Cabinet damping material

Discussion in 'High Efficiency' started by Salectric, Feb 10, 2018.

  1. I will post some pictures after I get my Jensen/Altec speakers running again, but that won’t be for a couple weeks since I need to get the woofers back.
  2. Celt

    Celt Peanut Head

    That was the way to do it back then...and with a good reason...
  3. dowto1000

    dowto1000 Junior Member

    Hi Salectric,

    I liked your post, thanks for sharing. The 825 VOTT ( early ) boxes I run are also only 5/8 ths thick. Dennis advised me NOT to re-make them using one inch Baltic Birch.

    He specifically told me to do a single 2 by 2 inch pine internal brace, on each left and right side wall, covered with see-through Batting , NO cross bracing ( across - L. to R .) wanted in the speaker, and leave the thin stock ALTEC woofer horn flares totally stock.

    He tells me that this mass loading I did carefully, incrementally by ear ( 400 pounds of patio pavers, on each 825 enclosure) will be bettered..... by just doing the minimal bracing of the stock 825 enclosure. Dennis says, all the excess mass I added " takes the FUN " out of the presentation, deadens it too much.

    He also was very specific, for me to get the 825 / VOTT box off the floor, either on industrial casters, or a speaker stand, or cheapo bricks, .... as this also sounds best to him. He said, I had to place the box on the floor, when I was mass loading, but once I remove the mass-loading weight, having the A7s " off the floor" will be the most lively and fun to hear.

    There are similarities between what you report, and where I plan to go !! Interesting for to me to hear this, and not have to do all the experimental work.

    These posts may help others.

    Have a lovely day !!

    Last edited: Feb 12, 2018
  4. Funny coincidence. I just read Herb Reichert’s review of a KEF speaker in the latest Stereophile and Herb talks about cabinet walls and damping. He says “To my ears, dense, highly damped boxes and/or steep sloped crossovers can sound subliminally thick and restrained. In contrast lightly damped boxes with first-order crossovers add some loose, not-so-subliminal noise to the midrange—-but they can also jump, sound expansive, and dance like Fred and Ginger.”

    While I wouldn’t have used the same words, Herb is describing basically the same things described in this thread.
    Bernie and JimPA like this.
  5. JimPA

    JimPA Junior Member

    I have been using low density polyurethane foam since building my first Fried model C speaker kit which are an aperiodic design.
    When it comes to attaching it inside of the enclosure of an aperiodic or transmission line design I use liquid nails.

    I am sure that many know that is does help suppress standing waves from the rear of the enclosure.

    Once I tried fiberglass in a transmission line enclosure and the sound was hollow.
    I tried increasing the density and very little sound came out of the line terminus [the vent] of the enclosure.

    This sound can't be heard but it can be felt by placing one's hand in front of the vent which is at the rear of this enclosure.
    This is the anti resonant sound from the back wave of the woofer cone.

    I have enclosed a diagram of the speaker to illustrate where the vent is.
    [BTW I hope my ammunition in photo doesn't offend anyone.]

    Below is an example, the foam has bent a little over time but still serving it's purpose in absorbing the higher sound frequencies. DSC_0121.JPG DSC_0056.JPG
    Last edited: Apr 18, 2018
  6. TubeHiFiNut

    TubeHiFiNut Administrator Staff Member

    No offense here. :)
  7. JimPA

    JimPA Junior Member

    When it comes to using foam for a damping material there are many densities available.

    Take note of the weight per cubic foot when comparing it to other types of damping material used in loudspeaker enclosures.

    The type I have used is the first one on the list.

    Take note of all the specifications comparing the different types of foam.
    The longevity is referring to the ability of the foam being able to return to it's shape.
    Last edited: May 6, 2018
  8. TubeHiFiNut

    TubeHiFiNut Administrator Staff Member

  9. ICTWoody

    ICTWoody Junior Member

    Anyone have any insight into the best way to attach fiberglass batts to the inside of the boxes? I am thinking about using 3M Super-77 spray adhesive, but I'm not totally sure yet. I could use 2.5" screws... but I am not sure I want to screw into the boxes.

    - Woody


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