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Linn Isobariks - replacing the mid and bass drivers with Falcon units

While I was waiting for the gaskets, I've been looking at what the Willys have that might be useful to these Isobariks. So I ordered 400g of Mundorf wadding and replaced nearly all of the original Linn wadding with this supposedly superior stuff (should be for the cost). I also got some of their butyl rubber sealing cord, which I had never come accross before. For anyone wanting to go the mastic route on their project I would suggest they use this stuff, it's eminently easier to work with and would provide a really good seal and also allow for future removal, although it is not completely mess free like the neoprene gaskets above. It can also be bought in different daimeters and more cheaply on Amazon.

I took the old wadding out of the two Linn cushions and put in the Mundorf stuff and then sealed up the bags with the CT-1 clear mastic I had already bought. I also put it behind the hesian curtain at the back and attached it back with same mastic.
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Now I need some help and advice guys! I went a bit mad, while looking at the soft 'cardboardy' bits of wood that Linn had stapled to the inside of the bass enclosure to dampen it I guess and stop the box from resonating. I got an idea for improving on this and maybe even the new 'KuStone' I heard of that @Richard Lines had found in his later Isobariks.

So I bought this: from Willys and have inserted it into the bass enclosure see below. My question:....is this a bad idea? I could easily remove it as I've not fitted the drivers yet. Also I have not put it behind the rear B139, but I could (just needs me pulling open the hesian curtain again). Will this change the volume of the cabinet enough to make it a bad move? Will it change the characteristics of the Isobarik bass sound? Could it possibly be a good idea? Please tell me straight. My thoughts are that if it sounds bad/off in the bass department I'll just open them up and remove it (I don't plan to put it behind the rear B139s unless someone recommends it as I don't fancy pulling open that hesian curtain unless I have to).

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Shouldn’t be a problem, anything that reduces the volume of the sub chamber
Is a good thing as the trapped air is not
helpful to both drivers moving in tandem.
 
Good evening @nostromo

The issue you'll have here is that when you get these Isobariks back up and running you won't know which of the changes you've made will be the one(s) you're actually hearing.

Yes it would be a pain to keep dismantling the damn things to conduct each and every change but you would be more easily able to identify which change caused any one difference in what you'd be hearing.

This is one reason why I'm reluctant to start the 'woofer' project on my Isobariks.........

Regards

Richard
 
Last edited:
GWM said:
Shouldn’t be a problem, anything that reduces the volume of the sub chamber
Is a good thing as the trapped air is not
helpful to both drivers moving in tandem.
Click to expand...
Excellent news...Thanks! I wish I'd spent some time doing the same to rear the cabinet behind the internal B139 now. You have put my mind at rest, I was rather worried it would change things for the worse....Cheers!
 
Richard Lines said:
Good evening @nostromo

The issue you'll have here is that when you get these Isobariks back up and running you won't know which of the changes you've made will be the one(s) you're actually hearing.

Yes it would be a pain to keep dismantling the damn things to conduct each and every change but you would be more easily able to identify which change caused any one difference in what you'd be hearing.

This is one reason why I'm reluctant to start my 'woofer' project on my Isobariks.........

Regards

Richard
Click to expand...
Yes Richard, I fully agree. My intention at the outset was just that, B139s first (have a good listen) then the mids, but once I laid the buggers down I felt it was physically going to be too much trouble for me to do it twice (could easily pull a muscle in my back). Then I didn't expect the job to take so damn long and while waiting for the bolts and gaskets I wandered further off track.

I'm currently in the process of fitting all the drivers back now (mids and rear B139s done), just having to wait for the CT-1 to go off holding the cushion behind the front B139, had to do it over two days...just couldn't figure out a way of putting it in and have it held in place, off and away from the rear B139. So opted to stick half of it (Just about stayed up while curing) and then the other half the next day. Fingers crossed I'll have music playing end of next week ( I work Fridays-Mondays).
 
So, I've managed to get everything done now....thanks to everyone for they're suggestions and moral support.

A top tip from @david ellwood of sticking the gaskets to the units before installing came in very handy (thanks David), (I actually used some rubber solution), it was almost impossible to position the gasket correctly without sticking them first down first.

1) I replaced the Linn wadding with the Mundorf stuff (costly though).

2) I put in some self adhesive damping (10mm thick) obatined from Willys inside the front enclosure, I wish I had done the same to the rear enclosure too but I had already stuck the rear hesian curtain in place before getting reasurance it was a good idea from @GWM and didn't want to rip that off .... maybe I should have.

