AR-2ax - AR-3 "supertweeter" DC Resistance

[johnieo]

Recently I examined a pair of early AR-2ax, serial numbers 117,xxx produced in May 1969. They use the 1-3/8-in.-diam phenolic-dome "super-tweeter" originally designed by Villchur for the AR-3. To my surprise I measured Rdc = 1.9-to-2.0 Ohms for each unit. The tweeters, rock wool, and putty were original, as were the twists in the tweeter and mid wires, which took up their slack. I expected Rdc to be approximately 5-to-6 Ohms like the woofer and midrange drivers. After asking about, learned that:

* The "Comparative AR-2ax" document says the AR-2ax used 8-Ohm super-tweeters, not their 4-Ohm AR-3 counterparts.

* RoyC has opened several early AR-2ax cabinets and measured only 2-Ohms Rdc in the 1-3/8-in. tweeters.

* There is currently an e-Bay auction: 110209884627 for a pair of AR-2ax tweeters with Rdc of 1.9 and 1.7 Ohms.

* Villchur replied: " I have no memory of changing the 4-ohm AR-3 super-tweeter to 8 ohms for the sake of the AR-2ax (the x referred to the super-tweeter), but I was not up on every production change if it had no effect on final performance. A 4-ohm speaker will have a higher output level than an 8-ohm speaker when connected across the same amplifier terminals. I don't think there was any change when I was at AR."

* Tom Tyson thinks there were separate drivers -- that Villchur -- as he said himself, was not up on every production change, and that there were different part numbers for the AR-2ax tweeter and the AR-3 tweeter. Tom will research this further.

These comments apply only to the early AR-2ax (‘64-‘69) that used the 1-3/8-in-diameter “super-tweeter” – see photo attached -- and not to the later version, which used the 8-Ohm version of the 3/4-in-diameter AR-3a tweeter.

So, as an experimentalist, I would ask what dc resistances have others AR-2ax owners measured? For me, I am satisfied to clean the pots, replace caps, and play this pair without worry that I will do irreparable damage, as they are not unique.

Cheers

[Guest matty g]

Recently I examined a pair of early AR-2ax, serial numbers 117,xxx produced in May 1969. They use the 1-3/8-in.-diam phenolic-dome "super-tweeter" originally designed by Villchur for the AR-3. To my surprise I measured Rdc = 1.9-to-2.0 Ohms for each unit. The tweeters, rock wool, and putty were original, as were the twists in the tweeter and mid wires, which took up their slack. I expected Rdc to be approximately 5-to-6 Ohms like the woofer and midrange drivers. After asking about, learned that:

* The "Comparative AR-2ax" document says the AR-2ax used 8-Ohm super-tweeters, not their 4-Ohm AR-3 counterparts.

* RoyC has opened several early AR-2ax cabinets and measured only 2-Ohms Rdc in the 1-3/8-in. tweeters.

* There is currently an e-Bay auction: 110209884627 for a pair of AR-2ax tweeters with Rdc of 1.9 and 1.7 Ohms.

* Villchur replied: " I have no memory of changing the 4-ohm AR-3 super-tweeter to 8 ohms for the sake of the AR-2ax (the x referred to the super-tweeter), but I was not up on every production change if it had no effect on final performance. A 4-ohm speaker will have a higher output level than an 8-ohm speaker when connected across the same amplifier terminals. I don't think there was any change when I was at AR."

* Tom Tyson thinks there were separate drivers -- that Villchur -- as he said himself, was not up on every production change, and that there were different part numbers for the AR-2ax tweeter and the AR-3 tweeter. Tom will research this further.

These comments apply only to the early AR-2ax (‘64-‘69) that used the 1-3/8-in-diameter “super-tweeter” – see photo attached -- and not to the later version, which used the 8-Ohm version of the 3/4-in-diameter AR-3a tweeter.

So, as an experimentalist, I would ask what dc resistances have others AR-2ax owners measured? For me, I am satisfied to clean the pots, replace caps, and play this pair without worry that I will do irreparable damage, as they are not unique.

Cheers

John -

Checked a pair of 1963 AR2a systems with the serial #26321 and they measure 2.2 and 2.5 with the super tweeters disconnected from the terminals. These should be the same super tweeters as used in the first generation 2ax systems.

