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Old 3rd April 2013, 12:47 AM   #1
kinku is offline kinku  United States
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Default Damping

I am wondering if there is any guidlines on how to to fill damping materials inside a bass reflex design.
1. Do you have to pad all 5 walls of the box? or just 3?
2. What is the density of material to use for damping?High vs Low
3. Is there any volume adjustments that need to be done for a damping pad of 2 inch thick?
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Old 4th April 2013, 07:59 PM   #2
DrBoar is offline DrBoar  Sweden
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1. 5 is the common method but in theory 3 would do.

2. That depend of what you mean by dense and light.

3. That depend on how much of the total volume that 2" layer makes .
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Old 4th April 2013, 08:47 PM   #3
ra7 is offline ra7  United States
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First, use fiberglass. Other materials are not as good. Fiberglass is the pink stuff that is sold as insulation. It's itchy, so wear gloves. It's fibers are not good for your lungs, so wear a mask if you are going to play with it for long.

Yes, cover all sides with a couple of inches. It shouldn't cause a drastic change in box alignment. Depending on the box dimension, you may want to put a layer in the middle to absorb the longest standing wave. Read here for more:
Box colourations - really ?
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Old 4th April 2013, 09:15 PM   #4
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Rockwool is a good alternative to fiberglass. The newer products are easier on your lungs.
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Old 5th April 2013, 12:15 AM   #5
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The fear of whatever is going to be caused by fiberglass is irrational. Yes, it is bad for the lungs. If you breath in a lot, you might get silicosis. That what the pharaohs died of. It is not a carcinogen, but use realistic protection while installing it.

No one has ever reported a yellow spot of the floor in front of their speakers. given a 2-3" or longer port there is no net are transport out of a port. Anything that dislodges from the stuffing/lining will be deposited in the bottom of that speaker. Yes, I have opened up an old MLTL and found a layer of yellow on the plinth. But noting ever actually exited the speaker.

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Old 5th April 2013, 09:30 AM   #6
kinku is offline kinku  United States
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Drboar total volume is going to be 0.25 or 0.35 cubic feet. So if there is 2 inch panells on 5 sides it may take up some volume?
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Old 5th April 2013, 10:24 AM   #7
AndrewT is offline AndrewT  Scotland
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Don't use lung damaging fibres in a vented box.

The air flow from the port will contaminate the air in the listening room.

I would not recommend lung damaging fibres in a sealed box either.
There are many other damping fibres available that are safe.
eg, long hair wool, BAF wadding, some types of open cell foam.
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Old 5th April 2013, 11:20 AM   #8
oshifis is offline oshifis  Hungary
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This type of damping is useless in a bass reflex box, because the velocity is zero at the walls. The vibration of the walls can be damped by bitumen pads, sorbothane etc.
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Old 5th April 2013, 11:28 AM   #9
kinku is offline kinku  United States
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I think we are getting deviated from topic.My concerns are more about the volume ,density and type of filling (resistive vs wall) than actual material.s you can see my box volume is small so wants to know how the wall damping is going to affect the volume.
The Loudspeaker designcook book 7th ed pages 80-83 for vented boxes says the lining the wall with even 50% thickness(3inch regular fiberglass) showed minimal changes in computer generated SPL and Impedence plots.But it will reduce standing waves.

Series Resistive vent model by filling(not lining) the box with fiberglass or Dacron can
Increase F3 from system
Reduce efficiency(output) of the system
Lower Qts
Increased cone excursion near cutoff.
At the end author recommends using straw filled vent ,which he explains as filling vent with rolled decorative corugated cardboard or bundle of plastic straw, which offers rather easly controllable way for trial and error.
Any one know how that can be done and what exactly it lookes like ?
I guess incresed F3 means higher roll off for bass frequencies(low bass)?
What is the effect of low Qts?
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Old 9th April 2013, 11:13 AM   #10
oshifis is offline oshifis  Hungary
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Quote:
Originally Posted by kinku View Post
...lining the wall with even 50% thickness(3inch regular fiberglass)...
The wall thickness is usually 1/2" to 1", take the half of it...
Quote:
Originally Posted by kinku View Post
...by filling(not lining) the box with fiberglass or Dacron can
Increase F3 from system
Reduce efficiency(output) of the system
Lower Qts
Increased cone excursion near cutoff
Neither of these is desirable.
Quote:
Originally Posted by kinku View Post
At the end author recommends using straw filled vent ,which he explains as filling vent with rolled decorative corugated cardboard or bundle of plastic straw, which offers rather easly controllable way for trial and error.
Any one know how that can be done and what exactly it lookes like ?
Search for Aperiodic Enclosure, here are two random hits:
How should we model aperiodic boxes
How do I design an aperiodic sub enclosure?
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