LIMP - ARTA
Contents
1. Low cut aff Sampling rate 48000 ad Mute switch off transients v Figure 4 14 Measurement setup The dialog Measurement setup has following controls In section Measurement config Reference channel sets the reference channel U to Left or Right Reference resistor enters the value for the reference resistor In section Frequency range High cut off enters measurement upper frequency margin Low cut off enters measurement lower frequency margin Sampling rate Hz chooses the sampling rate from 8000 to 96000 7 In section Stepped sine mode Frequency increment sets to 1 24 or 1 48 octave Min integration time ms enters minimum integration time higher values give higher noise reduction Transient time ms enters transient time to allow the system to get to the steady state before starting the integration Intra burst pause ms enters time needed for system to release the energy from reactive components 20 B A Arn l am m M m mex zm In D lear Mania LUG P2 E TI e l 1 po w tel S Ger Sl QA Mute switch off transients check box to remove annoying sound due to sine burst abrupt switch off In section FFT mode pink noise excitation FFT size chooses the length of the FFT block 32768 or 65536 Type chooses None Linear or Exponential averaging Max Averages enters the maximum number of averaging for the Linear mode Asynchronou2. Changes graph lowest freguency margin Figure 4 4 Top and right dialog bars Images of graphs and windows can be copied to Windows clipboard or saved to the file in a three image formats png bmp and jpg It is recommended to use png format Obtaining copy of the full window picture is simple User needs to simultaneously press keys Ctrl P After that command the window picture will be saved in the System Clipboard from were the user can paste it in other opened Windows applications MS Word MS Paint Keys Ctrl Alt P activate command to save that image in the file To copy or save the graph picture that is shown inside the window user needs to simultaneously press keys Ctrl C or activate the menu command Edit gt Copy or press appropriate Copy button In the main window toolbar the Copy button is shown as toolbar icon The Copy command opens the dialog box Copy Save Image with Extended Information shown in Figure 4 5 Here user has to setup following options 10 1 2 3 4 5 In AT V panja MI HDU JE 7i gf Era sE LIMF User Manuali By using the combo box above OK button user chooses one of three modes of saving the image Copy to Clipboard Save to File and Save to File Copy to Clipboard In the Edit box user optionally enters the text that will be appended at the bottom of the graph Check box Add filename and date enables adding text to the graph that shows file na
3. Magnitude ahms Impedance Phase soo ETT eno TT Cursor 28 02 Hz 35 08 Ohm 1 5 deg Frequency Hz Figure 5 5 Impedance curves the one with lower resonance frequency is obtained by adding mass to the membrane Then we activate the menu Analyze gt Loudspeaker parameters Added mass method to get the Loudspeaker Parameters dialog box shown in Fig 5 6 Loudspeaker parameters User Input Fs 45 27Hz Voice coil resistance Re ohms Re 7 20 ohms dc Membrane diameter cm 519 29 uH 12 70 ohms ee at 0 32 Added a 20 Qes 0 37 Oms 2 08 Ss Mms 10 83 grams Nonlinear LSE Optimization a Estimate TSP by LSE minimization Cms 0 001182 m N Vas 12 45 liters Estimate voice coil resistance Re Sd 86 59 cm 2 Bl 7 754399 Tm Estimate lossy inductor model 0 29 9 m Added Mass Method Added mass 20 00 grams Diameter 10 50 cm Figure 5 6 Dialog box for the estimation of loudspeaker parameters 34 Finally we enter values for Voice coil resistance Membrane diameter and Added mass in appropriate edit boxes Press on the button Calculate gets the report shown in the left edit box This report can be pasted to the clipboard by pressing the button Copy The click on button Export saves data in file using the Excel csv format In the section Nonlinear LSE Optimization user sets three check boxes to allow more accurate
4. The check box Automatically subtract cable impedance from measured impedance must be checked if user wants that cable compensation be applied during the measurements 4 8 File Manipulations Impedance data can be saved in LIMP binary format LIM files and in ASCII format TXT or ZMA files Beside impedance data LIM files can contain user defined text of arbitrary length The user can enter any text in edit box of the File Info dialog box see Fig 4 23 This dialog box can be opened by clicking menu command File gt Info File Info X e Untitled umPoints 480 rom 30 0Hz to 20000 0Hz User supplied additional informations Impedance of woofer WX100 Measured with stepped sine Date 12 11 2005 Figure 4 23 Dialog for file information Textual files have extension txt or zma They contain lines of text with three numeric literals frequency in Hz magnitude in ohms and phase in degrees The line ends with new line character The only difference between txt and zma files is that txt files can contain comment lines Comment lines start after arbitrary number of space or tab characters with nonnumeric characters while data lines start with digit or dot character The file can be loaded as regular impedance data or as data for the overlay plot Only one overlay is allowed Binary file LIM format is as follows char 1941 tour Characters d JI L TIT TOT Ja unsigned version ver
5. Mor B S Garbow and K E Hillstrom User Guide for MINPACK 1 Argonne National Laboratory Report ANL 80 74 Argonne Ill 1980 39
6. parameters in their loudspeaker data sheets An old industry standard assumed that voice coil electrical impedance contains resistive Rg and pure inductive components Voice coil inductance was usually specified as inductive component of driver impedance at 1 kHz In modern instrumentation that model is abandoned and voice coil 15 treated as lossy inductor whose impedance Z z depends on frequency Physically Zrz represents the input impedance of the transformer whose secondary winding is the pole piece Eddy currents in the pole piece give rise to primary circuit resistance The simplest model 8 for a primary input impedance is K 1 j 2 where K is constant It is expressed in unit called semiHenry sH The impedance of such semi inductance increases with rather than This model is not practical as engineers in many numerical simulations use some form of an equivalent electrical circuit that closely matches measurement data The most commonly used equivalent circuit for the electrical voice coil impedance in modern instrumentation 10 11 is serial connection of resistor inductor and parallel connection of resistor R and inductor It is denoted in Fig 5 1 as L2R model For many years it has been proven as useful model in many simulations 28 LIMP also enables estimation of two additional and more accurate equivalent circuits for lossy inductor L3R and L2RK models They are also
