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A center channel project...?


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Hey Guys,

I want to build a center channel speaker, to match my AR90's.  I'm not sure why I want to do this, other than I 'think' it will be fun.  I already have some of the drivers (a pair of AR18 woofers, a pair of AR90 LMR mids, and a AR90 UMR dome), and a spare AR90 crossover, I can use.  I might even have a set of AR91/92 crossovers, if I can find them, that I could try too.  But, my main issue is finding a suitable pair of drivers, that when wired together, will match the impedance of a single LMR.  Does something like that exist?  Did AR ever build a true 8 ohm mid or woofer?  Any thing from 4.0 to 8.0 inches would be fine.  I'm thinking that 2 smaller drivers, would work better, as this should improve dispersion.  I know I could change out an inductor and change capacitance, to compensate for an impedance mismatch, if needed.  But,  i have the crossovers, which I'd like to use as-is, if possible?  Plus, I'm still debating the layout.  I'm definitely going to use a tweeter/dome midway centered pair, with the tweeter over the mid, as in my 90's.  But, then what layout; W LMR T/D LMR W, or W T/D W?  I guess that hinges on if I use a 4-way or a 3-way crossover board?

Any suggestions?  I know I'm already crazy, so that suggestion won't be anything new to me!  B)

Thanks!

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I'd think the easiest way would be to run a single tweet and UMR in a vertical array, and one 8" lower midrange to one side with the same crossover as you 90's, but w/o the woofer section and the high pass to the LMR deleted (so that runs "full range" on the low end if it doesn't already).....if you wanted 8"W (MID/Tweet) 8"W arrangement with the woofers (LMR) wired in parallel,  theoretically whatever components are on the LMR low pass crossover, you should be able to halve the inductance and double the capacitance and get pretty darn close.  if you wire the woofers in series, you'd do the opposite (double inductance and halve capacitance)....

I'd size the enclosure something between an AR17 and 18 for 1 woofer, about double for 2.....

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Thanks!  That's pretty much what I've been thinking too.  Especially since it would be easy to unwind an inductor, and order a new cap.  Now, I just need to get this out of my head, and onto paper and birch plywood!  I tend to 'plan' forever, before any action physically happens.  I aggravate myself sometimes, by being so slow.

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  • 4 months later...
  • 3 years later...

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?

AM-JKLUtI31TmUQFNNImvfG6PX5BdguSL_WDLRyz

AM-JKLWu4eIWFlUMDbwJHisCPCQ_nk_CFvixMHL_

7a6-St05oYgeqnBaXnqTyBOTOxFyskmxQq8-C0rz

comb-filtering-20220207-20-20k-psy-jpg.1

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.

55aJGWOndFzZ_Jq0K-2VI1Cib_gDOmeqPq_qdAKt

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Years ago I measured the sealed enclosure behind the AR9 8" ' LMR. I remember it was made of a concrete former of about 6" in diameter and 6.5" long. So the volume of the enclosure was less than 0.1 cubic feet.  I hope someone else can confirm this. 

 

George

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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.

AM-JKLU6_6H0YcUAE5Eyx1ciIo8Bes9gGNo59EB8

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.

 

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I think you are right. I now remember 30 years ago,  I constructed 2 tubular structures trying to have the same internal volume as the factory AR9 LMR. But instead of looking up the original drawing as you did I just took the measurements of the the two home-made enclosures. Senior moment struck again. 

 

George

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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

255-202_HR_0.default.jpg?resizeid=103&re

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

255-210_HR_0.default.jpg?resizeid=103&re

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

255-258_HR_0.default.jpg?resizeid=103&re

 

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

255-272_HR_0.default.jpg?resizeid=103&re

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

007-6_HR_0.default.jpg?resizeid=103&resi

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:

On 10/20/2017 at 7:33 AM, Stimpy said:

I believe in at least using poly caps for the high pass, series capacitors.  Those are:

4 uF  PMPC   x 2     
6 uF  PMPC   x 2
8 uF  PMPC   x 2
24 uF  Electro   x 2
30 uF  Electro  x 2
40 uF Electro   x 2
80 uF Electro   x 2

The series capacitors will have the biggest impact on sound quality (IMHO), since they are wired in a direct line to the drivers.  So, when I recapped my AR90's, that's what I did.  Plus, it's a 'little' cheaper that way, as you can use NPE caps for the shunt values.

