All woofers & mids Refoarmed. I’ve not heard better speakers for there articulation of mids & highs. The bass is specked down to 18hz. Interested purchasers should be end users/. The AR9 was a large floor-standing, vertical, 4-way, 4-ohm loudspeaker with two 12-inch acoustic-suspension woofers, an 8-inch acoustic-suspension lower-midrange speaker, a 1½-inch upper-midrange dome speaker and a ¾-inch dome tweeter. Dimensions were 52 ¾”H x 15″W x 15 13/16D with a net weight of 130 lbs. And the tower configuration eliminated most room-placement issues found with conventional speaker designs. The crossover frequencies chosen for the speaker were 200 Hz, 1200 Hz and 7000 Hz. Well within the safe-operating range of each driver. By using two (AR-3a/AR-11) 12-inch, high-excursion, low-resonance (18 Hz) woofers in an enclosure of 4¼ cu. (nearly three-times the size of the AR-3a enclosure), the AR9’s system low-frequency output was extended, sound-output level increased and distortion level decreased from the existing AR-3a-for many years considered a reference standard for low-distortion bass and extended low-frequency response. Using two side-mounted 12-inch woofers in the larger enclosure doubled the radiating surface and lowered system resonance, but also resulted in over-damped bass response at resonance. The net result is a critically damped system with a Q of 0.5-optimum for a system with two woofers close to the floor-wall boundary and with uniform output down to below 30 Hz. The LCR circuit thus obviates excessive roll-off in output at resonance-indigenous to a system with such a low Q-by raising output 6 dB; on the other hand, the low Q provides nearly ideal woofer damping, thus preventing any response “ringing” or hangover. When room gain is added, the AR9 has prodigious bass output down to below 20 Hz. When measured in half space. As such, the AR9 proved to be an exceptionally potent low-frequency loudspeaker, but one that hardly called attention to itself. The speaker has such low harmonic distortion and smooth response, that some listeners-expecting heavier bass-felt the speaker was perhaps bass-shy, yet the true measure of a high-quality bass reproducer is no bass reproduction unless called for in the program material. The woofer section of the AR9 crossover utilizes a full-section, 18 dB/octave filter with excellent damping to seamlessly blend the output of the two 12-inch woofers with the 8-inch lower midrange driver. This important, highly damped filter provides optimum low-frequency damping while keeping unwanted woofer output away from the lower midrange; moreover, a hallmark of the AR9 is the virtually undetectable blending of the woofers and the lower midrange unit, as though all sound emanates from one source at the system crossover of 200 Hz. The components of the AR9 crossovers present low series resistance (thus not dissipating power themselves) with large-gauge wire used in the air-core chokes in addition to heavy-duty, high-power, computer-grade capacitors, and of the three AR9 crossover boards, the woofer section alone weighs nearly 10 pounds. The importance of the AR9 woofer-crossover characteristic is clear when contrasting it with a system composed of satellite speakers and a separate subwoofer. Any serious audiophile will tell you it is not a trivial task to seamlessly blend the output of these components; the subwoofer will eventually call attention to itself because of the lack of precision blending of the two systems, even when the subwoofer is turned down to a low output. By mounting the AR9 woofers close to the floor on either side and utilizing the low 200 Hz crossover, AR engineers were able to deal with the room-boundary effects (“Allison” effect) on low-frequency reproduction which moved the reflected energy to approximately 500 Hz. Well above the woofer’s operating range. During AR’s presentation of the AR9 to the Boston Audio Society, Tim Holl acknowledged Roy Allison’s work in this area in describing the design of the AR9, similar in approach of the Allison: One speaker’s pioneering “Room-Matched” design. Operating range-giving the speaker a great sense of midrange clarity and smoothness. This special driver is highly damped and operates within a sealed enclosure within the larger main-cabinet interior. The lower-midrange driver, with a sharp transition at 200 Hz, is always operating well above its mounted-resonance frequency of 175 Hz. Much of the AR9’s excellent clarity throughout the midrange can be attributed to the attention paid to the design of this driver. In a vertical array above the 8-inch lower midrange driver is the 1½-inch upper-midrange dome driver, an adaptation of the original 1967 AR-3a 1½-inch treated-fabric, soft-dome midrange driver but devoid of the screen and fiberglass covering of the original version. This fabric-dome driver has an energy-absorption dope applied to the outer portion of the diaphragm; it also has a “semi-horn” top plate that improves loading in the 3 kHz – 7 kHz range. Energy-absorbing dope is applied to this dome as well, and the top plate provides slight loading at the highest operating frequencies for an extended treble response. All drivers on the front face of the AR9 are vertically aligned, a common practice today to reduce horizontal