7. Audio Eng Soc vol 37 June 1989 4 Bendat J S and Piersol A G Engineering applications of Correlation and Spectral Analysis Wiley New York 1980 5 L L Beranek Acoustics 1986 Edition Published for the Acoustical Society of America by the American Institute of Physics 6 R H Small Direct Radiator Loudspeaker System Analysis JAES Vol 20 No 5 pp 383 395 1972 June 7 A N Thiele The Thiele Small Parameters for Measuring Specifying and Designing Loudspeakers PALA International Conference Singapore 2004 8 J Vanderkooy A Model of Loudspeaker Driver Impedance Incorporating Eddy Currents in the Pole Structure JAES Vol 37 No 3 pp 119 128 1989 March 9 W M Leach Loudspeakers Voice Coil Inductance Losses Circuit Models Parameter Estimation and Effect on Frequency Response Journal of the Audio Engineering Society JAES vol 50 June 2002 10 MLSSA SPO Speaker Parameters Option Reference Manual ver 4WI DRA Laboratories Sarasota USA 2001 11 Klippel Analyzer System Linear Parameters Measurement Klippel Gmbh Dresden Germany 2003 12 K Thorborg C Futtrup Electrodinamic transducer Model Incorporating Semi Inductance and Means for Shorting AC Magnetization Journal of the Audio Engineering Society JAES vol 59 September 2010 13 Mateljan I Sikora M Estimation of Loudspeaker Driver Parameters Proc AAA 2012 Zadar Croatia 2012 14 J J
8. Low enters the lowest frequency shown in Hz 22 LIMP User Manual View All enables the view of all DFTspectrum components that are used in impedance estimation View Phase enables a phase plot Update updates the graph with a new setup Color Setup X Plot pen color 1 Plot pen color 2 Overlay calor Target color Marker color HUE T 1 a Figure 4 18 Dialog boxes for a graph colors setup Color Setup X Figure 4 19 Standard Windows dialog for color setup 23 LIMP User Manual Graph colors can be changed in two ways The first one 1s to change the background color from Black to White by clicking the menu command View gt B W color or by clicking the toolbar icon rF The second way to change graph colors is a user mode User sets an arbitrary color for every graph element using the Color Setup dialog box shown in Fig 4 18 This dialog can be activated by clicking the menu Edit gt Colors Clicking the left mouse button on colored rectangle opens the standard Windows dialog box Color Fig 4 19 Button Default restores default colors A check box Use dotted graph grid enables drawing of grid with dotted line style We can browse the graph by moving the cursor At the bottom of the graph the label Cursor denotes values of the magnitude and the phase at the cursor position 4 9 Calibrated Measurements In previously described measurements we have assumed that both sound
9. The LIMP generates the Pink PN as a discrete periodic sequence with a period equal to N We assume that this sequence drives the generator shown in Fig 2 1 2 After one preaveraging cycle which is necessary to reach the steady state voltages at both ends of the reference resistor are measured as discrete time series and of length N 3 The DFT 15 applied to time series and to get spectral components U f and U2 f They are used in the equation 1 to calculate the impedance Z f Important note The signal generation in the stepped sine mode gives sinusoidal components with at least 30dB higher level than it is possible in FFT mode That is why in FFT mode the measurement results can be greatly affected by the noise that can be generated by the measured loudspeaker 2 4 Measurement in a Noisy Environment The main source of the measurement noise is a loudspeaker that acts as a microphone for the environmental noise and vibrations Fig 2 2 shows modified circuit for the loudspeaker impedance measurement with the noise generator included Rg Generator a eee ee Coie D ee NS ee Figure 2 2 A circuit for the loudspeaker impedance measurement with the noise generator En If we apply equations for impedance measurement 1 to this circuit we get the estimated impedance value U R Z R orn qm U 1 E E 3 What this equation shows is that estimated impedance differs from th
10. WDM Audio Driver Setup for Windows Vista 7 8 aaa aaa 16 2D ASO E 18 Ae SUGENERATOR SETUP o P S AE S S S 19 AA MEASUREMENT SETUP so icit ZSE S S E di AR a eters GBE 20 ZO MEASUREMENT PROEEDURES 25 S i E E AE a 21 GRAPE SETUPANDBROWSING tate S E bd dd o LS 22 ZSOKALIBRATED MEASUREMENT S ci vene eso A E i tutu MEDI E M UM LU a 24 Zo PEEEGNTANSIPDPA TION E SE E TE MM ATEM aT E ETE I SSA TT 26 S LOUDSPEAKER PARAMETERS ciciedeccci vecdeccsicecccecrecedensietedeueseccdcseiessuceaveccdacauecsvevsvescecsbieucudseveccvossiaucdeseeccdes 27 5 1 DEFINITION OF PHYSICAL AND DYNAMICAL LOUDSPEAKER PARAMETERS csccscesceccecceccscescescecescesceseess 27 5 2 THEORY FOR THE ESTIMATION OF LOUDSPEAKER PARAMETERS cceccecescescecceccscescecceccecescesceseecescesceseuss 29 5 2 1 Estimation of Lossy Inductor Equivalent Circuit Elements sees eene nnns 20 5 2 2 Thiele Small Method for the Estimation Of eene 29 5 2 3 Nonlinear LSE Minimization Method for the Estimation of 31 5 3 ESTIMATION OF PHYSICAL LOUDSPEAKER PARAMETERS sccscescescecceccecescesceccecescescescesescescescesessescesceseucs 31 5 4 AUTOMATIC ESTIMATION OF PHYSICAL AND DYNAMICAL LOUDSPEAKER PARAMETERS 32 EREC MEASUREMENT iso O ss A o ce eU reca osta 37 6 L IMPORTANCE OF CALIBRATION edo APEIRI
11. block FFT black EE Acquired signals Figure 2 4 Signal generation and acquisition during the asynchronous frequency domain averaging 3 Hardware Setup The simplest measurement configuration is shown in Fig 3 1 The soundcard phone out headphone output is used as a signal generator output The soundcard left line input is used for recording the voltage U and the soundcard right line input is used for recording the voltage U If the soundcard has no headphone output then we have to connect external power amplifier to the soundcard line out output as shown in Fig 3 2 Loudspeaker Figure 3 1 Measurement setup for loudspeaker impedance measurements using the headphone output soundcard left out Power amplifier Figure 3 2 General Loudspeaker measurement setup for loudspeaker impedance measurements soundcard To protect the soundcard input from large voltage that is generated at a power amplifier output 1t 1s recommended to use the voltage probe circuit with Zener diodes as shown on Fig 1 3 Values of resistors and R2 have to be chosen for arbitrary attenuation 1 e R128200 and R2 910 ohms gives probe with 20 7dB 0 0923 attenuation if the soundcard has usual input impedance 10kQ e H f T M R1 Power Sound Figure 3 3 Voltage probe with Amplifier Card the soundcard input channel Output Input overload protection LIMP User Manual 4 Working with
12. denotes parallel connection To apply NLSE method impedance measurement have to be done in full frequency range 20kHz or at least to frequency that is hundred times larger than loudspeaker resonance frequency 32 Loudspeaker Parameters Added Mass Method Loudspeaker parameters E Fs 45 27 Hz Voice coil resistance Re ohms Re 7 20 ohms dc Le 293 10 uH Membrane diameter cm L2 519 29 uH R2 12 70 ohms A Qt 20 32 Added mass Qes 0 37 Nonlinear LSE Optimization Load overlay data Estimate TSP by LSE minimization to calculate all parameters Estimate voice coil resistance Re Estimate lossy inductor model 4 Cw Le 12182 Calculate e Figure 5 4 Dialog box for estimation of loudspeaker Q factors 5 4 1 Added Mass Method To estimate all physical and dynamical loudspeaker parameters we must make two impedance measurements of the loudspeaker impedance in a free air In one of the two measurements the membrane must be loaded with an additional mass This is what we need 1 measured impedance data impedance data measured with an additional mass set on the membrane as in Fig 5 5 one of the curves 1 or 2 must be set as an overlay graph measured additional mass in grams measured voice coil dc resistance in ohms diameter of the membrane in cm cone diameter that includes 1 3 of the surround NO O W 33 LIMP User Manual
