Great Plains Acoustic
The home of vintage Altec Lansing loudspeakers
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
Here are two articles I contributed to from Sound Practices magazine. They are reprinted here with permission from Sound Practices. Sound Practices, Vol. 1, #4, Altec "Voice of the Theatre" Speakers for Hi-Fi Sound Practices, Vol. 1, #9, Horns Revisited - The Exemplar Project...
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
In the spring of 2008 I was loaned a pair of Altec Lansing Super Duplex 604E for testing and research about possible crossover improvements. Unfortunately, one of the drivers had sustained damage to a compression driver binding post during shipment, and as I removed its rear cap for an inspection of the damage I discovered that the 604E had been equipped by Altec with compression driver rear loading caps. I remember the first time I removed the rear cover of an Altec Lansing small format compression driver (1” dia. throat) and saw a black plastic factory loading cap mounted over......
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
I received an unexpected opportunity to perform electro-acoustic measurements on a pair of 604E Super Duplex speakers in early 2008 thanks to a long-time owner seeking improvement in their sound. He had been using the original Altec Lansing N-1500A series type crossovers, and wondered if an improved crossover implementation might make them sound better. I had wondered that too. The drivers had original factory cones and voice coils, as well as identical production date codes of 391611, signifying the 11th week of 1966. My initial measurements suggested weakened magnets, so the drivers were sent to Great Plains Audio in Oklahoma......
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
The Great Plains Audio 604-8H-III is a much improved version of the vintage ferrite magnet Altec 604 family, and is currently in production. Compared to the early production ferrite Altec 604-16X discussed elsewhere in these pages, the GPA 604 exhibits very smooth and extended response. I was given the opportunity to measure these drivers some time ago, and came to the conclusion that a Butterworth 2nd order filter centered at 1500Hz with the crossover points spread 30% would both accomplish the necessary phase correction and also yield reasonably flat SPL magnitude throughout the crossover region. The drivers’ owner, and subsequent......
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
The parts and bi-wiring layout I have specified here for building my various 604 and 605 phase correct crossovers are ones I have used successfully with vintage Altec Lansing drivers in the past. The parts are not inexpensive, nor the layout quick to implement, and for good reason - they sound better! I've received a number of questions from prospective builders about part substitutions and construction techniques, so I thought it would be a good idea to present a few thoughts on the subject for your consideration. Capacitors My circuits specify Hovland Musicaps. Hovlands are truly premium items, and are available......
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
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......
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
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 –......
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
Enter the H Model... In early 2004 I acquired a pair of 604-8Hs, the last ALNICO magnet duplex model Altec produced before they switched to ferrite magnets. It was also the first Altec duplex model that combined the Tangerine phase plug with a constant directivity high frequency horn and a crossover that utilized dual equalization of the compression driver output. I swapped out my 604Bs for these Hs using the same cabinets, and was immediately impressed by the differences in output - well controlled upper mids, significantly more high frequency extension, improved imaging detail and more apparent bass & mid bass. What was in......
GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
I acquired a pair of 604Bs in the early 1990s, and had them refurbished with new 604E low frequency (LF) cones and new 16 ohm high frequency (HF) diaphragms at the Altec factory in Oklahoma City, Oklahoma. I subsequently used them with Altec N1500A crossovers for years in a secondary audio-visual system. (Follow the Vintage Altec Lansing N1500A schematic link for a look at that vintage series type crossover) My main system had horn loaded Altec 515-8Gs and 909-8As with custom phase corrected passive crossovers, and the 604Bs seemed to lag behind them in a number of sonic areas. In......
GPA's Vintage Altec E-Zine, Todd W. White's Corner
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......
