The Design of a 2 way crossover for 8 Ohm loudspeakers    4 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: 35 Volt
• up to 200 Watt: 50 Volt
• up to 400 Watt: 70 Volt
• up to 800 Watt: 100 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 8 Ohm loudspeakers:         ... 4 Ohm calculation  

Frequency in Hz	120	180	270	400	550	800	1250	1800	2300	3100
Cap. C in uF	100	82	47	33	22	15	10	6.8	5.6	4.7
e.g. ClarityCap PX	EUR 64,90 excl. VAT: € 54.54 / $ 59.45	EUR 53,70 excl. VAT: € 45.13 / $ 49.19	EUR 26,60 excl. VAT: € 22.35 / $ 24.36	EUR 29,00 excl. VAT: € 24.37 / $ 26.56	EUR 17,50 excl. VAT: € 14.71 / $ 16.03	EUR 13,80 excl. VAT: € 11.60 / $ 12.64	EUR 7,50 excl. VAT: € 6.30 / $ 6.87	EUR 10,50 excl. VAT: € 8.82 / $ 9.62	EUR 5,00 excl. VAT: € 4.20 / $ 4.58	EUR 11,70 excl. VAT: € 9.83 / $ 10.72
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 25 Watt	H71 15 mH 1,2 Ohm EUR 18,50 excl. VAT: € 15.55 / $ 16.95	H71 10 mH 0,87 Ohm EUR 15,50 excl. VAT: € 13.03 / $ 14.20	H71 6,8 mH 0,70 Ohm EUR 13,60 excl. VAT: € 11.43 / $ 12.46	H71 4,7 mH 0,46 Ohm EUR 12,60 excl. VAT: € 10.59 / $ 11.54	L100 3,3 mH 1,1Ohm EUR 29,30 excl. VAT: € 24.62 / $ 26.84	L100 2,2 mH 0,83 Ohm EUR 23,40 excl. VAT: € 19.66 / $ 21.43	L100 1,5 mH 0,62 Ohm EUR 19,50 excl. VAT: € 16.39 / $ 17.86	L100 1,00 mH 0,49 Ohm EUR 16,10 excl. VAT: € 13.53 / $ 14.75	L100 0,82 mH 0,44 Ohm EUR 14,60 excl. VAT: € 12.27 / $ 13.37	L100 0,56 mH 0,36 Ohm EUR 12,60 excl. VAT: € 10.59 / $ 11.54
Coils up to 50 Watt	H100 15 mH 0,83 Ohm EUR 34,20 excl. VAT: € 28.74 / $ 31.33	H100 10 mH 0,64 Ohm EUR 29,30 excl. VAT: € 24.62 / $ 26.84	H100 6,8 mH 0,46 Ohm EUR 23,40 excl. VAT: € 19.66 / $ 21.43	H71 4,7 mH 0,46 Ohm EUR 12,60 excl. VAT: € 10.59 / $ 11.54	H100 3,3 mH 0,27 Ohm EUR 17,50 excl. VAT: € 14.71 / $ 16.03	L100 2,2 mH 0,83 Ohm EUR 23,40 excl. VAT: € 19.66 / $ 21.43	L100 1,5 mH 0,62 Ohm EUR 19,50 excl. VAT: € 16.39 / $ 17.86	L100 1,00 mH 0,49 Ohm EUR 16,10 excl. VAT: € 13.53 / $ 14.75	L100 0,82 mH 0,44 Ohm EUR 14,60 excl. VAT: € 12.27 / $ 13.37	L100 0,56 mH 0,36 Ohm EUR 12,60 excl. VAT: € 10.59 / $ 11.54
Coils up to 100 Watt	BS125 15 mH 0,59 Ohm EUR 63,60 excl. VAT: € 53.45 / $ 58.26	BS125 10 mH 0,46 Ohm EUR 55,70 excl. VAT: € 46.81 / $ 51.02	BS125 6,8 mH 0,37 Ohm EUR 50,80 excl. VAT: € 42.69 / $ 46.53	BS125 4,7 mH 0,30 Ohm EUR 46,90 excl. VAT: € 39.41 / $ 42.96	H100 3,3 mH 0,27 Ohm EUR 17,50 excl. VAT: € 14.71 / $ 16.03	H100 2,2 mH 0,21 Ohm EUR 15,50 excl. VAT: € 13.03 / $ 14.20	H100 1,5 mH 0,17 Ohm EUR 13,60 excl. VAT: € 11.43 / $ 12.46	L140 1,00 mH 0,30 Ohm EUR 31,20 excl. VAT: € 26.22 / $ 28.58	L140 0,82 mH 0,26 Ohm EUR 28,30 excl. VAT: € 23.78 / $ 25.92	L140 0,56 mH 0,2 Ohm EUR 23,40 excl. VAT: € 19.66 / $ 21.43
