whitepaper duo vs single speakers

8/2/2019 Whitepaper Duo vs Single Speakers

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McSquared System Design Group, Inc.

#102 145 West 15th Street, North Vancouver, BC V7M 1R9 Ph 604.986.8181 Fax 604.988.9751website: http://www.mcsquared.com e-mail: [email protected]

Sound Field Speaker Coverage Modeling Study

Prepared for:

Phonic Ear Inc.

3880 Cypress DrivePetaluma, CA

File: 5325

June 11, 2004


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Phonic Ear Sound Field Speaker Coverage Study Page 2

McSquared System Design Group Inc.

Purpose of the Study..................................................................................................... 3The Sample Classroom.................................................................................................. 4

The room model of Upper Lynn Valley Elementary room #211 ......................................... 5Speaker Configurations Modeled ..................................................................................... 6

Direct Sound versus Total SPL..................................................................................... 6RaSTI Predictions ...................................................................................................... 7C50 (Clarity Ratio) .................................................................................................... 8Conclusions and Recommendations.............................................................................. 8Sound Field Configuration: ToGo corner mounted at 7 to the center of speaker............. 11Sound Field Configuration: ToGo on Desk or Table top.................................................. 27Sound Field Configuration: single small speaker (flat panel, etc.) mounted in corner......... 44ToGo 3D polar response prediction produced by EASE 4.0............................................. 60


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Purpose of the Study

The purpose of the study was to look at predictions of sound field speaker performance usingEASE 4.0 computer modeling software, one of the most widely used sound system design

packages in the industry. The study would include the most common speaker systemconfigurations and common speaker models employed in the sound field application.

The study would be based on acoustical measurements taken in a real elementary schoolclassroom currently using a sound field speaker system, and then the existing acoustical

conditions would be extended in the model to include two higher levels of background noise andtwo longer values for reverberation time to examine which speaker system solution worked best

in varying acoustical conditions that are the primary factors in reducing speech intelligibility.

The results of interest include:

1. Direct sound coverage of the seated ear plane using phase information to calculateexpected interference patterns to show the uniformity of direct sound, which affects bothintelligibility and gain before feedback.

2. Total SPL (direct + reverberant sound energy) at three different reverberation times toassist in showing the relationship between direct sound coverage and the reverberantsound level, and how that can be misleading in predicting improved intelligibility.

3. RaSTI (Rapid Speech Transmission Index) predictions for three different background noiselevels and three different reverberation times to assist in showing which speaker systemconfiguration is the best for rooms where excess noise or excess reverberation time are

the dominant problems.

The study would help to identify common errors in speaker placement and application; speaker

system configurations that reduce the effectiveness of a speech reinforcement system; speakerconfigurations that will reduce gain-before-feedback when used with an open microphone; and

the benefits of one type of speaker over another in providing effective coverage.

These issues have been studied extensively over the past 20 years since the advent of accessibleand affordable time domain measurement capability appeared in the form of the Techron TEF

analyzer. This measurement system allowed sophisticated Time Delay Spectrometry

measurement methods to be applied to sound systems. It would not be an overstatement to saythat more has been learned about the behavior of loudspeakers in an acoustic environment in the

past 20 years than had been understood for the previous 60 years, since Rice and Kellogdeveloped the moving coil loudspeaker in 1925.

The TEF analyzer plainly disclosed the cause of problems with sound systems that could not be

corrected with an equalizer because the response variations were created by a non-minimum

phase system, in other words, a speaker system that had signal delays present in excess of awavelength. That single breakthrough in observation of speaker system performance changed the

understanding of what happens when sound sources interact with each other in the acousticenvironment.

When sound is cancelled out by destructive interference of the sound waves, it cant be repaired

using an equalizer. When the sound is cancelled out, it also begins to have a response that looksvery similar to someone with a significant 4kHz hearing notch. It is possible to install speaker

systems with a frequency response that replicates hearing loss, and presents a different response

at every seat in the house. And thats not a good thing.


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The Sample Classroom

The classroom is a 24x30 room with a 9 T-bar ceiling, and an entry vestibule area in the front

corner. There are windows on two outside walls, with operable windows. The neighborhood is

very quiet with no through traffic nearby so exterior noise is minimal. The most significant noisesource was an air pump on the small fish tank on the south exterior wall.

