Pete B
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Posts posted by Pete B
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It is interesting to take a look at a modern driver such as the Peerless XLS:
http://www.d-s-t.com/link/main/tech/xls.jpg
from: http://www.d-s-t.com/link/main/tech/xls_intro.htm
Key from the DST site:
A. Aluminum Spacer
The aluminum spacer serves as heat sink for the coil to reduce power compression.
B. Black Anodized Voice Coil
The 2-inch 4-layer voice coil is wound on thick black anodized aluminum for improved heat dissipation.
C. Stacked Magnet System
The twin stacked magnetic system is optimized by FEA (Finite Element Analysis), to create a symmetric powerful magnetic field in the air gap, and provide space for the 44 mm max excursion of the voice coil.
D. Distortion Reduced Motor
A long 4 layer voice coil normally results in high self induction and impedance varying with excursion. Its many ampere turns react on the magnetic field in the air gap. These two main factors causing motor distortion in subwoofers are practically eliminated by the combined impact of the Aluminum Short Circuiting Ring (D) and the Aluminum Spacer (A) on the pole piece.
At the same time they both contribute as heat sinks for the voice coil, reducing power compression.
The result is unbelievable clean bass reproduction.
E. Vented Cone
To eliminate compression under the dust cap the cone is vented by 8 large holes.
This way the coil is cooled and there is no need for a bore in the pole piece.
F. Nomex® Spider
The spider is made of high tech Nomex® material. This material is chosen for its high rigidity and long term stability. The suspension will stay in shape for a very long time under heavy load.
G. Rubber Surround
The surround is made from SBR rubber because of the wide operating temperature, low creep and long term reliability.
H. Fiber CompositeCone
The cone is molded from a propriety air dried wood free pulp with a blend of Nomex®, Kevlar® and glass fibers bonded together by deep impregnation with polymers.
This creates an ultra stiff and relatively light cone that will stay stable even under very large sound pressures.
I. Rigid Cast Aluminum Basket
The rigid cast basket with an aerodynamic profile provides the necessary sturdy base for the magnet structure and suspension and allows for the 44 mm max excursion of the cone.
The spider is ventilated to achieve the lowest possible compression and allow air to flow freely to create a cooling effect for the voice coil.
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It is intersting to note that the Extremis is a 6.5" woofer with a mechanical Xmax limit of 20 mm one way, the AR is an 11/12" with 12.5 mm one way. I've used the term Xmax50 as the point where the motor has half of it's rest position Bl, this is about +/- 15 mm for the Extremis and theoretically +/- 12 for the AR. Measured for the AR is hard to define due to the asymmetry and mechanical Xmax limits.
I've stated that the AR woofer is a primitive driver and it's design features are very similar to the better stamped frame drivers made in the USA such as the Swan 305 or the Eclipse W1238R:
http://www.madisound.com/images/product/SWAN305.jpg
http://www.madisound.com/images/product/small/W1238R.jpg
One area where the AR woofer has been optimized is midrange response smoothness and cone breakup. Here's the distortion performance of a modern high priced 12" woofer (SC12NRT), note that the conditions are for 96 dB SPL in a 41 liter sealed enclosure. Note distortion peaks around 300 and 700 Hz. It should also be noted that this driver is probably intended for true subwoofer use below 150 Hz:
http://www.madisound.com/images/sc12nrthar...cdistortion.gif
Pete B.
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The recent Klippel data for the Tonegen woofer offers some insight into the driver design and large signal performance.
It is interesting to look at the THD vs. frequency and level as is shown in the file AR3ATHD+N.PDF. This is a fairly reasonable plot, and shows the typical increase in THD as frequency decreases due to increased excursion and the BL and compliance non-linearity that goes along with it. This is typical for a driver that has not been highly optimized with it reaching 7% distortion at 30 Hz and 5W.
It should also be noted that as frequency increases and power decreases, within the piston range, we should expect the THD to continually decrease, but it does not, it seems to reach a lower limit of about .5% midband, this is something we should keep in mind. The increases at about 750, and 1.2 Khz are due to cone break-up modes as we leave the piston range.
