The Design of a 2 way crossover for 4 Ohm loudspeakers    8 Ohm crossover

For a 2 way system or to separate satellites from a subwoofer a 12 dB / octave filter according to the picture on the left should be used. For 8 Ohm systems the values of the following tables are applicable.

To choose a capacitor is straight forward: select the value from the table below and choose a capacitor according to the desired quality level. Standard means: a MKT in series to the tweeter and an unetched electrolytic capacitor in parallel to the woofer (in high powered PA application possibly a MKT). Please take into account the maximum voltage Vac:

• up to 100 Watt: 25 Volt
• up to 200 Watt: 35 Volt
• up to 400 Watt: 50 Volt
• up to 800 Watt: 70 Volt

Selecting the right coil is a bit more complicated. Important aspects are:

• The saturation, if it's not an air core coil (core coils lose their characteristics when overdriven),
• the maximum power handling (possibly causing overheating!)
• the coil's inner resistance which shouldn't be too high. A coil with a too high value and mounted in parallel to the bass drivers causes the driver's magnet to weaken, resulting in a loose and boomy bass.

Taking these aspects into consideration, we suggest the coils listed in the table below, indicating coil type, order no and DC resistance.

The colour code indicates the coil's material:
- iron, high power handling
- ferrite, low distortion - even at low volume
- ferrite, T-Core with extremely low distortion
- air, type 1 or 2 with lowest distortion
- large air core coil, type 3 or 4, with lowest distortion

