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Some interesting? measurements


Guest Bret

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Found a little something interesting, thought it might interest others, and might start a dialogue about whether all of us old AR enthusiasts are out of our minds.

I was recently blessed with a number of AR-9 / AR-92 / 10pi drivers. I'm thinking, "Now why would anyone build these tweeters with different specs (other than impedance)? I mean, with a tweeter wouldn't you, a manufacturer or speaker builder, build or buy the best driver you could then adapt it using the crossover, cabinet design, to blanket or not-to blanket? If your "high end" speakers are of a single design philosophy, surely they would all have the same response characteristics and so all be able to use the same driver?"

Ah, but there are mounting differences and other differences in the actual drivers used in the 10pi/11, the 9, the 90 and 91 and 92 of the AR-lines. Would that mean that the drivers were different because the crossovers are different? I mean, a tweeter you like is a tweeter you like is a tweeter. . . you get my point.

As I said, I have these drivers sitting here. I have one from an AR-9, a 200029-1. How do I know it is from an AR-9? The aesthetic is slightly different on the one in the early versions of the 9 and those from the 90,91,92. The driver in the 90, 91, 92 which also bears the number 200029-1. These drivers should all be identical electrically and sonically. They all mount the same, bear the same part number, are of a like era, and most importantly to my point, are going in the 9, 90, 91,and 92 which have different crossovers.

So, my trusty Radio Shack digital VOM says the AR-9 driver (unused) measures at 3.4 ohms. One driver from a 92 measures 3.3 ohms and one measures 3.5 ohms (both used). Then we move to the 200011-1, from an AR-10pi, used, original. . . 3.5 ohms. Then there is a 1-200084-0 (the currently available replacement driver for the 11/10pi) and it measures 3.8 ohms.

I've seen it written that the 10pi and the 11 use a 4 ohm tweeter and that those are very different from tweeters in the other speaker models. Yet, as I look at this information I collected I only see the "new" driver showing 3.8 ohms, and a very old driver measuring at 3.5 ohms.

Is impedance not a good indicator of anything in terms of frequency response and output? Almost can't be if two drivers out of a pair of AR-92s can be 3.3 and 3.5 ohms - and three drivers all bearing the same number having 3.3, 3.4, 3.5 ohms. That's not much less variation than the 3.5-3.8 ohms between the "old" and "new" 10pi drivers.

Wouldn't dc impedance be a pretty easy measurement to see variations in voice coil length, etc? Wouldn't you almost have to change the dc impedance to change the desired throw or sensitivity and wouldn't you just cope with that in the crossover rather than making a very specific driver for one or two model-runs?

Is it then fair to say that new, replacement drivers are somehow or other inferior or less desirable than the new replacement drivers? Why? It certainly isn't showing up in their dc impedances and same number speakers are showing as much difference as the new vs the old bearing different part numbers.

Why not mount an AR-9 driver in a 10pi, for instance (ignoring for a moment that it won't fit)?

What else is there to measure assuming all these drivers (except the 1200084-0) passed AR's QC department?

Bret

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HELLO BRET

I have the AR replacement Number As of 1992 being 1200011-1 and it fits the 10,11,9,90,92,915,58s The 10Pi is not listed

I'm trying to find The specs on the LST and LST II tweeters or the AB techs replacement information such as manufacture and part number with the specs. or what other tweeters would fit with in the same peramitores.

Jim

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>I have the AR replacement Number As of 1992 being 1200011-1 and it fits the 10,11,9,90,92,915,58s The 10Pi is not listed<

The 10 and 10pi are the same speaker since, as far as I know, there was never a 10 without the pi designation.

I am only familiar with the 1200011-1 as the original number for the second-generation 10pi and 11 tweeter. I *think* you will find that the screws are larger and I *know* you will find different connecting posts on these than the 200029-1 (from the 9 series) The only new replacement drivers for any of these speakers I've seen are the ones from Simply Speakers with the number 1- 200084-0 on them. I seriously doubt you can mount these in the 9-series cabinets using the original screws - but I'm not completely sure.

The point I'm driving at, and question I'm asking (both at once), is that these drivers should all be virtually identical with two exceptions: 1) mounting differences, particularly since the 10pi and 11 drivers must have the electrical connections fully "behind" the driver while the 9 etc drivers had the connections slightly further out and not 180 degrees from one-another. 2) impedance - however, I'm not seeing much in the way of differences between them even though they were supposed to be different.

