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AUDIO & MUSIC BULLETIN
Living with Infinity Kappa 7 A Loudspeaker Systems
Installing a pair of Second Hand Infinity Kappa 7A Loudspeakers.
consider that the publication of this article comes quite late and should
have been done some 25 years ago, in 1987, the year when the Kappa 7 was
introduced or a year or two later after it had evolved to 7 A. Although
I was publishing a critical audio magazine at the time, I never had the
chance to review Infinity loudspeaker systems despite the fact that I
had heard big IRS systems.
Trouble in the House!
The pair was bought from a firm in Germany. I had bought from them equipment previously and those purchases were without complication. After the Kappas had arrived and the packaging of cardboard and all sorts of fillers to prevent damage during transport were removed, I gave them a few days rest in the small and narrow entrance hall so they could relax and adept to the new climate. After a week I was in the mood to move my old cabinets and connect the 7 A speaker systems. Now was the big moment to enjoy the sound as I remembered hearing it in a shop in 1995.
sound was not at all what I had expected it to be. It certainly was not
what I should have been hearing. In fact it was a big disappointment!
The mids sounded edgy, the highs were fierce, and the woofers did not
Careful listening made it clear that the scratching woofer in the left cabinet had quite a different sound if compared to the other system. It appeared that the woofer of the repaired system had been connected out of phase, the polarity had been reversed. In order to check this, I connected a 1,5 Volt C battery to the binding posts. The woofer of the left system exerted out of phase. The battery made the cone move inwards, let it inhale so to speak, while the piston action had to be forward/outward. The woofer of the other system was connected correctly, in phase. That box had not been repaired and was in its original state.
The "scratching woofer" had to be repaired. For that I ordered myself a new foam roll surround. When it arrived I followed the instructions found on YouTube. Also the dustcap did not look well centered. So I cut it out to glue it again but correctly. After removing the dustcap a circuit was visible. Friends and I suspected that this woofer was meant to serve in a Motional Feedback Loudspeaker System, a la Philips (MFB) and Cabasse (Albatros, Galion, Atlantis, Sphere) This was confirmed by Klaus Pohlig, owner of www.infinity-classics.de. Infinity used this kind of woofer in the IRS Gamma and certainly not in the Kappa 7 A.
I prefered not to use this woofer. Fortunately a seller on www.eBay.de sold a single woofer of the same design (902 3054A 391) and for an affordable amount. A few days later the woofer arrived and was installed, in phase of course, and it performed as it should, without the scratching of the voice coil that is.
Avoid Exchanging a 12 inch Woofer
was more. While checking the systems for polarity and replacing the woofer,
I had noticed that the way the damping material (Bonded Acetate Fiber
- BAF), arranged in the cabinets, differed from speaker to speaker. Units
may differ slightly and therefor a compartment should be damped specifically
for this or that unit. However the difference in damping should not be
excessive. The left cabinet however had a much larger space behind the
woofer while in the right cabinet the BAF was much closer to the basket
of the woofer.
So I checked www.infinity-classics.de once again. There was a picture of one of the models showing that the B.A.F. should be close to the basket. In the picture the BAF was originally separated by a mesh fabric (netting) put there in the factory it seems.
was not sure whether the assistant of the German firm from which I bought
the Kappa speaker systems, could have pressed the BAF to the back of the
cabinet with a firm hand in order to be able to handle the internal wires
when installing the woofer.
The arrangement sounded not correct. It affected the frequency characteristic severely. There was no open and natural transition from the 12 inch woofer with graphite cone to the 3" Polydome. The first thing to do was to pull the BAF in the left cabinet more towards the opening, hopefully with a positive results. But I found that the picture on www.infinity-classics.de was not valid for the Kappa 7A. There needed to be much more free space behind the bass unit and that it was necessary to do some experimenting to achieve a harmonious sound. You will read about that on the next pages.