AR 3a Phasing

[Guest lmrosenthal]

Hello to everyone,

I've owned my pair of AR 3a's new since 1970.

I understand that the midrange in the 3a is wired out-of-phase from the woofer and tweeter. Since I have ordered the crossover upgrade kit from Layne Audio, I was wondering what experience any of you have had in wiring the midrange 'in-phase' with the woofer and tweeter. What are the sonic differences you've heard? Any potential harm in wiring the midrange in-phase?

Thanks in advance for your feedback.

Larry Rosenthal

[Guest Nigel]

Hi Larry;

No harm in doing it.

How it sounds depends on your listening environment more than anything else. You may not be able to tell the difference, or it may be very pronounced. Try both ways.

Nigel

[mrdb]

The woofer has a two-pole lowpass filter ahead of it and the midrange has a two-pole highpass and a single-pole lowpass feeding it. The total electrical phase shift is (nominally)180 degrees between the drivers at the crossover frequency when driven by these filter sections. (Acoustically there is additional phase shift due to driver characteristics, driver mounting location, listening location, etc.) By reversing the leads to one of the drivers, the relative phase between the drivers is restored. If the polarities were not reversed, then there would be a notch at the crossover frequency. In reality, the "summed" frequency response is not absolutely flat. It depends on each filter's Q and the driver characteristics, among other things.

There are a number of good sources for crossover design on the net. They will explain all of this in much greater detail. See, for example, Siegfried Linkwitz's sight.

Bob

[tysontom]

>What are the sonic differences you've heard? Any potential harm in wiring the midrange in-phase?<

Originally, AR was going to wire both the tweeter and midrange out of phase with respect to the woofer, but only the midrange phase was reversed. I think the main purpose for reversing the phase was apparently to smooth some response irregularities in the region of crossover, as measured in the anechoic and semi-reverberant chamber at AR. This change occurred back in the early 1960s with the AR-3.

Can't do any harm by wiring in phase, but it probably will not sound as good. AR tested this pretty extensively, so the decision was not made lightly. There might have been some frequency lobing due to overlapping at the lower crossover frequency, but I am not sure.

--Tom Tyson

[tysontom]

As I understand it, Roy Allison originally noticed a response irregularity in the AR-3 in AR's anechoic chamber, and the phase of the woofer was first reversed to see if this would make a difference (this was actually prior to the construction of the reverberant-test chamber). The transition through crossover apparently did look better. Subsequently, he connected a double-pole, double-throw switch at the end of a long cable to accomplish the same thing remotely, and listened to pink noise and music, throwing the switch to put the midrange driver into and out of DC phase alternately. The difference was audible, which might be expected because of the fairly low crossover frequency and the small distance between the two drivers. Villchur and Allison agreed that the DC-out-of-phase condition was more natural and reversed the midrange phase. The tweeter polarity, on the other hand, made no audible difference and was left as it was.

No harm would necessarily come from wiring the AR-3a back in phase, but most agree that the midrange out-of-phase condition resulted in a more natural, smoother response through the crossover frequency.

--Tom Tyson

[Guest lmrosenthal]

I want to thank all of you for responding to my question. I really appreciate it!

Based on what you've all said, I believe I'll leave the mids wired out of phase.

If anyone's interested, I'll post the results of replacing the crossover caps, etc with the updates from Layne Audio when I'm finished. I should be receiving the parts by the second week of September (Layne's on vacation till then), so I'll have to wait till then.

Again, thanks for all your help.

Larry Rosenthal

[Guest]

Hi, I'm new to the forum, but not to AR speakers, and I am so glad that there is such a forum for classic speakers doing so well and that I found it once again... Thanks Mark.

This AR-3a phasing thread caught my attention, since I have restored several AR-3a's and AR-5's and always thought that the tweeter and the midrange drivers were in phase with each other but together they were wire out of phase with the woofer.

I also have an original pair of AR-11's bought back in 1976 and through time I was bothered by what seemed to be a blaring peak in the upper midrange or lower highs region. This was noticed in the mid 1980's so I was not sure if aging of the speakers had anything to do with it. But nevertheless it was there. So one day in 1997 I was able to buy the classic AR-3a speakers and I jumped on it. After all these were the speakers I had always dreamed of and wanted as a young teenager in the late 1960's, early 1970's. The pair I got was in very good condition, was an earlier production model with the bute looking old cloth surround woofers (I wanted those!) and all they needed was for the level controls to be cleaned. They played fantastically after the pots cleaning.

