soundminded

The four AR9 woofers will fill a room in practically any home with lots of powerful undistorted bass. The AR9 woofers are interchangeable with all other AR 12" woofers. My pair bought as store demos had some issues so the store replaced all of the drivers that came directly from the factory before I took delivery on them. The originals had round magnets, the replacements had square magnets. As this happened in 1984 I probably got the Tonegen manufactured version. They work very well. Any AR 12" woofer is likely its equal. The original LvR demo at Riverside Church against an Aolean Skinner pipe organ only used four AR 12" woofers.

I can't speak for AR90 but in AR9 the subwoofer stuffing is in the top half of the enclosure. I forget how it is kept up there. This effectively creates two resonant chambers, one undamped above the cutoff frequency of the woofers and the other correctly damped at the intended resonant frequency of the system. IMO it was very clever and works very well. The ability to do this is because the high end of the woofers are cut off at a very low frequency of 200 hz. It would not be possible to successfully use this configuration with a 3 way design where the woofer had to operate at higher frequencies. The woofer/enclosure/stuffing works on exactly the same principle as all other AS speakers. The damping is created by forcing the woofer to work to push and pull air between the stuffing fibers. This creates an aerodynamic drag due to the very high total surface area of the fibers and their close packing. The math for this is explained exactly by Newton's second law of motion applied to forced oscillation. Thiel and Small used it and the electrical properties of woofers to turn it into an easy to use cookbook recipe so that you don't have to understand it to correctly design speakers and enclosures to get the F3 and Q you want if you know the T-S parameters.  

There were never any stands made by Acoustic Research for the AR9.  The reason is that it would have defeated the purpose of having the woofers close to the floor-wall intersection, part of the original design of the AR9 to avoid the "notch" (now referred to as the "Allison Boundary Effect") in the lower frequencies caused by a reflection from the floor and from the back wall that bounces back out of phase with the speaker's output at certain bass frequencies.  Furthermore, stands would actually hurt the low-bass capabilities of the speaker slightly by raising the woofer up away from the floor boundary, much like pulling the AR9s out from the wall.

 

Therefore, if someone told you that the stands were made for the AR9, that might have been true, but the stands were likely fabricated by someone else.  For best sound, leave the AR9s on the floor -- at least a couple feet from the corners -- and not more than a few inches out from the front wall itself.  Positioned this way, the AR9 can hold its own with just about any loudspeaker ever made when it comes to delivering low-distortion, smooth and extended bass response.

 

A couple of interesting historical tidbits: (1) the AR9 was principally designed by Tim Holl and was originally going to be called the "AR-25," but the name was changed to "AR9" before the final prototypes were completed; (2) some engineers at AR were hard at work on a "powered" version of the AR9, but for some reason it never saw the light of day.  Nevertheless, the AR9 became one of AR's more successful high-end speakers ever, and the speaker is considered to be one of the company's top designs.

 

--Tom Tyson

It's been 35 years since AR9 was introduced to the market yet surprisingly few if any speakers at any price seem to be able to equal let alone outperform its bass. Certainly nothing remotely close to the price even allowing for inflation. How would an AR9 with 2 12" woofers stack up against Ken Kantor's NHT 3.3 with one Tonegen 1259 12" based presumably on the AR woofer although it has a plastic cone and a Vas I think about double the AR 12"? It's also a side firing woofer. Parts Express RS1200 series subwoofer seems to have also borrowed from knowledge gained in AR9. Its got 2 side firing 12" AS subwoofers, one on each side as with AR9 along with a fairly powerful plate amplifier. Any thoughts on either of these two designs? Genesis G1.1 and 1.2 refinements of the Infinity IRS in various versions seems to have 2 towers with six 12" AS woofer each. Servo control over one woofer in each tower (2 in the G1.2) is said to reduce distortion but this doesn't really seem necessary given the already inherently low distortion of high quality AS woofers.

The LF section of the crossover must cut off two nominally four ohm loads in parallel at 200 hz. As explained in the excellent write-up in the library by Tim Holl it must also keep the load impedance above acceptable limits for amplifiers it would typically be used with. The complex network accomplishes both. The use of the 12" driver as a true subwoofer IMO is a concession that a 3 way system simply cannot cover the entire audible range without compromise. Finally an AR speaker that does.

My foam kit has arrived & I must admit I'm very excited now! I just need to order caps now ready for the task of replacing them all!!

I only have a gas soldering iron with various tips will this be ok or should I get a mains variable one?

If you're talking about a small gas torch no this will not do. You will likely damage the equipment. Buy a soldering Iron suitable for use with electronic components. Use only rosin core solder. Practice soldering technique with scrap wire before you work on your speakers. There are many instruction manuals on line, surely on YouTube. Its very easy to learn the correct technique. apply the heat to the wire, and the solder to the wire. Do not try to melt the solder with the iron. You should heat the iron, clean it with a damp rag, and then tin the iron with solder before soldering. Make the mechanical connection between the leads first before you solder, don't rely on the solder to do that. Use an iron that's large enough. For this I'd probably use about a 100 to 150 watt iron. An iron that's too low in wattage will take too long to heat the wire. The iron should be fully hot first before you use it. Actually soldering should take no more than a couple of seconds. The flow of solder should be even and cover both wires. It should cool shiny, not dull. If it's dull you probably have a cold solder joint that will not be reliable. Reheat it and melt it again. The solder should create one smooth continuous flow between the two wires. Do not use too much solder it isn't necessary. Be careful of dripping solder damaging, shorting other components. I like to place something non flammable under the work. Before finishing, be sure to remove any loose small droplets of solder, pieces of wire, etc. that could cause a short circuit. Good luck with your speakers. Many people  who know what they are but don't have the opportunity to acquire them would be envious.