Joseph Audio RM7si loudspeaker Manufacturer's Comment

Sidebar 3: Manufacturer's Comment

Editor: We'd like to thank John Atkinson for his review of our RM7si Signature loudspeaker. We were very happy to see that "The '7 Signature laid bare all manner of recorded detail." Perhaps this is why it's been the editing and mastering monitor used by Chesky Records for the last three years.

And JA's vertical-response measurements look superb—most speakers show large response errors within a small 15 degrees window. Thanks to John Atkinson, we can see how little the response changes over a much broader 90 degrees window (45 degrees in each direction!). We hope that this will become a standard feature of Stereophile's loudspeaker tests. [Unfortunately, I can only do this with speakers that are small enough to sit on their sides on my Outline speaker turntable, which rules out most floorstanders.—Ed.]

We were also pleased to read that "There was no discontinuity apparent in the crossover region." The Infinite Slope technology makes this possible. By silencing the woofer before it becomes too directional, a truly seamless transition to the tweeter is accomplished. Of course, the fact that "the speakers' imaging was excellent, individual images being precisely positioned within a detailed, stable stage," fits in nicely with our experience of the '7 Sig as well.

The review samples were built in early 1998. They were measured shortly before I submitted them in the fall of that year for review, and both were working properly. JA's comments about the region from 1.6kHz to 3kHz sent me running to see if I could detect the same characteristics. My reference pair sounded pristine.

A few days before I received back the review pair, I spoke with our drive-unit supplier. He had received the magazine, read the review, and suggested the possibility that the review samples might have a tweeter with an earlier formulation of ferrofluid in the gap. The earlier formulation, if left unplayed for a period of time, had the possibility of migrating so that it was no longer evenly distributed in the gap, and could take the tweeter out of specification. An improved ferrofluid was implemented in October 1998 that would hold to specification regardless of whether they were played or not.

Now, this is not to say that a ferrofluid clog would definitely form. In most cases, it wouldn't. But there was a possibility that it could, under the right combination of circumstances. Could that be the case here?

The first speaker of the review pair I measured looked superb, correlating well with the excellent measurements published in the review. The second speaker was a different story. The tweeter had a sag in the lower end of its passband, along with a broad peak from 5 to 8kHz. I removed the tweeter and measured its impedance. The tweeter is specified for a free-air resonance of 1200Hz. This tweeter's F(s) had drifted up to 1600Hz, with a lower Q, so the impedance was still elevated into the low end of the tweeter passband.

I installed a new tweeter in the speaker and measured correct results. I then applied signal to the old tweeter for 30 minutes. The F(s) gradually began lowering in frequency. A gentle touch around the tweeter's surround quickly knocked it back into spec. I reinstalled and measured again. The speaker was now working correctly.

Was the ferrofluid to blame? We think so, but the truth is I don't really know for certain. All I do know is that the speakers were operating properly when I tested them in 1998, that one tweeter had gone out of spec between then and last week, and that it was very easy to restore the driver to spec (which I think rules out any overdriving).

In an Infinite Slope design it is critical that each driver be functioning correctly, as there is no wave interference to mask any flaws. There's nowhere to hide!

Why bring this up, in light of the positive nature of the review? Even though the review was very positive, I believe that it would've been even better! Perhaps a Follow-Up will put all our minds at rest?

In the meantime, we take comfort in JA's conclusions that, "Overall, it gets the musical message right," and that "the bighearted RM7si Signature will offer its owner long-term listening pleasure."—Jeff Joseph, JosephAudio

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