揚(yáng)聲器等效模型

1、揚(yáng)聲器等效模型 You can simulate the behaviour of a speaker and its crossover by professional speaker design software. In case you do not have access to these software, an alternative would be to use the SPICE simulation software to do the speaker simulation. Here I will demonstrate how to do this using OrC

2、ad. There is a demo version of OrCad release 10 which you can download from Orcads web site to try. Thiele-small eqivalent circuitBefore you can simulate your driver in Orcad, you need to calculate the eqivalent circuit for your driver unit. This circuit can be derived from the Thiele-small paramete

3、rs. For example, if a driver has the following Thiele-Small Parameters : Thiele-SmallParametersRevc 5.8 ohms DC resistance of voice coilLevc 0.55 mHvoice coil inductanceBl6.5 T.mforce factorQts0.35total QQes0.45electrical QQms1.55mechanical QFs37 Hzresonant frequencyMmd0.014 kgmass of cone + voice c

4、oil + etcRms2.08resistance of suspensionCms1.34 mm/Ncompliance of suspensionSd0.0136 sq.meffective cone areaVas0.0347 cu.mequivalent acoustic volumeXmax0.004 mlinear travel of voice coilFR37 - 5000kHzfrequency responseVd0.0005 cu.mdriver unit volume displacementThen this driver can be modelled with

5、the following circuit :Some of the circuit values above are already obvious. Veg represents the amplifier and is assumed to have no output resistance. The remaining values were calculated from, Cmes = Mmd/(Bl*Bl) = electrical analog of driver mechanical cone mass Lces = Cms*Bl*Bl = electrical analog

6、 of driver mechanical suspension compliance Res = Bl*Bl/Rms = electrical analog of driver mechanical suspension resistance Cmef = 8*po*Ad*Ad*Ad/(3*Bl*Bl) = electrical analog of air load on the driver units cone where: po = air density = 1.18 kg/cu.m Ad = effective radius of the driver units cone = S

7、quare Root of (Sd/3.14) Some of these parameters can be look up from the drivers specification. This missing one could be calculated using the Unibox excel file. Unibox is a free tool that can help you to design speaker enclosure.Speaker Driver Unit SimulationAfter you created your driver models, yo

8、u could start by testing if your driver models impedance response is similar to your drivers actual impedance response. Now you need to familiar yourself with OrCad if you have not used it before. Here is a great Orcad tutorial that I suggest you to read if you have not used Orcad before.You can sav

9、e some time by downloading my Orcad project file for a single driver unit, just change the RLC values and you can start trying OrCad simulation right away. Lets do the woofer as an example. First, start up Orcad Capture and create a new empty project. Then in the schematic draw the driver model usin

10、g Place-Part. command. The R, L and C are all under the ANALOG library. (You may need to add all libraries first if you have not done it.) Then add the AC voltage source (called VAC under the SOURCE lib.) and also add a ground reference by Place - Ground. - 0/Source. Connect all components by Place-

11、Wire. You should now have a circuit similar to the one below :Lets do some simulation: Add a new simulation profile by select PSpice- New Simulation Profile, type in a name. A simulation settings dialog will pop up. In the Analysis tab, set Analysis type to AC Sweep/Noise. Select Logarithmic, start

12、frequency of 10Hz, End Frequency of 20kHz, Points/Decade to 50. Click OK.Now place a voltage probe and a current probe at input of the of the resistor, by selecting PSpice - Markers - Voltage Level, and then point the probe at the line between the VAC and the resistor. Select PSpice - Markers - Curr

13、ent into Pin, and select the input pin of the resistor.Select PSpice - Run to start simulation. After the simulation is done, the result will pop up in another PSpice A/D window. Now you can see the voltage and current that go into the driver at different frequency. To get a impedance plot, you have

14、 to add a trace, by selecting Trace - Add Trace, then type V(V2:+)/I(R1) in the Trace Expression input line, then OK. Now you should see the driver units impedance vs frequency, like the one below.You can compare the result to the impedance plot from the driver units datasheet, or better yet, compar

15、e it to your measured impedance. If they look similar, then this should be a good model to use, if not, tune your circuits RLC value until they are close enough.Crossover + Drivers Simulation After you have done your woofer and tweeter simulation, you can add your crossover to the schematic. I separ

16、ated the driver units and the crossover into 2 pages, you can do this by using the Place - Off-Page connector to connect the 2 pages. My speaker has 2 woofers connected in parallel, as shown in the schematic below.You can use the db Voltage probe to check the frequency response of each individual dr

17、ive unit. If you want to check total response, you need to sum the 2 outputs of the crossover. In some crossover design, you will have to reverse the polarity of the tweeter. You can simulate this in Orcad by either changing the polarity of the voltage source of the tweeter circuit (Set the phase pr

18、operty of the VAC to 180 degree), or you can add a FTABLE part to change the phase of the signal before it goes into the SUM part. Below is the frequency of the dB voltage response of crossover + tweeter + wooferYou can also check the phase response by putting a phase of voltage probe to the output.

19、Now you have simulated a perfect model of a speaker driver, but real speaker units do not give smooth and flat response. I simulated the peaks, dips and natural roll off of a speaker by using the FTABLE part to add response variation at different frequencies. You could also use FTABLE to adjust the

20、sensitivity of the tweeter/woofer unit by adding/subtracting a few dB across the entire frequency range :After I added the FTABLE to both the tweeter and woofer I ran the simulation again:After I added the FTABLE to both the tweeter and woofer I ran the simulation again:When you compare the simulated result to my measured result in my speaker page, you will find them quite simular.Updated 5th Oct, 2005 - You can