2pSAa8 – A Study on a Sound Extinguisher Using Sound Lens

Ik-Soo Ahn, aisbestman@naver.com
Hyung-Woo Park pphw@ssu.ac.kr
Myung-Jin Bae, mjbae@ssu.ac.kr
Soongil University
369 Sangdo-ro, Dongjak-gu
Seoul, Korea 06978

Seong-Geon Bae sgbae@kangnam.ac.kr
Kangnam University
111, Gugal-dong, Giheung-gu, Yongin-si
Gyeonggi-do, Korea 16979

Popular version of paper 2pSAa8“A study on a sound fire extinguisher using special sound lens”
Presented Tuesday afternoon, May 24, 2016, 3:10 A in Salon E
171st ASA Meeting, Salt Lake City
Click here to read the abstract

In 2012, DARPA, Defense Advanced Research Projects Agency of the United States, demonstrated that fire can be put out by surrounding it with two large sound speakers. This verified the possibility of a fire extinguisher utilizing sound. Since then, many people have tried to develop a more efficient sound extinguisher, recognizing its future value. For example, in 2015 a couple of American graduate students introduced a portable sound extinguisher and demonstrated it on YouTube, but it was too heavy and too weak with long cables. The basic mechanism for a sound extinguisher can be summarized as follows: When the sound extinguisher produces low frequency sound of 100Hz, its vibration energy touches the flame, scatters its membrane, and then blocks the influx of oxygen, so the flame goes down.

Picture 1 Fire with strong flame

Picture 1 Fire with strong flame

Picture 2 Applying the extinguisher

Picture 2 Applying the extinguisher

Picture 3 The result

Picture 3 The result

Recently, a research team of SSERI, the Sori Sound Engineering Research Institute, introduced an improved device, a “sound-wind extinguisher,” by installing a sound lens in a speaker to produce more focused power of sound, roughly 10 times stronger in its power than the previous one. This sound-wind extinguisher is very light, weighting only about 2 kg, 1/3 of the previous one, and can be carried around with one hand without any connecting cable. It is also small in size measuring 40cm in length. With an easy on-off switch, you can use it anywhere, up to 1~2m distance from the flame.

The most important improvement to be found in our sound extinguisher from the previous one is the installation of a sound lens. If you use the sound in a usual way with a normal speaker, it scatters into the air without displaying any effect on the flame. On the other hand, when the sound lens is used with a speaker, the lens concentrates the sound generated from the speaker into one place and makes it possible to reach the fire more directly. In other words, it amplifies sound to maximize its efficiency without losing the power of sound which might be caused by the interference of the air. air. The team also succeeded in reducing the size and weight of the extinguisher, so that anyone can carry it anywhere at any time, improving its portability with an easy on-off switch. The experimental sound extinguisher is shown in the following pictures and video clip.

The following figure illustrates how and where to install a sound lens inside of the sound extinguisher.
Int Structure

We believe that the sound-wind extinguisher is fit best for the beginning stage of a fire. It can be used at home, at work, on board in aircrafts, vessels, and cars.


[1] DAPRA Demonstration, https://www.youtube.com/watch?v=DanOeC2EpeA

[2] American graduate students (George Mason Univ.), https://www.youtube.com/watch?v=uPVQMZ4ikvM

[3] Ahn, I.S., Bae, M.J. “On a Compact Extinguisher Using Sound Lens,” KICS, Proceedings of 2016 Conference of KICS, Vol. 32, No. 1, pp. 10C-13-1~2. Jan. 20-22, 2016.

[4] Lee, E.Y., Bae, M.J. “On a Focused Transducer for Fire-extinguishing,” ASK, Proceedings of 2015 Fall Conference of ASK, Vol. 34, No.2(s), pp. 35, No. 13, 2015.

[5] Park, S.Y., Yeo, K.S., Bae, M.J. “On a Detection of Optimal Frequency for Candle Fire-extinguishing,” ASK, Proceedings of 2015 Fall Conference of ASK, Vol. 34, No. 2(s), pp. 32, No. 13, 2015.

[6] Yeo, K.S., Park, S.Y., Bae, M.J. “On an Extinguisher with Sound and Wind,” ASK, Proceedings of 2015 KSCSPC, Vol. 32, No. 1, pp. 170-171, Aug. 14, 2015.

