Orthoacoustic simple two way Unity corner waveguide

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Back in the late eighties I got very interested in Stig Carlssons Orthoacoustic speakers, but the OA52.2 was way to expensive for me.

Carlsson Ortho-Acoustic Loudspeakers: Design and Performance Principles (English) - CarlssonPlanet

A friend on a Swedish forum bought a pair of old OA5 (late 60ies OA speakers) and commented on the surprising sound quality of those late 60ies loudspeakers.
I wrote a short remark about the importance of a true point source keeping the room reflections as phase-linear and tonally similar as possible in OA speakers, and I started to think about how to make a simple OA-Unity hybrid.
I wanted a simple two way speaker. A simple built, preferably only simple 90 degree cuts and square pieces.

This is what I finally built:

An externally hosted image should be here but it was not working when we last tested it.


It is a Faital Pro 3FE20 fullrange driver in a corner wave guide with three 4 inch alu-cone SB-Acoustics drivers in closed boxes.

An externally hosted image should be here but it was not working when we last tested it.


Here is two measurements taken one meter from the 3FE20. The red line is without EQ.
I need to enlarge the opening for the 3FE20. The top end response gets much better with a slightly larger opening.

I use a MiniDSP 2X4HD for crossover and EQ. The crossover is 48 dB/octave at 407 Hz (21 cm distance between the acoustic center of the 3FE20 and the 4 inch bass drivers).

It sounds really good, despite being a work in progress project.

Regards,
Johannes
 
An externally hosted image should be here but it was not working when we last tested it.


Stig Carlsson had a patent on a three way OA-speaker that never got built during his life time.
I think it is easy to see that he was closing in on the Unity principle. Sadly he passed away 1996. He was one of those brilliant engineers that was way ahead of his time.

I built a crude proof of concept back in May. I worked through several throat-variations:

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


And I made a lot of measurements.

My wife and kids really hate the sound of REW sweeping through the frequency range....
 
unityortho.png

I saw that all my posted pictures are gone, so I just want to reupload this conceptual rendered picture today. I plan on getting these speakers up and running again and I hope I can post some measurements soon.
 
what about the sound?

This is only a first crude proof of concept without much finesse and optimization, but they have me baffled.

This project has got me convinced that the normal freestanding rectangular box 2 or 3 way direct radiating speaker is not the way to go.

Imaging and definition is really good. At first I found myself constantly put of by the sound quality, but in very different ways from different records.... After a while it dawned on me that I was not at all prepared for this kind of revealing resolution. It was the quality of the records I was hearing, not the speakers.

A quite unnerving experience.

It is the lack of early reflections from the room and the coherent phase and tonal balance over the whole dispersal pattern that makes for a surprising level of resolution. Quite similar to listening to quality head phones or with unity-horns in free field (outdoors).
 
are they available elsewhere?

No. They are sadly all gone. I am going to make new measurements and post both pictures of the setup and spl-graphs soon (as in the coming month or two).

There is a thread on the Swedish site hififorum.se with all my ramblings and thoughts along the development process, but it is only text (in Swedish).

Congratulations on achieving this level

I only used Tom Danleys Unity and Stig Carlssons OA ideas and combined them into something slightly new.

Cheers,
Johannes
 
OA-hörnmedutan.jpg

This is without EQ (red trace) and with EQ (yellow trace) measured with my Umik from across the room approximately 4 meters from the speaker.

I EQ mainly by ear, and check afterwards with REW and Umic, and this is where I usually end up. If I EQ to a flat level all the way up to 20 kHz the speaker sounds extremely bright and bass-shy, similar to other constant directivity horns or waveguides. A normal direct radiating speaker will reduce the radiation angle as the frequency increases. This speaker has a uniform dispersal pattern throughout its whole bandwidth, which tends to sound overly bright in a normal listening space.

The large waveguide increases the efficiency in the midrange from 180 Hz to 3,1 kHz, and this needs to be compensated with (DSP) EQ. I use my MiniDSP 2X4HD for crossover and EQ in this project.
 
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