Monday, 29 November 2021


Acoustic Research AR-25
Two Way Loudspeaker System (1979)


Type: 2 way, 2 driver loudspeaker system
Frequency Response: 40Hz to 25kHz
Power Handling: 50W
Recommended Amplifier: 15 to 60W
Crossover Frequency: 2000Hz
Impedance: 8Ω
Sensitivity: 86dB
Bass: 1 x 200mm acoustic suspension
Tweeter: 1 x 32mm pressure
Dimensions: 298 x 544 x 197mm
Weight: 11kg

"If God wanted us to go to concerts, He would have given us tickets.  AR circa 1980."

Sunday, 28 November 2021

Waldorf School, Project Year, Loudspeaker Design

Waldorf High Schools like Michael Oak Waldorf School tuition covers all the requirements of the SA Schools syllabus, but also offers a richer depth of learning.

The subwoofer featured in this article, was part of my son's Class 12 project at Constantia Waldorf School for that year.
Michael Oak did not have a high school at the time.

Brief summary of the design strategy:

I worked for Prosound in Johannesburg during the '80s and early '90s, running an R&D department that was tasked to produce assembly-line-style professional sound equipment on demand.
For example, we had less than 2 weeks to prepare and deliver everything that was required for Paul Simon concerts.
Ad Valorem taxation applied to the components we stocked.
It's basically a disincentive to produce certain commodity items locally, such as:
"Motor Vehicles, Electronic Equipment, Cosmetics, Perfumeries and other products generally regarded as “luxury items” ".

Armed with my EV equipment, experience and familiarity with Thiele-Small speaker alignment based on Chebyshev filters, my son and I worked our way through the design process and ended up with what is presented below:

The Sub Woofer 13 years later (November 2021):

The Workshop (May 2008):

The Design - Thiele-Small DIY:

Cabinet Making