ResonantLive Sound Archive

Equipment file · Moving-coil transducer patent

Moving-coil transducer patent

Oliver Lodge · 1898

Evidence status · documented

Identity and core specifications are documented; some historical fields remain unavailable.

Oliver Lodge's British patent 9712 of 27 April 1898 refined the moving-coil transducer, using non-magnetic spacers to hold a precise air gap between the magnet's poles, as part of a 'telephone relay'. It built on Siemens's 1874 moving-coil patent and became practical only once valve amplifiers could supply power.

Introduced
1898
Category
Moving-coil transducer patent
Intended use
Telephone relay and loudspeaker motor using a coil in a magnetic gap
Production
Experimental; parts preserved at the Science Museum, London

Equipment photographs · 1

US patent 609,154 (1898): moving-coil apparatus

1 / 1 · US patent 609,154 (1898): moving-coil apparatus

US patent 609,154 (1898): moving-coil apparatus·Oliver J. Lodge·Public domain (US patent)

Why it mattered

  1. 01

    It anticipated the motor of the modern dynamic loudspeaker.

  2. 02

    It sits in the direct line from Siemens to the [[magnavox-telemegafone|Magnavox]] moving-coil horn driver of 1915.

Engineering record

Patent claim
British patent 9712 (1898): a coil on a diaphragm suspended in a magnetic field, with non-magnetic spacers fixing the gap[1]
Context
Followed Siemens's 1874 moving-coil patent and Cuttriss and Redding's 1877 transducer; built as part of a carbon-microphone-driven telephone relay[2][3]

Original pricing

No reliable period price located

2026 equivalent

Not calculated without a reliable original price.

Public price evidence was not sufficient to publish a defensible original figure.

Use in the field

No named deployment could be tied to this exact item by a checked source yet. Know of one? Suggest it on the contribute page.

Manuals & original documents

Sources

  1. 1Loudspeaker: Oliver Lodge 1898Made Up In Britain · reference
  2. 2A brief history of electroacoustics, pt. 4: Early moving coil loudspeakersAcoustics Research Centre · technical paper · 2015
  3. 3Pole pieces for same magnet altering to annular gap, 1898Science Museum Group Collection · archive · 1898

Contribute to the record

Know more about Moving-coil transducer patent?

Corrections, firsthand information, original documents, and credited photograph sources are welcome.

Your email is private and will not appear in the archive. Contributions are not published automatically.

Back to all equipment Back to Origins of electrical sound

Help build the archive

A missing piece? A correction?

Contribute to Resonant

Support the archive

Resonant is built one verified record at a time: research hours, archival image rights, and the hosting that keeps every era, equipment file, and citation free to read. If this archive is useful to you, a donation of any size keeps the next entry moving.

How donations are used
Venmo@mercer-aplinOpen Venmo, tap the pay field, type the handle, then send any amount.Send any amount · no account needed to viewCash App$MercerAplinOpen Cash App, tap the $cashtag field, type the tag, then send any amount.Send any amount · no account needed to view

Payments go directly to the archive’s editor through Venmo and Cash App. Resonant is an independent project rather than a registered charity, so donations are not tax-deductible and nothing is sold or subscribed to in return.