ICaD 2013 6–10 july, 2013, Łódź, Poland international Conference on auditory Display

The 19th International Conference on Auditory Display (ICAD-2013) July 6-10, 2013, Lodz, Poland

The 19th International Conference on Auditory Display (ICAD-2013) July 6-10, 2013, Lodz, Poland The 19thPRACTICAL International Conference on Auditory RECOMMENDATIONS Display (ICAD-2013) FORJu USINGly 6-10, 2013, Lodz, Poland PRACTICAL RECOMMENDATIONS FOR USING SOUND TRANSDUCERS WITH GLASS SOUNDMEMBERANE TRANSDUCERS AS AUDITORY DISPLAY WITH BASED GLASS ON MEASUREMENTS MEMBERANE AND SIMULATIONSPRACTICAL RECOMMENDATIONS FOR USING SOUND TRANSDUCERS WITH GLASS ASPRACTICAL AUDITORY RECOMMENDATIONS DISPLAY FOR BASED USINGMEMBERANE SOUND ON TRANSDUCERS MEASUREMENTS AS AUDITORY WITH DISPLAY GLASS BASED ON MEASUREMENTS AND MEMBERANE AS AUDITORY DISPLAY BASED ON MEASUREMENTSSIMULATIONS AND György WersényANDi SIMULATIONS József Répás György Wersényi József Répás SzéchenyiGyörgyGyörgy István WersényiWersény Universityi , SzéchenyiJózsefJózsef IstvánRépás Répás University, DepartmentSzéchenyi of István Telecommunications University, , DepartmentSzéchenyi of Telecommunications, István University, Department of Telecommunications, SzéchenyiDepartment István University of Telecommunications,, Széchenyi István University, Széchenyi István University, Széchenyi István University, H-9026,H-9026, Győr, Győr, Egyetem Egyetem t. 1, Hungaryt. 1, Hungary DepartmentH-9026,H-9026, of TelecommunicationsGyőr, Győr, Egyetem Egyetem t. t.1, Hungary1,,Hungary Department of Telecommunications, [email protected] of [email protected] , H-9026,Department Győr, Egyetem ofrepas [email protected], t.@ 1sze.hu, Hungary H-9026, Győr, Egyetem t. 1, Hungary H-9026, Győr, Egyetem t. 1, Hungary H-9026,wersenyi Győr,@sze Egyetem.hu t. 1, Hungary [email protected] a range up to 18 kHz, size-independent directivity, wersenyiABSTRACT@sze .hu [email protected] but with low sensitivity for lower and insufficient ABSTRACT a frequency range up to 18 kHz, size-independent directivity, stereophonic image. The applicability of DML panels for wave Newly designed vibrating ABSTRACT transducers can be used coupled a frequency range up to 18 kHz, size-independent directivity,but with low sensitivity for lower frequencies and insufficient field synthesis (WFS)-based sound reproduction has been also directly to solid surfaces such as wood or glass as plane waveNewly designedbut with vibratinglow sensitivity transducers for lower can frequencies be used coupled and insufficient stereophonic image. The applicability of DML panels for wave investigated, where large number of closely spaced short-distanceNewly designed . vibrating Our transducers former analysis can be evaluated used coupled thedirectly tostereophonic solid surfaces image. such The as woodapplicability or glass of as DML plane panels wave for wavefield synthesis (WFS)-based sound reproduction has been also loudspeakers is necessary. It has been incorporated into a SolidDrivedirectly to transducer solid surfaces glued such on as to wood glass or surfaces glass as ofplane different waveshort-distance field synthesisloudspeakers. (WFS)-based Our former sound analysis reproduction evaluated has the been alsoinvestigated, where large number of closely spaced sizesshort-distance and forms. loudspeakers. Further investigations Our former concludedanalysis evaluated that these theSolidDrive investigated,number transducer of novel glued where products on large to glass such number surfaces as school of of differentequipment, closely spaced portableloudspeakers is necessary. It has been incorporated into a parametersSolidDrive do transducernot influence glued the ontransmission to glass surfaces and quality of different of thesizes andloudspeakersfolding forms. speakers Further is necessary. investigationsetc. [1]. It has concluded been incorporated that these into number a of novel products such as school equipment, portable coupledsizes and system forms. significantly. Further investigations The second concluded part that of these thisparameters numberRecently, do not of influence anovel new groupproducts the transmission of loudspeakers such as schooland qualityhas equipment, been of introduced:the portablefolding the speakers etc. [1]. investigationparameters includeddo not influence only one the sizetransmission and geometry and quality for further of thecoupled foldingso system called speakers significantly. “invisible etc. [1 ]. audio” The second [2-4]. part Manufacturers of this