
Note: You can request a free to short-term reflections from room surfaces or echoes due to longer-term reflections. How-
acoustical model for your ever, the calculation is complex and a full discussion of the calculation is beyond the scope of
project at www.ctgaudio. this paper. But you can get help from mic manufacturers like CTG Audio, which provide free
acoustical modeling services based on a project survey.
com/survey.htm
Ceiling mics have many advantages, but some rooms are not acoustically suited for a ceiling
microphone solution. In this case some rooms may be treated for improved acoustics, or
table top or implant microphones used instead.
Determine microphone placement
Ceiling mounted omnidirectional mics can cover much larger areas than conventional micro-
phones, especially in larger rooms. This large pickup area creates risk of using too few or too
many mics in a room.
Over miking can cause too many mics to gate on as meeting participants talk, which degrades
performance and increases reverberation effects in reflective room environments. It also will
increase equipment costs, negating one of the big advantages of using ceiling mics.
Under miking creates uneven coverage of the meeting room. Depending on where they are
sitting, some participants will have poor coverage while others will have good coverage. As
participants move around the room while talking, the audio quality can vary significantly.
To determine the appropriate number of mics, you will need to calculate the effective mic
distance based upon the characteristics of the mic and the acoustic properties of the room
itself. These calculations will result in the proper quantity and the correct spacing between
mics for the room. Even more importantly, these calculations will indicate how the system
will perform.
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WHITE PAPER: MEETING THE DEMAND FOR CEILING MICS IN THE ENTERPRISE
Figure 1. Large Meeting Room Figure 2. Medium Meeting Room
Figures 1 and 2. Consider two examples. The first is a room 34’ x 19’ and the second is a room
23’ x 21’. Even though one room is larger, with a larger table, the rooms require the same
number of mics to achieve the desired coverage. If an acoustical model had not been devel-
oped, the larger room would have been over miked.
Best practice guidelines for mic placement
• Analyze acoustical properties of the room. Use ceiling microphones only when the
acoustical model indicates they will produce good intelligibility.
• Request an acoustical model to determine the number of mics and their placement in
the room.
• Seek a room reverberation time of less than .35S and an NC (noise criteria) no greater
than 48dBA (A-weighted decibels). The dBA measurement uses an A-weighted filter to
more closely represent the characteristics of human hearing.
WHAT ABOUT HANGING MICS?
Hanging mics were designed to close the talker-to-element distance. While hanging mics succeed on that front, the
design creates new problems. Hanging microphones are more sensitive to air motion, which creates white noise in the
background. Because white noise is “steady state” noise, it requires special algorithms to remove it from the signal path.
When you factor in a ceiling mounted projector, or high velocity HVAC air vents, that is a lot of wind noise.
The second problem is that moving the mic closer to the talker, you reduce the pickup pattern area, requiring more mics
for a specific room. This adds more complexity and noise into the system. There have been attempts at multi-element
mics using array or beam-steering technologies. While these show some promise, they are also expensive and somewhat
complex to install. Most are proprietary systems unable to work across a wide range of DSP manufacturers.
4
WHITE PAPER: MEETING THE DEMAND FOR CEILING MICS IN THE ENTERPRISE
2. MINIMIZE CEILING NOISE
Ceiling noise can be an issue. In a typical conference or distance-learning room, there is
HVAC air movement from the ceiling. This noise is extremely hard to remove from the audio
path because of its wide frequency content and steady state nature. Usually, only mixers
with sophisticated algorithms with individual per-channel processors can reduce the noise
without generating audible artifacts.
The source of this noise is airflow through the microphone windscreen. Because air vents
Note: Airflow is directed
push air down toward the floor, flush-mount ceiling mics have a natural advantage over
downward and does not hanging mics since they are mounted out of the air path and aren’t impacted by this type
blow across the microphone of noise.
element to create noise. The
noise reduction processing Air Vent
Flush-Mounted
Ceiling Mic
of the microphone mixer Ceiling
eliminates any constant long
period sound coming from Air Flow Pattern Hemispheric Mic Pattern
the air register.
Floor
Figure 3. Air Flow Patterns
A secondary issue created by HVAC systems is physical vibration transmitted to the micro-
phone element when mounted in the ceiling surface. A typical ceiling grid does not have the
mass to isolate itself from vibration caused by air handlers.
