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KEF 104/2 - restoring, surrounds, ferro fluid and caps

 
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sorenb
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PostPosted: Sun Jun 03, 2018 3:41 pm    Post subject: KEF 104/2 - restoring, surrounds, ferro fluid and caps Reply with quote

Have been restoring an old pair of KEF 104.2: new surrounds for the internal woofers, replaced the ferro fluid in the tweeter and replaced all caps with a set from Falcon Acoustics, and have a few questions in that regard?

After replacing the fluid, applying new fluid by eye balling. Noticed different output from the tweeters. Re-moved the ferro fluid once again, and re-applied using a syring so each got close to 0.1ml.
Hereafter the output sounded very much identical.

Is the amount of ferro fluid very critical to correct function?

Before replacing the caps the speakers sounded a bit muffled and harsh at times. After replacing much better, using my Maggies as ref.

Now, all caps I have replaced seems to be very close to correct value, and ESR is between 40-100 mohm ... apparently the components should work, however the result seems to contradict this, any idea as to why?
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oldandintheway
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PostPosted: Tue Jun 12, 2018 10:59 pm    Post subject: Reply with quote

Are you saying they sound worse since the cap replacement? Maybe they need to bed in?
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sorenb
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PostPosted: Wed Jun 13, 2018 7:38 am    Post subject: Reply with quote

Quite the opposite:
Before replacing the caps the speakers sounded a bit muffled and harsh at times.
After replacing much better.

Since the caps are more than 30 years old, I would expect them to be worn out by now.
However, they all measure very close to specified value, and ESR below 100mohm, and thus seems to be working correct although sounding bad.

I am just wondering how to spot bad sounding caps ithen?


As for the ferro fluid, I haven't seen any recommendation to be very accurate when applying. However, my experience seems to suggest that using a syring for controlling the amount is actually needed.
The two tweeters where clearly different in output (hearing not actual measurement) after applying by eyeballing.
re-applying using a syring and aiming for 0,1mL, they sounded identical.
The postings by Speakerguru suggests (as far as I understand) that the fluid is only there to enhance power dissipation. So, I was just wondering whether the ferrpfluid enhance the sensivity or whether a bibt too much would attenuate the tweeters somehow.
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audiolabtower
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PostPosted: Wed Jun 13, 2018 11:31 am    Post subject: Reply with quote

Perhaps a surplus of viscosity makes the coil more difficult to move and thus reduces sensitivity to produce a less bright sound?
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oldandintheway
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PostPosted: Thu Jun 14, 2018 1:50 am    Post subject: Reply with quote

I don't think the qty of ferrofluid should change the viscosity, but it being ferrofluid may change things! More magnetic material (in the ferrofluid) will change the way the magnetic flux interacts between the permanent magnet and the voice coil. I tried my tweeters with no ferrofluid (low volume only) and they sounded ok (i wanted to check before i continued!).

I did find out that one of my voice coils had come detached from the diaphragm (i had used rubber cement and the excess ferrofluid had softened the cement). So keep an eye out for that too.

I know it sounds basic, but did you check the crossover connections? If you replaced everything and they check out good, i see no reason why they would sound 100% unless they need to get worn in with a sound thrashing!
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sorenb
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PostPosted: Thu Jun 14, 2018 12:47 pm    Post subject: Reply with quote

oldandintheway wrote:
I don't think the qty of ferrofluid should change the viscosity, but it being ferrofluid may change things! More magnetic material (in the ferrofluid) will change the way the magnetic flux interacts between the permanent magnet and the voice coil. I tried my tweeters with no ferrofluid (low volume only) and they sounded ok (i wanted to check before i continued!).

Did the sensivity change due to applying the ferrofluid?

oldandintheway wrote:

I did find out that one of my voice coils had come detached from the diaphragm (i had used rubber cement and the excess ferrofluid had softened the cement). So keep an eye out for that too.

I did inspect the attachment of voicecoil, and didn't find any problems.
oldandintheway wrote:

I know it sounds basic, but did you check the crossover connections? If you replaced everything and they check out good, i see no reason why they would sound 100% unless they need to get worn in with a sound thrashing!

Sorry for being unclear:
Before re-cap it sound bad.
After re-cap is sounds fine.

But all the old caps (the caps which was taken out) measures fine, which is what puzzels me.
All spades/connectors has been cleaned and a bit of deoxit applied.
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speakerguru
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PostPosted: Thu Jun 14, 2018 1:34 pm    Post subject: Reply with quote

sorenb wrote:
But all the old caps (the caps which was taken out) measures fine,


"measures" over the whole audio frequency band or at one spot frequency (1kHz?) with an LCR meter? Maybe the loss factor increases with frequency? Maybe the Capacitance varies with frequency. Many things can happen when the electrolyte dries out.
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speakerguru
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PostPosted: Thu Jun 14, 2018 1:38 pm    Post subject: Re: KEF 104/2 - restoring, surrounds, ferro fluid and caps Reply with quote

sorenb wrote:
After replacing the fluid, applying new fluid by eye balling. Noticed different output from the tweeters. Re-moved the ferro fluid once again, and re-applied using a syring so each got close to 0.1ml.
Hereafter the output sounded very much identical.

