Pete B

Sincere condolences to you and your family, Steve will certainly be missed. Pete Basel

Yes, good point, if those ads were widely run then Olson probably saw them and it is impressive that Goodmans came up with the idea in the 1930s. Especially with air and suspension as a key feature.

Read the Olson patent (if you can find it) it calls for a high compliance suspension which would give the woofer a very low free air resonance that WOULD require a small enclosure to bring it back up to the correct operating range. Olson called it "Air Suspension Loudspeaker". In my opinion that story from Villchur made him feel better about what happened and sounds good for the public. https://techtalk.parts-express.com/forum/tech-talk-forum/65475-ed-villchur-s-acoustic-suspension-invention

Here's another reference to Olson's patent from 1962 where Electrovoice challenges Villchur's patent and provides the Olson patent as prior art. As I read this Villchur lost this case essentially invalidating his patent: https://casetext.com/case/ar-inc-v-electro-voice-incorporated

1949 patent "Air Suspension Loudspeaker" #2,490,466 is also correctly listed here on page 11 in the .pdf: https://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/olson-harry.pdf

When I made the previous post at Tech Talk years ago I'm certain that I found Olson's patent: 1949 patent title was "Air Suspension Loudspeaker" #2,490,466 Now when I search for it, it doesn't show up, very strange. It is listed here, correctly, under the list of patents as "Air Suspension Loudspeaker" #2,490,466 but the link there also no longer goes to the correct patent. Very strange! https://usenclosure.com/Olsen/DR. OLSEN.html WHERE DID IT GO!

I measured an AR11 back around 2006 and noted the dip in impedance around 6-7 KHz and also found that the high pass crossover filter had amplitude peaking in that region around/above the crossover point. The reason for this very low impedance is first due to the very low impedance of the tweeter, and second the XO is passive but when there is peaking due to the highish Q chosen for the XO filter the amplitude peaking "gain" has to come from somewhere and this is by lowering the input impedance. This is referred to as a transformer "like" circuit in electrical engineering. From memory the tweeter filter is a 10uF cap and a .1 mH inductor, the cap is too large and the inductor too small, also the crossover point is rather high. A better .75" tweeter could be crossed much lower. Also, if we had .zma impedance files for all of the drivers (I think that I do somewhere) we could produce an Xsim simulation to plot the crossover filter transfer functions. The DC resistance of the inductor and the ESR of the original NPE cap should be duplicated in any component replacements and for simulations. If the NPE cap is replaces with a film type .47 to 1 ohm of resistance should be places in series with the cap to emulate the ESR of the cap. This will raise the system impedance in that region. That low impedance is dangerous for many SS amps by triggering the protection circuits for any amp not designed to drive 2 ohm or lower loads. Many protection circuits are not well designed and may oscillate resulting in burned out tweeters and potential damage to the amp. It is a mess. The Adcom GFA555 and 555II are good in that the only protection is fuses that don't have such problems.

I made the mistake of starting a thread at Parts Express Tech Talk giving credit to Villchur: "Ed Villchur's Acoustic Suspension Invention" I should note that I made this mistake assuming that I could rely on information gotten from the Internet. https://techtalk.parts-express.com/forum/tech-talk-forum/65475-ed-villchur-s-acoustic-suspension-invention Then after actually looking up Olson's patent, made this correction: Correction: I called this "Ed Villchur's Acoustic Suspension Invention" and I've known for many years that Villchur's patent didn't hold up in court with the reason that I read on the internet being that Olson had previously patented the closed box speaker. I thought logically, why would Villchur bother if there were no differences, that Olson's was sealed but that the air was not the dominant compliance. I just read that his 1949 patent title was "Air Suspension Loudspeaker" #2,490,466, clearly the air spring is part of Olson's patent. This is from the patent: ----------------------------------------------- An object of the invention is to increase the power handling capacity of a small speaker, making *it comparable to one substantially larger in size in its output of undistorted acoustic energy and fidelity reproduction of desired low as well as high frequency sound waves. Another and more specific object of the invention is to provide an improved diaphragm suspension structure in a loudspeaker characterized by a reduction in the effect of the suspension impedance, thus lowering the natural resonant frequency of the speaker of a given size, without increasing the mass reactance of the moving parts. A further object of the invention is to provide an improved compliant suspension in a limited space for a piston-type*loud speaker diaphragm of small mass reactance whereby the diaphragm is free to vibrate at large amplitude over a substantially extended portion of the lower audio frequency range without amplitude distortion. A still further object of the invention is to improve the low frequency response of loudspeakers mounted in small housings as in small radio receivers. ----------------------------------------------- It seems that this patent clearly covers everything that Villchur claimed in his work done about 10 years later. It is odd that Olson's patent is written to cover small radios, this makes no sense since all the theory applies to larger speakers. Why didn't they design and market bookshelf speakers? Villchur applied it to bookshelf systems and essentially changed the world but I have to say, IMO, that he did not invent the concept. He certainly popularized "small" high performance loudspeakers. I do enjoy the history, but I'm not a historian so I'm not going to go into it in anymore detail, or dig any deeper. I welcome well researched additions to the history.

I wonder how this Visaton paper cone tweeter with a smooth response would do as a replacement, with a parallel resistor to match the impedance: https://www.mouser.com/ProductDetail/Visaton/TW-70-8-Ohm?qs=VWNNG7jHlrLkQoY0VZlmUA%3D%3D Mounting would have to be worked out, perhaps 3D printed.

Next year this thread will be 20 years old, time flies!

As the title says don't want to ship but will try to figure something out if further. Anyone? Don't mind doing a few or more repairs.

I have a pair of LA woofers here that were refoamed by Bill LeGall of Millersound about 6 months ago and there's no sign of the dust caps being removed.

If you found an 8 ohm SA woofer I'd say that it was probably worked on with a VC replacement or they mixed up some LA woofer voice coils in with the SA ones. It is in the "engineering" sales literature that while they SA maintains the same F3 as the LA they lowered the impedance to 4 ohms in order to keep the system voltage sensitivity as close to the LA as possible. However, even the LA is lower than 8 ohms with the DCR usually measuring under 5 ohms. When I worked on a few SA woofers I was surprised how similar, if not the same the magnet pole piece, VC were to the LA, probably a parts commonality thing for mass production. I repair two SA woofers here with some notes: https://audiokarma.org/forums/index.php?threads/small-advent-woofer-repair-some-measurements.819443/ I measured a DCR of 3.3 ohms for the SA woofer.