We should next look at file 12N12100032.mht_w_laser.mht to see how the different components contribute to this distortion. The first two plots are compliance Cms and stiffness Kms versus x displacement. They are reciprocal measures of the same thing. There is very good symmetry for +/- x displacement but it is not very linear, the suspension is nearly twice as stiff at +/- 6mm as compared to the rest position. This is due to the spider stretching and will help to stop the motor at the ends of it's displacement, but it contributes to the distortion. Note that the derivative or slope of the curve is zero at x=0 which indicates that it is linear for small displacements.
The force factor or Bl(x) curve is not so pretty because this is a very primitive driver. The Bl peaks at almost 10 but at x= -3 mm, that's nearly half way through it's "linear" excursion. It has no small signal linear excursion due to this offset in the peak and this probably explains why the distortion does not continually decrease with decreased excursion. This can also be seen by the fact that the derivative or slope of this curve is not zero at x= 0. Indeed, the Bl varies from 10 to 9 over the small displacement of -2.5 to +2.5 mm, whereas the theoretical model (zero fringe field) suggests that the BL should be constant from -6 to +6 mm, and should fall by 50% at -12 and +12 mm. Instead we see a Bl of 9.5 at -6 mm and about 7 at +6 mm. We also see a Bl of about 7.5 at -12 mm and 3.5 at +12 mm, very poor symmetry.
It is important to look at the absolute limits of the mechanical Xmax, the point where things hit destructively and one can compute that the voice coil hits the back plate at about - 12mm where the motor should theoretically have half it's Bl strength, it actually has much more than half. I prefer this mechanical limit to be at least the point where the motor strength goes to zero which would be -18 mm for this driver, 24 mm would be even better to allow for overshoot.
Lces, Res, and Cmes are the mechanical components reflected into the primary circuit and are distorted due to the Bl curve. Le(x) is also interesting, this is the inductance of the voice coil and just as with an RF tuning slug, the inductance goes up as the VC moves in with more pole iron in the coil, and down as the VC moves out with less iron in the coil. This can also contribute to the midband distortion. All of these curves would ideally be a flat line. Shorting rings help reduce the inductance variation.
Fs(x) and Qms(x) have symmetry because they are not dependent on Bl, whereas Qes(x) and Qts(x) are distorted by the Bl curve. The driver has a Qts well under .5 at x=0, however it is nearly 2 at the positive limit of excursion. High Q systems tend to overshoot and this probably contributes to mechanical destruction of the driver.
There are many ways to improve a motor's linearity which were covered in this old paper: "Moving Coil Loudspeaker Topology as an Indicator of Linear Excursion Capability", by Mark R. Gander (JBL), JAES 1981 January/February. There are also many patents covering the subject.
The Adire Audio Extremis Bl curve:
http://www.adireaudio.com/Home/Images/eX6BL.gif
Pete B.
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>I'm not sure who supplied that AR woofer in Ken's Klippel test
>jig, but I can tell that it was an earlier 200003 or 1210003
>factory woofer that had been repaired with a new surround. It
>might have been one of Bret's woofers; I'm not sure. It is
>not the Tonegen version.
Ah, I had the impression that Bret's woofers were not tested on a Klippel system probably because I only noticed the small signal data, I have not looked at the data for some time. This makes sense just never made the connection with the old drivers.
>Incidentally, I plan to send (to Ken) an earlier AR-3/AR-3a PN
>3700 Alnico woofer and an early AR-3a ARNP 200003-0 woofer
>recently refurbished with a new 5/8-inch surround.
Should be interesting to see the results.
>Regarding
>surrounds, I use Speaker Works Northwest surround kits with
>satisfactory results, although I am sure there are numerous
>other good suppliers of the proper surround. These Speaker
>Works surrounds are similar to samples I received from Minh
>Luong a few years ago that had the proper 5/8-inch half-round
>size and the angled-inner flange.
Good to have the feedback on this supplier.