Is the amount of ferro fluid very critical to correct function?


Ferrofluid clinging to the voice coil is an additional moving mass. For a given electromagnetic force the s.p.l. produced is inversely proportional to the mass of the moving parts.


Last edited by speakerguru on Thu Jun 14, 2018 8:15 pm; edited 1 time in total
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sorenb
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PostPosted: Thu Jun 14, 2018 1:49 pm    Post subject: Reply with quote

speakerguru wrote:
sorenb wrote:
But all the old caps (the caps which was taken out) measures fine,


"measures" over the whole audio frequency band or at one spot frequency (1kHz?) with an LCR meter? Maybe the loss factor increases with frequency? Maybe the Capacitance varies with frequency. Many things can happen when the electrolyte dries out.

100kHz (PEEK ESR70+)
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sorenb
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PostPosted: Thu Jun 14, 2018 7:39 pm    Post subject: Re: KEF 104/2 - restoring, surrounds, ferro fluid and caps Reply with quote

speakerguru wrote:
sorenb wrote:
After replacing the fluid, applying new fluid by eye balling. Noticed different output from the tweeters. Re-moved the ferro fluid once again, and re-applied using a syring so each got close to 0.1ml.
Hereafter the output sounded very much identical.

Is the amount of ferro fluid very critical to correct function?


Ferrofluid clinging to the voice coil is an additional moving mass. For a given electromagnetic force the spl produced is inversely proportional to the mass of the moving parts.

The T33 spec, moving mass is 0,36g, and the density of ferrofluid cp75 is around 1,14g/cm3, and you have stated 0,1ml to be the correct amount, so the ferrofluid would have about a total mass of 0,11g.
Also, I would assume eyeballing the amount of ferrofluid visual would be within some 0,1ml, thus the total mass by eyeballing would be somewhere between 0,11g and 0,22g.

From hearing a clear difference in loudness from the two tweeters I'd assume the difference to be in order 3dB at least, which doesn't seems to correspond with the added mass alone?
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speakerguru
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PostPosted: Thu Jun 14, 2018 8:18 pm    Post subject: Reply with quote

sorenb wrote:
100kHz (PEEK ESR70+)


why such a high frequency?
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speakerguru
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PostPosted: Thu Jun 14, 2018 8:20 pm    Post subject: Re: KEF 104/2 - restoring, surrounds, ferro fluid and caps Reply with quote

sorenb wrote:
From hearing a clear difference in loudness from the two tweeters I'd assume the difference to be in order 3dB at least, which doesn't seems to correspond with the added mass alone?


Then it's most likely your eyeballing assumption is incorrect.
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sorenb
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PostPosted: Thu Jun 14, 2018 8:23 pm    Post subject: Reply with quote

speakerguru wrote:
sorenb wrote:
100kHz (PEEK ESR70+)


why such a high frequency?


Industry standard according to PEEK: https://www.peakelec.co.uk/acatalog/jz_esr70.html

Not back in the day at KEF. We tested and specified capacitace and loss factor in the audio range 20Hz -20kHz
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sorenb
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PostPosted: Thu Jun 14, 2018 8:25 pm    Post subject: Re: KEF 104/2 - restoring, surrounds, ferro fluid and caps Reply with quote

speakerguru wrote:
sorenb wrote:
From hearing a clear difference in loudness from the two tweeters I'd assume the difference to be in order 3dB at least, which doesn't seems to correspond with the added mass alone?


Then it's most likely your eyeballing assumption is incorrect.

Might be so, but why isn't your sticky more explicit about the right amount then?
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speakerguru
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PostPosted: Thu Jun 14, 2018 9:21 pm    Post subject: Re: KEF 104/2 - restoring, surrounds, ferro fluid and caps Reply with quote

sorenb wrote:
speakerguru wrote:
sorenb wrote:
From hearing a clear difference in loudness from the two tweeters I'd assume the difference to be in order 3dB at least, which doesn't seems to correspond with the added mass alone?


Then it's most likely your eyeballing assumption is incorrect.

Might be so, but why isn't your sticky more explicit about the right amount then?

I left KEF in 1999. The ferrofluid KEF used in the 80s is no longer available. I do my best to provide as much information as I can recall, to help people out.
If that's not enough and you want more up to date, precise and specific information I'm afraid you'll have to do the experiments and measurements for yourself.
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