AR Placement/Orientation

[charger3834]

I noticed in some of the Ads and catalogs, ARs are shown sitting vertically with the woofer/badge end up. Why would anyone place them that way ? Why did some of our "famous users" seem to favor this ?

[tysontom]

>I noticed in some of the Ads and catalogs, ARs are shown

>sitting vertically with the woofer/badge end up. Why would

>anyone place them that way ? Why did some of our "famous

>users" seem to favor this ?

>

>

If the speaker were mounted on shelf above the normal-listening position, the woofer should probably be up and the tweeter closer to ear level. An good example of this is the picture of singer Judy Collins sitting below a pair of AR-4xs in the 1970 AR catalog.

Mounting position might be subjective and the choice of a listener, of course, but most of the classic AR bookshelf models were originally intended to be placed horizontally on a shelf, with the "AR" logo to the lower left-side. If mounted vertically, the woofer usually was oriented down, with the "AR" logo on the lower-right side. Incidentally, this mounting configuration was carefully explained to one of the curators at the Smithsonian's National Museum of American History, but the AR-3 speaker on display was inverted anyway. Who's to argue with them, I suppose?

Probably more important than woofer-up or woofer-down orientation is the actual placement of the speaker in the listening room. In general, classic AR bookshelf speakers seem to perform best when placed back against a wall. This is the 2-Pi, or 180-degree-solid- angle position, and the bass response is probably flattest in this position. The problem with this, however, is the boundary-interference, or "Allison Effect" that exists when the speaker cabinet orients the woofer a certain distance from the boundary due to the cabinet depth or height from the floor. This back-wall or floor reflection results in a slight out-of-phase cancellation, or "suck out" at certain low frequencies which disturbs the low-frequency balance. There is some disagreement as to audible effect of this effect, but it is a measurable anomoly. Therefore, pulling the speaker well away from the wall alleviates part of this problem, but then there is the reflection from the floor to deal with -- same problem. Pulling out from the wall also attenuates low-bass response as well. The best "theoretical" solution, therefore, is to cut a rectangular hole in the wall and recess the speaker flush with the wall. Virtually no one is willing to do this, so mounting the speakers in a bookshelf -- flush with the front of the bookshelf -- helps solve the problem.

--Tom Tyson

[Steve F]

Tom is quite correct in his explanation.

In addition, it should be noted that speaker designers have control over which way the speaker's output will "lobe," and this is the usual determinant of the proper speaker-to-listener orientation. With straight vertically- or horizontally-oriented drivers, the speaker's lobbing is very predictable. With staggered mids and tweeters, as in the 5 and 3a, it's not perfect--or worst--whether the speaker is mounted vertically or horizontally.

(BTW, look at the old High Fidelity magazine review of the new 2ax. You'll see a sharp, high-Q dip at 5kHz in the on-axis response curve. This is clearly a response artifact of the horizontally-oriented side-by-side midrange and tweeter in the crossover region. The 2ax's mid and tweeter crossed over at 5kHz. In the other curves, the front hemispheric and omnidirectional curves, this dip fills in completely. HF doesn't even mention any of this in the text of the review, indicating that there was really very little understanding of this phenomenon at that time.)

It's entirely possible that concepts like speaker lobbing and primary output axis were not as well understood in the mid-60's as they are today. It could also be that AR did not feel that that was the most important aspect of performance, since they relied mostly on far-field reverberant measurements for performance evaluations.

As far as the logo badges go, I suspect VERY STRONGLY that those dreaded marketing people just wanted to make sure the "AR-3a" name was clearly visible in the photos.

Steve F.

[charger3834]

Gentlemen,

Thank you for the great info. It just struck me as a little odd.