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Got me some nice new AR7s - and they're lovely!


RobHolt

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Landed this morning for £30 and in beautiful condition.

Real teak veneer and even the covers are in good clean shape.

Two tiny scratchers that will polish out no problem.

Need new foams of course and I'll update the thread with the restoration pics and measurements once they arrive.

Unlike with my 4xa I intend to keep these 'stock'.

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IMG_0955 by trebor1966, on Flickr
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IMG_0953 by trebor1966, on Flickr
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  • 2 weeks later...

Time for an update since these are now fully restored.

For the driver foam I was aware that the driver in the AR7 has a lower Fs than some others and therefore needed a very soft surround.

I decided to try the type supplied by http://www.audiofriends.nl since this claims to be the correct type with compliance carefully matched to the particular loudspeaker.

If they are correct the Fs should sit around 25h..... well 24.4Hz will do very nicely and the driver is working to factory spec. Also when fitted into the AR7 cabinet, the system resonance is 64Hz, again perfectly to factory spec:

Here's the drivers impedance showing the Fs and minimum impedance at 5.5 Ohms:

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Here's the system plot showing the driver in box at 64Hz and confirming the crossover at 2khz, again to spec.
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The cabinets were in great condition but had a few superficial nicks, so I gave them a very light sanding and refinished with some Feed n Wax. One very liberal coat left to sit on the veneer overnight, then buffed and another coat added, left for half an hour or so and buffed.
The covers were excellent. Looking behind the brass badge showed that the exposed cloth hadn't discoloured so the covers were left alone.
The badges had turned back due to adhesive from the plastic protective covering which had never been removed. Wire wool followed by Brasso has them looking like new.
Backs were fine and have the speckled Euro finish. Switch was cleaned with Deoxit and the old cap replaced with a new Solen.
More to follow but for now some pics:
Before with disintegrated foams:
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AR7 by trebor1966, on Flickr
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IMG_0956 by trebor1966, on Flickr
Driver re-foamed:
13297539565_c28a880afe_c.jpg
IMG_0958 by trebor1966, on Flickr
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Those AR-7s look fantastic! It is interesting that your pair is strictly European, made from US components and assembled in probably the UK or Holland using that beautiful teak veneer, very popular over there. The grill material is slightly different from the original beige AR grill, but the European models may have used something slightly different anyway. The US AR-7s were originally available briefly in birch veneer stained in "Walnut Finish" or later, vinyl-clad veneer. They looked okay, but nothing as nice as the European version! All of the European "classic" ARs also had that Spackle-finished back panel, a decidedly European touch that was never done in the US. You definitely got the woofer free-air resonance correct; however, the original AR-7s had a small-radius half-round foam surround, enough to allow sufficient excursion for the small woofer, but also low enough not to cause problems with the grill molding, which was quite close to the front baffle board.

I have a pair of AR-3s that were finished in oiled-teak veneer with solid-teak grill molding, and I love the wood! I also have solid-teak tripods on which to mount the AR-3s, similar to those used in AR's Live-vs.-Recorded concerts with the AR-3 and the Fine Arts Quartet.

My large equipment cabinet is made from solid-teak Hatteras Yacht sport-fisherman doors and 5/8" teak plywood over 3/4-inch marine plywood. It is on huge industrial rollers, and the total weight is 950 lbs.

—Tom Tyson

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Those AR-7s look fantastic! It is interesting that your pair is strictly European, made from US components and assembled in probably the UK or Holland using that beautiful teak veneer, very popular over there. The grill material is slightly different from the original beige AR grill, but the European models may have used something slightly different anyway. The US AR-7s were originally available briefly in birch veneer stained in "Walnut Finish" or later, vinyl-clad veneer. They looked okay, but nothing as nice as the European version! All of the European "classic" ARs also had that Spackle-finished back panel, a decidedly European touch that was never done in the US. You definitely got the woofer free-air resonance correct; however, the original AR-7s had a small-radius half-round foam surround, enough to allow sufficient excursion for the small woofer, but also low enough not to cause problems with the grill molding, which was quite close to the front baffle board.

