J1400™ JUL2017

SURFACE VEHICLE
RECOMMENDED PRACTICE Issued 1982-05
Reaffirmed 1989-05
Revised 2017-07

Superseding J1400 AUG2010

(R) Laboratory Measurement of the Airborne Sound Barrier Performance of

Flat Materials and Assemblies

RATIONALE

This document defines an alternative method to ASTM E90 and ASTM E2249 for measuring sound transmission loss (STL)
or noise reduction for flat sample materials.

FOREWORD

This SAE Recommended Practice has been modified in response to user comments and to clarify some of the theoretical
basis for the testing. The fundamental methodology of this procedure has not been changed from previous revisions.

INTRODUCTION

This document is intended to provide a means of measuring the STL of materials. At each test frequency, the STL is
determined based on the measured noise reduction (MNR) of the test specimen using a correlation factor (CF). The
respective CF for the test condition is determined as the difference between the MNR of a homogeneous limp panel, such
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as mass loaded vinyl, and its theoretically calculated field-incidence STL. Note that the calculated STL is for a theoretical
panel of infinite dimensions, and the intent is to remove the effect of different size test windows found in different labs, with
consideration of low frequency limitations imposed by smaller openings. This recommended practice then recognizes that
many laboratories have measurement variances that can be corrected to a certain extent using this methodology.

__________________________________________________________________________________________________________________________________________
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 SAE INTERNATIONAL J1400™ JUL2017 Page 2 of 23

TABLE OF CONTENTS

1. SCOPE .......................................................................................................................................................... 4

2. REFERENCES.............................................................................................................................................. 4
2.1 Applicable Documents .................................................................................................................................. 4
2.1.1 SAE Publications ........................................................................................................................................... 4
2.1.2 Accredited Publications ................................................................................................................................. 4
2.1.3 INCE-USA Publications................................................................................................................................. 4
2.1.4 ASTM Publications ........................................................................................................................................ 5
2.1.5 AES Publications ........................................................................................................................................... 5
2.1.6 Published Books ........................................................................................................................................... 5

3. INSTRUMENTATION.................................................................................................................................... 5
3.1 Sound Level Meter ........................................................................................................................................ 5
3.2 Filter Requirements ....................................................................................................................................... 5
3.3 Microphone Calibrator ................................................................................................................................... 5
3.4 Source Room Speakers ................................................................................................................................ 5
3.5 Instrumentation ............................................................................................................................................. 5
3.6 Ambient Sensors ........................................................................................................................................... 6

4. FACILITIES ................................................................................................................................................... 6
4.1 Layout of Chambers ...................................................................................................................................... 7
4.2 Receiving Chamber....................................................................................................................................... 7
4.3 Chamber Sizes .............................................................................................................................................. 7
4.4 Source Room Lower Cutoff Frequency and Diffusion .................................................................................. 7
4.5 Ambient Conditions ....................................................................................................................................... 8
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4.6 Facility Design ............................................................................................................................................... 8

4.7 Maximum Measurement Capability............................................................................................................... 8
4.8 Test Sample Fixture ...................................................................................................................................... 8
4.9 Loudspeakers ................................................................................................................................................ 9
4.10 Microphones .................................................................................................................................................. 9
4.10.1 Microphone Placement in Reverberant Source Room and Reverberant Receiving Room .......................... 9
4.10.2 Microphone Placement in Anechoic or Hemi-Anechoic Receiving Room .................................................... 9
4.11 Test Window Opening ................................................................................................................................... 9

5. PROCEDURE ............................................................................................................................................. 10
5.1 Sample Mounting ........................................................................................................................................ 10
5.2 Sample Conditioning ................................................................................................................................... 10
5.3 Measurements ............................................................................................................................................ 10
5.3.1 Background Noise ....................................................................................................................................... 10
5.3.2 Reference Sample ...................................................................................................................................... 11
5.3.3 Reference Sample Surface Density ............................................................................................................ 11
5.3.4 Signal-to-Noise Ratios ................................................................................................................................ 11
5.3.5 Measurement Conditions ............................................................................................................................ 11
5.3.6 Test Samples .............................................................................................................................................. 12
5.4 Data Analysis .............................................................................................................................................. 12
5.4.1 Background Noise Correction ..................................................................................................................... 12
5.4.2 Measured Noise Reduction ......................................................................................................................... 12
5.4.3 Correlation Factors ...................................................................................................................................... 13
5.4.4 Sound Transmission Loss ........................................................................................................................... 13
5.4.5 Insertion Loss .............................................................................................................................................. 13
5.5 Reporting ..................................................................................................................................................... 13
5.5.1 Basic Information ........................................................................................................................................ 13
5.5.2 Ambient Conditions ..................................................................................................................................... 13
5.5.3 Sound Transmission Loss ........................................................................................................................... 14
5.5.4 Confidence Limits........................................................................................................................................ 14
5.5.5 Maximum Measurement Capability............................................................................................................. 14
 SAE INTERNATIONAL J1400™ JUL2017 Page 3 of 23

6. GENERAL COMMENTS ............................................................................................................................. 14

6.1 Qualified Personnel ..................................................................................................................................... 14
6.2 Routine Calibration...................................................................................................................................... 14
6.3 Control Sample Construction ...................................................................................................................... 14
6.4 Control Sample Target Results ................................................................................................................... 14

7. NOTES ........................................................................................................................................................ 15
7.1 Revision Indicator........................................................................................................................................ 15

APPENDIX A RECOMMENDED SAMPLE MOUNTING SYSTEM ................................................................................... 16

APPENDIX B ACCURACY, PRECISION, AND REPEATABILITY ................................................................................... 17
APPENDIX C RECOMMENDED CONSTRUCTION - CONTROL SAMPLE .................................................................... 19
APPENDIX D CALCULATION OF THE SPEED OF SOUND ........................................................................................... 20

