Why don’t speakers use electro magnets?
Subscribe to Ask Paul Ask a QuestionSpeakers work with coils of wire and permanent magnets. But, why not use coils of wire for both the permanent magnet as well as the voice coil?
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Indeed, Paul, you are ignorant in this matter – as we all are ignorant concerning specific topics. Voxativ, Berlin, orders loudspeakers featuring field coil drivers: https://voxativ.berlin/products/acx . And if permanent magnets degrade over time I guess that the permanent magnets of the different drivers in a multi-driver speaker design will degrade most differently thus that the sound characteristic defined by the initial voicing will change over time! This wouldn’t be the case will field coil drivers, is it?
Hi Paul,
paulsquirrel is in some aspects right. There do indeed exist field coil designs still on sale today. Besides the company mentioned above, Wolf von Lange reintroduced that concept in Germany https://wolfvonlanga.de/. But you are right as well. It is a rather exotic approach nowadays. And the musical benefits are, if one compares it with permantent magnets of comparable quality, at least questionable. This was not true all the times in the past. Field coil chassis dominated the late twenties and thirties of the last century. For a reason. The permanent magnets of this area were inferior to field coils due to the weaknesses of the material. Since than material research has improved the permanent magnets enormously. So, there is no need, rooted in a superior sound, to use field coils. Except for the engineering design challenge, of course. What one really should abandon – the myth of degrating magnets. No measured proven physical evidence came so far to my knowledge.
Best regards, Klaus
Electromagnet speakers were a lot more common in days of year. I’ve seen several in old radios, including a Delco in a 1951 Buick convertible I owned decades ago.
Several other practical examples from days of yore
HiFi Critic (Martin Colloms’ magazine)
http://enjoythemusic.com/hificritic/vol5_no4/supravox_field_coil.htm
[…The fact that field-coil (electromagnet) energized loudspeaker drive units still exist is a triumph for the enthusiasts who’ve managed to conserve what they consider to be a worthwhile engineering approach, in spite of the fact that it has subsequently been almost swamped by advances in technology and mass production….]
No one mentioned that using an electromagnet also introduces another possible source of noise. That type of driver would require its own power supply, and as we all know there are good and bad ones. Combine increased manufacturing costs of drivers with the cost of using a good low noise power supply and it’s no wonder that most of the industry went the permanent magnet route.