6 replies to this topic

[ben76]

Hi,

I was just wondering what would be the result of putting one of the AR90 series floor speakers on a shelf.

I guess this is irrelevant for the AR9 and probably also the AR90, being so big. However, the AR92, AR93, and AR94 are not much larger than the AR3a, so it is not so much of a physical problem, but maybe an acoustic one.

My impression is that it really depends on the room, and the position inside the room, so it may be a viable option. However, maybe I am missing something and the floor reflections (even if the floor is carpeted?) are really factored into the design.

I would love to be educated .

Thanks,
Ben

[amanteyzapata]

I've got a small office in a finished basement with two AR94Sx sitting on top of two New Large Advent. They can be A-B switched but I like the combination of them. I noticed an incredible improvement in sound once I got the AR94Sx'es off the floor...so yes, go for it! Guess I should mention the NLA speakers are stock and the AR94 speakers were stock until recently when I swapped out the working stock tweeters with Daytons. Found the AR94Sx tweeters harsh as some have said...confirmed that when I raised them. BTW, I'm new to collecting speakers but I'm a music prof so I "use" my ears all day...I like loud Classical mostly. Best, -Joseph

[ben76]

It turns out that this is indeed an illusive question, and that the only answer is to just try it.
I do not own any of these speakers (yet : :-), so I was wondering what other people's experience has been.

I understood that Roy Allison from AR came up with some cancellation scheme for reflections that is used in these floor speakers, and I was not sure if the floor reflections were not a crucial element in that scheme. However, I could not find any technical details, nor an informal description of the principal.

Thanks for sharing your experience Joseph.

Ben

[tysontom]

Hi,

I was just wondering what would be the result of putting one of the AR90 series floor speakers on a shelf.

I guess this is irrelevant for the AR9 and probably also the AR90, being so big. However, the AR92, AR93, and AR94 are not much larger than the AR3a, so it is not so much of a physical problem, but maybe an acoustic one.

My impression is that it really depends on the room, and the position inside the room, so it may be a viable option. However, maybe I am missing something and the floor reflections (even if the floor is carpeted?) are really factored into the design.

I would love to be educated .

Thanks,
Ben

Ben,

All of the AR Tower speakers of that era, such as the AR9, 90, 91, 92 and 93 were designed to optimize floor placement to (1) extend the bass response, (2) lower harmonic distortion and (3) minimize or eliminate the so-called "Allison Effect," whereby (in general terms) the back wave from the woofer bounces off the wall behind the speaker (and the floor) at certain bass frequencies out of phase and then cancels the woofer's signal at certain frequencies. This results in a cancellation dip or "suck out," as some called it, and it has been well publicized since the first Allison products hit the market in 1974. The audibility of this phenomenon is somewhat debatable, but the cancellation is very noticeable with measurement.

Therefore, if you do raise the speakers off the floor onto a shelf, you will experience some of this boundary cancellation, and the speakers will be less than optimum. Will it matter that much? You need to experiment to see if there is a noticeable difference. Also, if you know the frequency of the dip, you could use a one-third octave equalizer to bring up the dip, but you would need to measure the speaker's output to determine that need. Few people are capable or willing to go to that trouble, so just try it and see if it sounds okay.

--Tom Tyson

[tysontom]

More information on the cancellation dip is in this paper written by Roy Allison two years after he left AR.

--Tom Tyson

Attached Files

•  22_Allison_Influence_of_Room_Boundaries # 5 p.314.pdf   704.46K   249 downloads

[Steve F]

One of my favorite AES articles, and one of the most influential and revealing.

Some very highly-regarded speaker engineers have expressed doubt as to the ultimate audibility of the Boundary Effect as identified by Allison. (I don't want to name names, so as not to put words in their mouths, but some of them are posters on this Forum.)

In all honesty, from the typical listening position, the sound of a high-performance loudspeaker with documented, verifiably correct anechoic/2 Pi behavior does not seem to evince the dip and hollowness that Allison's research implies it will. A 3a or 11 on stands somewhat away from the side wall and wall behind it will "measure" much worse than it sounds.

I have no ready explanation for that, but it will measure quite poorly and yet it will sound quite normal and good. Many experts say that the ear/brain system has an easier time filling in a dip than it does eliminating a peak.

Steve F.

[ben76]

Thank you very much Tom for the explanation and the copy of the Allison article.

After reading both, I believe I understand much better what is going on.

Ben