A question for Geoff Martin on BL8000 Damping…

[matador]

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.

 

[matador]

Before

After…

[geoffmartin]

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

 

[matador]

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.

[geoffmartin]

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.

[matador]

Thank You Geoff.

[billbriscoe]

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

[matador]

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

This is a schematic view of the Beolab 8000 internals:

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

The new damping looks like this:

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:

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

[Beobuddy]

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

 

[Beobuddy]

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.

[YannChris]

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.

[Beobuddy]

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.

[YannChris]

Thanks Beobuddy.

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

 

 

[matador]

Beobuddy wrote:

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.

[Beobuddy]

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.

[YannChris]

Beobuddy,

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

 

[matador]

Beobuddy wrote:

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.

[Tignum]

Beobuddy wrote:

I’m not allowed to do it inside anymore.

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.

[mojofml]

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.

[Beozip]

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

 

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