shipRecently, the a new group of loudspeakers has been introduced: the numericalcoupled simulations system significantly. using COMSOL The secondFEM, as part well of as this forinvestigation Recently,vibrating included atransducer new only group one only of size loudspeakers about and geometrya size has of been fora beer furtherintroduced: can that cantheso be called “invisible audio” [2-4]. Manufacturers ship the acousticinvestigation measurements included of only the one transfer size and function geometry at for selected furthernumerical somounted simulations called on “invisible usingany glass COMSOL audio” or wooden [2-4]. FEM, Manufacturers surface as well such as for as ship windows, thevibrating transducer only about a size of a beer can that can be frequencies.numerical Examination simulations usingof different COMSOL wall-fixing FEM, asand well mounting as foracoustic vibratingdoors, measurements tables transducer etc. of In the only this transfer aboutway the a functionsize vibrating of a atbeer surface selected can that becomes can bemounted the on any glass or wooden surface such as windows, methodsacoustic were measurements also included. of Concluding the transfer results function show at that selected thefrequencies. mountedmembrane, Examination on radiating any of glass different almost or wooden wall-fixing plane surface waves. and mounting such According as windows, todoors, the tables etc. In this way the vibrating surface becomes the overallfrequencies. sound Examination quality is of inferior different to wall-fixing regular loudspeakers,and mountingmethods doors,weremanufacturers also tables included. etc. the In soundthisConcluding way quality the resultsvibrating is “good”, show surface that but becomesthe brochures themembrane, and radiating almost plane waves. According to the however,methods using were a alsosupplementary included. Concluding subwoofer resultsresults show in enjoyable that theoverall soundmembrane,commercial quality radiatingmaterials is inferior almostdo not to planecontain regular waves. reliable loudspeakers, According measurement to themanufacturers data. the sound quality is “good”, but brochures and musicoverall transmission sound qualityfor a short is inferiordistance. to Furthermore, regular loudspeakers, placementhowever, manufacturersBecauseusing a supplementary these the systems sound subwoofer could quality be is anresults “good”, alternative in enjoyable but brochuresalso for auditory andcommercial materials do not contain reliable measurement data. of thehowever, transducer using a in supplementary the middle of subwoofer the membrane results in and enjoyable havingmusic transmissioncommercialdisplays, for materials anarrative short distance.do applications not contain Furthermore, reliable(installations, placement measurement museums), data.Because for these systems could be an alternative also for auditory Because these systems could be an alternative also for auditorydisplays, for narrative applications (installations, museums), for mountingmusic transmission points at the for cornersa short distance. are recommended Furthermore, in placement practicalof the transducerpersonal inuse the etc., middle we analyzed of the membranethe possibilities and having of one of them. displays, for narrative applications (installations, museums), forpersonal use etc., we analyzed the possibilities of one of them. applications.of the transducer in the middle of the membrane and havingmounting Our points investigation at the corners included are recommended numerical simulations in practical using Finite- Our investigation included numerical simulations using Finite- mounting points at the corners are recommended in practicalapplications. personalElement-Methods use etc., we (FEM) analyzed with the the possibilities COMSOL of software one of them. package, Our investigation included numerical simulations using Finite-Element-Methods (FEM) with the COMSOL software package, applications. as well as acoustic and vibration measurements for comparison Element-Methods (FEM) with the COMSOL software package,as well as acoustic and vibration measurements for comparison [5-8]. Our goal was to determine the technical parameters, 1. INTRODUCTION as well as acoustic1. INTRODUCTION and vibration measurements for comparison[5-8]. Our goal was to determine the technical parameters, [5-8].overall Our sound goal quality was to and determine application the areastechnical depending parameters, onoverall the sound quality and application