bjmsam

Introducing the AR9C! 🙂 For the acoustic blanket I used 1/2" thick F26N wool felt with adhesive backing, which seems like a very good alternative (more here). Here is a quick look before I re-hang the screen. The red protective ring pressed in over the LMR mounting flange (to help form the felt while repairing my cut irregularities) was popped out before use. A quick test confirmed that it works and sounds great! The timbre is consistent across the soundstage, dialogue localization is much improved off-axis, the comb filtering effects are gone, and I can't tell that lower (less directional) frequencies are from left and right rather than center. REW measurements coming soon!

The crossovers are finished! The photos of the backs below are flipped to align with the fronts so it's easier to double-check the circuits. I didn't think to use red and black for all input jumpers before tackling the UMR (last) but annotated them that way below to differentiate between amp in and speaker out. The hole in the right UMR board is due to not measuring twice before drilling - doh! I am reasonably happy with how these came out as my first attempt at building crossovers (constructive criticism welcome!), and there is room for 4uF and 6uF MKPs on the TWTR board if I decide to replace the NPEs. TWTR: UMR: LMR: Here they are mounted to the back of my "cabinet." And I found the perfect LMR enclosure in my barn (the "crock" material is very dense but I adhered an 80 mil dampening membrane to the thinner bottom to avoid any resonances).

Well, considering the shallow depth of my enclosure, the original AR design around NPE caps, and the analysis posted in such threads as Capacitor upgrade in crossover - Is it audible? ("according to these measurements a film capacitor does not make a better sound when used in the crossover compared to an electrolytic capacitor") and Cap Value Accuracy ("At this point my opinion on using new npe's has improved considerably, and I no longer believe the "high" measurement results to be one of questionable npe quality. I strongly suspect better npe's last much longer than they are given credit for in speaker forums."), I opted to see how the speaker measures and sounds with smaller NPEs before pursuing MKPs (easy enough to replace, so nothing but a few dollars to lose). All of the parts arrived today and I began laying out sections of the network. Exciting! *** WARNING! Images of crossovers with NPEs rather than MKPs below! Viewer discretion is advised! *** Example tolerance: Tweeter and LMR: Test fitment of all three drivers in my "cabinet:" Attached are the spec sheets MSR provided for their MW Audio MM-2044: Acoustic Research Copy Midrange and MW Audio MT-4121: .75 inch Dome AR Copy Tweeter (Simply Speakers has no documentation on their SS AR-12000840 Acoustic Research Genuine .75" Dome Tweeter and recommended that I "try the AR forum"). I used WebPlotDigitizer (very slick!) to generate CSV files representing the frequency response and impedance curves and loaded them into XSim as FRD and ZMA files, respectively, to model the AR spec UMR and TWTR sections of the crossover network (using default ESR and new inductor DCR values since that's all the info I have). Below is how XSim models each network with AR Spec values vs. new component values as received. TWTR: UMR: LMR: Below is how XSim models all three sections of the upper network together with AR Spec values vs. new component values as received vs. new component values with inductors unwound to AR Spec (which is all I can and will do). The Air Core Inductor Designer / Calculator estimate was very close; I had to unwind 49" to adjust the LMR inductor from 2.77mH to 2.63mH. Since my AVR has an adjustable HPF for the center channel that can be set no higher than 250Hz, I considered omitting (or further increasing the value of) the 84.9uF capacitor in the LMR section of the network for more flexibility, but XSim predicts significant attenuation at higher frequencies: MM-2044.pdf MM-2044.frd MM-2044.zma MT-4121-4.pdf MT-4121-4.frd MT-4121-4.zma

Thanks! That presents an interesting comparison: Solen 80uF 400V $40.00 vs. Dayton 40uF 250V $13.96 + Dayton 40uF 250V $13.96 = $27.92 vs. Axon 39uF 250V $7.45 + Axon 41uF 250V $7.83 = $15.28

