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Replacement Woofer for Infinity Kappa 8.1i

Sam1879

Sam1879

Member
Hi folks

I'd like to start a thread about replacing Infinity Kappa 8.1i woofer driver with more modern (sub-)woofer drivers.

The Kappa 8.2i (Series 2) have the same woofer driver as far as i know.
The "i" relates to the versions port-design, but the driver should also be the same as fas as i know.

The discussion was started by me in an other, older thread. But it would be great to discuss this topic further here.

Older discussion: https://audiokarma.org/forums/index...acement-infinity-kappa-8-2i-series-ii.691031/

Thanks for everyones support and sharing of thoughts.

The Idea is to replace both drivers of the two speakers, as the replacement driver will probably not be the same as the original driver.

I did some research and found the mentioned driver. It's ordered as i didnt found another one meeting the specs i had from the old driver. (was not much.)

Would be great if anyone shares some thoughts or technical information with me.



Sam1879 said:
Hi there
I think i've damaged one of my loved Kappa 8.1i woofers (902-6236) at the last home party.
There are now unwanted noises at some lower frequencys at higher volumes, not really bad but compromising sound on focused listening.

After doing some research it's hard to find exact specs of these drivers, and replacement parts.

What i know is:

- It's 12" size
- Woofer-Crossover is at 180 Hz
- Measures 3.8 Ohm at DC, so shoulI be around 4 Ohms rated.
- Sensitivity for the whole Speaker is at 89dB 2.8V/1 meter.
-> Assumption, (Bass has seperate crossover, crossover has some little impact on efficiency) Helpful: http://www.infinity-classics.de/technik/manuals/Kappa_8.1_technical_sheet.pdf

Whole Kappa 8.1 ist:

6 ohms
RMS up to 300 watts
SPL is 89dB/2.8Vrms

As a possible option I've found the DaytonAudio RSS315HF-4 to match most of the criteria quite well.

So, under consideration i could use my DSP do adjust frequency response and i'd like to have some more low-end-bass, would you think it's a good idea or am i missing something important here?

Is there maybe even a chance to damage the crossover when using this driver?

Sorry if any purist doesn't like the idea, I'm also thinking about using original spare parts, but if there are no huge issues with this replacement, I'd prefer this solution.

Thanks for your comments. I'm gonna comment how it has worked out if anyone is interested.

Edit:
Chain: Sony SCPH-5502 / Sony PS-HX500 - Bluesound Node2i - MiniDSP DDRC22d - SMSL SU8v2 - NordOne NC500DM - Infinity Kappa 8.1


View attachment 2130547
Click to expand...



Sam1879 said:
thanks so much for your support :)

if it's going to sound a bit different in deep/midbase up to, maybe 70 Hz i think that could be even positive, as in my setup and perception this lower area was lacking some clarity/continuity.
though i'm a bit unsure about the area above approx. 70 Hz up to 200 Hz, as the original driver here does a wonderful job and its ability to present a wonderful and "living" sound is almost incredible .
i just really don't know if a rubber surround - or other design differences - may limit the details in reproducing the dynamics or fine elements of the music in this area to much. there ist for sure a reason why arnie nudell (he was one of the masterminds behind this speaker/driver design, right?) took a foam surround and not rubber for the original driver, along with other design differences to the driver i'm planing to use as replacement.

do you have, or does anyone have experience if the reproduction in this frequency area with a similar designed (sub-)woffer driver as the RSS315HF-4 are usually perceived as dynamic, detailed, living - as with in this case the original driver ?
Or am i maybe really on the wrong track because it's just a too different design and not really tuned for this frequency area as the original driver was?

Interesting is here, the frequency chart of the dayton looks quiet aceptable and some missmatches with the other drivers (even phase shift) could be fixed with dsp-equalizing, though i dont think it's the end of the story and i dont have information about the frequency ( or q factor or other specifications) response of the original driver. Does anyone?



