Koss Corporation
Corporate brand
UnclaimedKoss Corporation is a Milwaukee-based audio company best known for pioneering high-fidelity stereo headphones.
Last updated August 25, 2026
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Overview
Koss Corporation is a Milwaukee, Wisconsin-based audio manufacturer whose identity is closely associated with headphones and personal listening. The business began in 1953 when John C. Koss established the J.C. Koss Hospital Television Rental Company. Koss initially worked in television rental and electronics-related services, but the company’s defining product emerged from an attempt to promote a portable phonograph. Working with engineer Martin Lange, John Koss developed a stereo headphone intended to demonstrate high-fidelity sound in a private listening environment. The resulting Koss SP/3 Stereophone was introduced at a Milwaukee hi-fi trade show in 1958. At the time, headphones were used principally in communications rather than as a consumer music accessory. The SP/3 helped reposition headphones as a personal entertainment product, using a privacy feature that allowed listeners to enjoy stereo sound without disturbing others. Following the trade-show response, Koss began manufacturing and marketing stereophones from a basement apartment. The concept was soon imitated by other manufacturers, but Koss established an early leadership position in the consumer headphone category. During the 1960s and 1970s, Koss expanded its product range and became associated with higher-quality, repairable headphones. Its electrostatic ES series targeted the premium end of the market and was noted for broad frequency response. The company also maintained electronics, television-rental, musical-instrument, and repair operations, with repairability becoming a practical characteristic of many Koss products. By the 1970s, Koss was a leading headphone supplier in the United States, competing notably with Telex. Rapid growth led the company to move to its present Milwaukee location in the late 1970s. Koss attempted to diversify into other consumer-electronics areas during the 1980s, but the expansion was unsuccessful. The company reported a net loss of approximately $6 million in 1984 and filed for Chapter 11 bankruptcy protection that year. It emerged from bankruptcy in 1985 and subsequently returned its focus toward audio products. In 1991, the separate Koss Audio & Video Electronics operation began producing and selling consumer-electronics products from Hazelwood, Missouri, while the broader Koss organization retained its Milwaukee base. The company has remained primarily focused on headphones, earphones, communications headsets, and related personal-audio products. Its portfolio has included the Porta Pro, KSC series, Plug, Spark Plug, and other models spanning entry-level, portable, on-ear, over-ear, noise-isolating, and communications applications. Koss products have also been sold through third-party retailers, including RadioShack, under the Koss brand. Since 1989, Koss has offered a limited lifetime warranty on headphones manufactured in North America for normal use by the original owner, a policy that supports the brand’s reputation for durability and serviceability. Koss has also faced significant corporate and legal events. In 2009, the company discovered a large embezzlement by its former vice president of finance, Sujata Sachdeva. The incident resulted in federal charges, a prison sentence, and the restatement of several years of financial statements. In 2020, Koss sued Apple, Bose, JLab Audio, Plantronics, and Skullcandy over alleged infringement of headphone-related patents. Koss and Apple settled the dispute in 2022 for an undisclosed amount. During the 2021 GameStop-related market volatility, Koss shares experienced unusual attention and substantial price movement, and company executives and directors sold shares for approximately $40 million according to the referenced account. Koss remains an active, family-influenced public company centered on branded personal audio.
History
John C. Koss founded the J.C. Koss Hospital Television Rental Company in Milwaukee in 1953. The early business was connected to television rental, electronics service, and repair rather than being exclusively a headphone manufacturer. Koss later worked with Martin Lange, an engineer, while seeking a way to demonstrate a portable phonograph. Their work produced a stereo headphone that transformed the company’s direction. The Koss SP/3 Stereophone debuted at a Milwaukee hi-fi trade show in 1958. Its significance lay not only in its technical performance but also in its consumer proposition: people could listen privately to high-fidelity stereo music. Before this period, headphones were mainly associated with communications equipment. Koss began producing and selling stereophones after the favorable trade-show response, initially operating from a basement apartment. Other manufacturers copied the idea, but Koss became one of the early category leaders. By the early 1970s, Koss operated from two nearby Milwaukee locations. One housed the television-rental, electronics, musical-instrument, and repair activities, while another served as the principal manufacturing and business facility. The company developed an electrostatic ES headphone line that pursued premium sound reproduction and wide frequency response. Koss products were designed to be serviceable, and repairs to cords and earpads helped extend product life. During this period, Koss competed particularly with Telex and was regarded as a higher-quality supplier with a broad model range. Growth accelerated during the 1970s, prompting Koss to move to its current north Milwaukee location in the late part of that decade. The company attempted to broaden its business into related consumer-electronics categories during the 1980s. The diversification did not succeed; after recording a reported $6 million net loss in 1984, Koss filed for Chapter 11 protection. It exited bankruptcy in 1985 and subsequently concentrated more strongly on its established audio expertise. In 1991, founder John C. Koss’s son, Michael J. Koss, became president and chief executive officer. That same year, Koss Audio & Video Electronics began operating as a separate consumer-electronics production and sales company from Hazelwood, Missouri. The Koss family continued to hold a controlling economic interest, with the family owning more than 75 percent of the firm according to the referenced account. Koss’s later product strategy emphasized a wide range of personal-audio formats. The company sold full-size headphones, portable models, in-ear products, passive noise-isolating earphones, communications headsets, and premium electrostatic designs. Products such as the Porta Pro and KSC series became associated with affordable portable listening, while the Plug and Spark Plug served the in-ear segment. Koss products were also distributed through retailers such as RadioShack. A limited lifetime warranty introduced for North American-manufactured headphones in 1989 became an important part of the brand’s ownership proposition for original purchasers. The company experienced a major governance and financial crisis in 2009. Koss discovered that former vice president of finance Sujata Sachdeva had diverted approximately $34 million through fraudulent transactions. She was charged with wire fraud, later received an eleven-year federal prison sentence, and served six years according to the referenced material. Koss restated five years of financial results and recovered more than $12 million through claims involving its former auditor, Sachdeva’s credit-card company, and sales of merchandise purchased with the misappropriated funds. In 2020, Koss initiated patent litigation against Apple, Bose, JLab Audio, Plantronics, and Skullcandy. The suits concerned alleged infringement of Koss intellectual property related to headphone technology. Koss and Apple settled in July 2022, with no settlement amount identified in the reference material. Koss also became a prominent small-cap stock during the retail-trading volatility associated with the 2021 GameStop short squeeze. The episode brought unusual public attention to the company and was followed by reported stock sales by executives and directors. Despite these disruptions, Koss continues to operate as a specialist personal-audio company with a strong historical association with headphones.