4aAA5 – Conversion of an acoustically dead opera hall in a live one

Wolfgang Ahnert1, Tobias Behrens1 (info@ada-amc.eu) and Radu Pana2 (pana.radu@gmail.com)

1 ADA Acoustics & Media Consultants GmbH, Arkonastr. 45-49, D-13189 Berlin / Germany
2 University of Architecture and Urbanism “Ion Mincu”, Str. Academiei 18-20, RO-010014 Bucuresti / Romania

Popular version of paper 4aAA5, “The National Opera in Bucharest – Update of the room-acoustical properties”
Presented Thursday morning, November 5, 2015, 10:35 AM, Grand ballroom 3
170th ASA Meeting, Jacksonville

The acoustics of an opera hall has changed dramatically within the last 100 years. Until the end of the 19th century, mostly horseshoe-shaped halls were built with acoustically high-absorbing wall and even floor areas. Likewise, the often used boxes had fully absorbing claddings. That way the reverberation in these venues was made low and the hall was perceived as acoustically dry, e.g. the opera hall in Milan. 100 years later, the trend shows opera halls with more live and higher reverberation, preferred now for music reproduction, e.g. Semper Opera in Dresden.

This desire to enhance the acoustic liveliness in the Opera House in Bucharest led to renovation work in 2013-2014. The Opera House was built in 1952-1953 for around 2200 spectators and it followed a so-called style of “socialist realism”. This type of architecture was popular at the time, when communism was new to Romania, and the building has therefore a neoclassical design. The house was looking inside the hall like a theatre of the late 19th century. The conditions in the orchestra pit for the musicians, as far as mutual hearing is concerned, were bad as well. So, construction works took place in order to improve room acoustical properties for musicians and audience.

Ahnert-Fig.1 - opera hall

Fig. 1: Opera hall after reconstruction

The acoustic task was to enhance the room acoustic properties significantly by substituting absorptive faces (as carpet, fabric wall linings, etc.) by reflective materials:

  1. Carpet on all floor areas, upholstered back- and undersides of chairs
  2. Textile wall linings at walls/ceilings in boxes, upholstered hand rails
  3. Textile wall linings at balustrades, upholstered hand rails in the galleries

All the absorbing wall and ceiling parts were substituted by reflecting wood panels, the carpet was removed and a parquet floor was introduced. As a result, the sound does not fade out anymore as in an open-air theatre but spaciousness may be perceived now.

The primary and secondary structures of the orchestra pit were changed as well in order to improve mutual hearing in the pit and between stage and pit.  The orchestra pit had the following acoustically disadvantageous properties:

  • Insufficient ratio between open and covered area (depth of opening 3.5 m, depth of cover 4.7 m)
  • The height within the pit in the covered area was very small.
  • The space in the covered area of the pit was highly overdamped by too much absorber.

Ahnert_Fig.2 - opera hall

Fig. 2: new orchestra pit, section

The following changes have been applied:

  • The ratio between open area and covered area is now better by shifting the front edge of the stage floor to the back: Depth of opening is now 5.1 m, depth of cover only 3.1 m.
  • The height within the pit in the covered area is increased by lowering the new movable podium.
  • The walls and soffit in the pit are now generally reflective, broadband absorbers can be placed variably at the back wall in the pit.

After an elaborate investigation by measurements and simulation on site a prolongation of the reverberation time of 0.2-0.3 s was reached to actual values of about 1.3 to 1.4 s.

Together with alterations of the geometric situation of pit, the acoustic properties of the hall are now very satisfactory for musicians, singers and the audience.

Beside the reverberation time, other room acoustical measures such as C80, Support, Strength, etc. have been improved significantly.

2aAA9 – Quietly Staying Fit in the Multifamily Building

Paulette Nehemias Harvey – pendeavors@gmail.com
Kody Snow – ksnow@phoenixnv.com
Scott Harvey – sharvey@phoenixnv.com

Phoenix Noise & Vibration
5216 Chairmans Court, Suite 107
Frederick, Maryland 21703

Popular version of paper 2aAA9, “Challenges facing fitness center designers in multifamily buildings
Presented Tuesday morning, November 3, 2015, 11:00 AM, Grand Ballroom 3
Session 2aAA, Acoustics of Multifamily Dwellings
170th ASA Meeting, Jacksonville

Please keep in mind that the research described in this Lay Language Paper may not have yet been peer reviewed.

Harvey 1 Treadmill - fitness centerTransit centered living relies on amenities close to home; mixing multifamily residential units with professional, retail and commercial units on the same site. Use the nearby trains to get to work and out, but rely on the immediate neighborhood, even the lobby for errands and everyday needs. Transit centered living is appealing as it eliminates the need for sitting in traffic, seems good for the environment and adds a sense of security, aerobic health and time-saving convenience. Include an on-site fitness center and residents don’t even have to wear street clothes to get to their gym!