There is a low bookshelf beneath the windows on the east side and a collection of shelves and

tables below the windows on the south side.

Measured Background Noise

The background noise measurements were made with an unoccupied room, the windows openand the aquarium pump running. Measurements were made in a number of locations and the

highest levels were used near the aquarium to capture the worst-case noise condition.

125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz 8000Hz

48 dB 36 dB 35 dB 33 dB 26 dB 21 dB 19 dB

Measured Reverberation Time

We measured the reverberation time with the room unoccupied. There was a small area carpet on

the floor near an upholstered couch, and a substantial amount of books and materials in theshelves around the perimeter on two sides, so the reverberation time was quite short in the voice

bands.

125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz 8000Hz

0.50 Sec 0.30 Sec 0.32 Sec 0.30 Sec 0.5 Sec 0.45 Sec 0.3 Sec

The room model is shown on the next page. It features the major architectural shape features,

and the ear plane is set at 36 above the floor to reflect the shorter listeners. The image of theroom model shows the ear plane where the coverage and STI plot was calculated. The STI plots

have the room model boundaries turned off for clarity of display, but they were part of thecalculations.


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The room model of Upper Lynn Valley Elementary room #211

Upper Lynn Valley classroom #211 ear plane off

Upper Lynn Valley classroom #211 ear plane on


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Speaker Configurations Modeled

We modeled several configurations and types of loudspeakers, including:

1. Four speakers mounted on side walls (including variations in mounting and product)2. Four ceiling loudspeakers3. Six ceiling loudspeakers4. Soundsphere ceiling mounted speaker5. TOA F121C ceiling speaker6. Ceiling speaker cluster with 4x 8 drivers in a 24 tile replacement7. FrontRow ToGo mounted in room corner at 7 to speaker center8. FrontRow ToGo sitting on desk or table top9. Phonic Ear Logia mounted in corner10.One 5 2-way speaker in room corner

Most of the device files were available in EASE 4.0, the exceptions were the ToGo and Logiadevices. We created these devices as clusters of existing measured single full range drivers using

the driver size and spacing in the drawings provided to us by Phonic Ear and EASE created thepolar balloons as shown in the section at the end of the document. In the Logia model we shaded

the line array by rolling off the response of the upper and lower drivers above 1000z to reducethe lobing and interference at higher frequencies, this produced a tight vertical pattern. There

may be some slight variation between the predicted and actual coverage of the ToGo and Logia,

but most of the line array coverage behavior is a result of driver spacing and interference, notindividual driver characteristics, so the variations should not be significant.

Direct Sound versus Total SPL

Weve plotted both the direct sound and the total SPL for each speaker configuration. The direct

sound is the direct output from the loudspeaker without reflections or room reverberationconsidered. The direct sound is the most important aspect of a speakers behavior, as the human

brain attempts to process and isolate the direct sound for localization and for timbre or soundquality. All the other reflections that arrive up to 50 milliseconds after the direct sound can

augment the direct sound but those reflections dont improve the audible sound quality, eventhough they may add to the perceived sound level and intelligibility (when the reflections contain

useful bandwidth).

The reflections also affect sound system function such as gain-before-feedback, as the reflections

and lobes can create hot spots that lower the feedback threshold. A 6dB bump in the frequency

response can lower the feedback threshold at that spot by 6dB. The smoother and more uniformthe direct sound coverage, the better behaved the sound system will be around an activemicrophone. Where the teacher will be walking through various lobes in the direct coverage, there

is a chance that the system will be sent into feedback by the sudden increase in level at a fewspecific frequencies.

The direct sound coverage is affected by the interference generated by having multiple soundsources separated in physical space and time. The distance between speakers creates non-

minimum phase response variations that are different depending on the frequency involved.Where the direct coverage is subject to wide variations over a wide range of frequencies, weve


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plotted direct coverage as low as 250Hz (approximately middle C on a musical scale, which

sounds like high frequencies to most listeners) to show vulnerabilities to early feedback when amicrophone is used.

