Speaker System Design Guide for
Yamaha Sound System Simulator
Direct and Reflected:
Understanding the Truth with Y-S
3
-Speaker System Design Guide-
December 2008
© 2008 Yamaha Corporation
1
Speaker System Design Guide for
Yamaha Sound System Simulator
Introduction
Y-S
3
is a speaker system design software application. It is especially useful in
determining speaker placement. The user can easily enter the desired venue
shape and calculate the three-dimensional coverage area for given speaker
placements and angles.
Furthermore, Y-S
3
can provide valuable information about many of the points that
must be considered when designing a speaker system by (1) calculating sound
pressure distribution while taking into account speaker interference, (2) calculating
the responses at specific points, and (3) calculating floor SPLs (sound pressure
levels) caused by changing the system gain.
This guide explains how the Y-S
3
computations can be used in the actual system
design process by using examples of speaker target configurations, response
evaluations for specific points, and output level configurations. Y-S
3
is based
around the concept of inputting simple room geometry information to determine the
appropriate speaker configuration, so it only computes the effects of direct sound.
However, actual sound fields are affected by reflected sound waves from walls,
floors, and ceilings. Therefore, it is advantageous to understand at the
system-design stage how the results of direct sound computation will correspond to
the response of the actual sound field. This guide includes actual measurements to
show how computed results correspond to actual sound field responses.
The examples in this guide use a 600-seat multi-purpose hall with a trapezoidal
floor plane. The width of the hall is 22 m, the depth is 24 m (from the front of the
stage to the wall behind the seats), the height of the ceiling is 14 m (the maximum
ceiling height above the seats), and the reverberation time is 1.2 seconds (for a
500-Hz octave band sound with empty seats and the curtains down).
Conditions of the Venue
Hall: 600-seat, multi-purpose hall
Speaker type: One speaker array composed of two IF2112/64 speakers
Speaker location: In the front at a height of 8 m (7.2 m above the stage floor)
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Speaker System Design Guide for
Yamaha Sound System Simulator
1. Setting the speaker arrangement
Y-S
3
can produce contour diagrams for each speaker array or for each speaker within a
speaker array. This allows the user to adjust the speaker arrangement while checking the
floor-level coverage area. If the areas covered by individual speakers overlap significantly,
sections of phase interference appear over a wide area and cause reinforcements (peaks)
and cancellations (dips)*. Y-S
3
can produce color maps of the sound pressure distribution
that can be used to evaluate phase interference. However, because Y-S
3
only computes the
effects of direct sound, the computed results will be different than the actual sound pressure
distribution in a hall, which is affected by direct and reflected sound. When designing a
speaker system, it is important to understand how the effects of reflected sound will be
manifested.
In the example below, a two-speaker array is placed in the center position. This example
compares the computed areas of phase interference for the given speaker configuration to
the actual measured sound pressure distribution in a real hall.
* Please note that all speakers produce phase interference when arrayed to some extent.
; Speaker target configuration
¾ How splay angle affects the speaker targets
The first example shows an evaluation of each speaker target based on the splay
angle. In Y-S
3
, the user can click to switch to Single Mode display and view
contour diagrams of the target areas of each speaker in the array. The user can
also change the bandwidth and the central frequency of the contour diagram by
changing the Frequency and Band items in the upper left of the window. The
example below shows the average of the results for each octave (1/1 OCT Band).
For example, if Splay Angle is set to 60.0, the black squares that represent the
speaker targets appear very close to the walls, giving the impression that the splay
angle is too wide for the seating arrangement. If the Splay Angle is then set to 50.0,
the speaker targets appear near the middle of the left and right areas, just about
where they should be.
Figure 1: Splay angle adjustment (left: 60.0, right: 50.0)
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Speaker System Design Guide for
Yamaha Sound System Simulator
¾ Viewing the coverage area
The next step is to check whether the coverage area of the speakers is appropriate.
In Y-S
3
, the user can click to switch into Array Mode and view a contour
diagram for the entire array. The figure below shows the results for a splay angle of
50.0. Looking at this contour diagram, it is clear that the current array configuration
covers the important central area of the seats, but in the 1 kHz contours (an area of
midrange critical for good speech intelligibility), areas of phase interference
between speakers are also evident.
