Vandersteen 2Ci Design Overview and XO Schematic

Pete B

AK Member
Subscriber
I reverse engineered the Vandersteen 2Ci back in 1994 and am posting the crossover
schematics here in order to help others that have problems with burnt out resistors and
for general educational purposes. I never intended to post these in public and never
redrew them with CAD tools. I chose to show how component values were built up from
smaller values, obviously it can be redrawn with some simplifications.
Don Keele's extensive review of the 2Ci in the June 1992 issue of Audio page 73 in the .pdf:
https://www.americanradiohistory.com...io-1992-06.pdf

Stereophile measurements of the 2Ci unfortunately before he got better measurement gear:
Vandersteen 2C loudspeaker Measurements | Stereophile.com

The 2 series has gone through several model revisions over the years including parts
changes even with the suffix retained such as 2Ci. From what I remember speaking
to RV the rear plate has Model 2 written on it but the serial number will end in a letter
if it is a later model. My serial numbers end in i for example.
Mine have 1" Audax ferro fluid cooled tweeters, Peerless poly cone mids that look
exactly like the 821615, custom Vandersteen 8P2C woofers and a stamped frame
acoustic coupler. Both woofers have rubber edges and the mid has a plastic edge - no foam.

TWEETER - out of production:
The tweeter is an Audax DTW9X8T25FF8, the 9X8 is the rectangular face plate size in
cm, 25 is the dome size, FF indicates ferro fluid, and 8 for the 8 ohm version. There were
many versions of this tweeter, the DTW100 was the 100 mm round version, there were
4 ohm versions, and I think big and small magnet versions. This has a small face plate
and was probably the small magnet version. This has a hemispherical dome, the next
version in the evolution had a catenary shaped dome. This is the current production of
the big magnet, catenary dome version with a bigger rectangular face plate:
https://www.madisoundspeakerstore.c...-12x9-1-textile-dome-tweeter-with-ferrofluid/
I have the data sheet around here somewhere for the correct tweeter and will try to find it.

MiDRANGE - out of production:
Peerless 821615 midrange spec sheet:
http://www.madisound.com/pdf/peerless/821615.pdf

WOOFER - custom by Vifa:
I was working on a design inspired by the 2Ci around the time that I did this work,
and I ordered a pair of the Vifa P21W020 which were the closest stock Vifa to the
custom 8P2C. This Vifa woofer has been brought back by Scan Speak under the
same P21W020 part number and the spec sheet and response curves look like a
cut and paste from those from Vifa:
https://www.madisoundspeakerstore.com/approx-8-woofers/scanspeak-classic-p21wo20-8-woofer-poly-cone/
What is interesting is that I measured the 8P2C and the Vifa woofers and the Fs of
the Vifa s measured higher than spec and Vas lower making them very close to the
8P2C. Visually they look the same except for the edge being slightly wider in the
8P2C. They sounded the same with the 8P2C handling very slightly more Xmax.

MID/TWEETER CROSSOVER
First is the mid/tweeter crossover, it can be seen to be a simple 1st order cap to the
tweeter, one ohm fixed resistor pad, an Lpad, a shunt 20 ohm fixed R, and an RLC
with a resonance at 918 Hz - very basic.
The mid also has basic HP and LP first order filters with an Lpad and some shunt
resistance to flatten the driver impedance.
VAN 2Ci MT XO.jpg

WOOFER/ACOUSTIC COUPLER CROSSOVER
Second is the woofer/coupler crossover with a 2.8 mH inductor providing some baffle
step and a total of 554uF HP to the main 8" woofer and a huge 20 mH inductor to the
10" acoustic coupler (AC) assist. They share a common air cavity with the AC coupled
like a passive radiator but with drive to boost the output. Keele, in his Audio Review
confirmed this by disconnecting the AC and noting the change in output level around
Fb the box AC resonance. That was 38 Hz from memory with 5 dB of boost. The AC has a
thermal switch that trips at about 5 minutes into a bass heavy track played at a level that I
like, it is also close to the displacement limit of the main woofer. Some say that the switch
doesn't age well and the trip point lowers and suggest removing them. Note that in
the next post the picture of the woofer inductor has the number 3 on it and I seem to
remember it being 3 mH and I'm not sure why my notes have 2.8 mH instead.
Edit: Notice the date on my notes of 1994 so that was a while ago, when I wrote the above
I forgot that the picture below is of the 2Ce that probably has a 3.0mH inductor but thinking
back I now trust the 2.8mH value in the schematics for my 2Ci s.

