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AR-11 Woofer (200003) Measurement, Refoam, Repair


Pete B
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I've been comenting on these woofers #1 and #2 in this thread:

http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#7030

but I though I'd discuss the measurements here in this new thread. I mentioned this background in the other thread but please note the correction that woofer #2 is a replacement unit. Here's a picture:

http://members.aol.com/basconsultants/AR11WMAG.jpg

I've got a pair of AR 11/12" woofers out of AR-11s from the late 70s, both part #200003 (MADE IN U.S.A.) without any dash number. These do not have the screen material over the back and they do have the small hidden masonite ring. The original owner of these 11s informs me that no outside work has ever been done to the woofers, and woofer #2 was a factory replacement.

The first woofer (#1) out of what I'll call system #1 seems in good shape and only needs replacement of the foam edge. This one is marked: 561 7830 and has an RDC of 2.49 ohms.

The second woofer (#2) was damaged when driven with excessive power (300W), and the voice coil rubs in such a way that the cone sticks wherever you leave it. The voice coil was driven out past the pole piece, shifted off center, and became stuck there. This bent part of the former in toward the pole piece causing it to rub. It is marked: 561 7838 and has an RDC of 2.37 ohms. I've disassembled the driver and there's much discussion about it in the other thread, I'll come back here to report measurements when I'm finished with the repair.

The date codes suggest that these were manufactured in the 30th and 38th weeks of 1978.

The spider is so loose that the weight of the cone causes it to drop when the magnet is face down. I thought the spider had sagged and lost center until I flipped the woofer over magnet up and now it sagged the other way. It just seems that the spider is so loose that it will not return the cone to center without help from the foam edge. I've not seen this in most woofers with deteriorated edges. I also note that there does not seem to be much clearance around the voice coil and it easily rubs with the edge missing.

I used a 5/8" wide foam replacement from RSSOUND, it was a perfect fit and highly compliant. I was concerned about the very loose spider that the voice coil would scrape, and that the cone would not return to the center rest position, however I wanted to measure the driver in as close to original condition as possible so I proceeded thinking the worst would be one wasted foam edge. I thought the driver needed a new spider and that this was bound to fail. Let me mention that it is important to position the foam to cone glue joint at the right height because the foam plays a large part in returning the cone to center. The center position will be off if the foam is above or below the correct position. I used the old position as a guide. The end result was impressive, no scrape even with slightly off center pressure on the cone and good return to center position. The driver seems to be in fine shape from a repair standpoint.

I did not use shims for this repair as I prefer this method but I wanted to point out that if shims are used it is preferable to try to reuse the dust cap as is described in this thread because it impacts the midrange performance of the woofer:

http://www.classicspeakerpages.net/dc/dcbo...ype=search#3764

WOOFER #1 FREE AIR MEASUREMENTS:

Here are the measurements based on input impedance only, right after repair:

Rvc = 2.52

Fs = 15.2

Qes = .226

Qms = 1.64

Qts = .199

This is a very low Fs, the spider is probably very well broken in and the RSSOUND foam seems to work well. Qms is also low and one possiblity is that the air leakage through the spider is acting as an acousto-mechanical resistance lowering Qms. I mentioned this about the air flow in another thread: "The spider is very loose, yet the cone moves slowly as if there's some resistance, it feels like air flow and I wonder if it's air leaking slowly through the spider which is porous. This would probably act as a combined compliance/resistance element but would be non-linear since the air volume is small. Vents in the woofer frame below the spider might eliminate this effect and improve the driver.

There does seem to be a problem in that I'm not able to get the rest of the T&S parameters by the added mass method that I usually use, the results do not pass a sanity check, and there is wide variation in repeated tests. I'm thinking that the delta compliance method with a test box is probably better for this particular driver due to the already high cone mass. The additional mass might be causing the voice coil to rub but I also wonder if the air flow through the spider might have something to do with it.

I let the driver run overnight with about .1" excursion at Fs to test the break in theory, here are the figures. Please note that the temperature the night before was about 75 to 80, and in the morning about 65 degrees:

Rvc = 2.49

Fs = 15.3

Qes = .205

Qms = 1.70

Qts = .183

Still could not get consistent added mass results.

