Loudspeakers: When is Good Enough, Enough? Part 1 - page 2

Back when we designed the tri-amped Imperial 9s we found that we needed to add +6dB boost at 30Hz to get the system to stay flat that far down in our lab. Then, because the free air resonance of the 9's woofers was 26 Hz we added a 24 dB/octave filter at 28 Hz. It worked. Bass reproduction in the big Marantz lab was unlike anything we'd ever heard. As articulate as we'd ever heard at the time, powerful and effortless.

Much later, I purchased the prototype tri-amplified system from Marantz and set it up at home. Imagine my surprise when the low bass now sounded way over-boosted with less articulation. It was only many years later that I realized part of the magic Bart Locanthi had seen in that neutral listening room. Once we got music with 30-40Hz low bass hitting peak levels over 110dB the drop ceiling panels would move, relieving the low bass pressure and thus not allowing the formation of standing waves of any strength.

Up until the development of the Imperial 9 there had not been a speaker in the lab with enough piston area and power to move the panels. We had slowly added boost at 30Hz on the 9's woofers until, at +6 dB, the amount of air pushing on the panels equaled the amount of air leaking out. Actually, we had gone up to +9 dB but we were clipping the heck out of the bass amp and we were still getting the same flat response curve. So we decided to stay with +6….not because we realized what was really going on. But because we wanted to keep the bass amp from clipping.

At the end of the tri-amp Imperial 9 "reference" project we were measuring 117 dB peaks at 4 meters in the lab. Frequency response was 30Hz - 17KHz ±1dB. It was only many years later that I came to understand why we could only get that ±1 dB at 30Hz in that room.

It's a little suprising that the intervening 30 years have seemingly seen so little forward progress when it comes to the speaker-room interface. Passive bass traps are available but most versions are bulky and almost impossible to integrate into a home system. And there have been numerous attempts during the 90's to market both home and professional computer driven speaker-room equalization devices. Most though, were both prohibitively expensive and hard to set up and use.

Then in 2001, the second-to-last issue of Audio magazine devoted several pages to a review of Infinity's new flagship speaker system, the Prelude. The most innovative aspect of the Prelude system was incorporated into its 850-watt powered subwoofer. Called R.A.B.O.S . for Room Adaptive Bass Optimization System, the Prelude's single-band parametric was the first consumer-level electronic speaker-room interface.

A R.A.B.O.S. Accessory Kit necessary for proper set-up comes with many of the R.A.B.O.S. subwoofers now offered by Infinity. A kit consists of a manual with several blank 20Hz -100Hz level vs. frequency graphs, a CD with test tones, a special protractor for measuring the width of the peak and an a calibrated SPL meter.

The grueling two-hour (minimum) set-up is a lot to ask of a consumer. And can you realistically expect a R.A.B.O.S. demo sub to be and remain properly calibrated, on an ongoing basis, in a dealer's showroom?

In their original Prelude review Audio wrote about the rather tedious but ultimately very satisfying results after set-up. They described the marvel of the increased bass articulation that was immediately apparent. But along with the superb bass articulation came another surprising revelation. They could hear more bass extension.

In the middle of their Prelude review Audio hinted that this obviously painstaking-to-set-up first version of R.A.B.O.S. might be a precursor of an automated system to come…..

It is now three years later. I have R.A.B.O.S. on both my 850-watt 12" Infinity Intermezzo sub and on a 250-watt 10" Infinity Interlude. I've run this double-sub setup in two different homes. It takes a couple of days and several run-throughs with each sub's three different potentiometer settings to get the sound balanced within ± 1.5 dB from 30Hz to 100Hz. But the effort has paid off big time. The system's bass is excellent, accurate and repeatable on all formats, music or video.

If a movie is mixed with accurately captured real effects, like an explosion, you hear and feel the leading edge transient of the blast which imparts the true concussive impact of a bomb.

On a jazz track with both a soft double kick drum set and a fretless Fender bass guitar each instrument's initial attack, difference-of-tone and decay envelope are contained at their exact, separate locations within the soundstage. Gone is the feeling of a woofer and room trying to puff out one monotonous note, masking the individual instrumental information on the recording. The whole presentation is more real, more dynamic, yet relaxed at the same time.

I'd like to end part 1 on "Speakers, when good enough, is enough" with an introduction to a product which may be able to finally, and incredibly inexpensively, close the loop on the speaker-room interface. It is called the Subwoofer Optimizer System by Automated Controlled Environments, Inc. To quote from their literature, " The SOS is an automatically calibrating, subwoofer optimization component, that acts to attenuate an audio system's major room mode resonance to provide significant improvement in measured and subjective bass system performance. After installation your system will have a more linear frequency response, bass evenness, tightness, extension, and improved clarity. " The system retails for only $299.95.

I've suggested to Audioholics staffer Gene DellaSala that he request a sample to evaluate within his RBH T-2 reference system which appears to need only this last tweak to knock out his +15dB bump at 40Hz.

If the SOS performs as well as I suspect it will in Gene's system, watch how abruptly the market for $299.95 speaker and interconnect cables dries up. Then we can go back and take another look at the "Speakers; When is "good enough", enough?" question.