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Old 19th April 2007, 01:02 PM   #1
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Default Help me kill a fostex artifact.

Hi,

Does anyone know the driver characteristic responsible for the annoying 5kHz peak in the response of the Fostex 206E.
There are other peaks at 2.5kHz and 10kHz acording to the fostex plot, but they are not annoying me at all, maybe because all I can hear is this emphasised SSSSS!
It was evident before I cut the dustcaps out, it was equally evident with no dustcaps. I can't kill it with a cylindrical phase plug, and now my mind is dissolving into madness, and I can no longer see the light
!
Is damping the whizzer the solution, of does the nasty artifact originate elsewhere, perhaps a main cone break up mode?

I would also be curious to know which bump in the 206 impedance curve is the whizzer resonance, and the origin of the other (1kHz and 2.5kHz)

Apart from the 1kHz bump, it all looks a bit harmonic to me.. 2.5k, 5k, 10k.
Anyone shed any light on this for me?
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Old 19th April 2007, 02:16 PM   #2
MarkMcK is offline MarkMcK  United States
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Could you supply an image of the frequency response chart showing the resonance modes?

This would be useful in trying to answer some of your questions. Keep in mind that Fostex has a habit of overlapping cone and dustcap/whizzer resonance modes. Instead of one resonance, there may well be a cone problem and a whizzer problem at the same frequency.

Mark
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Old 19th April 2007, 04:03 PM   #3
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Old 19th April 2007, 04:23 PM   #4
BudP is offline BudP  United States
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Bob,

How brave are you?

One of the guys following the Walsh thread got brave and did what you see in the attached pic. Here are his words.

"I re-enabled my Fostex drivers per your template posted at the diy forum. Easy to do since the blocks are acrylic and wipe off with alcohol. Apparently, I was off by about 18 sets of blocks! This time I enabled the inside of the cone and whizzer as well as the outside, except that on the inside of the whizzer I "Mambonied" felt triangles. I also, Mambonied the back of the cone.

Right now I'm experiencing sound as if it were not coming from the speakers. Sounds now appear to come out of solid objects. The sounds in the background are now clear. And the sibilance is now gone; violins and close miked female vocal recordings don't cut my ears off anymore. The musical picture is/sounds more complete. I think this is quite remarkable coming from a near full range driver"

[*LINK REMOVED*]

Be glad to help you scare yourself, just to preserve your sanity. I will be treating a Lowther shortly .

Bud
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Old 19th April 2007, 05:45 PM   #5
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Thanx Bud, that is a VERY illustrative. Thanx.

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Old 19th April 2007, 06:21 PM   #6
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You guys are brave men. Might have to give this a shot on my next pair of drivers.
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Old 19th April 2007, 07:07 PM   #7
chrisb is offline chrisb  Canada
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Bud - this and the several other threads on which your EnAbl and the Mamboni process are discussed are dizzying to try to follow.

In regards to the photo of the EnAbled FE206, the colour of the cone is certainly not stock Fostex paper. Can you shed any light on the material used?
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Old 19th April 2007, 07:14 PM   #8
MJK is offline MJK  United States
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Do you have any measurements of SPL response or electrical impedance before and after treating the driver?

It would be interesting to see what changes in driver performance occured. Intermediate measurements would also be interesting to be able to assess which modification produced which change in response.
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Old 19th April 2007, 07:32 PM   #9
BudP is offline BudP  United States
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Hi Chris,

You guys know lot's more about what Fostex has used than I.

I will say that the semi translucent nature of the paper, as we see it, would be typical of a thin, calendered, low rag content, high wood pulp content paper, when the conformal coating, I, and the brave soul who did this work, use.

I am trying to entice him to join in so you can all grill him in detail but that will be up to him.

Here is the other pic he sent to me and it shows the thickness of the felt he used and also the inner cone pattern. Scary thick felt pieces from my perspective, but I really have no idea how bad the problems he had were and this might be just the ticket for whizzer cones.

Dave, is it time to start an EnABL thread, that begins to collect all of the different posts in one spot? Is that even possible? Hate to have Chris fall out of his chair just trying to keep track of me jumping about.

Bud
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Old 19th April 2007, 07:44 PM   #10
BudP is offline BudP  United States
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Martin,

I do not have any quantitative data from this treatment. I have some data from other speakers and it is fairly generic, seems to have happened to all of the 2 or 3 hundred drivers I have gone through in 40 years of fooling around. Go here and look at the dissected CSD plots, at the end of the paper, from a "phenolic ring" cone tweeter as was popular in inexpensive speakers in the 80's.

http://www.positive-feedback.com/Iss...ndingwaves.htm

I will say that high frequency drivers will gain guite a bit more efficiency if you apply more than one coating of conformal /speed control material.

Other tests I have run, with an early generation Lincoln Audio test set up, show no observable alteration in the amount or distribution of harmonic distortion, throughout the first nine categories.

Bud
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