WOOFER #1 IN BOX MEASUREMENTS:

The next test was with the driver in the AR-11 box with normal stuffing and directly driven without the crossover. We should expect a low Qtc without the series resistance of the crossover inductor:

Fc = 44.5

Qec = .79

Qmc = 3.16

Qtc = .63

As above with 2 ohm series resistor to simulate inductor DCR and perhaps a low damping factor amplifier. Note the large increase in Qec and Qtc:

Fc = 44.3

Qec = 1.35

Qmc = 3.17

Qtc = .945

These in box results are not far off, the DC resistance of the inductor will raise Qtc and .63 is not far off from the advertised value of about .7. Fc is a bit high especially considering the low Fs but the crossover impedance can shift the measured value down somewhat and 44.5 is also not far off.

Does anyone have the measured system input impedance for the AR-11 from AR or a test report? I've seen the AR-3a measurements but I'm wondering about the AR-11 specifically.

Pete B.

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  • 2 months later...

200003 woofers #3 and #4 purchased from ebay.

They look fairly good in the pictures but they are not usable as is but can probably be repaired.

Woofer#3 is the one with the original dust cap, left in top picture:

Marked 200003

Rvc = 2.38 ohms

date code = 43 week of 1978

Cone = 3013F

Spider looks to be correct with 6 corrugations.

Dust cap is correct and non porous

Screen: no

The cone moves easily without the feeling that air is slowly escaping as I noticed on one of the other drivers.

It has the wrong size surround that was cut with the overlap placed under the mating piece, it is not even glued all the way around. It is a pathetic job.

Woofer #4:

Marked 200003

Rvc = 2.61 ohms

date code = ?3 week of 1978 (cannot read it)

Cone = 5030 or 5036 (cannot read it) could this be the higher mass cone?

Spider has been replaced with a smaller one with 3 corrugations.

Dust cap has been replaced with one that is larger and porous.

Screen: yes

The edge seems to fit, but looks to be .5" wide instead of 5/8" and it seems stiff.

Front view, #3 on left:

http://members.aol.com/miscpubacnt/AR11/AR11W3_4F.jpg

Back view #3 on right:

http://members.aol.com/miscpubacnt/AR11/AR11W3_4B.jpg

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  • 3 weeks later...

This woofer #4 has a different cone (by part #), the screen on the back and a different spider, could this be a sample of the earlier woofer with a heavier cone? If the cone is heavier, it typically would need a stiffer spider to keep it centered which might be the reason for a smaller one with 3 corrugations. AR might have made the cone lighter, and suspension more compliant in an attempt to keep the in box resonance (Fc) the same.

I'd like to hear from others with woofers with the screen on the back as to how many corrugations the spider has, and the part number on the back of the cone.

The date code, any part number markings, and DC resistance would also be helpful.

Pete B.

>Woofer #4:

>Marked 200003

>Rvc = 2.61 ohms

>date code = ?3 week of 1978 (cannot read it)

>Cone = 5030 or 5036 (cannot read it) could this be the higher

>mass cone?

>Spider has been replaced with a smaller one with 3

>corrugations.

>Dust cap has been replaced with one that is larger and

>porous.

>Screen: yes

>The edge seems to fit, but looks to be .5" wide instead of

>5/8" and it seems stiff.

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Pete,

I have looked at 8 woofers with screens on the back, dating from 1968 to 1972. Two have alnico magnets and cloth surrounds. The other 6 have ceramic magnets, with two 1971 woofers having indented round magnets.

-They all have spiders with 6 corrugations and feel quite soft to the touch.

-They all measure from 2.5 to 2.7 ohms DCR

-One alnico magnet woofer cone is stamped with the number 109

-One ceramic magnet (Oct 1972) cone has the number 4725. I could not find numbers on the other cones.

Hope this info is helpful...

Roy

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  • 12 years later...

Back in 2005 I measured woofer #1 in the AR-11 box with the factory white poly fill stuffing,

and obtained these results driven directly without the crossover:

Fc = 44.5

Qec = .79

Qmc = 3.16

Qtc = .63

I've hardly used the system all these years and pulled it out a few weeks ago to recap it and

decided to do the same measurement (woofer #1) with these very similar results:

Fc = 45.2 Hz

Qec = .80

Qmc = 3.20

Qtc = .64

The crossover inductor DCR is .75 ohms and I ran the test again with .8 ohms in series to simulate

the inductor DCR with these results:

Fc = 45.2

Qec = 1.04

Qmc = 3.20

Qtc = .78

I don't recall the Qtc spec for the AR-11 but .78 with the simulated DCR is right in the ball park.