>
>Description: "11-inch Acoustic Research Angle Attach Surround
>Kit." Price is $24.00 per set, with a small discount for
>larger numbers. Unfortunately, the kit is incorrectly
>labelled as an "11-inch" surround, but I guess it's too much
>trouble to change the description at this point. Despite the
>incorrect description, the surround kit works very well in my
>experience. Shims are not supplied nor are they recommended,
>and the dust cap is left alone. Slow-drying glue is used,
>similar to white glue, and this method works the best in my
>opinion.
>
>--Tom Tyson
Yes this works well in my experience also.
Pete B.
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>The term "Fs 18Hz" is definitely written by someone after the
>woofers were manufactured because of "Fs" and "Hz." Neither
>of these terms was used in the 1950s. The 18 Hz value is
>correct for this woofer.
I believe that Fs went down with the half roll edge as I was told, by the audio engineering professor that I studied under, that it was in the low teens for the very early woofers. I'm not sure if this low figure was what it should have been according to the patent or actual, a figure of 11 Hz was mentioned, and I've also heard the 14 Hz figure. This professor was critical as a scientist of several other areas/issues concerning AR.
>The first AR woofers with sand-cast frames also did have
>"pleated" surrounds, which was not shown in Villchur's patent.
> His patent shows the half-round surround, but Henry Kloss
>felt the pleated surround would work better since it was the
>conventional method of the day. Therefore, Villchur decided
>to compare the harmonic distortion of woofers with both the
>pleated surround and the half-round surround, and the once
>that had lower distortion would set the rule. After the
>initial production run of AR-1s and AR-1Ws, the pleated
>surround was changed to half-round.
I've read this somewhere, probably your writing Tom but had the impression that they made the comparison in the prototype phase before shipping product, but yes it makes sense that this was a production unit. I wondered, after posting above, where a repair shop would get the pleated surround for the non-standard cone and also thought that it looked original.
>The surrounds have been treated with some material, but the
>pleated surrounds are original.
Yes, this makes sense.
Pete B.
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I posed a question about the new data for the Tonegen driver:
http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#7359
The parameter that stands out is moving mass which for this Tonegen is about 68 grams, whereas the older 200003's measured the last time were around 110 grams. I have a 200003 replacement woofer with the cone, voice coil, and spider removed as a unit. I weighed it some time back as 67.5 grams on a scale noting the difference from the other units tested here. I believe AR moved to a lower moving mass in later years and this, along with Bl differences are the reasons for the lack of "growl" from the newer woofers.
Some here state that we will never know the sound of the older AR systems which is not true since they've been documented in the journals and AR's own literature. "The Sound Field in Home Listening Rooms" by Allison and Berkovitz, AES July/August 1972 gives many measurements of an AR-3a. The authors write, "is 6 dB down at 30 Hz exactly what an AR-3a woofer is supposed to do.", note that this is half space.
An NHT document here lists 33 Hz as the -6 dB point for an AR-3a and 24.5 Hz for the AR303, anechoic. An AR303 woofer was measured in the last group of drivers and had a moving mass of 139 grams.
We see large differences in moving mass which correspond to large differences in F3/F6 and efficiency as can be seen below:
I've added the Tonegen to the list:
------ moving mass (Mms)
DUT2 103 g (AR-9 1978, new surround by Simply Speakers)
DUT3 104.36 g (AR-9 1978, new surround by Simply Speakers)
DUT4 123.95 g (AR-9 1978)
DUT5 107 g (early 10pi soft cone, surround, spider by Tri-State)
DUT6 115.16 g (early 10pi soft cone, surround, spider, VC by Tri-State)
DUT7 164.88 g (mass added by reconer) (AR-9 1978)
DUT1 139g (actually a 303 woofer)
Tonegen 68.1 g
200003 67.5 g (Replacement driver, Cone stamped 3013F on back)
------ Bl ------- Ref Eff
DUT2 11.76 Tm .572 %
DUT3 11.78 Tm .531 %
DUT4 11.59 Tm .358 % (estimated used RDC = 2.5 ohms)
DUT5 10.10 Tm .391 %
DUT6 9.89 Tm .319 %
DUT7 13 Tm .289 % (was the voice coil replaced?)