- 2022
Settlement with Apple
[1]Koss and Apple settled the patent dispute for undisclosed terms.
- 2021
Retail-trading surge brings market attention
[1]Koss shares attracted extraordinary attention during the GameStop-related short squeeze and broader retail-trading surge.
- 2020
Patent litigation launched
[1]Koss sued several major headphone and electronics companies over alleged infringement of its headphone-related patents.
- 2009
Embezzlement scandal discovered
[1]The company uncovered approximately $34 million in embezzlement by its former vice president of finance, triggering criminal proceedings and restatement of five years of financial statements.
- 1991
Michael J. Koss becomes chief executive
[1]Michael J. Koss, the founder’s son, became president and chief executive officer. Koss Audio & Video Electronics also began separate consumer-electronics operations in Missouri.
- 1985
Emergence from bankruptcy
[1]Koss completed its Chapter 11 proceedings and continued operating as an audio-focused company.
- 1984
Chapter 11 bankruptcy filing
[1]After an unsuccessful diversification effort and a reported net loss of approximately $6 million, Koss filed for Chapter 11 protection.
- 1978
Move to larger Milwaukee facilities
[1]Rapid growth led Koss to move to its present north Milwaukee location in the late 1970s.
- 1970
Expansion of premium and repairable headphone lines
[1]During the early 1970s, Koss operated multiple Milwaukee facilities and developed electrostatic ES-series headphones while maintaining repair operations.
- 1958
SP/3 Stereophone introduced
[1]Koss presented its SP/3 stereo headphone at a Milwaukee hi-fi trade show, helping establish high-fidelity headphones as a consumer listening product.
Products and positioning
Koss positions itself around accessible personal audio, recognizable headphone design, long-term durability, repairability, and the heritage of having helped establish high-fidelity stereo headphones as a consumer product category. Its portfolio spans affordable everyday models as well as premium and specialist products, including electrostatic and communications headsets.
High-fidelity stereo headphones · 1958
SP/3 Stereophone
Introduced in 1958, the SP/3 was the product that made Koss a headphone company. It was designed to demonstrate the sound quality of a portable phonograph and featured a privacy-oriented listening concept. Its launch helped move headphones from communications use into personal music listening.
Portable on-ear headphones
Porta Pro
The Porta Pro is one of Koss’s best-known portable headphone families. It represents the company’s emphasis on compact design, accessible pricing, and personal listening, and has been marketed as a lightweight option for mobile use.
Budget and portable headphones
KSC series
The KSC series comprises budget-oriented Koss headphones associated with practical portable listening. The range supports the company’s long-standing role in offering comparatively affordable alternatives to premium headphone products.
In-ear passive noise-isolating earphones
Plug
Koss Plug earphones are compact in-ear products designed to reduce outside sound through passive isolation. The model belongs to Koss’s effort to extend its headphone expertise into small-format portable earphones.
In-ear passive noise-isolating earphones
Spark Plug
Spark Plug earphones are an in-ear, passive noise-isolating design. They are part of Koss’s portable earphone assortment and are intended for users seeking a compact listening product with physical isolation from ambient sound.
Electrostatic headphones
ES series
Koss’s ES series represented its premium electrostatic headphone work during the 1970s. The designs pursued broad frequency response and higher-end sound reproduction, demonstrating that Koss’s portfolio extended beyond budget and portable models.
Headsets with microphones
Koss communications headsets
Koss also produces communications headsets equipped with microphones. These products broaden the company’s use cases beyond music playback into voice communication and other headset applications.
Controversies
2009
Sujata Sachdeva embezzlement case
Koss discovered that former vice president of finance Sujata Sachdeva had embezzled approximately $34 million. She was prosecuted in federal court and received an eleven-year sentence, while Koss restated five years of financial results and pursued recovery from related parties and the sale of misappropriated merchandise.
Brand decisions
2020
Initiate patent litigation against major headphone companiesOtherBackground
Koss alleged that several major companies had infringed intellectual property relating to headphone technology.
Action taken
Koss filed suits against Apple, Bose, JLab Audio, Plantronics, and Skullcandy.
Aftermath
The dispute with Apple concluded in a settlement in July 2022. The referenced material does not identify the settlement amount.
1984
Seek Chapter 11 protection after diversification lossesStrategyBackground
Koss had attempted to diversify into related consumer-electronics categories, but the expansion produced losses and weakened the company’s financial position.
Action taken
The company filed for Chapter 11 bankruptcy protection after reporting a net loss of approximately $6 million for the year.
Aftermath
Koss emerged from bankruptcy in 1985 and returned its strategic emphasis toward audio products.
Net loss. $6 million loss (1984)
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