Solve this conductive noise issue by specifying a mic that isolates the electret elements from
vibration and mechanical noise. This practice ensures the mic is not impacted by the surface
it is mounted in.
The distance between the mic and the table surface makes other types of background noise
such as paper shuffling, keyboard strokes, or pen tapping negligible. This type of noise is
considered intermittent, while ceiling noise is constant. Constant noise sources are easier for
mixers with noise-suppression algorithms to eliminate or minimize.
Best practice guidelines for minimal noise
• Specify a microphone element that has a vibration isolation of greater than 70dB to
reduce background noise from mechanical systems.
• Enable noise suppression in the mixer.
• Specify flush-mount mics where air vents are an issue.
5WHITE PAPER: MEETING THE DEMAND FOR CEILING MICS IN THE ENTERPRISE
3. CONFIGURE MIC SETTINGS FOR BEST PERFORMANCE
Mics must be configured for the mixer to which they are connected in order to perform as in-
tended. The first consideration is mixer input sensitivity, which for most ceiling-installed mics
tends to be higher than for tabletop or gooseneck mics. These mics have an input sensitivity
in the low to mid -40dB range, while a typical ceiling mic has an input sensitivity in the low to
mid -50dB range. All professional mixers that support multiple mic types allow you to set the
proper mic sensitivity. This is not an arbitrary value. If a microphone has a specified sensitiv-
ity of -54dB, set the mixer input to 54dB to normalize the microphone to the mixer’s gain
structure. Once sensitivity is set, adjust the input level setting to the desired volume.
Gating/Beamforming
Most professional mixers use gating or beamforming, which allows only the microphones in
actual use to fully turn on. Gating reduces random noise caused by people in the room, as
well as noise from heating and ventilation systems. Although advanced DSP mixers can filter
continuous noise, intermittent noise like that caused by human activity is difficult for even
the most sophisticated processing circuits to distinguish from speech.
In a typical conference room with multiple mics, restrict the number of open mics to two or
three. Typically the last mic used is held open until the next person speaks or the mic that
is designated as the chairman mic is used. This arrangement not only minimizes noise but
keeps the room from going completely silent when no one is speaking.
Best practice guidelines for mic settings
• In most cases, a microphone element that is flush to the ceiling adds an additional 6dB
because of the boundary surface, reducing the amount of gain needed at the micro-
phone preamp.
• Limit number of open mics to two or three mics.
• Configure mic sensitivity based on the mic type.
BIAMP GAIN STRUCTURE AND DSP SETTINGS FOR CTG CEILING MICROPHONES
The correct setting for the sensitivity of CTG microphones is 52dB to 54dB. Gating with a Nexia usually creates the best
results. Depending on the size of the meeting, a maximum NOM of 2 or 3 is best. It’s best to designate a “chairman
microphone” so that the participants at the distant end of the conference always hear the characteristic sounds of the
room. If every microphone is gated off when no one is speaking, the lack of sound cutting in or out is annoying and
degrades the illusion of a face-to-face dialog between parties.
A gating threshold of -20dB works well and makes the gating sound transparent. EQ, if any, depends entirely on the
acoustics of the room. In general, smaller rooms accentuate lower frequencies, as do combinations of room dimensions
that create standing low-frequency waves. If applying EQ, cutting rather than boosting frequencies prevents distortion. A
flat response is not the goal. The goal is a slight peaking in the upper voice frequency range to enhance intelligibility.
6WHITE PAPER: MEETING THE DEMAND FOR CEILING MICS IN THE ENTERPRISE
4. CREATE ZONES FOR VOICE LIFT
Voice lift is the concept of allowing participants in large rooms to hear each other within the
room. A technique used to accomplish this is to divide a large room into two or more zones
for speakers and mics. The mics in each zone feed the speakers in the other zones, thus mini-
mizing the occurrence of feedback. Voice lift is often used in rooms where participants may
be more than 30 feet apart.
Note: An approach that The audio is amplified in the target zones at low levels to provide just enough volume to
works well with ceiling mics replace the loss in dB that occurs because of the distance between zones. Typical gain in-
is essentially the reverse of creases are between 3dB to 9dB.
mix-minus. In this technique,
ducking is used to reduce the
gain of all the mics in Zone A
except the one that is used to
transmit audio to Zone B. The
participants in Zone A can hear
the participants in Zone B and
Zone B can hear the person
speaking in Zone A. The DSP’s
matrix mixer controls the fully
active microphone.
