Klipschorn Timeline

This is a timeline for the evolution of the Klipschorn speaker from inception to the current date. Having been in continuous production for over 60 years there are still few speakers that can do what the Klipschorn can do, despite having hardly changed from the original design.
Date Event Media
1930 While working In Chile, S.A. Paul W. Klipsch was an amateur radio enthusiast. Comparing various types of radio speakers, he recognized the superior efficiency of horns.
1933 Back in the U.S. at Stanford University, PWK made note of a classmates comment that "speakers sound better in a corner".
1934 Still at Stanford, PWK read the Symposium on Auditory Perspective by Bell Telephone Laboratories.
1939-1941 The above mentioned facts were blended into a design philosophy. PWK drew pictures and built paper models that were to become the "Klipschorn®".
February 5th, 1940 Paul applies for a patent on his first prototype cornerhorn, the X-1. It was during patent "negotiations" that he first learned of prior art cornerhorns. There were several.
1941 While stationed at the Aberdeen Proving Grounds, PWK reviewed and corrected his first manuscript on corner horns.
(Exact date unclear) A second design was prototyped as X-2, but was destroyed by termites before meaningful measuremets could be made.
May 1942 The first successful prototype (X-3) was built in PWK's garage using only hand tools. This basic corner woofer has changed little over the years. This was serial number 1.
October 3rd, 1942 Paul applied for a patent on X3.
February 9th, 1943 Paul received a patent on his first (unsuccessful) prototype, the X-1.
April 17th, 1945 A patent was granted for the third prototype (X3) which was to become the Klipschorn.
June 15th, 1945 Another patent was applied for describing Paul's second high frequency horn (X-5). This later became the K-5-H horn.
1946 Klipsch and Associates was incorporated
Early 1947 The first production run of 12 units (S/N 2 - 13) were built to Paul's specifications by the Baldwin Piano & Organ Company of Cincinnati Ohio. The high frequency driver in these was the WE713A. At least one of the woofers was a JBL.
Late 1947-Early 1948 Seven more (S/N 14-20) were built by hand in a local cabinet shop. Paul recalls that no more than two were alike. It was during these "experiments" that the LF horn's "sinus" cavities were added to the woofer's back air chamber to maximize acoustic capacitance. Component Designations: High frequency Western Electric 713A, Woofer unknown.
June 1st, 1948 The first Klipschorn to be built in the first actual Klipsch factory was S/N 121. The building was formerly the telephone exchange building for the Southwest Proving Grounds and is currently the Klipsch Museum of Audio History. Component Designations: The early production logs (1949) first make reference to the use of the Jensen P-15-LL woofer. The production log makes reference to a total of 26 Klipschorns built this year.
(Editor's note: as of 2007-2008, the museum is in the process of moving to Indianapolis)
1949 The Stephens P52LX2 becomes the primary woofer. This driver is used through August of 1953 when the transition to the Stephens 103LX2 was made. The Stephens P15 High frequency driver starts appearing in the logbook.
August of 1950 The Electrovoice EV 15WK woofer is first referenced in the production logs and is used interchangeably with both of the Stephens woofers and the early K-33-J woofers until March of 1961.
1951 The University SAHF replaces the Stephens P15 as the primary high frequency driver.
June 2nd, 1951 The first three-way Klipschorn incorporated a Jensen RP203 tweeter. This tweeter came from the famous Jensen G-610 Triaxial 15" driver and required considerable negotiations with Jensen. It was not until mid-1952 that all Klipschorns were three-way. A two-way Klipschorn with response to 12Khz was generally adequate for program material up to that time. The University MID-T- 4401 replaced the Jensen unit as the tweeter of choice later in 1951.
July 25th, 1952 The original K-5-H high frequency horn of the patent was modified to become the K-5-J. This involved changing the vertical taper so that the dividers ("boats") could be removed. This resulted in a production cost savings, not an acoustical improvement.
September 2nd, 1952 A cardboard shipping container was used for the first time. Prior to this all Klipschorns® were shipped in wooden crates. The last wood crate was used on S/N 912 on June 13, 1955
August, 1953 The Stephens 103LX2 Woofer starts to be used.
1955 K-500 / 5000 network phased out in favor of the 1 RC (Type A network)
November 25th, 1957 through May 5th, 1958 This was the transition period between the University 4401 tweeter and the Electrovoice Alnico magnet T-35 (K-77) which yielded substantially flat response to 17Khz.
August 26th, 1959 The first shipment of Electrovoice T-35 tweeters designated as K-77 is received. The K-77 is first used in S/N 1445 on Oct 15, 1959.
November 14th, 1958 Driver polarities were first observed and made consistent. This practice was initiated due to marginal improvements noted during listening tests.
April 1960 Transition to the K-33-J Woofer (Jensen) from the EV 15WK began. And University SAHF mid-range drivers started to be designated and labeled as K- 55.