I have a pair of AR-3s that were finished in oiled-teak veneer with solid-teak grill molding, and I love the wood! I also have solid-teak tripods on which to mount the AR-3s, similar to those used in AR's Live-vs.-Recorded concerts with the AR-3 and the Fine Arts Quartet.

My large equipment cabinet is made from solid-teak Hatteras Yacht sport-fisherman doors and 5/8" teak plywood over 3/4-inch marine plywood. It is on huge industrial rollers, and the total weight is 950 lbs.

—Tom Tyson

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Tom, many thanks for the comments.

Now you mention it, the grille frame is thinner than on for example, my AR4xa giving less clearance between the foam roll and fabric.

You prompted me to check and I think it should be fine but will check tomorrow with some dynamic bass at a good level. I'll report back the results.

Re the teak, it's generally one of my least favourite veneers probably because so much of it looks too pale and featureless. However these 7s have nice detailing and are quite rich in colour, as are your 3s judging by the pictures.

On a separate note, the flat dust cap feels much thicker than the domed caps fitted to other 8" AR woofers. I'm wondering if this was to add a little mass and bring down the Fs, giving the ability for similar bass extension to for example the AR4 series which appear to have lighter cones and caps.

The woofer on these is very nicely produced - feels superior in finish to those from the AR4 and those from later 18s. The baskets are very smoothly pressed and painted black all over.

<edit> Given Tom's information I placed a steel rule across the cabinet edges straddling the bass driver. Driving the unit very hard with some Dub and Reggae at levels considerably above those I'd usually listen, there was about 3-4 mm between the roll surround and the rule. Since the velcro on the 7 holds the cloth flush with the cabinet edge i think this particular make of surround is a safe choice. However anyone re-foaming the 7 should definitely consider Tom's warning as I certainly have foams which might cause an issue.

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Here's the response at 1m.

This was taken with the 'speaker pulled into the middle of the room and raised 26" from the floor.

The dip at 160hz or so should be ignored - its a room effect, likely a ceiling of floor bounce cancellation:

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AR7 1m by trebor1966, on Flickr
This shows the difference between measuring on the tweeter axis and the bass driver axis. That latter is clearly preferable, indicating that you want the 7s up high if listening reasonable near-field.
The red trace is the tweeter axis:
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Overall there is some mid rise apparent and that is audible. Interesting to note that the AR6 used the same drivers but drove the bass unit via an inductor to pull down the upper end of its range. Looks like it would benefit the 7 too. Perhaps it was omitted on cost grounds given this was a small entry level model. You can't have everything for $70!
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Overall there is some mid rise apparent and that is audible. Interesting to note that the AR6 used the same drivers but drove the bass unit via an inductor to pull down the upper end of its range. Looks like it would benefit the 7 too. Perhaps it was omitted on cost grounds given this was a small entry level model. You can't have everything for $70!

Rob,

Actually, the earlier AR-6 had the inductor, but it was ultimately dropped in favor of the same single cap crossver as the AR-7. The few AR-8's I have seen, which had a 10 inch woofer and the same tweeter as the 6 and 7, also only had a single cap. I'm willing to bet it was a cost consideration. They were probably considered to be "good enough" with just the cap. Competitors of the day such as EPI and Avid were also using inductor-less/single cap designs with their similar sized models.

Roy

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Rob,

Actually, the earlier AR-6 had the inductor, but it was ultimately dropped in favor of the same single cap crossver as the AR-7. The few AR-8's I have seen, which had a 10 inch woofer and the same tweeter as the 6 and 7, also only had a single cap. I'm willing to bet it was a cost consideration. They were probably considered to be "good enough" with just the cap. Competitors of the day such as EPI and Avid were also using inductor-less/single cap designs with their similar sized models.