13. shown in Fig 5 1 The L3R model extends L2R model with more parallel circuit L5ll amp 5 while in L2RK model as defined by Thorborg 12 a semi inductance is added parallel to circuit 5 2 Theory for the Estimation of Loudspeaker Parameters For the estimation of Thiele Small parameters TSP LIMP offers two methods Thiele Small method and Nonlinear Least Square Error LSE minimization method LIMP also uses LSE minimization for estimation of lossy inductor equivalent circuit elements 5 2 1 Estimation of Lossy Inductor Equivalent Circuit Elements LIMP estimate values of lossy inductor equivalent circuit elements as values that give the least sum of squared differences between lossy inductor impedance Z z f and a measured input impedance Zy f over all frequencies that are above the frequency of minimum of impedance LSE error function is defined as E gt F Zi f where Zrr f is a low frequency loudspeaker impedance estimated by Thiele Small method which is described in the next Section By default LIMP estimates elements of L2R model by stable linearized LSE error minimization method sometimes also called a linear regression method In addition user can choose more accurate nonlinear LSE minimization methods for L2R L3R and L2RK model circuit elements For full discussion of these and TSP estimation methods it is recommended to read the paper 13 5 2 2 Thiele Small Method for the Estimati
14. will be set more precisely Mixer device Restek HD Audio output Adjust volume for Playback Recording C ther Show the following volume controls Master Volume Wave SW Synth CD Player Mic Volume PC Beep Figure 4 7 Dialog for choosing soundcard and input output channels 15 13 Master Volume Options Help Master Volume Wave CD Audio Line In Microphone Balance Balance Balance Balance Balance Volume Volume Volume Volume Volume Ne ST que Mute all Mute Mute V Mute Iw Mute Advanced Advanced Intel r Integrated Audio Figure 4 8 Typical setup of a soundcard output mixer in Windows XP Note Most professional audio soundcards have their own program for adjustment of input and output channel or have hardware control of input monitoring and input and output volume controls 4 2 2 WDM Audio Driver Setup for Windows Vista 7 8 Microsoft has changed their approach in control of sound devices in Vista Win7 Now operating system also sometimes in conjunction with control programs of professional soundcards is responsible for setting soundcard native sampling rate and bit resolution Operating system changes native resolution to floating point format for high quality mixing and eventually for the sample rate conversion For LIMP this means that it is strongly recommended to use Float resolution and sets the sampling rate to the nati
15. A file exports textual file with rows containing values of frequency impedance magnitude and phase CSV Excel file exports CSV file containing frequency impedance magnitude and phase Recent File opens a recently opened file Exit exits the program Overlay Set as overlay sets the current impedance curve as an overlay Delete deletes overlay Load loads an overlay from an impedance file Set as target curve sets current curve as target curve Load target curve loads an target curve from an impedance lim or zma ofile Delete target curves deletes all target curves Edit Copy copies the graph bitmap and user defined text to the clipboard or saves that image to the file Setup colors and grid style sets graph colors and grid style B W Color changes the background color to black or white Use thick pen uses thick pen for plotting curves Subtract overlay subtracts overlay impedance from current impedance Add overlay add overlay impedance to current impedance View Toolbar shows or hides the Toolbar Status Bar shows or hides the Status bar Fit graph range changes graph top margin to show full impedance curve Magnitude shows only impedance magnitude curve Magnitude phase shows impedance magnitude and phase curves Record 12 Start starts recording measurement Stop stops recording measurement Calibrate opens the dialog box for calibration of line input channels Setup Audio devi
16. AN SE S 38 LEERATURE 2200 i e o s 5 2450805021000 e e A S 39 1 What is LIMP The LIMP is a program for the measurement of the loudspeaker impedance and estimation of loudspeaker physical and dynamical parameters also called Thiele Small parameters It is also a general purpose program for measuring impedance in the range from to 200 ohms Requirements to use the L MP are Operating systems Windows XP Vista 7 8 o Processor class Pentium clock frequency 600 MHz or higher memory 256M for Windows 2000 XP or 2MB for Vista Windows 7 o Full duplex soundcard with synchronous clock for AD and DA converters o WDM or ASIO soundcard driver ASIO is trademark and software of Steinberg Media Technologies GmbH The installation of program is through common setup program for the ARTA Software All Windows registry data for LIMP will be automatically saved at first program execution and files with extension LIM will be registered to be opened with a program LIMP Results of measurement can also be saved as ASCII formatted files in ZMA format The LIMP does not dump graphs to the printer instead of this all graphs can be copied to the Windows Clipboard and pasted to other Windows applications 2 Impedance Measurement Theory 2 1 Basic Circuit for Impedance Measurement The measurement of the loudspeaker impedance is based on the system shown in Fig 2 1 The reference resistor R is connected between the signal generator and a loud
17. LIMP Program for Loudspeaker Impedance Measurement User Manual Version 1 8 5 Ivo Mateljan Artalabs J Rodina 4 21215 Ka tel Luk i Croatia May 2015 Copyright Ivo Mateljan 2005 2015 All rights reserved Content IS EDMEPY iiti teste nce seco rs eese eel esa el sen ese S et ee ee oco coss decr A eee eee 3 2 IMPEDANCE MEASUREMENT THEORY 25 n egeo o aus eve eue Duel pagus ever era gue iu Cove e eua eu Coe oe cu e eee oe eo ex oe gus coe res 4 2 1 BASIC CIRCUIT FOR IMPEDANCE MEASUREMENT sccsceccsceccececscececsceccscucescesescecscscsesctsescesesceseeceseseeess 4 2 2 STEPPED SINE AND PERIODIC PINK NOISE GENERATOR cccsceccecescsceccscccsceccececescecescecccscesescesescusescesescncess 4 2 3 SIMPLE NIEASUREMENT PROGEDURE aa disa onda a up Pe 5 24 MEASUREMENTINA NGISYENVIRONMENT te estet ina dada a 6 2 4 1 Lowering Measurement Noise in Stepped Sine Mode 7 2 4 2 Lowering Measurement Noise in FFT Mode with Periodic Noise Excitation eese 7 3 HARDWARE SETUP s cee a a e A od ae es 8 4 WORKING WITH LIMP iona ed e oso wae aud pes te vea dee ca poe s EUR 9 a o E INI E D IM DM ede Se D E D UA cdo be dn qu 12 d 2SOUNDCARD SETUPA S S ee ree a E MD AE a 14 4 2 1 WDM Audio Driver Setup for Windows 2000 14 4 2 2
18. LIMP When you start the L MP you get the program window shown in Fig 4 1 There are menu bar toolbar and a dialog bar at the top of the window and a status bar on the bottom of the window The central part of the window will show the magnitude and the phase plot Untitled Limp inl xj Overlay Edit View Record Setup Analyze Help a CAL NS Maa Gen Fink FN Fstart Hz 40 FstopiHz 20000 4 Avg Linear Reset Magnitudefohms Impedance Phase 50 0 90 0 Cursor 5 0 Hz 0 00 Ohm 0 0 deg Freguency Hz L 0dB R 0dB Impedance Measurement 7 Figure 4 1 Main program window Open Copy to Thick Stop Measurement file clipboard lines recording setup magnitude i E i ST ED T I 1 Save Background Start Calibrate Generator View file color recording inputs setup magn phase Figure 4 2 Toolbar icons Ready L dB 8 098 Impedance Measurement Figure 4 3 Status bar shows the peak level ref full scale of left and right line inputs Generator Sampling Size of Averaging Reset type Frequency Hz FFT block type averaging Y Y Gen Pink FM Fs Hz 44100 FFT Size 32768 Avg None Changes graph maximum magnitude margin Fit magnitude graph margins Changes graph minimum magnitude margin Opens dialog for setup of graph margins Eg g 0 Leg Changes graph high frequency margin X
