AR-11 Tweeter (200011-1) Measurements

[Pete B]

Some measurements on an AR-11 tweeter (200011-1) are given below. Measured with LAUD.

The input impedance curve showed a double bump which is common with chambered tweeters, has anyone had the dome off to see if the center pole is vented into the rear? The impedance peaks were heavily damped due to the ferro fluid. The lower frequency peak at 1360 Hz was 5.26 ohms, the minimum in between at 1865 Hz was 4.65 ohms, and the upper peak at 2427 Hz was 5.30 ohms. The tweeter was 4.0 ohms in the passband at 5 kHz.

Here are the basic measurements based on only the input impedance, and assuming that the upper peak is the fundamental resonance:

Fs = 2427 Hz

Re = 3.55

Qe = 2.76

Qm = 1.57

Qt = 1.00

The 2.83 Volt sensitivity is also important in selecting a replacement driver.

Pete B.

[Pete B]

I'm going to refer to the above tweeter and the speaker it came from as #1 and the other from the pair as #2. Tweeter #2 has an open voice coil.

I should point out that tweeter #1 also had the markings 561 8304 and Made in USA. The 8304 is probably a date code for manufacture, 4th week of 1983. Tweeter #2 has the date code of 561 8224, for the 24th week of 1982.

Pete B.

[Pete B]

I've taken a look at tweeter #2 and it looks internally just like this tweeter, but the "nose" on the center pole is made of wood:

http://www.classicspeakerpages.net/dc/user_files/427.jpg

The failure was a break in the lead in wire right at the point where the surround meets the voice coil.

One side of the voice coil has about a 1/16" gap as you would expect from the top of the windings to

the point where the treated fabric edge is glued to the VC. The other side has no gap, the fabric

meets up against the windings. I first thought that the VC was mounted at an angle then noticed

that the fabric was just cut unevenly. This does not offer any sense of quality in construction.

I didn't see an reason for the V cuts in the top plate, wondered what they are for. At first glance

there does not seem to be any reason for the double bump in the impedance curve. Most tweeters

have small vent holes in the top of the voice coil providing a path from the chamber under the dome

to the air cavity under the outer suspension, the AR tweeters do not have these holes. Ferro fluid

normally seals off these chambers when vent holes are not used. I believe that the V slots in the

top plate provide a leak past the ferro fluid, however because this leak is a narrow passage way it

acts as an acoustical mass coupling these two chambers and this explains the double bump.

Not a very clean design.

I happen to have a pair of Dynaudio D21AF tweeters that I designed into an old system but later removed.

The build quality is impressive, especially after looking at these ARs. They both measure 5.04 ohms DCR.

[Pete B]

Dynaudio D21AF tweeter looks right at home in this AR-11, unfortunately it is no longer available, and the face plate is about .25" smaller than the AR tweeter:

http://members.aol.com/basconsultants/AR11DYNT.jpg

[mluong303]

Hi, Pete

Did you listen to the D-28 tweeters in your AR-11 at all? What did they sound like as direct drop in without modified the tweeter crossover section? What modification had to be done to make them sound correctly? I remember Layne Audio at one point has the Dynaudio upgraded kit to kick the AR-3a speakers another notch. Did anyone have experience with this modification and what the modified crossover look like? I love Dynaudio drivers due to their smooth sound and well built, tight quality control even from different batches and excellent design. Unfortunately, Dynaudio drivers no longer available to the DIY consumer market anymore!

Minh Luong

[mluong303]

Correction, The question I have is related to the Dynaudio D-21AF (3/4~{!1~}) tweeter you had. The D-28 (1-1/8~{!1~}) is what I like better.

[Pete B]

These AR-11s are generously on loan to me from a friend and as you can see the woofer foam has not yet been replaced so I've not yet listened to them. I expect to have one in working order soon and will look into it, however as you might have noticed I do this for the enjoyment and often get sidetracked.

Was the upgrade that Layne offered the D28, or the D21 which would make more sense in terms of being a closer match to the original. Does anyone have the suggested crossover mods? I also like some of the Dynaudio drivers but they often seemed to skimp on the magnet and used thick (non-linear) ferro fluid as can be seen in the analysis by Linkwitz which I pointed out in another post:

http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#5239

AR also uses the thick fluid and the behavior of tweeter #1 that I tested above changed after I ran it at 1W for an hour or so. The lower peak became higher than the upper peak, it went back to the original measurement after I let it cool overnight.