Roy

Roy, you are right about the AR-6 LCR crossover being dropped in favor of a simple capacitor with level control being dropped, too, in favor of the switch. This happened around the time AR moved on to Norwood in 1973; prior to that, all but the last AR-6s had the original crossover, and the earliest AR-6s had the powerful, long-throw woofer voice coil. These earliest AR-6s are harder to find these days. This, too, was dropped in favor of the "universal" woofer found in the later Norwood versions. The AR-7 always had the simple crossover, but the response was carefully tailored (part of the woofer's configuration of small surround and mass, etc) to make that little speaker as smooth as possible, and it worked well in that speaker's price category. As you state, Roy, cost was definitely a consideration, and with the forthcoming new ADD speakers, AR wanted to reduce the manufacturing cost of these earlier (and soon-to-be-discontinued) "classic" AR speakers. Most listeners could not detect much difference in the new and the old, but it was there.

Ultimately, the reliability of the AR-6 was higher, but the response of the speaker was not quite as uniform as with the original version. The AR-8 was always built to the least-demanding standards of frequency response flatness, pretty much in deference to a speaker that sounded good on jazz and rock music. The crossover in all versions of that speaker was a simple capacitor, I believe.

The first picture attached is of an actual AR-6 system anechoic-chamber calibrated response curve of the later AR-6 (except for the deep bass, the AR-7 is very similar); the second image of the original-version of the AR-6 measured in AR's semi-reverberant chamber, showing the much more important acoustic-power response (more of what you actually hear in a real room), and the final image is of the AR-6 very long-throw voice coil in the original, early version of the AR-6, compared with the famous The Advent Loudspeaker 12-inch woofer coil. The AR-6 had significantly longer linear woofer travel than the Advent, meaning that the AR-6 was probably a match for the Advent in terms of harmonic distortion, but not in system resonance frequency, as the two were about a third octave apart in that regard.

—Tom Tyson

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post-100160-0-29699100-1395503461_thumb.

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Fascinating to compare the AR6 anechoic response with my plot for the AR7.

The null in output at 1kHz followed by the peak at 2khz, followed by the gently depressed tweeter response with recovery in the final octave are common.

Tom, your comment re the change in sound between the earlier models and later versions using just the capacitor is spot on.

On the cap only models you can hear a degree of nasality and cupped hands on vocal. It's not destructive and in some instances can assist presentation - e.g. with guitar and snare which has added attack, but it's presence is certainly audible.

On my modified AR4xa I run the universal driver with a series inductor tuned to bring the driver response closer to that of the original, cloth surround driver. The result is a more natural sound IMO. The useful thing about AR drivers is the degree of performance uniformity. They all broadly track each other and where they depart it tends to be at the very upper end of the response. This makes them amenable to subtle response shaping with a single crossover component. A huge advantage over many of the drivers from other companies in later years, which rely heavily on external response shaping.

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Yet another great thread from one of the excellent UK ambassadors. Great looking Euro-AR speakers, fine diagnosis, terrific pics, test results, and overall analysis.

I often like to see these speakers with lighter-toned wood cabinets, and I normally find teak veneer to be somewhat exotic, since we rarely ever encounter this wood on AR's found here in the U.S. This pair of AR-7's, however, is a bit odd, in my opinion, but nonetheless quite attractive. Very different from the wood shown on Tom's AR-3's, this teak veneer exhibits a very pronounced linear grain structure that I would more normally associate with oak, albeit with a very golden tone here. Nonetheless, these are indeed gorgeous speakers.

Am curious about the final paragraph in post #15 - - - I reviewed your 4xa mod project but did not see any inductor used - - - am I missing something?

On both of these restoration projects (4xa's and now, the 7's), I did not find any rear views of woofers or any mention of part numbers. Not sure if your 4xa mod project utilized a woofer from an AR-18 or an AR-18s, but I'm inclined to think this was p/n 037, whereas your AR-7 resto project had the p/n 001 woofer?

Really great work, enjoyable to follow.

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The original AR-7 8-inch acoustic-suspension woofer was part number 10708-1; when mounted in the original 1973 (first year) AR-7 sealed cabinet, the system bass resonance was 68 Hz, (the fs was 25-27 Hz). This woofer was characterized by the flat cardboard dust cap, slightly thicker, and the small-radius, half-round urethane-foam surround that characterized all original AR-7s.