Developers know that a state-of-the-art fitness center is icing on their multifamily residence cake as far as attracting buyers. Gone is the little interior room with a couple treadmills and a stationary bike. Today’s designs include panoramic views, and enough ellipticals, free weights, weight & strength machines, and shower rooms to fill 2500-4000 square feet, not to mention the large classes offered with high energy music and an enthusiastic leader with a microphone. The increased focus on maintaining aerobic health, strength and mobility is fantastic, but the noise and vibration it generates? Not so great. Sometimes cooperative scheduling keeps the peace, but often residents will want to have access to their fitness center at all hours, so wise project leaders involve a noise control engineer early in the design process to develop a fitness center next to which everyone will want to live.

Remember the string and two empty cans? Stretch the string taut and conversations can travel the length of the string, but pinch the string and the system fails. As noise travels through all kinds of structures and through the air as well, it is the design goal of the noise and vibration experts to prevent that transmission. Airborne noise control can be effective using a combination of layered gypsum board, fiberglass batt insulation, concrete and resilient framing members that absorb the sound rather than transmit it through a wall or a floor/ceiling system. Controlling the structure borne noise and vibration can involve much thicker rubber mats, isolated concrete slabs and a design that incorporates the structural engineer’s input on stiffening the base building structure. And it’s not simply noise that the design is intended to restrict, it is silent, but annoying vibrations as well.

Harvey 2 Kettleball exercise - fitness center

Reducing the floor shaking impact of dropping barbells on the ground is the opposite of hearing a pin drop. Heavy, steel plates loaded on a barbell, lifted 6-8 feet off the ground and then dropped. Repeatedly. Nobody wants to live under that, so designers think location, location, location. But big windows are pointless in the basement, so something has to go under the fitness center. Garage space, storage units or mechanical rooms won’t mind the calisthenics above them. And sometimes the overall design of the building structure, whether it be high-rise with underground parking, Texas wrap building (u-shaped building with elevated parking garage on interior.), or a podium style building can offer an ideal location for this healthy necessity.

It’s not an acoustical trade secret that the best method of noise control is at the source so consider what makes the noise. Manufacturers have met the demand for replacing the old standard graduated barbell steel plates for free weight combinations with a rubber/urethane coated steel weight. These weights make much less noise when impacting each other, but are still capable of generating excessive structure-borne noise levels. This is a great example of controlling both air borne (plates clanking together) and structure borne (barbells impacting the floor) transmission paths. Speakers and sound systems and the wall/floor/ceiling systems can work together to offer clarity and quality to listeners and limitations for what the neighbors will hear, but it takes expertise and attention.

Disregarding the recommendations of noise and vibration professionals can result in an annoying, on-site gym that brings stressful tension and ongoing conflict, nothing that promotes healthy well-being.

Foresight in design and attention to acoustical specs on building materials, under the direction of a noise and vibration engineer, assures a fitness center that is a pleasant, effective space for fitness and social opportunities, an asset to the transit centered neighborhood. Do everyone a favor and pay attention to good design and product specification early on; that’s sound advice.

4aEA10 – Preliminary evaluation of the sound absorption coefficient of a thin coconut coir fiber panel for automotive applications

Key F. Lima – keyflima@gmail.com
Pontifical Catholic University of Paraná
Curitiba, Paraná, Brazil

Popular version of paper 4aEA10, “Preliminary evaluation of the sound absorption coefficient of a thin coconut fiber panel for automotive applications”
Presented Thursday morning, November 5, 2015, 11:15 AM, Orlando Room
170th ASA Meeting, Jacksonville, Fl

Absorbents materials are fibrous or porous and must have the property of being good acoustic dissipaters. Sound propagation causes multiples reflections and friction of the air present in the absorbent medium converting sound energy to thermal energy. The acoustic surface treatment with absorbent material are widely used to reduce the reverberation in enclosed spaces or to increase the sound transmission loss of acoustics panels. In addition, these materials can be applied into acoustics filters with the purpose to increase their efficiencies. The sound absorption depends on the excitation frequency of the sound and it is more effective at high frequencies. Natural fibers such as coconut coir fiber have a great potential to be used like sound absorbent material. As natural fibers are agriculture waste, manufacturing this fiber is a natural product, therefore an economic and interesting option. This work compares the sound absorption coefficient between a thin coconut fiber panel and a composite panel made by fiberglass and expanded polyurethane foam, no-woven woven, and polyester woven, which are used in the automotive industry as a roof trim. The evaluation of sound absorption coefficient was carried out with the impedance tube technique.

