A sad day for the Audio industry and DIY builders indeed.
He will live on in his wonderful contributions to our love of sound reproduction systems and the pleasure it gives to listen.
Those of us who have built and use his designs on a daily basis will know the giving man he was and the inspiration to many.
Goodbye Siegfried
Oh, that’s pretty shocking news. I knew he was old but still. I remember having some nice conversations with him about dipole loudspeaker design. He learned me (and many others) a lot. There are not many people that have had such an impactfull contribution to the audio industry as he had.
Beye Siegfried
For those who don’t know of the man…
http://www.linkwitzlab.com/about_me.htm
is where you can find out about him.
And not to forget the Linkwitz crossovers find in many loudspeakers, electronic crossovers and dsp units around the world. Everyone knows them.
Its in the Subject 
Oh no, that’s sad news. I remember sitting next to Mr. Linkwitz in a hifi show demo room - I was too intimidated to ask him what he thought. He was a talented and thorough engineer, and he used those empirical skills to bring joy to the world. My salute to a life well lived.