VAN 2Ci W XO.jpg

ACOUSTIC COUPLER MEASUREMENTS:

PICTORIAL XO LAYOUT
Third is a pictorial layout of the double sided circuit board which is glued in and very
difficult to remove so I didn't. I used an ohm meter to confirm how the traces are
connected.
VAN 2Ci XO PICTORIAL.jpg

CABINET SIDE VIEW
Fourth is a side view where I measured the driver offsets in order to enter them into
CALSOD, the program I used to model the system.
VAN 2Ci SIDE.jpg

CABINET FRONT VIEW
Fifth is a front view providing the height positions of each driver also for use in the
CALSOD program.
VAN 2Ci FRONT.jpg

CROSSOVER BOARD PICTURES (2Ce burnt resistors)
Next is a snapshot of a 2ce crossover board, not this model but looks exactly like mine:
VAN 2Ce XO front.jpg

And the back:
VAN 2Ce XO REAR.jpg
 
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Have always found Vandersteen design philosophy intriguing. An epic crusade in pursuit of perfect time and phase alignment. Haven't seen a post detailing workings of the crossover like this. Though analysis from your level of how "basic" much of this is has me wondering what "complex" must look like! :yikes:

Between my poor viewing monitor and even worse eyesight, I squinted a bit over the schematics. So I amused myself by sketching them in Paint (a welcome diversion from ruminating over pandemic confinement).

Vandersteen_2ci_C.png

Vandersteen_Woof.png

Haven't necessarily gained a better understanding from this. But these days afford ample time to ponder further ...
 
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Don Keele's extensive review of the 2Ci in the June 1992 issue of Audio page 73 in the .pdf:
https://www.americanradiohistory.com...io-1992-06.pdf
He notes that the newer 2Ce model is about to come out so these are very late model 2Ci s.

I always enjoyed reading Don Keele's speaker reviews in Audio because of his excellent
measurements and in depth analysis. It is interesting to note Vandersteen's rated on axis
frequency response of 28 to 29 KHz +/-3 dB and 32 to 21 KHz +/-1.5 dB. This is very
optimistic but not uncommon for manufacturers, Keele writes:
"Salient points of the on-axis curve include a somewhat rough overall response, a gentle
peak-dip combination at 250 and 500 Hz, and a sensitivity of 86 dB, moderately lower
than rated. The curve fits within a fairly tight, +/- 2.5 dB window from 70 Hz to 20 KHz
and is 10 dB down at 35 Hz. Below 40 Hz, the response rolls off at about 18 dB/octave.
A right/left comparison revealed a close, +/- 0.5dB match except for a narrow band
between 3 and 4 KHz, where the levels differed by +/- 1 dB. Note that all measurements
were taken with the grill on, as it is not designed to be removed."

Later in the review Keele does an experiment where he disconnects the Acoustic Coupler
on the rear and vector sums the outputs from the two woofers. He finds that the Acoustic
Coupler drive boosts the output at box tuning of 38 Hz by 5 dB. This is very similar to a
B6 alignment where a peaked high pass provides 6 dB of boost. The -3dB frequency of the
woofer system is lowered from 51 to 43 Hz.

I grew up building my own speakers so these were the first high end speakers that I ever
owned and lived with for several years. My impression of the bass is that it is about equal
to a Large Advent that is also a few dB down in the low 40s, however I often felt that when
the bass notes hit the Acoustic coupler range it seemed as if the source moved to the back
of the system - just a minor annoyance. In time I felt that the 2Ci had a very complicated
woofer system to get bass about the same as a Large Advent. I also felt that they should
reach lower given the spec of -3dB at 28 Hz.

The 2Ci does not pass the sit down stand up test as Keele measures and is well known for
1st order systems with non-coincident drivers the vertical off axis response is quite bad.
So these are only for seated listening.

Keele does his distortion measurements at 50W (20 Vrms) input where the system
produces 96 dB at 41.2 Hz, 101 dB at both 110 and 440 Hz.