FIGURE 1 TYPICAL MEASUREMENT SYSTEM .......................................................................................................... 6

FIGURE 2 TYPICAL MEASUREMENT FACILITY ......................................................................................................... 6

TABLE 1 SUGGESTED MINIMUM SOURCE ROOM VOLUME AT LOWEST MEASUREMENT FREQUENCY ...... 8
TABLE 2 EFFECT OF DIAGONAL DIMENSION OF A SQUARE TEST WINDOW AT LOWEST
MEASUREMENT FREQUENCY AND COMPARISON WITH ¼-WAVELENGTH OF LOWEST
1/3-OCTAVE BAND FREQUENCY ............................................................................................................ 10
TABLE 3 TARGET SOUND TRANSMISSION LOSS VALUES - CONTROL SAMPLE ............................................ 15
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 SAE INTERNATIONAL J1400™ JUL2017 Page 4 of 23

1. SCOPE

This SAE Recommended Practice presents a test procedure for determining the airborne sound insulation performance of
materials and composite layers of materials commonly found in mobility, industrial and commercial products under
conditions of representative size and sound incidence so as to allow better correlation with in-use sound insulator
performance. The frequency range of interest is typically 100 to 8000 Hz 1/3 octave-band center frequencies.

This test method is designed for testing flat samples with uniform cross section, although in some applications the
methodology can be extended to evaluate formed parts, pass-throughs, or other assemblies to determine their acoustical
properties. For non-flat parts or assemblies where transmitted sound varies strongly across the test sample surface, a more
appropriate methodology would be ASTM E90 (with a reverberant receiving chamber) or ASTM E2249 (intensity method
with an anechoic or hemi-anechoic receiving chamber).

2. REFERENCES

2.1 Applicable Documents

The following publications form a part of this specification to the extent specified herein. Unless otherwise indicated, the
latest issue of SAE publications shall apply.

2.1.1 SAE Publications

Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA
and Canada) or +1 724-776-4970 (outside USA), www.sae.org.

SAE J184 Qualifying a Sound Data Acquisition System

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Ebbitt, G. and Hansen, M., "Mass Law - Calculations and Measurements," SAE Technical Paper 2007-01-2201, 2007,
doi:10.4271/2007-01-2201

2.1.2 ANSI Accredited Publications

Copies of these documents are available online at http://webstore.ansi.org/

ANSI S1.1 Acoustical Terminology

ANSI S1.4a Specification for Sound Level Meters

ANSI S1.40 Specification for Acoustical Calibrators

ANSI S1.11 Specification for Octave Band and Fractional Octave Band Filter Sets

ANSI S1.26 Method for Calculation of the Absorption of Sound by the Atmosphere

2.1.3 INCE-USA Publications

Available from INCE-USA, 12100 Sunset Hills Road, Suite 130, Reston, VA 20190. Tel: 703-234-4073, www.inceusa.org.

Beranek, Leo L., Noise and Vibration Control - Revised Edition, Institute of Noise Control Engineering, Washington, DC,
1988

Moritz, C., Shaw, J. and Carrera, A., “The Influence of Test Fixture Damping on the Measurement of Sound Transmission
Loss,” proceedings of NOISE-CON 2014
 SAE INTERNATIONAL J1400™ JUL2017 Page 5 of 23

2.1.4 ASTM Publications

Available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, Tel: 610-
832-9585, www.astm.org.

ASTM C423 Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation
Room Method

ASTM E90 Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions

ASTM E2249 Standard Test Method for Laboratory Measurement of Airborne Transmission Loss of Building Partitions
and Elements Using Sound Intensity

2.1.5 AES Publications

Available from Audio Engineering Society, 551 Fifth Ave., Suite 1225, New York, NY 10176, Tel: +1 212-661-8528,
www.aes.org

Bohn, D., A., “Environmental Effects on the Speed of Sound” J. Audio Eng. Soc., Vol. 36, No. 4, April 1988

2.1.6 Published Books

Beranek, Leo L. and Vér, István L., Noise and Vibration Control Engineering: Principles and Applications, John Wiley &
Sons, New York, NY, 1992 (2nd edition published 2005)

3. INSTRUMENTATION
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Instrumentation to be used is as follows:

3.1 Sound Level Meter

A sound level meter that meets the Type 1 requirements of ANSI S1.4a is required. As an alternative to making direct
measurements using a qualified sound level meter, a microphone, measuring amplifier and a sound data acquisition system
may be used, provided the system meets the requirements of SAE J184.

3.2 Filter Requirements

A third-octave filter set covering the range of center frequencies of interest. The filters shall meet the Class III requirements
of ANSI S1.11.

3.3 Microphone Calibrator

A sound level calibrator that meets the Class 1 requirements of ANSI S1.40.

3.4 Source Room Speakers

An acoustical sound generating system shall be selected to generate random noise containing a continuous distribution of
frequencies over each test band.

3.5 Instrumentation

A schematic diagram of the instrumentation is shown in Figure 1.

 SAE INTERNATIONAL J1400™ JUL2017 Page 6 of 23

Random
Spectrum Power
Noise Speaker(s)
Shaper(s) Amplifier(s)
Generator(s)

Source Room Noise

Source
Room
Preamp &
Spectrum
Amplifier Computer
Analyzer
Channels
Receiving
Chamber
Data Processing System

Stationary Single Microphones, Spatially-averaged Single Microphones

or Averaged Multi-point Microphones

Figure 1 - Typical measurement system

3.6 Ambient Sensors

Temperature and humidity sensors should be used to monitor and record ambient test conditions in the source and receiving
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chambers, preferably in the vicinity of the sample mounting location.