19. card input channels have the same sensitivity but usually it is not true If the difference in sensitivity of the input channels is larger than 0 2 dB we have to make a calibration 4 9 1 Calibration of Input Channels The LIMP has a built in calibration procedure It has to be done for a particular generator sequence length and a sampling rate In the calibration procedure both input channels have to be connected to the generator output By clicking the menu Record gt Calibrate or by clicking the toolbar icon CAL we get the Calibrate Input Channels dialog box shown in Fig 4 20 Calibrate Input Channels Calibrate zr Connect left and right input Seq length 32768 channel to signal generator Sampling rate 48000 nami Mumber of averages Output volume dB ada gt m Channel diff 0 15dB Figure 4 20 Dialog for calibration of input channel sensitivity In section Generate we set the output volume for Pink PN signal of known sampling rate and sequence length Pressing the button Generate activates the signal generation and monitoring of 24 sma m Wi row ae TI 4 les A 115 wi VECAN uu uu Ly ALSE en eA input levels on the Input Level Meter If necessary we can adjust the output volume by using the combo box Output volume Finally in section Calibrate we enter the Number of averages recommended value is 1 as we measure high level signals and press the butto
20. ces sets current input and output devices Generator sets generator parameters Measurement sets measurement parameters Cable compensation sets resistance and inductance for cable impedance compensation Graph sets graph margins CSV format opens dialog box for setup of decimal separator character in CSV files Analyze Loudspeaker parameters Added mass method shows the dialog box for the estimation of loudspeaker parameters using Added mass method Loudspeaker parameters Closed box method shows the dialog box for the estimation of loudspeaker parameters using Closed box method RLC impedance values at cursor position estimate values of impedance serial RLC elements Help About gets information about the LIMP Registration shows the user license registration User Manual shows the help file Useful shorcut keys are Up and Down keys change the top graph margin Left and Right keys move the cursor left and right Ctrl S key saves the file Ctrl N key makes a new file Ctrl O key opens the file Ctrl C key copies the graph bitmap and user defined text to the clipboard or saves that image to the file Ctrl P key copies a whole window bitmap to the clipboard Ctrl Alt P key saves a whole window bitmap to the file Ctrl B key changes background color F3 key make target curve by calculating loudspeaker impedance using current TSP parameters 13 4 2 Soundcard Setup Activate the menu Setup gt A
21. e low frequency cut off frequency can be changed in the Signal Generator Setup dialog box The pink noise is usually used with a cut off frequency set close to the frequency where loudspeaker has an impedance maximum 20 100Hz The pink periodic noise has the statistical distribution close to the normal distribution and in LIMP it is generated with a crest factor lower than 12 dB 2 3 Simple Measurement Procedure In Stepped sine mode a simple measurement procedure is as follows 1 The LIMP generates burst of sine signal with frequency f We assume that this signal drives the generator shown in Fig 2 1 2 After an arbitrary transient time that is necessary to reach the steady state voltages at both ends of the reference resistor are measured as discrete time series u and u of length N The magnitude and phase of signal u and at frequency f are estimated by finding fundamental sinusoidal components U and U at generator frequency f It is done by directly solving Fourier integral in integration time T These fundamental harmonics are used in the equation 1 to calculate the impedance Z 4 After some arbitrary time we call it intra burst pause that is necessary for measured system to release reactive energy a frequency is incremented for 1 24 octave or 1 48 octave and the process is being repeated from step 1 until the predefined stop frequency is reached In FFT mode a simple measurement procedure is as follows 1
22. e true impedance Z by the term that is dependant on the S N ratio E E and values of resistors R R and the impedance Z We can conclude 1 The signal generator must supply a high voltage to assure high S N In practice we need a generator with at least 1V of peak output voltage This can easily be achieved with stepped sine excitation 2 When we use FFT method the measurement results are highly affected with noise The loudspeaker acts as a microphone with a highest sensitivity in the region of the membrane resonance It means the highest level of the noise is at low frequencies so we must generate the signal with highest level at low frequencies 1 e the pink noise 3 Values of resistors R and must be small an optimum being a value close to the magnitude of the measured impedance Practically we can use R 2 10 27 ohm to get a very good impedance estimation but then we need a power amplifier to supply large current If we use the soundcard headphone output as a signal generator then we can use R 47 100 ohms If we use the soundcard line output as a signal generator due to the limited current capability we must use R gt 600 ohms In that case we can t get a good estimation with FFT method but we still can with stepped sine method 2 4 1 Lowering Measurement Noise in Stepped Sine Mode In stepped sine mode L MP uses heterodyned principle to filter all spectral components that are out of the passband which is centered at the m
23. easured frequency The bandwidth of the filter 1s equal to 1 T where T is integration time of the Fourier integral For example if we use integration time 200ms then the width of the passband of the heterodyne filter is 5Hz 2 4 2 Lowering Measurement Noise in FFT Mode with Periodic Noise Excitation The noise can be partly lowered by using the averaging technique in the estimation of U and U2 The LIMP averages the auto spectrum of U1 and the cross spectrum of U and giving the following estimated impedance mE 4 esitimated UU 40201 Note brackets lt gt denotes averaged values and star denotes the conjugate complex value Two types of averaging can be applied in the LIMP In a time domain synchronous averaging the LIMP generates multiple periods of one noise sequence Fig 2 3 In a frequency domain asynchronous averaging the L MP generates a different noise sequence for every acquired FFT block Fig 2 4 The Frequency Domain Asynchronous Averaging can give slightly better results than the synchronous averaging in systems with nonlinear distortion but it needs longer time for measurements Pra averaging l1 T T T J Sms PN noise FFT block FFT block FFT block FFT block Acquired L T T smena Measurement Figure 2 3 Signal generation and acquisition during the synchronous time domain averaging process Pra Pre averaging Pause averaging Generated signals PN noise FFT
