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15 Years of www.linkwitzlab.com

A Retrospective

When I launched this website in November of 1999 with DIY plans for the PHOENIX open-baffle loudspeaker, I wanted to spread knowledge, educate and preserve for the future what I had learned from building loudspeakers for my personal needs. I knew that even professional loudspeaker designers could benefit, as I had heard many speakers and hardly any rendered stereo sounds in outstanding naturalness. For me un-amplified sounds and symphony hall experiences have always been my hearing's references, not other loudspeakers.

I built my first loudspeaker for my father, who had a large LP collection of piano music. The design came from a 1957 TELEFUNKEN Laborbuch and used a single 8" driver towards the top of a 1600 mm tall and 500 mm wide baffle across one corner of our living room. The baffle was sealed to the walls at the top and 100 mm open at the bottom for increased bass. The mono speaker worked well as I remember. 

My real interest was in radio frequencies, not audio and therefore the Laborbuch. I was a Ham operator (DJ1SX). After studying electronics and graduating from TH Darmstadt I worked for a few months in the Zentrallabor of SIEMENS in Munich on a tunnel diode based and therefore very fast switching analog-to-digital converter. 

That ended when In 1961 I took the opportunity to work for 2 years in the Microwave Division of Hewlett Packard Co in Palo Alto, California. Well, that turned into 37 years at HP's R&D laboratories for electronic test and measurement equipment and it became also the beginning of my fascination with speaker design. 

I learned much about listening and audio design from colleagues and friends at HP, such as Russ Riley, Lyman Miller and Brian Elliott. I met also Laurie Fincham from KEF's R&D, who was a customer for HP's Fourier Analyzer. We sent long air-mail letters back and forth across the Atlantic, exchanging ideas, questions and answers. 

Towards the end of my career at HP I partnered with Marshall Kay and Kurt Pasquale and designed the Dvorak, Vivaldi and Beethoven open-baffle loudspeakers for Audio Artistry. I pulled out of the partnership in 1999 and soon after started this website in order to publicize for everyone's benefit what I had learned about speakers, rooms and hearing. Any income should pay for my hobbies. Indeed it has and also helped to pay some household bills in retirement.

The initial PHOENIX demo project from 2000 grew into a 6-baffle setup with the addition of THOR subwoofers in 2001. Simplification came in 2002 in the form of the 2-baffle, 3-way ORION, which served my domestic needs really well. The ORION was not only a DIY project, but was also available turnkey, superbly crafted by Don Naples of Wood Artistry. Don Barringer, former recording engineer for the US Marine Band and I spent endless hours refining the electronic equalization of the speaker. I chose SEAS Excel midrange and tweeter drivers for their consistency and performance in this all-out, cost no objective design. The Peerless XLS woofers were chosen for their quietness at large cone excursions, i.e. low distortion, when accelerating air in an open baffle. I tend to push drivers to their physical limits and they must deteriorate gracefully. Eventually SEAS developed a powerful woofer driver that met my demanding dipole requirements. John Stone had leaned on SEAS R&D for a long time to develop such driver and Olav Arntzen came through on this major challenge. These woofers topped out the ORION.

In 2012, after 10 years, the ORION was eventually surpassed by the 2-baffle, but 4-way LX521. The LX521 was designed from the ground up as an electro-acoustic transducer, as a machine and not a piece of furniture, and strictly designed for obtaining dipolar radiation behavior from the bass to the highest frequency. The different SEAS drivers that I use are optimal for my acoustic requirements. They were chosen from a selection of SEAS drivers that John Stone had suggested and which I experimented with. All this in the pursuit of illuminating the listening room in such a way that a listener will perceptually ignore the room and the speakers and focus attention solely upon the rendering of the recorded acoustic scene, upon the auditory illusion. With the LX521 I have raised the bar for achievable sound quality in the home. 

In 2005 I introduced PLUTO, a small, 2-way, omni-directional speaker. The 2" AURA tweeter was the starting point for the design. SEAS provided an extremely capable woofer driver. In the local hardware store I found the plumbing pipes and parts for ready made enclosures.  I needed such speaker for a small vacation cottage, where ORION would not have had enough breathing room. PLUTO was a much simpler DIY project and had its power amplifiers, crossovers and equalization built into the base, and was ready to be driven from an iPod. 

My attempt to improve upon the PLUTO design for the cottage room application led in 2014 to the LXmini. I surprised myself a bit as to how effectively this speaker can set up a large and transparent sound stage and deliver a dynamic rendering. Using DSP technology and sounding similar to the LX521, the LXmini raises the bar for sound quality from any 2-way speaker.

Madisound.com offers kits of wooden parts and drivers for DIY assembly and completion of LX521 and LXmini speakers. Frank Brenner of LINKWITZ.store can even provide these speakers in nearly finished assembly, in selections of beautiful wood and with a DSP and power amplifier module. 

So here we are in November of 2014, after about 50 years of a hobby, and a passion for natural sound and music in a domestic setting. Often times I can now thoroughly enjoy what I hear in my living room, and even if the recording/mixing engineer could have done better, because the musicians and the music come through. 

It has been a satisfying journey, the more so because I have heard about many of you PHOENIX, THOR, ORION, PLUTO, PLUTO+, LX521 or LXmini builders, by following the discussions on the OPLUG. I give Mike a big THANK YOU for starting the forum soon after my website was launched and to Davey, mac, BrianL, popeye, wizardofoz and the many others, who have given of their time and expertise, which has kept my email inbox under control and provided support where I could not have done it.

Some of you have followed my writings since the 1976 'Active crossover networks for non-coincident drivers' paper in the JAES or my 1978 Wireless World articles about 'Loudspeaker System Design'. Some, many?, have built more than one of my designs. I read of your dedication and learning from the construction, and how you felt rewarded by its outcome in looks and sound. It gives me joy that I could add to the joy in your life.

Let's continue to have fun,

Siegfried Linkwitz




What you hear is not the air pressure variation in itself 
but what has drawn your attention
in the streams of superimposed air pressure variations 
at your eardrums

An acoustic event has dimensions of Time, Tone, Loudness and Space
Have they been recorded and rendered sensibly?

Last revised: 02/15/2023   -  1999-2019 LINKWITZ LAB, All Rights Reserved