Infinity Kappa 8 speaker rebuild with DSP crossover

[HAL]

A friend found a pair of Infinity Kappa 8 speakers that need the Polydome K's and 12in woofers rebuilt.  Picked them up awhile ago. Not going to complain for $80/pair.

These are the original version 4-way speaker with the bipole EMIT planar tweeters, Polydome K, Polygraph K dome and 12in woofer.

Found out that Miller Sound in PA does the rebuilds, so hope to be dropping them off this weekend.

Will post pictures of the process along the way of replacing the passive crossover with the DSP crossover from measurements.

[Nick B]

Sounds quite interesting, Rich. Millersound is still around, huh. Have heard their name for years, but haven't had need to use them yet.
Nick

[malloy]

I've only seen these in magazines and on display. Always wondered what they sounded like.

These the ones?



Late 80s early 90s?

Paul

[HAL]

Yes. They were built from '87-'89 from what I can find.

The Polydome K midrange dome and 12in woofer foam surrounds are being replaced due to age deterioration.  The new replacement parts should last a lot longer.

This just happened to be something a friend that worked at a retirement community spotted in their donation closet.  For $80/pair, might as well see what happens.

[Nick B]

Yes. They were built from '85-'89 from what I can find.

The Polydome K midrange dome and 12in woofer foam surrounds are being replaced due to age deterioration.  The new replacement parts should last a lot longer.

This just happened to be something a friend that worked at a retirement community spotted in their donation closet.  For $80/pair, might as well see what happens.

For $80, indeed 👍

[malloy]

That is indeed a good deal.
Some new binding posts cost more than that! 

Paul

[HAL]

Looks like the Polydome K and 12in woofer drivers repairs are complete and should be shipping back soon.

The other parts are starting to arrive.  Have the Belden 1309A 14awg stranded speaker wire and the P-E 5-way binding posts.

My idea is to remove the back plates and make new ones with the 8 binding posts to the drivers.

Going to keep the EMIT K tweeters wired as a pair as in the original design.  I probably will try them as a Bipole and have a spare EMIT K planar tweeter arriving for a test of the idea.  Since their impedance is less than 4 ohms, will have to use a good power resistor to bring up the impedance to drive them correctly to full range with Class D amps.  Mills non-inductive power resistors should do nicely.

Probably will not need the protection diodes with the high roll-off rate DSP crossovers.  Will be there for the passive side.

Also building an AB box to switch from passive to active crossovers to hear the difference.  Have some solid state relays coming to test for sound quality.  Not that happy on using mechanical relays for audio switching.

[malloy]

Nice.

Curious as I have never heard the originals. What is the sound signature of the original Kappas?

[HAL]

I am the same as you.  Never heard the original speakers.

Once I get the repaired drivers, will be checking them out.  Could not afford them back in the day.  I had Magnepan MGIIB's and Hafler DH220 amps when these came out.

[malloy]

Doubly exciting then!

Back then, all I had was my Sony midi system. I always had my face pressed against the glass of the local hi-end store that had an Infinity IRS Beta on display wondering how those would have sounded.

Please keep us posted.

[HAL]

Will do.

Waiting on the drivers to return from repair.  Original estimate was they would complete repairs tomorrow.  Hope they are one schedule.

Everyone that has reported on the Millersound repaired Polydome K midranges have said they are quite an improvement over the original material.  Should be interesting.

Have a few spare EMIT K's coming as well.  Suggestion by a friend with Infinity Beta's with the same EMIT's.  There are now replacement planar driver diaphragm's for them that are easy to replace from American Vintage Audio.  He also makes replacement planar diaphragms for the larger EMIM planar mids.

Did discover that over time Infinity changed the planar magnets from Samarian Cobalt to Neodymium magnet material.  The Neo style have a part number with an N suffix.  The Neo's are higher field strength magnets, so increases the sensitivity of the drivers.

Interestingly it will be a pair of Kappa 8's brought up to 2024 status for the AB listening.

[HAL]

Things lead to things.

A pair of Infinity RS8 2-way speakers popped up for $100 that were made from 1982-1984.  These have the earlier Samarian Cobalt magnets for the EMIT planar tweeters.  The woofers are 8in diameter polypropylene cones that have had new foam surrounds installed.

Found pictures of the 2 pole high pass and low pass filter passive crossovers.  Looks like iron core inductors, a metalized mylar cap in the tweeter and non-polar electrolytic cap in the woofer circuit. A protection fuse on the tweeter.  The price for the speakers was $299/pair. 

These are the same type of parts use in the passive crossovers in my pair of Magnepan MGIIB's from 1982.  Polypropylene replacement caps were a great upgrade to those.  Now we have even better DSP crossovers.   

[malloy]

Wow! Where do you get all this nice gear? The local thrift stores only have Radioshack-level equipment. 

[HAL]

Facebook Market Place has a lot of great equipment. 

[HAL]

The Infinity Kappa 8 Polydomes and 12in woofers are back from repair.

Now to see if the passive crossovers are still working with the drivers connected. 

Will be rewiring the speaker drivers to binding posts to use with the DSP crossover and the passive crossover exterior to the original box.