The Total SPL (direct plus reverberant levels) is indicative of what would be measured if a sound

level meter were used to evaluate the uniformity of the sound field coverage in a room. This is

not representative of the speech intelligibility that would result from the sound system. The

2000Hz STI plots show that the STI values are closely related to the direct sound and not theTotal SPL. This is the equivalent comparison of measuring a sound system using a TEF analyzerand a sound level meter, by isolating the direct sound we get a much better idea of what we can

expect for intelligibility. Any manufacturer using a sound level meter to promote the uniformity oftheir sound field system is not presenting an accurate indication of how the output from the

system will be perceived.

The reader should notice that as the Total SPL becomes more uniform with increasingreverberation time and the difference between maximum and minimum SPL values is reduced,

the RaSTI values generally increase in spread between maximum and minimum values, and the

maximum STI values go down.

RaSTI Predictions

The 2000Hz RaSTI predictions show the predicted intelligibility, factoring in the direct sound

coverage, the room reverberation and the room background noise. Both background noise andexcess reverberation will degrade speech intelligibility. Weve plotted the RaSTI prediction for the

existing room conditions as measured, plus higher levels of background noise (NC-45 and NC-55)and longer reverberation times (0.75 seconds and 1.0 seconds).

For each speaker configuration this shows the trend in speech intelligibility performance loss.Some speaker configurations will produce better results in rooms where the acoustical problem is

excess reverberation, and some speaker solutions may be better suited to a room where theproblem is excess noise.

In general, where the acoustical problem is excess reverberation a speaker configuration thatplaces the speakers close to the listener usually gives the best results.

Where the acoustical problem is excess background noise, any speaker system that can improve

the listeners signal to noise experience will improve intelligibility. Then the key design issuebecomes whether or not good uniformity in sound level can be achieved so that when the sound

system is loud enough for the furthest listener, it is not too loud for listeners closer to the source.

The existing test room acoustical conditions are such that almost any solution works adequatelywell, even an unaided talker can function in the room and provide adequate level at the furthest

listener. As noise and reverberation are increased, the spread in STI values increases betweenworst and best seats.

Thats the key thing to look at in the RaSTI plots for each scenario, look at the minimum STIvalues and the spread between the maximum and minimum STI values. The best speaker

configuration is the one that provides the least difference between best and worst seats, and thehighest overall STI rating. Those speaker configurations will be the ones that have the most

uniform coverage and the highest direct-to-reverberant ratio.

A good STI design target for a classroom would be 0.60 (fair) or higher.


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C50 (Clarity Ratio)

The C50 or clarity ratio is the ratio in dB of the sound arriving in the first 50 milliseconds

compared to all the sound arriving later. This is roughly equivalent to the U50 rating that JohnBradley at the National Research Council in Canada promotes as a measure of Useful Energy in a

classroom. The most beneficial energy arrives within the primary Haas zone of 35 milliseconds,

but energy up to 50 milliseconds can provide additional level to speech as long as these late

arrivals have enough spectral content to assist the speech information.

Conclusions and Recommendations

As with any speech reinforcement system, the goal of these classroom speech reinforcementsystems is to provide superior speech intelligibility performance to unaided speech. Those goals

would include: uniform speech levels for all seats; uniform frequency response of reinforcedsound in all seats; improved signal to noise ratio; improved direct to reverberant ratio; and

improved articulation of consonants or modulation transfer function.

For a sound system designer, that list of goals has to be balanced with practical architectural and

budget limitations, so there is always some degree of compromise between the perfect solution

and the available solution. The key to good sound system design is to understand what the actualeffects of a design compromise will be, and to avoid making compromises that affect the ability todeliver the minimum required performance. The limits of those design compromises are set by

functional requirements of the users and the environment the system operates in. In a swimmingpool, where the minimum requirement might be to understand a simple command such as

Everyone clear the pool a speech reinforcement could have an STI rating as low as 0.45 and itcould still provide effective communication. In a classroom where the minimum requirement may

be to successfully communicate the properties and uses of polytetrafluoroethylene, a minimum

STI rating may need to be as high as 0.65.

If the speech reinforcement system fails to meet the design goals, it fails as a useful item, nomatter how inexpensive or easy to install it might have been. This would be equivalent to using

strings of Christmas lights for general room lighting instead of fluorescent lights, because the

Christmas lights are cheaper and easier to install and do not require an electrician or otherspecialized technician. The installation may have been inexpensive, but they arent very effectivein providing a suitable work light level.

