A question for Geoff Martin on BL8000 Damping…

Viewing 20 posts - 1 through 20 (of 24 total)
  • Author
    Posts
  • #4474
    matador
    Moderator
    • Paris France
    • Topics Started 19
    • Total Posts 169

    Hi alls,

    UPDATE: the foam in my pictures are not set correctly, good way to install them is as on Beobuddy pictures or the third drawing some post below, in the center of the speaker, around the woofers. Apologies.

    Sorry for the catchy title but better ask god than its saints. Nevertheless any comment is of course welcome.

    Today I replaced the damping foams in a Beolab 8000.
    First thing that hits me was that the replacement kit isn’t a piece for piece set.
    The main difference is that the upper part now consist in vertical pieces along the aluminium pipe and two horizontal pieces, one around the bass port tube and the other above the tweeter, where before there was just a gasket from amplifier board to top plate around the pipe but without any horizontal separation.

    I vaguely remember an answer from Geoff once, I can’t remember the precise topic but it was something like “the problem is the speed of the air in the bass port tube…”. Sorry for being imprecise but its just from memory. Still, that was something that made me think “whoa, this things are more complicated that you think…”

    So here is the question: with the new damping kit, isn’t the bass port intake “sealed” by the V shaped piece that separates the speaker area from the bass port area ? Aren’t the air movements altered in some way?

    And the “outrageous” question: With all the instances of Beolab 8000, are the kit you can order by now (3332084) adapted to any BL8000 whatever the period?

    For the record, when looking after this sets to buy, somebody (in the business) told me the foam are “useless” and they remove them each time they have 8000’s to repair.

     

    • This topic was modified 2 months, 2 weeks ago by matador.
    #4475
    matador
    Moderator
    • Paris France
    • Topics Started 19
    • Total Posts 169

    Before

    IMG_9431

    After…

    IMG_9447

    #4936
    geoffmartin
    GOLD Member
    • Topics Started 1
    • Total Posts 14

    Hi,

    Sorry it took a while – I didn’t know that we sold these kits so I had to do some investigating…

    After asking all the right people, we’ve agreed that the thick foam is mounted incorrectly. It  has a hole in it that allows you place it so that the bottom of the port is flush with the bottom of the foam. This will also make it perpendicular with the sidewall of the loudspeaker – not angled as it is in the second photo.

    Hope this helps.

    Cheers

    -geoff

     

    #4940
    matador
    Moderator
    • Paris France
    • Topics Started 19
    • Total Posts 169

    Thank you Geoff for your answer, I was just worried my question became “invisible” with new topics coming along…

    I adjusted the piece around the bass port tube, but what I don’t understand is isn’t the V shaped piece (the one just below the entry tube one) preventing the air coming from the woofer movement going through the bass port?

    Actually I did “feel” that something is coming from the bass port by getting closer to the sounding speaker, but I’d like to understand the rough theory behind this since the original foams and the replacement are not alike at all.

    Below, the foam kit guide…

    Thank you Geoff.

    20210718_145755

    #4946
    geoffmartin
    GOLD Member
    • Topics Started 1
    • Total Posts 14

    It was only invisible to me, since I don’t drop by here very often.

    As I said, I didn’t know that B&O made this kit until you asked about it – and the only information I have about it is what you’ve shown here.

    However, if one of the pieces of foam is blocking the entry to the port, then something isn’t placed correctly.

    #4948
    matador
    Moderator
    • Paris France
    • Topics Started 19
    • Total Posts 169

    Thank You Geoff.

    #4978
    billbriscoe
    GOLD Member
    • Topics Started 0
    • Total Posts 1

    Hi,

    The foam material does breathe. The sound absorption is greater the higher the frequency, so the base port should be getting all the lower frequencies. I have changed the foam damping in my BL8000s to the updated version a number of years ago. The base response was not impacted. I use a pink noise generator along with a real time spectrum analyzer to adjust my system to be as “flat” as best I can. The lowest frequencies needed to be turned down a bit to get to “flat” response.

    I think the foam materials and location info provided by B&O are just fine to use as-is.

    Bill

    #4995
    matador
    Moderator
    • Paris France
    • Topics Started 19
    • Total Posts 169

    Hi Bill, thank you for the explanation. It helps.

    This is a schematic view of the Beolab 8000 internals:

    BL 8000

    From top to bottom: top plate, bass port, tweeter, 2 woofers, amplifier section, base cone.

    The new damping looks like this:

    Damping Original

    Then after your comment, it blocks the high frequencies from the tweeter, but allows low frequencies coming from the woofers to “fill” the whole speaker, right?

