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Old 14th March 2012, 02:39 PM   #1
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Default AR-94R Rebuild

Hello there!

A few years ago I picked up an old pair of AR-94Rs. While 'working', they are in pretty poor shape.

Yes, I realize these were pretty mediocre when they were new, but still they are classic 80's speakers and I think it would be fun to put some new life into them. They do, however, have some problems. I am hoping all the accumulated knowledge and talent here would be very helpful!

The first problem is that through net research I have discovered the two 8" drivers originally came with rubber surrounds. Unfortunately, somebody put foam surrounds on them. Not only that, but though the two drivers share the same basket and magnet, the two cones are slightly different, and whoever refoamed them got one pair of foam surrounds mixed up - so the question is should I worry about that, or does anybody know someone who can put the correct surrounds on correctly for a fairly reasonable cost, or perhaps where I could source the correct surrounds?

The next problem is that though the tweeters still 'work' the dust caps have been pushed in. The sound is pretty much as if there was a thick blanket over them , unless one is directly facing the tweeters.

Yes, I know, for a fairly low cost I could put far superior tweeters in their place, but I would like to make some reasonable effort at preserving that 80's sound, for posterity's sake. I do have an idle pair of JBL LE-20s I am considering substituting in them, which while not entirely authentic are paper cone tweeters of around that era so I think close enough.

The last problem is the crossovers. I am wondering if there are any improvements anybody could recommend. I do know that the non-polarized electrolytics should be replaced, and would doubtless improve the sound a lot. Also, if I put the JBL tweeters in I will have to pad them down. I will eventually be posting a schematic and driver info (WT-3!) for discussion.

Any help would be much appreciated.

Last edited by LafeEric; 14th March 2012 at 03:36 PM.
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Old 14th March 2012, 06:59 PM   #2
system7 is offline system7  United Kingdom
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LafeEric, there's plenty of info just a google away on the AR-94R model. Quite a difficult 3.5 ohm load at 200Hz apparently, but some people love them for their neutrality. It's what we call a 2.5 speaker. One bass only works at sub 500Hz to add a bit of bafflestep correction.

I think it is meant to have foamed surrounds, and a lower bass unit that is slightly different from the top one.

The tweeter should be fixable by pulling the crushed dome out with a bent pin and applying a bit of glue to the hole.

My inclination would be to try and get it back to original spec, except for better capacitors, maybe clean the tweeter level adjust pot if it has one. The AR paper cone tweeter is decent and replaceable and still available remanufactured as a CTC (?), but benefitted from the damping resistance of the pot originally.
Replacement Speakers Cone Phenolic Ring Tweeter T-135
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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Old 14th March 2012, 07:13 PM   #3
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I'm not an AR or rebuild expert, so this is just a general piece of advice: as far as the "thick blanket' quality of the tweeters, I've heard many tweeters with pushed-in dust caps which sounded fine. So combined with the fact that AR's "house sound" back then was usually described as warm but detailed, what (I think) you are hearing could probably actually be explained by aging capacitors in the xover network, because such caps can restrict - and sometimes completely prevent - the flow of power to their respective tweeter. And the end result is a speaker system with a muted high end,* but not because the tweeter itself is malfunctioning.


* IMO the end result is the creation of the reputation that generally speaking, older speakers sound "soft" and lack detail compared to modern designs....when really it's just out-of-spec components causing that sound! BUT....many speakers back then were designed to have a slightly warm personality to 1) soften the harshness of questionably engineered recordings (which still happens to this day ) and/or 2) to appeal to those people with hearing systems that are more sensitive to higher frequencies than other people, and physically cannot tolerate the output of speakers that exhibit a "brighter" sound quality.
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Old 14th March 2012, 07:21 PM   #4
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Thank you system7 for your response.

I actually looked at that tweeter at parts express:
Phenolic Ring Tweeter 8 Ohm 270-252

Trouble with that is two-fold, the AR-94 is a 125 watt speaker, and though most of that will go to the other drivers, I will always be afraid the 30 watt tweeter would sooner or later run into some hefty dynamics, and then I would be worse than when I started, because I'd have to pad those by at least 3 db too - these really don't look anything like the tweeters in the AR-94. Also, I already have the other tweeters, and they physically drop in, which the other ones wouldn't.

I actually had previously pulled out the centers just as you said, but a couple of kids birthday parties left them mashed in to the point I knew I needed to do something else - so good advice, I wish I could do it again!

This site is a source of a lot of the info I have on the AR-94:
TNT : re-building the Acoustic Research AR94

Unfortunately the page is 12 years old, so his source for replacing the surrounds no longer exists. His model is AR-94ER. Not sure of the difference, they look exactly the same - could it be the only difference is the surrounds?

The site also states that the speakers present a tough load at some frequencies, but my Adcom 5500 amp doesn't seem to have a problem with it, so I don't worry about it.