Keele does a test where he applies a very high power (kilo Watts) short term burst in order
to explore the displacement limited output without worry for thermal limits. The system
does very well in this test Keele writes:
"With room gain the system exceeds 110 dB above 55 Hz and 120 dB SPL above 180 Hz."

Those are good numbers, the 120 dB figure is not usable because it requires so much
power, and Keele notes that the system is taking 300W just above 38 Hz in the bass
range. I would expect these speakers to work well with a 200W/ch amp except for the
thermal cutout activating with long bass passages.

The problem with the bass is that the thermal switch limits the useful level in my
experience, Keele writes:
"The woofer-protection circuitry was triggered above about 18V rms (46.3W into 7 ohms)
at 38 Hz. From a cold start, at this frequency and level it took about 20s to engage." He
mentions LEDs on the front illuminating, my 2Ci s do not have LEDs.
I'm not sure but I believe that the LEDs and perhaps the thermal cutout were deleted in
later 2C revisions.

It is clear that they do not want you driving this system very hard, the 10 ohm resistors in
the midrange path are only 2W and there are reports of them burning out. RV knows he
can up the wattage on those but I think that they are a way for him to know when a system
has been over powered. He asks customers to return them in such cases which is going to
be very costly just for shipping.

Keele states that the phase fits a window of +/-45 deg from 180 Hz to 20 KHz but it seems
to me that it fits about +/- 25 deg from 200 Hz to 20 KHz - much better. That is a good spec
especially considering the design.
 
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I reverse engineered the Vandersteen 2Ci back in 1994 and am posting the crossover
schematics here in order to help others that have problems with burnt out resistors and
for general educational purposes.

Nice work Pete!

I do have a question though. In the midrange circuit the series coil is marked as .08mH. Is that right? It seems kind of small for a 5KHz crossover to the tweeter. What am I missing?
 
Have always found Vandersteen design philosophy intriguing. An epic crusade in pursuit of perfect time and phase alignment. Haven't seen a post detailing workings of the crossover like this. Though analysis from your level of how "basic" much of this is has me wondering what "complex" must look like!

Dahlquist DQ-10 or any LS3/5A.

Thanks for the nice redraw job. Looks nice.
 
Nice work Pete!

I do have a question though. In the midrange circuit the series coil is marked as .08mH. Is that right? It seems kind of small for a 5KHz crossover to the tweeter. What am I missing?

Remember that the mid has a built in acoustical rolloff so that low value is just
shifting it or altering the phase for better combining with the tweeter. The AR-3a
uses a .04 mH for example.
 
Remember that the mid has a built in acoustical rolloff so that low value is just
shifting it or altering the phase for better combining with the tweeter. The AR-3a
uses a .04 mH for example.

So he's just running it wide open at the high end. Just looked at the Peerless data sheet. It does have an impressive top end.

Thanks
Chris
 
Remember that if you face the speakers forward (not toed in) then you
are a bit off axis, in the listening position, where the mid does roll off.
The inductor filter is about -3dB at about 16 KHz.
 
I purchased a used pair of the Vandersteen model 2, but was told the small "ce" at the end of the serial number, that I was told would make them model 2CE. I've had the set almost a year and love the low end and mid range performance, but found the high frequency range to be lacking. I called Vandersteen and asked if they had replacement tweeters and explained that the high end sounded a little weak or suppressed, and mentioned if the ferro fluid could be the problem. Was told that the fluid should not be a problem and age would not impact the tweeters performance, something that I did not agree with. And was also told to send the speakers in to be evaluated, and that made no sense to me so I've been on a mission to figure out how to get a better high frequency response from the speakers, without swapping in very different tweeters. So far and initially, I removed the tweeter from my right speaker to check the fluid out for myself. Found it to be a little too thick and not like what I've usually seen in tweeters. After more searching I found several of the same models on Ebay. But thought it would be a gamble so later decided to remove the fluid from the right tweeter and see if there was an improvement. Removing the fluid improved the response slightly, but could not compare things to the left tweeter because there was an significant difference between the left speaker and the right speaker before the fluid removal. But did find that the change in the right speaker after the fluid change also opened up the response from it sounding like it was coming from a tiny tweeter.