Thanks for taking a look! MSR does have a nice selection of Solens, though surprisingly not the 24uF sold by PE. I asked about use of NPE caps for shunts in the Capacitor upgrade in crossover - Is it audible? thread on ASR and the first reply includes, "Shunt vs. in-series doesn't have much impact as they are all effectively in the signal path" and "if you are recapping an old speaker, please be aware that the crossover designer may be expecting some series resistance to exist across some of the caps and there could be a negative impact if the replacement caps have no ESR even if they are better caps." Earlier in the thread, someone else stated, "Whenever I replaced electrolytics capacitors to film, speakers became overly bright, after some time I have to put back the original caps." 🤔 Tweeter: The 0.100mH inductor seems close enough to AR spec 0.105mH. According to the resonant frequency calculator, the difference for the 4uF cap section is 7958Hz vs. AR spec 7766Hz and for the 6uF cap section is 6497Hz vs. AR spec 6341Hz averaging 7228Hz vs. AR spec 7053Hz. Using a 4.2uF cap and a 6.3uF cap with the 0.100mH inductor would match the AR spec precisely (7766Hz and 6341Hz averaging 7053Hz) with < 0.5dB boost in amplitude (at frequencies my "AT" screen likely attenuates anyway). UMR: I should be able to unwind the two 1.4mH inductors to achieve AR spec 1.37mH. Given N turns in the 1.4mH coil, I would expect to remove N*(1-sqrt(1.37/1.4)) turns or about 1.6ft. (Credit: Ron E at DIYAudio and Air Core Inductor Calculator, Air Core Inductor Designer / Calculator, etc.) This section of the crossover network is most enigmatic; @RTally and @Pete B offered insight in the My AR-9 Capacitor Recap/Upgrade Project thread. LMR: I've read that NPEs work well for the lower frequencies, and my AVR will pass through to the center channel only frequencies above whatever threshold makes sense, so perhaps I won't spend $40 on a "better" 80uF cap. Regardless, I should be able to unwind the 2.7mH inductor to achieve AR spec 2.63mH and confirm with my LCR meter. Are the Equivalent Series Resistance (ESR) and Direct Current Resistance (DCR) values known for the original AR spec capacitors and inductors, respectively? Are Frequency Response Data (FRD) and Impedance (ZMA) files available for the original AR 200027, 200028, and 200029 drivers? I loaded XSim with the FRD and ZMA files that @Zilch posted in the Crossover mods for the AR4x II thread to approximate my LMR but have no leads on files for the UMR or tweeter. LMR FRD: LMR ZMA: LMR AR Spec network: LMR AR Spec response: The AR9 is rated to handle 400W input, at which power XSim estimates the 4uF capacitor will see the most voltage at just under 100V, while the 6Ω 22W resistor will be expected to dissipate over 42W (or 32W at 300W input, which the AR90 is rated to handle with virtually the same crossover). The Dayton resistor on my parts list is rated for 20W, which would be reached at about 175W input, but I won't worry about it any more than AR did. 🙂

Yes, please! I suspect it is more effective for the tweeter and UMR than the LMR anyway. Thank you! Meanwhile, I'm eager to see what you put "onto paper and birch plywood." 😉

Thank you for the suggestion! With <6" between the acoustically treated wall and the acoustically transparent screen, a custom build seems to be the only feasible option. Elevating one of my AR90s front and center to align its tweeter, UMR, and LMR drivers with those of my AR9s, setting the crossover to 200Hz (also tried 250Hz to simulate potential inductor differences, since I have found only 2.5mH/.88Ω and 2.7mH/.92Ω vs. 2.63mH/??Ω), reversing the phase, adjusting the timing to account for the distance, and playing source material that panned across those three channels sounded seamless to me! Pushing those three drivers behind the screen would be perfect. My research uncovered your AR915 Crossover Help thread among many others and I sincerely appreciate the perspectives offered through insightful banter between you and @Stimpy (the OP of this thread!), @ra.ra, @DavidR, @ar_pro, @Carlspeak, @RoyC, @r_laski, @Pete B, @tysontom, and other experts from whom I am benefiting tremendously. Many of my questions posed above are from differences of opinion expressed, as I have no opportunity to audition identical speakers with Daytons vs. Solens vs. Mundorfs, or all poly vs. all NPE vs. a hybrid (shunts), etc. With the help of this forum, I hope to assemble appropriate crossover components the first time and avoid purchasing any that are incorrect or inaudible. Thank you! Meanwhile, I knew those 3/4" MDF cabinet doors from an old kitchen renovation would come in handy someday... 🙃 So far I have only an original 200027 LMR driver and no leads on an original 200028 UMR driver or an original 200029 tweeter. Any opinions on the MW Audio MM-2044: Acoustic Research Copy Midrange and SS AR-12000840 Acoustic Research Genuine .75" Dome Tweeter as alternatives? And where can I find an acoustic blanket? 🙂

According to the comment from @r_laski below, the schematic posted in the library has at least three errors (the mislabeled cap I noted above, a missing inductor in the upper section, and a missing value on an inductor in the lower section). Why hasn't it been updated? It would be a shame for someone to assume the library reference is authoritative and be misled! The diagram and photo below posted by @mluong303 in the AR9 crossover parts verification thread from 2009 highlight the two of those three errors in the schematic that are relevant to my project: Below I have highlighted these components on the original AR engineering file dated 6 April 1981: Here is a revised schematic that incorporates all of the changes I found in case someone can update the library:

