AR1 WOOFER REPAIR

[Carlspeak]

I recently received a woofer from the classic AR1 loudspeaker sent to me by a gentleman in New Jersey. Since this was one of the first of it's type, I thought it best to document the repair job for the historians and engineers who may have an interest in its physical construction and test properties.

When I took it out of the box I discovered the cone assembly was completely loose from the frame and Alnico magnet structure. The customer had unsoldered the wires from the connector terminals, but that was all he had done. Apparently, the spider and cloth surround masonite shims had come completely unglued from the cast aluminum frame. He told me the woofer on his other AR1 was working fine.

An inspection showed the spider had essentially no stiffness and thus the whole cone sagged almost 1/4 inch below where the vc windings should have been located relative to the top magnet pole plate. The sagging caused the intact, flexible cloth surround to buckle and wrinkle in a number of places around its diameter.

Dcr meas. was 7.6 ohms @ 1 khz and 2.48 ohms at 120 hz. VC I.D. was 1.995 inches.

Length of windings 1 inch (about 1/8 inch shorter than AR3a VC winding length).

There were ten 1/4 inch diameter vent holes equally spaced around the VC just above the top of the windings. The overall length of the VC was 1.5 inches. Pole plates were 1/2 inch thick.

The weight of the cone, vc, surround, spider and surround shims was 114 grams. T/S test data from a WT2 testing showed the Mms to be just over 54 grams - pretty heavy for an 11 inch speaker.

What I have noticed with these very early Alnico magnet AR woofers is the shallow height of the cone. In this AR1 woofer, the distance from the top of the frame to the top of the pole piece was only 2.5 inches. This shallow height necessitated the spider be glued part way up the backside of the cone - something I had not seen before. Typically, spiders are glued to the OD of the VC just below the bottom of the cone.

I carefully removed the old spider and glued a new one in its place. The new spider is one I normally would use for a 3a recone job. The mesh of the fabric on the new spider was considerably coarser than the ultra-fine mesh of the original. I don't believe you can get spiders with that fine a fabric mesh any longer.

Surprisingly, the fabric surround was in very good shape. It was made from what looked like the same ultra-fine weave fabric as the spider. Although it looked porous when observing thru backlight, when I put my lips to the fabric, I could barely suck any air thru it. Hence, I didn't feel the need to re-seal it.

Here is some of the T/S data from the woofer test (pm me and I'll send you the complete graphic and data results from the test).

Fs = 22 hz (about 4-5 hz higher than desired, but expect it would drop with break-in of the new spider)

Re = 2.35 ohms

Qes = .1872

Qms = 4.7212

Qts = 0.18

Zmax = 61.8 ohms

Le = .643 mh

Vas = 9 cu ft

Sens = 93.4 dB 1W/1M

Below is a link to a 3 page .pdf file showing 6 pictures of the repair.

AR1_3_page_repair_doc.pdf

[dynaco_dan]

I recently received a woofer from the classic AR1 loudspeaker sent to me by a gentleman in New Jersey. Since this was one of the first of it's type, I thought it best to document the repair job for the historians and engineers who may have an interest in its physical construction and test properties.

When I took it out of the box I discovered the cone assembly was completely loose from the frame and Alnico magnet structure. The customer had unsoldered the wires from the connector terminals, but that was all he had done. Apparently, the spider and cloth surround masonite shims had come completely unglued from the cast aluminum frame. He told me the woofer on his other AR1 was working fine.

An inspection showed the spider had essentially no stiffness and thus the whole cone sagged almost 1/4 inch below where the vc windings should have been located relative to the top magnet pole plate. The sagging caused the intact, flexible cloth surround to buckle and wrinkle in a number of places around its diameter.

Dcr meas. was 7.6 ohms @ 1 khz and 2.48 ohms at 120 hz. VC I.D. was 1.995 inches.

Length of windings 1 inch (about 1/8 inch shorter than AR3a VC winding length).

There were ten 1/4 inch diameter vent holes equally spaced around the VC just above the top of the windings. The overall length of the VC was 1.5 inches. Pole plates were 1/2 inch thick.

The weight of the cone, vc, surround, spider and surround shims was 114 grams. T/S test data from a WT2 testing showed the Mms to be just over 54 grams - pretty heavy for an 11 inch speaker.