24. ect the sample rate and bit depth to be used when running in shared mode 16 bit 48000 Hz DVD Quality be Test Exclusive Mode v Allow applications to take exclusive control of this device Give exclusive mode applications priority Restore Defaults Figure 4 11 Setting the native bit resolution and sampling rate in Vista Note There are a lot of drivers that do not work stable under Windows 7 In that case please use ASIO driver if it is available for your soundcard 4 2 3 ASIO driver setup ASIO drivers are decoupled from the operating system control They have their own control panel to adjust native resolution and memory buffer size The buffer is used for transfering sampled data from the driver to the user program User opens the ASIO control panel by clicking button Control Panel in the Audio Device Setup dialog Fig 4 12 shows an example of ASIO control panel Preferences Buffer Size 20 ms m Bit Depth 32 bit m Cancel Per Application Preferences Figure 4 12 E MU Tracker Pre ASIO Control panel for setting bit resolution and buffer size In music applications user usually sets buffer size as small as possible with stable operation That gives the lowest input output latency system introduced delay 18 TIRNA l ww s Fa gt n n mne 1 ser Manual In LIMP the latency is not problem as it is encou
25. is section 36 5 4 3 Monitoring the Quality of Loudspeaker Parameter Estimation LIMP doesn t show any single number indicator of TSP estimation quality but user can visually check the quality of estimation by pressing F3 key in measurement window It will generate impedance curve from currently calculated loudspeaker parameters and show it as target curve 6 RLC Measurement The LIMP can be used to measure value of resistors capacitors and inductors simply by calculating resistive inductive or capacitive parts of the measured impedance For example Fig 6 1 shows impedance curves of an inductor with nominal value of 110uH Magnitude ohms Impedance Phase 7 50 0 14 5 45 0 12 0 0 0 10 5 45 0 9 0 90 0 p Awvg U 6 0 L 45 3 0 M 15 P 0 0 100 200 500 1k 10k 20k Cursor 5076 60 Hz 3 50 Ohm 87 6 deg Frequency Hz Figure 6 1 The impedance graph of a 110uH inductor By clicking menu command Analysis gt RLC Impedance value at cursor position we get the dialog box with report as shown on Figure 6 2 LIMP reports that measured impedance has resistive part of 0 15 ohms and imaginary part is inductive with value of 112uH Impedance at cursor Inductive impedance at frequency 5076 60Hz R 150 761 mohm L 112 768 uH Figure 6 2 Impedance of an inductor The LIMP measures capacitance in the same way 37 6 1 Importance of Calibration When measuring impedance and capacitance it is very importa
26. mated impedance of plastic capacitor 4 7uF 250V measured after the calibration 38 Not all LIMP users will have this problem As explained before the problem exists when probe for impedance voltage V2 has higher sensitivity than the sensitivity of probe for generator voltage V1 To circumvent this condition we can change probes sensitivity or we can simply exchange input channels and also change the reference channel in the LIMP measurement setup Note To get good estimation of capacitance or inductance it is recommended to put cursor on frequency where impedance magnitude is lower than 100 ohms It assures measurement of impedance with 1 tolerance Why The answer lies in fact that measured impedance is bypassed with probe or soundcard input impedance that usually has value of 10k ohms A lot of professional audio sound systems like RME Fireface EMU 0404USB Yamaha G046 have unbalanced instrumentation inputs with input impedance in the range 470 1000kQ Using these systems a much better accuracy is possible Literature 1 Mateljan L Signal Selection for the Room Acoustics Measurement Proc 1999 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics New Paltz New York 1999 2 Mateljan I Ugrinovic The Comparison of Room Impulse Response Measuring Systems Proc AAA 2003 Portoroz Slovenia 2003 3 Rife D D Vanderkooy J Transfer Function Measurement with Maximum Length Sequences J
27. me date and time Check box Save text enables saving entered text for the next copy operation Bitmap size is chosen by selecting one of following combo box items Current screen size variable width and height option Smallest 400 pts fixed graph width 400 points Small 512 pts fixed graph width 512 points Medium 600 pts fixed graph width 600 points Large 800 pts fixed graph width 800 points Largest 1024 pts fixed graph width 1024 points The options with fixed width give graphs with the aspect ratio 3 2 The button OK copies the graph to the system clipboard or opens dialog to enter name of file in which picture will be saved The button Cancel cancels the copy operation Enter text that will be drawn on the bottom of the graph copy Bitmap size Current screen size Copy to Clipboard Add filename and date Add text Cancel Figure 4 5 Dialog box Copy Save with Extended Information 11 4 1 LIMP Menus Here is a brief explanation of LIMP menus File New initializes a new file content Open opens an existing impedance file LIM Save saves the file with a current name Save As saves the file under a new name Info shows information about current file Export ASCII exports the file content in a textual ASCII file Commented TXT file exports textual file with comment and rows containing frequency impedance magnitude and phase Plain ZM
28. n Calibrate After a second we have the calibrated system Attention If we change the sequence length or a sampling rate we have to repeat the calibration procedure The last section shows a report of the calibration procedure The most important is information is Channel difference in dB If the Channel difference is larger than 2 dB LIMP gives a warning as in Figure 4 21 and calibration is rejected Something is wrong channel difference larger than 2dB Check whether left and right input channels are connected on generator output Check whether input level controls are at same position Check whether input probes have same gain Check whether cables and connectors are OK Figure 4 21 Report when channel difference is larger than 2dB 4 9 2 Cable Compensation Sometimes we have to use long cables to connect the loudspeaker to the reference resistance If we know the cable resistance and inductance then we can enter them in LIMP and substract from measured impedance That procedure called cable compensation can be set by menu command Setup gt Cable Compensation It opens the dialog box shown in Fig 4 22 Cable Impedance Compensation X Automatically substract cable impedance from measured impedance Cable resistance ohm 10 Cable inductance 100 Figure 4 22 Dialog for cable impedance compensation setup 25 Two edit boxes are used for entering cable resistance 1n ohms and inductance in nH