Unless you want to get a Dremel tool after your 11 and 10pi cabinets, I *know* you can't mount a 200029-1 in them.

The real question is this: Other than the physical differences, what *should* be the differences in the specs of these drivers? They obviously aren't different in impedance, nor size, nor weight. The screw holes are different, yes. The connection posts are different, yes. So they don't really fit in each-other's cabinets, yes. But are they really, electrically or sonically, different?

But I'm absolutely, 100% certain, that you cannot mount a 9 driver in a 10pi cabinet (with a brass badge, I don't have an aluminum badged cabinet to check) without cutting the cabinet.

Bret

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>I was recently blessed with a number of AR-9 / AR-92 / 10pi

>drivers. I'm thinking, "Now why would anyone build these

>tweeters with different specs (other than impedance)? I mean,

>with a tweeter wouldn't you, a manufacturer or speaker

>builder, build or buy the best driver you could then adapt it

>using the crossover, cabinet design, to blanket or not-to

>blanket? If your "high end" speakers are of a single design

>philosophy, surely they would all have the same response

>characteristics and so all be able to use the same driver?"

>

>Ah, but there are mounting differences and other differences

>in the actual drivers used in the 10pi/11, the 9, the 90 and

>91 and 92 of the AR-lines. Would that mean that the drivers

>were different because the crossovers are different? I mean,

>a tweeter you like is a tweeter you like is a tweeter. . . you

>get my point.

>

>As I said, I have these drivers sitting here. I have one from

>an AR-9, a 200029-1. How do I know it is from an AR-9? The

>aesthetic is slightly different on the one in the early

>versions of the 9 and those from the 90,91,92. The driver in

>the 90, 91, 92 which also bears the number 200029-1. These

>drivers should all be identical electrically and sonically.

>They all mount the same, bear the same part number, are of a

>like era, and most importantly to my point, are going in the

>9, 90, 91,and 92 which have different crossovers.

>

>So, my trusty Radio Shack digital VOM says the AR-9 driver

>(unused) measures at 3.4 ohms. One driver from a 92 measures

>3.3 ohms and one measures 3.5 ohms (both used). Then we move

>to the 200011-1, from an AR-10pi, used, original. . . 3.5

>ohms. Then there is a 1-200084-0 (the currently available

>replacement driver for the 11/10pi) and it measures 3.8 ohms.

>

>I've seen it written that the 10pi and the 11 use a 4 ohm

>tweeter and that those are very different from tweeters in the

>other speaker models. Yet, as I look at this information I

>collected I only see the "new" driver showing 3.8 ohms, and a

>very old driver measuring at 3.5 ohms.

>Is impedance not a good indicator of anything in terms of

>frequency response and output? Almost can't be if two drivers

>out of a pair of AR-92s can be 3.3 and 3.5 ohms - and three

>drivers all bearing the same number having 3.3, 3.4, 3.5 ohms.

> That's not much less variation than the 3.5-3.8 ohms between

>the "old" and "new" 10pi drivers.

>

>Wouldn't dc impedance be a pretty easy measurement to see

>variations in voice coil length, etc? Wouldn't you almost

>have to change the dc impedance to change the desired throw or

>sensitivity and wouldn't you just cope with that in the

>crossover rather than making a very specific driver for one or

>two model-runs?

>

>Is it then fair to say that new, replacement drivers are

>somehow or other inferior or less desirable than the new

>replacement drivers? Why? It certainly isn't showing up in

>their dc impedances and same number speakers are showing as

>much difference as the new vs the old bearing different part

>numbers.

>

>Why not mount an AR-9 driver in a 10pi, for instance (ignoring

>for a moment that it won't fit)?

>

>What else is there to measure assuming all these drivers

>(except the 1200084-0) passed AR's QC department?

>

>Bret

Bret,

Well, here we are again, back on The Classic Speaker Pages -- good to have it back!