DUT1 12.94 Tm .320 % (actually a 303 woofer)
Tonegen 9.52 Tm .731 %
------ Qms
DUT2 2.89
DUT3 3.11
DUT4 2.82
DUT5 7.92
DUT6 7.89
DUT7 9.3 (reconned)
DUT1 5.02 (actually a 303 woofer)
Tonegen 3.53
I believe that there is hope for the Tonegen woofers and adding mass is probably the way to duplicate the deeper extension of the older drivers. Adding mass will lower Fs which indicates that the spider is probably not the issue, this is also supported by the 161 l Vas value. One has to be cautious about voice coil heating and midrange break up modes when adding mass, and therefore it is not so simple.
Pete B.
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This picture, from an ebay sale, has Fs 18 Hz written on the back. I wonder if it was from the time of manufacture, my guess is not since CPS was in common use not Hz, and the Villchur patent uses the term Fr for free air resonance not Fs which is a more recent term:
http://www.unclepapa.com/AR1Woofer_11.JPG
These drivers have accordion edges, which I don't believe is correct:
http://www.unclepapa.com/AR1Woofer_2.JPG
I believe that these woofers have been worked on and the 18 Hz figure was measured after the repair.
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Tom,
I ask this specifically because the Klippel data shows significant voice coil offset or magnetic field asymmetry. This is to be expected if they assemble the driver assuming that the magnetic field is symmetric when in reality it is not. It is hard to tell if this is a manufacturing tolerance issue which I would not expect from Tonegen, or if it is due to assumptions made about the symmetry of the magnetic field and the center position chosen for the voice coil.
An even better solution is a simple mod to the voice coil that can be used to compensate for an asymmetric magnetic field.
Pete B.
>With the woofer mounted in the enclosure, it probably makes no
>difference whatsoever how the enclosure is pointed. Even in
>free air it probably doesn't matter that much, but I would
>think that vertical mounting, such as the Ken's Klippel setup
>below, would be the norm.
>
>
>--Tom Tyson
>
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Just wondering if this picture is of the current woofer that we have test data for: Tonegen 12N12100032. It doesn't look like the Tonegen currently being sold, rather it looks like a 200003 type.
Pete B.
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I believe I've seen pictures of the Klippel stand with the driver in a vertical orientation and if this is correct then yes it answers my question and thank you once again.
I think Tom Tyson mentioned that this driver had the correct 5/8" foam and I read this to mean that the driver was refoamed. Tom, anyone, would you please verify this?
It would be very interesting to see Klippel data for a new Tonegen and also the NHT1259/Tonegen as a baseline comparison. I'm just thinking out loud and don't expect you to do this.
Thanks,
Pete B.
Edit: I did not see Tom's post above as we were writing at the same time, so yes I see it is vertical.
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Hi Ruchi,
I was just wondering if you tested the woofer face up, down, or in a vertical position?
Pete B.
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Thanks very much Ruchi, look forward to seeing that data.
Pete B.
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Hi Ruchi,
I just wanted to ask, again if it's not too much trouble, for an in box input impedance plot to go along with the frequency response plot.
It would also help to know Fc and Qtc in box, with and without the crossover network.
Thanks again,
Pete B.
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There's a lot of data to digest, but something jumped out at me in this data.
I suggested that the problem with the Tonegens might be a high Bl, yet this driver is slightly under 10, comparable to the lowest in the last group tested. Bl is not the issue. Fs is slighly high with this Tonegen but let's ignore this for the moment.
Question for the group here to stimulate conversation: There is one parameter that stands out to me as compared to the 200003 woofers tested, does anyone see it?
Pete B.
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Hi Ruchi,
I have a few questions if it's not too much trouble. The caption in the Freq Resp .pdf file reads: AR3a 12" Woofer, Re 2.83 Ohms ...