Recommended accuracy of the sensors

• ±1 °C for temperature

• ±3% for relative humidity

• ±30 kPa for barometric pressure

4. FACILITIES

A schematic diagram of a typical measurement facility is shown in Figure 2.

Reverberant
Source Room Receiving
Chamber

Spatially- Point or Spatially-

averaged averaged SPL
SPL
Field Sample Mounting
Incidence Window
Sound
Speaker Diffuse
Sound
Field

Figure 2 - Typical measurement facility

 SAE INTERNATIONAL J1400™ JUL2017 Page 7 of 23

4.1 Layout of Chambers

Two adjacent chambers are located such that they share a common test window, into which test samples are mounted.
The two chambers must be isolated from each other so that the only significant transmission path is through the sample
window. Test windows are normally oriented in the vertical plane, but may also be oriented horizontally or even non-
orthogonally to the vertical or horizontal planes.

4.2 Receiving Chamber

It is recommended that the receiving chamber be fully anechoic in order to minimize the influence of flanking paths and
modal coupling between the chambers. However, good results can also be achieved with semi-anechoic or even reverberant
receiving chamber designs if proper care is taken for isolation between the chambers, modal decoupling through the test
window and spatial averaging of receiving chamber microphone(s).

4.3 Chamber Sizes

Source room volume is required to be at least 50 m3 (1765 ft3), with approximately 200 m3 (7100 ft3) being the recommended
volume. Ideally, room/chamber sizes should be established based on the presence of at least twenty (20) natural frequency
modes within the lowest 1/3 octave frequency band of interest for good diffusion of sound. For rectilinear design, room
proportions of 1:21/3:41/3, or 1:1.26:1.59, are also recommended for good diffusion and modal separation. Table 1 shows
low frequency cutoff for various room sizes using the recommended dimensional proportions. However, rooms smaller than
those specified in Table 1 may be usable if measured diffusion criteria are met – this can be accomplished by use of low
frequency absorbers. Appendix X1 of ASTM E90 suggests some alternate volume criteria based on a smaller number of
resonant modes in each 1/3-octave band. Reverberant receiving chamber proportions should be the same; but sized at
least 10% smaller or larger in interior volume to avoid natural frequencies which coincide with the source room. It is also
advisable to keep reverberant receiving chamber boundaries and sound absorber elements at least ¼-wavelength from the
sample test window. It is possible to do a test using the methodology of SAE J1400 using a small reverberation chamber
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as a source room, but this will increase the low frequency cutoff for valid test results.

4.4 Source Room Lower Cutoff Frequency and Diffusion

To qualify a test chamber once it has been built or whenever changes are made to the chamber which may affect diffusion,
it is recommended that the population standard deviation of twenty randomly located sound pressure measurements in the
source room be no more than 2 dB at the 1/3-octave center frequency which is one octave higher than the low frequency
cutoff and above (for example, 200 Hz and above for a room with 100 Hz low frequency cutoff), with a representative test
sample mounted in the test window. Microphones should be spaced at least ¼-wavelength from each other, from diffusers
and from any room boundaries at the lowest measurement frequency. Diffusion in the reverberation source room can be
enhanced by the use of rotating or stationary diffusers. Note that excessively large reverberant source rooms may not exhibit
diffuse field characteristics at high frequencies due to air absorption. See Section 7 of ASTM C423 for guidance on
reverberation room design. See Annex A3 and Appendix X1 of ASTM C423 regarding room qualification and the use of
diffusers to reduce the variability of sound pressure levels within the source room. See 4.9 regarding proper location and
orientation of source room speaker(s). NOTE: ASTM C423 and ASTM E90 procedures specify 5000 Hz as the highest
1/3-octave band. In order to measure accurately at higher frequencies, diffusion at these higher frequencies must be
adequate. It is reasonable to extend the 5000 Hz values in Table A3.1 of ASTM C423 to higher frequencies for the purposes
of room qualification. Ambient conditions (temperature and relative humidity) in the source room must be controlled to
minimize air absorption – see Section 6 of ASTM C423 and ANSI S1.26.
 SAE INTERNATIONAL J1400™ JUL2017 Page 8 of 23

Table 1 - Suggested minimum source room volume at lowest measurement frequency

Lowest 1/3-Octave Band Minimum Room

Measurement Frequency Volume
Hz m3 (ft3)
80 410 (14479)
100 205 (7240)
125 105 (3708)
160 52 (1836)

NOTE: Minimum room volume figures are based on a minimum of 20 resonant modes in the lowest 1/3-octave band of interest using
recommended dimensions of 1:1.26:1.59. The low frequency limit for a given size room may be extended even lower by good
design of low frequency absorption/diffusion.
NOTE: Calculations use sound speed of 343 m/s (1125 ft/s) corresponding with an air temperature of 20 °C (68 °F).

4.5 Ambient Conditions

Source and receiving chamber temperatures should be controlled to 22 °C ± 5 °C. Relative humidity should be controlled
for both chambers at 40 to 70%. Temperature and humidity should not vary by more than ±3 °C and ±5% RH between
measurements of the reference sample(s) and the test sample(s).

