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Acoustic Research AR-4X

Two Way Loudspeaker System (1971)

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Acoustic Research AR-4X

Specifications

Type: 2 way, 2 driver loudspeaker system

Recommended Amplifier: 15W (minimum)

Impedance: 8Ω

Bass: 1 x 8" cone

Tweeter: 1 x 2.5" wide dispersion cone

Finish: oiled walnut, birch, pine

Dimensions: 10 x 19 x 9 inches

Weight: 8.4kg

Price: USD $63

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Reviewed May 31st, 2015 by

My first serious speaker in the mid 70s. Bought second hand, used with a Pioneer SA 7300, which drove them well for my domestic use.
Having also had AR2ax, AR16 and AR6, I must say that the unassuming, pleasant and coherent voice of the 4x was, in retrospect, my preferred one.
I now have another pair, very old, but it still sounds as good as I remember. Modern designs offer much more, of course, but a pair of these in good health can really make music.
I tried them with a Naim Nait 3 and the match was very very enjoyable. No very deep bass, but balance and good timbres. Nice speakers.

 

Comments

AR-4X Power Requirement

Regarding the AR-4x's minimum 15 watts per channel amplifier power requirement ....

Does one interpret the requirement to mean that the amplifier unit (basic, integrated or receiver) must have a rated continuous output of at least 15 watts per channel at 8-ohms ??

If yes to that, then it would definitively confirm something I've always believed -- that normal volume listening with a minimum 15-watt-per-channel unit would actually occur within approximately the one to five watt range, and that any watts above that range would occur when certain passages in program material required such power.

For the record, my family once owned a Sony STR-6036a AM/FM stereo receiver, rated at 15 watts per channel at 8-ohms, and it did service a pair of AR-4x's very well, playing a mix of rock, pop, country, jazz, early new age electronic and classical.

re: AR-4X Power Requirement

Most loudspeaker power requirements are based on a bunch of parameters. One of the very worst things you can do to a loudspeaker is clip the amplifier driving it. When the amplifier clips it stops making AC (sound) and instead makes DC (at a higher than usual voltage). This DC changes how the loudspeaker works and is very likely to cause damage. For this reason you will see both minimum and maximum recommended power ratings. The minimum is so that you have enough power to listen at reasonable levels and not clip. The maximum is so that you do not exceed the thermal (RMS or long term) or excursion (peak or short term) power limitations of the components (woofer, tweeter, etc).

In the case of the AR 4x, which is a very old design, the type of music also figures into the ratings. Most music up through the 1980's had a peak to average ratio of 8 to 12. So the peak power would be 8 to 12 times the continuous (or RMS) power. So with an amplifier that could deliver 15 watts you would effectively get 1 to 2 watts before starting to clip the peaks.

Amplifier ratings also play a role here. Up through at least the 1990's amplifiers were rated based on continuous RMS power. Some included ratings for peak power (of IHF dynamic headroom), but those ratings were all over the map. In 1993 I worked at a pro-audio shop that also sold consumer gear. We had a peak power meter in the showroom and could measure what a receiver or amp could do. A receiver from company J rated at 110 watts would make peak power of about 110 watts, yet a receiver from company D rated for 65 watts would make peak power of 120 watts. So the receiver from company D would play louder before distortion than the one from company J even though rated for less power.

Back to the AR 4X, that 8" woofer probably has a 1" voice coil which is good for about 10 watts RMS and peaks of 100 watts, the tweeter much less. Whether a 15 watt rated receiver (amplifier) would be good enough for you will depend on how loud you want to listen, how big the room is, and what type of music you listen to. I would be comfortable using a receiver rated for up to 100 watts on them as long as I was careful to not clip the amplifier.

re: AR-4x Answer

Thank You.

You confirmed what I suspected -- Use the amplifier within its limits, but never more than that for both amp and speakers sake. If you chose an amp with a bit more than power than actually needed, but still use it wisely, then all should be OK.

The Sony STR-6036a and AR-4x system was situated in a 10 x 25 (foot) room with furniture, built-in shelves, a brick fireplace and wood-panel walls. The volume control position was very rarely above 9 O'Clock.

re: AR-4X

For their size, they really are very sweet. My pair has been recapped, controls cleaned, and surrounds have been doped with Vintage AR goop, so are back to original specs. Used in a small room on the floor with felt pads on their bottoms. Daily driver and so pleasing!

This website is not affiliated with or sponsored by Acoustic Research. To purchase AR-4X /AR-4xa spares or accessories, please contact the company via their website or visit an authorised retailer.