The "short" answer to your question(s) is that with AR tweeters, at least, each AR speaker's driver was designed around the crossover and vice-versa. There was definitely an interdependence in the original design. An AR-10Pi tweeter won't work properly in an AR-3a, for example, because of sensitivity differences, etc., even though both tweeters are 3/4-inch in diameter and the crossover frequencies are the same. The crossover components and values are also somewhat different. In any event, the sound characteristics will certainly be different. An AR-9 tweeter, if you could fit it into the AR-10Pi/AR-11 tweeter hole, has different response characteristics than the original-type AR-10Pi 3/4-inch tweeter, and it also has different sensitivity and bandwidth characteristics. Incidently, the DC resistance of all the 4-ohm tweeters will be close to the same value, but this is only an index to the impedance, not the characteristics of that driver.

--Tom Tyson

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>An AR-9 tweeter, if you could fit it into the AR-10Pi/AR-11 tweeter hole, has different response characteristics than the original-type AR-10Pi 3/4-inch tweeter<

Not that I'd know what to do with the information if I had it, but do you know where I could find driver specs quite independent from speaker-system specs?

Bret

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>I have some of that information in various bits and pieces, and from a few blue-line drawings, etc. Which drivers?<

Do you have them for the 200029-1 and the 200011-1? Those would be highly instructive since I can look at them and know what they are.

Bret

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>

>Do you have them for the 200029-1 and the 200011-1? Those

>would be highly instructive since I can look at them and know

>what they are.

>

>Bret

Well, as you know, the AR #200029-1 is the 4-ohm, 3/4-inch-dome tweeter designed for the AR-9, 90, 91, 92 and 915, and it was optimized for the 7 KHz. AR-9 crossover. The AR-91, for example, has a 7.5 KHz crossover. The tweeter has a 2 KHz fundamental resonance (well below its operating range), and has a ferro-fluid voice coil. The magnetic circuit has a total flux of 21,000 maxwells and a flux density of 18,000 gauss, but these figures are largely meaningless to anyone other than a speaker designer. It also has a recessed "horn" of sorts that increases the efficiency at the higher frequencies, but very slightly decreases off-axis dispersion at the highest frequencies compared to the flush-mounted tweeters.

The AR #200011-1 was an earlier design, 3/4-inch-dome, treated-fabric, flush-mounted designed for the AR-10Pi and AR-11. I am not certain if the earliest versions (brownish-orange) of this tweeter had ferro-fluid cooling; later "B" versions definitely did. Just as with the AR-9 tweeter, it is also a 4-ohm tweeter, has the 2 KHz resonance, same magnet assembly, but operates at a 5 KHz crossover.

In the end, therefore, the two are not really interchangeable -- despite the similarities -- any more than the AR-10Pi tweeter is interchangeable with the AR-3a tweeter.

--Tom Tyson

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>it was optimized for the 7 KHz. AR-9 crossover. <

Tom,

Thanks for that information, and it is interesting.

It always annoys me when someone asks me to teach them everything I know about a subject I've studied for years, and they want it in 25 words or less. I will try not to do that to you.

Is there a "simple" explanation of what you might do differently to design a driver for a 7kHz crossover or a 5kHz crossover when the drivers (diaphrams) are the same size? What is reasonable to change?

I don't expect you to teach me everything you know, just sorta point me in a direction.

Bret

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>Is there a "simple" explanation of what you might do

>differently to design a driver for a 7kHz crossover or a 5kHz

>crossover when the drivers (diaphrams) are the same size?

>What is reasonable to change?

>

Bret, I think the differences relate to damping and sensitivity of each driver. But since the magnet structure and dome resonances are the same, the drivers have to be very similar. There might be some slight differences in the voice coils and dome fabric; and certainly in the case of the AR-9 tweeter, the recessed small "horn" shape would makes some sonic difference. However, with the tweeter on the AR-9 optimized for the high crossover frequency, the driver's response might roll off below 7 KHz, and that would not fare well in the AR-10Pi with its 5 KHz crossover. The AR-9 tweeter is also optimized for strong treble output and high power-handling capability, since it does not operate much below 7 KHz.

--Tom Tyson

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> think the differences relate to damping and sensitivity of each driver. But since the magnet structure and dome resonances are the same, the drivers have to be very similar.<

Thanks, Tom. That's the conclusion this non-EE drew from looking, measuring, etc.

It almost seems wasteful to design a driver all-over-again when such fine drivers already existed. Hmmmmm.

Thanks again.

Bret

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