AR-4 crossover network

[ra.ra]

Yes, this is about the original AR-4 and not the 4x or the 4xa. I am well familiar with the 4x speaker, but because I have been mostly unsuccessful locating much specific information about the crossover of the AR-4 speaker (searching both CSP and AK sites), I thought I'd try to pick thru some more knowledgeable brains here. I do know the 4 has a slightly different woofer and a very different tweeter (I have 2ax's, so I know this tweet, or mid) from the 4x which results in a different x-o frequency, but here I have assumed that the crossover construction assembly must be similar to that of the later 4x (one cap, one pot, one coil).

1. Anyone know of a wiring schematic available for view?

2. Value for capacitor? (Did I see somewhere that maybe it was 6 mf?)

3. Value and number of inductor coil?

4. Crossover frequency?

5. Anything else?

Thanks in advance.

[tysontom]

The AR-4 schematic and part-number list is attached.

--Tom Tyson

[tysontom]

The AR crossover-coil chart:

--Tom Tyson

AR-COIL specs_002.pdf

[ra.ra]

Thanks so much, Tom, for the excellent replies. Since I made my initial post over two weeks ago, I did some additional digging on CSP and came up with this note (below in blue) made by you a few years back, which is where I probably developed my suspicion that the AR-4 might have a 6mf capacitor. By the way, that is a terrific little schematic diagram shown with the parts list you posted.

from January 2008

The AR-4 used a 6 mfd capacitor but the same 1.24 mH choke. The 3-1/2-inch midrange used in the AR-2ax from 1964 onward was the same as the tweeter used in the AR-4. The variation in the fiberglass over the top of the 3-1/2-inch occurred early, but the standard (and most common) version had fiberglass covering the entire area of the cone under the metal grill. There is no difference in the 3-1/2-inch AR-2ax midrange and the AR-4 tweeter, and they are interchangeable.

--Tom Tyson

My original query was an attempt to gather more details about this particular speaker before I considered obtaining a pair of AR-4's for sale locally. Fast forward two weeks, and in exchange for a very modest sum (one Jackson + one Hamilton), I now own a fine pair of very early, all-original AR-4's. I will share the nice story and additional pics in the coming days, but let me include just one in-progress restoration pic here which seems to show a #4 coil instead of the #5 shown in your chart. I also have two pairs of 4x's, which all have the #5 coil, and I seem to recall that each of these coils found their way into the 4x, so perhaps the same was true for the original 4 speaker as well.

[ra.ra]

Thanks again to Tom T. for the helpful response and the great schematic - - - I've been meaning to post this follow-up for a couple weeks now. I've had the AR-4's re-assembled, and I've been conducting some A-B listening against some recently refurbished AR-4x's ..... no conclusions just yet.

I bought these speakers locally from an interesting guy who runs a small operation installing home audio-video systems and computer set-ups. Sometimes, as in this case, when replacing the "old audio" with the "new audio", his clients ask him to dispose of (sell) the old and then reduce their final bill by the amount of the sale proceeds. According to my seller, the one and only owner (his client) purchased these speakers in 1964 from the Macy's department store in New York.

The speakers appeared a bit tired but otherwise seemed solid and in fine shape in most regards - one noticeable blemish on one cabinet and the usual slightly discolored grille cloth - - - these had "restore" written all over them. Also, even though this model was only in production for a relatively short time, the serial numbers seemed to represent the early portion of that production run : s/n F00105 and F00242. Briefly, my efforts consisted of:

1. carefully remove 11 or 12 tiny, tight staples per speaker to remove grille cloths.

2. remove and unsolder woofers to access inside of cabinet.

3. remove and clean tweeter pots (see #5).

4. replace capacitors with Erse Pulse-X 6.0 mf.

5. install Aetna-Pollak pots salvaged from someone else's AR-2a's (the two pots from the 4's, although heavily corroded, produced great readings from 0.2 to 16.0 ohms after cleaning, but had a few "void" spots thruout the sweep).

6. re-dope woofer surrounds with light coat of liquid butyl.

7. add wire lead extensions to woofers, connect with wire nuts.

8. re-install all drivers with fresh duct seal.

9. mildly recondition cabinets with Howard's love potion (will probably do more work here later).

These speakers are almost 50 years old, so a few other observations worth mentioning:

A. I am fairly certain these speakers had never been opened up since leaving the factory.

B. the cloth woofer surrounds were still extremely pliant, and there's no extra damping (floral pattern or hot-cross buns) on the woofer cones.

C. the original rope caulk driver sealant was still softish and malleable.

D. original caps (dated june 1964) and rear pot strap were partially clad with, or set in black rope caulk.

E. inside of cabinets were stamped with 'tag' by original assembly person.

Pics attached:

1. serial numbers

2. original x-o with smaller wax cap box

3. original x-o with larger wax cap box (4mf is crossed out) - see personal stamp which reads "Denny Roll, June 1964".

4. AR-4 pot before

5. AR-4 pot after

6. AR-4's after

So far I am really enjoying these little speakers - - they look great; they represent a very early iteration of the classic bookshelf speaker; and best of all, the sound seems to improve ever-gradually as the new caps gain more hours of use.

 

[dynaco_dan]

Hi there

Thank you for the very clear nice closeup shots of the pots.

Interesting seeing that the woofer basket is not perfectly round but similar to the horned Dynaco/Seas 10" woofer.

[ra.ra]

Thanks, Vern.

One note about the photos of the tweet controls (potshots?) - - - these were taken with a cheesy old digital camera, but I placed the camera lens directly on an 8x magnifier (photographer's loupe) sitting directly on the potentiometer.

Just a couple further points here, with additional pics:

A. side-by-side comparison of AR-4 (left) and AR-4x (right) drivers.

B. similar comparison of badges: AR-4 (black w/INC.) are 15/16" square, while AR-4x (brown w/o INC.) are 7/8" square