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Unconventional Infinity Kappa 7 A Loudspeaker Systems

Part Two

 

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Insight

What you read on these 5 pages may give you some insight in the design if you are not a Kappa user, and in case you own similar Kappas, it may confirm your experiences. To others it can be of help to get more out of the systems. Only of course, if the systems you bought do show irregularities. And only if you suspect that they have been tampered with. But actually, the systems I bought should have been re-adjusted by the factory in the US. Sending them back was out of the question. So I had to optimize the systems myself.

Complexity

There is talk about Infinity Kappa 7 loudspeakers on the net. Most owners seem to love these speakers. Yet there are a few who are not satisfied with the performance. In fora people write that they do not have the right power amplifier. Or that the mid band is not open. There is never talk about addressing the basic problem, namely the damping of the woofers, in any case if the damping material was rearranged by some nitwit.
OK, I have found that the amplifier is important. But only than if the woofers are functioning as they should. Only then the fine tuning of mid and high frequency units in relation to each other and in relation to the 12 inch woofer can give perfect results. Yes, I have found too that the adjustments are related to the power amplifier you use, but only slightly if the systems are not optimised. The importance of the power amp is real. But the sort of power amplifier and the design of it is less significan after the damping of the cabinet has been arranged correctly.

Nevertheless there is reason to believe that a few owners are not aware of how to make the best out of this design. Well, as many certainly know, it is possible to make them sound right if they do not. But you really have to take your time and learn how the systems work.

Normalcy

Normalcy is that you buy a loudspeaker system which has a frequency characteristic, a dynamic behaviour, and a certain level of efficiency, all determined by the designer. The designer has chosen the size and shape of the cabinet, the volume of the compartment for the woofer and the dampening of it. The designer has decided how the transition of the woofer to the mid range driver will be realized and how, finally, the tweeter unit takes over. Normalcy is that there is no possibility to adjust the system by means of variable resistors, potentiometers or L-pads. With most speakers the only parameters that can be changed are those of the position in the listening room and the acoustic properties of the listening environment which can be altered in relation to the speaker systems.

Different Surroundings

Yes, the designer may take various room characteristics into account and calculate the behaviour of his design accordingly. He will most certainly test his design in a reverberant room and in a sufficiently damped room as well. He has to be aware of reflective walls and take rooms with different shapes and sizes into account. His aim is that his design shall function in as many rooms as possible. He wants to sell numbers! Not just a few speakers. Only in rare cases there may be an L-Pad, a potentiometer, or a switch activating a few fixed resistors, all for adjusting the level of the tweeter or mid range unit. The Yamaha NS-1000 has switches for adjusting the levels, but the steps are not large. And fixed settings can have frequency related compensation. Being able to adjust the levels has its advantage, but, at the same time has its drawback. By changing levels the crossover frequency changes slightly and this can have a minute influence on the phase of the system.

Closed Box

Despite all this, the fact remains that the behavier of the woofer will determine the functioning of the mid and high frequency units. The drawback of a closed box is that the woofer should have a powerful magnet in the first place. Depending on the efficiency of the unit, and the size of the cone, you do need a powerful amplifier as well to drive such a woofer. Much of the energy will be absorbed in the damped box. It is therefore easier to configure a nice sounding reflex loudspeaker system what most designers do. There is less need for quality components. Even small and cheap units in little boxes will do the trick. However what I found attractive about the Kappa 7 A, and what was an important argument to purchase these systems, was the closed woofer cabinet. That promised good phase in the lower register and this would certainly be repeated by the mid and high frequency units.

Frequency curve closed box and ported enclosure.

Three Units in Phase

Both the true hobbyist and the avid seaker for the perfect reproduction has heard many systems during demonstrations in high end shops and at audio fairs. You may remember an instance when you were struck by a perfect demonstration. That must have been a pivotal experience. As a kid in fifth grade I heard the Philips 9710M. They were housed in the famous corner enclosure of the nineteen fifties, complemented by two mid high units hanging on the wall on the left and the right of the large cabinet. The system was fed by a valve amplifier. The records were played on a luxurious Philips record changer. It was the audio set of one of my teachers. In fact the box had the 9710AM, the 800 Ohm version, fed by the Philips OTL amplifier which was later picked up by Futterman. Like the 9710M, the 9710AM was a wide range unit with a whizzer (small center cone). I myself had at one time small wide range Philips units driven by a tube amplifier. These AD3800M speakers performed so very well, that, when I heard early Goodmans boxes with 12 inch woofers topped by a small midrange and tweeter, I found that the sound was not right. I was used to coherent phase even if the linearity of the 9710AM and the AD3800M in their respective cabinets were not flawless, yet the phase was correct! I discovered that perfect phase (coherency) is far more important than a straight frequency curve.

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