...but saw posts like this from the Capacitor upgrade in crossover - Is it audible? thread on ASR:

Quote

Bipolar electrolytic capacitors do work in speaker crossovers but the ac current exceeds the bipolar capacitor rated current. This result in higher distortion and shorted lifetime of the capacitor. Bipolar capacitors make a low-cost solution at small dimensions but they are wrong engineering solution and should not be used in speaker crossovers.

With my basic understanding of electronics, I can't get my head around this:

On 8/22/2021 at 11:29 AM, AR surround said:

Whatever you do, DO NOT put a Solen MKP capacitor in series with the UMR.   You will get noise and harsh sound.   I recommend using NPE's on the UMR of the AR90.

...but it appears to be corroborated by posts like this from the Capacitor upgrade in crossover - Is it audible? thread on ASR:

Quote

I will not use a Solen in series with a mid or tweeter as they can sound gritty, but across the lower range they seem to be well placed. I wonder if this is not a function of the 'dirty' sound that they portray in series, and actually shunt the dirty crud down the chain when going to ground.

...and perhaps has something to do with ESR as @iso stated in the Capacitors, the GOOD, the BAD & the UGLY thread:

Quote

One issue that should be considered when old electrolytics are replaced is ESR of capacitor. Film and foil caps have generally lower ESR`s than non polar electrolytics. When ESR of cap or DSR of choke do change, this will also change slope of crossover and this will change phase relationship near crossover frequency, especially if higher slope crossovers are used. So... upgrade can actually be downgrade, if the original design was made properly.

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.

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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!

On 12/3/2020 at 10:21 PM, r_laski said:

image.thumb.png.2c1f4d8be5b515869f325b9350d0a29b.png

IMG_0727.thumb.JPG.790bb6b73789ce0c99d1bfa7a9fb877f.JPG

I'm posting this AR9 crossover schematic and picture to show there is a second 1.37mH (6) coil in the Upper MidRange (UMR). It is the one to the right in the picture. One (outside) wire is connected to the 24uF cap and 0.2mH coil. The other (inside) wire is connected to the upper black (-) binding post. The other 1.37mH (6) coil is on the lower left corner. One wire (outside) is connected to the 0.2mH coil, orange wire to UMR (+), and 8uF cap. The other wire (inside) is connected to the 6 Ohm resistor, as shown in the schematic (resistor not in the picture).

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:

Quote

 

post-101112-1239541090.jpg

post-101112-1239683778.jpg

 

Below I have highlighted these components on the original AR engineering file dated 6 April 1981:

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Here is a revised schematic that incorporates all of the changes I found in case someone can update the library:

AM-JKLWTDuDM7TTxudeIikM2FM9PBSN24QyOPRy3

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On 2/24/2022 at 7:20 PM, bjmsam said:

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.

Another possible alternative is to get hold of an AR58, AR91 or AR915.  All three use the same drivers.  I am using an AR915 as the center channel speaker between two AR9's and I am pleased with the results.  I found that having a big 12" woofer in the center channel speaker makes a positive difference in the sound quality.  The AR91 has attenuation switches to better match the output of the tweeter and midrange to the AR9's if necessary.  The AR58 and AR915 do not have the switches.

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On 2/27/2022 at 10:26 PM, AR surround said:

Another possible alternative is to get hold of an AR58, AR91 or AR915.  All three use the same drivers.  I am using an AR915 as the center channel speaker between two AR9's and I am pleased with the results.  I found that having a big 12" woofer in the center channel speaker makes a positive difference in the sound quality.  The AR91 has attenuation switches to better match the output of the tweeter and midrange to the AR9's if necessary.  The AR58 and AR915 do not have the switches.