Thanks, George! It seems unlikely that the original drawings were available 30 years ago when you needed them. 😉 For anyone willing to help a crossover noob: I have exactly zero experience but understand some values are more critical than others. Are these close enough to those indicated in the schematic? The Acoustic Research Crossover Inductors (Classic) thread suggests that none of these will work and I must look for old parts or wind my own, while the AR9 crossover parts verification thread shows that some of these are closer to AR spec than the original inductors... For AR spec: 0.105mH Jantzen Audio 0.10mH 0.13Ω 18 AWG Air Core Inductor Crossover Coil (5% under) Part #255-202 Per item price: $4.51 For AR spec: 0.20mH Jantzen Audio 0.20mH 0.2Ω 18 AWG Air Core Inductor Crossover Coil Part #255-210 Per item price: $5.30 For AR spec: 1.37mH Jantzen Audio 1.4mH 0.65Ω 18 AWG Air Core Inductor Crossover Coil (2.2% over) Part #255-258 Per item price: $11.29 For AR spec: 2.63mH Jantzen Audio 2.7mH 0.92Ω 18 AWG Air Core Inductor Crossover Coil (2.6% over) Part #255-272 Per item price: $15.33 For AR spec: 6Ω 22W Dayton Audio DPR20-6.0 6 Ohm 20 Watt Precision 1% Audio Grade Resistor (2W low) Part #007-6 Per item price: $4.98 For AR spec: 4uF 100V Solen 4uF 400V $6.00 For AR spec: 6uF 50V (schematic also shows 6uF 100V!) Solen 6uF 400V $7.00 For AR spec: 8uF 100V SHUNT (schematic correction for 6uF 100V?) NPE 8uF 100V $0.81 For AR spec: 24uF 100V Solen 24uF 400V $13.69 (see @AR surround's concern with this quoted below) For AR spec: 30uF 50V SHUNT NPE 8uF 100V $0.81 NPE 22uF 100V $1.04 For AR spec: 40uF 50V SHUNT NPE 40uF 100V $3.50 For AR spec: 80uF 100V Solen 80uF 400V $40.00 I based those capacitor choices on posts like this: ...but saw posts like this from the Capacitor upgrade in crossover - Is it audible? thread on ASR: With my basic understanding of electronics, I can't get my head around this: ...but it appears to be corroborated by posts like this from the Capacitor upgrade in crossover - Is it audible? thread on ASR: ...and perhaps has something to do with ESR as @iso stated in the Capacitors, the GOOD, the BAD & the UGLY thread: My AR9s were recapped about 15 years ago and the originals I kept had the following measurements: 4uF 100V: 7.6uF 6uF 50V: 14.6uF 8uF 100V: 7.8uF <-- presumably this goes across the UMR rather than the 6uF 100V shown in the schematic? 24uF 100V: 24.8uF 30uF 50V: 34.6uF 40uF 50V: 52uF 80uF 100V: 86uF Potential alternative: The ACOUSTIC RESEARCH AR 9 & AR 90 REPLACEMENT CROSSOVER CAPACITOR KIT sold by Vintage-AR that "replaces all the tweeter and upper midrange capacitors in one cabinet" appears (from the photo) to include seven caps but no values are listed.

Thank you! According to the AR drawings (kudos to @dxho for indexing the TIFF files), the dimensions of that LMR enclosure are 9-in (outside diameter) x 3-in (inside depth), so the total depth of a 3/4-in MDF enclosure would be 4.5-in, which will fit behind my screen. I managed to source an original 200027 driver, but in case I am unable to find 200028 or 200029, I would appreciate opinions on this UMR and this tweeter as substitutes, and whether it would be better to find a crossover to modify or to just build one from scratch.

So much innovation. Thank you for posting! (I have the 9, 90, and 94 from that series and was tempted by the 91 but would have had to give up the 3a due to space)

I am considering this as well, specifically to eliminate annoying comb filtering effects associated with my current phantom center channel configuration. According to Engineering the AR-9, the tweeter and UMR are fully sealed while the LMR is mounted in its own acoustic suspension enclosure. Is the volume of that enclosure known? I need to determine whether it is feasible to build something that fits behind my AT screen. Judging by the AR-9 schematic, the crossover for these three drivers conveniently is separate from that for the woofer section I will exclude (C below 200Hz will be routed to L+R). Have any of you completed this project? I am not willing to cannibalize my AR90s but essentially want to install a set of front drivers behind the middle of my screen flanked by my AR9s.

Thanks for the terrific overview, Steve! I am looking for background on my T830 and A60-II, but there is nothing in the CSP library, and including "brochure" as a search term revealed this thread. Any suggestions? Interesting: Ken Kantor posted, "I had a pair of T830's in my stable of "competitive samples" for several years... a very nice speaker for the $$."