May 31st - September 18th 1961 This was the transition period between the 6" high woofer horn throat and the current 3" high throat. This boosted output in the 400 - 500 Hz range further smoothing the response. Multi-tapered wedges were also added to the woofer throat (opposite side of the motor board from the driver) to further improve the response in this region. The use of these wedges was soon abandoned but the smaller throat dimensions were retained and are in use today.
November 14th, 1961 The Atlas K-55-V Alnico magnet mid-range driver is introduced. This driver was patterned after the famous Western Electric 555-W.
1963 - May 15th, 1964 The K-5-J mid-range horn was replaced with the K-400 resulting in a flatter overall spectral balance, particularly in both crossover regions.
October 24th, 1966 The designation for the Type 1RC crossover network was changed to Type A.
September 1967 Transition to the K-33-M. The records are not clear as to the origin of this driver but it is believed to be an Eminence driver with an Alnico magnet.
January 1968 Transition to The K-33-P Woofer (CTS Paducah KY)
July 1971 The Type AA crossover network was introduced featuring Zenor diode tweeter protection.
1975 Transition to The K-33-B Woofer (CTS Brownsville TX)
1975-1979 K-33-E (Eminence) and the K-33-B were used interchangeably. The records are not specific about the actual start date for the K-33-E but it is believed to be in the early to mid 1970's.
1979 The Eminence K-33-E woofer is used exclusively
February 1st, 1983 The two piece Type-AK crossover network was introduced incorporating fusing and steeper filter slopes for enhanced tweeter protection and smoother response in the crossover regions. Heavy gauge (10 AWG) internal wiring was used throughout and binding posts replaced the traditional screw type barrier block as input terminals. The tweeter was flush mounted in the baffle using "Z" brackets. Rubber wall gaskets were added to the sides of the tailboard to improve the seal to less than perfect wall surfaces.
October 19th, 1983 The Type AK-2 network was introduced to accommodate the new Ceramic Magnet K-55-M mid-range driver. This Electrovoice sourced driver was essentially the same as the previous K-55-V with a ceramic magnet and a smoother response.
April 1st, 1987 The "D" style decorator cabinet (no cosmetic panels or grilles) was discontinued.
November 20th, 1987 The Aluminum K-400 horn was replaced with the K-401 structural foam horn resulting in slightly improved distortion figures.
October 1st, 1989 The AK-3 network was introduced to correct for a shift in the output of the K- 55-M mid-range driver.
1995 A limited edition of the Klipschorn is produced to mark the 50th anniversary of the company and the Klipschorn. A total of 150 pairs were offered in three different finishes but less than 50 pairs total were sold. The only changes to this model were cosmetic. 50th Anniversery Photo
August 1st, 1995 The "C" style cabinet (no intermediate collar or kick plate) was discontinued.
2000 Electrovoice ceases production of the K-77-M and K-55-M tweeter and mid- range drivers. The search for replacement drivers and the acquisition of the EV tooling is sought. Very limited production of a few pairs occurs at the end of 2000 and the early months of 2001 using existing part stocks.
May 2001 The Atlas PD-5VH (Current version of the previous K-55-V) is modified slightly and christened the K-55-X. The various components of the K-77-M tweeter are either retooled or sourced from the new owners of the tooling and assembled by a third party. This variant of the tweeter is designated the K-77-F. An entirely new one piece network, located on the woofer door, (AK-4) was created to accommodate these driver changes. Fusing is eliminated in favor of a polyswitch for tweeter protection and a trap circuit was added to tame the longstanding response peak in the middle of the woofer's pass band, resulting in an improved spectral balance. The number of variants available was reduced by the elimination of the Brown and Cane grille cloths and oil finishes.
December 2005 The Type AK-5 network was introduced to compensate for the improvement in low frequency response resulting from the addition of a horizontal wall seal to the top of the low frequency cabinet. The style "B" cabinet was discontinued by the elimination of the inset "intermediate collar" and visible "woofer top" panel in favor of a 3/8" gap between the cabinets. The long standing angle brackets, hanger bolts and wing nuts used to attach the HF and LF cabinets together were replaced with thick rubber spacers, on the LF cabinet, indexed into recesses on the HF cabinet.
April 2006
The horn portion of the K-77-F tweeter was re-tooled to include a recessed flange eliminating the need for the separate "Z" bracket and attachment rivets. This also allowed the updating of pre-Z bracket Klipschorns (prior to Feb 1,1983) to flush tweeter status without motor board modification. This variant was designated as the K-77-D.
A special limited edition Klipschorn was produced to commemorate the 60th anniversary of the company and the speaker itself. Low frequency response was enhanced with the addition of rear low frequency horn panels. This eliminated the need for a tight fit into the corner and permitted toe-in and toe- out flexibility for the first time. Additional upgrades were made to the binding posts, internal wiring, and network component specifications. Aesthetic enhancements included a Lacewood veneer finish on the LF cabinet and a high gloss Black finish on the HF cabinet. The traditional wood kick plate was replaced with a machined and anodized Aluminum version containing a Silver finish PWK logo containing a real diamond. The rear of the HF cabinet was totally enclosed with finished panels featuring display windows for a commemorative numbered plaque and the HF network. 200 pairs were produced.