Checking the coverage area
(left: 250 Hz, center: 1 kHz, right: 4 kHz, all 1/1 OCT Band)
; Checking sound pressure distribution
¾ Sound pressure distribution differences between frequency bands
The next step is to check the effects of phase interference between speakers. In
Y-S
3
, the user can click to switch into SPL mode and view a color map of the
sound pressure distribution.
In the 250 Hz band, areas of phase interference do not appear. This is because the
wavelengths contained within the band are long compared with the distance
between the speakers.
In the 1 kHz band, areas of phase interference do appear between the speakers.
Whether or not these areas of phase interference are tolerable depends on the
purpose of the system being designed, but because the volume differences in the
central area of the room are within approximately 10 dB, one could conclude that
the level of phase interference is tolerable.
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Speaker System Design Guide for
Yamaha Sound System Simulator
250 Hz 500 Hz
1 kHz 2 kHz
Figure 2: Sound pressure distributions for different frequency bands
(all 1/1 OCT Band; the listed frequency is the center frequency)
; Comparison with Actual Measurements
In the actual sound field, the areas of phase interference between speakers will be
affected by reflected sounds. To help explain how the effects of reflected sounds are
manifested, a comparison between the computed results and actual measured results
is given below.
¾ Measurement Conditions
In the actual measurement, two IF2115/64 speakers were installed with a splay
angle of 50 degrees. They were hung on a pole and installed 7.2 m above the
stage floor. Omnidirectional condenser microphones were installed in thirty
different locations to measure impulse response.
¾ Areas of Phase Interference in the Middle to High Frequency Bands
Figure 3 shows the sound pressure distributions for the 500 Hz, 1 kHz and 2 kHz
bands. The right sides of the figures show the actual measured results, and the left
sides of the figures show the computed results. Both show the 1/1 OCT Band
results. The measured results show the values integrated over 1 second after the
reception of direct sound. As discussed earlier, the YS3 computed results indicate
areas of phase interference between the two speakers in the 1 kHz and 2 kHz
frequency bands. A similar pressure distribution appears in the measured results.
Pressure distribution differences between computed and measured results vary
depending on how sound is reflected from the walls, but if the target area has been
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Speaker System Design Guide for
Yamaha Sound System Simulator
configured appropriately, similar phase interferences between speakers will appear
in both the computed and measured results in the middle frequency bands.
Therefore, it can be concluded that using the computed results of direct sound only
to reduce areas of phase interference will have beneficial effects on the actual
sound field.
500 Hz
1 kHz 2 kHz
Figure 3: Sound pressure distributions by frequency band (middle frequency bands)
(left diagram: the results of Y-S
3
, right diagram: measured results)
¾ Effects of Reflected Sound in the Low Frequency Bands
Figure 4 shows the sound pressure distributions for the 250 Hz and 125 Hz octave
bands. In the computed results on the left side of each figure, no dips caused by
6
Speaker System Design Guide for
Yamaha Sound System Simulator
phase interference are indicated between speakers because the wavelengths of
the frequencies in question are relatively long compared to the distance between
the speakers. However, areas of phase interference do appear in the measured
results on the right side of each figure. These areas are most likely formed through
interference between direct sound from the speakers and initial reflections from the
walls. The wide and even areas of phase interference between direct and initial
reflected sounds indicated in the low frequency bands are caused by two factors.
One factor is the large amount of sound reflected from the walls caused by the
wide directivity of the speakers. The other factor is that because the variations in
the wall surface are small compared with the wavelengths in the low frequency
band, there is no diffusion effect. The influence of reflected sound may manifest
itself as unevenness in sound pressure distribution levels. This can also be
interpreted as the influence of the venue type. For typical enclosed speakers,
directivity is difficult to control in the low frequency bands, so you cannot change
the phase interference in the low frequency bands by changing the speaker angles.
It is important to understand that this type of interference will not appear in speaker
arrangement evaluations that only take direct sound into account, but that it will
appear in the actual sound field.
125 Hz 250 Hz
Figure 4: Sound pressure distributions by frequency band (low frequency bands)
(left diagram: the results of Y-S
3
, right diagram: measured results)
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Speaker System Design Guide for
Yamaha Sound System Simulator
2. Evaluating the Response at Specific Points
The effects of interference between multiple speakers are manifested in the response at a
specific point through dips in frequency characteristics. In the actual sound field, it is
expected that the depth of the dips will be reduced by reflected sound.