4.6 Facility Design

The source and receiver chambers should have wall constructions of a sufficient STL to minimize flanking paths into the
receiving chamber. If the existing isolation between test chambers is adequate, supplemental insulation added to potential
flanking noise surfaces should have little or no effect on measured STL of maximum transmission loss samples. If
supplemental insulation is beneficial, it should be left in place where feasible.
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4.7 Maximum Measurement Capability

When the STL of the wall(s) separating the receiving chamber from the source room is not sufficiently greater than the
sample under test, the measurements may be compromised by sound transmitted from source to receiving chamber via
paths other than through the specimen under test. The maximum STL measurement capability of the system should be
determined by measuring the STL of an insulator assembly composed of a 10 to 50 mm foam or fiber decoupler layer in
combination with a 2 to 10 kg/m2 septum or barrier layer. Continue to add successive insulator assemblies and measure
STL after adding each insulator assembly until no further changes in STL are noted (less than 1.0 dB change at all
frequencies). Note that a second set of measurements may be required using an insulator assembly composed strictly of
mass layers to determine the maximum STL at lower frequencies. The maximum STL capability is limited by flanking paths
or residual noise in the overall measurement system. Measured sample STL values should fall at least 10 dB below
maximum STL capability levels at all frequencies. Maximum STL levels can be improved by increasing the STL of the
common wall between the rooms, by improving the sample sealing system, increasing the structure-borne vibration isolation
between rooms or by decreasing the residual noise of the measurement system. Maximum STL measurement capability
does not need to be run with every sample; but, it should be measured periodically (recommended annually) or whenever
changes may have been made affecting the measurement facility and/or data acquisition system.

4.8 Test Sample Fixture

A test sample fixture should hold the test sample securely between the source and receiving chambers. The fixture should
be well sealed to prevent leakage between the source and receiving chambers through the fixture (see recommended
sample mounting system in Appendix A). The fixture should provide means to maintain typical in-use contact between the
various layers of the test assembly. Unless intended, care must be taken to assure that no air gaps are induced in a
multilayer assembly or within sample layers during sample mounting or sealing. Although it is common practice to use a
vertical test window orientation, horizontal test windows may provide a means of using gravity to naturally hold test layers
properly together or to represent the in-use compression of layers.
 SAE INTERNATIONAL J1400™ JUL2017 Page 9 of 23

For materials with low inherent damping, the sample fixture may impart significant damping into the assembly, influencing
the measured STL, especially near coincidence. This effect is more significant as the sample size decreases. The STL of
a measured substrate should be compared with the theoretical or large sample value to insure that the test fixture does not
adversely affect the results.

4.9 Loudspeakers

One or more broadband loudspeakers of sufficient sound power capability should be used to produce sound pressure levels
in the receiving chamber at least 10 dB above the noise floor of the measurement system and chamber at all frequencies
with the test sample in place. It is recommended that sound spectrum shaping in the source room be utilized in order to
reduce the span between the lowest and highest levels versus frequency of the measured sound spectrum in the receiving
chamber to within the dynamic range capability of the measurement system. Typically, a source room sound pressure
spectrum rising at 6 dB/octave will significantly reduce the dynamic range requirements in the receiving chamber. Selection,
exact placement and orientation of the loudspeaker(s) within the source room are often trial-and-error processes to achieve
desired source levels and diffusion. Should multiple loudspeakers be used, it is recommended that uncorrelated signals be
fed to the broadband loudspeaker sources for best low frequency diffusion. To help define proper loudspeaker placement
and orientation, the population standard deviation of the randomly located or spatially averaged sound pressure
measurements in the source room should follow the population standard deviation guideline as previously defined in 4.4.

Once placed and qualified, loudspeaker position(s) and orientations must be maintained for all tests.

4.10 Microphones

One or more random incidence microphones (reverberant chambers) or free field microphones (hemi-anechoic or anechoic
chambers) shall be positioned within the source and receiving chambers. The number and spacing of microphone positions
required in each room depends on the statistical precision desired in the time and space average band sound pressure
levels.
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4.10.1 Microphone Placement in Reverberant Source Room and Reverberant Receiving Room

Randomly placed microphones or the traverse of a spatially averaged microphone should maintain at least ¼-wavelength
distances from room boundaries, room diffusers, noise sources and the test sample window at the lowest test frequency
consistent with the microphone placement for source room qualification specified in 4.4. For more specifics please refer to
Section 10.1 of ASTM C423.

4.10.2 Microphone Placement in Anechoic or Hemi-Anechoic Receiving Room

The exact number and placement of receiving chamber microphones for best results is often a trial-and-error process. A
recommended starting point is to place microphones 10 to 100 mm from the receiving room surface of the test sample. The
population standard deviation of the randomly located or spatially averaged sound pressure measurements in the source
room should still follow the population standard deviation guideline as previously defined in 4.4 – i.e., be no more than 2 dB
at 200 Hz 1/3-octave center frequency and above, with a representative test sample mounted in the test window. The
distance of the microphone from the surface of the sample facing the receiving room should remain constant. For example,
if 20 mm from the face of the sample is selected for a test of an initial sample, and the next sample in the test is substantially
thicker or thinner than the previous sample, the microphones should still be placed 20 mm from the face of the new sample.

Note that the construction of a control sample is defined in 6.3, with target STL values that are defined in 6.4. These can
be used to aid in the above trial-and-error process.

Once placed, microphone positions must be maintained throughout the test sequence and ideally for all tests.

4.11 Test Window Opening

For finite size panels, random incidence or field-incidence transmission loss in the mass-controlled region will be higher for
smaller panels, and this effect will be more pronounced at lower frequencies. The CF calculated using the reference limp
barrier essentially converts the MNR to field-incidence STL for an infinite panel.
 SAE INTERNATIONAL J1400™ JUL2017 Page 10 of 23

There is not a specific limit to window size. However, in order to meet the CF requirements in 5.4.3 (in terms of difference
between MNR and calculated limp barrier STL) the user should be aware of the low frequency effect of finite window size.
Appendix E contains a brief discussion of the theory behind this. Table 2 shows the minimum window size necessary for
5 dB or 10 dB deviation of ideal MNR from calculated limp barrier STL. The actual CF for a given window may be somewhat
higher or lower, depending on microphone placement and other factors. As long as CF requirements are met as specified
in 5.4.3 the window opening sizes in Table 2 do not need to be strictly observed. However, the smaller the test window is,
the more the CF will approach the specified limits. Although Table 2 is specific to square test samples, the theory is generally
applicable to non-square openings and these figures are useful as a guideline. A useful empirical rule of thumb is to consider
the low frequency limit to be that for which the diagonal opening of the test window is ¼ of the wavelength (in air).