3) I couldn't resist putting down a bead of the Dow neutral silicone around the inner corner of the bevel for peace of mind on the air-tightness requirement in addition to the gaskets that I used. I did this for the mids too.

4) The round gasket for the mids was double the thickness (6mm) of the B139 gasket and was just too thick to fit in the baffle recess fo the mids, so I didn't end up using it. Instead I used the rather thin one provided with the Falcon B110s. Actually I now understand why that gasket is so thin, it's actually about the right thickness otherwise the B110 unit would protrude from the baffle. As I said, I also put in a bead of silicone as insurance.

5) The bolt holes were all given a dab of silicone so that the bolt holes would be air tight. I tightened the bolts up fairly tightly but didn't go mad.

6) The front hesian cushion (now filled with Mundorf wadding) was rather difficult to put in place using CT-1 silicone adhesive. Had to do it in two parts with a day inbetween to allow the adhesive to set. In hindsight I should have done this with hot melt glue (as Linn) and it would have only taken me about an hour with instant bonding. It's important to ensure there is enough slack in these hesian cushions because of the extra (20mm) depth on the Falcon B139 unit, so only the extreme edges of the cushions should be bonded (this is a difficult task, so plan ahead).

7) I protected the tweeters and mids (once fitted) with thick paper and some masking tape, it's amazing how many tools and bits and bobs you need for this job and the paper helps keep out dust, fluff etc.

To declare this project as success or a failure I need a good listening session or two which I can only do next week....I will report back after.

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@nostromo - now ALL you need to do is assemble some amplification to get the beasts under control................now there's a rabbit hole to avoid going down :D

Regards

Richard
 
Richard Lines said:
@nostromo - now ALL you need to do is assemble some amplification to get the beasts under control................now there's a rabbit hole to avoid going down :D

Regards

Richard
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Thanks for the warning....but I'm limbering up to call Avondale and ask for a list of everything I need for a complete Se200 build and a full quote. I need a rabbit to follow...could be great fun...at least surviving electrocution ...lol. Hopefully you can recommend the transformer?....also saw something about the new Avondale bridge rectifiers being rather good... I'll be getting those.

Everyone should have an audio DIY project going on the side ...makes you feel useful.
 
Hello everyone,

Last night I turned everything on and left music playing overnight at a low volume to warm everything up and loosen up the drivers a little.

So today, I entered a really nice warm room, I was excitedly looking forward to having a good listen and was expecting big things. Having spent the best part of this afternoon listening and checking everything, I'm really not a happy bunny at all. The SQ is rather awful and I'm crestfallen.

The bass is rather muffled, lacking snap, detail and is withdrawn. The mid's too, lack openness and sound muffled. I've taken a large retrograde step with this project.

So I've been doing a mental 'post mortem' (I do feel as if I've killed these isobariks, they're lifeless) and will put in the effort to recover from this disaster.

My thoughts:

1) Putting in the extra damping was a mistake....maybe it's absorbing too much sound from the rear B139 hence causing the muffling effect.
2) Replacing the original wadding with the mundorf stuff was a bad idea and maybe I've put too much in. The cushions maybe over-filled. and maybe I've put too much wadding behind the rear B139 too.
3) Same for the mids, maybe I put too much wadding in the cabinet so the driver is unable to operate and move properly.

My plan:

1) Remove everything and start again. Remove the damping stuck to the insides behind the front B139, and reduce by half, the wadding everywhere.

Plan B: after 1) put the original drivers and wadding back and hope that recovers things. If all fails I have a spare pair of Briks but they're DMS and will need some work converting to PMS (they are old).

Your thoughts and recommendations will be much appreciated.

Edit: maybe these Falcon units are not as good as the original Kef's....but this seems unlikely to me.
 
nostromo said:
Hello everyone,

Last night I turned everything on and left music playing overnight at a low volume to warm everything up and loosen up the drivers a little.

So today, I entered a really nice warm room, I was excitedly looking forward to having a good listen and was expecting big things. Having spent the best part of this afternoon listening and checking everything, I'm really not a happy bunny at all. The SQ is rather awful and I'm crestfallen.

The bass is rather muffled, lacking snap, detail and is withdrawn. The mid's too, lack openness and sound muffled. I've taken a large retrograde step with this project.

So I've been doing a mental 'post mortem' (I do feel as if I've killed these isobariks, they're lifeless) and will put in the effort to recover from this disaster.

