Altec 511B Sectoral Horn

The Altec 511B is a compact sectoral horn with a 90° x 40° coverage pattern and exponential expansion. It is the horn that started Iwan Arjanto on 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 made for the mid and high-frequency sections of two-way or three-way sound systems. Its straight throat and exponential expansion give uniform control of sound dispersion while keeping middle and high frequencies accurate.

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

Resistor Magazine covered the 511B in its restoration profile of Iwan Arjanto's vintage speaker collection. It was 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 Altec horn systems. After he acquired the 511 horn, he learned to build Altec A7 speakers - four pairs to date for customers. Each pair gets extensive testing before delivery.

Comparison to 811B

The 511B has the same 90° x 40° coverage pattern as the larger 811B, in a more compact size:

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, so they sound similar 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 came out of Altec's horn design experience from the golden age of cinema audio. The larger 811B became the "Voice of the Theatre" horn. The 511B offered similar performance in a more compact package suited to 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.