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How to simulate speaker / crossover using OrCad




Crossover + Drivers Simulation

After you have done your woofer and tweeter simulation, you can add your crossover to the schematic. I separated 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 drive 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 property 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 + woofer

 

You can also check the phase response by putting a phase of voltage probe to the output.

 

 

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 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:

 

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 actually simulate the phase shift due to the mis-alignment of the tweeter and woofer acoustic center. In my case, the tweeter is about 30cm closer to the listening position than the woofer. So the phase shift (tweeter leading) at various frequency can be detemined by the following formula : 

 

v = f * λ

Phase lead = Tweeter Woofer Acoustic center offset / λ * 360

where :

v = speed of sound = 345 M/s

f = frequency

λ = wavelength


In my case, the acoustic center offset = 0.03M

         

Phase lead @ 1000 Hz = 0.03 / (345/1000) * 360 = 31.3 degree

Phase lead @ 2500 Hz = 0.03 / (345/2500) * 360 = 78.3 degree


By entering these phase lead in the tweeter F-table, you can do a more accurate simulation.

 

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