What I have noticed with these very early Alnico magnet AR woofers is the shallow height of the cone. In this AR1 woofer, the distance from the top of the frame to the top of the pole piece was only 2.5 inches. This shallow height necessitated the spider be glued part way up the backside of the cone - something I had not seen before. Typically, spiders are glued to the OD of the VC just below the bottom of the cone.

I carefully removed the old spider and glued a new one in its place. The new spider is one I normally would use for a 3a recone job. The mesh of the fabric on the new spider was considerably coarser than the ultra-fine mesh of the original. I don't believe you can get spiders with that fine a fabric mesh any longer.

Surprisingly, the fabric surround was in very good shape. It was made from what looked like the same ultra-fine weave fabric as the spider. Although it looked porous when observing thru backlight, when I put my lips to the fabric, I could barely suck any air thru it. Hence, I didn't feel the need to re-seal it.

Here is some of the T/S data from the woofer test (pm me and I'll send you the complete graphic and data results from the test).

Fs = 22 hz (about 4-5 hz higher than desired, but expect it would drop with break-in of the new spider)

Re = 2.35 ohms

Qes = .1872

Qms = 4.7212

Qts = 0.18

Zmax = 61.8 ohms

Le = .643 mh

Vas = 9 cu ft

Sens = 93.4 dB 1W/1M

Below is a link to a 3 page .pdf file showing 6 pictures of the repair.

Hi Carl;

Thank you for posting your project.

[Carlspeak]

By pure coincidence I happened to have an AR1W woofer in my possission and took some time this morning to take some pictures and make some comparisons with the AR1 woofer discussed in my original post. The 1W was not in need of repair and I suspect it is in original form. It came from a cabinet marked with the Ser. #1938. Ser. # for the AR1 speaker is not known.

The 1W woofer tested similar to the AR1. Although it's Fs was about 4 hz lower.

The 1W woofer was constructed somewhat differently from the AR1 woofer. The cones appeared to be the same shallow shape. Dust caps were different. The surrounds were quite different as shown in the pictures. The 1W had a flat accordian fabric surround similar to those seen on professional woofers, whereas the AR1 woofer had a more 'traditional' large single roll.

The 1W woofer frame was similar in size to the AR1 woofer but was from a different casting. The 1W woofer had much thicker walls and no protrusions where the connector wires were attached (see close up photo).

Questions about differences come to mind. Why different surrounds, dust caps and frames? Was it by design during a similar time period or, was it due to incremental design changes which typically took place during a longer period of time?

The Ser. # of the AR1 may shed some light on the latter question.

TEST DATA: (again, WT2 test chart and data available, pm me for a copy)

Fs = 18 hz

Re = 2.44 ohms

Qes = .131

Qms = 2.68

Qts = .124

Zmax = 52.4 ohms

Le = .611 mH

Vas = 10.8 cu. ft.

Mms = 68 grams (heavier wgt. may be due in part to more mass in the 1W dust cap)

Sens. = 93 dB 1W/1M

[Pete B]

The weight of the cone, vc, surround, spider and surround shims was 114 grams. T/S test data from a WT2 testing showed the Mms to be just over 54 grams - pretty heavy for an 11 inch speaker.

Here is some of the T/S data from the woofer test (pm me and I'll send you the complete graphic and data results from the test).

Fs = 22 hz (about 4-5 hz higher than desired, but expect it would drop with break-in of the new spider)

Re = 2.35 ohms

Qes = .1872

Qms = 4.7212

Qts = 0.18

Zmax = 61.8 ohms

Le = .643 mh

Vas = 9 cu ft

Sens = 93.4 dB 1W/1M

Below is a link to a 3 page .pdf file showing 6 pictures of the repair.

Hi Carl,

It does not really make sense that Mms (54g) is so much lower than the measured

weight of the cone, VC, etc (114g). I computed years ago that an Mms of about 100g

is required for the AR woofer to have the correct system resonance with a high

compliance suspension. Your scale weight needs to have the weight of the shims,

part of the spider and edge subtracted to get closer to Mms, but these are small

and I therefore believe that the true value is closer to 100g. The measured

value is sensitve to SD errors and added mass or compliance depending on the

measurement method used.

Sensitivity, which should have units of 2.83V/m typically, also does not pass a

sanity check as 93.4 is quite high. This could be a result of the Mms error since

sensitivity is strongly dependent on Mms.

Thanks for sharing your data. I've been curious to know the moving mass for the

early woofers as compared to later. I measured an AR-11 woofer VC, spider, and

cone assembly on a scale and got a much lower value, in the 60s going from

memory.