Coils up to 180 Watt	PA-Trafo mo-123200 0,12 Ohm EUR 89,00 excl. VAT: € 74.79 / $ 81.52	PA-Trafo mo-125490 0,19 Ohm EUR 35,00 excl. VAT: € 29.41 / $ 32.06	PA-Trafo mo-125470 0,16 Ohm EUR 31,41 excl. VAT: € 26.39 / $ 28.77	H140 4,7 mH 0,26 Ohm EUR 38,10 excl. VAT: € 32.02 / $ 34.90	H140 3,3 mH 0,19 Ohm EUR 32,20 excl. VAT: € 27.06 / $ 29.49	H140 2,2 mH 0,14 Ohm EUR 25,30 excl. VAT: € 21.26 / $ 23.17	H140 1,5 mH 0,11 Ohm EUR 21,40 excl. VAT: € 17.98 / $ 19.60	L140 1,00 mH 0,30 Ohm EUR 31,20 excl. VAT: € 26.22 / $ 28.58	L140 0,82 mH 0,26 Ohm EUR 28,30 excl. VAT: € 23.78 / $ 25.92	L140 0,56 mH 0,2 Ohm EUR 23,40 excl. VAT: € 19.66 / $ 21.43
Coils up to 330 Watt	PA-Trafo mo-123200 0,12Ohm EUR 89,00 excl. VAT: € 74.79 / $ 81.52	PA-Trafo mo-125490 0,19Ohm EUR 35,00 excl. VAT: € 29.41 / $ 32.06	PA-Trafo mo-125470 0,16Ohm EUR 31,41 excl. VAT: € 26.39 / $ 28.77	PA-Trafo mo-125450 0,14Ohm EUR 29,28 excl. VAT: € 24.61 / $ 26.82	BT140 3,3 mH 0,22 Ohm EUR 88,10 excl. VAT: € 74.03 / $ 80.70	BS140 2,2 mH 0,16 Ohm EUR 37,10 excl. VAT: € 31.18 / $ 33.98	BS140 3,3 mH 0,12 Ohm EUR 34,20 excl. VAT: € 28.74 / $ 31.33	H140 1,0 mH 0,08Ohm EUR 18,50 excl. VAT: € 15.55 / $ 16.95	H180 0,82 mH 0,06 Ohm EUR 93,00 excl. VAT: € 78.15 / $ 85.18	H180 0,56 mH 0.05 Ohm EUR 28,30 excl. VAT: € 23.78 / $ 25.92
Coils up to 550 Watt	PA-Trafo mo-123200 0,12Ohm EUR 89,00 excl. VAT: € 74.79 / $ 81.52	VT180 10 mH 0,27 Ohm EUR 161,60 excl. VAT: € 135.80 / $ 148.02	VT180-68 6,8 mH 0,21 Ohm EUR 151,80 excl. VAT: € 127.56 / $ 139.04	VT180 4,7 mH 0,17 Ohm EUR 127,30 excl. VAT: € 106.97 / $ 116.60	VT180 3,3 mH 0,14 Ohm EUR 117,50 excl. VAT: € 98.74 / $ 107.63	BT140 2,2 mH 0,12 Ohm EUR 78,30 excl. VAT: € 65.80 / $ 71.72	BT140 1,5 mH 0,09 Ohm EUR 62,60 excl. VAT: € 52.61 / $ 57.34	L200 1,0 mH 0,18 Ohm EUR 44,00 excl. VAT: € 36.97 / $ 40.30	H180 0,82 mH 0,06 Ohm EUR 93,00 excl. VAT: € 78.15 / $ 85.18	H180 0,56 mH 0,05 Ohm EUR 28,30 excl. VAT: € 23.78 / $ 25.92
Coils up to 1000 Watt	T236 15 mH 0,24 Ohm EUR 209,90 excl. VAT: € 176.39 / $ 192.26	T236 10 mH 0,18 Ohm EUR 189,90 excl. VAT: € 159.58 / $ 173.94	T236 6,8 mH 0,14 Ohm EUR 179,90 excl. VAT: € 151.18 / $ 164.78	T236 4,7 mH 0,12 Ohm EUR 134,90 excl. VAT: € 113.36 / $ 123.56	T236 3,3 mH 0,10 Ohm EUR 126,90 excl. VAT: € 106.64 / $ 116.24	BT180 2,2 mH 0,11 Ohm EUR 107,70 excl. VAT: € 90.50 / $ 98.65	BT180 1,5 mH 0,09 Ohm EUR 88,10 excl. VAT: € 74.03 / $ 80.70	BT180 1,0 mH 0,08 Ohm EUR 84,10 excl. VAT: € 70.67 / $ 77.03	VT236 0,82 mH 0,06 Ohm EUR 146,90 excl. VAT: € 123.45 / $ 134.56	VT236 0,56 mH 0,08 Ohm EUR 117,50 excl. VAT: € 98.74 / $ 107.63

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.
 

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