29. nonlinear LSE minimization Estimate TSP by LSE minimization Estimate voice coil resistance if voice coil resistance is unavailable Estimate lossy inductor model Three lossy inductor circuits Le L2 IR2 Le L2IIR2 L3IIR2 1 2 are selectable by using list box at the bottom of this section 5 4 2 Closed Box Method To estimate all loudspeaker parameters we must have two impedance measurements In one of measurements the loudspeaker must be mounted in a closed box of known volume That is what we need measured impedance data impedance data measured with loudspeaker mounted in a closed box one of the curves 1 or 2 must be set as an overlay graph as in Fig 5 7 measured value of the box volume in liters measured voice coil dc resistance 1n ohms diameter of the membrane in cm cone diameter that includes 1 3 of the surround D LE E dE E an Magnitude ahms Impedance Phase 7 m 45 0 50 45 0 40 0 0 0 35 0 45 0 30 0 90 0 23 0 Avg 20 0 15 0 10 0 L 50 100 200 500 1k 2k 5k 10k Cursor 36 45 Hz 13 28 Ohm 6 7 deg Frequency Hz Figure 5 7 Impedance curves the one with higher resonance frequency is obtained by mounting the loudspeaker in a closed box 35 Then we activate the menu Analyze gt Loudspeaker parameters Closed box method to get the Loudspeaker parameters Closed Box Method dialog box shown in Fig 5 8 Loudspeaker Parameters Added Mass Method Loud
30. ns that are defined in Table 5 1 we get V 1 M M us 3o gt sus E Ryg m S C 5 Ons Qus 5 4 Automatic Estimation of Physical and Dynamical Loudspeaker Parameters LIMP procedures for the estimation of basic loudspeaker parameters are as follows To estimate Q factors of a loudspeaker we need 1 measured impedance data measured voice coil dc resistance in ohms 3 estimated membrane diameter in cm cone diameter measurement that includes 1 3 of the surround By clicking the menu Analyze gt Loudspeaker parameters Added mass method we get the Loudspeaker Parameters Added Mass Method dialog box shown in Fig 5 4 In this dialog box we enter values for Voice coil resistance and Membrane diameter in appropriate edit boxes Press on button Calculate gets the report shown in the left edit box This report can be pasted to the clipboard by pressing the button Copy The click on button Export saves data in file using the Excel csv format In the section Nonlinear LSE Optimization user sets three check boxes to allow more accurate nonlinear LSE minimization Estimate TSP by LSE minimization Estimate voice coil resistance if voice coil resistance is unavailable Estimate lossy inductor model Three lossy inductor circuits Le L2 IR2 Le L2IIR2 L3IIR2 Le L2IIR2IIK are selectable by using the list box at the bottom of this section Note denotes serial connection I
31. nt to calibrate the system before the measurement and it is best to make the calibration with the impedance connected DUT Why Even if there is a very small difference between channel sensitivities 1 e 0 1dB the LIMP can give very erroneous result because inductor impedance has phase close to 90 degree and capacitor impedance has phase close to minus 90 degree In that case if there is a difference in sensitivity of measured generator voltage V1 and impedance voltage V2 if sensitivity of probe V2 is larger than sensitivity of probe V1 estimated impedance gives phase values that are larger than 90 degree and graph shows warped jump in the phase for 180 degree Figure 6 3 shows the case of measuring a capacitor without the calibration In half the range the phase 1s close to 90 degree It is very erroneous results as it suggest that we deal with an inductance Figure 6 4 shows capacitor impedance after the calibration We see correct values for phase in the whole frequency range em e ahms Impedance Phase nans ne i g mi per 248 0 oo I LILI 100 1000 10000 Cursor 1009 3 Hz 32 82 Ohm 89 7 deg Frequency Hzj Figure 6 3 Wrongly estimated impedance of plastic capacitor 4 7uF 250V measured without the calibration Magnitude ahms Impedance Phase 7 245 0 90 0 Cursor 242 7 Hz 132 99 Ohm 88 4 deg Frequency Hzj Figure 6 4 Correctly esti
32. ntered in software but it is not recommended to use buffer with size larger than 2048 samples or smaller than 256 samples Some ASIO control panels express the buffer size in samples while other express the buffer size in time ms In that case we can calculate the size in samples using the following expression buffer size samples buffer size ms samplerate kHz number of channels Some ASIO drivers allow setup of buffer size in samples that is a power of number 2 256 512 1024 In that case Limp adjusts buffer size automatically LIMP always works with two input channels and two output channels treating them as a stereo left and right channels As ASIO support multichannel devices user has to choose in a dialog box Soundcard Setup which pair of channels will be used 1 2 3 4 4 3 Generator Setup Two types of excitation signals are possible in the LIMP e Sine e Pink periodic noise Pink PN Choose the signal type in the top dialog bar or in the Generator Setup dialog box shown in Fig 4 13 You get it by clicking the menu Setup gt Generator or by clicking the toolbar icon Generator Setup Sine freq Hz 1000 Pink cut aff Hz m Figure 4 13 Signal generator setup The dialog Generator Setup has following controls Type chooses the excitation signal Sine or Pink PN Sine freq Hz enter test frequency of the sine generator Pink cut off Hz enters the low frequency c
33. on of TSP It is easy to estimate Thiele Small parameters if we have measured data for the loudspeaker impedance The voice coil resistance Rr should be measured with a DC ohmmeter At low frequencies the influence of a voice coil inductance and eddy currents is small and an expression for the loudspeaker input impedance has the following form a f fg if MfsQr Z f EZ p i 4 jf G sQus The impedance has maximum value at the resonance frequency cus Z f f R 0 10 Rg Res Because lt gt 29 SL SELLE ES Zia s min Re oi dress ss pA R nime fi fa dh amin Figure 5 3 Typical impedance curve of a loudspeaker that is mounted in free air At frequencies fi and f2 where lt lt ff 5 impedance values are of equal magnitude 2 6 d fif If we substitute this expression in expression for input impedance we get n Ve Qus i f fs From this equation we get the mechanical Q factor Now we can define a step by step procedure for the measurement of Q factors 1 Measure a voice coil resistance RE with a dc ohm meter 2 From impedance curve find f and 2 Define r 2Z Rr 3 Choose some impedance magnitude Rr lt lZil lt Z and find both frequencies and fa where Z Zi Then define ZZVRy 4 Calculate from the above equation Calculate Qr using the e
34. or Windows Vista Windows 7 it is recommended to choose resolution type Float This control has no effect in the ASIO mode where a bit resolution has to be setup in the ASIO control panel Important notice Please mute the line and microphone channels at the output mixer of the soundcard otherwise you might have positive feedback during measurements If you use a professional audio soundcard switch off the direct or zero latency monitoring of the line inputs 4 2 1 WDM Audio Driver Setup for Windows 2000 XP After selection of the soundcard user has to disable mute line in and microphone inputs in output mixer Also user has to select which input will be used for recording Line In or Microphone Mic For a standard PC soundcards the procedure 15 as follows 14 oa zA LIMP User Manual In Audio device setup dialog click the button Control panel to open the Windows Master Volume dialog box which is shown on Fig 4 8 Click on menu Options gt Property and select soundcard channel that will be used for output playback as shown in Fig 4 7 Mute Line In and Mic channels in dialog Master Volume Fig 4 8 Set Master Volume and Wave Out volume to maximum Click on menu Option gt Property and select soundcard channel that will be used for input and enable Line In and Mic channels in recording mixer Choose Line In Input Set volume control of Line In to some lower position Later it
