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DUPLEX

GPA 604-8H-III-Rev-02

Great Plains Audio 604-8H III Rev. 2 Duplex

The Great Plains Audio 604-8H III Rev. 2 is more than just an evolution in the classic series of 604 Duplexes, it's an AUDIO REVELATION! For more than fifty years, there has been one studio monitor loudspeaker that has been the defacto standard by which all others have been measured. Though it has been through various generations, it is still known by the simple model number which graced the very first unit manufactured – 604. The popularity of this outstanding loudspeaker grew until, by the 1970's, 604-based systems were used in more recording studios than all other types combined. It’s......

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Altec 604-8K

Altec Lansing 604-8K Duplex Studio Monitor

In early 2008 I had the opportunity to evaluate a loaned Altec Lansing 604-8K utilizing the CLIO system. The driver was an early unit (serial # 3403, date stamped DEC 1982) and was equipped with the original factory low frequency cone and high frequency diaphragm. This model was manufactured by Altec from the early 1980s thru the company’s demise in the late 1990s and was marketed for use as a studio monitor, musician’s stage monitor and a premium ceiling speaker. The 8K had 8 ohm impedance voice coils and was supplied with a dual EQ passive crossover that had first been introduced for use......

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Phase Correction for Altec Ferrite Duplexes

Ferrite Magnet 604s As I mentioned on the Home Page, horizontal separation between voice coil gaps for ferrite magnet Altec Lansing 604 & 904 duplexes is 2.8125”. This distance produces 112 degrees of phase shift between the driver’s acoustic centers at 1500Hz. The Altec supplied passive crossovers for most of these units were essentially the same as for the ALNICO 604-8H, namely third order high pass and second order low pass sections at 1500Hz with MF and HF EQ circuitry. Might there be a better circuit to phase correct ferrite motor Altec Duplexes than the 8H filter? A good question –......

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Original Altec-Lansing 604

Altec-Lansing DUPLEX Speakers

Altec Lansing invented the first DUPLEX® Loudspeaker System in 1941 (some sources say 1943 - we're really not sure). Called the "601", it was of the field-coil type and included a small-format HF compression driver mounted to a 12" low frequency loudspeaker with a hole bored through the pole piece of the woofer which connected to a 2 x 3 multicellular horn. Thus began the famous DUPLEX® series of loudspeakers. In 1944, the first of the world-renown ALTEC "604" series of DUPLEX®Loudspeakers (left) was introduced. It utilized a new, permanent magnetic structure of Alnico V, had a 15" low frequency......

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About Us

Great Plains Audio was born out of the Altec Lansing corporation in 1998. It carries forward the loudspeaker design and manufacturing tradition that began with Western Electric in the early 20th century. Great Plains Audio is the only place where the legendary Western Electric/Altec Lansing sound reproduction technologies live on.

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7127 Northwest Third St. Oklahoma City,
Oklahoma, USA, 73127
405-789-0221