AR-3 Driver Impedance Values

[Guest Mandrake]

I bought a somewhat abused pair of AR-3 speakers at a local auction for one dollar last week, and I am working on getting them back into proper working order.

I am trying to evaluate the health of the drivers, especially the tweeters and midranges. Following the advice I got from Onplane on another board, I scratched some paint off the fat part of the driver binding tabs where these frontwired drivers are attached to take some measurements. Using a digital multimeter, I measured the resistance across the drivers from these points. I got the following results:

Tweeter: 1.9 ohm

Tweeter: 1.9 ohm

Midrange: 2.7 ohm

Midrange: 2.9 ohm

Are these values normal for the AR-3?

Thanks for your help.

http://www.classicspeakerpages.net/dc/user_files/1611.jpg

[dynaco_dan]

Hi there;

I do hope that there was at least some taxes at that price. lol

Very nice close-up photo.

One dollar will buy you a speaker terminal nut, usually.

The cabinets can be restored to a very close original appearance with some time and a labour of love.

You removed the grills, for what reason?

It is normal that removing the grills breaks the frames.

Usually, no one will suggest removing them, unless, they need further servicing.

Your readings would indicate that the tweeter and mid voice coils are not open, at least.

Can you please expand upon the speakers, what they do or don't do, when connected to a functioning stereo system.

The pots, when corroded, are often a cause of no output from these drivers.

If you turn them back and forth gently for 10 or so turns, there should be intermittant output, gradually.

If so, do a google, there is oodles of help cleaning those pots.

Looking at the normal center position, the pots only turn about 1/4 turn to the left or right of center.

If they do not turn by finger turn, do not force them with pliers.

Good luck, absolutely an outstanding buy.

[Carlspeak]

I think the best way to assess the health of the tweeter and mid is to play some music thru them as Vern suggests.

The odd VOM readings you got are the result of measuring multiple components - a definite no no unless you are versed in electrical circuitry. To get accurate individual readings you must disconnect each component from the rest of the circuit. Judging from the vintage shown in the photo, you most likely have a 4 ohm speaker there. Generally, 4 ohm drivers DCR runs around 3 ohms.

As Vern noted, the important result of your readings is that you got one. I wouldn't worry about what values you got.

Simply play them and judge for yourself how they sound. Hopefully the rheostats are still functional and allow some output from the mid and tweeter.

If the purpose of taking those reading in the first place was that you didn't get any sound from the tweeter and mid, then the problem is most likely with the rheostats, not the drivers themselves.

Take out the woofers and open the the rheostats up to see if there is an green corrosion. If so, clean them up. There are many posts about doing this.

Enjoy!

[onplane]

Hi, Mandrake!!

Those readings are meaningless if you haven’t cut the black wire from the pots. If you haven’t cut those black wires, then you are measuring the drivers + pots.

Now, if the wires are still connected to the pots, you can still do some diagnosis as follows:

1. center the pots and take a reading

2. move the pot all the way clockwise and take another reading

3. move the pot all the way counter-clockwise and take another reading

If all readings are exactly the same, that can only happen when the wiper on the pot is corroded and making no contact with the balance of the pot.

If you read 16 ohms and then zero (or a very low value like .7) ohms, this is bad news as it means the driver is probably open.

Now, the above tests always will work on the tweeter. They WILL work on the mid as well, if you have the AR-3 version WITHOUT the coil across the mid-range.

Hope this helps …

Jerry

[dynaco_dan]

Hi again;

The readings that you took do have a meaning.

The drivers voice coils are not open, that is all.

It does not tell us whether they are burnt or blown, only not open, as in a cut or burnt wire.

By your testing method, the pot is not being tested, nor could it be with a cap in series.

There is no parallel path in this loop.

But other than running a music or a sine wave source through the speaker system, we won't know if they work or not.

Absolutely do not cut one or both leads and try to run a signal through the drivers, without the caps or coils in line.

To do so is almost instant destruction.

If you have a raw driver, please not these ones, in your hand, you can, using any 1 1/2 volt battery, place the battery across the two leads for a quicky test.

I try to always polarize the drivers.

Usually there is a red dab, cross or first aid plus sticker on the postive terminals.

Touch the positive of the battery to this terminal and the negative to the other.

It won't hurt anything if you happen to reverse these connections.

You only need to touch very briefly for a bleep to happen or not.

For a woofer, the cone will move out when touched, very visible in it's effect.

For mids and tweeters their movement is too slight to usually see with the naked eye.

These few suggestions are for other drivers you may have in the shop.