lobing, making this interaction between drivers less intrusive. Note: AR further reduced vertical interference with the next-generation AR9, the AR9Ls with its Dual-Dome “Lambda” midrange-tweeter. Part of the research into the AR9’s performance was the study of diffraction and reflection of short-wavelength frequencies in the operating area of the upper-midrange driver and tweeter, and Associate Engineering Director James Kates performed extensive impulse testing on many loudspeaker enclosures using AR’s new Digital Equipment Corporation (DEC) PDP-11/40 16-bit minicomputer, previously specified by R&D director Robert Berkovitz. Kates and Berkovitz had patented a loudspeaker system equalization network, and the two worked together to develop the PDP-11 computer for speaker-testing research. This research revealed problem areas-particularly with wide-dispersion drivers-that resulted in the introduction of the AR9’s “Acoustic Blanket, ” a method of using a felt/foam pad on the face of the speaker’s front panel to suppress unwanted reflection from the front baffle, adjacent to the lower-midrange driver, upper-midrange driver and the tweeter, in effect to absorb unwanted refracted energy. This absorption of energy on the panel helps to reduce small dips and peaks, thus further smoothing output energy and improving response clarity. The early use of AR’s PDP-11 computer for loudspeaker design and testing was one of the earliest applications of this type of testing in the high-fidelity industry, leading the way for digitized speaker testing. During the AR9 presentation to Boston Audio Society members, Kates showed graphs of impulse tests of AR speakers (and several other speaker brands), describing how to interpret the very short-duration energy bursts being studied while researching means of suppressing unwanted diffraction and reflections. One investigation was to determine the relevance of phase relationships over time periods of more than a few milliseconds and its audible perception by listeners. It was found that phase relationships were inconsistent and not generally audible when lasting longer than a few milliseconds; however, other tests showed that reflections and refraction of sound from within the speaker structure itself, from cabinet edges and molding, contributed to a smearing of the spectral image, often reducing clarity and intelligibility. This differed from the efforts by some speaker designers to mount drivers in a physical alignment to adjust (“time align”) the arrival time of signals; AR found that this stepped-baffle arrangement actually made things worse by increasing early reflections and thus degrading performance. AR’s Acoustic Blanket, however, reduced the reflections and bounced energy before it could be reflected from the cabinet edges, thus smoothing system frequency response. Many tests were performed with and without the energy-absorbing pads before determining that the pads helped reduce coloration, improve localization and smooth frequency response. Kates worked for Bob Berkovitz in R&D from 1975 until 1978 and contributed to the AR9 design both with crossover work but particularly his PDP-11 impulse testing. After AR, Kates has had a career as a scientist in audio, psychoacoustics and digital design, most recently as Scholar in Residence, Department of Speech Language and Hearing Sciences at the University of Colorado in Boulder. The AR9 received universally excellent critical reviews from the U. And European high-fidelity audio press. It was extensively reviewed, but probably the best description came from the dean of audio testing and review, Julian Hirsch of Stereo Review. The measurements we made on the Model AR9. Yielded the widest and flattest frequency-response curve we have yet obtained from a speaker system. The AR9 Inspiration of Future Audio Products? After forty-four years, the AR9 remains one of the finest loudspeakers ever designed for home use. Over the next decade, the AR9 became the foundation for new speakers. Certainly, as speaker designs have evolved, improvements in quality, reliability and value have occurred-especially in professional digital monitors used in recording studios or sound reinforcement-with the application of digital designs, advanced materials and methods of manufacturing. Changes are occurring less frequently in this mature industry with far fewer “revolutionary” advances and improvements, a reflection of the slow and inevitable decline of home audio and the diminished interest in audio equipment for the home. Nevertheless, the AR9 was a no-compromise design and regained much of AR’s reputation for engineering excellence. Without Teledyne AR’s eagerness to restore engineering excellence and its virtually unlimited financial and technical resources, the AR9 could not have been possible. The AR9 speaker design reached a high mark in engineering excellence and arrived just as the popularity of stereophonic sound reproduction with individual components began its slow downturn. As AR used to say, the accurate reproduction of music is one of man’s more benevolent technological gifts to himself. Known as New Acoustic Dimension by AR. At NAD-essentially spun off by Teledyne AR-the company developed many innovative electronic designs by Erik Edvardsen.