Today, I went further and removed the left tweeter to examine and found that the fluid had dried up. So I also then cleaned out the magnet structure using fuel injector cleaner and cleaned the voice coil with a cotton swab and alcohol. After the reinstall I fired the system up and WOW. The improvement was impressive and I found out how important the tweeter is concerning imaging and overall openness. It also seem like I may need to adjust the high gain on the speaker slightly lower. But for now and since I play my system loud I'm not concerned about the fluid, and for what they cost me used, I can live with things not being perfect on a spectrum. I went from a very flat and not spacial high end response to a very delicate, open and spacial overall sounding system. I also like how I'm so easy able to hear the finer high frequency detail that really makes for a great sound. I'm happy and have learned that in future used speaker I would be replacing any ferro fuid tweeters, because I found out today how important it is that both tweeters are matching, something the fluid cannot guarantee.
 
The 2Ce had a lot of changes, from memory I believe that early production had a
Vifa .75" aluminum dome tweeter, later they went to the 1" Vifa chambered back
aluminum dome with no change in the model number.

What tweeters were in your speakers?
 
Test at Erin's Audio Corner of the 2C not the 2Ci that I have:
https://www.erinsaudiocorner.com/loudspeakers/vandersteen_model_2/

Amusing YouTube video:

There are no foam edged drivers in the 2Ci but the woofer and midrange in the
2C had foam edges, perhaps also the coupler - not sure. Have to wonder if the
pair that Erin tested were ever re-foamed.
My overall impression of the 2Ci is that they need about 2 dB more baffle step,
and -1 to -2 dB on the mid to provide a more natural sound. As I mention above
they run out of steam with the thermal cut-out activating at satisfying SPLs so
not a speaker that I'd want to live with.
 
I mentioned above that the crossovers are glued in, and in case anyone is wondering
how I determined the inductor values this is it:
1. Traced out the crossover based on what I could see on the top and with an ohm
meter to confirm logical connections as I traced it out.
2. Desoldered the drivers and loaded the XO with a known resistive value 8 ohms 1%.
3. Measured the frequency response of the network loaded with the resistive load and
the L-pads all the way up.
4. Entered the schematic and known component values into the CALSOD simulation
package loaded by 8 ohms rather than the driver.
5. Adjusted the inductor values to make the simulated response match that measured.

I might have also measured the impedance looking back into the tweeter network to
determine the minimum impedance frequency of the RLC network to determine the L.
This is basic circuit analysis and makes it easy to determine the values.

Note also that the 2.8 mH woofer inductor has one end connected to the LF positive input
and therefore an inductance meter can be used across it for the measurement. The 20 mH
Acoustic Coupler (AC) inductor has one free lead after the AC is disconnected and can also then
be measured directly. This is what I did.

Making the CALSOD simulation match the real system:
1. Measured the input impedance of the drivers with them disconnected and saved
them as .ZMA files.
2. Removed the 8 ohm dummy load from the CALSOD simulation and loaded up the
.ZMA files for each driver. Now the crossover simulation provides an accurate frequency
response of the real crossover.

I should have these .ZMA files around here and I'll try to find them.
 
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Don Keele's extensive review of the 2Ci in the June 1992 issue of Audio page 73 in the .pdf:
https://www.americanradiohistory.com...io-1992-06.pdf
He notes that the newer 2Ce model is about to come out so these are very late model 2Ci s.

I always enjoyed reading Don Keele's speaker reviews in Audio because of his excellent
measurements and in depth analysis. It is interesting to note Vandersteen's rated on axis
frequency response of 28 to 29 KHz +/-3 dB and 32 to 21 KHz +/-1.5 dB. This is very
optimistic but not uncommon for manufacturers, Keele writes:
"Salient points of the on-axis curve include a somewhat rough overall response, a gentle
peak-dip combination at 250 and 500 Hz, and a sensitivity of 86 dB, moderately lower
than rated. The curve fits within a fairly tight, +/- 2.5 dB window from 70 Hz to 20 KHz
and is 10 dB down at 35 Hz. Below 40 Hz, the response rolls off at about 18 dB/octave.
A right/left comparison revealed a close, +/- 0.5dB match except for a narrow band
between 3 and 4 KHz, where the levels differed by +/- 1 dB. Note that all measurements
were taken with the grill on, as it is not designed to be removed."