Table 2 - Effect of diagonal dimension of a square test window at lowest measurement frequency
and comparison with ¼-wavelength of lowest 1/3-octave band frequency

Minimum Diagonal of Minimum Diagonal of

Square Test Window Square Test Window ¼-Wavelength of
Lowest 1/3-Octave Band Opening for 5 dB Opening for 10 dB Lowest Frequency in
Measurement Frequency Deviation Deviation 1/3-Octave Band
Hz m (ft) m (ft) m (ft)
80 2.42 (8.0) 1.21 (4.0) 1.21 (4.0)
100 1.93 (6.4) 0.96 (3.2) 0.96 (3.2)
125 1.52 (5.0) 0.76 (2.5) 0.76 (2.5)
160 1.22 (4.0) 0.61 (2.0) 0.61 (2.0)
200 0.96 (3.2) 0.48 (1.6) 0.48 (1.6)
250 0.78 (2.6) 0.38 (1.3) 0.38 (1.3)
315 0.60 (1.0) 0.30 (1.0) 0.30 (1.0)
400 0.48 (1.6) 0.24 (0.8) 0.24 (0.8)
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500 0.38 (1.2) 0.19 (0.6) 0.19 (0.6)

NOTE: Calculations use sound speed of 343 m/s (1125 ft/s) corresponding with an air temperature of 20 °C (68 °F)
NOTE: Diagonal dimensions are based on maximum deviation of either 5 dB or 10 dB from infinite panel field-incidence STL to finite panel STL
calculated per Equation 2 at the lowest frequency of interest

5. PROCEDURE

5.1 Sample Mounting

Test samples must be mounted and sealed completely within the test fixture so as to ensure a minimum of sound flanking
the test sample. The recommended sample mounting system is shown in Appendix A.

5.2 Sample Conditioning

Test samples should be conditioned to the same temperature and humidity as the test chambers for at least 12 hours prior
to testing.

5.3 Measurements

5.3.1 Background Noise

Background noise levels within both the source and receiving chambers shall be measured and noted in all measurement
bands and averaged over all measurement positions for each measurement series. Background noise levels in the receiving
chamber must be measured at the same gain settings as during normal measurements in order to include the noise floor of
the measurement system. Ultra-low noise microphones and preamps are available for laboratory use and can be effective
in lowering the noise floor of the measurement system.
 SAE INTERNATIONAL J1400™ JUL2017 Page 11 of 23

5.3.2 Reference Sample

Install and seal the reference sample, a homogeneous limp material such as lead, PVC sheet, EVA sheet or another
monolithic limp material that does not show a critical frequency phenomenon in the frequency range of interest, into the test
opening so that its field-incidence STL can be calculated from the relation:

  β 2 +1 
STL(reference sample) = -0.192 + 10log(β 2 ) - 10log ln  
  0.043227β +1  
2
(Eq. 5)

where:

β = ρsω/2ρ0c

ω=2πf

f = center frequency of the one-third octave measurement band

ρs = surface density of the reference sample (kg/m2)

ρ0 = volumetric density of air (kg/m3) at measurement barometric pressure, temperature and humidity

c = speed of sound (m/s) at measurement barometric pressure, temperature and humidity

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The procedure for calculating the speed of sound accounting for temperature, humidity and barometric pressure is found in
Appendix D.

5.3.3 Reference Sample Surface Density

The surface density of the reference sample should be selected to be within 50 to 200% of the surface density of each test
panel or multi-layer test assembly as long as the requirements of 5.3.1 are met and the reference sample surface density
does not exceed 10.0 kg/m2. Reference samples of different surface densities may be required to cover various test sample
materials

5.3.4 Signal-to-Noise Ratios

The source signals may be amplified or filtered versus frequency so that, with the test sample sealed in place, the source
room and receiving chamber signal levels are each at least 10 dB, and preferably more than 15 dB, higher than the
background noise levels within the respective chambers and within the dynamic range capability of the measurement system
at all frequencies of interest.

5.3.5 Measurement Conditions

The time and spatially-averaged third-octave band levels in both the source and receiving chambers shall be measured and
recorded over the desired measurement bands with the reference sample sealed into the fixture in the test opening.
Optionally, time averaged, single point measurements may be used on the receiving side of the sample mounting window
if they can be shown to give STL results within ±2.0 dB at all measurement frequencies to time and spatially-averaged
measurements. Averaging times shall be long enough to provide an estimate of the time-averaged level to within ±0.5 dB
for 95% confidence limits at all measurement frequencies. See 5.5.4 and Appendix B. Measurement distance to the sample
mounting plane and number of measurement positions in the receiving chamber which give best results will vary from lab
to lab and are usually determined through trial and error. See 4.10 for microphone placement guidelines.

Note that the construction of a control sample is defined in 6.3, with target STL values defined in 6.4. These can be used
to aid in the above trial-and-error process.
 SAE INTERNATIONAL J1400™ JUL2017 Page 12 of 23

5.3.6 Test Samples

After removing the reference sample, the test sample is installed and sealed into the same opening and in the same manner
as the reference sample. The measurements are then repeated as in 5.3.5. The test sample may be a homogeneous single
layer material, a multi-layer material, a combination of multilayer materials with a sheet metal backing, a porous material
without an impervious layer, or any of the previous materials with a pass-through, opening or intentional leakage path. The
results for each of these systems are compared to the results for the reference sample tested in 5.3.5. If microphones are
moved during test sample mounting, they must be accurately replaced (within 3 mm) to the same positions as in prior
measurements, including reference sample measurements. In a hemi-anechoic or anechoic receiving room, distance from
the surface of the sample facing the receiving room shall remain the same.