Pete B.

>Hi, Pete

>

>Did you listen to the D-28 tweeters in your AR-11 at all? What

>did they sound like as direct drop in without modified the

>tweeter crossover section? What modification had to be done to

>make them sound correctly? I remember Layne Audio at one point

>has the Dynaudio upgraded kit to kick the AR-3a speakers

>another notch. Did anyone have experience with this

>modification and what the modified crossover look like? I love

>Dynaudio drivers due to their smooth sound and well built,

>tight quality control even from different batches and

>excellent design. Unfortunately, Dynaudio drivers no longer

>available to the DIY consumer market anymore!

>

>Minh Luong

>

[Guest mc]

regarding possible datecodes - are these replacement tweeters? The 11 was out of production before 1982.

[mluong303]

Since you started the post with the Dynaudio D21 driver picture, I was hoping you already have some answers or analysis data to share with us. Personally I would never bother with the Dynaudio tweeter and midrange combo since modified the crossover network is unavoidable to get them sound right in the AR-3a design. After then the woofer may be too slow to keep up with the new tweeter and midrange tonal balance! If Money is not an issue then I will definitely purchase a pair of tweeters from AB Tech Services since they are the closest matched tweeters to be used as a drop in replacement. Here is what the new tweeter looks like.

Minh Luong

[Pete B]

>regarding possible datecodes - are these replacement

>tweeters? The 11 was out of production before 1982.

Hi mc,

I gave this background in another thread:

"Interesting, I was checking out a friend's new system and there in his basement were a pair of AR-11s. He said they've not been out of the boxes in 10 years. He also said that even though they had the ferro fluid tweeters he blew about 10 of them during the time he was in college. I asked if he had enough power. He said 110W/ch at first then 300W/ch later (bridged amps, these are 4 ohm speakers and it's possible that the output protection was tripping), I guess he had enough. He says everything else is original. This confirms what I'd heard from other reliable sources about tweeter problems."

So yes the tweeters were replaced many times and I'm certain that those are date codes. Anyone know what the 561 is, I'd guess that it's a customer code for the driver manufacturer. The tweeters have it and I've seen an AR-15 that has it on the woofers.

Pete B.

[Pete B]

I'm not going to debate with you how complex the crossover mods might be, and I'll probably mod the D21AF to make it fit more easily. I believe that it will be very simple based on my experience.

Pete B.

[tysontom]

>

>I didn't see an reason for the V cuts in the top plate,

>wondered what they are for. At first glance

>there does not seem to be any reason for the double bump in

>the impedance curve. Most tweeters

>have small vent holes in the top of the voice coil providing a

>path from the chamber under the dome

>to the air cavity under the outer suspension, the AR tweeters

>do not have these holes. Ferro fluid

>normally seals off these chambers when vent holes are not

>used. I believe that the V slots in the

>top plate provide a leak past the ferro fluid, however because

>this leak is a narrow passage way it

>acts as an acoustical mass coupling these two chambers and

>this explains the double bump.

>Not a very clean design.

>

Pete,

The "V cuts" (referred to as "notches") were a vestige of the original AR-3a tweeter top plate, which used the notches for the poured-in urethane-foam suspension pieces. I think that those top plates existed for quite awhile after the end-of-production for the hard-dome 3a tweeter.

--Tom Tyson

[tysontom]

>...modified the crossover network is unavoidable to get them

>sound right in the AR-3a design. After then the woofer may be

>too slow to keep up with the new tweeter and midrange tonal

>balance....! >

>Minh Luong

>

What is meant by "the woofer may be too slow to keep up with the new tweeter?" Do you mean that the woofer "rings," or is "sluggish" and unable to follow the signal waveform? I don't follow what you mean by this.

--Tom Tyson

[Pete B]

I repaired tweeter #2 by adding new lead in wires and gluing the joint to the voice coil former as is done in most modern tweeters. I used fine strand silver wire for the first one, but did not like the way the wire flexed and therefore did the second one with true tinsel lead wire. I'll be using tinesl lead wire from now on. I added a flex loop where the wire comes out of the dome as can be seen in the pictures.