In 1980, Chung and Blaser evaluated the normal incidence sound absorption coefficient through transfer function method.  The standard ASTM E1050-10 and ISO 10534-2 was based in Chung and Blaser’s method, Figure 1. In summary, this method uses an impedance tube with the sound source placed to one end and at another, the absorbent material backed in a rigid wall. The decomposition of the stationary sound wave pattern into forward and backward traveling components is achieved by measuring sound pressures. This evaluating is carried out simultaneously at two spaced locations in the tube’s sidewall where two microphones are located, Figure 1.

Impedance Tube Fig1

Figure 1. Impedance Tube

The wave decomposition allows to the determination of the complex reflection coefficient R(f) from which the complex acoustic impedance and the normal incidence sound absorption coefficient (a) of an absorbent material can be determined. Furthermore, the two coefficients R(f) and a are calculated by Transfer Function H12 between the two microphones through:fig1, where s is the distance between the microphones, x1 is the distance between the farthest microphone and the sample, i is the imaginary unity and k0 is the wave number of the air. If R(f) is known, the coefficient a is easily obtained by expression:fig2.

In this work, eight samples of coconut fiber and eight samples of composite panel made by fiberglass and expanded polyurethane foam, no-woven woven, and polyester woven used in the automotive industry, Figure 2 and 3. The material properties are shown in Table 1.

Sample Fig2 - coconut coir fiber

Figure 2. Samples

Composite Panel Fig3 - coconut coir fiber

Figure 3. Composite panel structure.

Table 1. Material Properties.
Coconut Fiber Composite Panel


















1 28,25 5,17 0,67 649,5 1 28,05 5,78 0,41 360,6
2 28,20 5,04 0,62 618,8 2 28,08 5,66 0,42 376,6
3 28,20 4,93 0,60 612,6 3 28,15 5,59 0,42 379,6
4 28,35 5,09 0,69 674,7 4 28,23 5,54 0,44 398,8
5 100,43 4,98 8,89 708,0 5 99,55 5,86 5,40 371,9
6 100,43 4,84 9,73 797,7 6 99,55 6,20 5,54 360,9
7 100,73 5,34 9,64 712,1 7 99,68 6,06 5,57 370,4
8 100,45 4,79 9,13 755,2 8 99,55 5,99 5,62 378,9

The random noise signal with frequency band between 200 Hz and 5000 Hz was utilized to evaluate a.  The Figure 4 shows the mean normal incidence absorption coefficient obtained from the measurements.

Comparison absorption coeff Fig4

Figure 4. Comparison of normal absorption coefficient (a)

The results shows that the composite panel have a better sound absorption coefficient than coconut fiber panel. To improve the coconut fiber panel acoustical efficiency it is needed to add some filling material with the same effect of the polyurethane foam of the composite panel.

Chung, J. Y. and Blaser D. A. (1980) “ Transfer function method of measuring  in-duct acoustic properties – I Theory,” J. Acoust. Soc. Am. 68, 907-913.

Chung, J. Y. and Blaser D. A. (1980) “ Transfer function method of measuring  in-duct acoustic properties – II Experiment,” J. Acoust. Soc. Am. 68, 913-921.

ASTM E1050:2012. “Standard test method for impedance and absorption of acoustical materials using a tube, two microphones and a digital frequency analysis system,” American Society for Testing and Materials, Philadelphia, PA, 2012.

ISO 10534-2:1998. “Determination of sound absorption coefficient and impedance in impedance tubes – Part 2: Transfer-function method”, International Organization for Standardization, Geneva, 1998.

3aSA7 – Characterizing defects with nonlinear acoustics

Pierre-Yves Le Bas, pylb@lanl.gov1,  Brian E. Anderson1,2, Marcel Remillieux1, Lukasz Pieczonka3, TJ Ulrich1

1Geophysics group EES-17, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
2Department of Physics and Astronomy, Brigham Young University, N377 Eyring Science Center, Provo, UT 84601, USA
3AGH University of Science and Technology, Krakow, Poland

Popular version of paper 3aSA7, “Elasticity Nonlinear Diagnostic method for crack detection and depth estimation”
Presented Wednesday morning, November 4, 2015, 10:20 AM, Daytona room
170th ASA Meeting, Jacksonville

One common problem in industry is to detect and characterize defects, especially at an early stage. Indeed, small cracks are difficult to detect with current techniques and, as a result, it is customary to replace parts after an estimated lifetime instead of keeping them in service until they are effectively approaching failure. Being able to detect early stage damage before it becomes structurally dangerous is a challenging problem of great economic importance. This is where nonlinear acoustics can help. Nonlinear acoustics is extremely sensitive to tiny cracks and thus early damage. The principle of nonlinear acoustics is easily understood if you consider a bell. If the bell is intact, it will ring with an agreeable tone determine by the geometry of the bell. If the bell is cracked, one will hear a dissonant sound, which is due to nonlinear phenomena. Thus, if an object is struck it is possible to determine, by listening to the tone(s) produced, whether or not it is damaged. Here the same principle is used but in a more quantitative way and, usually, at ultrasonic frequencies. Ideally, one would also like to know where the damage is and what its orientation is. Indeed, a crack growing thru an object could be more important to detect as it could lead to the object splitting in half, but in other circumstances, chipping might be more important, so knowing the orientation of a crack is critical in the health assessment of a part.