areas depending on the 1. INTRODUCTION material of the vibrating surface, size and geometry, placement In auditory display design we usually incorporate withIn auditoryoverall display sound design quality weand applicationusually incorporate areas depending with on thematerial of the vibrating surface, size and geometry, placement of the transducers and mounting methods [9]. Figure 1 andof the 2 transducers and mounting methods [9]. Figure 1 and 2 headphonesIn auditory and/or display loudspeakers. design we Both usually methods incorporate have their withheadphones material and/or of the loudspeakers. vibrating surface, Both methodssize and geometry, have their placement show pictures of the transducers. Because they cannotshow be pictures of the transducers. Because they cannot be advantagesheadphones and and/ordisadvantages. loudspeakers. In case Both of a methodsloudspeaker have setup, theiradvantages of and the transducersdisadvantages. and In mounting case of a methods [9]. Figuresetup, 1 and 2 disassembled and the inside construction is classified, wedisassembled also and the inside construction is classified, we also oneadvantages of the main and disadvantages disadvantages. is Into casehave of quite a loudspeaker large boxes setup, andone of theshow main picturesdisadvantages of the is transducers.to have quite Becauselarge boxes they and cannot be X-rayed the SolidDrive for an inside look. X-rayed the SolidDrive for an inside look. usuallyone ofthey the are main fixed disadvantages or hard to transport.is to have quite large boxes andusually theydisassembled are fixed or and hard the to insidetransport. construction is classified, we also Besidesusually the they classical are fixed electromagneticor hard to transport. dynamic loudspeakersBesides theX-ray classicaled the SolidDrive electromagnetic for an inside dynamic look. loudspeakers thereBesides exist the different classical types electromagnetic of alternative dynamic loudspeakers. loudspeakers Theythere exist different types of alternative loudspeakers. They havethere generally exist different reduc ed types size of, different alternative shape loudspeakers. and layout, Theyhave generally reduced size, different shape and layout, however,have generallyusually also reduc a decreaseded size, differentbandwidth, shape sensitivity and layout,andhowever, a usually also a decreased bandwidth, sensitivity and a higherhowever, price. usuallyNevertheless, also a decreased some special bandwidth, applications sensitivity may focusandhigher a price. Nevertheless, some special applications may focus on higherthis technologyprice. Nevertheless, to replace some classical special applications loudspeaker may setups, focuson this technology to replace classical loudspeaker setups, includingon this auditory technology displays. to replace classical loudspeaker setups,including auditory displays. As including an example, auditory a Distributed displays. Mode Loudspeaker (DML) isAs a an example, a Distributed Mode Loudspeaker (DML) is a flatAs panel an loudspeaker example, a Distributed technology, Mode developed Loudspeaker by NXT, (DML) in which isflat a panel loudspeaker technology, developed by NXT, in which soundflat panel is loudspeaker produced bytechnology, inducing developed uniformly by NXT, distributed in whichsound is produced by inducing uniformly distributed vibration modes in the panel through a special electro-acoustic vibrationsound modes is produced in the panel by through inducing a special uniformly electro-acoustic distributed vibration modes in the panel through a special electro-acousticexciter. Transducers for distributed mode loudspeakers include exciter. Transducers for distributed mode loudspeakers include exciter. Transducers for distributed mode loudspeakers includemoving coil and piezoelectric devices, and they are placed to moving coil and piezoelectric devices, and they are placed to moving coil and piezoelectric devices, and they are placed correspond to to the natural resonant model of the panel. correspond to the natural resonant model of the panel. Figure 1: Left the SolidDrive, right the Feonic Transducer correspond to the natural resonant model of the panel.The “SurfaceSoundFigure 1: ”Left is a thetraditional SolidDrive, flat-panel right application the Feonic with Transducer TheThe “SurfaceSound “SurfaceSound” is” isa traditionala traditional flat-panel flat-panel application application withwith Figure 1: Left the SolidDrive, right the Feonic Transducer [2, 4]. [2,[2, 4].4].

