The Mani-2 seems to be a "vented push-pull", so not quite the same as the Linn isobarik design.
I assume the review is full of the usual Stereophile hyperbole?
Well, I've had the chance to hear the Sara's, and the Mani-2-s too, (because I designed them.. 
) so before you quickly jump to judgements, do yourself a favour, and at least TRY to hear them before you give your "hyperbole" verdict.... I am sure that you will hear the difference. Anyway, you are right in the respect, that the M-2'-s are vented designs, not like the the Linn's. Also, the Mani-2 is a push-pull (back-to-back) woofer configuration,(as you noted correctly) which helps to cancel the bass nonlinearity of the drivers.
) so before you quickly jump to judgements, do yourself a favour, and at least TRY to hear them before you give your "hyperbole" verdict.... I am sure that you will hear the difference. Anyway, you are right in the respect, that the M-2'-s are vented designs, not like the the Linn's. Also, the Mani-2 is a push-pull (back-to-back) woofer configuration,(as you noted correctly) which helps to cancel the bass nonlinearity of the drivers.
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Well, I've had the chance to hear the Sara's, and the Mani-2-s too, (because I designed them..
My "hyperbole" reference was in respect to Stereophile, not the actual speakers. I agree with you - try to get to hear them, rather than rely on something like the Stereophile.
Indeed, back-to-back is in general the better way to do it.
Back to back is not as good as face to face, for low distortion LF- the coupling volume is necessarily larger for it, compared to a clamshell. It'll play higher, though, so there's a tradeoff there.
For distortion cancellation the volume of air (assuming either a back-to-back or clamshell) is a key limitation.
The ONLY reason to use face-to-back mounting as linn did is for a smaller box for a given voltage input. More power handling? Sure, it doubles- just like the doubling of input power required for a given SPL. The individual coils see as much as they would in a box twice the size for a given SPL.
For distortion cancellation the volume of air (assuming either a back-to-back or clamshell) is a key limitation.
The ONLY reason to use face-to-back mounting as linn did is for a smaller box for a given voltage input. More power handling? Sure, it doubles- just like the doubling of input power required for a given SPL. The individual coils see as much as they would in a box twice the size for a given SPL.
I am old enough to remember the sound of the Linn Isobarik. Not much treble and the bass was nothing to brag about either. In the parlance of Stereophile; "When listening to familiar music, it's as if veils had been dropped".
Two decades ago I made the isobaric from 10" Seas woofers. Method ref. fig.C was applied getting the lowest possible volume between the drivers. Q for back chamber approx 0,57. The low bass appeared to perform very good. My experience is to keep the xo point low as this is not a good solution for the mid-bass (in my not so humble opinion).
Was that the "domestic" (passive) or "professional" (active) version?
The Linns I heard were the SARA's. I believe it was their first WAF approved design. I read that because of the isobaric design, they had great bass for such a small speaker. I was eager to hear them because I wanted to build some isobariks of my own. Unfortunately, they didn't seem to have much bass below 80hz.
Ah, yes, the SARAs were OK for their size, but nothing like the "proper" isobariks.
The Isobarik DMS/PMS did have some compelling properties back then, the biggest being transient power/punch, bass extension & dynamics. Tonally, it was a bit colored and the upward facing drivers created a diffuse soundfield somewhat at odds with the punchy character. It's fair to say they sounded best with rock, jazz -- music with lots of rhythm. They were great audiophile party speakers. Not as good with classical. The Isobarik design seemed ingenious, but in retrospect, it was a product of its time -- ie, full computer modelling of drivers, cabinets & xovers had not yet come, and driver technology was not as advanced.
I agree with sreten that the right choice of a single modern bass driver can equal or better the performance of the old briks today in a similar size sealed enclosure. As for the rest of the range, the bextrene cone KEF B110 wasn't very linear in the mids & easily bettered by many mid drivers today. It needed lots of freq. tailoring in BBC's LS3/5a to provide the neutral sound those speakers are famous for. The Scanspeak D2008 tweeter is still good by today's standards but certainly no world beater.
I have intimate knowledge of the DMS/PMS of the mid 80s -- was a Linn/Naim dealer in those days and modded a handful of them (for active or to revert to passive in one case).
I agree with sreten that the right choice of a single modern bass driver can equal or better the performance of the old briks today in a similar size sealed enclosure. As for the rest of the range, the bextrene cone KEF B110 wasn't very linear in the mids & easily bettered by many mid drivers today. It needed lots of freq. tailoring in BBC's LS3/5a to provide the neutral sound those speakers are famous for. The Scanspeak D2008 tweeter is still good by today's standards but certainly no world beater.
I have intimate knowledge of the DMS/PMS of the mid 80s -- was a Linn/Naim dealer in those days and modded a handful of them (for active or to revert to passive in one case).
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I have used dual isobaric to make a much better sub for a given box size than sealed, given that I had a number of woofers to utilize purchased on clearance. By putting them in a force-cancelling arrangement of dual clamshells, I got some serious performance advantages over a single woofer in the same box volume- double the displacement, four times the power handling, lower distortion, and force cancellation.
So yes, while one could use a 3dB less efficient woofer to get the same box size, the "right" woofer may not always be available, and if one gets a bargain, or has an inventory of, existing woofers, it can be a nice method to allow some design flexibility.
I wouldn't advocate piggyback or magnet-magnet isobaric though, there seems to be very little argument for either of those methods.
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I have used dual isobaric to make a much better sub for a given box size than sealed, given that I had a number of woofers to utilize purchased on clearance. By putting them in a force-cancelling arrangement of dual clamshells, I got some serious performance advantages over a single woofer in the same box volume- double the displacement, four times the power handling, lower distortion, and force cancellation.