I take it that should be Volts?
So this was 1W into 8 ohms or the standard voltage sensitivity type of measurement? Further, I take it the mic was 5 cm from the cone or near field so that the environment is not an issue?
Are the 1W, 2W, and 5W figures in the distortion plots also referenced to 8 ohms, or Re of the driver, or?
I'd like to see 2nd and 3rd harmonic distortion level plotted since it gives an indication as to the source of the non-linearity, if it's not too much trouble in the future.
I notice that some of the parameters in the Klippel measurements are prefixed by (imported), Re and Mms for example, does this mean that they were measured outside of the current test. It looks like Mms was measured in the small signal section using the laser, then imported to the other tests. Am I reading this correctly?
One last request, I'm having trouble reading the large signal plots, it would help if they were 2 or 4 time larger again if it's not too much trouble in the future.
Thanks again for this effort,
Pete B.
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Thank you very much for this data, very nice work.
I'm not familiar with that part number, would you or Tom please provide some details about this driver. Is it a ceramic magnet driver? Early or late production? Or is this a Tonegen?
Pete B.
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I should probably clarify my thinking as to why a collector might be interested in spiders. I'm thinking that some might want to have the "correct" spider and edge so that they can provide them to a reconer when he works on their driver.
Pete B.
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Bret,
I have to wonder if you could have misinterpreted me and jumped to conclusions to any greater degree than in your most recent post. Don't misrepresent my intentions with your assumptions.
I'm not going to respond blow by blow to your post, people should simply disregard it, as it pertains to me, or read what I actually said to see the facts. You suggest that I will get into driver manufacturing, I don't think so, there are many companies who know this very well. It would be foolish so drop the assumptions will you? I may prototype drivers from time to time, for my own use and perhaps for some associates.
Back to the subject, there's been no response to my suggestions for having a spider made so we might as well drop it. I might have had 100 to offer to the group but there is no interest so the point is moot. I would make no money on this deal, just in case your thinking of jumping to more conclusions, given the amount of time I spend on this subject.
You do misinterpret me, over and over.
You dream about what a "pro" reconer does, you might be surprised by the reality.
I explained what happens with an offset voice coil assuming (a reasonable assumption) that perhaps an extended pole piece was used for better fringe field symmetry. You'll have to read the paper to really understand the facts. I doubt you will since it seems that you look only for the "facts" that support your leaps to conclusions based on listening.
I don't have time for this and I don't enjoy this type of discussion at all.
Pete B.
>>I don't agree with your theory that the 200003 variations
>went with specific systems, rather I think it was time of
>manufacture and parts being used at the time.<
>
>Pete - I have absolutely no interest whatsoever in getting
>into the speaker (driver) manufacturing business. The only
>reason I said something about calling them is that you had
>said you *were not interested* in being the person to
>spearhead an attempt to get an order together. I thought the
>matter was closed as far as you were concerned and if someone
>didn't follow-up an opportunity might be lost. I hate missed
>opportunities.
>
>It's hard to stay out of your way if you weave a bunch.
>
>BUT - having said that, I'd suggest that you don't tell us if
>you have 5,000 "correct" spiders made because some of us might
>want a few pairs and you're indicating exclusive manufacture
>for yourself. That might make some people sorta glum.
>
>Or maybe I'm misreading you all the way around. Sorry about
>that.
>
>Second - Why yes, Pete. Yes, I am aware of what happens to the
>performance of a speaker when the cone is not returned to the
>correct 0 position. In fact, you and I have gone over the
>DUTs where two of them were refoamed with bad spiders and were
>not returning to the correct 0 position. They stunk-up the
>place. They rolled-off sooner, were louder, and . . .
>something else nasty that I don't recall, but I do recall you
>were doing your best to chalk-it-up to a difference in motor
>and I was trying my best to reassure you that there was none.
> Remember the whole "stronger magnet" thing? I'm guessing the
>measurement you were using to conclude the stronger-magnet
>theory was caused by the lousy spider sucking the voice coil
>back into the magnet too much.
