New AR-9 Project

[ar_pro]

We've begun work on our fifth AR-9 restoration - this one has involved rounding up replacement drivers for all but the original woofers, which Millersound re-foamed with typical quality and care.

New this time will be an *external* crossover, which will give us the ability to try different component layouts, and more easily compare any effects from capacitor/choke orientations and substitutions. At some point, it will also be possible to use this speaker with an electronic crossover and multiple amplifiers, but that's down the road.

Internal wiring will be completely replaced, with all connections soldered and routed to 4 pairs of binding posts. New level control switches will be located at the crossover, and the original switch covers will be filled in, and powder-coated to match the appearance of the tweeters and mids, whose plate surfaces have been finished in the same manner. All of the front-panel stickers and paint have been removed, prior to sanding and refinishing.

The completed speaker will not have an Acoustic Blanket - after listening to with & without-blanket 9s, we've concluded that the speaker tends to open up a bit more in a large listening area, especially with the front grills removed. Tom Tyson commented some time ago that he wasn't completely convinced that the Blanket was an altogether useful addition, and I'm tending to agree at this point.

Photos of the crossover area are attached, and we're open to suggestions on how best to compensate for the increase in cabinet volume from the removal of the crossover components. Any "outside-the-box" (sorry) thoughts, boys?

[tysontom]

>We've begun work on our fifth AR-9 restoration - this one has

>involved rounding up replacement drivers for all but the

>original woofers, which Millersound re-foamed with typical

>quality and care.

>

>New this time will be an *external* crossover, which will give

>us the ability to try different component layouts, and more

>easily compare any effects from capacitor/choke orientations

>and substitutions. At some point, it will also be possible to

>use this speaker with an electronic crossover and multiple

>amplifiers, but that's down the road.

>

>

>Photos of the crossover area are attached, and we're open to

>suggestions on how best to compensate for the increase in

>cabinet volume from the removal of the crossover components.

>Any "outside-the-box" (sorry) thoughts, boys?

>

ar_pro

Great job on the AR-9 project and images! As we have discussed previously, there are some critical things to keep in mind, however, regarding the crossover:

(1) The AR-9’s cabinet is approximately three-times larger than the volume of an AR-3a, and with two woofers, has double the radiating surface. These two standard 4-ohm 200003-type flat-side woofers are mounted in *parallel,* which gives them 6 dB more output in the deep bass, but at frighteningly low impedance (less-than 2 ohms). The large cabinet also seriously over-damps the woofers at low frequencies.

(2) AR’s solution for this was to design a “tank” or resonant circuit (designed by Alex DeCosta, a senior design engineer working under Engineering Director Tim Holl). This circuit was nicknamed AR’s “Electronic Automatic Transmission,” by AR publicists. The crossover network for the two *parallel* woofers is a choke and capacitor in series, and a resistor across these two elements, on one leg of the parallel-woofer circuit.

(3) At or near system resonance, the choke and capacitor are essentially a short-circuit; the presence of the resistor is irrelevant. As the signal frequency increases, the impedance of the resonant circuit also goes up, and the speaker system output goes down. Thus, the deep bass is pulled up as much as 6 db by the parallel connection of the speakers, but above resonance system output is pushed down to blend with the upper drivers.

(5) A critical amount of polyester cabinet wadding is placed *above* the woofer cavity brace to achieve proper damping. It is therefore extremely important not to add material or to change the density or change the material-type of the filling or to add filling to the bottom cavity. This is critical to proper performance.

The result of all this is that the lowest point in the impedance curve now is now an acceptable 3.2 ohms, and the system is flat at its 35 Hz resonance and down only 3 dB at 28 Hz.! The system is also critically damped with a Q of 0.5. This accounts for much of the AR-9s outstanding bass response, rivaled by few full-range speakers even to this day.

--Tom Tyson

[tysontom]

>

>(2) AR’s solution for this was to design a resonant

>circuit (designed by Alex DeCosta, a senior design engineer

>working under Engineering Director Tim Holl).

