General Question on Speaker Internal Stuffing

[bencat]

I am just about to start a new project which is listed on here of converting a pair of KEF 103 Reference (1976 - 1977 Model) . In the main I am going to by pass the passive crossovers and use a Minidsp unit to generate both a full digital active crossover and also DSP room correction filters.

As I am using an existing model there are certain things that I need to change . One I need to have an additional pair of speaker inputs added to each speaker so that I can connect to the Treble and Bass units directly . To do this I need to get inside the speaker and I have some general questions that i would like advice on .

The KEF units have a heavy metal frame inside the wooden sides which makes the cabinet both heavy and stiff . There is also some thin foam tape around the driver fixing frame which seals the cabinet when you tighten the frame back in as this is a sealed baffle unit. Can you buy this black foam tape to replace it with new or would draught excluder tape (thin black stuff with adhesive back) be suitable ?

Then my main question for advice is insdie the cabonet there is wadding / stuffing material I presume to dampen the space in the enclosure . Is it best to remove this , essentail so I can get access to the speaker binding / 4mm Plug sockets and then just try and put it back as close to what it was ?

I have read that  some speakers of this time were over filled and there is a sonic advantage to reducing the amount of filling in the cabinet or in at least two extreme cases it was suggested that the filling could be removed altogether .

What have you all found when making your own units ? Did you use any stuffing inside the cabinets ?

 

[Shadders]

Hi,

I bought my wadding from Falcon Acoustics - reasonably cheap. My interpretation of the use of wadding is a trial and error approach - try and see what sounds best.

For my current transmission line speakers i have just built, which has internal folds - there are 3 internal sides which face forward (back panel, and two internal panels) which have 30mm egg crate/convoluted foam (adhesive backed).

Then all panels sides that face downwards have the same. The remaining panels (rear facing sides, upward facing sides, and left/right facing sides) all have 6mm acoustic foam.

Then i have internal wadding along the entire length of the line.

Cannot tell you how they sound yet since i am painting the speakers.

Regards,

Shadders.

 

[MF 1000]

Internal wadding is used to dampen cabinet reflections which lead to colouration.  In a transmission line the wadding (normally long haired wool) is actually a form of low pass filter to help lower the bass - the theory is that higher frequencies cause the will fibres to vibrate and are dissipated, whereas bass frequencies being long length waves pass through the stuffing. Varying the density of stuffing in a TL wil adjust the bass response

 

[MF 1000]

I am just about to start a new project which is listed on here of converting a pair of KEF 103 Reference (1976 - 1977 Model) . In the main I am going to by pass the passive crossovers and use a Minidsp unit to generate both a full digital active crossover and also DSP room correction filters.

As I am using an existing model there are certain things that I need to change . One I need to have an additional pair of speaker inputs added to each speaker so that I can connect to the Treble and Bass units directly . To do this I need to get inside the speaker and I have some general questions that i would like advice on .

The KEF units have a heavy metal frame inside the wooden sides which makes the cabinet both heavy and stiff . There is also some thin foam tape around the driver fixing frame which seals the cabinet when you tighten the frame back in as this is a sealed baffle unit. Can you buy this black foam tape to replace it with new or would draught excluder tape (thin black stuff with adhesive back) be suitable ?

Then my main question for advice is insdie the cabonet there is wadding / stuffing material I presume to dampen the space in the enclosure . Is it best to remove this , essentail so I can get access to the speaker binding / 4mm Plug sockets and then just try and put it back as close to what it was ?

I have read that  some speakers of this time were over filled and there is a sonic advantage to reducing the amount of filling in the cabinet or in at least two extreme cases it was suggested that the filling could be removed altogether .

What have you all found when making your own units ? Did you use any stuffing inside the cabinets ?

As I remember from when I owned a pair of R103's they are infinite baffle speakers.  They may benefit from some deadsheet applied to the rear of the front baffle plate which again (this was over 20 years ago) is metal or thin ply covered with leatherette? And could be rotated thro 90deg to use them as bookshelf units

 

[orangeart]

The stuffing will have been worked out pretty well when the speakers were built to give the speakers the correct over all Q. So change it by all means but the fall off of the bass will change shape (on an FR plot)

I use (and sell) neoprene gasket for seating drivers. The problem with the foam tape is that once it has been compressed it stays that way and loses its ability to seal. Neoprene keeps pushing back so keeps a good seal.

Stefan

 

[bencat]

The stuffing will have been worked out pretty well when the speakers were built to give the speakers the correct over all Q. So change it by all means but the fall off of the bass will change shape (on an FR plot)

I use (and sell) neoprene gasket for seating drivers. The problem with the foam tape is that once it has been compressed it stays that way and loses its ability to seal. Neoprene keeps pushing back so keeps a good seal.

Stefan

Thanks Stefan , that is helpful . When I changed the passive CR in my KEF's it looked like they had not been opened for years and the foam had become thin and brittle . I changed it then but was pretty sure if i disturbed it again that it would need to be replaced. As Neoprene does ot disintergrate like foam I will look at your site and buy some for when I do the internal work . Over the next few months there may well be a need for the fronts to be removed a few times so having something that will keep the sela would be great .

Hi Keith - Front panel is all metal and yes you do have the option to use the units either upright or on their side (never seen any used on their side but it is their if you want to ) Have not had the front off for about six months or so but I seem to rememebr that it already has sticky panels around the edge between the driver units. Will check and if not I think that is one area that might well benefit some attention .

 

[greybeard]

I always use self adhesive bitumen sheets on all the panels before I use the wadding. The egg carton style acoustic foam is good, as it stops internal reflections. I often use good old fashioned felt carpet underlay first to dampen cabinet resonance, and then the egg carton foam on top of that for the reflections, I have even on occasion used loose long haired wool to fill what void is left, but this is only on infinite baffle not ported. It is very much suck it and see.

 

[bencat]

I always use self adhesive bitumen sheets on all the panels before I use the wadding. The egg carton style acoustic foam is good, as it stops internal reflections. I often use good old fashioned felt carpet underlay first to dampen cabinet resonance, and then the egg carton foam on top of that for the reflections, I have even on occasion used loose long haired wool to fill what void is left, but this is only on infinite baffle not ported. It is very much suck it and see.

Thanks Colin great information and a little more food for thought . As I love these speakers and how they sound now I think it is best to leave as much as possible unchanged with them so it will be as careful as possible removal of what is already inside , perhaps a little front pany deadening as noted above remove the passive cr and drill those extra holes . Quick solder of the drive units to to 4mm plugs then try and put the original dampening material back as close as it was .

Once I have the active element in place and see what the general sound and balance is like can hear if there are any areas that might need a little attention and as always just ask what can help .

With these units and weight of the metal front baffle it is not a qucik easy job getting it open and then refitted. However this does mean that the integrity of the seal is very good and you get a real sealed baffle with no leaks . This is something I will try and keep after my changes.

 

[greybeard]

However this does mean that the integrity of the seal is very good and you get a real sealed baffle with no leaks . This is something I will try and keep after my changes.

Yes my cabinets are airtight for the B200.