If you were to place your VOM leads across the mid or tweeter, with the leads not connected, you will find a DCR reading close to 2.75 ohms for these 4 ohm drivers.

Good luck.

If you are successful thus far, please do not remove the drivers just to look inside.

There is a very good chance you will damage or destroy a driver.

[onplane]

>Hi again;

>

>The readings that you took do have a meaning.

>

>The drivers voice coils are not open, that is all.

>

>By your testing method, the pot is not being tested, nor could

>it be with a cap in series.

>

>There is no parallel path in this loop.

>

>Absolutely do not cut one or both leads and try to run a

>signal through the drivers, without the caps or coils in

>line.

>

>To do so is almost instant destruction.

Hi, Vern!

Vern, since the pots are also across each driver, with those readings the drivers COULD be open. Mandrake could be measuring the resistance in the pots! That's why I instructed Mandrake to move the pots and take additional readings. (Now, it gets further complicated in the mid-range, when we have the AR-3 version that has a coil shunting the mid-range. I'm fairly certain Mandrake doesn't have this version from comments he made on another forum.)

The only thing we can say with certainty is that the drivers are NOT shorted out. Shorted drivers would cause a reading of zero ohms.

As for "instant destruction", I never instructed Mandrake to run a signal with the black wire cut from the center wiper. However, if he did there would be NO sound as the driver is out of the circuit. Further, there would be little risk for with the driver out, the amp would see the full 16 ohms of the pot as a load.

Circuit diagram is below.

Regards,

Jerry

http://www.classicspeakerpages.net/dc/user_files/1614.jpg

[Guest Mandrake]

Thanks for these helpful replies. I should clarify some of the facts concerning these AR-3s. When I first got them, there was no sound from the tweeters or mids of either speaker. Turning the pots back and forth did not help. So I ordered some replacement parts (8 ohm L-pads and new Dayton caps from Parts Express) and have installed those parts in one speaker so far.

The pot I removed from that unit was heavily corroded. Merely spraying it with Deoxit did not clean it properly, and I don't have a Dremel to use on it. I may later decide to repair the original pots, but for now I am going to work with the L-pads.

After installation of the new parts, all of the drivers are producing sound.

The grills were already broken when I bought these, and I plan to fix them up as well as I can before reinstalling them. But for now, I'm just focusing on getting these speakers to work; cosmetics will come later.

Thanks for the help.

[Guest Mandrake]

I just got done replacing the other set of pots with L-pads. While the pots were out, I measured the resistance of the tweeter and midrange directly across the wires that go to each driver. The resistance values were the same as the ones I reported in the first post of this thread. Does anybody know if these values are normal, and if not, what do they mean?

Thanks again!

[dynaco_dan]

Hi there;

Sorry if I made it sound like you suggested cutting the wire, you did not.

My, "instant destruction", comment was for all readers in testing, directly, without a cap in series, or using larger than a 1 1/2 volt battery.

Even applying the larger voltage batteries across the terminal, as Mandrake did to do just a DCR reading, may do damage.

I for one don't want to waste a driver to find out.

I have not used a 9 volt or 12 volt car battery, these may be too much for a tweeter, if not also a mid.

A woofer may or may not survive those batteries, I would have the woofer in the enclosure to try them even.

A major point that I will make is, there is no need for more than a 1 1/2 volt battery for a quicky test.

The main point today is, they are up and running, hip, hip, hooray.

Enjoy them now.

I am still a bit frosted, that I never find these $1.00 deals. lol lol

[onplane]

>I just got done replacing the other set of pots with L-pads.

>While the pots were out, I measured the resistance of the

>tweeter and midrange directly across the wires that go to each

>driver. The resistance values were the same as the ones I

>reported in the first post of this thread. Does anybody know

>if these values are normal, and if not, what do they mean?

>

>Thanks again!

Mandrake:

The mids seem about right, but the tweeters seems a tad low. Like both Carl and Vern said, the best test once we've established that the drivers are neither open nor shorted, is to listen closely to the sound.

Unfortunately, you'll need the woofer for that as the sound from just the mid and tweeter is NOT pleasant. As I recall you need to replace the woofer surrounds. Seems to me, you are pretty much in a "holding pattern" until that is completed.

Regards,

Jerry

[Carlspeak]

>I just got done replacing the other set of pots with L-pads.

>While the pots were out, I measured the resistance of the

>tweeter and midrange directly across the wires that go to each

>driver. The resistance values were the same as the ones I

>reported in the first post of this thread. Does anybody know

>if these values are normal, and if not, what do they mean?

They mean you still are measuring DCR of the two drivers. Your well done picture shows each driver shares a common ground connection. Each driver still isn't isolated completely as I suggest earlier.