Figure 4. Large Training Room with Zones
With conventional close talk microphones, mix-minus techniques are often used to accom-
plish voice-lift. However, these techniques are not as effective with ceiling mics because sev-
eral mics could be within the range of a single speaker. Ceiling mics in large rooms can have a
usable radius of up to 10 feet or more.
If there is a presenter in the room, he or she can use a wireless lapel mic, which will not be
sensitive enough to cause feedback. This type of mic will allow the presenter to move around
the room freely.
Best practice guidelines for voice lift
• Create zones or ducking to provide voice lift instead of mix-minus.
• Only increase the volume enough to replace dB lost over distance—typically 3dB to 9dB.
• Give presenters a wireless lapel mic.
7WHITE PAPER: MEETING THE DEMAND FOR CEILING MICS IN THE ENTERPRISE
5. TEST SYSTEM TO ENSURE QUALITY
In a teleconference application, the benefits of a good install typically accrue to the far-end.
On completion of installing the equipment, the performance of the system needs to be
evaluated. Call a remote location from the system and perform these steps:
1. Move around the coverage area and ask these questions:
Note: Testing the system can • Is the level comfortable for normal conversation?
make a significant difference • Is the intelligibility good from all locations?
in audio quality and customer • Were you aware that the technician was moving around the room?
satisfaction. • Do you detect any reverberation and/or echo?
• Is the pick up the same from all locations?
2. Adjust the send levels and count from 1-10 while doing it.
• Ask what number was the most comfortable.
3. Have the near-end introduce some constant noise, such as a fan. Test that the noise
suppression in the mixer eliminates it at the far-end.
Success Story
A large multi-national company installed a ceiling based audio system in a large training
room. They had been using it for about 5 weeks when a representative from CTG Audio vis-
ited the site. While the client was very pleased with the system, the rep suggested they call
his engineering department on the system to test quality.
The engineer noticed some reverberation and minor artifacts as the person talking moved
around the room. He asked the client make some adjustments and they were able to hear
the results real-time. These changes improved the quality of the sound by at least 20%—a
difference that improves intelligibility and reduces listener fatigue in training meetings.
Clients often have different standards for quality. Calling an experienced listener can gener-
ally optimize the settings and deliver sound quality that exceeds customer expectations.
ABOUT CTG AUDIO
CTG Audio manufacturers high-performance, flush-mounted ceiling microphones. Beyond
engineering expertise, CTG Audio offers AV integrators a variety of free support services that
will ensure project success starting with developing an acoustical model. Based on a short
project survey that the integrator completes, CTG Audio will calculate critical distance, rever-
beration, and determine the number and placement of mics in the room. Once installation is
complete, integrators can call CTG Audio’s engineering department from the install room to
test and optimize audio quality.
8Figure 5. Typical Placement Layout for a Training Room.
CM-01 CEILING MICROPHONE
The CM-01 ceiling microphone use a special, pressure sensitive, tensionless low-mass ele-
ment enhanced with an integrated FET low-noise amplifier. These characteristics result in
ultra-smooth frequency response, providing excellent feedback stability for voice reinforce-
ment and teleconferencing applications. The high temperature stability assures exceptional
system performance in fixed-gain situations. In an average acoustical environment, the CTG
ceiling microphone has a pickup range with a radius of up to 10 feet or more. These mics:
• Eliminate the need to walk up to a table to be heard in a room with perimeter seating
• Allow furniture to be rearranged without compromising the audio system
Figure 6. CM-01 Microphone
• Provide even pickup for the maximum number of participants with the minimum num-
ber of microphones
• Create a clean, clutter-free environment without visible cables
• Are virtually invisible because they are flush mounted in the ceiling and the visible por-
tion is smaller than a dime
• Minimize unwanted table noise such as paper shuffling, pen clicking, or key strokes
• Free participants to turn their backs to the table, walk around, and still be heard evenly
LEARN MORE
To learn more about the CM-01 microphone or to hear it in action with a Biamp DSP/mixer
call 941-922-2322 to request demo equipment.
If you would like an acoustical model developed for your ceiling mic project, simply complete
the form at http://www.ctgaudio.com/support.htm
© 2012 Conference Technology Group, LLC. All Rights Reserved. 9You can also read