[Carlspeak]

The weight of 114 g was obtained using a ditigal kitchen scale with a g option. The 54 g weight came from the WT2 T/S output using delta wgt Vas test method.

I very roughly calculated the weight of the spider and surround shims on the AR1 woofer to be about 45 grams based on the sizes of those items and the density of an old piece of masonite grille frame I had available which may or may not be the same as the shims.

So, are you saying the total weight of the cone, surround, spider and their shims and v.c should have been more in the range of 150 g or so based on your 100 g calc. plus my calc. shim weights?

[Pete B]

The weight of 114 g was obtained using a ditigal kitchen scale with a g option. The 54 g weight came from the WT2 T/S output using delta wgt Vas test method.

I very roughly calculated the weight of the spider and surround shims on the AR1 woofer to be about 45 grams based on the sizes of those items and the density of an old piece of masonite grille frame I had available which may or may not be the same as the shims.

So, are you saying the total weight of the cone, surround, spider and their shims and v.c should have been more in the range of 150 g or so based on your 100 g calc. plus my calc. shim weights?

Don't know Carl, that 45 gram estimate sounds high.

All I'm saying is that 54g does not pass a sanity check based on

what I know. It also does not agree with the woofers that

Ken measured some time ago. Not trying to be critical, just

want to determine the correct value.

The cone I measured had no surround, or masonite shims, it

did have the full spider but the foam type does not weigh much

at all. Yours had the full edge if I read you correctly, is that right?

Can't say for sure Carl, I just think that the numbers are off and

would like to determine the correct values if possible.

[tysontom]

The 1W woofer tested similar to the AR1. Although it's Fs was about 4 hz lower.

The 1W woofer was constructed somewhat differently from the AR1 woofer. The cones appeared to be the same shallow shape. Dust caps were different. The surrounds were quite different as shown in the pictures. The 1W had a flat accordian fabric surround similar to those seen on professional woofers, whereas the AR1 woofer had a more 'traditional' large single roll.

The 1W woofer frame was similar in size to the AR1 woofer but was from a different casting. The 1W woofer had much thicker walls and no protrusions where the connector wires were attached (see close up photo).

Questions about differences come to mind. Why different surrounds, dust caps and frames? Was it by design during a similar time period or, was it due to incremental design changes which typically took place during a longer period of time?

The Ser. # of the AR1 may shed some light on the latter question.

Carl,

What you are seeing with your two AR woofers is the evolutionary development of the AR 12-inch acoustic-suspension woofer from the earliest iteration to the more-modern variant with the half-round surround. The cone's relatively shallow depth and straight-side configuration was completely intentional; the original woofer cones were very stiff, and this caused some problems with upper-bass reproduction. The pleated surround and felt dust cap were Henry Kloss' brain-child since this was the conventional wisdom of the day, despite the disclosure in Villchur's patent of a half-round surround (first of its kind used commercially). Remember, it was Villchur's patent and idea, but Kloss contributed about 75% to the actual prototype construction details, including the woofer layout in the earliest versions. Since AR could not afford to have an outside firm construct the woofer (no one knew how to make highly compliant drivers at the time anyway), Kloss decided to build everything in-house, and the early woofer frames were sand-cast 3/8-inch aluminum vs. the 1/4-inch later production versions. A controversy arose about the use of a pleated vs. half-round surround, with Kloss preferring the pleated version. It was decided to compare the two quantitatively, and Villchur's half-round version was superior in terms of lower harmonic distortion and flatter response; thus the die was cast, no pun intended. Kloss later changed the felt dust cap to paper and eventually a treated-cloth dome-shaped cap was adapted, which survived over time for twenty or more years afterward. The design length for the AR-1 voice coil (includes the AR-1W) was 1-1/8 inches approximately, and the length of the AR-3a (ceramic version) was closer to 1-1/16", but both woofers were considered to have an overhang of .5-inches. The fs of the earliest half-roll AR-1 woofers was closer to 16 Hz, with some measuring 13-14 Hz. These were so compliant that many suffered collapsed spiders, similar to the one you have. Your changed spider has stiffened the rebuilt AR-1 to a higher fs than desired, but the differences are not far off.

--Tom Tyson

[Carlspeak]

Thanks Tom for your post. I was hoping you would read this thread at some point and shed some light on my questions.