    I should add that if the kit didnt come with instructions, I would have placed them like that:

    Damping Alt

    To “push” all the air towards the bass port.

    #5260
    Beobuddy
    GOLD Member
    • Topics Started 0
    • Total Posts 12

    I’m not allowed to do it inside anymore. 🙂

     

    BL8000

    #5262
    Beobuddy
    GOLD Member
    • Topics Started 0
    • Total Posts 12

    The newer version of foam has been improved compared with to the previous one. The foam sits tight around the bass pipe to prevent audible resonance at lower frequencies.
    The V-shape sits on top of the other parts and provides a “chamber” for the drivers.

    • This reply was modified 2 months, 2 weeks ago by Beobuddy.
    #5269
    YannChris
    GOLD Member
    • Brittanny, France
    • Topics Started 7
    • Total Posts 47

    Beobuddy,

    On your picture, I notice that you replaced the foam-tape placed on the sides of the column.

    Are they part of the foam-kit?

    If not, what did you use?

    Regards,

    Yann.

    • This reply was modified 2 months, 2 weeks ago by YannChris.
    #5273
    Beobuddy
    GOLD Member
    • Topics Started 0
    • Total Posts 12

    Correct.
    I strip the BL8000’s always completely. To the bare tube.
    The foam tape isn’t part of the foam-kit. There are 2 different types used. A 6mm and a 19mm wide foam-tape.
    I use the original foam-tape used by B&O to keep the BL8000 as original as possible.

    #5276
    YannChris
    GOLD Member
    • Brittanny, France
    • Topics Started 7
    • Total Posts 47

    Thanks Beobuddy.

    Aren’t you afraid that over time the foam will disintegrate and cause a new “Foam-Rot” crisis?

     

     

    #5277
    matador
    Moderator
    • Paris France
    • Topics Started 19
    • Total Posts 169

    The newer version of foam has been improved compared with to the previous one. The foam sits tight around the bass pipe to prevent audible resonance at lower frequencies. The V-shape sits on top of the other parts and provides a “chamber” for the drivers.

    Ok, now I feel totally stupid. I mount them wrongly because the picture wash cut at the top and I believed it was top of the speakers. I’m good to open them again.

    That mount make sense.

    Apologies to Geoff.

    #5278
    Beobuddy
    GOLD Member
    • Topics Started 0
    • Total Posts 12

    I think that it will not disintegrate as the old version did. But the new type of foam isn’t perfect either. From around 2003 (where the newer version was used) and upwards I also see and experience that the new foam affect circuitboards. More noticeable in BL4000’s for instance.

    #5280
    YannChris
    GOLD Member
    • Brittanny, France
    • Topics Started 7
    • Total Posts 47

    Beobuddy,

    Are you talking of the new white foam or of the foam-tape?

     

    • This reply was modified 2 months, 2 weeks ago by YannChris.
    #5281
    matador
    Moderator
    • Paris France
    • Topics Started 19
    • Total Posts 169

    There are 2 different types used. A 6mm and a 19mm wide foam-tape. I use the original foam-tape used by B&O to keep the BL8000 as original as possible.

    Could you tell us where you get it, and what’s the thickness for the two strips?

    Thank you.

    • This reply was modified 2 months, 2 weeks ago by matador.
    #5305
    Tignum
    GOLD Member
    • Netherlands
    • Topics Started 1
    • Total Posts 45

    I’m not allowed to do it inside anymore. 🙂 BL8000

    I remember you said that when you did save my 8000s 🙂
    Still very happy with them. Good to see you take such care to keep the speakers as close to original as possible.

    • This reply was modified 2 months, 1 week ago by Tignum.
    #6035
    mojofml
    BRONZE Member
    • Topics Started 3
    • Total Posts 9

    Thanks for your great write up. I’m fixing up my BL6000 and the foam has completely fallen apart as well. I will check with my local B&O store whether I can get replacement foams (unlikely), but if not can anyone suggest what alternative foam I can use? Ie thickness, density, material, etc. Greatly appreciate your advice.

    • This reply was modified 1 month, 2 weeks ago by mojofml.
    #6065
    Beozip
    BRONZE Member
    • Topics Started 0
    • Total Posts 25

    Your dealer should be to order the foam for your BL 6000 as a spare part from B&O.

    In this auction can you see the number …..

    https://www.ebay.de/itm/154203121920?hash=item23e738e900:g:O1IAAOSwSXFdpIDw

    good luck

     

Viewing 20 posts - 1 through 20 (of 24 total)
  • You must be logged in to reply to this topic.