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The co-in­ven­tor of the Linkwitz-Reilly loud­speaker crossover has crossed over…

Siegfried Linkwitz, the co-in­ven­tor of the Linkwitz-Ri­ley crossover, a favourite of loud­speaker man­u­fac­tur­ers and DIY speaker builders the world over, has died, aged 82. When asked about his many in­ven­tions over the years, Linkwitz would of­ten in­voke one of his favourite Ralph Waldo Emer­son quotes: ‘We are all in­ven­tors, each sail­ing out on a voy­age of dis­cov­ery, guided each by a pri­vate chart, of which there is no du­pli­cate. The world is all gates, all op­por­tu­ni­ties.’

Although Linkwitz de­signed and built loud­speak­ers his en­tire adult life, and was as­so­ci­ated with sev­eral well-known loud­speaker man­u­fac­tur­ers, in­clud­ing Au­dio Artistry, where he was vice-pres­i­dent of en­gi­neer­ing, and his own com­pany, Linkwitz Labs, he worked full time in the re­search and de­vel­op­ment depart­ment of test and mea­sure­ment com­pany Hewlett-Packard (now Keysight Tech­nolo­gies) for 37 years, de­vel­op­ing and help­ing de­velop state-of-the-art elec­tronic test equip­ment in­clud­ing mi­crowave spec­trum anal­y­sers, net­work anal­y­sers and EMI re­ceivers. In his later years at Hewlett-Packard, he trav­elled the world ex­ten­sively, giv­ing sem­i­nars on test and mea­sure­ment. He also helped de­velop US Na­tional and In­ter­na­tional stan­dards for Elec­tro­mag­netic Com­pat­i­bil­ity Test In­stru­men­ta­tion.

Linkwitz was born on No­vem­ber 23, 1935, in Bad Oeyn­hausen, Ger­many. His fa­ther was a sur­veyor and his mother a school teacher. He was a sec­ond son, his brother be­ing eight years older. Af­ter grad­u­at­ing with a Di­plom In­ge­nieur de­gree in Elec­tri­cal En­gi­neer­ing from Darm­stadt Tech­ni­cal Univer­sity in Ger­many, Linkwitz moved first to Hanover in 1957, where he worked for Tele­funken, and four years later to Mu­nich, to work for Siemens.

Linkwitz mar­ried his wife Eike in 1961 while the two were work­ing for Siemens. Both were dis­en­chanted by the sit­u­a­tion in post-war Ger­many and they de­cided they’d em­bark on what Linkwitz called ‘a cul­tural ex­pe­ri­ence’ by mov­ing to Cal­i­for­nia for two years so Linkwitz could do post-grad­u­ate stud­ies at Stan­ford Univer­sity and be­come in­volved in the ‘New Age’ move­ment. Whilst study­ing, Linkwitz also started work­ing for Hewlett-Packard, first in Palo Alto and then in Santa Rosa… where he con­tin­ued to work un­til his re­tire­ment in 1998.

It was while he was at Hewlett-Packard that Linkwitz and his co-worker Russ Ri­ley de­vel­oped their ‘Linkwitz-Ri­ley’ crossover in 1975. Later, Linkwitz ex­tended this work to de­velop what he called the ‘Linkwitz Trans­form’ cir­cuit. The cir­cuit had noth­ing to do with work either of them were do­ing at HP. Linkwitz said that it came about sim­ply be­cause the two were both au­dio hob­by­ists.

First de­scribed in the Jour­nal of the Au­dio En­gi­neer­ing So­ci­ety in the pa­per ‘Ac­tive Crossover Net­works for Non­co­in­ci­dent Driv­ers’ (Vol 24 No 1, Feb 1976), a Linkwitz-Ri­ley fil­ter (also known as a But­ter­worth Squared fil­ter) is an in­fi­nite im­pulse re­sponse fil­ter. Ap­plied to a loud­speaker’s crossover net­work, it con­sists of low-pass and high-pass But­ter­worth fil­ters in par­al­lel. This re­sults in −6dB gain at the cut-off fre­quency, so that when the low-pass and high-pass out­puts are summed, the gain at the crossover fre­quency is 0dB, so the crossover has a flat am­pli­tude re­sponse. (A stan­dard But­ter­worth crossover has a 3dB peak at the crossover fre­quency.)

