Inductor DCR

[jim henderson]

As you all know, some JBL inductors have rather large DCR values. JBL was careful to factor the DCR into the network design, so substituting high quality, low DCR, air core inductors can have disastrous effects. For example, Giskard wrote, “…the 3.5mH air core inductor often used across the LE5’s is very tiny and has a DCR of 7.5 ohms…” “Rich” wrote “The 1.8mH iron-core inductors that JBL used the 4350 monitor’s N-3107 network, to crossover from the 2202 mid-bass to the 2440 midrange drivers, each have a DCR of 3.5 ohms.” Giskard wrote, “[The 3124’s L1s] are little 1.0mH air core inductors wound on plastic square bobbins and they have a DCR of 7.5 ohms.”

My immediate concern is purchasing inductors for a 4344 MKII network that I’m building. The schematic calls out iron core inductors and I need to know if I can use low-DCR air core inductors instead.

[Ian Mackenzie]

The iron core chokes are specified in certain areas of the 4344mk11 crossover network, like the woofer low pass and mid high pass filters.

The idea IMHO is to control the size of the inductor, provide high power handling and minimise losses as air core inductors are likely to be very expensive and large. You can of course use air core inductors but I cannot see the point.

I would tend to use low dcr inductors every where as series DC reistance can be added later if required to trim the operation of the various filters "IF " required. (resistance can only be added here not taken away).

You are right about the higher DCR values in some of the vintage crossovers, and this may have been to maintain low production costs, and in some instances raise the QTS of the driver to extend the low frequency extension of the bass system a degree where the combination of a large magnet for hi sensitivity and other parameters are unavoidable. (example of this the 4343 network and 4345 network, again this is only my theory)

Ian