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...  🙃

AM-JKLVg75Ne_sfOiF4yADCZMBI5vHMcvAlZZyE8

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? 🙂

AM-JKLVkew-1h8lBqjkJAfkGnZt3NsgFp5dL7EgP

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Excellent work @bjmsam.  Vey inventive use of a cabinet door too...!  :D

I don't have any spare mids or tweeters, but I did buy a set of acoustic blanket from an AR-91, for my "center speaker project".  It's not the full piece, like 9s and 90s use, so it wouldn't cover the LMR woofer.  It'd cover the UMR and tweeter.  You're welcome to one, if interested?  I'll save the second for my dream center speaker...!  ;)  Until then, a spare AR-92 works well as a center too...!  :rolleyes:

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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."  😉

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I'm no crossover expert, but your cap choices look good.  All the correct values too.  Even the 8.0uF shunt.  Poly for the series capacitors, and NPE for the shunts, is a good cost savings move as well, since poly caps would be most effective for the series values.  I've done that too, depending on speaker coast and parts budget.  Good find on the 80uF cap as well.  I didn't even know Mid West Speaker sold capacitors.

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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).

AM-JKLUK69hjyk-DYkuByOE9booiSKvKptmTpaIV

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:

AM-JKLU1VqgYgou54cIfwyaBtedKf8PZu4D6wwmB

LMR ZMA:

AM-JKLXIoh2QHORPB4KQrh4ytpFie_9foino0aUO

LMR AR Spec network:

AM-JKLUXOst2ziHdxfbjLHgHxURD55mILnh4MLhO

LMR AR Spec response:

AM-JKLUrIom0rYDkf-389benxgjoQHpBvZo3hQXa

 

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. 🙂

AM-JKLWY2xaQ0KLHVhrK3-lIU3gRyhFMikc7AFEY

AM-JKLU9gw6q5s-Mg6XwJyNj37f5YOne2P83Npg4

AM-JKLWa-GrlY0nwPwrs3YwXklYIhNgX0yvvaze7

 

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Parts Connexion sells Axon poly capacitors.  Axon caps are made in the same French factory that makes Solen caps.  Some very decent prices, that could allow the use of more poly caps, or save money, whichever is best.  I used Axon for the shunts on my AR-90s, with no issues.  I used Mundorf for the series caps, which worked out great.  Very open and detailed caps, with a very palpable midrange.

NPE caps shunt to ground.  But, they do help roll off the high end of the woofers.  So, their effect on sound can be audible.  Use the best you can.

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On 3/1/2022 at 2:27 PM, Stimpy said:

And most would recommend this:

NPE 80uF 100V $2.43 :huh:

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!  ***

AM-JKLW_2N79t9hQm2bmmeyI5xn9_kANq_QnXx2K

Example tolerance:

AM-JKLW71zLbDxtZRYvwfv6EwqnetszrtWApNT_U

Tweeter and LMR:

AM-JKLWy9ebWvUHkhNYO9UFzUJBHW8Zb3fGb2xbA

Test fitment of all three drivers in my "cabinet:"

AM-JKLWpbUtTcF-gmHsgON0PtdUktnNxJQlqMeN7

 

On 3/1/2022 at 1:04 PM, bjmsam said:

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.

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:

AM-JKLX45Cy6vsqMptkW6eoYmXa77nHcNSFUcsks

UMR:

AM-JKLWq9iSlcysx6G0cxSYKSVWS54LLB1fAd5jz

LMR:

AM-JKLVVBiHllO3jC5ikDYS8siY4UJuwmdP2KCgB

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).

AM-JKLXYTnHu4D_564-5NUsEGX6LfpAKWIn590yR

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.

AM-JKLUbT3sYPfDD6CGlIgVzmaV4yo9jR-jc4Zxn AM-JKLXuGU8G9CRsHznxVZ6rirsKzlXPMOlYyYVm

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:

AM-JKLUcuN6_O56_ZAmCSkuxZJogDN5UQAK6ls3c

MM-2044.pdf

MM-2044.frd MM-2044.zma

MT-4121-4.pdf MT-4121-4.frd MT-4121-4.zma

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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:

AM-JKLWm2Hb3vUjmy7O9zEF2Lbeiml40ygn-eGNa

UMR:

AM-JKLU6FZa3XxiY6ADFoAyTGhL2qC-BXSnVJrJw

LMR:

AM-JKLU3omLXCCc3GSw1tTNEW-OqDoHzLvC2-5bf

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).

