8 inches paper cone treatments

[graaf]

Hi to all!

Has anyone tried "Rehdeko cone treatment" or other similar (NOT "EnABL") cone treatments with 8 inches fullrangers?

here is Weber Rehde's patent description:

http://www.freepatentsonline.com/4100992.html

I have Fostex FE206E. This particular driver suits my needs very well, almost perfectly BUT it has a big problem
it is sharp nasty ringing (=howling) resonance at around 2.8 kHz. I know that it is a break-up resonance of the main cone - not of the whizzer
I wonder how it could be effectively treated.

best regards,
graaf

[GM]

Originally posted by graaf

here is Weber Rehde's patent description: http://www.freepatentsonline.com/4100992.html

I recommend using a mechanic's stethoscope to isolate it, then decide on a course of action rather than using the 'sawed off shotgun' approach, though I've found variations of Fig. 7 to work well if it's a broadband problem.

GM

[LineArray]

Hi,

i used "Ponal" as coating for paper cones with good results.

Another possibility is to use a small aluminium pipe, bend it
as a ring to stabilize the cone along a certain radius.
Use an appropriate glue, not too hard and only very little
amount . You can use a piece of a toothpick e.g. to close the
ring tightly.

In both cases it is useful to know, how the breakup mode
looks like. I have used cork powder to visualise it with some
success so far ...

The "Ponal" wood glue applied to the whole cone ia a good
broadband "quietener" but to do selective damping or bracing
to save moved mass is preferable.

If the picture you have posted shows the breakup mode
correctly, maybe an alu ring stabilizer placed slightly outside the
phase coherent center of the cone would work -
just a gut feeling ...

Cheers

[graaf]

thanks You GM and LineArray for Your interest and suggestions

Originally posted by LineArray

If the picture you have posted shows the breakup mode
correctly,

a qui pro quo - the picture shows one of the cone coating patterns that can be found in Rehde's patent

what I found most interesting is that He recommended coating of only part of cone area, sometime only a small part

I have made some tries with Fostexes and the posted pattern is mostly similar to the one I used
mine looks more like the "radioactivity symbol" and coated cone surface area more or less equals the uncoated

I chosed it because I wanted an asymmetric pattern - I read somewhere that it is good to break the symmetry of the cone because most harmful are axis-symmetric modes

Originally posted by LineArray

i used "Ponal" as coating for paper cones with good results.

I have also used a kind of glue but cyanoacrylic
I chose it after some tries on sheets of paper. The cyanoacrylic glue seemed to penetrate the paper best and to stiffened it most
Weber Rehde recommended "varnish of cellulose type" (nitrocellulose)
I have tried nitrocellulose based nail varnish on sheet of paper and it seemed to work less effective than cyanoacrylic glue

Unfortunately I cannot do any genuine measurements but a "measurement" I did using DEQ2496 RTA function and ECM8000 showed that after the treatment of the FE206E resonant frequency response peak got a bit smaller and shifted from around 2.8 to around 4 kHz
audibly it certainly became less offensive but not enough, therefore I think what can be done next/better

Originally posted by LineArray

The "Ponal" wood glue applied to the whole cone ia a good
broadband "quietener" but to do selective damping or bracing
to save moved mass is preferable.

what do You think of applying the treatment only to a part of the cone - like in Rehde patent?

Have You tried Stabilon and Vinylflex paper cone treatments offered by Intertechnik Deutschland?
they are both polyvinylacetate based but the first is said to be a stiffener and the second to be a dampener

what about treating of half of the cone surface with stiffener and the rest with dampener? what do You think?

best,
graaf

[LineArray]

Originally posted by graaf

what about treating of half of the cone surface with stiffener and the rest with dampener? what do You think?

best,
graaf

Hi,

i found that thinking too much about cone treatment,
breakup modes and coating drives me mad.

I modified lots of drivers and basically i think that someday
you will end up with building drivers by yourself.

An 8 inch fullrange will inevitably suffer from breakup to
a certain extent. I basically think you cannot win using
a stiffener. With a paper cone, a dampener is the way to go.
Most paper is stiff and has little damping, you have to add
what is missing to get a composite material with better
habits.

"Ponal" introduces some stiffness but is mainly a dampener.
If you bend a sheet of coated paper and watch how it
goes back into its shape, you get a feeling how much damping
is introduced by the coating.
One way might be to make a foam of the coating material
to increase the thickness of the coat and keeping mass low ...