My thoughts:

1) Putting in the extra damping was a mistake....maybe it's absorbing too much sound from the rear B139 hence causing the muffling effect.
2) Replacing the original wadding with the mundorf stuff was a bad idea and maybe I've put too much in. The cushions maybe over-filled. and maybe I've put too much wadding behind the rear B139 too.
3) Same for the mids, maybe I put too much wadding in the cabinet so the driver is unable to operate and move properly.

My plan:

1) Remove everything and start again. Remove the damping stuck to the insides behind the front B139, and reduce by half, the wadding everywhere.

Plan B: after 1) put the original drivers and wadding back and hope that recovers things. If all fails I have a spare pair of Briks but they're DMS and will need some work converting to PMS (they are old).

Your thoughts and recommendations will be much appreciated.

Edit: maybe these Falcon units are not as good as the original Kef's....but this seems unlikely to me.
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Mo - as you say maybe best to go back to ground zero and carry out changes one at a time. Laborious and time consuming yes but much much easier to identify the cause of any changes.

Regards

Richard
 
nostromo said:
I'm really not a happy bunny at all. The SQ is rather awful and I'm crestfallen.
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That's a major bummer. I'd be surprised if the added damping would make that much of a difference (doesn't sound like it's subtle). Are all the speakers phased correctly? I recall the B110s use in the 'Brick were different from the ones used in the LS3/5a (which the FB110 is designed to mimic). I'd give Falcon a call and see if Jerry has any insights as to what has gone wrong.
 
First of all dont be discouraged, ive lost count of the number of times ive upgraded my system for it to sound worse. Im afraid its part and parcel of running an active system. Because changing stuff alters the response of your speakers and the system will require a reset for it to realise the improvement. Its very likely that your crossover and speaker position will need revision.

Unfortunately this makes doing an A-B incredibly difficult and id normally not recommend making more than one change at a time so that you can get your head around whether its actually an improvement.

FWIW I can heartily recommend the Falcon B139s , they definitely arent the source of your angst (assuming theyre all working and in phase of course).

How far apart and how far from the wall do you have your speakers and what settings do you have in the crossover?
 
Hello guys,

Thank you for your supportive words....very much appreciated. It's nice to have an ear out there that understands.

Just a quick update; as @sktn77a suggested above I tried calling Jerry but he's in the USA and so was advised to email, which I have done. I have requested his generall thoughts on too much wadding and dampening behind the drivers casuing a 'muffling' effect and whether he could supply me with replacement gaskets for the units, as I'll need new ones once I remove the units again (I used mastic too depite David advisng me against).

I have tried what @david ellwood suggested and repositioned the speakers and that does change the sound a fair bit, but I still feel the new drivers are being 'muffled' leaving me unsatisfied with the sound. I've currently got them toe'd-in with rear corners 3" and 6" from the rear wall, 6ft (73") apart and 6.3ft (95") from the front of the listening position. I've tried them flat against wall too; 3" from the rear wall. I do prefer the better stereo image with the toe-in.

So I'm preparing (mentally) to give this all another go next week and remove all my fools-errand attempts at bettering the Linn design, i.e. reduce the wadding (to approximately what Linn had) everywhere and remove the damping sheets in the Isobarik cabinet.

While I'm in this anxious state, would you please reassure me: that the slight buzz that I can hear from the units up very close without music playing and which doesn't increase with volume is normal with LK280 amps? This cannot possibly translate into subtle distortion on vocals?

Many thanks.

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The new drivers will take some time to break in ,the suspensions will be quite stiff
to start with. It can take 50-100 hours before they settle.ee
I’d put in the original damping material and
then just give them a good run in before
jumping to any conclusions.
It may be their peramiters are not quite the
same as the originals but hard to determine
this before they are run in.
 
The original Kef spec sheets quote a sensitivity pink noise input for 96dB @ 1 metre on axis 12.5 volts RMS for the SP1003 versus 11.2 volts RMS for the SP1057. Maybe worth increasing the midrange level?
 
If you can, leave them playing quite loud with full range signal for a few days. you can do this with the two speakers facing each other a few inches apart and some blankets over them if continuous noise is an issue.
The wool linn used is very good and will have been weighed to the designers specs.
They do look a bit over stuffed to me, but free them up and go from there.
 
david ellwood said:
My money is on a change in midrange sensitivity causing the issue. What settings have you got in the aktiv?
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The settings in the Aktiv are flat... with resistors soldered. I could remove the resistors and use the dip switches to try and increase on the mids. I'll see what decreasing the wadding and damping does first.
 
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