Does a lot of damping material have any negative effects in a closed box?

[test1223]

Hello,

from my experience a lot of midrange and bass enclosures sound much better with a lot of damping material in it. I often use very dense material for the walls and stuff a lot of usual material in the box so that it is very compressed with the exception directly behind the driver.
The sound for me is "smoother" you can see some changes in the impedance plot which is also a bit smoother.

Hardly any company puts a lot of damping material in such boxes. Consistently doing a stuffed damping isn't very easy so this might be the reason? But I wonder if there are any objective negative effects like none linear behavior which is dependent on the sound pressure level or on the cabinet temperature? I have often heard the anecdotal "evidence" that to much damping destroys the liveliness of the box. The claimed lack of "liveliness" may be the absence of small resonances or are the any other subjective negative effects?

Best
Thomas

 

[fpitas]

I've seen designers I tend to trust saying to not "stuff" the material hard; for example, with fiberglass or cotton waste lay the sheets in the box uncompressed.

I have often heard the anecdotal "evidence" that to much damping destroys the liveliness of the box. The claimed lack of "liveliness" may be the absence of small resonances or are the any other subjective negative effects?

That just seems like audiophile twaddle.

 

[fpitas]

FWIW, I completely filled my bass and mid driver boxes. I have not noticed any lack of liveliness.

 

[LTig]

from my experience a lot of midrange and bass enclosures sound much better with a lot of damping material in it. I often use very dense material for the walls and stuff a lot of usual material in the box so that it is very compressed with the exception directly behind the driver.
The sound for me is "smoother" you can see some changes in the impedance plot which is also a bit smoother.

AFAIR the amount of damping material changes the Q and the center frequency of the resonance of the driver in this housing such that more material lowers both. I'm happy to stand corrected if this is false.

Hardly any company puts a lot of damping material in such boxes. Consistently doing a stuffed damping isn't very easy so this might be the reason? But I wonder if there are any objective negative effects like none linear behavior which is dependent on the sound pressure level or on the cabinet temperature?

Not that I know.

I have often heard the anecdotal "evidence" that to much damping destroys the liveliness of the box. The claimed lack of "liveliness" may be the absence of small resonances or are the any other subjective negative effects?

Many small speakers are designed with an underdamped (higher Q) woofer to get a peak in FR to emulate the sound of a bigger speaker. Adding more damping material flattens this peak and results in less "punch" which some people used to it may experience as "less livel"y.

 

[Roland68]

Hello,

from my experience a lot of midrange and bass enclosures sound much better with a lot of damping material in it. I often use very dense material for the walls and stuff a lot of usual material in the box so that it is very compressed with the exception directly behind the driver.
The sound for me is "smoother" you can see some changes in the impedance plot which is also a bit smoother.

Hardly any company puts a lot of damping material in such boxes. Consistently doing a stuffed damping isn't very easy so this might be the reason? But I wonder if there are any objective negative effects like none linear behavior which is dependent on the sound pressure level or on the cabinet temperature? I have often heard the anecdotal "evidence" that to much damping destroys the liveliness of the box. The claimed lack of "liveliness" may be the absence of small resonances or are the any other subjective negative effects?

Best
Thomas

Yes, you can over-dampen a speaker very quickly.
You also write something about dense material for the loudspeaker walls, that is insulation of the housing vibration, that has nothing to do with damping, you should differentiate between them.
There is really a lot of information about this topic in speaker construction on Google.
The basic rule is to use as much damping material as necessary, but as little as possible.

Two of the best speakers I've heard in my life had no damping material at all.

 

[thewas]

But I wonder if there are any objective negative effects like none linear behavior which is dependent on the sound pressure level or on the cabinet temperature?

Very good question, if, I would also rather guess some non-linearities of the air spring force compared to the front side of the driver (but those being more dominant with a too small rather than with an overdamped rear volume) but would love to hear the opinion of some expert on it.

 

[fpitas]

AFAIR the amount of damping material changes the Q and the center frequency of the resonance of the driver in this housing such that more material lowers both. I'm happy to stand corrected if this is false.

