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Re: What are some general sonic characteristics of field coils?

Posted by Bold Eagle (A) on April 15, 2004 at 17:22:17

In Reply to: What are some general sonic characteristics of field coils? posted by Resident Hopekiller on April 14, 2004 at 20:37:02:

You're asking a pretty broad question. If you raise the flux in the gap, you do increase sensitivity, but you also increase the back EMF which restricts the low end and requires higher amplifier drive voltage (EQ) or a cabinet that augments the bass. Like a ported or horn loaded system. There is definitely such a thing as too much magnet. So a speaker with a stronger magnet needs to be carefully matched to its cabinet. Really, any speaker does.

Back int the 50's, when people were building their own cabinets, bigger magnets and higher flux densities were all the rage. Magnetic system weight (including the iron) was one of the major deciding factors on selecting drivers. It got kind of crazy. In the 50's I had a Wharfedale 12/FS/AL 12" full range with a flux density of 17,500 Gauss and an AlNiCo magnetic structure of nearly 20 lbs. The top of the line E-V's weighed 41 lbs. Great midrange, no bass. Tomcik's landmark paper from 1954 looked at that and showed that to get proper bass out of the overdamped E-V's you needed several ohms of series resistance to get the bass Q into a range where response was flat. That, or horn load them.

Jerry

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