Photo of the original and planed replacement drivers attached.
Original:

View attachment 2130862
View attachment 2130887

Planed replacement:




View attachment 2130857
View attachment 2130858



And the crossover in the case anyone wonders :)

View attachment 2130875

Crossover for low pass:
View attachment 2130846





View attachment 2130846
Click to expand...
 
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I wouldn't recommend this for a couple of reasons:
  1. The Kappa x.1/2 series use a bass reflex enclosure. All woofers have different Thiele/Small parameters. The cabinet volume, port size and port length are designed around those parameters. While a replacement woofer will work, its performance will not be ideal (the odds of having two totally different woofers with the same T/S parameters are extremely low)
  2. The crossovers in the Kappas (and in fact most of Infinity's high end speakers) are very complex, and again are designed around the original woofer. Even if both woofers are nominally 4 ohms (and I'm not 100% sure of this, even with your DC measurement), impedance is a curve, not a single number, and again, the impedance curves for those different woofers will be different.
But as was mentioned in your other thread, it does seem as if your mind is made up. Experimentation is part of the hobby, so good luck, and let us know what you decide to do. Before you start, you should take frequency response measurements of the good speaker (you can do this with a phone app), and redo that after the replacement, preferably doing both in the same location of your home, so room effects can be ruled out.
 
Hello swechsler

Thank you for your reply and sharing your thoughts.

Do you know if - and how much - the crosover frequency of a crossover/driver-combination is impacted by the specs of the driver itself? And if yes, is the most important factor the impedance curve or anything else?

Could it be possible to get T/S-parameters or impedance curves of an original woofer anywhere? Type: 902-6236

Your right, i'm going to try it with the RSS315HF-4. but i'm really not sure if its the best (new design) replacement.

But i'm already curious about the results. As the chance of damaging anything seems to be not to high, and i could still sell the daytons if it won't work - it's worth a try.

It's maybe (and understandable so) a controversal discussed topic, but in my setup i could tune some frequency-missmatches with the dirac-dsp.
but it would be much better to keep the corrections on a smaler scale or unneccessary for sure.

When i'm going to replace the drivers i'll do some measurements using a UMIK1-microfone and publish it here.

thanks, and if anyone did something similar before on a kappa 8.x it would be great to here the stories.
 
Sam1879 said:
Hello swechsler

Thank you for your reply and sharing your thoughts.

Do you know if - and how much - the crosover frequency of a crossover/driver-combination is impacted by the specs of the driver itself? And if yes, is the most important factor the impedance curve or anything else?
Click to expand...
It depends on how different the drivers are. And it's not just the frequency. Speaker design is almost as much of an art as it is a science. Speaker engineers can spend lots of time subtly tuning a crossover after they've chosen the drivers.

This video has some more info.


Sam1879 said:
Could it be possible to get T/S-parameters or impedance curves of an original woofer anywhere? Type: 902-6236
Click to expand...
To my knowledge they've never been published (bespoke drivers made by speaker manufacturers for their own products rarely are). But you can measure them yourself.

 
swechsler said:
It depends on how different the drivers are. And it's not just the frequency. Speaker design is almost as much of an art as it is a science. Speaker engineers can spend lots of time subtly tuning a crossover after they've chosen the drivers.

This video has some more info.



To my knowledge they've never been published (bespoke drivers made by speaker manufacturers for their own products rarely are). But you can measure them yourself.

Click to expand...

Thank you very much.

Didn't know the guy in the TS-Video, but learned a lot from this one.
Oh yes, PS Audio, also learned a lot from their podcasts and videos. There are also some great interviews published online by them or with people involved in PS Audios engeneering. Still almost like a ritual for me to listen to the daily "ohms law" podcast on the way to work.
They make great products for sure, and their marketing is fabulous.

