Best method for damping stamped steel frames?

BHTX

Member
2006-02-16 10:49 am
Apologies if this topic has been covered multiple times, but I couldn't find a whole lot in regards of what to use. Was thinking along the lines of the tar based damping sheets primarily used in automotive applications, but I thought I'd post a question for any specific suggestions. Unfortunately, I can tap the woofer's cone and hear the frame ringing like crazy, especially when it's not mounted on anything. What's the best thing to use?
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
damping sheets work.
I have also heard that oil based modeling clay works well. - you know, the kind you made dinosaurs out of as a kid? ;)

Basket reflections may be something to worry about if the basket dimensions are on the order of a wavelength to be reproduced, but I doubt they are any more significant than reflections off the back wall....
 

peter_m

Member
2007-05-14 7:33 am
I've recently started to build a B3S design from Zaph and since it was just a budget system, I tried to minimize my expenses by using anything I could find in my garage. To fasten the foam to the back of the speaker enclosure, I used a floor adhesive I had just sitting in the garage. I looks like tar and it smells like tar but when it dries, it keeps a ruberry texture... I bet it would be the best thing to dampen that steel frame. You might not need to cover the whole surface either... You could use rubber cement if you have it as well.

Just a word of caution... the tar or any glue you might use can release solvants as it dries... I would let it dry completely before putting the speaker back in the enclosure to avoid any damage to the speaker from the fumes.

Merry Christmas to all!

PS: If you have contact cement, it does harden very much when completely dry. But you could use the contact cement to fasten any kind of rubber strip to the metal frame and that should help as well while still being inexpensive.
 
The technique that I used to good effect was to use a product called "no more nails" to stiffen the basket.

No more nails is a product designed to attach dado rails, coving etc to walls. it is a very strong adhesive also designed to fill gaps between the objects it is fixxing.


speakerframe.jpg


In the diagram (not the best I know) you can see the basket of a typical steel basket. The areas in red indicate the space that has been filled with the material.

Using a spatula I apply it to the baskets in the gap between the magnet and the pressed steel frame. Others have used duct seal in the same places.

The no more nails when dry goes hard, so is effectively stiffening the frame. As I see it this is different to the duct seel which is acting as a dampener. No more nails on the other hand is not a reversible modification. Not that I expect that would be a problem.

I intend to go back to the speakers to apply dampening later. I had planned to use dynamat to damp the legs, however its costly stuff. Another thought was to glue bitumen backed carpet tile material instead of dynamat.

With just the no more nails, I got a worthwhile improvement in the sound of the speakers. Clarity in the lower and mid ranges was definately better. The sound of the speakers as a whole was more transparent after the mod.

I had the speakers apart several weeks later, what I had found was that the no more nails had contracted. I had filled out the gap to be flush to the magnet, but now it no longer fills the whole gap. I will apply another application of NMN or alternatively pad it out if I can find duct seal.

Well worth doing for any pressed metal speaker. If anyone reading has not tried this cheap and easy mod yet you are probably not getting as much out your speakers as you could.

materials that people have used....

Childrens Modelling clay (plasticine)
Ducseal
No more nails
other filling adhesives
 

zBuff

Member
2004-11-24 8:45 am
NZ
justblair said:
I had the speakers apart several weeks later, what I had found was that the no more nails had contracted. I had filled out the gap to be flush to the magnet, but now it no longer fills the whole gap. I will apply another application of NMN or alternatively pad it out if I can find duct seal.

I used automotive body filler instead of no more nails, it hasn't contracted on me as of yet(been a few years now)

I have had much the same impressions as you from the sound improvements of filling in the junction between the basket and the magnet.
 
Just a note of caution with some of these products. Many moons ago I read of a guy who used a bitumous based damping product inside a l/s/box. If it contains solvents he suggested around two weeks exposure to the atmosphere prior to sealing the box as they (the fumes) can dissolve/weaken some of the adhesives used in the construction of the drivers apparently. Wisdom probably gained through bitter experience.........
 
I had a friend in Japan who used some floor tile cement. The stuff he had dried but stayed rubbery. He added sand to the mixture to add density and break up the composition and he coated the inside walls of his enclosures. It worked VERY well in that application and I have long since wondered what would happen if I did the same on the driver frames (both steel and alum).


Edit: Like wise we left the enclosures open and let them dry for a week before installing drivers.
 
Magnet/Basket Junction

For filling or stabilizing the junction between the magnet and frame of the driver, I've found that a paste made up of epoxy and pulverized limestone works well.
I use System Three epoxy and the pulverized limestone is purchased in a 30 lb bag for about 3 or 4 dollars and is the stuff that is used for making the lines on ballfields. Don't get the stuff with chunks in it, the pulverized limestone is like a fine flour. It can be sanded if need be, although it's not easy. If the appearance of the driver is important, then leave it a little "shy" and finish with a skim coat of MicroLite Bondo, which is easier to sand.

BTW, I'd make up the epoxy/limestone mix into a thick dough and before applying give the surface of the area to be filled a primercoat of epoxy, to be followed by the dough.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Stamped Basket "Legs"

Someone earlier mentioned modelling clay, but don't confuse it with plasticene, which hardens. What you want is "Oil Based Modelling Clay" which never hardens and can be removed, reused or reworked at any time and because it doesn't set up, it retains it's damping properties forever. Dick Blick is a good source for the Clay.

Dave's use of DuctSeal also works very well, is easy to use, but is often confused with other sorts of products, like caulk, which don't attain the same level of damping and are often a waste of time.

Best Regards,
TerryO
 
EmergencyDpt said:
I made the mistake of using the oil based clay in an application that applied heat to it (vacuum forming) and it melted. I'm not sure at what temperature it started liquafying but if a speaker were exposed to sunlight during the day, it might get hot enough to start to melt the clay.


It's never happened to me, but I live near Seattle, so we never see the Sun. Actually, in the Pacific Northwest we fear the sun, with it's death-dealing ultraviolet rays, etc.

In a recent poll, 94.3 % of the people interviewed in the Greater Seattle Area, indicated that dark gray was their favorite color.
;)

Best Regards,
TerryO;)
 
Hi,

to insert a damping sealant between basket and magnet
seems a good idea.

If the bonding between basket and magnet is more tight
then, it may be advantageous to fix the magnet somewhere
to keep it from vibrating.

The force generated by the current through the voice coil acts
in equal manner on the magnet and will excite vibrations
of Magnet > Basket > Mounting Baffle > Whole Cabinet.

Thinking of fixing the magnet on a either a very stiff structure
or adding Mass to it may be reasonable.

If you manage to find such an inert structure, magnet mounting
is IMO preferable to basket mounting of the driver.

Kind regards
 

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