So yes, while one could use a 3dB less efficient woofer to get the same box size, the "right" woofer may not always be available, and if one gets a bargain, or has an inventory of, existing woofers, it can be a nice method to allow some design flexibility.
I wouldn't advocate piggyback or magnet-magnet isobaric though, there seems to be very little argument for either of those methods.
Sorry if this has been answered already. Jerryo asked why would Linn put the crossover in the space between the 2 bass drivers. From a vibrational point of view, this is a very clever place to put the crossover, since this space has (theoretically) no sound pressure at all, and is akin to placing the crossover outside the cabinet, which many consider beneficial.
Plus it saves on other box space and stiffens the isobaric behavior by reducing volume. Only concern would be woofer magnetism screwing with the XO.
Exactly right. Interestingly, there were two passive 3-way xovers in there, one for each set of speakers; the speaker system was essentially two 3-ways.
Yup. This is one of the reasons why in later versions (~1988 & later), Linn went to a single model for the Isobarik (instead of DMS & PMS for passive/active), with 3 pairs of banana jacks for highs, mids & bass, putting the huge single xover (optimized for dual drivers in each band) into the bottom of the steel stand, which was enclosed on 3 sides with MDF.
If that's an advantage, why (in project) not just reducing the distance between drivers to the desirable (stiffness) final volume (between drivers).(?!)Hmmm!
Fair points made about the location of the crossovers, however I do not think they were positioned there in order to reduce the volume, as there many more elegant ways to do this. I also cannot think it would be an advantage to the inductors of the crossover to be so close to the bass driver magnets. Positioned as the were, the crossovers are also very difficult to access, with each driver being siliconed into place and with a flat cloth bag of cotton wadding stretched across the back of them. Then there is the construction: routing the wiring in and out of the inter-driver space with all that hot melt glue squeezed all over the place to fill the holes that the wires go through; not what I would call a satisfactory method, nor time efficient. No wonder they were so expensive!
Actually, I cannot think of any logical reason to place the crossovers where they were placed. I removed them from their original position and mounted them on the rear panel, which is now removable (still hermetically sealed) when I had to replace burnt out parts when I bought them.
Fair points made about the location of the crossovers, however I do not think they were positioned there in order to reduce the volume, as there many more elegant ways to do this. I also cannot think it would be an advantage to the inductors of the crossover to be so close to the bass driver magnets. Positioned as the were, the crossovers are also very difficult to access, with each driver being siliconed into place and with a flat cloth bag of cotton wadding stretched across the back of them. Then there is the construction: routing the wiring in and out of the inter-driver space with all that hot melt glue squeezed all over the place to fill the holes that the wires go through; not what I would call a satisfactory method, nor time efficient. No wonder they were so expensive!
Actually, I cannot think of any logical reason to place the crossovers where they were placed. I removed them from their original position and mounted them on the rear panel, which is now removable (still hermetically sealed) when I had to replace burnt out parts when I bought them.
Oops!
This was not what I meant to confirm -- "Plus it saves on other box space and stiffens the isobaric behavior by reducing volume."
Rather, this was what I meant to confirm (not quite used to the way the forum software quoting works):
This was not what I meant to confirm -- "Plus it saves on other box space and stiffens the isobaric behavior by reducing volume."
Rather, this was what I meant to confirm (not quite used to the way the forum software quoting works):
As I wrote earlier, Linn did consolidate the active & passive versions around '88~'89 by going with one version that had terminals for each pair of parallel-wired drivers that could be drive by three amps directly or connected to an external passive crossover in the stand.
Although by its name, isobaric, implies that there is no pressure change within the cavity between the two drivers, this is not actually true. A simple analysis or measurement will reveal this.
Linn used the isobaric technique simply to get the right driver parameters for their chosen box volume and lf limit, something that was not readily available at the time from a single driver, and they were not about to manufacture a custom driver.
Isobaric produces the equivalent of a single driver with double the moving mass, double the Bl and half the impedance, but wastes the output capability that usually two drivers would give. Not a good trade off.
Interestingly, do you know on of the reasons for using the B139? Its because it was the only driver unit that would pass through its own hole!! Think about it, how did they mount the internal driver.....they mounted it through the hole for the front driver by rotating it sideways. You cant do this with a round driver!
And do you know why KEF made the B139 in the first place? At the time there was an extra sales tax on professional speakers. Professional was defined as any speaker having a driver of 10" diameter or greater. By making it 13" x 9", technically KEF could claim it was only 9" wide, avoiding the tax, while its till had the area of a 10" driver.
Linn used the isobaric technique simply to get the right driver parameters for their chosen box volume and lf limit, something that was not readily available at the time from a single driver, and they were not about to manufacture a custom driver.
Isobaric produces the equivalent of a single driver with double the moving mass, double the Bl and half the impedance, but wastes the output capability that usually two drivers would give. Not a good trade off.
Interestingly, do you know on of the reasons for using the B139? Its because it was the only driver unit that would pass through its own hole!! Think about it, how did they mount the internal driver.....they mounted it through the hole for the front driver by rotating it sideways. You cant do this with a round driver!
And do you know why KEF made the B139 in the first place? At the time there was an extra sales tax on professional speakers. Professional was defined as any speaker having a driver of 10" diameter or greater. By making it 13" x 9", technically KEF could claim it was only 9" wide, avoiding the tax, while its till had the area of a 10" driver.
A Linn Isobarik PMS clone for the 21st century
I would be interested in the simple analysis.
I would be interested in the simple analysis.