Speaker System Issues

Of the speaker types and configurations reviewed in this study, there are a few consistentbehaviors that were observed.

Two Way Surface Mount Speakers

While there are some minor variations between the various brands and models of small two way

speakers (5 woofer and a separate dome tweeter), but they all share a common problem of acollapse of the vertical coverage pattern at the crossover point where both the woofer andtweeter are operating at the same level. This is typically an octave wide band at 3-4kHz, right in

one of the more critical bands for articulation of consonants. The only small speakers that dontbehave in this fashion are devices with the tweeter coaxially located in the centre of the woofer.

The effect of that vertical coverage collapse is often an octave wide frequency band that can have

a coverage pattern as narrow as 20 degrees vertical. If these boxes are turned sideways andmounted horizontally, as is commonly done when yoke mounting them, that becomes a very

narrow horizontal coverage pattern in that critical octave. This makes placement and aiming of

these small two way speakers very critical if full speech band performance is going to be delivered


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to the seats. The mounting positions that would provide the best overall level uniformity are not

necessarily the mounting positions that work best for 3-4kHz.

Single Speaker Solutions with Spherical Spreading Wavefronts

All single speaker solutions that have a coverage pattern that approximates a sphericalwavefront, and therefore inverse square law attenuation of the direct sound, have the same basic

limitation in covering a large area uniformly. This would include the single TOA F121C speaker,the Soundsphere, a small speaker in one corner, the four speaker pyramid ceiling speaker, anNXT flat panel, etc. This is the same basic behavior as an unaided talker. The only way to be loud

enough in the back is to talk louder at the front.

For any single speaker installation there will be a significant drop in direct sound level withincreasing distance, and this will always result in having the sound levels be much higher for

listener close to the speaker than the most distant listener would experience. If the distance islarge enough it may be too loud for the closest listener when it is adequately loud at the most

distant listener.

These systems will always have an issue where the feedback threshold with an open microphone

will limit the maximum available sound level. By the time the system gain is increased to thepoint where it would be louder than the unaided voice, it will likely be prone to feedback when the

teacher was close to the speaker and will operate safely when the teacher is furthest away fromthe speaker. If this is the only way the system is used, where the single loudspeaker is on the

opposite side of the room from the teacher, then there can be some small benefit to the increased

sound level at the greatest distance from the teacher, but that also limits how close the teachercan get to the speaker and the students on that side of the room.

Typically any room that can be covered by a single small speaker could just as effectively be

covered by a talker with louder voice, and the primary acoustical problem would be elevatedbackground noise levels and not excess reverberation.

Single Speakers with Shaped Coverage

The ToGo and Logia line arrays show some real promise for good sound level uniformity over amoderate size of classroom. The key aspect in using any line array is to make sure the audience

seating is kept far enough away from the loudspeaker so that they are beyond the nearfieldanomalies in a line array, and instead they are all seated in the area where there is minimal

change in level or frequency response.

The other major issue to consider when placing line arrays is that they do have a nominal

cylindrical fan shaped coverage pattern. That speaker coverage should not be pointed at the rearand side walls, the fan shaped coverage should be tilted down so that the centre of the coverage

pattern aims at the most distant seated listener. In that scenario, most of the sound is directedinto the seating and not at the rear and side walls. All the seats are typically within the vertical

coverage if the most distant seat is the selected target. The speaker should be mounted high

enough that the entire coverage pattern does not have to make its way through a forest of headsto get to the rear row. For elementary school seating, the bottom of the line array should be at or

just above seated student head height and at least 6-8 away from the closest listener. If the linearray is tilted down from that position and aimed at the most distant seat, the direct sound

coverage should be fairly uniform.

Even line arrays may not be the best choice when excess reverberation is the primary acoustical

problem as they are still limited by the available direct-to-reverberant ratio that a single speakercan provide in a reverberant room. They might have 3-5dB better D/R than a conventional single

speaker, but that may not be adequate in all reverberant classroom settings.