Hope this helps

Matt

[tysontom]

Recently I examined a pair of early AR-2ax, serial numbers 117,xxx produced in May 1969. They use the 1-3/8-in.-diam phenolic-dome "super-tweeter" originally designed by Villchur for the AR-3. To my surprise I measured Rdc = 1.9-to-2.0 Ohms for each unit. The tweeters, rock wool, and putty were original, as were the twists in the tweeter and mid wires, which took up their slack. I expected Rdc to be approximately 5-to-6 Ohms like the woofer and midrange drivers. After asking about, learned that:

* The "Comparative AR-2ax" document says the AR-2ax used 8-Ohm super-tweeters, not their 4-Ohm AR-3 counterparts.

* RoyC has opened several early AR-2ax cabinets and measured only 2-Ohms Rdc in the 1-3/8-in. tweeters.

* There is currently an e-Bay auction: 110209884627 for a pair of AR-2ax tweeters with Rdc of 1.9 and 1.7 Ohms.

* Villchur replied: " I have no memory of changing the 4-ohm AR-3 super-tweeter to 8 ohms for the sake of the AR-2ax (the x referred to the super-tweeter), but I was not up on every production change if it had no effect on final performance. A 4-ohm speaker will have a higher output level than an 8-ohm speaker when connected across the same amplifier terminals. I don't think there was any change when I was at AR."

* Tom Tyson thinks there were separate drivers -- that Villchur -- as he said himself, was not up on every production change, and that there were different part numbers for the AR-2ax tweeter and the AR-3 tweeter. Tom will research this further.

These comments apply only to the early AR-2ax (‘64-‘69) that used the 1-3/8-in-diameter “super-tweeter” – see photo attached -- and not to the later version, which used the 8-Ohm version of the 3/4-in-diameter AR-3a tweeter.

So, as an experimentalist, I would ask what dc resistances have others AR-2ax owners measured? For me, I am satisfied to clean the pots, replace caps, and play this pair without worry that I will do irreparable damage, as they are not unique.

John,

I asked Roy Allison about the AR-2ax super tweeter. In a message to me he confirmed that the AR-2a (and the subsequent AR-2ax) did in fact use the AR-3 4-ohm tweeter. So this should conclude speculation about the impedance of this tweeter. I am pretty confident I have seen two part numbers for this tweeter, but for now I'm convinced that there was only one 1-3/8-inch tweeter, known as the famous "fried-egg" super tweeter.

--Tom Tyson

[Carlspeak]

I have worked on a number of speakers, both US made and a high-end European made unit that had drivers with mis-matched impendances. My AR3a Super-Mod has a new 8 ohm tweeter and mid doing duty with the original 4 ohm woofer. If the crossover is designed right, it shouldn't present a problem for an amplifier to drive.

[RoyC]

I have worked on a number of speakers, both US made and a high-end European made unit that had drivers with mis-matched impendances. My AR3a Super-Mod has a new 8 ohm tweeter and mid doing duty with the original 4 ohm woofer. If the crossover is designed right, it shouldn't present a problem for an amplifier to drive.

I agree with Carl.

...A driver's rated impedance is an approximation, an average within a given frequency range. The "4 ohm" tweeter in question above has a dcr of 2 ohms. The later 3/4" 4 ohm AR tweeter has a dcr closer to 3 ohms, and the later still AR-11 and AB Tech tweeters have a dcr closer to 4 ohms.

In reality most speaker systems are made up of drivers of varying impedances. The combination of these drivers, crossover circuits, and such things as level controls, all go into creating the overall system impedance...which is also a rated average. So, not all "4 ohm" speaker systems will measure 4 ohms. They will simply average closer to 4 ohms than to, say, 8 ohms. The AR-3a, for example, is 4 ohm rated, but is a tough load for many amps because it stays below 4 ohms for much of its range.

The only real problem with "mismatched" driver impedances occurs when replacement drivers of differing impedances are dropped into existing speaker systems. Crossover adjustments are almost always necessary to compensate for the differing impedance and frequency response characteristics of the new driver.

Roy

[genek]

I asked Roy Allison about the AR-2ax super tweeter. In a message to me he confirmed that the AR-2a (and the subsequent AR-2ax) did in fact use the AR-3 4-ohm tweeter. So this should conclude speculation about the impedance of this tweeter. I am pretty confident I have seen two part numbers for this tweeter, but for now I'm convinced that there was only one 1-3/8-inch tweeter, known as the famous "fried-egg" super tweeter.

Bump

There's someone listing an orange-dome tweeter he says is from an AR-2a that he measured as 5.4 ohm. Just to confuse the issue yet again.

[johnieo]

Bump

There's someone listing an orange-dome tweeter he says is from an AR-2a that he measured as 5.4 ohm. Just to confuse the issue yet again.

Its the ohmmeter not the issue that is confused. Either the seller's meter was not been zeroed, or it came as a freebie in a Wheaties box.

Cheers,