Good work with the L-pads. Do they work okay? Purists who post here say the results aren't the same as with true 15-16 ohm Rheostats.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[onplane]

>>I just got done replacing the other set of pots with

>L-pads.

>>While the pots were out, I measured the resistance of the

>>tweeter and midrange directly across the wires that go to

>each

>>driver. The resistance values were the same as the ones

>I

>>reported in the first post of this thread. Does anybody

>know

>>if these values are normal, and if not, what do they

>mean?

>

>They mean you still are measuring DCR of the two drivers. Your

>well done picture shows each driver shares a common ground

>connection. Each driver still isn't isolated completely as I

>suggest earlier.

>Good work with the L-pads. Do they work okay? Purists who post

>here say the results aren't the same as with true 15-16 ohm

>Rheostats.

>

>

>Remember, it's all about the music

>

>Carl

Carl, if the pots are out, then his measurements are really of just the individual drivers. There is one exception and that is if by chance he has an older AR-3 which has that shunt coil hidden behind fiberglass someplace. Then his measurement will be of the mid and coil together.

The common line you see in the photo, is the line that ends at terminal T. The caps will block DC and prevent the other driver from influencing the readings.

(You can actully learn quite a bit by taking several measurements from the front and changing the position of the pots. For one you can determine whether the drivers are shorted or opened. For another, you can determine whether the pot wipers are corroded.)

Regards,

Jerry

[dynaco_dan]

Hi there;

I missed the woofers needing new surrounds.

Not shown in that great photo.

Being AR-3 speakers, I assumed, that they would have the older cloth surround types.

I do not know with any certainty, that the AR-3's were still being produced, after the foam surrounds were introduced.

Live and learn, I say.

[Guest Mandrake]

When I took my measurements, I was using the three wires inside the cabinet that go up to the front wiring posts. They are Green (mid), Black (tweeter) and Yellow (common). As far as I know there is no choke coil on the mid. The mid dome has a felt pad over it, which I thought indicated there was not a mid coil (based on a Layne Audio diagram, attached below). There was certainly no mid coil visible in the area of the crossover components, just the woofer coil.

The sound of these speakers, now that they are firing on all cylinders, is a lot better than when they were playing through the woofers only, but there seems to be something missing. From what I've read here and elsewhere, these should sound fantastic. They still seem a bit muddy in the low end, and as if there is something missing in the high end. I would not say that they have great clarity or precision. Since I don't have another, perfect, pair to compare to, I am not sure exactly what they are supposed to sound like.

Thanks again for your helpful remarks!

[RoyC]

Your dcr measurements are on the money. If you are satisfied with the l-pads, you are good to go.

It wouldn't hurt to measure the capacitors at some point.

Roy

[Guest Mandrake]

Actually, the woofers do not need surrounds. I should have corrected that sooner. They are the cloth surrounds. I suppose they may need to be treated for airtightness. Below is a pic.

Thanks.

http://www.classicspeakerpages.net/dc/user_files/1618.jpg

[Guest Mandrake]

>Your dcr measurements are on the money. If you are satisfied

>with the l-pads, you are good to go.

>

>It wouldn't hurt to measure the capacitors at some point.

>

>Roy

Roy,

Do you mean it is normal for an AR3 tweeter to have dcr of just 1.9 ohm? Have you measured others that were in this range, or is there some literature that shows this is the correct value? I appreciate any leads.

I replaced the stock capacitors with new Dayton units, so those should be up to snuff.

Thanks for your help.

[soundminded]

Having read your original posting and below, I think this is excellent news. There is every reason to believe that the drivers are all in perfect condition. I base this on the fact that both units test similar and that there is no obvious buzzing or distortion which would be likely if they were damaged. The photo of the woofer and your posting suggests its suspension is in excellent condition. At most, a suitable resealant such as XL-49 sold by Orange County Speaker inc (1-800-897-8373) is all that is needed to restore the drivers. A foam gasket to seal the driver against the cabinet may also be a good idea to restore air tightness. With replacement of the capacitors and cleaning up or replacing the pots, they might sound as good as new. Congratulations and good luck.

[onplane]

>Hi there;

>

>Sorry if I made it sound like you suggested cutting the wire,

>you did not.

>

Hi, Vern!!

For people that have no meters, I often recommend that they cut the wiper wires and solder to the low (non-yellow wire) terminal of the pot.

Then, when you connect an amp, it's exactly the same as if you set both pots to the "max increase" position.

Vern, this is a perfectly valid way of testing the drivers to see whether they are working OK. The 16 ohms is still in the circuit as are all of the other components.