>
>Sigh. . . I guess we'll never actually know.
>
>This is one of my "harps" about letting a pro do the
>re-foaming. Someone who can find "0" and check the doggone
>spider. If Tom hadn't told me what to look for, poor-old-me
>would probably have thought the motor was different. I might
>have even pitched the re-foamed and well-traveled units in the
>garbage.
>
>Perhaps you are right about my thinking about the early
>10pi/11 version of the 200003 being an accident of birth,
>rather than a design parameter for that speaker. Makes sense.
> The driver I associate with the 10pi/11 is evident in the
>brochures for both speakers - the first brochures. The second
>round, the "B" series with the aluminium badges, have a silver
>basketed driver. BUT - you correctly point-out that this old
>black version could have also appeared in the latest version
>of the 3a, or even perhaps in the LST. I don't know. I do
>know that earlier 3a's did not use this same cone material and
>the cone changed along with the basket color for the "B"
>series speakers.
>
>Still, anything that gets us closer to either of those "era"
>of spider is a great leap forward. . . so long as you don't
>hog all the spiders!
>
>I hope you "go for it" and get into the speaker manufacturing
>business. It'd be nice for there to be another company of
>quality willing to operate in the good-ol' U.S.A. and put-up
>with the EPA, OSHA, the wage and hour division of the DOL,
>IRS, etc, etc, etc, instead of sending the jobs to China where
>they don't worry so much about that stuff.
>
>Bret
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>>This came up in my discussion with them, but they normally
>sell in quantity<
>
>Was quantity or price a topic of your discussion? I don't
>mind calling them myself, but thought joining the conversation
>late might just cause a lot of repeated redundancy.
>
>The biggest question I'd have is since the spiders changed
>over the years, which spider would be the spider of choice?
>The later 9-spider with a little more power-handling, or the
>earlier 3a with a lower Fs and a greater tendency to bottom,
>or the middle-of-the-road 11/10pi? (although early ones of
>those had slightly different cones that might have been just a
>tad heavier)
>
>Bret
Please do not call them, the last thing I want is several different people calling them as a result of a post I make here. I want to stay on good terms with them. They do not normally deal with the public, and I was honest about the low volume. On the other hand go ahead if your getting into the speaker business and are able to rebuild a driver and test the Thiele and Small parameters. I'm slowly moving into the speaker business and I don't mind doing the R&D to restore, improve, or design new drivers. I'm actually very interested in being able to prototype completely new drivers so I do have a business interest in this.
Yes quantity came up and he said it's usually something like 5000 units. And we did discuss lower quantities that would involve a setup charge. I'm not sure if I want to get into it on a public forum with you.
I don't know what you mean by joining the discussion? The discussion between myself and NuWay is private between two businesses. If I refine a spider I'll probably ask for it to be exclusive to me because I'm the one spending the time to do the analysis, take measurements, and get it right. I'm probably going to build a simple jig to measure spider compliance. And I'll certainly measure them in several drivers.
As far as your question goes, I'd shoot for an approximate 18 Hz Fs for the 200003 woofer. Fs is really not that important, cone mass is much more important as I've said over and over. The important reason to make the spider stiffer is to return the cone/voice coil to center and to keep the entire assembly from tilting when mounted in the system which can result in the voice coil rubbing. These are very good reasons for having a stiffer spider. I wonder how many here are aware of how important it is for the voice coil to return to the correct zero position, do people know what the result is of a 1 mm offset, especially in a driver with an asymmetrical fringe field? Read here: "Moving Coil Loudspeaker Topology as an Indicator of Linear Excursion Capability", by Mark R. Gander (JBL), JAES 1981 January/February. I'm surprised by how primative the 200003 woofer is given that they had the opportunity to make simple improvements. I'm curious if anyone knows who at AR did the design for the 200003 woofer, and the AR-11 also?