I also removed some of the excess fabric that was increasing the mass.

The tweeter measures 3.29 ohms DCR but I've not done any other tests besides listening through an 8 uF poly cap. It seems fine and I'll do measurements when I have the time.

Further improvements would be to add VC former vents and light weight ferro fluid, but these are more experimental changes that I'll probably do another time.

Tweeter #2 foam front removed:

http://members.aol.com/basconsultants/AR11TDMZ.jpg

Dome removed, note notches in top plate and wood cap on center pole:

http://members.aol.com/basconsultants/AR11TGPZ.jpg

Dome and voice coil:

http://members.aol.com/basconsultants/AR11TVCS.jpg

Tweeter #2 repaired with new lead wires:

http://members.aol.com/basconsultants/ARTWFX1.jpg

Tweeter #2 close up:

http://members.aol.com/basconsultants/ARTWFX2.jpg

Pete B.

[Pete B]

Thanks for you comments Tom,

I remember you mentioning this in another thread and I do believe the notches are now serving to vent the two chambers, however VC former vents are a much better way and are the industry standard.

Pete B.

[Pete B]

They're back, but unfortunately not the D21:

http://www.speakerbits.com/Default.aspx?cat=8

Pete B.

[mluong303]

What I meant was it may be a bad idea to mate Dynaudio Tweeter and midrange combo to the AR-11 woofer even if one is knowledgeable enough to modify the crossover to get them to work together. The result will obviously steer away from the original AR sound. Still I would like to hear others listening experience and feeling of the modified AR-11 or AR-3a with the Layne Dynaudio upgrade kit installed to tell what the modified AR speakers sound like, Great, So-So or it is better off stay with the Original. I believe the Dynaudio tweeter, midrange and woofer are all 8 Ohms drivers (unless you get a hold of the cheaper automobile driver line which are rated at 4 Ohms). The 12~{!1~} Dynaudio woofer to go with these tweeter and midrange has lighter polypropylene cone, bigger voice coil and higher sensitivity so it will be quite different from the AR-11 woofer ( the original US made or the later Tonegen replacement).

Minh Luong

[Pete B]

I'd like to hear more about the Layne Dynaudio upgrade, however a new thread should probably be started. As I read you now it sounds like the kit included a mid and woofer which seems odd since they don't really match the crossover or enclosure as you point out. I like the D21 as a top of the line upgrade because it is so similar and there is a need, as the original tweeters were lacking, but I also believe there is a need for a low cost replacement. My intent is to upgrade/replace only as needed. I heard an all Dynaudio 3 way by Mark Levinson at an audio show many years ago and it did sound very good.

Pete B.

>What I meant was it may be a bad idea to mate Dynaudio

>Tweeter and midrange combo to the AR-11 woofer even if one is

>knowledgeable enough to modify the crossover to get them to

>work together. The result will obviously steer away from the

>original AR sound. Still I would like to hear others listening

>experience and feeling of the modified AR-11 or AR-3a with the

>Layne Dynaudio upgrade kit installed to tell what the modified

>AR speakers sound like, Great, So-So or it is better off stay

>with the Original. I believe the Dynaudio tweeter, midrange

>and woofer are all 8 Ohms drivers (unless you get a hold of

>the cheaper automobile driver line which are rated at 4 Ohms).

>The 12~{!1~} Dynaudio woofer to go with these tweeter and

>midrange has lighter polypropylene cone, bigger voice coil and

>higher sensitivity so it will be quite different from the

>AR-11 woofer ( the original US made or the later Tonegen

>replacement).

>

>Minh Luong

>

[Pete B]

...

[Pete B]

I emailed Speaker Bits asking if they could make the D21 available and they said that they'd be getting more later this year or early next year.

Pete B.

[Pete B]

I should mention here that after seeing the internals of the AR tweeter and measuring some of the dimensions I believe that it should be fairly easy to adapt a replacement dome/voice coil from those commonly available as I mentioned in another thread:

http://madisound.com/images/product/small/600058.jpg

Lots more replacement parts here:

http://www.madisound.com/cgi-bin/index.cgi...id=141931.21326

Pete B.