Does anyone know of an impedance sweep for the AR-11 or was the spec for Fc ever provided by AR, 

or stated in a test report?

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I also was looking for a spider to fix the second woofer and contacted Nuway to see if they

might be able to fabricate a very high compliance spider.  They sent me some samples of a 

spider that they already made with the correct ID, OD, and the correct  6 corrugations.  I got those

out for the first time and they are very STIFF.  I think Fs would probably be 100 Hz if I was to install

one of those.  Thinking back I seem to recall him saying check the fit and then they could make

a very high compliance version.  It looks like a perfect fit but it is a bit late to get back to him.

I also contacted MWA, a supplier to professional rebuilders and obtained:

6002  C

6004  B

They were out of the higher compliance A rated spiders.  C and B just by feel are way to stiff,  A

might be close enough and I should try again to get a few.  They all look to be made on the same die.

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  • 3 weeks later...

I'm not going to reassemble that 2nd woofer until I find a spider that is a good match.

Remembered that I have 4 more woofers with exactly the same construction from the AR-9s

(200003) and decided to use one of those.  Refoamed it with what I think was from Msound several

years ago that is more light gray as compared to R-sound dark gray foam that I used years ago on

woofer number one. 

I'm calling this one from the 9 PLB9-A2 with a DC resistance of 2.45 ohms.

Measured the T&S parameters with the following results:

Rvc = 2.45

Fs = 14.8 Hz

Qes = .226

Qms = 1.60

Qts = .198

Pd = 9.25"   measured with a ruler

Tried the added mass method to obtain the rest of the parameters but had trouble obtaining 

reasonable results.  Added 50g of mass to the cone with several erroneous measurements,

probably due to the very low Fs and even lower Fshift with mass.  Reconfigured the system to

start at 5 Hz and run to only 100 Hz and obtained these much more reasonable but probably

incorrect results.  The cone mass should be about 70 g, it is interesting that Ken Kantor's group

also measured a much higher than actual cone mass.  We know the actual mass by placing 

a cone, VC, and spider on a scale and most often getting 68 - 70g:

Vas =8.90 ft^3  252l

Mms = 121.54 g

no = .341%

Bl = 11.95 T-m

Cms = .954

SPLref = 87.3 dB

Fsm = 12.46

Frequency shift = -16%

 

I trusted Ken Kantor's people's data that reported the AR 11" woofer moving mass at a bit over 100g

and we hypothesized that the moving mass changed in the later woofers but this post suggests that

is not true and that the moving mass was always around 70g:

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/1497-ar-11-the-good-the-bad-and-the-ugly/&do=findComment&comment=58142

Aquila wrote:

Using a scale I weighed the moving mass (voice coil + spider + cone)of:

two 3a ceramic woofers labelled 1970

two 10 Pi ceramic woofers labelled 1975

two 11 ceramic woofers labelled 1977

They all weighed exactly the same (about 70 g). I never measured 105g.

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Tried this again changing the piston diameter to 9" and 50g added mass with very similar results:

I'm calling this one from the 9 PLB9-A2 with a DC resistance of 2.45 ohms.

Rvc = 2.45

Fs = 14.8 Hz

Qes = .226

Qms = 1.60

Qts = .198

Pd = 9.0"   measured with a ruler and not including part of the surround.

Added 50g of mass:

Vas =8.00 ft^3  226l

Mms = 120.9 g

no = .312%

Bl = 12.02 T-m

Cms = .954

SPLref = 86.9 dB

Fsm = 12.48

Frequency shift = -16%

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Success!  Decided to try the delta compliance method since I had an AR-11 box with wires set up to

drive the woofer directly, took out the fiber fill and used 1.48 cu ft for the volume.  Used a compromise

piston diameter of 9.15".  The moving mass is slightly low but this does pass a sanity check:

Woofer  PLB9-A2 with a DC resistance of 2.45 ohms.

