AR-3a Response Curves and Test Reports

[tysontom]

Some of what I am saying here has been debated previously, so I apologize for the repetition. However, I have some very interesting response curves and speaker measurements regarding this great loudspeaker.

A great deal has been said about the AR-3a’s performance from an objective-measurement standpoint, and in my opinion, this discussion has for the most part been excellent! Despite some naysayers, the fact is that the AR-3a measures extremely well: in its day it was perhaps the flattest, smoothest loudspeaker money could buy; even today it is still a superb loudspeaker, capable of holding its own against many of the top loudspeakers currently available! It also shows that a speaker that measures well will also sound good! And regardless of all the criticism from some interlopers in this forum, AR was a pacesetter and pioneer in the world of objective-measurement techniques, and Acoustic Research relished in publishing the results of these tests! What other speaker company was willing to display the results of their objective speaker testing? The real question, however, has to do with trying to reconcile the simplistic, direct, steady-state, frequency-response measurement of a wide-dispersion loudspeaker such as the AR-3a in a listening room vs. the true acoustic output of that speaker, thinking as it were by some that the direct fr response measurement is exactly what you would hear in that same listening environment. The two do not reconcile, as has been known for decades.

There is really little question that what you hear in a normally damped listening room is a combination of direct and reflected sound, not primarily direct sound (the exception might be some high-energy, on-axis horn tweeters). This has been known for many years and reported in the literature (and vigorously disputed by some on this forum and elsewhere), but there were no published objective measurements of the home-listening environment that existed prior to the time the AR-3a was introduced in 1967, and for this specific reason, Roy Allison and Robert Berkovitz did the research in the Boston area and reported in their landmark AES paper, The Soundfield in Home Listening Rooms, posted on the CSP in its complete form thanks to the effort of Howard Ferstler. Allison and Berkovitz set about to answer the primary question, “…is the field at any practical listener location primarily direct rather than reverberant?” Their conclusion, verified by their extensive response-curve data, was simply “We are convinced that home music listeners perceive the spectral balance of the sum of the direct and reverberant fields, and that the very small time difference between them has no effect on this perception of balance.” Therefore, anywhere in the listening environment what the listener hears is reverberant energy -- the sum of the speakers’ radiation at all angles. It is difficult to interpret this paper in any other way! The direct radiation is embedded in the total energy radiation, and it does not predominate. AR’s experience was that any normal listening room integrates the total output of a speaker system at all angles and that beyond three to four feet from the speaker a listener is no longer in the direct field but actually in the reverberant field. The AR-3a has such wide dispersion at all frequencies it is definitely affected by cabinet-molding diffraction, and this anomaly causes the direct frequency-response measurement to look jagged and rough, but this has no affect on the total acoustic output. The same is true of driver overlap at crossover and so forth, but these anomalies aren’t audible in the reverberant field, as shown by the total acoustic output of the speaker. This up-close fr measurement of the AR-3a also caused the Consumer Reports reviewers to be critical of the AR-3a. In order to measure the total energy output prior to the development of computer-generated tests, AR developed its semi-reverberant test chamber, and an accurate representation of the total energy of the loudspeaker could be assessed without having to factor in room-response curves for every different room. “Semi-reverberant” in that there was a 2π baffle facing into a reverberant chamber.

AR measured each driver individually, on- and off-axis, in the anechoic chamber. This quantified the accuracy and smoothness of each individual driver without the influence of interaction of drivers at crossover, diffraction effects and other anomalies. The woofers were measured out doors flush in the ground facing upward, 2π-fashion, and these curves were spliced to give one an idea of what the overall frequency response of the speaker would look like without interference effects. Nonetheless, the acoustic-power curve is the most revealing data in that it shows what the speaker will be doing in a real room and what is being heard by the listener.

--Tom Tyson

Attachments 1-7:

In 1994 I supplied a pair of AR-3as for Julian Hirsch to use in comparison to the then-new AR-303. AR had me ship this pair out to AR/NHT in California to be checked and tested before sending to Mr. Hirsch. The result of the curves show that the AR-303 and the AR-3a were actually very similar in the in-room noise and distortion curves at 1 meter and 2 meters (using the highly accurate AP test equipment). Note that this testing was not first-arrival impulse testing, which would present interference effects as well as lobing and so forth. These anomalies aren’t noticeable in the reverberant field. Predictably, the AR-303 was superior in overall smoothness, but the important thing to note is the similarity of the AR-3a to the AR-303. Few will criticize the frequency-response measurements of the AR-303 -- even John Atkinson of Stereophile -- so the results of the AR-3a test and measurement about to be published will be very interesting indeed!

[tysontom]

Following attachment is the Electronics World test of the AR-3a showing the frequency-response averaged curves done by Julian Hirsch:

--Tom Tyson

[tysontom]

Following attachment is the Electronics World test of the AR-3a showing the frequency-response averaged curves done by Julian Hirsch:

--Tom Tyson

Please read the comments made by Julian Hirsch in the Electronic World test report regarding the AR-3a frequency-response smoothness. Also, some other reviews of the AR-3a are attached.

--Tom Tyson

[tysontom]

AR published this ad on speaker measurements, and it was a short primer on measurement experience and methodology. As someone at AR once said, "anyone can put a microphone in front of a loudspeaker and get a response curve, but properly interpreting the measurement is a different matter altogether." The second attachment may be currently in the library, but it was the complete measurement technical data sheet for AR speakers in the 1969 time-period. Also attached is the sensitivity (efficiency) rating for most of the early AR classic-period speakers.

--Tom Tyson