Neither his speakers nor mine have a tweeter adjust pot.
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Old 14th March 2012, 07:23 PM   #5
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Quote:
Originally Posted by River757 View Post
I'm not an AR or rebuild expert, so this is just a general piece of advice: as far as the "thick blanket' quality of the tweeters, I've heard many tweeters with pushed-in dust caps which sounded fine. So combined with the fact that AR's "house sound" back then was usually described as warm but detailed, what (I think) you are hearing could probably actually be explained by aging capacitors in the xover network, because such caps can restrict - and sometimes completely prevent - the flow of power to their respective tweeter. And the end result is a speaker system with a muted high end,* but not because the tweeter itself is malfunctioning.


* IMO the end result is the creation of the reputation that generally speaking, older speakers sound "soft" and lack detail compared to modern designs....when really it's just out-of-spec components causing that sound! BUT....many speakers back then were designed to have a slightly warm personality to 1) soften the harshness of questionably engineered recordings (which still happens to this day ) and/or 2) to appeal to those people with hearing systems that are more sensitive to higher frequencies than other people, and physically cannot tolerate the output of speakers that exhibit a "brighter" sound quality.
That could very well be - perhaps I should start with the crossover to see what it may be affecting. I sincerely doubt a 30 year old electrolytic could be working all that well....
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Old 14th March 2012, 07:25 PM   #6
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I have a set of AR94 and both woofers have foam surrounds. Try replacing all the aging capacitors in the crossover. That should bring the original sound back.
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Old 14th March 2012, 07:28 PM   #7
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Quote:
Originally Posted by LafeEric View Post
Hello there!

A few years ago I picked up an old pair of AR-94Rs. While 'working', they are in pretty poor shape.

Yes, I realize these were pretty mediocre when they were new, but still they are classic 80's speakers and I think it would be fun to put some new life into them. They do, however, have some problems. I am hoping all the accumulated knowledge and talent here would be very helpful!

The first problem is that through net research I have discovered the two 8" drivers originally came with rubber surrounds. Unfortunately, somebody put foam surrounds on them. Not only that, but though the two drivers share the same basket and magnet, the two cones are slightly different, and whoever refoamed them got one pair of foam surrounds mixed up - so the question is should I worry about that, or does anybody know someone who can put the correct surrounds on correctly for a fairly reasonable cost, or perhaps where I could source the correct surrounds?

The next problem is that though the tweeters still 'work' the dust caps have been pushed in. The sound is pretty much as if there was a thick blanket over them , unless one is directly facing the tweeters.

Yes, I know, for a fairly low cost I could put far superior tweeters in their place, but I would like to make some reasonable effort at preserving that 80's sound, for posterity's sake. I do have an idle pair of JBL LE-20s I am considering substituting in them, which while not entirely authentic are paper cone tweeters of around that era so I think close enough.

The last problem is the crossovers. I am wondering if there are any improvements anybody could recommend. I do know that the non-polarized electrolytics should be replaced, and would doubtless improve the sound a lot. Also, if I put the JBL tweeters in I will have to pad them down. I will eventually be posting a schematic and driver info (WT-3!) for discussion.

Any help would be much appreciated.
If the woofer cones are not the same, one or both might not be the original. Substitutes won't work.

The tweeter doesn't have a dust cap, what's pushed in is the dome itself. This will substantially affect the sound. One way to undo the damage if that's possible is with a vacuum cleaner and hose. The vacuum will often pull the dome back to its original shape. Other people have tried pulling it out with tape. I'd be less inclined to try that. The capacitors in the crossover network should be replaced, especially the one in series with the tweeter. I'm not getting into the capacitor debate but I recapped my AR9s with NPEs and they work just fine.

Millersound in Pa is the best place I know of for speaker repairs.

There is a great deal of information and knowledgeable assistance at Classic Speaker Pages web site. Among many who post there are former employees of Acoustic Research.
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Old 14th March 2012, 10:51 PM   #8
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I haven't read the entire (very detailed) rebuild article at this site, but it includes a pic - scroll down - of the AR94 speaker and it looks like it does employ two slightly different woofers.

And some info from the article which helps reinforce why I usually prefer acoustic-suspension to bass reflex designs:
Quote:
Thus, in practice, one subjectively feels acoustic suspension boxes have just as deep, and sometimes deeper, bass than reflex boxes - this is not really so, but appears to be so because of less phase shift. Something like tubes having a "sweet" sound, when in reality they are delivering 2-5% THD and 1-3% IM distortion, both being above the threshold of hearing. It's hardly true to life, but it sounds good.

Also, it can be shown even by measurement that in general, acoustic suspension boxes will reproduce transients better, and in AR's case much better, than most reflex boxes. This is so because the air in the box, being trapped, acts as a spring which progressively resists cone excursions backwards. This generally yields less bass overhang, since the air tends to prevent the cone from freely vibrating - something that is not possible with reflex enclosures.
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