5.3.6.1 Test Sample Sealing

Some studies have found that the method of sealing the edges of a lightly damped test sample (e.g., a steel or aluminum
panel) can affect the STL measured according to SAE J1400, particularly in the vicinity of the coincidence frequency of the
test panel. To minimize this artifact it is strongly recommended that the minimum necessary amount of material be used to
seal the edges of the sample to the test fixture. A convenient tool to use to check for sealing gaps is an ultrasonic leak
detector.

5.4 Data Analysis

The following procedures are used to calculate the field incidence STL of the test sample.

5.4.1 Background Noise Correction

If the difference between background noise level and signal plus background noise level is between 10 and 15 dB, correct
for background noise levels at each measured third octave frequency band of interest and at each microphone for both the
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source and receiving chambers using the equation:

LS =10 log10 (10LC /10 -10LB /10 ) (Eq. 6)

where:

LS = corrected sound pressure level of the signal, dB

LC = sound pressure level of the signal and background noise combined, dB

LB = sound pressure level of the background noise alone, dB

NOTE: Correction is not necessary if LC - LB is greater than or equal to 15 dB.

5.4.2 Measured Noise Reduction

For both the reference sample and the test sample, compute the measured noise reduction (MNR) at each one-third octave
band of interest. Using the corrected band pressure levels, if required, for each measurement band, subtract the receiving
chamber band pressure level from the source room band pressure level to obtain the MNR for both samples. Where
applicable, use spatially-averaged values for source and/or receiving room/chamber.

MNRf = SPLf (source room) - SPLf (receiving chamber) (Eq. 7)

NOTE: Subscript “f” indicates frequency-dependent variables.

 SAE INTERNATIONAL J1400™ JUL2017 Page 13 of 23

5.4.3 Correlation Factors

Determine the correlation factor applicable to the test opening and source/receiving chamber pair at each test frequency
(CFf) as the difference between the measured noise reduction of the reference sample, MNRf (reference) and its calculated
STLf (reference).

CFf = MNRf (reference) – STLf (reference) (Eq. 8)

NOTE: Correlation factors at all frequencies should fall within +10/-0 dB for a well-implemented test system, +15/-0 dB for
a typical system and should not exceed the range of +15/-5 dB. Methods to reduce the correlation factor without
major facility changes would include changing the position of the receiving microphone(s), increasing the absorption
in the receiving chamber, improving the sealing and/or sample mounting system, increasing the number of receiving
room microphones, averages or spatial averaging in the receiving room.

NOTE: The correlation factors (CFf) determined using this methodology are subsequently used for computing the STL of
multi-wall samples as well as single wall samples.

5.4.4 Sound Transmission Loss

Compute the sound transmission loss (STLf) of the test sample at each test frequency by subtracting the CFf from the MNRf
of the test sample:

STLf (sample) = MNRf (sample) – CFf (Eq. 9)

STLf (sample) at each frequency band of interest should be rounded to the nearest whole dB.
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5.4.5 Insertion Loss

Sometimes an insertion loss (IL) is desired. In the context of SAE J1400, IL is defined as the difference between the STL
of a substrate (e.g., a metal panel) and the STL of the substrate plus insulator. This can be easily calculated at each
frequency band as:

ILf (insulator) = STLf (substrate + insulator) – STLf (substrate) (Eq. 10)

Similarly, if the CF meets the requirements of 5.4.3, then the IL may be calculated directly from the MNR as:

ILf (insulator) = MNRf (substrate + insulator) – MNRf (substrate (Eq. 11)

5.5 Reporting

The following shall be included when reporting results of these test procedures.

5.5.1 Basic Information

Measurement date, test location, person performing tests, sample description(s) and reference sample(s) used. It is also
required to specifically state any deviations to the SAE J1400 procedure requirements, if any. Sample description shall
include dimensions, weight, overall composition/number of layers, which surface faces the source room and sample
orientation (horizontal, vertical or other). Photos of the each sample as installed should be included. Microphone positions
within source/receiving rooms, number of microphones used (or a single microphone on a rotating boom) should all be
identified. Microphone/preamp model numbers should be recorded.

5.5.2 Ambient Conditions

Ambient temperature, local barometric pressure and humidity conditions in each test chamber at time of measurements.
 SAE INTERNATIONAL J1400™ JUL2017 Page 14 of 23

5.5.3 Sound Transmission Loss

Sound transmission loss rounded to the nearest whole dB versus 1/3-octave center frequencies in Hz. Measurements
which have been corrected for background noise should be marked with an asterisk and a note explaining such. See 5.4.1.
If the user does not have specific data presentation requirements (e.g., internal company standards) the SAE J2629
document and spreadsheets provide data presentation formats for SAE J1400 and other acoustical tests.

5.5.4 Confidence Limits

95% Confidence Limits in dB versus 1/3-octave center frequencies in Hz are defined in Appendix B. Calculations for
Confidence Limits do not have to be made for each test, but should be done annually or following any changes made to the
chamber and/or measurement system which may affect Confidence Limits. Confidence Limits may be shown graphically
as upper and lower bounds for STL at each frequency (i.e., “error bars”).

5.5.5 Maximum Measurement Capability

Maximum STL capability rounded to the nearest whole dB versus 1/3-octave center frequencies in Hz. See 4.7.

6. GENERAL COMMENTS

6.1 Qualified Personnel

It is essential that technically qualified personnel trained in the current techniques of sound measurements select equipment
and perform the tests.

6.2 Routine Calibration

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Instrumentation manufacturers' or quality standard recommended calibration practices should be followed before each test.

6.3 Control Sample Construction

A control sample has been developed to aid in the assessment and minimization of intra-laboratory variability and/or bias.
See Appendix C for construction details. Specific sources of construction materials are mentioned as guidelines. Alternative
sources may work as well.