The first iteration of the earlier and larger AR-6 (1970) had a very different and unique 8-inch woofer (originally with a different Alnico-5 magnet structure, different from the later ceramic-magnet models), and the part number for the AR-6's woofer was 10708-2, but it was very different from the AR-7 woofer. (The early AR-4xa speakers, also 1973, actually used a third version of the 8-inch woofer, the 10708-3).

An important distinction was that the AR-6 woofer was much more compliant, and it had far greater linear excursionactually close to .75-inches peak-to-peak, vs. .375-inches for the standard wooferthan any of the other 8-inch or even 10-inch AR woofers. This earliest AR-6 woofer also had a special magnet structure with multiple pole magnets, but apparently only a few of this version were produced (this would be the super-rare AR-6s!), with later ones sharing the AR open-yoke magnet structure type with the AR-4x, AR-2ax, AR-5 and so forth, but still the very long voice coil that I described in my last post, showing significantly longer throw than even the Large Advent! The original AR-6s could out-point the AR-2ax and AR-5 in deep-bass output at lower levels due to the very long excursion and the identical 58 Hz fc as the larger 10-inch cousins! Thus... early serial number (under #1000) AR-6s from the original late-1970 productionwith original partsare probably the best AR-6s out there, and these are quite rare, and really only exceeded in bass power by the biggest AR brethren, the AR-3-series.

Enter the post-1973 era. Everything by this time had moved from Cambridge to Norwood (the very first AR-7s with wood did come from Cambridge), and the different models began to adopt a shared, standardized woofer, the #200001-1 "Universal" and ubiquitous 8-inch woofer, which was then used in AR-4, 4x, 4xa, 6, 7, 15, 16, 17, 18 and 25 models. No more open-yoke, long-voice-coil woofers.

There were other versions of the 8-inch woofer as the 1980s wore on, but basically, the original "classic" speakers all shared the exact-same woofer. This woofer began the utilization of the ceramic magnet and each of these woofers was designed with a 27 Hz fs (+/- 15%).

All a part of this great AR history!

—Tom Tyson

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Hey Tom,

It seems the "universal" woofer was quite universal. It is not unusual to find the early flat paper dust cap under rubber or plastic dome dust caps of later woofers. These woofers are mostly found in early 80's models with different part numbers, but seem otherwise identical to the universal 8 incher. Woofer Tester 2 software suggests they have very little, if any, significant response variations.

Roy

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Yet another great thread from one of the excellent UK ambassadors. Great looking Euro-AR speakers, fine diagnosis, terrific pics, test results, and overall analysis.

I often like to see these speakers with lighter-toned wood cabinets, and I normally find teak veneer to be somewhat exotic, since we rarely ever encounter this wood on AR's found here in the U.S. This pair of AR-7's, however, is a bit odd, in my opinion, but nonetheless quite attractive. Very different from the wood shown on Tom's AR-3's, this teak veneer exhibits a very pronounced linear grain structure that I would more normally associate with oak, albeit with a very golden tone here. Nonetheless, these are indeed gorgeous speakers.

Am curious about the final paragraph in post #15 - - - I reviewed your 4xa mod project but did not see any inductor used - - - am I missing something?

On both of these restoration projects (4xa's and now, the 7's), I did not find any rear views of woofers or any mention of part numbers. Not sure if your 4xa mod project utilized a woofer from an AR-18 or an AR-18s, but I'm inclined to think this was p/n 037, whereas your AR-7 resto project had the p/n 001 woofer?

Really great work, enjoyable to follow.

attachicon.gifAR-18s2.jpg attachicon.gifAR-7.jpg

Many thanks for the comments. UK ambassador - I like it :)

Re the inductor, I conducted further testing on the one original working woofer (cloth surround, open yoke, ribbed cone) I managed to repair. I found that by utilising the original AR4xa inductor and unwinding 30 turns, the response of the later universal driver matched the original more closely. Interestingly this gives 0.8mh. I think I updated the thread but will check later. <edit> Here you go: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=8011&p=99224

The driver I used in the 4xa was from the normal AR18. The 18S is quite different on testing - more sensitive and extended at the top allowing for an even smaller tweeter cap of 5uf in the 'S' models. In other areas it seems mechanically the same as the older woofer, and therefore gives less LF in smaller sealed cabinets. No free lunch - push up voltage sensitivity and change nothing else and gain mid band output at the expense of LF, all else being equal.

