Steve F Posted May 10, 2018 Report Share Posted May 10, 2018 This is an in-room curve of the 3a from the Berkovitz-Allison AES paper on Soundfields in domestic rooms. It’s a fascinating curve, because it demonstrates AR’s honesty and technical proficiency, attributes that put AR well ahead of other speaker companies of that time. First of all, it’s doubtful if any other company would let anything other than some phony-baloney hand-drawn ruler-flat response curve even see the light of day. Sure, this was an AES paper (not an ad in Stereo Review), but it was out there in the public domain. Nonetheless, AR had such high principles of broadening the general understanding of speaker behavior/performance and had such (justifiably) high confidence in the correctness of their design ideals and approach that they willingly let an imperfect-looking FR curve of their best speaker—warts and all—out of the secret confines of their marketing department. Let’s look at the curve a bit more closely. It’s the FR of an AR-3a in a home living room, with the Mid-Hi controls all the way up. The speakers were on stands, somewhat away from the room’s walls. This was not an uncommon usage scenario, although certainly not an optimum one. Using the speakers on stands, away from the walls, is a classic “4π” placement. This placement provides the least amount of bass reinforcement. The 3a (like all AR speakers at that time) was designed for 2π bookshelf placement (as in Tom’s bookshelf). You can see the woofer’s response falling off from the midrange level below 500Hz as the solid angle that the speaker “sees” transitions from 2π to 4π. (The 25” front baffle of the 3a serves as the 2π baffle for frequencies above around 5-600Hz. A 565Hz wavelength is 2 feet long, and 25 inches is…..it’s the math, the math…..). BTW, any box-type bookshelf speaker on a stand away from the walls will show the same mid-to-bass falloff as the 3a, when placed similarly. If you raise the under 200Hz woofer level up to the mid’s level (as the woofer level would be in a 2π setting), you can see that the speaker’s response from just under 40 Hz to a bit over 2,000 Hz is remarkably flat and accurate. This is the bass-midrange region, where virtually all the music lies. Above than, you see the falloff—but very smooth—in the upper-end response, partly due to AR’s willingness to sacrifice flat on axis upper treble for wide dispersion (in the days before ferrofluid-cooled tweeters) and party because RA’s somewhat misguided (IMO) view that the loudspeaker should intentionally introduce the particular coloration of the performance venue (in this case, the HF rolloff of major orchestral halls) into the domestic playback chain. In my opinion, the speaker should simply reproduce the electrical signal fed into it as accurately as possible. Nothing more, nothing less. It should be up to the recording engineer/record producer to impart any sense of the performance space into the recording, if desired. Not the loudspeaker. In any event, with the woofer level raised to the mid’s level as it would be in a 2π space, the 3a’s real-world, in-room performance is quite excellent. If you were to tweak the treble just a hair, it goes from quite excellent to unconditionally superb. This was quite a loudspeaker. Steve F. Link to comment Share on other sites More sharing options...
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