When moved mass is an issue, i think it is preferable to
coat only near the surround, but i have litte experience with
fullrangers. For most bass and midrangers a total area coating
will give best results IMO.

With some drivers i had good results introducing slots into
the cone and then closing them with a dampener ...

Very expensive experiments, maybe get some cheap and
evil sounding drivers to practice ...

At present i do not want to spend much time in modifying
drivers anymore, i think it is better to use drivers of smaller
size. Unsufficiently damped breakup modes are worst in the
nasal to precence region from 1-6 Khz, if you find a driver
which behaves well in that range one can tolerate some
uncontrolled breakup at higher frequenies.

Since you cannot supress breakup totally in my present
fullrange design i use multple drivers and balance them
taking advantage of the tolerances of individual drivers.

Using that method i obtained the best results ever, thereby
keeping the need for compensation in the XO at minimum.

Cheers

[graaf]

Originally posted by LineArray

An 8 inch fullrange will inevitably suffer from breakup to
a certain extent. I basically think you cannot win using
a stiffener. With a paper cone, a dampener is the way to go.
Most paper is stiff and has little damping, you have to add
what is missing to get a composite material with better
habits.

stiffener moves break-up resonance higher in frequency
isn't it reasonable to move it higher? in case of my FE206E moving it from around 2.8 kHz to around 4 kHz was certainly beneficial to the sound quality

Originally posted by LineArray

Since you cannot supress breakup totally in my present
fullrange design i use multple drivers and balance them
taking advantage of the tolerances of individual drivers.

for conventional front firing speakers it would be also my choice
but I need one fullrange driver to fulfill my "room/loudspeaker interface" design priorities

best regards,
graaf

ps.
any more experience with coating of fullrangers anyone?

help please!

[tinitus]

I use liquid bitumen
With a very thin cone you may have to stiffen it first with something hard first
But be aware of likely loss of sensitivity
Also such FR drivers usually have very small voicecoil with short Xmax which may not be able to deal with the exstra weight and new lower Fs

[LineArray]

Originally posted by graaf


stiffener moves break-up resonance higher in frequency
isn't it reasonable to move it higher? in case of my FE206E moving it from around 2.8 kHz to around 4 kHz was certainly beneficial to the sound quality

Hi graaf,

i think it is a success to move the breakup from 2.8 to 4 Khz,
if it was a midranger then the difference would be between
nasty and perfect.

But i think in your case the resonance must have become less
prominent too, otherwise you would not feel it sounds better
now.

Moving resonance up in frequency is a way to go for midrangers
but what to do with a fullranger ? If it is a whizzer cone design,
maybe moving a resonance above the mechanical XO of the
whizzer works well ... so in some cases stiffener would be
in the race again, don't know.

[graaf]

Originally posted by LineArray

I basically think you cannot win using
a stiffener. With a paper cone, a dampener is the way to go.
Most paper is stiff and has little damping, you have to add
what is missing to get a composite material with better
habits.

paper is not that stiff
fortunately it has "some" damping

interesting papers on physical properties of diaphragms:
http://www.fostexusa.com/support/pdf...hite_paper.pdf
http://www.infinitysystems.com/home/...apers/cmmd.pdf
these are manufacturer information brochures of course, nevetheless presented facts and measurements are interesting (especially in the Fostex brochure))

Originally posted by LineArray

i think it is a success to move the breakup from 2.8 to 4 Khz,
if it was a midranger then the difference would be between
nasty and perfect.

yes indeed, therefore I think that this modification is worth to be further researched and perfected
this seems to be "the way to go" with a fullranger

Originally posted by LineArray

But i think in your case the resonance must have become less
prominent too, otherwise you would not feel it sounds better
now.

I agree
on the other hand I wonder why it has become less prominent. Is it a matter of added damping? or perhaps the diaphragm itself has more damping at this higher frequency? or perhaps this is a benefit of introducing of an assymetrical pattern in the diaphragm?

best,
graaf

[graaf]

Originally posted by tinitus
I use liquid bitumen
With a very thin cone you may have to stiffen it first with something hard first

what do You think of treating some parts of the cone with stiffener and some with dampener?

taking the image attached to the first post as an example - treating the grey coloured parts with stiffener and the rest with dampener? or the other way round?
or yet different - treating the grey coloured part in the center with stiffener and the radial coloured parts with dampener leaving the rest untreated? or the other way round?

so many options

does the theory of cone diaphragm suggest best/optimal one?
has anybody tried such an approach?

best,
graaf