153 ICAD 2013 PRaCTICaL RECOMMENDaTIONS FOR USING SOUND TRaNSDUCERS WITH GLaSS MEMBERaNE aS aUDITORY DISPLaY The 19th International Conference on Auditory Display (ICAD-2013) July 6-10, 2013, Lodz, Poland

At the first five setups both measurement and simulation were carried out, at the last two, only simulation results exist.

3. RESULTS

Figure 3 and 4 show simulated and measured data of the frequency response. The simulation was in good correlation with measurement data showing a frequency range up to only 10 kHz. The goal has been also to test the simulation method, whether it is capable of replacing acoustic and vibroacoustic Figure 2: Revealing some secrets: X-Ray images from the measurements. SolidDrive. They function based on the electromagnetic principle.

2. MEASUREMENT AND SIMULATION

Based on the operation manual of the SolidDrive transducer, acoustic parameters are listed as follow: - broadband, 70 Hz – 15000 Hz (depending on the vibrating surface), - impedance 8 Ohm, - mass 0,5 kg, - recommended power 10-100 W, - sensitivity: N.A., - vibrating membrane: glass or wood, - exciter: high-power neodymium magnet, two symmetrical motors, - achieved STI (Speech Transmission Index) is “excellent”: 0,75 points. For the measurements we applied both vibration measurements () and acoustic installations (). For Figure 3: Simulated transfer function of the 50x50x0,6 cm numerical simulations COMSOL Multiphysics was used. We glass membrane. Using different sizes and geometries, focused on the following parameters: sensitivity, frequency simulated transfer functions appeared to be very similar. range and directional characteristics. In case of the membrane, we used only glass surfaces of different geometries (size, thickness and shape), different placement of the transducer and different mounting methods (screws or frame). Some of the results are based on real measurements, some only based on simulation and some using both methods. Simulations and measurements of the 50x50x0,6 cm glass plate were conducted to determine the most appropriate fixing and mounting methods, both for the transducer on the plate as well as the for the plate on the wall. These included: - transducer glued in the middle of the plate and no wall fixing, - transducer glued randomly on the plate (avoiding any Figure 4: Measured transfer function of the 50x50x0,6 cm glass symmetry-axis or resonant nodes) and no wall fixing, membrane. - transducer glued almost in the corner of the plate and no wall fixing, Figures 5 and 6 show color plots from the simulation software. - transducer glued in the middle of the plate and plate Values of simulated acceleration are according to the color bar fixed on the four corners, on the right. The small black circle represents the transducer - transducer glued randomly on the plate and plate glued on to the plate. fixed on the four corners, Because numerical simulations are based on ideal models, - transducer glued in the middle of the plate and plate calculated results show high symmetries and mathematical fixed in a frame, approximations (vibrating modes). However, conducting a - transducer glued randomly on the plate and plate multichannel vibration measurement showed that these fixed in a frame. approximations are in good correlation with measured data [9].

154 ICAD 2013 Tuesday, july 9 • SESSION 5: auditory Display Technologies – Part II The 19th International Conference on Auditory Display (ICAD-2013) July 6-10, 2013, Lodz, Poland

obtained with point-source propagation. Similarly to the DML system, stereophonic sound image and directional information of sound sources are insufficient. - The use of a supplementary subwoofer system is recommended in case of musical reproduction even if one-channel reproduction is used. After selecting the most user friendly and appropriate size in our analysis, further investigations were made with the 50x50x0,6 rectangle glass membrane. Using this, the possible placement of the transducer on the plate as well as the wall- fixing methods were simulated and measured. Based on these, we concluded that: - A fixed (wall-mounted) plate does not differ significantly from a “free”, dismounted plate. The fixing method using the four corners with screws is recommended in contrast to fixing the glass in a frame, however, this version is also acceptable. - Placing the transducer on the plate is not a critical issue, neither frequency response nor directivity are influenced significantly. A symmetrical placement (e.g. in the center of the plate) is recommended.

Figure 5: Numerical simulation of the glass plate at 1000 Hz, without fixings, and having the transducer in the center (top) and in the corner (bottom).

4. DISCUSSION

Because measurements using different vibrating surfaces can be difficult, time and cost expensive, we decided to rely also on numerical simulations. These kinds of simulations have enormous computational load, but if results are in good correlation with measurement data, predictions can be made based on the numerical methods. Based on all of our results, the following recommendations could be a good summary, guideline for auditory display solutions: - Transmission between 200 Hz and 10 kHz can be maintained almost independently of the material of the vibrating surface (glass or wood). However, frequency response is far from being linear. - The geometry of the same size (rectangle or circular), and thickness of the vibrating surface is not significantly relevant. - Sensitivity and reproduced SPL is relatively low, Figure 6: Numerical simulation of the glass plate at 1000 Hz however, directional characteristics show almost having the transducer in the center and with screw fixings at the plane wave propagation. corners (top) and using a frame (bottom). Small circles in the - Due to plane wave propagation, localization of top image show simulated wall-fixing points where reproduced sound sources may differ from results displacement of the plate is zero.