It is true. You plan for that as you design the speaker.

 

[fpitas]

Dickason discusses this and has measurements for different stuffing materials. An empty box almost always has resonances. At least line the walls, if nothing else.

 

[fpitas]

Sort of on-topic:

Volume filling a reflex box

Volume filling a reflex box - tests and measurements showing how correct filling can improve performance

sound-au.com

 

[Deleted member 21219]

I seem to remember a program that took into effect the differences in stuffing. Maybe Bassbox, or Bassbox Pro???

Jim

 

[fpitas]

I seem to remember a program that took into effect the differences in stuffing. Maybe Bassbox, or Bassbox Pro???

Jim

You can adjust the box Q in WinISD, which models it pretty well.

 

[fpitas]

I have often heard the anecdotal "evidence" that to much damping destroys the liveliness of the box.

Since we're on ASR, I can say I have never seen anyone offer anything but anecdotes about that.

 

[dasdoing]

I asked Bard and it also says "Too much damping can make the sound too dry or lifeless."
I have to wonder: why would I want life and "wetness" in my speaker?

 

[fpitas]

I asked Bard and it also says "Too much damping can make the sound too dry or lifeless."
I have to wonder: why would I want life and "wetness" in my speaker?

Maybe you have plants?

 

[Schollaudio]

Here's a good discusion which I agree with. https://www.sound-au.com/articles/boxstuff.htm

 

[fpitas]

Here's a good discusion which I agree with. https://www.sound-au.com/articles/boxstuff.htm

It's a good article, but post #10 beat you to it

 

[fpitas]

Obviously too much damping material in a ported or transmission line enclosure is a whole different subject, since you want the back wave. Nonetheless it's good to suppress box modes.

 

[dasdoing]

How much material did Genelec use before actively reducing resonances with specific geometry?

 

[fpitas]

How much material did Genelec use before actively reducing resonances with specific geometry?

Somehow I doubt they'll share that information with us. But, maybe somebody will disassemble their Genelecs for us.

 

[test1223]

How much material did Genelec use before actively reducing resonances with specific geometry?

They use surprisingly few damping material in the mid range driver of there ones.

AFAIR the amount of damping material changes the Q and the center frequency of the resonance of the driver in this housing such that more material lowers both. I'm happy to stand corrected if this is false.

Yes but the damping factor only counts for the resonance frequency and you can adjust it with the volume and damping to your liking so that part isn't so interesting for me since it is documented in multiple ways.

What is also surprising that closed subwoofer almost always doesn't use much damping material but you can make the equivalent box size bigger with it. So I guess there has to be a negative effect.

Very good question, if, I would also rather guess some non-linearities of the air spring force compared to the front side of the driver (but those being more dominant with a too small rather than with an overdamped rear volume) but would love to hear the opinion of some expert on it.

It is likely that you have some front to backside difference of the driver spring. The ideal air in the box doesn't increase this unbalance rater the opposite it increase the symmetry of the spring since a typical (empty) box provides a very linear spring. Does the damping material change that? I thought the damping material changes the value of the air spring and if you look at it form a mechanical system perspective doesn't introduce a damping element, but I might be wrong here.

Yes, you can over-dampen a speaker very quickly.
You also write something about dense material for the loudspeaker walls, that is insulation of the housing vibration, that has nothing to do with damping, you should differentiate between them.
There is really a lot of information about this topic in speaker construction on Google.
The basic rule is to use as much damping material as necessary, but as little as possible.

Two of the best speakers I've heard in my life had no damping material at all.

What are the consequences with over-damping you have to measure the negative consequences in some way?

It is true that a lot of material also can change the sound transmission of the box. In this case less material should be not as good as more material.

The frequency response slightly changes with damping but you can compensate that with some filters.

Here's a good discusion which I agree with. https://www.sound-au.com/articles/boxstuff.htm

Thank you for the article but it doesn't answer my questions. If you have a look at bass reflex cabinets it is clear that you will also reduce the effect of the bass reflex port with to much damping material. But with a closed box it is different you don't want/ need the backside sound pressure level. So a lot of damping might be clever.