You‘re right, a crossover design is much more complex than just combining some parts and drivers and i agree there is a lot of art in it.
Though, i could imagine a woofer up to +/-180 Hz is much easier to change than a midrange or tweeter, especially here in a 4 way design.
Here used for the lower woofer is a more or less simple 3th order butterwoth design, and it seems like they put in a bigger than usual second coil to get a more steep frequency-curve. (i guess).
So i hoped, it will match together with a approximative driver, and it seems like its not going too bad.

The replacement-drivers arrived today and as far as i can say until now it's going quite well.
First subjective impressions were "it's working good but not great, subjectively sounds good, a bit different but very acceptable and low frequency response is ok" but there were unwanted noises in certain louder low frequencies. After doing some measurements and investigation i discovered the following: because of the drivers holding metal structure (basket, right?) is different designed than the original it doesn't fit to the milimeter on the frame what left little "air holes" open. And pressurized air came out there.
So i need to fix this - but not doday - . After fixing this and some driver burn in i'll bring an update and a photo.

Btw. visually it looks great, though i had to use new screws. The new drivers are really heavy...



So far ( NOT FINAL) IN-ROOM-MEASUREMENTS with the original and replacement driver:


Original: ca. 2m from Speaker
upload_2021-2-17_23-56-21.png

Replacement: ( NOT FINAL) ca 2 m from speaker
upload_2021-2-18_0-10-18.png

Replacement, ( NOT FINAL) microphone moved some centmeters:
upload_2021-2-17_23-59-33.png

Original, in room, calculated average, NOT standard mid/treble configuration (yellow curve is dsp target curve, must be ignored here) older measurement.
upload_2021-2-18_0-0-51.png


Replacement, ( NOT FINAL) in room, calculated average, standard mid/treble configuration, ( yellow curve is dsp target curve).
upload_2021-2-18_0-12-19.png
 

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Last edited:
goodolpg said:
Sam, just curious, how much was shipping to Switzerland?
Click to expand...

+/- 30 $ with UPS fast shipping.
Bought from "Soundimports", they delivered from the Netherlands as far as i know.

Btw. found a local infinity repair-service with an original driver. So the Kappas can be restored again when this shouldn't work out 100%. :)
 
so, finally fixed my poor work from last night....


upload_2021-2-18_13-56-33.png

sounds great now! though a little different than with the original. mids and treble are as clean as before.

better than the original? ... subjectivly: yes and no. maybe a bit more "stable" in deeper base, but a litte less "alive" or "fat" in the bass area from approx. 60 - 250 Hz.

(Drivers are just new, so sound may still change a little).

btw. the original screws are ok.

Are these the optimal replacement drivers? I don't know. probably not, but i'm really happy with the results so far. (giving a further update after some weeks).

Did some more measurements again, but the results did change every cm/inch i moved the microphone, so unusable (in room)...

Thats the measurement i achieved in my (not perfectly optimized) room with the new drivers. (quite ok i think):


NEW DRIVERS, in room, calculated average, Neutral mid/treble crossover rotary knob adjustment (yellow curve is dsp target curve, must be ignored here), placed speakers further apart than before.

upload_2021-2-18_13-33-39.png

Original, in room, calculated average, NOT neutral mid/treble crossover rotary knob adjustment (yellow curve is dsp target curve, must be ignored here).
index.php
 
Sam1879 said:
+/- 30 $ with UPS fast shipping.
Bought from "Soundimports", they delivered from the Netherlands as far as i know.

Btw. found a local infinity repair-service with an original driver. So the Kappas can be restored again when this shouldn't work out 100%. :)
Click to expand...

Ok. $30 seems reasonable.
Somehow I got the impression parts-express was the source and thought that might be expensive.
 
C055180D-BFE0-4CA0-9958-5DE2E4D66E6E.jpeg man, i just listened to this track, and it was like feeling in the chest the people are just in front of me playing and walking on the stage.
that‘s new in this way, love it :)

All problems solved!

it’s really quite good so far. not better, not worse. but different, in a way i really like.
 
but in tracks with many loud beats in the baseline i miss the peak at 70 Hz, but could also be because i placed them a bit wider appart.
 
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