AR-3a Original Design Considerations

[onplane]

I know many of you folks know a lot about the history and design considerations at Acoustic Research. Well, an individual on Usenet recently posted the following:

"No, the reason for this is that Roy Allison and Ed Villchur at AR decided on a balance that resulted in an overall downward trend

in the speaker's response toward the high end. That was their

choice, for whatever reaons. The midrange efficiency is about

2 db less than the woofer, and the tweeter is another 2-3 dB

less efficienct than that. That's what the people of AR designed

it to be.

Add to that the woofer was designed purposely to be under-

damped, with a system Qt at resonance of about 1.2-1.25.

One reaons for doing this is that it results in the highest

possible efficiency for a sealed-box system of that size and

cutoff frequency. Given the standard efficiency, enclosure

volume, cutoff frequency relation:

n0 = kn Vb F3^3

where n0 = reference efficiency, Vb is enclosure volume

F3 is -3dB cutoff frequency and kn is the alignment-

dependent efficiency constant, we find that kn is at a

maximum when Qtc = 1.1 or so, where kn reaches a

maximum value of 2.0 * 10^-6 (cf Small, JAES pp 290,

1972 Dec)."

I was under the impression, that the goal at AR was to get as flat a frequency response as possible. Yet, this individual seems to claim that the AR-3a was designed to "roll off" at the high end??

Comments please!

Thanks,

Jerry

[dynaco_dan]

>I know many of you folks know a lot about the history and

>design considerations at Acoustic Research. Well, an

>individual on Usenet recently posted the following:

>

>

>"No, the reason for this is that Roy Allison and Ed

>Villchur at AR decided on a balance that resulted in an

>overall downward trend

>in the speaker's response toward the high end. That was their

>choice, for whatever reaons. The midrange efficiency is about

>2 db less than the woofer, and the tweeter is another 2-3 dB

>less efficienct than that. That's what the people of AR

>designed

>it to be.

>

>Add to that the woofer was designed purposely to be under-

>damped, with a system Qt at resonance of about 1.2-1.25.

>One reaons for doing this is that it results in the highest

>possible efficiency for a sealed-box system of that size and

>cutoff frequency. Given the standard efficiency, enclosure

>volume, cutoff frequency relation:

>

> n0 = kn Vb F3^3

>

>where n0 = reference efficiency, Vb is enclosure volume

>F3 is -3dB cutoff frequency and kn is the alignment-

>dependent efficiency constant, we find that kn is at a

>maximum when Qtc = 1.1 or so, where kn reaches a

>maximum value of 2.0 * 10^-6 (cf Small, JAES pp 290,

>1972 Dec)."

>

>

>I was under the impression, that the goal at AR was to get as

>flat a frequency response as possible. Yet, this individual

>seems to claim that the AR-3a was designed to "roll

>off" at the high end??

>

>Comments please!

>

>Thanks,

>Jerry

>

>

Hi Jerry;

Everyone who writes here is welcome to add to our knowledge.

We all come here to share and read and to enjoy ourselves.

I am not a technical person, I'll have to leave that to the expert members.

Back in it's infancy, the birth of the AR 12" woofer, the amplifiers, cartridges and records were lower-fi not hifi.

FM stereo wasn't here yet.

If only we knew then, what we know now, heh?

Records were, and in some cases, aren't, too well recorded at all frequencies, especially the bass or the treble.

Highs were cut from speakers to eliminate distortions from the cartridges and amplifiers.

Also it maybe took another super tweeter to extend the higher frequencies beyond the capablities the 1 3/8" tweeter of the AR-3.

The AR-1 had the 8" mid/tweeter, which did not have a great high frequency output very much beyond 12khz, not to 20khz.

Janszen 1-30 tweeter arrays closely filled that bill for a while.

Even, Edgar Villchur, back then, claimed that there would be no audible improvement, if the damping factor was great than 5.

Go to Crownaudio.com and read, "Understanding Damping Factor".

Tube amps of that day, had very low damping factors as well as low power.

I am guessing that the frequency response of the amps and pre-amps of the day, may have been curtailed as well.

Go to our AR library and read the AR-3A and AR-5 level control settings, reducing the settings for normal use, too bright.

Even when some of the AR speakers were originally reviewed, the reviewer may not have turned the pots up full, but left them at their normal setting, as they were too bright.

Initially, I will say that AR speakers tend to sound bass heavy and treble shy.

I have lived with them over 30 years, the brighter sounding speakers that I used to hear as a comparison, have gone the way of the Dodo bird.

Good luck.

[ar_pro]

Nope, they're not rolled off - this nonsense was a sales-floor selling tool, used against AR speakers, and often enhanced by adjusting downward the midrange & tweeter level controls.

Seek out old reviews of the AR-3 and 3a, and check out the excellent dispersion and frequency-balance characteristics.

[kkantor]

The Qtc for those 3a's I have measured myself is 0.71, on average. This is "critically damped" or "maximally flat" response.

Quantifying the high frequency response of a speaker, any speaker, is a much more complex subject than (almost) anyone wants to think about. Short sounds can evoke a perceptually different response than longer tones. Distance from the speaker can have a profound effect, as can placement, listening position and room acoustics. Even more subtly, the whole idea that there is one uniquely "correct" frequency response is unjustifiable, as comforting as it may be. (I believe it to be a residue of the Logical Positivism that arose in the 1960's as an over-reaction to the magical thinking of 1950's High End subjectivism. Kind of like now...)

To this day, there is little agreement even between very experienced professionals about how to properly characterize what "flat" response is. AR had their methods, (which evolved over the years.) Within the limitations of those methodologies, AR always tried to make accurate speakers, at least near the top of their line.

[Guest Eunomians]

Interesting comments thus far.

My 'not so qualified' listening impression is that the AR3a highs are not rolled relative to many other 'seemingly comparable' speakers I that have heard. This is with both pots cranked up to maximum.