Later in the review Keele does an experiment where he disconnects the Acoustic Coupler
on the rear and vector sums the outputs from the two woofers. He finds that the Acoustic
Coupler drive boosts the output at box tuning of 38 Hz by 5 dB. This is very similar to a
B6 alignment where a peaked high pass provides 6 dB of boost. The -3dB frequency of the
woofer system is lowered from 51 to 43 Hz.

I grew up building my own speakers so these were the first high end speakers that I ever
owned and lived with for several years. My impression of the bass is that it is about equal
to a Large Advent that is also a few dB down in the low 40s, however I often felt that when
the bass notes hit the Acoustic coupler range it seemed as if the source moved to the back
of the system - just a minor annoyance. In time I felt that the 2Ci had a very complicated
woofer system to get bass about the same as a Large Advent. I also felt that they should
reach lower given the spec of -3dB at 28 Hz.

The 2Ci does not pass the sit down stand up test as Keele measures and is well known for
1st order systems with non-coincident drivers the vertical off axis response is quite bad.
So these are only for seated listening.

Keele does his distortion measurements at 50W (20 Vrms) input where the system
produces 96 dB at 41.2 Hz, 101 dB at both 110 and 440 Hz.

Keele does a test where he applies a very high power (kilo Watts) short term burst in order
to explore the displacement limited output without worry for thermal limits. The system
does very well in this test Keele writes:
"With room gain the system exceeds 110 dB above 55 Hz and 120 dB SPL above 180 Hz."

Those are good numbers, the 120 dB figure is not usable because it requires so much
power, and Keele notes that the system is taking 300W just above 38 Hz in the bass
range. I would expect these speakers to work well with a 200W/ch amp except for the
thermal cutout activating with long bass passages.

The problem with the bass is that the thermal switch limits the useful level in my
experience, Keele writes:
"The woofer-protection circuitry was triggered above about 18V rms (46.3W into 7 ohms)
at 38 Hz. From a cold start, at this frequency and level it took about 20s to engage." He
mentions LEDs on the front illuminating, my 2Ci s do not have LEDs.
I'm not sure but I believe that the LEDs and perhaps the thermal cutout were deleted in
later 2C revisions.

It is clear that they do not want you driving this system very hard, the 10 ohm resistors in
the midrange path are only 2W and there are reports of them burning out. RV knows he
can up the wattage on those but I think that they are a way for him to know when a system
has been over powered. He asks customers to return them in such cases which is going to
be very costly just for shipping.

Keele states that the phase fits a window of +/-45 deg from 180 Hz to 20 KHz but it seems
to me that it fits about +/- 25 deg from 200 Hz to 20 KHz - much better. That is a good spec
especially considering the design.
Hi Pete,

Thank you for this writeup. In your opinion, can the thermal switches be safely removed or should they be replaced with something newer? If they should be replaced, do you have a recommendation?
 
Hi,
Have you ever tripped them? It is very odd that they cut the acoustic coupler but leave
the main woofer in, so you have to listen for it carefully.
I'll probably short mine when I go in to recap them, but then you have to be careful with level.
I've not done any research on this, does anyone know of any writeups on this?
 
Hi,
Have you ever tripped them? It is very odd that they cut the acoustic coupler but leave
the main woofer in, so you have to listen for it carefully.
I'll probably short mine when I go in to recap them, but then you have to be careful with level.
I've not done any research on this, does anyone know of any writeups on this?
I think my crossover is toast right now. I went home for lunch today and heard some crackling in the right speaker followed by no low frequency. I'm assuming a component burned up and in anticipation of repairing it, I started doing a little research and saw that there was a thermal switch in there as well, which made me wonder if I can simply bypass it, like I've done in some Polk Audio speakers in the past.
 
Yes you can just short out the thermal switch.
I'd also replace all the NPE caps, spray inside the LPads with DeOxit, and check
for burnt resistors.
 
Yes you can just short out the thermal switch.
I'd also replace all the NPE caps, spray inside the LPads with DeOxit, and check
for burnt resistors.
Thanks again! Would you recommend replacing the two polarized 1000uf caps with a single 500uf NP cap?
 
That should be fine. Mine had Elna brand back to back, I don't know if you can get fresh ones of
the same kind but that would be the way to keep them authentic.
I think you mentioned a buzz, you should probably try to test the drivers for buzz
issues while you have it all apart.
Also, the 8" Vifa drive often has aging glue at the cone to the edge joint that might need fresh glue.
 
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