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In Reply to: RE: Mass load the frame posted by Dave_K on May 18, 2022 at 14:08:55
and, surprisingly ... it produced worse buzzing of the spkr frame. :-((
Sure - it's against theory ... but that's how it turned out.
The U-frame each side which the drivers are bolted to was initally just made of 13x5mm steel flat - and I found it resonated when I fed a 130Hz signal into the mid/bass drivers. (Pretty peaky - the resonance was induced only between 125 and 135Hz.)
So I had a number of 13x5mm steel flat pieces cut ... and glued them to the U-frames using thin, double-sided foam tape. So this should've been damping the structure - as well as adding mass.
But the result was ... the spkr frame now buzzed from 100 to 140Hz. :-((
So I decided to get some U-frames made from 12x6 aluminium flat. The result is (despite the reduction in mass, using aluminium) ... there is no longer any vibration!
So I'm happy ... but surprised that theory didn't seem to work. :-((
Andy
Follow Ups:
You also changed the compliance of the structure. two objects that are the same dimensions and weight may have completely different resonant frequencies depending on their relative stiffness.
Yes, understood. :-)
Andy
Mass per se is not dampening.
Edits: 07/16/22 07/16/22
Just to point out that's not mass loading, what you tried. Mass loading requires mass to be located above the object that's vibrating. Increasing the total load (weight). F=ma, the load is in the direction of the force of gravity, vertical. An example of mass loading is placing a heavy slab of granite on top of a speaker cabinet. Or placing a heavy glass weight on top of a preamp. What you did wasn't really damping either, for effective damping you need viscoelastic material or some constrained layer type dampener.
Edits: 06/08/22 06/08/22 06/08/22
Whilst I can understand that " placing a heavy slab of granite on top of a speaker cabinet " certainly is a form of 'mass-loading' ... I can't see why increasing the mass of the U-frames (from 1.7kg to 2.5kg) isn't also 'mass-loading'.
And a 'CLD' structure is "heavy-light-heavy" etc - so my use of thin foam tape with glue on each side meets this criterion. But, sure ... maybe I could've used a better (viscoelastic) material for the 'light' layer.
Andy
Mass
Mass is a measure of the amount of material in an object, directly related to the number and type of atoms present in the object. Mass does not change with a body's position, movement or alteration of its shape unless material is added or removed. The unit of mass in the SI system is the kilogram (kg).
Weight
In the trading of goods, weight is taken to mean the same as mass and is measured in kilograms. Scientifically, however, it is normal to state that the weight of a body is the gravitational force acting on it and hence it should be measured in newtons (N), and that this force depends on the local force due to gravity. To add to the confusion, a weight is an artefact of calibrated mass normally made from a dense metal. So, unfortunately, weight has three meanings and care should always be taken to appreciate which one is meant in a particular context.
Force
Force is a measure of the interaction between bodies. It takes a number of forms including short-range atomic forces, electromagnetic and gravitational forces. Force is known as a vector quantity, as it has both direction and magnitude.
Load
Load is a term frequently used in engineering to mean the force exerted on a surface or body.
I would say what you did was close to constrained layer damping, but not mass loading. In the case of constrained layer damping one would use a stiff layer like metal with a viscoelastic layer. Vibration is reduced by absorbing it as shear forces in the video layer.
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