My current thinking is to specify a very loose outer edge suspension and that the cone mass be adjusted if necessary to provide an in box resonance of 40 Hz +/- 2 Hz. A reconer can actually measure the cone/voice coil weight on a scale when they remove it to install a new spider and I will provide an acceptable range. Kind of like blueprinting a motor. I want nominal to be slightly on the low side to allow for a slightly wider tolerance.
This spider could be used with the older drivers and it might result in an Fc of 42 Hz +/- 2 Hz in box due to a slightly lighter cone. I probably would not add mass in this case because these drivers have a lower Bl and more sensitivity would be lost. This assumes that it fits, from a physical stand point and I cannot confirm this until I get one in hand. I think for now we should say that this is just a 200003 spider, if it fits in the older drivers or the Tonegens that's just another bonus. I believe that it should fit all the ceramic magnet 200003 style woofers and if the cone mass is adjusted, and the proper edge used they all should provide an Fc that is within the tolerance range. I'd actually prefer to specify an Fc of 38 Hz +/- 2 Hz for the stronger Bl versions to trade off some sensitivity for bass extension, what do the people think of this?
I can also have voice coils professionally wound to order and my preference is an aluminum former but Kapton is the current standard, not Nomex. Would there be interest in a classic rebuild spec say Kapton former, 40 Hz target Fc, and an enhanced-1 spec aluminum VC former, 38 Hz target Fc for the 200003?
I'd like to do several levels for the Tonegen:
Enhanced-2 spec for 35 Hz target Fc (more cone mass)
and I have other ideas for a better pole piece, inductance modulation reduction, and better VC venting.
The spec should also indicate modifications to provide proper in system Qtc. I may have to work closely with a few specific reconers because there's no guarantee that they'll generally follow a spec.
I don't agree with your theory that the 200003 variations went with specific systems, rather I think it was time of manufacture and parts being used at the time. The woofers here out of 1978 AR-11s have very loose spiders and probably 2 different voice coils. Very early AR-3a woofers probably had slightly lighter cones since the suspensions were more compliant to obtain the same target Fc.
Pete B.
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>Pete, How about sending an old spider to a place like NuWay
>and having them replicate it?
>
>Roy
This came up in my discussion with them, but they normally sell in quantity and I don't want to trouble them if a quantity buy would not happen in the end. I just need 2 spiders and had no plans of coordinating a group buy or handling the prototyping of a new spider.
I might consider it if there was serious interest, that means someone or a group putting up some cash. Sorry to be so blunt but as I'm sure you know people talk and BS, not you in particular.
It also seems to me that most just replace the foam, so who knows if there would be much interest. A new spider might help bring the Tonegens closer to 1970s specifications and this might be a good application for them.
Also note that the closest die from NuWay of the correct dimensions has 6 corrugations. The AR spider has in a sense 7 or 6.5 however half of one is essentially glued to the cone providing a larger contact area. The NuWay spider would have to be installed what appears to be upside down to get the same glue contact area and then if one counts the corrugations on that side there would only be 5. The point being that it is not *exactly* the same, however I do not see this as a problem if the correct compliance is provided. This spider is listed as a 6 corrugation spider however when installed in a way similar to the AR it might be viewed as a 5 or 5.5.
I just checked and the spiders will not fit into the frame upside down due to interference with the inside diameter of the masonite spacer ring so this point of gluing to the cone and loosing a corrugation is moot. The spiders would have to go in normally and be glued in such a way as to get a strong bond to the voice coil alone.
Constructive thoughts are welcome.
Pete B.
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Hi Roy,
I agree with Tom's comments concerning the magnet issue. You might note that we're finding the magnets to be too strong and we have the measured response by AR as a reference for the original performance.
I posted the links just to raise awareness that there is a "Professional Loudspeaker Reconers Association" and that they're seeing similar issues with the results of the repair work being done. They even mention the difference between aluminum and Kapton formers.
You've probably noticed my posts where I'd like to come up with a specification for rebuilding a classic woofer like the AR 200003.