35. quation lt lt OQ r 1 6 Calculate using the equation OrcQys OpsrOys UA This procedure gives good results under two conditions 1 if we have low noise level in measurement of impedance and if we first subtract magnitude of lossy inductor impedance 7 from the magnitude curve In first iteration IZ zl is unknown In that case TSP estimation procedure uses values of Z and fi from measured magnitude curve that are below the resonance frequency fs and sets f f f If we have noise in measurements we can reduce the estimation variance by repeating Thiele Small procedure for different frequencies and average value of Qys Good choices are frequencies where magnitude is 20 lower than maximum magnitude and 20 larger than minimum magnitude 30 These two simple modifications of standard Thiele Small procedure give accurate and reliable estimation of TSP 5 2 3 Nonlinear LSE Minimization Method for the Estimation of TSP Thiele Small procedure is realizable only if the value of Rz is known but sometimes that value is not known In that case we can use the nonlinear LSE minimization procedure where we minimize squared difference between measured impedance Zm and model impedance Zrr i e we define LSE function as c Gl Zu COIT f where optimization variables Rz fs Qus Ziz f 1s impedance of lossy inductor that is also estimated by LSE minimization If the value of Rg is kno
36. s averaging check box to use the asynchronous averaging 4 5 Measurement Procedures After you have done the audio device setup the generator setup and the measurement setup you are ready for measurements a Procedure in FFT mode Connect loudspeaker in test fixture Fig 3 1 or 3 2 and click the menu Record gt Start or click the toolbar icon Measurements will be periodically repeated and results shown as an impedance plot You will get the graph like one shown in Fig 4 15 You can stop the measurements by clicking the menu Record gt Stop or by clicking the toolbar icon e You can copy the graph bitmap by clicking the menu Edit gt Copy or by clicking the toolbar icon Magnitudefohms Impedance Phase deg 30 0 90 0 rin p TI n so W o MISERERI BL ALLE 1 DITHDE PV ee 1000 Cursor 985 5 Hz x Bi Ohm 20 9 deg FrequencyHz Figure 4 15 Impedance measurement without averaging a noisy measurement If you set averaging to Linear measurements will be repeated and averaged until the number of averaging reach the predefined value for Max averages in the Measurement setup dialog box You can stop the averaging at any time by clicking the menu Record gt Stop or by clicking the toolbar icon 9 You will get the graph like one shown in Fig 4 16 You can also choose the exponential averaging It differs from linear averaging in a way that it gives more weight to results from last five meas
37. sion number started from 0x0101 unsigned reserved 0 int numdata number of data points Int Gutsortpos last position of cursor int frftlen 4 Length of FFT in FET mode float s sampling frequency float data 3 numdata contains frequency magnitude and phase int infolength info string length char string infolength info string data 26 5 Loudspeaker Parameters This chapter gives some definitions and measurement procedures for the estimation of loudspeaker parameters 5 1 Definition of Physical and Dynamical Loudspeaker Parameters An electrodynamic loudspeaker that is mounted in an infinite baffle is characterized by the following physical parameters Electromagnetic parameters RE voice coil DC resistance Q ZLE impedance of voice coil inductance and coupling to the pole piece Q equivalent circuits used to characterize this impedance are shown in Fig 5 1c and denoted as L2R 10 11 L3R 7 and L2RK 12 13 Bl force factor Tm Mechanical parameters S effective area of membrane CMS membrane mechanical compliance m N Mms mechanical mass of membrane plus mass of air load on membrane RMS mechanical resistance plus membrane radiation resistance kg s Note The piston area S 15 normally obtained from a cone diameter measurement that includes 1 3 of the surround ONE ON L L Electrical circuit Mechanical circuit m Wideband analogo
38. speaker impedance Z HE eee Come Figure 2 1 A circuit for loudspeaker impedance measurement Impedance is defined in the frequency domain Z f If we measure voltages U f and U2 f at both ends of the reference resistor we estimate the loudspeaker impedance as UT pg 1 U J U U Z f 2 2 Stepped Sine and Periodic Pink Noise Generator The LIMP has two modes of impedance measurement 1 Stepped sine mode 2 FFT mode with pink periodic noise excitation Pink PN In the stepped sine mode L MP generates bursts of pure sinusoidal signal frequency by frequency with 1 6 1 12 1 24 or 1 48 octave increment and measures response to sinusoidal signal by filtering out noise and distortion components in sinusoidal response FFT mode is faster method for impedance measurement but with much lower measurement S N ratio than stepped sine mode In this mode the L MP simultaneously measures values of the impedance in the whole audio range of frequencies by using the signal generator with a wideband periodic pink noise excitation pink PN The wideband pink PN excitation 1s realized as periodic random phase multisine signals It is a zero dc periodic signal that contains M sine components each with a random phase M g t A cos 2akft Q p random e 0 27 2 k l This pink multisine has lt 2 and its spectral magnitudes roll off 3dB oct after specified cut off frequency In the LIMP a variabl
39. speaker parameters ica ae Fs 45 27 Hz Voice coil resistance Re ohms 7 2 Re 7 20 ohms dc Le 293 10 uH Membrane diameter cm 10 5 L2 519 29 uH R2 12 70 ohms Aum Qt 0 32 Added mass 20 Qes 0 37 Qms 2 08 Mms 10 83 grams Rms 1 504561 kg s Estimate TSP by LSE minimization V Cms 0 001182 m N Vas 12 45 liters Estimate voice coil resistance Re Sd 86 59 cm 2 Bl 7 754399 Tm Estimate lossy inductor model 0 29 Lp 2 83V 1m 87 20 dB Nonlinear LSE Optimization Added Mass Method Added mass 20 00 grams Diameter 10 50 cm Calculate parameters Figure 5 8 Dialog for the estimation of loudspeaker parameters using Closed Box Method Finally we enter values for Voice coil resistance Membrane diameter and Closed box volume in appropriate edit boxes Press on the button Calculate gets the report shown in the left edit box This report can be pasted to the clipboard by pressing the button Copy The click on button Export saves data in file using the Excel csv format In the section Nonlinear LSE Optimization user sets three check boxes to allow more accurate nonlinear LSE minimization Estimate TSP by LSE minimization Estimate voice coil resistance if voice coil resistance is unavailable Estimate lossy inductor model Three lossy inductor circuits Le L2 IR2 1 21162 L3IIR2 12 are selectable by using list box at the bottom of th