As in the previous section, this section compares the results of direct sound computations to
those of actual measurement results in the case when a two-speaker array is placed in the
center position of a hall.
; Frequency Characteristics at a Specific Listening Point
¾ Evaluating Sharp Dips
Figure 5 shows the computed and measured results at point A (x = 6 m, y = 6 m).
Point A is 6 m to the left of the center of the seating area (approximately in the
middle of the left side of the seating area). The blue line represents the Y-S
3
computed results. The red line represents the measured results in the actual hall. It
shows the values integrated over 15 ms after the reception of direct sound. The
pink line also represents the measured results in the actual hall, but it shows the
values integrated over 100 ms after the reception of direct sound. The spectrum of
the measured results was acquired through an 8192-point Fourier transform and
then converted into 25-point moving averages. The vertical axis of the graph
represents relative sound pressure levels, and the maximum value for each line is
set to 0 dB.
In the Y-S
3
computed results (the blue line), a dip of approximately 20 dB occurs at
approximately 1.2 kHz. It is difficult to determine the significance of this dip, but
Y-S
3
has an auralization feature that simulates the audio response so that you can
evaluate it.
One must be aware that in actual sound fields, these kinds of dips are mitigated by
the effects of reflected sound. In the values integrated over 15 ms (the red line), the
dip appears in a relatively high frequency range, but it is mitigated to within 10 dB
even at its deepest point. This dip also appears in the values integrated over 15 ms
and in the values integrated over 100 ms, indicating that the frequency response of
the strong direct sound that arrives from the speakers has a strong influence on the
overall frequency response of the initial reflected sound, and thus also has a strong
influence on the listening experience. This further underscores the importance of
checking the effects of interference between speakers at the design stage.
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Speaker System Design Guide for
Yamaha Sound System Simulator
-20
-10
0
100 1000 10000
[Hz]
[dB]
Figure 5: Measured and computed results at X = 6, Y = 6
Blue: Y-S
3
. Red: Measured results integrated over 15 ms. Pink: Measured results integrated
over 100 ms. (The measured results are moving averages.)
¾ Evaluation of High-Frequency Drop-Off
Figure 6 shows the computed and measured results at point B (x = 1 m, y = 10 m).
Point B is approximately in the center of the seating area. The blue line represents
the Y-S
3
computed results. The red line represents the measured results in the
actual hall. It shows the values integrated over 15 ms after the reception of direct
sound. The spectrum of the measured results was acquired through an 8192-point
Fourier transform and then converted into 25-point moving averages. The vertical
axis of the graph represents relative sound pressure levels, and the maximum
value for each line is set to 0 dB.
In the Y-S
3
computed results (blue line), there are no dips in any particular
frequency bands, but the frequency characteristics decline steadily starting at
approximately 4 kHz. The reason that the frequencies that are subject to phase
interference are rather high is because the difference between the distances
between the two speakers and point B is small.
This high-frequency drop-off also appears in the measured results at the actual hall.
In the values integrated over 15 ms (the red line), the characteristics begin
declining at approximately 2 kHz. They decline by as much as 20 dB. The dips
observed at point A that were caused by reflected sound from the floor do not
appear in the same frequencies at point B. The reason for this is probably that the
ways in which sounds are reflected are different at the two points because the
9
Speaker System Design Guide for
Yamaha Sound System Simulator
measurement for point A was made in the seats while the measurement for point B
was made in the walkway.
The above example shows that the frequency responses at specific points
computed using Y-S
3
are similar to those that appear in actual sound fields.
Understanding this during the design phase will facilitate better measurements and
adjustments after the speakers have been arranged.
-20
-10
0
100 1000 10000
[Hz]
[dB]
Figure 6: Measured and computed results at X = 1, Y = 10
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Speaker System Design Guide for
Yamaha Sound System Simulator
3. Configuring Output Levels
You can use Y-S
3
to estimate the sound pressure levels at different points for different amp
types, gains, and input levels. The computed levels can be used to determine whether the
system you are designing can obtain the sound pressure levels that you want. In
computations based on direct sound, the SPL attenuates linearly as the distance from the
speakers increases, but in an actual sound field, sound diffusion results in mitigation of the
rate of SPL attenuation as distances increase.
This section provides an example of how to configure levels using Y-S
3
, and it compares the
level attenuations at different distances in computed values based on direct sound to those
in the measured values in an actual hall.