In the en­su­ing years, Linkwitz wrote many im­por­tant pa­pers that were pub­lished in the Jour­nal of the Au­dio En­gi­neer­ing So­ci­ety, in­clud­ing: ‘In­ves­ti­ga­tion of Sound Qual­ity Dif­fer­ences be­tween Monopo­lar and Dipo­lar Woofers in Small Rooms’, ‘De­vel­op­ment of a Com­pact Dipole Loud­speaker’, ‘Loud­speaker De­sign for Re­duced Re­ver­ber­ant Sound Power Out­put’, ‘Shaped Tone-Burst Test­ing’, ‘Nar­row Band Im­pulse Test­ing of Acous­ti­cal Sys­tems’, and ‘Pas­sive Crossover Net­works for Non­co­in­ci­dent Driv­ers.’ He also con­trib­uted dozens of ar­ti­cles and speaker-build­ing projects to elec­tron­ics and DIY loud­speaker en­thu­si­ast mag­a­zines such as Elec­tron­ics (Wire­less) World, Speak­erBuilder, and Au­dioX­press.

Mean­while, at Hewlett-Packard, Linkwitz was pri­mar­ily re­spon­si­ble for de­vel­op­ing such fa­mous test in­stru­ments as the HP8566 100Hz–22GHz Mi­crowave Spec­trum Anal­yser, the HP8554 RF Spec­trum Anal­yser, the HP8405 RF Vec­tor Volt­meter, the HP8546 EMC Anal­yser, the HP85650 Quasi-Peak Adapter and the HP 85685 RF Pre­s­e­lec­tor.

Af­ter re­tir­ing from Hewlett-Packard in 1998, Linkwitz was able to con­cen­trate on de­sign­ing loud­speak­ers, the de­signs of which he made avail­able to DIY con­struc­tors. His most fa­mous speaker de­signs were the Phoenix (2000), Thor (2001), Orion (2002), Pluto (2005), Pluto+(2006), Orion++ (2007), Pluto2 (2008), Orion3 (2010), Orion4 (2011), LX521 (2012), LXmini (2014), LXs­tu­dio (2015), LX521.4 (2015), LXmini+2 (2016), LX521.5ASP (2016) and ASP.4 (2016).

He also took the op­por­tu­nity af­forded by his re­tire­ment to greatly ex­pand his web­site (www.linkwit­ to help ed­u­cate vis­i­tors to that site about loud­speaker de­sign, sound re­pro­duc­tion and record­ing. On the site you can find de­tailed plans for DIY con­struc­tion of state-of-the-art dipole and mono­pole loud­speak­ers us­ing ac­tive elec­tron­ics, all of which are op­ti­mised for op­er­a­tion in re­ver­ber­ant do­mes­tic spa­ces.

Linkwitz died peace­fully at his home in Corte Madera, Cal­i­for­nia, on Septem­ber 11, 2018, where he’d been re­ceiv­ing hos­pice care since 2016 for Stage IV prostate can­cer, af­ter first be­ing di­ag­nosed in 2002. He is sur­vived by his wife Eike, their son An­dras, daugh­ter Monika and three grand­daugh­ters, Ju­lia, Anja, and Danielle. In his fi­nal years, Linkwitz said of his life: ‘I feel blessed, hav­ing been given a life to con­trib­ute to un­der­stand­ing, con­scious­ness and joy.’ g.b.

Siegfried Linkwitz (left) pic­tured with fel­low speaker de­signer Jean-Marie Liere of Mi­crophase Au­dio De­sign.

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