Altec 511B Sectoral Horn

The Altec 511B is a compact sectoral horn that introduced countless listeners to the magic of horn-loaded high frequencies. With its 90° x 40° coverage pattern and exponential expansion, the 511B became the horn that launched Iwan Arjanto's journey into vintage audio restoration - a story featured in Resistor Magazine.

Specifications

Type	Sectoral Exponential Horn
Coverage Pattern	90° horizontal x 40° vertical
Throat Diameter	1.4 inches (for 288-series drivers)
Construction	Cast metal with straight throat
Dimensions	10.625" H x 23.625" W x 18.5" D
Weight	17.75 lbs (8 kg)
Recommended Drivers	Altec 288, 291 series compression drivers
Recommended Crossover	800 Hz

Design Overview

The 511B is a sectoral exponential horn designed for the mid and high-frequency sections of two-way or three-way sound systems. Its straight throat configuration and exponential expansion provide uniform control of sound dispersion while maintaining exacting reproduction of middle and high frequencies.

Key design features:

Sectoral Pattern: 90° x 40° coverage provides wide horizontal dispersion with controlled vertical pattern
Exponential Expansion: Smooth flare rate for accurate acoustic impedance transformation
Straight Throat: Minimizes phase irregularities at the high end
Cast Construction: Rigid metal casting prevents resonance and ensures consistent performance

In the Wild

Featured prominently in Resistor Magazine's restoration profile of Iwan Arjanto's vintage speaker collection. The 511B holds special significance as the horn that started Arjanto's obsession with horn-loaded speakers.

"The first horn-type speaker I bought was a Fostex FD600 because it was cheap. Then come opportunity to buy an Altec 511 horn, then I learned to make Altec A7 – I've made four pair so far for customers."

— Iwan Arjanto

"The first time I heard an Altec horn was at my friend's house – he used to play around with full range drivers too – after hearing that horn I couldn't forget its sound. That's when the journey began, I began hunting many horns."

— Iwan Arjanto

The 511B was Arjanto's entry point into the world of Altec horn systems. After acquiring the 511 horn, he learned to build Altec A7 speakers - four pairs to date for customers. Each pair receives extensive testing before delivery, reflecting Arjanto's commitment to quality.

Comparison to 811B

The 511B shares the same 90° x 40° coverage pattern as the larger 811B, but in a more compact form factor:

511B: Compact sectoral horn, 17.75 lbs
811B: Full-size sectoral horn used in VOTT A7, larger physical presence

Both horns use the same exponential expansion and straight throat principles, providing similar sonic characteristics in different physical packages.

Applications

The 511B was used in various professional and home audio applications:

Compact cinema and theater installations
Recording studio monitor systems
Sound reinforcement systems
High-efficiency home audio builds
Custom horn-loaded speaker projects

Historical Context

The 511B represents Altec's expertise in horn design developed during the golden age of cinema audio. While the larger 811B became the iconic "Voice of the Theatre" horn, the 511B offered similar performance in a more compact package suitable for smaller venues and applications.

Today, the 511B is prized by vintage audio enthusiasts for its combination of manageable size and classic Altec horn sound. Its historical significance is further elevated by its role in inspiring craftsmen like Iwan Arjanto to pursue vintage speaker restoration.