AM-JKLW_-6ALlBguAfTJvPbBAKXBBJnhTU7NIfFe

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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).

AM-JKLW2e-RREQjjxm5hSHzuAmMP0D-fpSkArTkY

AM-JKLUzTuWkSMbCiY_qPkKEnJHbsy5d3d7lUWxO

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.

AM-JKLWmxfKamzjcc5lCLQ3wVpqq2tIdM46S77pw

AM-JKLWM0VFLm333b1f0Ghrr1fMZR9BxmZBQo5X-

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!

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The first graph compares the response predicted by XSim for the AR spec crossover (red) and my crossover (green) to the response of my center speaker C (purple) as measured by an Audyssey microphone positioned on-axis aimed between tweeter and UMR from 1.0M, 2.0M, and 3.0M (RMS average).  The screen was not in place, Audyssey was off, and a GFA-585 was used for C (swapped with R temporarily).

AM-JKLVxWJVeVHy5jhP7Ejmx69YD3-LcATlqeiX1

 

The second graph compares the response of C alone (purple) vs. C with L+R handling frequencies below 200Hz (green) vs. R alone (red) as measured by a calibrated UMIK-1 positioned on-axis aimed between tweeter and UMR from 1.0M and 1.5M (RMS average).  The screen was in place, Audyssey was off, and a GFA-2535 was used in bridged mode for C.

AM-JKLVknMcK-Q-vHM1LMpk_B6nbpk1_BELg1I12

 

The third graph compares C with Audyssey off (purple) vs. C with Audyssey on DEQ off (orange) as measured by a calibrated UMIK-1 positioned at three locations left, right, and center of the MLP (RMS average).  XSim traces are included at the top for reference.  The screen was in place and a GFA-2535 was used in bridged mode for C.  The orange trace approximates what I hear when listening to content.

AM-JKLX2sFfRu9aEfWvYMlAMQNZVbyYDTy4_TlxW

 

Observations:

  1. The SS AR-12000840 Acoustic Research Genuine .75" Dome Tweeter seems uneven (but so is that section of the crossover, presumably to match the original 200029 driver - the AR9 R on-axis (red) trace in second graph looks flat); it would be interesting to see how the MW Audio MT-4121: .75 inch Dome AR Copy Tweeter measures in comparison.
  2. The MW Audio MM-2044: Acoustic Research Copy Midrange UMR seems to perform well, and arguably is most important.
  3. The AR 200027 original driver LMR is not performing to the spec below, which seems unrealistic.

From the library:

AM-JKLWiGMqIKasnaGnMQB0M5aTPdTCH_ZNJn9KD

 

I had overlooked Note 11 during assembly so just now stuffed the LMR enclosure with Roxul AFB to see if it would smooth and extend its frequency response but noted little difference between with wadding (light purple) and without wadding (purple).  Included for reference is the AR curve (red) digitized from the AR graph above and the crossover response predicted by XSim seen earlier.

AM-JKLXkwVtCd8cjYH0e8ghkMBZdHAdcIsVdRwMG

What I am measuring is consistent with what XSim predicts for the AR spec crossover (and my crossover is very close, at least when ignoring unknown ESR and DCR values).  Even ignoring my room challenges (note similar boost above and suck-out below 300Hz in my AR-3a curve), I really don't see how an AR spec LMR driver (which I am using) could roll off so low or steep without a change to the crossover.  Adding the woofer section of the network to XSim did not change the curve significantly above 200Hz.  I simulated some straightforward changes to my crossover that might help (comparison below) but probably won't bother since the HPF in my AVR seamlessly routes those frequencies elsewhere (green AR9 C on-axis sub 200 trace in second graph) and all of the speakers working together as a system sound well integrated.  I am very pleased!

AM-JKLXWItv8wjI-G15HiS6nyuW5wHbfcGVPLUNU

 

On 10/19/2017 at 12:43 PM, Stimpy said:

I 'think' it will be fun.

It sure was!  Thanks again for the inspiration and input.

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