; Configuring Sound Pressure Levels with Y-S
3
¾ On the Config tab in the Speaker Property dialog box, you can configure the input
level and the amp attenuator, and consider what configuration will yield the SPL
that you want.
¾ When you first set up the speakers or when you change the speaker type, the
recommended amp is selected and the level settings are at their default values
(+4.0 dBu for the input level and -10 dB for the attenuator level
).
For these settings, the overall SPL at a point where X = 0 and Y = 11.5 would be
90.7 dB.
Figure 7: Default level settings
¾ You can use Y-S
3
to change the input and/or attenuator levels and compute the
maximum SPL for the rated power or compute the approximate SPL for a certain
nominal input level.
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Speaker System Design Guide for
Yamaha Sound System Simulator
For example, to change the SPL to approximately 100 dB, you could set the amp
attenuator level to -6dB and set the input level to 10 dBu. Doing so would change
the overall SPL to 100.7 dB.
Figure 8: Adjusted level settings
¾ Given the settings shown above, the SPL at a distant point, X = 0, Y = 22.0 for
example, would be 95.4 dB. However, in an actual sound field, the level will not
decrease that much due to the effects of reflected sound. This must be taken into
account when evaluating results and configuring a system. The following section
reveals the effects of reflected sound by comparing the computed results to the
actual measured results in a hall.
; Comparison of Level Attenuations with Respect to Distance
We installed a speaker on the stage and compared level reductions for different
distances. We measured sound levels for every 2 m up to a distance of 18 m from the
speaker. We also computed sound levels for the same conditions using Y-S
3
. Figure 9
shows the results for the different distances. The horizontal (X) axis represents the
distance from the sound source, and the vertical axis represents the sound pressure
level relative to the level at 3 m from the sound source. The Y-S
3
computed results for 1
kHz attenuate steadily, but the measured results show that there is almost no
attenuation after 13 m because of sound diffusion. There is a central walkway at the
point 11 m away from the speaker, and the unique sound reflection conditions there are
evident in the plot of the measured data. The Y-S
3
computed results for 2 kHz attenuate
more gradually than those for 1 kHz. The reason for this is that the seats are on a rising
slope, so as the seats become further from the stage, they also face the speaker more
12
Speaker System Design Guide for
Yamaha Sound System Simulator
directly, and the sound pressure levels rise as a result of the speaker directivity. The
measured results for 2 kHz stop attenuating after 13 m, just like the results for 1 kHz.
Also, the effects of speaker directivity on the levels are hidden by the effects of the
reflected sound.
When configuring a speaker system based on computations of direct sound, it is
important to remember that at the actual venue, steady-state SPL will rise at more
distant points as a result of sound diffusion. If you fail to take this point into account
when trying to achieve specific SPLs at more distant points, you may be misled by the
computed results into selecting a system whose overall SPLs are much larger than
necessary. The point at which level attenuation caused by distance is mitigated varies
depending on the size and sound absorption conditions of the venue. Formulas for
determining theoretical values such as those shown in figure 10 have been proposed
by researchers.
-15
-10
-5
0
0 5 10 15 20 25
Distance (m)
Level (dB)
Meas 1kHz
YS3 1kHz
-15
-10
-5
0
0 5 10 15 20 25
Distance （m）
Level (dB)
Meas 2kHz
YS32kHz
Figure 9: Comparisons of level attenuations caused by distance
Top: relationship between the sound source and the points of measurement.
Bottom: measured and computed results.
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Speaker System Design Guide for
Yamaha Sound System Simulator
Figure 10: Theoretical attenuation levels of direct and reflected sounds based on revised
formula by Barron
(M. Barron, Auditorium Acoustics and Architectural Design, [E&FN Spon, 1993], 32)
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en otros idiomas
- français: Yamaha Y-S3 Mode d'emploi
- italiano: Yamaha Y-S3 Guida utente
- English: Yamaha Y-S3 User guide
- Deutsch: Yamaha Y-S3 Benutzerhandbuch
- Nederlands: Yamaha Y-S3 Gebruikershandleiding
- português: Yamaha Y-S3 Guia de usuario
- dansk: Yamaha Y-S3 Brugervejledning
- polski: Yamaha Y-S3 instrukcja
- čeština: Yamaha Y-S3 Uživatelská příručka
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