If you want to source suitable universal drivers for older AR 2 ways, the 17 and 18 are the best choice and most plentiful source IMO.

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Enter the post-1973 era. Everything by this time had moved from Cambridge to Norwood (the very first AR-7s with wood did come from Cambridge), and the different models began to adopt a shared, standardized woofer, the #200001-1 "Universal" and ubiquitous 8-inch woofer, which was then used in AR-4, 4x, 4xa, 6, 7, 15, 16, 17, 18 and 25 models. No more open-yoke, long-voice-coil woofers.

There were other versions of the 8-inch woofer as the 1980s wore on, but basically, the original "classic" speakers all shared the exact-same woofer. This woofer began the utilization of the ceramic magnet and each of these woofers was designed with a 27 Hz fs (+/- 15%).

All a part of this great AR history!

—Tom Tyson

Great additional information Tom.

I can confirm that my pair of 7s have the #200001-1 woofer (labelled).

The more you delve into the history of the different AR models the more you see a constantly moving picture.

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Hey Tom,

It seems the "universal" woofer was quite universal. It is not unusual to find the early flat paper dust cap under rubber or plastic dome dust caps of later woofers. These woofers are mostly found in early 80's models with different part numbers, but seem otherwise identical to the universal 8 incher. Woofer Tester 2 software suggests they have very little, if any, significant response variations.

Roy

Roy, I think you are correct: the flat cardboard dust cap was used on nearly all of the 8-inch and even 10-inch woofers until there was a cosmetic change to add a cloth dust cap. In many cases, the cardboard remained under the other cap. As far back as 1978, the lower-midrange 8-inch driver used in the AR9, AR90 and others, had the cardboard under the largish cloth dust cap.

The voice coil, spider and other details of the "Universal" woofer were virtually identical across the board. This was a "value-analysis" deal at AR once changes began at Norwood. Considering that there were numerous versions of the 8-inch woofer alone, engineers decided to standardize the drivers to simplify matters and obviously to cut costs. Attached is an image of the AR engineering area in Norwood in the 1970s showing several versions of test woofers.

—Tom Tyson

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Tom, when are you going to produce the illustrated history of AR book?

I think you should :)

I've been so inundated with business and personal issues over the past year or two that I have not had the opportunity to devote the time to it. I have been slowly working on it, and I do have the historical and archive data at hand. Time is the enemy, but hopefully I will be able to move forward on it this year.

Thanks for asking!

—Tom Tyson

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Tysontom

You have provided valuable info for anyone looking to purchase an AR6 for its unique bas performance and have raised the following question.

Both the 1975 and 1970 classic brochures describe the AR6 as having a woofer that achieves performance close to "theoretical" limits, intimating extraordinary bass performance for a cabinet its size. Do you know if the "special" woofer was still being used in 1975 or had production switched to a universal 8" by then? Asked another way, was the phenomenal bass performance limited to the first 1000 units around 1970, after which an AR6 was pretty much like any other AR 8" two way speaker?

Adams

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RobHolt, can it be assumed that your speakers have the normal (and only?) AR-7 crossover, with a single 6uF cap and a 3 ohm resistor (plus the two position switch), as shown in attached pics?

Final point about the teak veneer - - - I happened to see this page of veneer options from an Ohm speaker website and, to my eye at least, these two samples (oak, teak) illustrate very well the observations I was trying to make about the various grain structure found in teak.

And lastly, Tom's remarks (and Aadams' follow-up) about the AR-6 will prompt me to begin a new thread in the next few days (after I get a few good pics together) - - - I have recently come into possession of a fairly early pair of AR-6's which may be an excellent case study for this topic, and I'd rather keep this thread focused on the OP's AR-7's.

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