>

Correction: it is Alex de Koster, not “DeCosta.” Steve F pointed this out to me previously, but I forgot it. By the end of the 1970s, de Koster was AR’s Chief Engineer under Vice President of Engineering, Tim Holl. Alex de Koster was subsequently made Vice President of Engineering and Advanced Development at some point during the mid-1980s, and in 1984 de Koster and Ken Kantor co-authored a white paper entitled, “Magic Speaker MGC-1 -- New Directions in Loudspeaker Design.”

--Tom Tyson

[ar_pro]

Thanks for the information, Tom. Interestingly, I have not seen two AR-9 systems with identical cabinet wadding installations.

Viewed from above, the AR-9 blueprint clearly shows four individual rolls of cabinet damping, with some material lining the sides. The actual *amount* of polyester fill seems to be consistant, but the application seems to have been open to considerable interpretation!

I'm interested in what to use to fill in the volume once occupied by the crossover components - any ideas?

[tysontom]

>Thanks for the information, Tom. Interestingly, I have not

>seen two AR-9 systems with identical cabinet wadding

>installations.

>

>Viewed from above, the AR-9 blueprint clearly shows four

>individual rolls of cabinet damping, with some material lining

>the sides. The actual *amount* of polyester fill seems to be

>consistant, but the application seems to have been open to

>considerable interpretation!

>

>I'm interested in what to use to fill in the volume once

>occupied by the crossover components - any ideas?

ar_pro,

You could probably glue a large brick to the bottom of the cabinet, and that might compensate for the difference in interior volume; however, I doubt that doing *anything* would have any appreciable effect on system resonance and so forth. It's just too-little a difference to matter that much. You might lower the resonance one cycle or so, but probably not much else. You could add a couple of braces to the cabinet, and that would take up some of the added volume, but overall I really wouldn't worry much about it. Other members might have suggestions that make better sense. Just be sure to leave that "electro-automatic transmission" crossover in the circuit.

--Tom Tyson

[harry398]

On 10/28/2005 at 11:19 AM, tysontom said:

>We've begun work on our fifth AR-9 restoration - this one has

>involved rounding up replacement drivers for all but the

>original woofers, which Millersound re-foamed with typical

>quality and care.

>

>New this time will be an *external* crossover, which will give

>us the ability to try different component layouts, and more

>easily compare any effects from capacitor/choke orientations

>and substitutions. At some point, it will also be possible to

>use this speaker with an electronic crossover and multiple

>amplifiers, but that's down the road.

>

>

>Photos of the crossover area are attached, and we're open to

>suggestions on how best to compensate for the increase in

>cabinet volume from the removal of the crossover components.

>Any "outside-the-box" (sorry) thoughts, boys?

>

ar_pro

Great job on the AR-9 project and images! As we have discussed previously, there are some critical things to keep in mind, however, regarding the crossover:

(1) The AR-9’s cabinet is approximately three-times larger than the volume of an AR-3a, and with two woofers, has double the radiating surface. These two standard 4-ohm 200003-type flat-side woofers are mounted in *parallel,* which gives them 6 dB more output in the deep bass, but at frighteningly low impedance (less-than 2 ohms). The large cabinet also seriously over-damps the woofers at low frequencies.

(2) AR’s solution for this was to design a “tank” or resonant circuit (designed by Alex DeCosta, a senior design engineer working under Engineering Director Tim Holl). This circuit was nicknamed AR’s “Electronic Automatic Transmission,” by AR publicists. The crossover network for the two *parallel* woofers is a choke and capacitor in series, and a resistor across these two elements, on one leg of the parallel-woofer circuit.

(3) At or near system resonance, the choke and capacitor are essentially a short-circuit; the presence of the resistor is irrelevant. As the signal frequency increases, the impedance of the resonant circuit also goes up, and the speaker system output goes down. Thus, the deep bass is pulled up as much as 6 db by the parallel connection of the speakers, but above resonance system output is pushed down to blend with the upper drivers.