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Multiple Speaker Locations and Positioning

When installing multiple ceiling or wall mounted speakers, the two most important considerations

are having the distance between the speaker and the listener be as short as practically possible;and having the density of the speakers be high enough to keep the notches caused by destructive

interference narrower than 1/3 octave in any seat. If the speaker spacing is equal to the ceilingheight, that will often provide enough overlap in coverage to keep the cancellation notches below

1/3 of an octave. Some ceiling loudspeakers have a broad enough 2-4kHz coverage pattern toallow center to center spacing up to 1.5 times the ceiling height, but not all ceiling speakers arecreated equal.

The installation of multiple ceiling speakers will often provide a higher D/R ratio in a reverberant

environment, primarily because the speaker is closer to the listener, and all listeners have asimilar speaker to listener distance. When the reverberation time becomes very long, increasing

the number of speakers can begin to reduce to the intelligibility. This can be calculated in advanceof installation using conventional spreadsheet sound system calculations, software is not required.

Room Acoustics and Speaker Selection

In rooms where excess background noise is the major problem and reverberation time is fairlyshort and controlled, almost any loudspeaker can provide an improvement in speech intelligibility

by making speech louder and improving signal to noise. The primary design consideration isuniform sound level and frequency response. That might be provided using a single line array, or

multiple ceiling speakers, or even the side wall mounted speakers in a narrow enough room.

In rooms were excess reverberation is the primary problem and there are also problems with

elevated background noise exacerbated by the excess reverberation time, the speaker selectionprocess needs to be considered more carefully. Ceiling speakers are often a good choice in this

setting. Having the speakers closer to the listeners definitely helps improve intelligibility byimproving both S/N ratio and D/R ratio. Single speaker solutions may not deliver adequate

performance in highly reverberant environments.

Available Amplifier Power

One of the most significant performance aspects of sound system design is having adequate

headroom for the signals being reproduced. Many small loudspeakers have very low efficiency,often in the range of 80-85dB @1watt @1metre. To deliver reinforced speech levels higher than

unaided speech with a dynamic signal like speech often requires much more power than is

provided. One of the observations we have made of several sound field systems is that they aredrastically underpowered and so they often exhibit severe clipping just as they are producing a

sound level that would be louder than an unaided talker. It is not unreasonable to assume a 20dBdynamic range for a speech source unless it is heavily compressed. Any speech reinforcement

system should be designed so that it will not clip in normal operation. The system gain limitshould be the feedback threshold and not the amplifier output power.


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Sound Field Configuration: ToGo corner mounted at 7 to the center of speaker

500Hz direct sound field

The ToGo is mounted at 7 to the center of the speaker and the speaker has a 10 degree downtilt

so that the axis of the speaker is aimed at the ear plane in the opposite corner of the room.

The ToGo achieves a large area of uniform coverage even though there are some large variationsclose to the speaker. The maximum level is 91.28dB and the minimum level is 76.6dB for a total

variation of14.68dB. The seating area is within 6-7dB in uniformity.


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ToGo corner mounted


At 2000hz there is a very large uniform area of coverage. The maximum level is 88.04dB and the

minimum level is 67.77dB for a total variation of 20.77dB. The bulk of the seating area is within5-6dB of level uniformity.


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ToGo corner mounted


At 4000Hz the patch is a different shape but similar in overall size. The maximum level is 89.61dBand the minimum level is 68.07 for a total variation of 21.54dB. The bulk of the seating is within

4-5dB although there are some large blue areas near the seating on the side near the speaker

system.


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ToGo corner mounted

2000Hz Total SPL (direct + reverberant) at current reverberation time

The maximum level is 88.75dB and the minimum level is 80.76dB for a total variation of 7.99dB.


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ToGo corner mounted

2000Hz Total SPL (direct + reverberant) at 0.75 second reverberation time

With the 0.75 second reverb time the level variation drops to 3.99dB.


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ToGo corner mounted

2000Hz Total SPL (direct + reverberant) at 1.0 second reverberation time

At 1.0 second reverb time the level variation drops 3.19dB.


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ToGo corner mounted

RaSTI with current background noise and current reverb time

The single ToGo has a very large area of superb STI value. The maximum is 0.77 and theminimum is 0.72, but the area of 0.74 to .75 is very large.


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ToGo corner mounted

RaSTI with NC-45 background noise and current reverb time

Increasing the noise level does not affect the STI values.


