Altec Lansing 729A (1970)

Name: Altec Lansing 729A
Brand: Altec Lansing

A stereo active equalizer designed for precise room and speaker correction using 1/3-octave filters.

Overview

The Altec Lansing 729A "Acousta-Voicette" is a stereo active equalizer released in 1970, developed to improve the acoustic characteristics of listening environments. It uses narrow 1/3-octave band filters to correct room-induced response irregularities without affecting adjacent frequencies. Designed originally for commercial installations, it was later applied in high-fidelity home systems. The unit is inserted into the tape-monitoring loop of an amplifier or receiver and features a switch to cut the equalizer in or out, or restore tape monitoring when a recorder is connected. A transparent plastic cover protects the controls from accidental adjustment.

Specifications

Format	2-Channel, 1/3 Octave Band, 24-Element Active Filter Used
Filter Bandwidth	1/3 Octave
Frequency characteristic	20 Hz to 20 kHz ± 1 dB
Filter Center Frequency Range	63 to 12,500 Hz
Number of filters	2 channels, 48 pcs
Maximum Insertion Loss	-14dB at center frequency
Filter adjustment range	0 to 12 dB per band
Maximum reinsertion gain	17dB
Unity gain	Yes, with no reinsertion gain added
Input level	Maximum 4.5 Vrms (minimum gain control)
Output level	4.5 Vrms (at 10k Ω load)
Input impedance	100k Ω
Noise level	80 dB (Maximum rated output or less)
Channel separation	60 dB or more
Harmonic distortion	Less than 0.32% up to 1.0 volt output; 0.66% at 2 volts; 1% at 3 volts
Dimensions	18 3/4" wide by 6" high by 8" deep

Design

The 729A uses a special filter design with sharp shoulders to achieve a 1/3-octave bandwidth, allowing precise adjustment of room and speaker response. It contains 24-element filter blocks stacked in two channels for stereo operation. The technique, called "Acousta-Voicing," enables fine correction of narrowband irregularities while preserving overall tonal balance. The unit is housed in a large black enclosure with a protective transparent cover over the control panel.

Context

Originally intended for commercial sound installations, the 729A was developed as part of Altec-Lansing's "Acousta-Voicing" system to optimize speaker-room response at a specific listening position. It was designed to correct room-related acoustic problems rather than serve as a tone-shaping tool. While effective in typical living rooms—where it delivered dramatic improvements in sound neutrality—it showed mixed results in lab environments, sometimes sounding dull when high-frequency peaks were removed.

Market

The Altec Lansing 729A had an original price of $799 and is described in modern listings as "Very Rare." It was considered expensive even for correcting speaker deficiencies, with its primary value lying in solving difficult room acoustics.