(5) A critical amount of polyester cabinet wadding is placed *above* the woofer cavity brace to achieve proper damping. It is therefore extremely important not to add material or to change the density or change the material-type of the filling or to add filling to the bottom cavity. This is critical to proper performance.

The result of all this is that the lowest point in the impedance curve now is now an acceptable 3.2 ohms, and the system is flat at its 35 Hz resonance and down only 3 dB at 28 Hz.! The system is also critically damped with a Q of 0.5. This accounts for much of the AR-9s outstanding bass response, rivaled by few full-range speakers even to this day.

--Tom Tyson

I would love to here more from Alex de kostera, on his theories on the AR 9 woofer crossover.

Do these people ever visit this site?

[tysontom]

What theories about the AR9 woofer Crossover?  The crossover is 200 Hz, but I think you are referring to the woofer resonant circuit, described above, right?  One word of advice: don't try to redesign it or modify it if you want the system to perform properly.  If you have a full acoustics-testing laboratory, you might be able to make worthwhile changes, but that is unlikely.  The AR9 design was truly optimized for flat, linear output in the deep bass.  It is not perfect, but it is not far from it.  The design took over two years to complete from start to finish if I understand it correctly, literally thousands of hours of testing and design work, so it was not an insignificant effort on the part of those engineering and marketing personnel!  AR threw a lot of weight behind the design and spent considerable R&D money developing it.  The company went all out on the tower speakers, and the results show it.

I made a mistake in my original description above.  The AR9's woofer impedance-crossover design was I believe primarily the work of Alex P. deKoster, not "DeCosta," as I stated.  I apologize for the gross misspelling of his name.  He became Chief Engineer working under Engineering Director Tim Holl.  Much of the design was a collaboration of several engineers, including James Kate, Alex deKoster, Tim Holl, and others, and long-time visionary C. Victor Campos (Campos worked at AR in the early 60s and left in the mid-60s for KLH, but he returned again in the 1970s).  I don't think any one person can take full credit for the design of the tower speakers of that period. 

These guys are quite a bit older now and have long-since retired from the audio rat race.  After spending many years working around loudspeakers, most have lost interest in the intricate details of the products they designed, and most have moved on to other things.  So, it is not easy to get these veterans to "drop in" to visit the website.  We have been very fortunate to have Ken Kantor visit over the years to give us insight on these products, so we have to be thankful for what we can get. 

--Tom Tyson

[harry398]

Well thanks for the follow up Tom.

 

I did not say I wanted to improve it, I'm not bright enough.  However, the ar9lsi gives it a run for its money to the lowest frequencies, and beats it in some areas in fullness.    I'm Still baffled as to Why the area behind the woofers where overstuffed in the ar9lsi, and wide open on the 9.    Simply removing some of the overfill yields Tremendous bass gains.

I read the comparison of the ar9 vs nht3.3, and seriously doubt the ar9lsi would lose out to the nht3.3 on bass.  It's deep with SLAM.

 

what I like about the ar9 is the neutral tone, extreme balance, and I LIKE the appearance unlike some have expressed.   Proud owner of both 9,9lsi, 3a,98,5, connoisseur 50, and 11.   

 

[tysontom]

22 hours ago, harry398 said:

Well thanks for the follow up Tom.

 

I did not say I wanted to improve it, I'm not bright enough.  However, the ar9lsi gives it a run for its money to the lowest frequencies, and beats it in some areas in fullness.    I'm Still baffled as to Why the area behind the woofers where overstuffed in the ar9lsi, and wide open on the 9.    Simply removing some of the overfill yields Tremendous bass gains.

I read the comparison of the ar9 vs nht3.3, and seriously doubt the ar9lsi would lose out to the nht3.3 on bass.  It's deep with SLAM.

 

what I like about the ar9 is the neutral tone, extreme balance, and I LIKE the appearance unlike some have expressed.   Proud owner of both 9,9lsi, 3a,98,5, connoisseur 50, and 11.   

