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Living with Infinity Kappa 7 A Loudspeaker Systems

Part One

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Infinity Kappa 7 A Loudspeaker Systems

Installing a pair of Second Hand Infinity Kappa 7A Loudspeakers.

Some may 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.
I am only writing about my experiences now, October 2011, about my thoughts and analysis of the Kappa 7A speakers. Why? Because I had bought a pare of second hand Kappas in April of 2011. I certainly would not have written these pages if after connecting and positioning the cabinets everything was Ok. But it was immediately clear that "just connecting" did not suffice at all. The loudspeakers did certainly not function as it was intended by the designer and manufacturer.

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.

Ill Performance

Alas! The 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 perform well.
First, it was immediately evident that the voice coil of the woofer of the cabinet (which I had placed at left) was not centered. It scratched inside the gap of pole plate and magnet. The advertisement of the seller had stated "new roll surround". The management may have ordered an inexperienced worker to glue the surrounds and afterwards did not check the result of his work adequately. When I contacted the German firm in a polite manner and explained what was the case, the only thing they could do was holler! So that was a dead end. Furthermore the wooden pannels of both cabinets vibrated. Not just slightly, but excessively. That meant that there was fundamentally someththing wrong. The heavy vibration meant that the woofer did not "use" the entire volume of the compartment and the excursion was obstructed. This vibration naturally interfered with the functioning of the Polydome and the EMIT naturally.

Further Discoveries

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.

Checking polarity of the woofer.

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.

Damping material.
 
BAF Bonded Acetate Fiber

Avoid Exchanging a 12 inch Woofer

But there 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.

I 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.

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Audio&Music Bulletin - Rudolf A. Bruil, Editor - Copyright 1998-2011 by Rudolf A. Bruil and co-authors