1. ALMA Europe 2009 Paper Presentation:
Crossover Design by
Software
Peter Larsen

2. The Purpose of the Crossover:
Protect midrange and tweeter from LF overload
Obtain smooth transition between drivers
Equalize frequency response
Control off-axis response
Obtain smooth power response
Minimize number of components to reduce costs

3. Ideal 3rd order - 18dB/Oct Crossover Example
Perfect transition between drivers

4. Ideal 2nd order - 12dB/Oct Crossover
Cancellation x-over frequency (2kHz)

5. Ideal 2nd order - 12dB/Oct Crossover
Improved response with Tweeter inverted
Tweeter inv phase

6. Theoretical Solution with Real Drivers
This is the ideal 2nd order -12 dB/Oct crossover again, now using real drivers in phase.
The transition is imperfect and the response is not smooth.

7. 2nd order - 12dB/Oct Crossover optimized
Fitting the component values to the green target AND preventing impedance below minimum (here 3.2 ohms) is an effective solution

8. 3-way Crossover example
2nd order – 12dB/Oct with inverted phase midrange. Both acoustical and electrical phase is well behaved

9. 3-way Crossover example2
2nd order – 12dB/Oct with midrange in phase. The midrange and tweeter position was moved by simulated time delay

10. 2-way crossover optimized with off-axis responses
0__/15__/30__/45__ deg off-axis SPL. The 30deg response was optimized with the sloping green target for controlling the power response

11. RMS Power in circuit
The max RMS Power per IEC weighting may be calculated in all resistive components with the actual x-over. Also the calculated power in each driver is particularly important, because it can be used to simulate the power compression

12. 4th order - 24dB/Oct Crossover example
This woofer section has RC impedance compensation, which can be optimized for linear impedance above Fs. However in this case all 6 components were optimized to the 4th order Butterworth target

13. 4th order - 24dB/Oct Crossover
Total response after individual woofer and tweeter sections were optimized to 4th order Butterworth target. The total result can be further improved with system optimization

14. 4th order - 24dB/Oct Crossover Optimization
Total response after system optimization___. Removing redundant components reduced the components down to a total of 6___, saving 6 components . The difference is less than 0.5dB.

15. Import of responses from FEM simulation
In stead of real drivers, you may import simulated responses from Finite Element software. The total system can then be verified before building prototypes!

16. Requirements for Active Crossovers:
Driver response to be controlled in pass band
Driver phase response important
Well behaved driver off-axis response necessary for achieving good power response
Frequency response and baffle EQ still necessary
Midrange and tweeter must be protected from thermal and excursion overload
Actual power in drivers should be considered to minimize compression and prevent spectral frequency balance problems of system

17. Simulation v Measurement
The crossover simulation accuracy is very high: The difference is often from measurement due to slightly changed microphone position and cable resistance etc.

18. ADVANTAGES with Software Simulation:
SAVE Development time
Shorten Time to Market
Save Component and Costs
Extremely accurate results
Automatic guard against too low impedance
Calculation of POWER for drivers & components
Control of Power Response with off-axis responses

19. Resume
Passive crossovers do not behave as expected from simple filter theory due to the varying driver impedances.
This is well handled in modern software, and the crossover circuit can be optimised to obtain a given acoustic response both on- and off-axis while considering necessary equalisation.
Design examples are given, and the results include power calculations of all components and delay of individual drivers.
Active crossovers do not have problems with driver impedance, but equalisation and power/excursion limitations in drivers still exist, which will be briefly explained.