Altec 511B Horn
At 8 lbs and just over a foot wide, it's a compact horn built for focused projection. It's cast aluminum, with vanes that divide the sound.
Overview
The Altec 511B isn't one of those ornate, flared antiques. It's industrial. It's a sectoral horn cast from aluminum, built for a job and not for display. The shape is angular and almost utilitarian, with internal vanes dividing the acoustic path into sections. It isn't a multi-cell design. It's a single horn segmented to control dispersion. It measures 11.5" wide, 8.5" high, and 9.5" deep, and it weighs 8 lbs of dense, vibration-resistant metal.
The 511B was designed for the mid or high-frequency section of two-way or three-way systems. The 1" throat fits common vintage compression units, and sources recommend pairing it with Altec's own 902, 908, or 731C drivers. Some users report running it as a midrange with a Selenium 250. Others say to stay above 800 Hz for safe operation, and some secondary sources suggest 500 Hz. The consensus among Altec enthusiasts is 800 Hz as the reliable lower limit.
Owners like its focused output. One builder using FaitalPro drivers claimed it produced "the most natural sound I have heard from any system," and later bought a second pair with top-tier drivers. Vintage Altec horns like the 511B remain desirable for both PA applications and high-end home stereo mods. They aren't mythically rare, but clean, unblemished units are noteworthy. A recent listing described a pair as "pristine, as new 9/10," though even NOS examples from old live sound inventories can carry warehouse scratches from decades in storage, not use.
Specifications
| Manufacturer | Altec |
| Product type | Sectoral horn |
| Dimensions | 11.5" wide, 8.5" high, 9.5" deep |
| Material | Cast aluminum |
| Flange | 1/4" thick cast aluminum |
| Mounting | Four 1/4-20 tapped holes on 10" centers |
| Throat | 1" |
| Dispersion | 90° x 40° |
| Recommended crossover frequency | 800 Hz |
| Weight | 8 lbs |
Key Features
Sectoral Horn with Internal Vanes
Multi-cell horns use separate chambers to tame breakup and dispersion. The 511B is a single cast structure with vanes that subdivide the horn path. This sectoral approach controls directivity without the complexity of multiple cells. It's a simpler, sturdier design, suited to places where reliability matters more than cosmetic refinement.
Cast Aluminum Construction
The entire horn, including the flange, is cast aluminum, which is lightweight yet rigid. This reduces resonance and supports clean high-frequency reproduction. The 1/4" thick flange adds structural strength and gives a secure seal between driver and horn throat. That seal matters for efficient coupling and for avoiding air leaks that degrade output.
Front-Mounting Flange with Standardized Tapped Holes
Mounting uses four 1/4-20 tapped holes spaced on 10" centers across the front flange. That makes it easy to fit into cabinets or enclosures, since it attaches securely from the front. It works for permanent installations and modular builds. The front-mount design also makes driver servicing easier than on rear-loaded setups.
1" Throat for Standard Compression Drivers
The 1" throat opening fits a wide range of vintage and modern compression drivers. Compatible drivers include the Altec 902 and 908 series and the 731C high-frequency driver. That makes the 511B a workable choice for restoration projects or custom speaker builds where sourcing exact original components is difficult.
90° x 40° Dispersion Pattern
The horn projects sound with a 90-degree horizontal and 40-degree vertical dispersion. The pattern is asymmetric. It suits applications that need wide lateral coverage but limited vertical spread, such as PA setups or near-field monitoring. The narrower vertical dispersion helps reduce ceiling and floor reflections, which gives cleaner sound in reflective rooms.
800 Hz Recommended Crossover Frequency
The documented crossover recommendation is 800 Hz. Some sources suggest operation as low as 500 Hz, but user reports and enthusiast consensus say 800 Hz is the safer lower limit. Running it below that risks over-excursion and distortion, particularly with high-output drivers. Builders are advised to respect this threshold unless using specific driver combinations rated for lower loading.
Collectibility & Value
These horns remain in demand among DIY audio builders and PA restorers. A used pair was listed in a private forum for $350 AUD, described as "pristine, as new 9/10," which shows strong secondary market interest even for non-NOS units. Another example, listed as "* SOLD *," was described as NOS, never installed, with no driver ever attached, but it showed handling scratches from warehouse storage. Condition affects value, but even cosmetically imperfect units hold appeal. No original pricing or production years are documented.
Market Value
┌──────────────────────────────────────────────────────────────────────────┐ │ ALTEC 511B HORN Nov 2026 │ ├──────────────────────────────────────────────────────────────────────────┤ │ High $550 Latest $200 │ │ Median $190 Trend ▼ Down │ │ Low $138 Volume ~2/mo │ ├──────────────────────────────────────────────────────────────────────────┤ │ $600 ┤ │ │ │ . │ │ │ . │ │ $386 ┤ │ │ │ │ │ │ . │ │ │ ..│ │ $100 ┤. . . │ │ ├─────────────────────────────────────────────────────────────────│ │ vol │▄ ▄ ▄ ▄ ▄ █▄│ │ └─────────────────────────────────────────────────────────────────│ │ 2026-05 2026-07 2026-10│ └──────────────────────────────────────────────────────────────────────────┘
eBay completed sales. Excludes accessories, parts, and non-working units. Hover points for details.
eBay Listings
Recently sold on eBay: $150–$488 (median $190, based on 8 completed sales, past 12 months)
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