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Moving on from inductors in my insane pursuit of a passive crossover that is audibly indistinguishable from active, I turned my attention toward mid/high frequency gain reduction that horn loaded systems can't live without.   About 6 months before I was born, PWK published this paper supporting his use of auto-(Greek for self or one)-transformers instead of resistor pads. Automatic transmissions and washing machines! What will they think of next?! : )   The autotransformer (AX) route is interesting in part because it's WAY more expensive than a resistor - so why suffer the expense when they worked so hard to cut costs in every conceivable way to survive in the market? There must have been some choice words to PWK from whoever kept the books back then...   Be thankful that the engineer won this one. From my measurements, a well made AX behaves almost identically to active gain control, while the voltage division provided by resistors do not and can not. Is the difference audible? Probably not. IF you drive the loudspeaker at very low levels so the voice coil remains cool enough not to increase its impedance.   PWK's article claimed two AX advantages: 1. They allow user adjustable gain changes without screwing up crossover behavior. 2. They reduce series resistance from the amp to the driver, thus improving electrical damping with measurable improvement in the acoustic domain.   Claim #1: Is true and false.   Is not true unless you parallel a 10Ω (or thereabouts) resistor across the input of the AX, as recommended by @Al Klappenberger and others. The problem with this is that the lower impedance seen by the crossover will increase costs (larger caps) to maintain the same high pass behavior. Maybe the guy that kept the books won this round.   The great news is that this isn't a problem for us and we can use a 10Ω "swamping" resistor to give us a nearly flat 7Ω compression driver - thus claim #1 is fulfilled! BTW, you can't just add the resistor - you'll need to redesign the crossover.   Claim #2: Is true and false.   It is true that the AX results in almost zero added series impedance to the driver, and not just because of low DCR, but the electrical impedance transformation (the greater the gain reduction selected, the lower the impedance the driver sees). Remember this is an AC circuit. The swamping resistor improves things a bit more. BUT does this increase in electrical damping really make a difference to a horn loaded driver that gets the majority of its damping through acoustic impedance? BTW, acoustic impedance is the reason to fall in love with horns if you haven't already.   PWK's paper shows a measurement from an experiment he did in a shootout between the AX and a resistor based pad. I repeated the experiment this morning. For the most part. Unfortunately, PWK did not detail the measurement setup, but he did employ a two different passive crossovers, one designed for the AX and the other for the resistive pad. I don't like the smell of that and prefer to hold all variables constant excepting, in this case, the gain reduction method.   Even if PWK had revealed the crossover components used, the stuff available today wouldn't be the same, thus it's impossible to recreate his experiment exactly, which is fine with me as I already implied. The other items that aren't available to me are the driver/horn combination and AX model he used, but what I used instead is more relevant to us - a Crites A-55-G on a K-400 horn with the Crites 3636 AX. The quality of this setup and the possibly additional acoustic impedance of my '74 vintage horn could be the reason I saw no improvement I could attribute to the higher electrical damping of the AX method.   Thus I'll assume PWK's setup used a lower quality (by today's standards) driver/horn/AX system than my stuff and as a result, the significantly higher electrical damping that played a role in reducing driver ringing for him, didn't help in my system.   All is not lost, the AX remains a superior method of passive gain reduction for additional reasons that'll be shown later.   My measurement setup used a 14.7Ω series resistance that resulted in a mid-passband 6dB SPL reduction from the driver/horn system. The 3636 AX -6dB gain setting nailed that SPL reduction exactly (0-5 input, 0-3 output).     Is it ringing yet?     Where's the meat? In the 3636 of course.     From an email exchange with Bob Crites about the 3636: On 30, Dec, 2016, at 3:14 PM, Bob Crites <...> wrote: When I had the autotransformers made, I went to the same place that built them for Klipsch.  I just asked if there were any improvements they could suggest over how they made them for Klipsch,  I was told that Klipsch had them sized for a maximum continuous rating of 40 watts.  That saved them a buck or so each compared to the standard 100 watt rating.  So I just told them to make them as good as they know how to make them and rated at the 100 watts.   I am a fanboy of the Crites. Bob was a gentle member of the No BS club. Salt what I say about them as you wish, but (proper) measurements don't lie (includes the T2A) in another post. I'm planning on three: My version of PWK's experiment, an impedance analysis attached to a driver/horn system and a transfer function analysis that includes wideband low-level and max. wattage, both into 10Ω.   God bless you and your precious family - Langston

LOL.  That was a ridiculous gaff.  Mine are going in the corners.  Already asked Roy a bunch of questions about placement in my room (with pictures) in a Facebook group thread.  He's so great about answering people's questions.

Roy has already stated that the YouTube video is in error due to showing the Jubilees outside of room corners--which are still required. (He said the marketing guys took a few liberties in the video without asking him first.)  If you were thinking about buying a pair and pulling them away from the room corners--think again.  Adding the horn lens change is just a small concern as compared to that error.   Chris

Well, then complain to whoever wrote the text for the video because that's what it says.  🙂 

Roger Waters denies ‘powerful idiot’ Mark Zuckerberg’s bid to use Pink Floyd song in Instagram ad: ‘No f—ing way’     https://m.youtube.com/watch?v=8IFVVmT2YhE  

The mounting bolts are quarter inch diameter. Shortly after getting my K-402s, I made a decorative frame to hide the extra holes.           The trim improves the appearance and does not affect the sound of the horn. I like the look of the wider frame on the New Jubilee.      

That's not a phase plug--it's actually an acoustic horn lens--mounted at the horn throat entrance.    Phase plugs are important to prevent high frequency cancellations, while horn lenses are used to spread out the polars via "refraction".    The only issue is that you also get unavoidable diffraction from horn lenses--just like the optical varieties do, too. It's a toss up whether the diffraction overcomes the refraction capabilities of the horn lens.    Chris

Are you going to build Klipschorn style bass bins? If so Altec 511B horns would be a better fit.

Up for grabs,  perfect condition, working without any issues  Velodyne F-1500 B  local pickup 92620  $400.00   

An excellent movie! We watched it a couple months ago. Very well done.