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ToGo corner mounted


Increasing the background noise to NC-55 reduces the minimum STI value but has no significanteffect on the area that scores good values of 0.74 to 0.75.


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ToGo corner mounted

RaSTI with NC-45 background noise and 0.75 second reverb time

Increasing the reverb time to 0.75 seconds reduces the maximum STI values and increases the

range of STI values. The maximum value is 0.69 and the minimum value is .58. The area thatachieves 0.62 to 0.65 is quite large and uniform.


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ToGo corner mounted


Increasing the noise level to NC-55 has no significant affect on the STI values


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ToGo corner mounted


Increasing the reverb time to 1.0 seconds reduces STI values overall. The maximum value is 0.65and the minimum is 0.54. The uniformity of the STI values is noticeably reduced from the 0.75

second values.


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ToGo corner mounted


Increasing the noise level to NC-55 does not significantly affect the STI values, there is only a

slight reduction. Any single source speaker solution is more affected by excess reverberation thana distributed speaker solution.


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ToGo corner mounted

2000Hz C50 with the current reverb time

The ToGo provides very uniform C50 values over a large area, most of the seating is between 11-15dB.


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ToGo corner mounted

2000Hz C50 with 0.75 second reverb time

Increasing the reverb time to a 0.75 second drops to a range of 2-7dB, with the bulk of the

seating area ranging from 3-5dB.


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ToGo corner mounted

2000Hz C50 with a 1.0 second reverb time

As with any single source speaker system configuration, the C50 values drop off with increasing

reverb time. At 1.0 seconds the range of C50 values drops from 5-0dB. The bulk of the seatinghas a value between 0-3dB.


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Sound Field Configuration: ToGo on Desk or Table top


With the ToGo speaker closer to the ear plane and closer to the listeners, the near field anomaliesare more likely to interact with the teachers microphone.

The maximum level is 95.77dB and the minimum level is 77.21dB for a total variation 18.56dB.

The bulk of the level difference happens within the first 4 radius of the loudspeaker. The bulk ofthe seating area is covered with a uniformity of 6-7dB.


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ToGo on Desk or Table top


The 1000Hz coverage is more constrained at this mounting height. The maximum level is

88.66dB and the minimum level is 68.8dB for a total variation of 19.86dB. The bulk of the levelvariation occurs in the nearfield of the speaker. There is about 10dB of variation throughout the

seating area.


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The 2000Hz coverage pattern appears as a largely square footprint at this mounting height. Themaximum level is 93dB and the minimum level is 58.91dB for a total variation of 34.04dB, with

the bulk of the variation in the nearfield of the speaker location.

The bulk of the seating area is covered to a uniformity of about 6dB. The nearfield exhibits someextreme behavior that could generate feedback when the microphone is in close proximity to the

loudspeaker.


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The 4000Hz coverage almost grazes the listening plane with the speaker sitting on a desktop andno tilt, there are some significant level variations in this band. The maximum level is 92.98dB and

the minimum level is 66.18dB for a total level variation 26.8dB. A large area of the seating iswithin 3dB but there are also several zones within the seating that are about 7-8dB lower in level.


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2000Hz Total SPL (direct + reverberant) at current reverb time

The level variation in the Total SPL is exaggerated by the very high level in close proximity to thespeaker painted on the listening plane. The maximum level is 93.24dB and the minimum level is

80.57dB for a total variation of 12.67dB. Most of the seating area is within 4dB in level/


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2000Hz Total SPL (direct + reverberant) at 0.75 second reverb time

At 0.75 second reverb time the far field coverage exhibits less variation. The maximum level is

93.82dB and the minimum level is 86.17dB for a total variation of 7.65dB. Most of the seatingarea has a level variation of about 2dB.


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Increasing the reverb time to 1.0 seconds reduces the total variation further. The maximum levelis 94.1dB and the minimum level is 87.6dB for a total variation of 6.5dB with less 2dB of variation

over the seating area.


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The ToGo provides similar STI performance to the corner mounting, the maximum level is

artificially high as the highs core appears on the desk top the speaker is sitting on. The maximumSTI value is 0.78 and the minimum value is 0.71. A large area of the seating is still 0.74 to 0.75

in STI which is very good.