155 The 19th International Conference on Auditory Display (ICAD-2013) July 6-10, 2013, Lodz, Poland

5. SUMMARY

The SolidDrive SD1g resonator with vibrating plates of different size, geometry and material were measured and analyzed based on FEM models and acoustic measurement. The simulation focused mainly on glass membranes, but both acoustical and vibration measurements supported the conclusions. The goal was to determine the possibility of applications in auditory display techniques as well as giving recommendations for fixing and mounting methods. A frequency response from 200 Hz – 10 kHz was measured with almost plane wave propagation. Due to the relatively low SPL (sensitivity), applications using vibrating plates near the listener are recommended (windows, tables etc.). These systems are not able to replace conventional loudspeakers if high audio quality is needed. On the other hand, “invisible audio” solutions, designer applications with acceptable quality of musical and speech transmission can benefit from this technology. Virtual audio displays can also realized if superior audio quality and proper directional information are not required, and loudspeaker installations ICAD 2013 should be replaced by other techniques (mobility issues). PRaCTICaL RECOMMENDaTIONS FOR USING SOUND TRaNSDUCERS WITH GLaSSFuture MEMBERaNE works include aS listening aUDITORY tests DISPLaY to verify the STI and The 19th International Conference on Auditory Display (ICAD-2013) subjective evaluation of sound quality.Ju ly 6-10, 2013, Lodz, Poland

5. SUMMARY 6. REFERENCES

The SolidDrive SD1g resonator with vibrating plates of [1] M. M. Boone, W. P. J. de Bruijn, “On the Applicability of different size, geometry and material were measured and Distributed Mode Loudspeaker Panels for Wave Field analyzed based on FEM models and acoustic measurement. The Synthesis-Based Sound Reproduction,” AES Convention simulation focused mainly on glass membranes, but both Paper 5162, AES 108th Convention, Paris, France, 2000. acoustical and vibration measurements supported the [2] http://www.feonic.com/ conclusions. The goal was to determine the possibility of [3] http://www.powerview.com/GlassResonator.html applications in auditory display techniques as well as giving [4] http://www.soliddrive.com/ recommendations for fixing and mounting methods. A [5] http://www.comsol.com/ frequency response from 200 Hz – 10 kHz was measured with [6] A. A. Piacsek, and R. T. Muehleisen, “Using COMSOL almost plane wave propagation. Due to the relatively low SPL multiphysics software to investigate advanced acoustic (sensitivity), applications using vibrating plates near the listener problems,” J. Acoust. Soc. Am., vol. 130, no. 4, pp. 2363- are recommended (windows, tables etc.). 2363, 2011. These systems are not able to replace conventional [7] C.-F. Liu, and Y.-T. Lee, “Finite Element Analysis of loudspeakers if high audio quality is needed. On the other hand, Three-Dimensional Vibrations of thick circular and annular “invisible audio” solutions, designer applications with Plates,” Journal of Sound and Vibration, vol. 233, no. 1, acceptable quality of musical and speech transmission can pp. 63-80, May 2000. benefit from this technology. Virtual audio displays can also [8] A-M. Bruneau, “Amplitude and Phase Measurements of realized if superior audio quality and proper directional Vibrations of Radiating Surfaces in Order to Determine the information are not required, and loudspeaker installations Emitted Sound Field,” J.Audio Eng. Soc., vol. 31, no. 12, should be replaced by other techniques (mobility issues). pp. 907-913, 1983. Future works include listening tests to verify the STI and [9] Gy. Wersényi, „Evaluation of Vibrating Sound Transducers subjective evaluation of sound quality. with Glass Membrane Based on Measurements and Numerical Simulations,” AES Convention Paper 8675, AES 132nd Convention, Budapest, Hungary, 2012. 6. REFERENCES

[1] M. M. Boone, W. P. J. de Bruijn, “On the Applicability of Distributed Mode Loudspeaker Panels for Wave Field Synthesis-Based Sound Reproduction,” AES Convention Paper 5162, AES 108th Convention, Paris, France, 2000. [2] http://www.feonic.com/ [3] http://www.powerview.com/GlassResonator.html [4] http://www.soliddrive.com/ [5] http://www.comsol.com/ [6] A. A. Piacsek, and R. T. Muehleisen, “Using COMSOL multiphysics software to investigate advanced acoustic problems,” J. Acoust. Soc. Am., vol. 130, no. 4, pp. 2363- 2363, 2011. [7] C.-F. Liu, and Y.-T. Lee, “Finite Element Analysis of Three-Dimensional Vibrations of thick circular and annular Plates,” Journal of Sound and Vibration, vol. 233, no. 1, pp. 63-80, May 2000. [8] A-M. Bruneau, “Amplitude and Phase Measurements of Vibrations of Radiating Surfaces in Order to Determine the Emitted Sound Field,” J.Audio Eng. Soc., vol. 31, no. 12, pp. 907-913, 1983. [9] Gy. Wersényi, „Evaluation of Vibrating Sound Transducers with Glass Membrane Based on Measurements and Numerical Simulations,” AES Convention Paper 8675, AES 132nd Convention, Budapest, Hungary, 2012.