For 4 Ohm loudspeakers:         ... 8 Ohm calculation  

Frequency in Hz	60	90	135	200	275	400	625	900	1200	1500
Cap. C in uF	400	330	200	100	82	68	47	33	22	15
e.g. ClarityCap PWA	4x EUR 27,50 excl. VAT: € 23.11 / $ 25.88	4x EUR 23,15 excl. VAT: € 19.45 / $ 21.79	2x EUR 27,50 excl. VAT: € 23.11 / $ 25.88	EUR 27,50 excl. VAT: € 23.11 / $ 25.88	EUR 23,15 excl. VAT: € 19.45 / $ 21.79	EUR 17,39 excl. VAT: € 14.61 / $ 16.37	EUR 12,59 excl. VAT: € 10.58 / $ 11.85	EUR 9,25 excl. VAT: € 7.77 / $ 8.71	EUR 7,16 excl. VAT: € 6.02 / $ 6.74	EUR 4,76 excl. VAT: € 4.00 / $ 4.48
Coil L in mH	15	10	6.8	4.7	3.3	2.2	1.5	1.0	0.82	0.56
Coils up to 12 Watt	H71 15 mH 1,2 Ohm EUR 16,90 excl. VAT: € 14.20 / $ 15.91	H71 10 mH 0,87 Ohm EUR 14,05 excl. VAT: € 11.81 / $ 13.22	H71 6,8 mH 0,70 Ohm EUR 15,00 excl. VAT: € 12.61 / $ 14.12	H71 4,7 mH 0,46 Ohm EUR 13,50 excl. VAT: € 11.34 / $ 12.71	L100 3,3 mH 1,1Ohm EUR 17,25 excl. VAT: € 14.50 / $ 16.24	L100 2,2 mH 0,83 Ohm EUR 14,35 excl. VAT: € 12.06 / $ 13.51	L100 1,5 mH 0,62 Ohm EUR 11,45 excl. VAT: € 9.62 / $ 10.78	L100 1,00 mH 0,49 Ohm EUR 9,70 excl. VAT: € 8.15 / $ 9.13	L100 0,82 mH 0,44 Ohm EUR 9,20 excl. VAT: € 7.73 / $ 8.66	L100 0,56 mH 0,36 Ohm EUR 8,30 excl. VAT: € 6.97 / $ 7.81
Coils up to 25 Watt	H100 15 mH 0,83 Ohm EUR 29,05 excl. VAT: € 24.41 / $ 27.34	H100 10 mH 0,64 Ohm EUR 27,15 excl. VAT: € 22.82 / $ 25.55	H100 6,8 mH 0,46 Ohm EUR 16,20 excl. VAT: € 13.61 / $ 15.25	H71 4,7 mH 0,46 Ohm EUR 13,50 excl. VAT: € 11.34 / $ 12.71	H100 3,3 mH 0,27 Ohm EUR 14,30 excl. VAT: € 12.02 / $ 13.46	L100 2,2 mH 0,83 Ohm EUR 14,35 excl. VAT: € 12.06 / $ 13.51	L100 1,5 mH 0,62 Ohm EUR 11,45 excl. VAT: € 9.62 / $ 10.78	L100 1,00 mH 0,49 Ohm EUR 9,70 excl. VAT: € 8.15 / $ 9.13	L100 0,82 mH 0,44 Ohm EUR 9,20 excl. VAT: € 7.73 / $ 8.66	L100 0,56 mH 0,36 Ohm EUR 8,30 excl. VAT: € 6.97 / $ 7.81
Coils up to 50 Watt	BS125 15 mH 0,59 Ohm EUR 48,35 excl. VAT: € 40.63 / $ 45.51	BS125 10 mH 0,46 Ohm EUR 43,55 excl. VAT: € 36.60 / $ 40.99	BS125 6,8 mH 0,37 Ohm EUR 40,70 excl. VAT: € 34.20 / $ 38.31	BS125 4,7 mH 0,30 Ohm EUR 38,70 excl. VAT: € 32.52 / $ 36.42	H100 3,3 mH 0,27 Ohm EUR 14,30 excl. VAT: € 12.02 / $ 13.46	H100 2,2 mH 0,21 Ohm EUR 14,00 excl. VAT: € 11.76 / $ 13.18	H100 1,5 mH 0,17 Ohm EUR 13,40 excl. VAT: € 11.26 / $ 12.61	L140 1,00 mH 0,30 Ohm EUR 17,30 excl. VAT: € 14.54 / $ 16.28	L140 0,82 mH 0,26 Ohm EUR 15,35 excl. VAT: € 12.90 / $ 14.45	L140 0,56 mH 0,2 Ohm EUR 13,45 excl. VAT: € 11.30 / $ 12.66
Coils up to 90 Watt	PA-Trafo mo-123200 0,12 Ohm EUR 74,44 excl. VAT: € 62.55 / $ 70.06	PA-Trafo mo-125490 0,19 Ohm EUR 26,80 excl. VAT: € 22.52 / $ 25.22	PA-Trafo mo-125470 0,16 Ohm EUR 25,58 excl. VAT: € 21.50 / $ 24.08	H140 4,7 mH 0,26 Ohm EUR 31,05 excl. VAT: € 26.09 / $ 29.22	H140 3,3 mH 0,19 Ohm EUR 29,15 excl. VAT: € 24.50 / $ 27.44	H140 2,2 mH 0,14 Ohm EUR 17,30 excl. VAT: € 14.54 / $ 16.28	H140 1,5 mH 0,11 Ohm EUR 15,30 excl. VAT: € 12.86 / $ 14.40	L140 1,00 mH 0,30 Ohm EUR 17,30 excl. VAT: € 14.54 / $ 16.28	L140 0,82 mH 0,26 Ohm EUR 15,35 excl. VAT: € 12.90 / $ 14.45	L140 0,56 mH 0,2 Ohm EUR 13,45 excl. VAT: € 11.30 / $ 12.66
Coils up to 165 Watt	PA-Trafo mo-123200 0,12Ohm EUR 74,44 excl. VAT: € 62.55 / $ 70.06	PA-Trafo mo-125490 0,19Ohm EUR 26,80 excl. VAT: € 22.52 / $ 25.22	PA-Trafo mo-125470 0,16Ohm EUR 25,58 excl. VAT: € 21.50 / $ 24.08	PA-Trafo mo-125450 0,14Ohm EUR 22,90 excl. VAT: € 19.24 / $ 21.55	BT140 3,3 mH 0,22 Ohm EUR 77,60 excl. VAT: € 65.21 / $ 73.04	BS140 2,2 mH 0,16 Ohm EUR 34,80 excl. VAT: € 29.24 / $ 32.75	BS140 3,3 mH 0,12 Ohm EUR 31,90 excl. VAT: € 26.81 / $ 30.02	H140 1,0 mH 0,08Ohm EUR 14,40 excl. VAT: € 12.10 / $ 13.55	L200 0,82 mH 0,16 Ohm EUR 33,85 excl. VAT: € 28.45 / $ 31.86	L200 0,56 mH 0,11 Ohm EUR 28,05 excl. VAT: € 23.57 / $ 26.40
Coils up to 275 Watt	PA-Trafo mo-123200 0,12Ohm EUR 74,44 excl. VAT: € 62.55 / $ 70.06	T250 10 mH 0,16 Ohm EUR 199,00 excl. VAT: € 167.23 / $ 187.29	T250 6,8 mH 0,12 Ohm EUR 189,00 excl. VAT: € 158.82 / $ 177.88	T250 4,7 mH 0,08 Ohm EUR 175,00 excl. VAT: € 147.06 / $ 164.71	T200 3,3 mH 0,10 Ohm EUR 106,00 excl. VAT: € 89.08 / $ 99.76	BT140 2,2 mH 0,12 Ohm EUR 71,70 excl. VAT: € 60.25 / $ 67.48	BT140 1,5 mH 0,09 Ohm EUR 57,60 excl. VAT: € 48.40 / $ 54.21	L200 1,0 mH 0,18 Ohm EUR 36,75 excl. VAT: € 30.88 / $ 34.59	L200 0,82 mH 0,16 Ohm EUR 33,85 excl. VAT: € 28.45 / $ 31.86	L200 0,56 mH 0,11 Ohm EUR 28,05 excl. VAT: € 23.57 / $ 26.40
Coils up to 500 Watt	T250 15 mH 0,17 Ohm EUR 242,00 excl. VAT: € 203.36 / $ 227.76	T250 10 mH 0,16 Ohm EUR 199,00 excl. VAT: € 167.23 / $ 187.29	T250 6,8 mH 0,12 Ohm EUR 189,00 excl. VAT: € 158.82 / $ 177.88	T250 4,7 mH 0,08 Ohm EUR 175,00 excl. VAT: € 147.06 / $ 164.71	T200 3,3 mH 0,10 Ohm EUR 106,00 excl. VAT: € 89.08 / $ 99.76	T200 2,2 mH 0,09 Ohm EUR 90,90 excl. VAT: € 76.39 / $ 85.55	T200 1,5 mH 0,09 Ohm EUR 77,90 excl. VAT: € 65.46 / $ 73.32	L250 1,0 mH 0,12 Ohm EUR 67,90 excl. VAT: € 57.06 / $ 63.91	L250 0,82 mH 0,10 Ohm EUR 62,90 excl. VAT: € 52.86 / $ 59.20	L250 0,56 mH 0,08 Ohm EUR 53,45 excl. VAT: € 44.92 / $ 50.31

Both, the two coils and the two capacitors, should have the values indicated in the table. A subwoofer filter requires only one capacitor and one coil.

The coil in parallel to the tweeter or satellite needs to handle only half / a quarter of the power, if the crossover frequency is higher than 400/800 Hz.

Hint:

1) 18 and 24 dB / octave crossovers only make sense when the driver's exact characteristics are known!

2) This is certainly not a high-end-crossover. Such a crossover needs to be designed according to the drivers used. A good example is the Cauchy-crossover.
 

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