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Increasing the noise level does not have a significant effect on STI values.


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Increasing the noise level to NC-55 reduces the minimum STI values, but its important to notethat those low scores are behind the loudspeaker.


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Increasing the reverb time to 0.75 seconds drops the overall STI levels, the maximum being 0.72

and the minimum being 0.58. Significantly, the STI values in the primary coverage area have

dropped from 0.74 to 0.66-0.62. This is typical of the effects of reverberation on any singlesource speaker configuration.


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Increasing the noise level to NC-55 produces no further reduction in STI showing that theperformance is most affected by excess reverberation.


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Increasing the reverb time to 1.0 seconds produces another major drop in STI values overall. Themaximum value is 0.69 and the minimum value is 0.53. Significantly, the area inside the directcoverage has dropped from 0.66 to 0.62 down to 0.62 to 0.57. The maximum and minimum

values are all very close to the loudspeaker.

Excess reverberation is the major limiting acoustical parameter for maintaining good speech

intelligibility with the ToGo.


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There is no significant effect on STI value by increasing the noise level to NC-55.


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2000Hz C50 with current reverb time

With the ToGo at desktop or table height, the C50 values are artificially high very close to thespeaker because these results are painted on an ear plane at 36 above the floor. The maximum

value of 23dB happens directly in front of the speaker. The C50 values over the seating arearange from 11-16dB, very similar to most other systems in the current acoustical environment.


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Increasing the reverb time reduces the C50 values. The seating area ranges from 2-5dB.


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The C50 values drop to 3-0dB over the seating area with the reverb time at 1.0 seconds.


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Sound Field Configuration: single small speaker (flat panel, etc.) mounted in corner


A single speaker mounted in a corner is entirely dominated by inverse square law for direct soundlevel drop off and will be seriously affected by increasing reverb time.

The maximum level is 92.13dB and the minimum level is 77.18dB for a total level variation of

14.95dB.


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Single small speaker mounted in corner


The maximum level is 90.19dB and the minimum level is 74.32dB for a total level variation of

15.87dB. There is more than 10dB of level drop across the seating area.


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The maximum level is 90.03dB and the minimum level is 74.28dB for a total level variation of15.75dB. There is almost 12dB of level variation across the seating area.

Any effort to get the speaker loud enough in the far corner will result in the speaker being 12dB

louder near the source. If the teacher has to walk near the speaker it is likely to be a feedback

problem.


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2000Hz Total SPL (direct + reverberant) at current reverb time

In the current reverb time there is 6.93dB of level variation in the room.


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As the reverb time increases the level variation drops to 3.36dB, an indicator of large variations in

STI value with increasing reverb time.


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With the 1.0 second reverb time the level variation drops to 2.66dB.


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With the current acoustical conditions a single speaker can provide good STI values, but may still

be a feedback problem.


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Increasing the noise level to NC-45 does not impact the STI values.


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Increasing the noise level to NC-55 does not have a significant impact on STI values.

What that means is that the speaker has enough sound level to provide the needed S/N ratio at

this reverb time. S/N ratio adjustment can be achieved by level adjustment whereas performancelimits caused by the reverb time in the room are a factor of direct/reverb ratio and cant be

corrected by turning it up.


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As expected increasing the reverb time drops the overall STI values significantly and reallyincreases the range of STI values in the seating area.


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Increasing the noise level to NC-55 doesnt have any significant impact on STI values.


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Increasing the reverb time to 1.0 seconds causes a further drop in STI values in the seating area

and increases the spread in STI values as well.


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Increasing the noise level to NC-55 has no significant effect on the STI values.


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2000Hz C50 with current reverb time

The single speaker works reasonably well when the reverb time is short. The range of C50

through the seating area is 15-10dB.


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Increasing the reverb time to 0.75 seconds drops the range of C50 to 5-2dB through the seating

area.


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At a 1.0 second reverb time the C50 values drop to 3-0dB through the seating area.


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ToGo 3D polar response prediction produced by EASE 4.0

500Hz 1000Hz

1600Hz 2000Hz

2500Hz 3150Hz


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4000Hz 5000Hz

6300Hz 8000Hz

whitepaper duo vs single speakers

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