Rich W

A good friend of mine in high school had Large Advents and every time he came over to our house and heard the 4’s—less than half the size of the Advents and half the price—he’d say, “It’s not fair! It’s not fair that they sound so good!” So my Dad and I called the 4’s the “Not fair” speakers from then on.

A familiar story.  I had sold my AR-3a's back in 1977 because I got tired of shipping them off to AR to have the tweeters replaced (I was seriously underpowering them).  A pair of large Advents replaced the 3a's as they were more "robust" when fed a diet of clipping distortion.  Of course, the 3a's sounded better, but it was a compromise I felt resigned to.  The gist of it is that I could never understand why my good friend's AR-18's sounded so much better than the Advents - especially in the upper midrange where the Advents were decidedly harsh.

Fast-forward to 2004 and my renewed interest in vintage gear.  The first thing I did was get a pair of AR-18's and refoamed them (the Advents were in need of a refoam and had wound up by the curb several years earlier - Advent lovers, don't flame me - I didn't know refoams were a possibility back then!).  Since then, I've happened upon a pair of AR-3a's (hey, they came back!), AR-7's and AR-17's, all of which I've restored.

I really have a soft spot for the AR-7's.  They just look so good, like a pair of mini- 3a's.  But based on my own pink noise tests, the AR-17's and 18's are more neutral sounding than the AR-7's, which have a mild peak centered around 1.8k.  The 17's and 18's sound almost identical (they should  - they use the same drivers), but the slightly larger cabinet give the AR-17's the edge with an extended bass response rivaling an AR-5 or AR-2ax.

So my choice, based on my limited experience, would be the AR-17 for best 8".

Rich W

I actually prefer their use with the AB Tech 3a replacement tweeter's new 12db/octave circuit (discussed elsewhere in the forum).

Hi Roy,

I installed AB-Tech tweeters in my AR-3a's with the requisite .07 mh parallel inductor coil. What subjective difference in sound did you notice with this configuration with L-Pads vs. Pots?

Best Regards,

Rich W

I'm jealous of your room which give an amazingly flat and extended response at LF. You are doing some spatial averaging, right? Are the individual curves nearly as flat?

David

Hi David,

Yes, I'm doing spatial averaging within an approximately 10 square ft. prime listening area. For the AR-17's, I ran pink noise through both speakers, set a very high number of averages in my RTA software, and moved the mic stand around within the test area. For the AR-7's, I ran individual tests at 10 different locations for each channel. The chart below shows 6 representative curves for the right channel, with the average curve for all 10 at the top. The individual curves are pretty decent. So you can see more clearly what's going on in the bass region, I limited the upper frequency to 2k. All the curves are in very close agreement above that.

 ar_7_curves_r_ch.jpg   283.85K   120 downloads

With all the room augementation below 60 hz, it's really a mind-bender to hear a little pair of AR-7's reproduce (albeit at a reduced level) a 32 hz sub-contra C organ pedal. I actually ran tests where I got them to respond to a 27 hz sine wave - with substantial fundamental that you could feel. As you can see from my first set of graphs, the AR-17's bottom octave response falls right between the AR-7 and AR-3a, which is just about what you'd expect.

As far as the midrange peak on the AR-7's, I'm going to run some near-field tests to rule out any interaction with the room. I expect that varying the tweeter level control should tell me whether the woofer or the tweeter is the prime culprit contributing to that extra energy at 1.7k. My one-third octave equalizer can tame that peak pretty well, but it would be so much more satisfying to have the speaker respond more evenly through the midrange on its own. It's somewhat of a mystery to me that the AR-17's are so much smoother in the midrange, considering that one of my AR-7's has a later AR-17/18 type replacement woofer. As you probably know, the AR-7 has a "minimalist" crossover, the woofer is allowed to roll off with no inductor, and the tweeter network is first-order with a single 6 uf series cap. To me, that make the tweeter network in the 7's suspect. Maybe the tweeters themselves have aged to the point where they're starting to show anomalies near their resonant frequency. In any case, I can definitely hear that midrange coloration - from past test reports and AR's own response curves from back in the day, these things should be more neutral sounding. That said, they still sound incredible. In the same manner as you with your AR-4x's, I want to wring that last ounce of performance out of these little guys!

Best Regards,

Rich W

Here I played with the external network values until I got a reasonable fit to the response of the internal part.  
David

David,

What method do you use to interface your external crossover network with the speaker drivers?  Does it require putting holes in the cabinet?

Best Regards,

Rich W

David,

Great job - and a superb thread.  It's getting me thinking about refining the crossovers in my AR-7's.  The tweeter is dead-flat above 2.2k, but there's a bump of about 5 db centered at 1.7k.  My AR-17's, measured under identical conditions, are flat right though the midrange.  I know the AR-7's should be measuring better!

Looking forward to further posts on your AR-4x's.

Best Regards,

Rich W