Linn Sara to EPOS ES14s - An insight

[pure sound]

Griffin got their Isobarik patent about the same time as Linn. Still some of those big Griffin around.

Someone recently sent me some images of a speaker that was made by Ariston which used Isobaric loading. Is this another example of an Ariston idea being 'borrowed' by Linn? What history is there regarding the origin of these speakers?

 

[Gaius]

Someone recently sent me some images of a speaker that was made by Ariston which used Isobaric loading. Is this another example of an Ariston idea being 'borrowed' by Linn? What history is there regarding the origin of these speakers?

Are these definitely pics of an Ariston speaker?

Are they older than Linn's Briks?

 

[pure sound]

The owner, a very chatty woman, was asking me for Isobarik grilles but these speakers appear to have a long, one piece grille that rolls around the top front edge. She said they were Ariston Isobarics, not sure of the date of origin.

 

[Joddle]

Never seen any of those before - a bit like Briks but the tweeters seem different as does the cabinet shape.

Re the Sara I was imagining something much smaller - say just a little taller than a real Sara but with enough space to form a chamber for a good mid range unit (not necessaraly a b110 - something with a bit more power handling!). I have never really understood why Briks need two tweeters and two mid range units unless to give additional power handling - but is this then at the expense of phase handling? Why not one good tweeter and one good mid range?

 

[david ellwood]

isobarik is a bass loading arrangement. it does nothing for the midrange.

The saras would benefit from not having the mid go to the back driver.

it might benefit from time alignment also, accounting for the time it takes the air to travel between drivers.

 

[sybil]

The speakers above are the original 1974-77 Linn Isobariks. They are the same dimensions as later Bariks, just turned round 90 degrees. They would originally have had Kef T27 tweeters as per the KefKIT 3 but these appear to have been replaced with Scanspeaks at some point. I had a pair like this in about 1998 which had a small metal plate on top enscribed 'Linn Isobarik, Patents Pending, SN 003'. They were from about 1974 and were driven by a Naim 12/160. They sounded pretty dire to be honest.

James.

 

[pure sound]

I found a thread on the Linn forum about the above speakers.

http://forums.linn.co.uk/bb/showthread.php?tid=21890

 

[Joddle]

isobarik is a bass loading arrangement. it does nothing for the midrange.

The saras would benefit from not having the mid go to the back driver.

it might benefit from time alignment also, accounting for the time it takes the air to travel between drivers.

I think most people would agree that the isobaric arrangments on the Saras is not absolutely ideal as the mid range is also covered by the B200s and therefore there is a problem in timing for higher fequencies - but taking the mid range off the rear speaker does not then leave an ideal situation for the mid range as the front b200 would be working in a strange confiiguration of a sealed box but with a flexible end to it - albeit of relitively constant volume due to the bass changing both speakers at the same time. I don't think we would really know how this would sound until someone actually tried it! Anyone up for an experiment?

I still think a mini Brik may be the answer 2 B200s, one mid and one tweeter - a possible project!

 

[flatpopely]

isobarik is a bass loading arrangement. it does nothing for the midrange.

The saras would benefit from not having the mid go to the back driver.

it might benefit from time alignment also, accounting for the time it takes the air to travel between drivers.

David you fail to understand the principal.

 

[RustyB]

No, it is you who fails in this.

Designing an "Isobaric" 3-way system is a predictable exercise.

When the Sara appeared, the talk was around the difficulty of making such an arrangement work satisfactorily in a 2 -way.

The reason for this is the unpredictability of the behaviour in the mid range where the audio wavelengths are comparable to the dimensions of the Isobaric chamber, and as David alluded to, the problem of time-delayed output from the rear cone impinging on the front cone.

Linn's solution was to heavily damp the chamber in order to soak up as much of the rear driver's midrange output as possible.

In summary, the "isobaric" or compound coupling is only a positive contributor in the bass, a liability elsewhere.

 

[Yank]

I have never really understood why Briks need two tweeters and two mid range units unless to give additional power handling - but is this then at the expense of phase handling? Why not one good tweeter and one good mid range?

I think there's two complementary reasons - to keep the nominal impedance the same across the frequency range, and for a sort of omnidirectional pattern. For people who are too busy tapping their feet to care about stereophony.

For the Sara they came up with a different solution for the impedance problem, they just put in a second high-pass crossover feeding a dummy load.

 

[Joddle]

I think there's two complementary reasons - to keep the nominal impedance the same across the frequency range, and for a sort of omnidirectional pattern. For people who are too busy tapping their feet to care about stereophony.

For the Sara they came up with a different solution for the impedance problem, they just put in a second high-pass crossover feeding a dummy load.

Using two speakers instead of one simply to offer the same load to the mid and high seems strange - why not just use a different tweeter and mid rage of higher impedence or use two bass units of higher impedence to match the mid and high. Anyway they could have used the Sara principle of a dummy load but then what a waste of power. I also never really understod why Linn did not simply couple the B200s togather in the Saras and treat them as a single speaker instead of using two crossovers - was it simply a lack of impedence options on the drive units or something else?