6.4 Control Sample Target Results

The following table is based on a weighted average of multiple control samples produced independently and tested in a
number of independent test laboratories. All qualified laboratories should be able to reproduce these results within 3 dB at
all frequencies. Laboratories having trouble with reproducibility particularly below 1000 Hz should seek improvements as
suggested in 4.3 and 4.8. If measured STL is too low relative to target levels above 2500 Hz, improvements as suggested
in 4.6 and 4.9 are recommended. Note that stiffness effects of finite size panels may affect low frequency STL. Every lab
may not be able to reproduce the table shown below in its full frequency and STL ranges. A good understanding of lab
limitations (flanking paths, source room diffuse field cutoff, effects of window size, etc.) should provide understanding of
how much of Table 3 is valid.
 SAE INTERNATIONAL J1400™ JUL2017 Page 15 of 23

Table 3 - Target sound transmission loss values - control sample

1/3-Octave Center Sound Transmission

Frequency [Hz] Loss [dB]
125 10
160 9
200 10
250 16
315 25
400 33
500 40
630 45
800 50
1000 54
1250 59
1600 63
2000 66
2500 69
3150 72
4000 74
5000 77
6300 79
8000 82

7. NOTES

7.1 Revision Indicator

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A change bar (l) located in the left margin is for the convenience of the user in locating areas where technical revisions, not
editorial changes, have been made to the previous issue of this document. An (R) symbol to the left of the document title
indicates a complete revision of the document, including technical revisions. Change bars and (R) are not used in original
publications, nor in documents that contain editorial changes only.

PREPARED BY THE SAE ACOUSTICAL MATERIALS COMMITTEE

 SAE INTERNATIONAL J1400™ JUL2017 Page 16 of 23

APPENDIX A - RECOMMENDED SAMPLE MOUNTING SYSTEM

Top Sectional View :

--- Source Chamber ---
Sealing Putty

Holding Clamp (Caution – excessive compression of the

sample edges may induce airgaps within multilayer samples)

Holding Frame

Sealing Putty
Test Sample

Sheetmetal
(optional)
Sealing Putty

Metal frame for opening

Split Frame Design

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Insulation as required

Min. Overlap 50 mm Optional: this opening may be

tapered away from the sample in
order to minimize “niche” effects

--- Receiving Chamber ---

Figure A1 - Recommended sample mounting and sealing system

The test sample shown here is installed from the source room, which is recommended for convenience of sample mounting.
In some cases, test samples may not have a sheet metal base panel or it may be a different material/composite. Test
window orientation may be horizontal or non-orthogonal in order to duplicate end-use orientation, particularly if gravity holds
test samples in place. The sheet metal-to-sample orientation may be reversed (sheet metal facing source room) in order
to have the sound field incident on the same face as the intended application.
 SAE INTERNATIONAL J1400™ JUL2017 Page 17 of 23

APPENDIX B - ACCURACY, PRECISION, AND REPEATABILITY

B.1 ACCURACY

Accuracy determines how well the test data measures the STL properties of the test specimen. Since this test protocol is
defined, the accuracy of a test conducted by this method is governed by the design of the test facility and by the sample
mounting and microphone placement procedures.

B.2 PRECISION

Precision determines the variation of the average measurement for a certain confidence level. The precision of this test is
determined by the variation in each measured data set and is calculated from the confidence intervals for each data set.

B.2.1 Confidence Intervals

The overall confidence interval for the resulting data is derived from the confidence intervals for the individual measured
quantities. The following paragraphs describe the steps to be taken to collect and calculate confidence intervals.

B.2.2 Standard Deviations

Calculate the standard deviation, sf, for the mean of each time and space averaged one-third octave band sound pressure
level for LSRf, LRRf, LSTf, and LRTf

where:

LSRf = source room sound pressure level for the reference sample
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LRRf = receiving chamber sound pressure level for the reference sample

LSTf = source room sound pressure level for the test sample

LRTf = receiving chamber sound pressure level for the test sample

using this expression

sf = SQRT {(1/(n-1))*SUM(Xif – XMEANf)2} (Eq. B1)

where:

sf = standard deviation at each frequency band of interest

Xif = individual measurement of sound pressure level at each frequency band of interest

XMEANf = arithmetic mean of the set of sound pressure levels at each frequency band of interest

n = number of measurements of sound pressure level in each set; a minimum of six (6) is recommended
 SAE INTERNATIONAL J1400™ JUL2017 Page 18 of 23

B.2.3 95% Confidence Interval

Calculate the 95% confidence interval for the individual measurement frequency bands from:

delta Xf = a • sf (Eq. B2)

where:

delta Xf = confidence interval at each frequency band of interest

sf = standard deviation at each frequency band of interest

a = factor which depends on the number of measurements and is given in Table C1

Table B1 - Factors for 95% confidence limits for averages

Number of Measurements, n Factor a for Confidence Limits

4 1.591
5 1.241
6 1.050
7 0.925
8 0.836
9 0.769
10 0.715
11 0.672
12 0.635
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13 0.604
14 0.577
15 0.544
16 0.533
17 0.514
18 0.497
19 0.482
20 0.468
21 0.455
22 0.443
23 0.432
24 0.422
25 0.413
n greater than 25 a = n0.5/(0.512n-0.71)

B.2.4 Overall Confidence Intervals

Calculate the confidence interval for each frequency band of interest from:

delta STLf = SQRT { (delta LSRf)2 + (delta LRRf)2 +(delta LSTf)2 +(delta LRTf)2} (Eq. B3)