I've looked into obtaining new spiders for the drivers that I'm working on. I've found that even the best people draw from their supply of old stock parts, even one of the major suppliers considers their stock of parts to be surplus, however they do have new parts for pro drivers. It's up to the driver manufacturer to provide a recone kit and this is done for drivers intended for professional use but commercial companies do not normally do this. No one rebuilding these drivers has the "exact replacement parts" because AR never provided them to the industry. Most spiders are made to order and are not stock off the shelf type parts.
What I thought were part numbers in the NuWay catalog for spiders are die numbers for pressing spiders, there are many materials to choose from and many chemical treatments to produce a finished spider from a given die. There are many combinations for each die number and therefore they're made to order.
Pete B.
>Hey Pete,
>
>In the link you provided there is mention of a "problem" with
>"magnet half-life" in a speaker more than 20 years old.
>
>I wonder what that translates into relative to the parameters
>of our 25 to 40 year old AR woofers? We've been wrestling with
>"if and when" AR increased the magnet strength of the 12
>incher. What if we are dealing with an overall net LOSS of
>magnet strength across the board? What are the likely symptoms
>of a "magnet half-life" issue? Would it affect alnico and
>ceramic magnets in the same way?
>
>Roy
-
Thanks for the information Rich,
Do you know what time frame these drivers are from?
One woofer of the pair I'm working on has a 51 turn voice coil and the other 55 based on my calculations below. I wonder what the story is with this replacement driver with a black anodized former. Was the shorter coil and aluminum former only used for replacement woofers? I'd think that they rebuilt drivers, so it's possible that this driver represented how drivers were being made in the early 80's if that's when it was rebuilt. The question is then if all drivers around that time were made with anodized formers and short coils? Any AR people willing to help out here?
Are there opinions on what people would want in a rebuilt driver to consider what we might want to put into a specification for driver rebuilding? My preference is an aluminum former, black anodized if possible, not sure if I like the resistance getting as low as 2.37, it was on the low side at 2.5.
I'd like to have two matching drivers for this pair, I'll probably look on ebay.
Pete B.
>>>Rich, did you notice if any of the woofers with aluminum
>voice coils were black anodized on the inside?<<
>
>I've refoamed five (5) AR-11 "B" and twelve (12) AR-9 200003
>woofers over the past few years. All with the silver flange.
>
>I'm a "shimmer" when I refoam so I saw the inside of the voice
>coil on all of them when I removed the dust cap. The Aluminum
>VC formers on all the woofers were all silver, none were black
>anodized like the one in your pictures.
>
>The same can be said for all the 10" woofers (pair of AR-90's)
>and 8" lower midranges (AR-90's and AR-9's)I've refoamed --
>all silver Aluminum VC formers.
>
>Rich
-
Just came across this site which talks about the "Professional Loudspeaker Reconers Association". I didn't know there was such a thing but I think that they mainly serve the proaudio industry. The reference is at the bottom of the page:
http://www.musicianshotline.com/archive/tech/reconing.htm
Here the writer speaks about the differences between Kapton and aluminum formers. I don't agree with all of the opinions stated here or in the previous link, but he does note a difference:
http://www.musicianshotline.com/archive/tech/reconing2.htm
Pete B.
-
I'm finding this thread difficult to navigate, so I'm posting this back at the top level. I mentioned what glues I thought were used in the 200003 woofer and confirmation from someone who knows what was actually used would be helpful.
Here's some interesting information on adhesives that are used in modern drivers:
http://www.loctite.com/int_henkel/loctite_...id=318&layout=2
Pete B.
Evolution of and Replacements for the AR 11/12" Woofer
in Acoustic Research
Posted
>The force factor or Bl(x) curve is not so pretty because this
>is a very primitive driver. The Bl peaks at almost 10 but at
>x= -3 mm, that's nearly half way through it's "linear"
>excursion. It has no small signal linear excursion due to
>this offset in the peak and this probably explains why the
>distortion does not continually decrease with decreased
>excursion.
This is why I previously asked about the orientation of the driver, it would be interesting to tilt the enclosure so that a bias is introduced into the rest position to bring the peak of the Bl curve to x=0, then retest the distortion.
Pete B.