Rvc = 2.45

Fs = 14.9 Hz

Qes = .228

Qms = 1.63

Qts = .200

Pd = 9.15"   measured with a ruler

Put in a 1.48 cu ft box:

Vas = 16.1 ft^3  455 l

Mms = 63.3 g  slightly low probably due to the Pd being closer to 9.25

no = .636%

Bl = 8.70 T-m

Cms = 1.80

SPLref = 90.0 dB

Fsc = 48.1 Hz   Test box volume 41.9l = 1.48 cu ft  acoustic mass ratio = .88

Frequency shift = -16%

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Repeated the above test using the 9.25" Pd value with the following results, Mms did increase

from 63.3 to 65.2 which is not enough since this should actually be a bit higher than a scale

measurement due to the acoustical air load on the cone.  Should be measuring about 73 g adding

a few for the air load.  The effective Pd might be closer to 9.5".  Here are the numbers:

Note that it is significantly cooler tonight and the soft part compliance changes

with temp which would explain the difference is Fs:

Woofer  PLB9-A2 with a DC resistance of 2.45 ohms:

Rvc = 2.45

Fs = 15.7 Hz

Qes = .231

Qms = 1.72

Qts = .204

Pd = 9.25"   measured with a ruler

Put in a 1.48 cu ft box:

Vas = 14.6 ft^3  413 l

Mms = 65.2 g  slightly low probably due to the Pd being closer to 9.25

no = .672%

Bl = 8.97 T-m

Cms = 1.56

SPLref = 90.3 dB

Fsc = 48.5 Hz   Test box volume 41.9l = 1.48 cu ft  acoustic mass ratio = .87

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On 10/12/2018 at 4:22 AM, Pete B said:

Aquila wrote:

Using a scale I weighed the moving mass (voice coil + spider + cone)of:

two 3a ceramic woofers labelled 1970

two 10 Pi ceramic woofers labelled 1975

two 11 ceramic woofers labelled 1977

They all weighed exactly the same (about 70 g). I never measured 105g.

Examining the AR drawings in the library, the mass without foam measured by @aquila2010 for the 200003 woofer moving mass should probably be correct ( around 70 g).

The drawing  #002 is dated 8 Jan 1984 and reports a mass of 41 +/-3g for the cone/surround assembly.

The drawing  #004 (it seems to be dated 7/1/69 ) should  show the first ferrite cone/surround assembly and its mass  is exactly the same as before. In other words, according to the above-mentioned drawings,  the mass of the cone/surround assembly did not  change during the 200003-(0/1) woofer lifespan.

The drawing  #299 (12-in W // 200003 // voice coil // 25-Jan-80 // 13-Feb_81) refers to the aluminum voice coil and reports a mass of 24g +/- 15% (from 20.4 g to 27.6 g) .

I coudn't find the spider and dust cap masses on their respective drawings. 

Therefore, without  spider and dust cup,  the mass of cone/surround/voice-coil assembly is about 41g+24g = 65 g (anyway it could ranges from 58.4g to 71.6g taking into account the maximum variations admitted in the AR drawings) for the aluminum-voice-coil woofer.  Realistically the spider and dust cup and glue could have a total mass of around 5-10 g,  so the "about  70 g" without foam reported by Aquila2010 is likely correct and probably applies to the aluminum-voice-coil woofer as well.

Anyhow I've several 200003 woofers disassembled  but haven't a very accurate scale at the moment. If I can somehow get one I'll report all their moving masses.

 

 

 

 

 

 

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On 9/22/2018 at 6:56 AM, Pete B said:

Does anyone know of an impedance sweep for the AR-11 or was the spec for Fc ever provided by AR, 

or stated in a test report?

From what I've read in your first post your AR-11's are MKII.  I coudn't found an impedance sweep for the AR-11 MKII but I've found one for both the AR-11 MKI and the 10 Pi MKI . I've also found some measurements for the AR-10 Pi MKII that essentially differs from the 11 MKII for the use of an autotransformer in the crossover network whereas the cabinet volume and drivers are the same (AR-11 MKI schematic,  AR-11 MKII schematicAR 10  Pi MKI and MKII schematic) .

The FC is 40.5 Hz for the AR-10 Pi MKII (besides the impedance sweep, see also the red highlighted text) and seems to be around 36-37 Hz and 38 Hz for the 10 Pi MKI and AR-11 MKI respectively.

