Using lead sheet for damping material

[Cal Weldon]

Has anyone done this? Is it better than batt? I was thinking of hanging it in the box, a little off the backwall and poke some holes in it to allow some of the air to pass through.

Any others tried this?

Any recommendations?

Thanks
Cal

[sreten]

Batt ?

Lead should be attached to the walls with a solvent based
contact adhesive, as with most damping thin layers seperated
by an adhesive with give works best.

Lead works well for cabinet damping, though it is expensive.
Secret here is for the walls not to be too thick, 12mm I'd regard
as a maximum, if you want a stiifer cabinet add bracing.

The amount is basically around the same mass or more as the
cabinet walls. Large cabinets get very expensive but lead is a
good choice for high quality miniatures / small sealed boxes
designed to be used with subwoofers.

sreten.

(P.S. your suggested usage won't work well at all IMO)

[Cal Weldon]

Thanks sreten,

By batt, I mean fiberglass, rock wool or poly batting.

You don't think that moving it away from the back of the cabinet is a good idea. Do you feel I should cover all sides of the cabinet then? I was hoping to suspend just one sheet [for weight reasons] with a slight gap around the sheet and spaced maybe an inch or two away from the back wall. Maybe 1" holes to allow some of the air through. No Good? Please help explain.

I can get a few 30" X 30" lead sheets for free, left over from a job. Hence the desire to use it.

Thank you
Cal

[sreten]

OK :

Lead sheet is useless for acoustic damping, you'll still need foam,
rockwool, fibreglass, BAF, Dacron, Polyfill or whatever is called for
acoustic damping.

Lead sheet is good for damping cabinet resonances in the walls.
Cabinet damping is out of favour as an approach except with
British firms like Spendor, Pro-Ac, ATC, Jordan and a few others.

Its the old BBC tradition still going in Blighty.

Jordan used to use Lead damping in all its speakers.

sreten.

PS how many 30" x 30" sheets exactly ? what thickness ?
And what speakers are you consider it for, could be wasted ?

Its ideal as the wall damping for this :

http://www.geocities.com/diyproac25/index.htm

[Timn8ter]

Cabinet damping is out of favour as an approach except with....

And has been replaced by what? Bracing or... ?

[sreten]

Originally posted by Timn8ter


And has been replaced by what? Bracing or... ?

Cabinet damping traditionally uses thin walls, the current trend
for thick walls makes effective damping prohibitively expensive.

So it has been replaced with much thicker walls with bracing
(or routing channels) to spread resonances. Personally think
thin walls with damping and offset bracing is still a valid
approach for a full range or two way speaker.

sreten.

[AldebaranTech]

Damping material has to do one thing, convert one form of energy into another. In the case of speakers, and most other devices, damping material changes unwanted sound energy into heat.

Two surfaces sliding past each other makes an effective damper. Fluid being forced through a small hole makes an effective damper. Bending a material past its elastic limit is also a good way to damp movement.

Adding a layer of lead to the surface of a speaker wall is going to do two things. First it is going to change the total mass of the panel, thus lowering the frequency at which the panel will resonate. Secondly it MIGHT add a damping effect if the adhesive used as a fluid between two surfaces that gets mushed around by the panel movement. The movement of the lead is probably not large enough to exceed the elastic bending limits of the lead IMHO. I have not calculated this so I cannot state it as a fact. If this is so, then the lead itself will not be acting as a damper.

By changing the mass of the speaker wall panel one can move the resonant frequency so that it does not coincide with some other resonance and help this way. Adding mass to a moving system has a good side and a bad side at the same time from another aspect. A larger mass takes more energy to get moving, but once moving takes longer to stop.

As far as hanging a lead sheet behind a driver.... It will act as a reflector of sound and have no beneficial effect unless the pacement of the sheet is such that it breaks up a specific problem standing wave or some similar consideration.

[critofur]

Originally posted by AldebaranTech

Adding a layer of lead to the surface of a speaker wall is going to do two things. First it is going to change the total mass of the panel, thus lowering the frequency at which the panel will resonate. Secondly it MIGHT add a damping effect if the adhesive used as a fluid between two surfaces that gets mushed around by the panel movement. The movement of the lead is probably not large enough to exceed the elastic bending limits of the lead IMHO. I have not calculated this so I cannot state it as a fact. If this is so, then the lead itself will not be acting as a damper.

By changing the mass of the speaker wall panel one can move the resonant frequency so that it does not coincide with some other resonance and help this way. Adding mass to a moving system has a good side and a bad side at the same time from another aspect. A larger mass takes more energy to get moving, but once moving takes longer to stop.

Lead has a very low Q ~ it is very much not "springy". I think your "adding mass to a moving system" point + assuming that the lead will not provide much damping would be valid IF you simply put a lead weight in the center of the panel.

However, if you glue a sheet of lead to say, a sheet of plywood it damps vibrations in the plywood dramatically, not simply moving them to a lower frequency.

(some) Sound can still pass THROUGH lead, but the lead does not continue to resonate to any significant degree, unlike hardwoods which are typically excellent resonators.

Most of the research I did while designing the Microwalsh speakers was designing the damping systems. Lead sheet, along with various other damping materials, is used in the Microwalsh cabinets where thick cabinets were not an option, or else they would not be "Micro" anymore.

[sreten]

Originally posted by AldebaranTech
Adding a layer of lead to the surface of a speaker wall is going to do two things. First it is going to change the total mass of the panel, thus lowering the frequency at which the panel will resonate. Secondly it MIGHT add a damping effect if the adhesive used as a fluid between two surfaces that gets mushed around by the panel movement. The movement of the lead is probably not large enough to exceed the elastic bending limits of the lead IMHO. I have not calculated this so I cannot state it as a fact. If this is so, then the lead itself will not be acting as a damper.

Does Lead have an elastic bending limit ? Common experience
of the stuff suggests it has no elasticity at all. Your surmisations
suggest Lead will support soundwaves, I'd suggest tapping a
piece of Lead sheet or pipe will conclusively prove it doesn't at all.

I quite agree if the elastic limit is not reached damping will not
occur, but IMHO it must be reached very easily, or Lead would
not have its all too obvious acoustic properties.

In speakers the adhesive layer for lead sheet has minimimal
effect, arguably multilayering has minimal effect too, but it
can't hurt. Mass will lower resonant frequency, with equal mass
by root2, (bracing can always restore this), but more importantly
equalk mass guarantees effective energy transfer from the panel
to the damping medium, for Lead this is achieved with minimal
impact on the cabinet volume, due to its high density.

Per unit mass, there are better damping materials, but they are
much less dense than Lead, and effect the cabinet volume more.

sreten.

[markp]

Originally posted by Cal Weldon
Has anyone done this? Is it better than batt? I was thinking of hanging it in the box, a little off the backwall and poke some holes in it to allow some of the air to pass through.

Any others tried this?

Any recommendations?

Thanks
Cal

Batting is used a sound absorber to control reflected sound in a cabinet. Lead is used as a cabinet damper to control the cabinet itself from vibrating, not the air inside the cabinet. Both work on different problems but can be used well together.