English: Drawing of the Klipschorn loudspeaker manufactured by Klipsch Audio Technologies from 1948. The Klipshorn is a high fidelity speaker system whose notable feature was its folded bass horn system, which is open at the back and is designed to use the walls and floor in the corner of a room as part of the horn structure, to achieve better bass response. The speaker is designed to be placed in the corner of the room.
This 1948 issue of Radio-Electronics magazine would have the copyright renewed in 1976. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1975, 1976, and 1977 show no renewal entries for Radio-Electronics. Therefore the copyright was not renewed and it is in the public domain.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.