Hope these graphs can be useful to you.

AR_11_MKI_impedance.jpg

 

 

 

 

 

 

AR_10_MKII.jpg

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Thanks again for all this info, I'll measure the system input impedance through the 

crossover to see if I can duplicate the AR-11 MKII curve.  It is possible that the impedance

of the woofer crossover network shifts the measured impedance peak lower in frequency.

I found a higher Fc around 44 Hz with the factory stuffing but that was driving the woofer 

directly and given the tolerance on moving mass it is certainly in the ball park.

I just noticed that the serial numbers have a C on the end and the single pole level switches

confirm that these are the later design.

Does anyone know if the stuffing quantity and/or type changed between the AR-11 MKI and II?

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On 10/17/2018 at 5:13 PM, Pete B said:

Does anyone know if the stuffing quantity and/or type changed between the AR-11 MKI and II?

From the AR drawings:

AR 11 MKI : 20 oz fiberglass

AR 11 MKII: 10 oz (white) polyester wadding .

 

 

Several types (and weights to always obtain the optimal damping) of polyester stuffing were used in the European factories for the MKII versions. As regards the white one (used only in the very late production),  I've generally found a single sheet of about 250g (8.82 oz). 

The 10 Pi MKII of the test (Fc: 40.5 Hz) had the multi-coloured poliester (in my experience i found about 450g =15.87 oz when this type of stuffing was used).

In another magazine that also tested  the 10 Pi MKII,  the Fc was 42.8 Hz and the woofer Fs 16.9 Hz . The suffing was multi-coloured polyester too.

As said in my previous post, unfortunately, I don't have any impedance graph (and Fc) for the AR 11 MKII but I think that its Fc is similar to that of the AR 10 MKII.

picture1.jpg

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On 10/18/2018 at 6:39 PM, Pete B said:

Thanks again, very interesting.

I'll take some measurements with stock poly stuffing and fiberglass.

You're welcome,

Your measurements are very interesting!  Please consider that 20 oz of fibergass could overdamp the late 200003 woofer generation (that is what I do hear with my ears but I never carried out measurements). To the best of my knowledge, AR 11 and 10 Pi MKII did only use 10 oz of "white" polyester in USA. The same type of white polyester was also used for the AR9 and (later) the AR9ls series. In Europe different types (with different densities and consequently different masses) of polyester were used for the AR 11 and 10 Pi MKII and only the late production in 1979 used the "white" polyester (about 9 oz).

On 10/19/2018 at 4:41 AM, Pete B said:

Do you know how the switches were set for the AR-11 MKI input impedance?

 I've read the AR 11 MKI review again but, unfortunately, they do not say how the switches were set during the impedance measurement. The frequency response shows 3 curves (0, -3, -6 dB). Since only the midrange and tweeter can be attenuated,  the 3 curves are  exactly the same up to about 500 Hz. So the minimum (4.8 Ohm) at 80 Hz should not be affected by the midrange and tweeter switch position. The minimum around 3 Ohm at 6000-7000 Hz may suggest that the switches were set for the maximum output (0 db attenuation) and furthermore the worst condition is what generally matters most.

Anyway, the minimum of 4.8 Ohm at 80 Hz  seems a little high in comparision with that of the AR 3a improved that had the same 200003 woofer generation used for the AR 11 MKI and a rather similar woofer low-pass crossover network.

As regards the AR-10 Pi impedance measurements (both MKI and MKII),  they say that the switches were set for the maximum output (4Pi, 0dB, 0dB for woofer, midrange and tweeter respectively). Examining the AR 10 Pi crossover network, when the woofer environmental control switch is set to obtain the maximum output (4Pi), the inductance in series with woofer is 4.73 mH (1.88 mH + 2.85 mH), the capacity in parallel is 100 uF  and thanks to the autoransformer, the output voltage that supplies the woofer is higher than the input one.

In the AR-10 Pi, because of the autotransformer the impedance varies according to the switch positions: the review says that when the woofer switch is set on 2Pi and Pi the minimum impedance is 7.5 and 13.6 Ohm respectively (around 100 Hz)  .

Link to AR 10 Pi crossover network

 

 

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