Eventually, something will have to be done about the pots, but this at least this quick test determines whether drivers need to be replaced as well.

Lastly, your comment about multi-meters and potential damage to drivers peeked my interest. You are correct most DMM's use 9 volt batteries. Turns out there is some currently limiting going inside the DMM. To test I connected the DMM leads to my scope. This is what I learned

Initial voltage: 3 volts

Voltage when measuring low resistance: <1 volt

Vern, this makes sense as otherwise the batteries wouldn’t last very long. I know that in the old fashioned analog multi-meters, they always had a 1.5 volt battery for ohms tests on the low resistance scales.

Hope this helps…

Regards,

Jerry

[onplane]

Mandrake:

I don't like the looks of that "crack" in your woofer that's around 4 o'clock from the dust cover.

I'd strongly recommend that you do the pressure test on that woofer.

Roy, can help here. He understands this test better than I.

Regards,

Jerry

[Guest Mandrake]

>Mandrake:

>

>I don't like the looks of that "crack" in your

>woofer that's around 4 o'clock from the dust cover.

Jerry,

I think that crack in the photo is just a trick of the light. Looking at it in real life, I don't see anything particularly noteworthy at that point.

Thanks.

[dynaco_dan]

Hi there;

Very nice photo. MMMMMMMMM

I like this woofer, can you tell. MMMMMMM

[onplane]

>>Mandrake:

>

>I think that crack in the photo is just a trick of the light.

>Looking at it in real life, I don't see anything particularly

>noteworthy at that point.

>

>Thanks.

Mandrake:

I'd still do the pressure test as it will tell you if you have "leaks". Actually, the leaks can be anywhere, surrounds, dust cap, hidden cracks, etc.

Regards,

Jerry

[RoyC]

>Do you mean it is normal for an AR3 tweeter to have dcr of

>just 1.9 ohm?

Yes, I have measured many AR drivers. The later 3/4" "4 ohm" dome typically measures 2.3 to 2.5 ohms dcr, and your earlier, orange 1" dome specimen typically measures .5 ohms lower, so 1.9 ohms dcr is right in the ballpark. Your woofers will measure around 2.6 ohms dcr.

Remember that the impedance will vary with frequency, and the crossover and level controls will have an effect. With that said, the AR-3 and 3a are well known to be very low impedance speakers. It is prudent to have a high current amp capable of driving low impedances if you intend to drive them at high volume.

>I replaced the stock capacitors with new Dayton units, so

>those should be up to snuff.

I remembered having read that after I posted..sorry...

Roy

[Carlspeak]

>>>I just got done replacing the other set of pots with

>>L-pads.

>>>While the pots were out, I measured the resistance of

>the

>>>tweeter and midrange directly across the wires that go

>to

>>each

>>>driver. The resistance values were the same as the

>ones

>>I

>>>reported in the first post of this thread. Does

>anybody

>>know

>>>if these values are normal, and if not, what do they

>>mean?

>>

>>They mean you still are measuring DCR of the two drivers.

>Your

>>well done picture shows each driver shares a common

>ground

>>connection. Each driver still isn't isolated completely as

>I

>>suggest earlier.

>>Good work with the L-pads. Do they work okay? Purists who

>post

>>here say the results aren't the same as with true 15-16

>ohm

>>Rheostats.

>>

>>

>>Remember, it's all about the music

>>

>>Carl

>

>

>Carl, if the pots are out, then his measurements are really of

>just the individual drivers. There is one exception and that

>is if by chance he has an older AR-3 which has that shunt coil

>hidden behind fiberglass someplace. Then his measurement will

>be of the mid and coil together.

>

>The common line you see in the photo, is the line that ends at

>terminal T. The caps will block DC and prevent the other

>driver from influencing the readings.

>

>(You can actully learn quite a bit by taking several

>measurements from the front and changing the position of the

>pots. For one you can determine whether the drivers are

>shorted or opened. For another, you can determine whether the

>pot wipers are corroded.)

>

>Regards,

>Jerry

>

Jerry. I just happened to have two stand alone similar drivers from an AR2 speaker. The mid meas. 6.3 ohms. The tweeter measured 4 ohms. When I touched one of the mid wires to one of the tweeter wires while measuring the tweeter impedence the VOM reading dropped to 2 ohms. This little experiment appears to support my earlier statement.

In any case, this discussion is moot now that Mandrake has replaced his corroded pots and at least gets sound out of those drivers, even though he seems a bit dissatisfied with it.

Regards,

Carl

Carl's Custom Loudspeakers