Jump to content

How Much Damping Material?


Recommended Posts

I bought a used pair of Avid 100 speakers, over 40 years old. While I'm not doing a restoration, I am opening them up and making minor

repairs.

 

Well, I opened them up and found they were positively STUFFED with fiberglass insulation. There was so much damping material you

had to push the drivers down to set them against the motorboard.

 

I looked up what the rule of thumb is for damping material and found it's 1-1.5 lbs./cu.ft. . I bought 2-8oz. packages of polyfill which would

be about right for the speaker's internal volume and  discovered trying to fit all of it into the cabinet yielded the same results as the fiberglass

I found.

 

Are my numbers right? I wound up only stuffing 1-8oz. polyfill bundle into the cabinet as from a practical standpoint that seemed more

reasonable. Can I tell a sound difference?- not really, but I'm wondering if I'm missing something.

Link to comment
Share on other sites

Hi Peter,

 

With 50 year old speakers, who knows if the damping is original or not. If it the factory damping, then they probably figured it out and I would recommend leaving it alone.
 

The amount of damping material affects not only the bass frequencies but also how much midrange in the box that is reflected back to the woofer and then into the room; some of the midrange reflection back into the woofer may or may not be desirable. 
 

Best,

 

Andy

Link to comment
Share on other sites

Your 1 to 1.5 lbs of stuffing per cu ft is "correct", is quite a large range, and will result in a tight fit, heavily stuffed cabinet.

 

From the YouTube videos I've watched, only a heavily stuffed cabinet will yield the desired effect: a slight lowering of the bass roll off point.

Link to comment
Share on other sites

11 hours ago, Racer X said:

Your 1 to 1.5 lbs of stuffing per cu ft is "correct", is quite a large range, and will result in a tight fit, heavily stuffed cabinet.

 

From the YouTube videos I've watched, only a heavily stuffed cabinet will yield the desired effect: a slight lowering of the bass roll off point.

True, but the effect on the midrange will typically be more audible than a few Hz at the bottom end. 

Link to comment
Share on other sites

Why would you even consider changing the damping material or amount?  Fiberglas does not deteriorate.  I recommend you replace the original material the factory determined to be correct.  Your range of 50% is no guidance at all.

  • Like 1
Link to comment
Share on other sites

Ignorant side question....

 

If his speaker is 'stuffed', why does the Cornwall only have damping material on (if I recall) one side and the bottom (or was it top?)  Either way, only has it on two surfaces, not "stuffed'????

 

Link to comment
Share on other sites

Thanks for the replies so far.

 

Remember; this speaker was clearly not factory stock; the woofers are from Radio Shack and the tweeters are something other than OEM. I found aftermarket crimp connectors inside. That's why I suspect the fiberglass was added "after the fact". Besides, I would imagine most manufacturers would NOT use house fiberglass insulation for damping material.

 

I haven't looked inside many speakers but in the couple I have peered inside there was substantially less damping material. In fact, compare my Heresy IIs, which only have a foam sheet curled around the woofer section of the cabinet.

Link to comment
Share on other sites

On 5/5/2023 at 6:59 AM, Peter P. said:

Well, I opened them up and found they were positively STUFFED with fiberglass insulation. There was so much damping material you

had to push the drivers down to set them against the motorboard.

 

This was common given that most manufacturers would just fold a long sheet of glass and stuff it into the enclosure. 

 

You should have left the glass in, much, much superior to the plastic crap.

Link to comment
Share on other sites

On 5/6/2023 at 9:31 AM, Coytee said:

Ignorant side question....

 

If his speaker is 'stuffed', why does the Cornwall only have damping material on (if I recall) one side and the bottom (or was it top?)  Either way, only has it on two surfaces, not "stuffed'????

 

 

 

The woofer is modelled (or trial and error tested in the old days) for its frequency response with a certain amount of damping material.  The material makes the box volume behave as though it is different because it changes its "springiness".  As though it is larger, I believe. 

Link to comment
Share on other sites

On 5/6/2023 at 12:25 PM, Peter P. said:

Thanks for the replies so far.

 

Remember; this speaker was clearly not factory stock; the woofers are from Radio Shack and the tweeters are something other than OEM. I found aftermarket crimp connectors inside. That's why I suspect the fiberglass was added "after the fact". Besides, I would imagine most manufacturers would NOT use house fiberglass insulation for damping material.

 

I haven't looked inside many speakers but in the couple I have peered inside there was substantially less damping material. In fact, compare my Heresy IIs, which only have a foam sheet curled around the woofer section of the cabinet.

 

 

My VMPS subwoofers are tightly stuffed with fiberglass that looks like insulation grade fiberglass.  It's yellow. 

 

https://www.audiokarma.org/forums/index.php?threads/avid-thread.116894/

 

The OEM tweeter description sounds like the tweeter in Marantz Imperial 7s among others.  Not sure how to id the OEM CTS woofer, unless Eminence has old CTS data. 

Link to comment
Share on other sites

Update: I found a post in another forum along with photos that clearly showed the Avid 100 DID come from the factory stuffed to the gills with fiberglass insulation.

 

Even though I've tossed the fiberglass and replaced it with polyfill albeit with 1/2 the volume and the woofer is NOT the factory woofer, I'm going to stuff each one back up to the full 16oz. of polyfill, because it's too late to recover the fiberglass!

 

Thanks for the recommendations; I've only peered inside two speakers in my life; a Mission bookshelf speaker which I don't recall having ANY material inside, and my Heresies which only has that sheet of foam surrounding the woofer. Kinda confuses someone, know what I mean?!

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...