To localize and characterize a defect, time reversal is a useful technique. Time reversal is a technique that can be used to localize vibration in a known direction, i.e., a sample can be made to vibrate perpendicularly to the surface of the object or parallel to it, which are referred to as out-of-plane and in-plane motions, respectively. The movie below shows how time reversal is used to focus energy: a source broadcasts a wave from the back of a plate and signals are recorded on the edges using other transducers. The signals from this initial phase are then flipped in time and broadcast from all the edge receivers. Time reversal then dictates that these waves focus at the initial source location.



-video file missing-

Time reversal can also be more that the simple example in the video. Making use of the reciprocity principle, i.e., that a signal traveling from A to B is identical to the same signal traveling from B to A, the source in the back of the plate can be replaced by a receiver and the initial broadcast can be done from the side, meaning TR can focus energy anywhere a signal can be recorded; and with a laser as receiver, this means anywhere on the surface of an object.

In addition, the dominant vibration direction, e.g., in-plane or out-of plane, of the focus can be specified by recording specific directions of motion of the initial signals. If during the first step of the time reversal process, the receiver is set to record in-plane vibration, the focus will be primarily in that in-plane direction; similarly if the receiver records the out-of-plane vibration in the first step of the process, the focus will be essentially in the out-of-plane direction. This is important as the nonlinear response of a crack depends on the orientation of the vibration that makes it vibrate. To fully characterize a sample in terms of crack presence and orientation TR is used to focus energy at defined locations and at each point the nonlinear response is quantified.  This can be done for any orientation of the focused wave. To cover all possibilities, three scans are usually done in three orthogonal directions.

Figure 2 shows three scans on x, y and z directions of the same sample composed of a glass plate glued on an aluminum plate. The sample has 2 defects, one delamination due to a lack of glue between the 2 plates (in the (x,y) plane) at the top of the scan area and one crack perpendicular to the surface in the glass plate in the (x,z) plane in the middle of the scan area.

2 - Nonlinear acoustics

Figure 2. Nonlinear component of the time reversal focus at each point of a scan grid with wave focused in the x, y and z direction (from left to right)

As can be seen on those scans, the delamination in the (x,y) plane is visible only when the wave is focused in the Z direction while the crack in the (x,z) plane is visible only in the Y scan. This means that cracks have a strong nonlinear behavior when excited in a direction perpendicular to their main orientation. So by scanning with three different orientations of the focused vibration one should be able to recreate the orientation of a crack.

Another feature of the time reversal focus is that its spatial extent is about a wavelength of the focus wave. Which means the higher the frequency, the smaller the spot size, i.e., the area of the focused energy. One can then think that the higher the frequency the better the resolution and thus higher frequency is always best. However, the extent of the focus is also the depth that this technique can probe; so lower frequency means a deeper investigation and thus a more complete characterization of the sample. Therefore there is a tradeoff between depth of investigation and resolution. However, by doing several scans at different frequencies, one can extract additional information about a crack. For example, Figure 3 shows 2 scans done on a metallic sample with the only difference being the frequency of the focused wave.

3 - Nonlinear acoustics

Figure 3. From left to right: Nonlinear component of the time reversal focus at each point of a scan grid at 200kHz and 100kHz and photography of the sample from its side.

At 200kHz, it looks like there is only a thin crack while at 100kHz the extent of this crack is larger toward the bottom of the scan and more than double so there is more than just a resolution issue. At 200kHz the depth of investigation is about 5mm; at 100kHz it is about 10mm. Looking on the side of the sample in the right panel of figure 3, the crack is seen to be perpendicular to the surface for about 6mm and then dip severely. At 200kHz, the scan is only sensitive to the part perpendicular to the surface while at 100kHz, the scan will also show the dipping part. So doing several scans at different frequencies can give some information on the depth profile of the crack.

In conclusion, using time reversal to focus energy in several directions and at different frequencies and studying the nonlinear component of this focus can lead to a characterization of a crack, its orientation and depth profile, something that is currently only available using techniques, like X-ray CT, which are not as easily deployable as ultrasonic ones.