B.3 REPEATABILITY

Repeatability determines the success in obtaining identical test results on the same sample. Within the limits for precision
defined in B.2.4, the repeatability of a test on any sample is influenced by the mounting and microphone
placement/replacement procedures. If mounting and microphone placement practices are closely replicated, then
repeatable results should be expected within the limits of precision.
 SAE INTERNATIONAL J1400™ JUL2017 Page 19 of 23

APPENDIX C - RECOMMENDED CONSTRUCTION - CONTROL SAMPLE

DAP® DYNAFLEX 230® McMaster-Carr #8943K25

Premium Elastomeric .024” Galvanized Steel
Latex Sealant

Apply light tack of spray

Press-fit fiberglass
adhesive* to inside of galvanized
into channel
sheets prior to assembly
(optional – trim
both surfaces for
easier fit)

McMaster-Carr #9001K35 Johns-Manville “Spin-Glas”

Aluminum Channel - 1”x 1” Fiberglass - 3 pcf, 1” thick

* DURO: All-Purpose Spray Adhesive: 11oz; UPC: 0-79340-81088-4

1-2 mm dia. Pressure Relief Hole (one or more sides)

Figure C1 - Control sample, typical edge section

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Figure C2 - Control sample, typical plan view

 SAE INTERNATIONAL J1400™ JUL2017 Page 20 of 23

APPENDIX D - CALCULATION OF THE SPEED OF SOUND

D.1 EFFECT OF TEMPERATURE, BAROMETRIC PRESSURE AND HUMIDITY

For accurate calculation of reference sample STL, and ultimately the STL of the test sample, the speed of sound should be
corrected to account for ambient conditions temperature, barometric pressure and humidity.

Step by step calculations to compute speed of sound (c) with temperature, humidity and
barometric pressure:
• Speed of sound in dry air (cd) with temperature:
𝑇𝑇
𝑐𝑐𝑑𝑑 = 331.45 �1 + 273
(m/s) (A-1)

where, T = atmospheric temperature in ̊ C

• The speed of sound of moist air (c) with per cent relative humidity hrel (%)
o The specific heat ratio γw for moist air is computed as:
ℎ+7
𝛾𝛾𝑤𝑤 =
ℎ+5
where, h = fraction of molecules water in air
0.01 ℎ𝑟𝑟𝑟𝑟𝑟𝑟 𝑣𝑣𝑣𝑣(𝑇𝑇)
ℎ=
𝑝𝑝𝑎𝑎
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where, hrel = Relative humidity in %

vp(T) = vapor pressure of water at measured temperature (T) in Pa
pa = Barometric Pressure in Pa
o Assuming dry air composition is 78% nitrogen (molecular weight = 28),
21% oxygen (molecular weight = 32) and 1% argon (molecular weight = 40)
Total molecular weight is:
𝑀𝑀𝑑𝑑 = 0.78 ∗ 28 + 0.21 ∗ 32 + 0.01 ∗ 40 = 29
The presence of water (with a molecular weight of 18) causes the total average
molecular weight to decrease to:
𝑀𝑀𝑤𝑤 = 29 − (29 − 18)ℎ = 29 − 11ℎ
o Ratio of speed of sound of moist air to that of dry air is:

𝑐𝑐 𝛾𝛾𝑤𝑤
= 4.5513�
𝑐𝑐𝑑𝑑 𝑀𝑀𝑤𝑤

o Speed of sound of moist air (c) is then computed as:

𝛾𝛾
𝑐𝑐 = 4.5513 𝑐𝑐𝑑𝑑 �𝑀𝑀𝑤𝑤 (m/s)
𝑤𝑤
 SAE INTERNATIONAL J1400™ JUL2017 Page 21 of 23

For example:

For T = 20 °C, hrel = 50% and pa = 101.325 kPa, c = 344.0 m/s

For T = 25 °C, hrel = 40% and pa = 99.5 kPa, c = 347.0 m/s

As a convenient reference, Table D1 shows water vapor pressure values at various temperatures.

Table D1 - Water vapor pressure as a function of ambient temperature.

Temperature (°C) Water Vapor Pressure (Pa)

15 1760
16 1820
17 1940
18 2060
19 2190
20 2340
21 2490
22 2640
23 2810
24 2980
25 3170
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 SAE INTERNATIONAL J1400™ JUL2017 Page 22 of 23

APPENDIX E - EFFECT OF WINDOW SIZE ON LOW FREQUENCY TRANSMISSION LOSS

The discussion following is based on chapter 9 of the first edition of Noise and Vibration Control Engineering: Principles and
Applications. Field-incidence includes angles of incident sound from 0 (normal to the panel) to 78°, as opposed to random-
incidence, ranging from 0 to 90°. Field-incidence prediction for infinite panels has been found to correlate better to measured
results for large panels than random-incidence prediction. A generally accepted rule is that for normal-incident STL greater
than 15 dB, field-incident STL at frequencies well under coincidence frequency and in the mass-controlled region for an
infinite panel can be found as:

STLfield = STLnormal – 5 Db (Eq. E1)

For a finite panel in the mass-controlled region and well below coincidence frequency, a random-incidence prediction which
agrees well with measured results is:

STLrandom = STLnormal – 3 – 10logσF dB, (Eq. E2)

where

σF = for >1 (Eq. E3)

and

k0 = π , m-1. (Eq. E4)

σF is the forced-wave radiation efficiency for random-incident sound, k0 is the wavenumber calculated for the 1/3-octave
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band frequency of interest and S is the panel surface area. σF increases with frequency and with panel dimensions.

To illustrate the effect of panel size see Figure E1, which shows nominal field incidence transmission loss in the mass
controlled region for an infinite plate as compared with finite size plates of 0.5 x 0.5 m and 1.4 x 1.4 m.
 SAE INTERNATIONAL J1400™ JUL2017 Page 23 of 23

Figure E1 - Comparison of calculated field incidence transmission loss for finite size square plates versus an
infinite plate
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