Now, when I compared them to my AR-11's (which by this time had their woofers replaced due to foam rot in 1986) that's when I noticed that the AR-11's (supposedly the improved version of the AR-3a) did not sound anything like the old original AR-3a's. The AR-11's were much brighter and nasally when A/B compared to the AR-3a's and that nasty peak in the upper mids region showed itself and was annoying. So I decided to modify the AR-11's crossover closer to the AR-3a's by replacing and rearranging the AR-11's crossover components. Even after that, the AR-11's still sounded brighter with more of a thin sound and not full and rich and mellow like the AR-3a. I figured it was differences in the efficiency and characteristics of the new AR-11 midrange driver. Then I noticed that all of the AR-11 drivers were wired in phase. I thought duh! that's why it sounds so much sharper and brighter and at the same time thinner... So I reversed the polarity of both the mid and tweeter to be out of phase with the woofer... and that improved things. But still not to the point of matching the AR-3a's sound.

The AR-11's still have a hotter top end and sounded thinner in the upper midrange region giving a slightly different (and less accurate) sonic character than the AR-3a. I play some of Santana's CD's with their great percussive instruments. On the AR-3a's the cowbells and wood block percussives sound almost real! but on the AR-11's they were close but something going on in that upper mids and lower highs region was making the cow bells and wood block percussions sound tinnier and this thinner, not like a live sound.

Anyway, point is, Tom Tyson thank you for you valuable clarification that I found here in this thread and forum... I have just today rewired the AR-11's tweeters back in phase with the woofer, leaving only the midrange out of phase with the woofer. And now when I A/B the AR-11's against the AR-3a's, they are much closer sounding and I am in love with my AR-11's again. Of course, the AR-11 drivers are placed differently on the baffle board than the original AR-3a's and that will always cause a sonic difference that can be heard and measured due to the different physical phase interactions between drivers, but I got them to sound close enough to be happy with them.

I am suprised there is not much talk about the AR-11's here. No matter, I for one think the AR-3a was a better sounding speaker.

The original crossover in the AR-11 in my opionion causes a peak in the tweeter region that makes it too bright for my tastes.

Anyway, that's all for now. I have drawn up schematics for the AR-11, AR-5 and AR-3a... of course they are my own drawings and I don't have all the exact original AR spec inductor values, just what I could measure. And this actually was done by me in the past few years so I don't remember all the details. Some of the info I initially got for the AR-3a's was from Mark's original website way back a few years ago and from talking to AB Tech. Okay, later.

Oh, I almost forgot why I started this post! Question to Tom Tyson about verifying for me what was the actual final decision of the AR-3a phasing of the drivers that went into production and released to the consumers? Was it wired one way and then mid-stream they changed later models or did all AR-3a's come out of the production line with only the mid wired out of phase. I never knew this, and could not tell from my 3 sets of AR-3a's because the tweeters positive leads were not marked or totally faded off and I never could tell which was positive for sure.

(which reminds me what I did try to do to determine which was positive and negative) I remember taking another spare tweeter with known marked positive terminal and using alligator clips and connecting it to the AR-3a tweeter lead clips while playing sound through them. Using the idea that when speakers are in phase, mono signals will sound clearly like they come from the center but if they are out of phase, the sound would be diffuse and directionless... I am not sure (can't remember really) if I did successfully determine which lead was positive on my AR-3a tweeters that way, but I think I did). Anyway, just an idea I figured I'd pass along, since no one can see the movement of the tweeter using the battery technique which works fine for woofers. Later! :-)

BTW, that's not me playing guitar on that default icon that shows up with my posts, although I did try to play guitar at one time in my teenage years.

[Guest]

Spelling Typo correction for my previous post here... in the phrase "...earlier production model with the bute looking old cloth surround woofers..."

It should have said:

"...earlier production model with the brute looking old cloth surround woofers...". People must have been wondering what the heck does "bute" mean! :-)