 

  

I may have misinterpreted your comments.  "Removing the overfill yields tremendous bass gains" implies that you felt it was better or improved.  But what I was trying to say is that pretty much everything on the AR9 and AR9Ls (and other AR speakers) was put there for a reason.  The goal was to have flat response and neutral, low-distortion reproduction. 

If you remove (or add) fiberfill to the bass enclosure, you will be changing the damping of the woofers, and if you remove material, the "Q" will go up and damping will go down.  The damping is very critical to the proper performance of this speaker, so a removal of the material in the cabinet will definitely cause a rise in bass output at resonance, giving a sense of bass gains. 

[harry398]

I got your point Tom.

 

But I believe AR was trying to TONE down the ar9lsi by overdampening it(for whatever reason).   Its TREMENDOUS NOW.  

 

the Theory of not putting stuffing behind the woofers on the AR9, then doing the opposite on the ar9lsi makes no sense.

 

I think they didnt want to surpass the bass of the AR9 like GM never wants a faster car built by them the exceedes the corvette.  Whatever the "theoretical reason" the speaker sounds fuller and outputs tremendous Bass now.  It was muffled before.

[Stimpy]

There is stuffing in the AR9 cabinet, to provide bass damping.  It just isn't directly between the woofers.  The lower 18 inches, of the cabinet is left empty, by design.  The rest of the cabinet is heavily stuffed.  Tim Holl discusses this aspect of the AR9, in his paper, on the design of the AR9.

"Cabinet Damping"

 

 

[tysontom]

1 hour ago, Stimpy said:

There is stuffing in the AR9 cabinet, to provide bass damping.  It just isn't directly between the woofers.  The lower 18 inches, of the cabinet is left empty, by design.  The rest of the cabinet is heavily stuffed.  Tim Holl discusses this aspect of the AR9, in his paper, on the design of the AR9.

"Cabinet Damping"

 

 

Stimpy is exactly right.  Here is Tim Holl's preliminary data on the prototype AR9 from December 9, 1977:

[ar_pro]

Wow. This 12 year old thread brings back some memories.

This was one of the first "naked" AR-9's that we played with (no blanket, no vinyl stickers), and we did wind up keeping the internal crossover with new caps. It was also the first one where we tried the AR-substitute polypropylene 8" lower midrange, which turned out to be a complete bust. My son kept a later set of "naked" AR-9's that originally had 8" lower-mids with badly damaged cones that Bill LeGall restored to perfect condition; he owned those for several years before finally parting with them.

It's hard to believe how easy it was to find inexpensive AR-9's on Craigslist in those days - A Golden Age!

[Stimpy]

9 hours ago, ar_pro said:

Wow. This 12 year old thread brings back some memories.

This was one of the first "naked" AR-9's that we played with (no blanket, no vinyl stickers), and we did wind up keeping the internal crossover with new caps. It was also the first one where we tried the AR-substitute polypropylene 8" lower midrange, which turned out to be a complete bust. My son kept a later set of "naked" AR-9's that originally had 8" lower-mids with badly damaged cones that Bill LeGall restored to perfect condition; he owned those for several years before finally parting with them.

It's hard to believe how easy it was to find inexpensive AR-9's on Craigslist in those days - A Golden Age!

I agree AR_Pro.  AR9's and AR90's are everywhere now, and for very good prices.  But, AR3's and AR3a's are bringing thou$ands...!!!  Unbelievable.  I'm not saying the AR3/A's aren't worthy; it's just that I would rather have the tower speakers, and save some cash. 

Oh yea, I loved those "Naked-9's".  A beautiful speaker.  I thought about doing the same thing with my 90's, but the fronts aren't veneered.  Just plywood.  So, I'll do a flat black again, when I ever finish my refinish. 

[Stimpy]

I was looking for this drawing.  It's the AR90 drawing, that shows the stuffing.  In it, you can see the upper two-thirds of the cabinet, with the four rolls of stuffing.  The AR9 used the same poly fill method.