Regarding Yanks comments I think more likely the reason for multiple speakers on the Briks was to give a wider sound stage but having never heard Briks I can't possbily comment on how effective or not that is.

 

[flatpopely]

No, it is you who fails in this.

Designing an "Isobaric" 3-way system is a predictable exercise.

When the Sara appeared, the talk was around the difficulty of making such an arrangement work satisfactorily in a 2 -way.

The reason for this is the unpredictability of the behaviour in the mid range where the audio wavelengths are comparable to the dimensions of the Isobaric chamber, and as David alluded to, the problem of time-delayed output from the rear cone impinging on the front cone.

Linn's solution was to heavily damp the chamber in order to soak up as much of the rear driver's midrange output as possible.

In summary, the "isobaric" or compound coupling is only a positive contributor in the bass, a liability elsewhere.

I'm not getting this, was the Sara only designed to be isobaric in the bass? What is the crossover frequency of this?

If this so why is the rear fed the same signal as the front, even down to the dummy tweeter load.

What you are saying and Linns implementation don't match.

 

[Mr Tibbs]

I'm not getting this, was the Sara only designed to be isobaric in the bass? What is the crossover frequency of this?

If this so why is the rear fed the same signal as the front, even down to the dummy tweeter load.

What you are saying and Linns implementation don't match.

Isobaric loading is good in that it extends bass response in a small sealed box. The problem with the Sara implementation is that the same drivers are covering the midrange. OK WRT the front driver. Not OK WRT the rear driver.

It therefore might be better if only the front driver reproduced the midrange and this is achieved by filtering the signal to the rear driver so that the rear driver only covers the bass range.

At least that's how I understand it from the comments above.

Mr Tibbs

 

[flatpopely]

Isobaric loading is good in that it extends bass response in a small sealed box. The problem with the Sara implementation is that the same drivers are covering the midrange. OK WRT the front driver. Not OK WRT the rear driver.

It therefore might be better if only the front driver reproduced the midrange and this is achieved by filtering the signal to the rear driver so that the rear driver only covers the bass range.

At least that's how I understand it from the comments above.

Mr Tibbs

But then the two drivers will be fighting each other in the mid range.

 

[Joddle]

I'm not getting this, was the Sara only designed to be isobaric in the bass? What is the crossover frequency of this?

If this so why is the rear fed the same signal as the front, even down to the dummy tweeter load.

What you are saying and Linns implementation don't match.

The Sara crossover is 3khz - a little higher than in the Naim SBL (2.7khz) but understandable as the B200 is a smaller drive unit than in the SBL and therefore quite able to carry more of the mid range.

The problem is the Sara isobaric unit is trying to reproduce from 30hz to 3khz whereas in a true brik the isobaric part only handles up to 200 hz. In a Brik from 200 to 2.7khz is fed to the mid range units. This means in practice that the Sara isobaric unit is trying to cope with the entire bass and middle ranges of a Brik in one go - and that is its potential weakness.

What some people are advocating is that perhaps it would be better to filter what gets to the rear B200 in a Sara so the front driver only handles from 200hz to 3Khz but both B200s handle from 30 to 200 Hz - but I think perhaps that would present even more issues!

 

[Mr Tibbs]

But then the two drivers will be fighting each other in the mid range.

Not at all. If you could effectively 'kill off' all the midrange output from the back driver then the front driver would still cover the midrange without a problem and the isobaric bass would continue to function as if the filter wasn't there. Linn attempted to do this by heavily damping the back chamber but a more effective approach would be to prevent (filter) the midrange from going to the back driver in the first place.

Mr Tibbs

 

[flatpopely]

Not at all. If you could effectively 'kill off' all the midrange output from the back driver then the front driver would still cover the midrange without a problem and the isobaric bass would continue to function as if the filter wasn't there. Linn attempted to do this by heavily damping the back chamber but a more effective approach would be to prevent (filter) the midrange from going to the back driver in the first place.

Mr Tibbs

But my question stands, that above arrangement must mean the drivers will not be in sync over a wide frequency range.

 

[Joddle]

But my question stands, that above arrangement must mean the drivers will not be in sync over a wide frequency range.

Not actually sure what you are trying to say here.

Of course if a filter was applied to the rear B200 then the isobaric principle would only apply to the frequencies below the filter point i.e. and so for those frequencies the speakers would be in sync.

For frequencies above the filter only the front speaker would be driven so it would act as the only mid range unit. The speaker in the rear would in effect be stationary as it and the front would be moving in tandem for the bass thus giving a constant volume box in theory - so yes you are right in that the front and rear speaker would not be in sync, but only for those frequencies.

 

[flatpopely]

Not actually sure what you are trying to say here.

Of course if a filter was applied to the rear B200 then the isobaric principle would only apply to the frequencies below the filter point i.e. and so for those frequencies the speakers would be in sync.

For frequencies above the filter only the front speaker would be driven so it would act as the only mid range unit. The speaker in the rear would in effect be stationary as it and the front would be moving in tandem for the bass thus giving a constant volume box in theory - so yes you are right in that the front and rear speaker would not be in sync, but only for those frequencies.

As that's a bad thing.