40. udioDevices You will get the Soundcard Setup dialog box shown in Fig 4 6 In this dialog box you choose which soundcard will be used as an input or output device Generally choose the same card as an input and output device x Control Panel Wave Format Float Soundcard driver WDM Windows multimedia driver Input channels Line In SoundMAX Integrated Di Output channels Speakers SoundMAX Integrated D Figure 4 6 Soundcard setup The Audio Device Setup dialog box has following controls Soundcard driver chooses type of soundcard driver WDM windows multimedia driver or one of installed ASIO drivers Input channels chooses the soundcard input stereo channels ASIO driver can have large number of channels Output Device chooses the soundcard output stereo channels Generally user chooses input and output channels of the same soundcard mandatory in ASIO driver mode Control panel button if WDM driver is chosen it opens sound mixer on Windows 2000 XP or Sound control panel in Vista Win7 If ASIO driver is chosen it opens ASIO control panel Wave format on Windows 2000 XP chooses Windows wave format 16 bit 24 bit 32 bit or Float Float means IEEE floating point single precision 32 bit format It is recommended to use 24 bit or 32 bit modes when using a high quality soundcard many soundcards are declared as 24 bit but their real bit resolution is less than 16 bits F
41. urements 21 LIMP User Manual Magnitude ohms Impedance Phase deg 90 0 _ 9 0 eo IJA LPE LET ee al op LLL S LETT 100 1000 10000 l Cursor 965 5 Hz 4 82 Ohm 21 3 deg Frequency Hz Figure 4 16 Impedance measurements with averaging a Procedure in Stepped sine mode Measurement procedures for stepped sine mode are almost the same as in FFT mode The only difference is that in FFT mode user will see the impedance plot for full measured frequency range almost instantly while in stepped sine mode procedure will be repeated for many frequencies Cursor will show current progress in measurements and that process will be very slow 4 6 Graph Setup and Browsing The menu command Setup gt Graph Setup or by right clicking mouse in the plot area opens the Graph Setup dialog box shown in Fig 4 17 Use this dialog box to adjust the impedance magnitude range shown and the frequency range shown Graph 5etup X Freq range Hz High 20000 Low 20 Imedance range ohm Graph range 50 Graph bottom 0 Update Cancel SEE v View Phase View all LIK Figure 4 17 Graph setup The Graph Setup dialog box has following controls Impedance range ohm section Graph range enters the impedance magnitude range Graph bottom enters the impedance magnitude for graph bottom margin Freq range Hz section High enters the highest frequency shown in Hz
42. us circuit L3R R R L L2RK WA pz b Low frequency analogous circuit c Models for Z Figure 5 1 a Wideband analogous circuit of an electro dynamic loudspeaker that is mounted in an infinite baffle b circuit for the estimation of the low frequency input impedance and c three circuit models for lossy inductor Zze L2R and L2RK model 27 Fig 5 1 shows wideband and low frequency equivalent circuits of an electro dynamic loudspeaker that is mounted in a infinite baffle The circuit for definition of low frequency input impedance uses the following elements Logs y Cus Regs y Rus Cues li Using these analogous circuit elements Thiele and Small 6 7 introduced dynamical loudspeaker parameters They are defined in the Table 5 1 Resonant frequency in free air Hz R R Total Q factor GC QusQes R Res Qus 2 Op Power available efficiency 90 Sensitivity 1W Im m Pot _ P AM L IW 1m m 20log p 112 1 1010g 14 Equivalent acoustical volume m Table 5 1 Thiele Small dynamical loudspeaker parameters po 1 18 c 345m s prer 20uPa Thiele and Small have shown that by using these parameters it is easy to express the low frequency response of closed loudspeaker box as 2 order high pass filter and response of bass reflex box as 4 order high pass filter Today almost every loudspeaker manufacturer gives physical and Thiele Small
43. ut off of the pink noise generator Output level dB chooses the output level 0 15dB Test starts stops generator with current settings Input level monitor the input volume peak meter Meter bars are shown in following colors green for levels below 3dB yellow for levels between 3dB and OdB and red for input overloaded 19 Recommendation e For most reliable results use sine generator but don t push loudspeaker into large displacement the largest displacement is at frequencies below the loudspeaker resonance frequency For measurements of bass or mid bass loudspeakers set the Pink cut off frequency close to the loudspeaker resonance frequency 20 100 Hz e Press the button Test to monitor input output levels If peak meter bars are in red color input channels are overloaded then lower the output volume until bars go to yellow or green color 4 4 Measurement Setup For setup of measurement parameters use the Measurement setup dialog box shown in Fig 4 14 You get it by clicking the menu Setup gt Measurement or by clicking the toolbar icon E Measurement Setup X Measurement config Stepped sine mode FFT mode pink noise excitation Reference channel Left m Frequency increment FFT size 5 536 Min integration time ms 200 Averaging None Frequency range Hz Transient time ms 100 Max averages 100 High cut off Intra burst pause ms 100 Asynchronous averaging
44. ve format Access to these values is in Windows sound control panel which user gets by clicking on the button Control Panel in Audio Device Setup dialog Fig 4 9 shows Vista 7 control panel that has four property pages As first step user has to adjust Playback page and later repeat the same procedure for Recording page Adjustment steps 1 Click on channel info to choose a playback channel It is not recommended to use the measurement channel as a default audio channel 2 Click on button Properties to opens channel Sound properties dialog 3 Click on the tab Levels to open the output mixer as in Fig 4 10 Then mute Line In and Mic channels if exist 4 Click on the tab Advanced to set the channel resolution and a sample rate as in Fig 4 11 5 Repeat previous procedure 1 to 4 for recording channel and choose the same sampling rate as in the playback channel 16 LIMP User Manual Sound Speakers GO46 Audio Device Ready Digital Output GO46 Audio Device Ready SPDIF Interface SoundMAX Integrated Digital HD Audio Ready SEL DerTauit r Figure 4 9 Vista Sound Control panel Speakers Properties Figure 4 10 Playback channel properties Output levels 17 InAF nav lle i i BONE JE i gr IE A T9 i LIMF User Manual E Speakers Properties xj General Custom Levels System Effects Advanced Default Format Sel
45. wn optimization variables are fs Qus and Qr In some rare cases a convergent LSE minimization cannot be realized In that case the modified standard Thiele Small procedure would be used 5 3 Estimation of Physical Loudspeaker Parameters Two methods are used 7 for the estimation of physical loudspeaker parameters M ys Cys and Rys 1 Added mass method 2 Closed box method Both methods are implemented in the LIMP 5 3 1 Added Mass Method In this method we first measure the impedance curve and estimate Thiele Small parameters fs and Orc for the loudspeaker mounted in free air Then we put an additional mass Madded on the membrane measure impedance curve and estimate the shifted resonance frequency fy and electrical Q factor QEM From equations for and Os we get _ M aea us f S _ 1 f M Ors M When we know M and fg it is easy to get the mechanical compliance Cys resistance Rus and force factor Bl By using equations that are defined in Table 5 1 we get Vos C OM ys OR OsM us M yss Os Qus 31 5 3 2 Closed Box Method In this method we first measure the impedance curve and estimate Thiele Small parameters fs Orc for the loudspeaker mounted in free air Then we mount the loudspeaker in a closed box of known volume VB measure impedance curve and estimate Thiele Small parameters fc Quc From these we find ae V 1 S ES Then by using equatio
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