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Old 21st May 2008, 11:15 AM   #1
rinx is offline rinx  Estonia
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Default Pickle or pitch layer

Hei all!
I just was talking with one audiofan and hea was suggesting me to cover inside of the enclosure with pitch layer (using in carsound field). Does anybody see there benefit?!
The point should be that you can do enclosure stiff as poseble but it still is rings, but after covering this with pitch it makes big difference...

Any ideas?!
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Old 21st May 2008, 11:35 AM   #2
sreten is offline sreten  United Kingdom
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Hi,

Mechanically damping cabinets walls basically needs a decent damping
layer compared to cabinet wall thickness, i.e. a particular thickness
layer works best with thinner cabinet walls. So how worthwhile it
is depends on the type / massiveness of cabinet construction.

/sreten.
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Old 21st May 2008, 02:06 PM   #3
rinx is offline rinx  Estonia
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Sreten.
Have you tryed this pickle?! If you knock on the cabinet without pickle-its sounds (lets say 22mm MDF), but after adding layer of pickle its makes totally different sound. It goes alot more low and doesnt ring aymore.
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Old 21st May 2008, 02:16 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

Pickle ? 22mm MDF would need a substantial damping layer to be a "lot" lower.

/sreten.

Click the image to open in full size.
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Old 21st May 2008, 02:47 PM   #5
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Pickle is a great damping material it just has a nasty habit of rotting.

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Old 21st May 2008, 03:53 PM   #6
rinx is offline rinx  Estonia
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..very funny..very funny!!
I just checked from dictionary and it gives me "pickle" and also "pitch". So i believe last one is correct...

But still, is there any point or not?! I can use just regular damping material also instead pitch (not pickle!)...
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Old 21st May 2008, 06:56 PM   #7
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If the cabinets are sufficiently thick and well braced damping layers are generally not necessary, but on the other hand they will do no harm either. I tend to err on the side of caution and always use damping layers - then foam, then polyfill.
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Old 22nd May 2008, 03:40 AM   #8
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One method I have found that seems to work well is to combine a thick, stiff, well braced cabinet wall with convoluted acoustic foam and polyester stuffing.

The idea for the convoluted open cell foam is to glue it to the wall in only a few spots. Just enough to keep it in place. The foam is not for the purpose of damping the wall vibrations but to absorb some of the internal acoustic energy and turn it into heat. So there is less energy to excite the wall. So it is best if the foam is decoupled from the wall as much as possible and only attached in a few random spots. The foam helps to reduce standing waves and higher frequency waves from bouncing back into the cone of the mid/bass driver.

The polyester fill of most of the internal volume of the cabinet further reduces the rest of the standing waves and internal pressure modes.

The stuff used for car audio is in my opinion insufficient for dampening of wood enclosures unless they are very thin walled. The stuff works good for thin sheet metal in cars.

I think a better use for that stuff in home audio is to cover part of the front baffle to create a mounting surface for the driver which helps to create a good seal and damp the driver frame.

On the other hand, some of the more expensive damping material for inside of cabinets combines several different materials that have a different acoustic impeadance. The acoustic open cell foam is bonded to a thin vinyl layer and then a 4-5mm layer of soft foam is used and then a thin layer of heavier Dynamat type material. So you have four layers that are then bonded to the wall.
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