A Linn Isobarik PMS clone for the 21st century? - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st July 2011, 11:49 AM   #1
diyAudio Member
 
Join Date: Apr 2011
Location: Pretoria
Default A Linn Isobarik PMS clone for the 21st century?

In the late eighties, I had the opportunity to listen to one of the classic setups of the day.
  • Linn Sondek LP12 turntable, with Linn Ittok tonearm and Linn Asak cartridge
  • Naim NAC32 preamp with SNAPS power supply
  • Naim NAXOS active crossover
  • Naim NAP250 power amp (3 of them)
  • Linn Isobarik DMS loudspeakers

This inspired me to gather all the pieces for myself. I only got to one NAP250 and had to make do with Linn Sara speakers . Life happened and I never got to own a pair of Briks, as they are called by those in the know.

The things is, I still want to. The memory of the sound they made has remained with me all those years. They are now long out of production. Some are still around in secondhand form on eBay e.a. but the sellers are invariably on the other side of the globe. Around here there are none to be had. Considering the original price, I don't think the local importer sold many.

I am therefore toying with the idea of creating a modern clone of this beast.

Click the image to open in full size.

The first problem is that the oval woofer (KEF B139) is also long out of production. There are of course two of them, the second one being inside the cabinet in an isobaric configuration. Yes, I know it's obvious but there may be readers who do not know that.

The piston area of the B139 is about the same as that of a round 10-inch driver - a good place to start investigations. There is a Linn replacement for the B139 but the price would probably make your eyes water. The midrange (Kef B110) is also long gone but at least it is conventional in shape. The tweeters were made by Scanspeak.

The second problem is that the Isobarik does not yield its inner secrets easily. They were notoriously difficult to dismantle and most owners left well enough alone. The only clues that I have is the image attached below. I also have the patent documents and a contemporary review that goes into some detail of the internal construction, if there is any interest.

The passive Isobariks were notorious for present a very difficult load to an amplifier. Electrically the crossovers were two three-ways in parallel. I am therefore thinking of going active with this one. It would make the tuning of the crossover easier, but at added cost. Then again, the passive crossovers will be far from cheap.

Any thoughts on the viability of such a mad project?
Attached Images
File Type: jpg briks5.jpg (97.8 KB, 1156 views)
  Reply With Quote
Old 21st July 2011, 11:57 AM   #2
diyAudio Member
 
Join Date: Dec 2004
Wasn't this a Linn Isobarik for the 21st century?

Linn Ketltik
Attached Images
File Type: jpg Keltik.jpg (128.0 KB, 1131 views)
  Reply With Quote
Old 21st July 2011, 03:09 PM   #3
diyAudio Member
 
Join Date: Apr 2011
Location: Pretoria
Ah yes, the Keltik. Those are the very woofers that I refer to in post 1.

I don't know much about them and have never heard them in action. From what I can gather, they never quite attracted the same fanatical following as the Bariks. Kind of like when Porsche tried to replace the 911 with the 928. Except that in this case the Isobarik and Keltik are both no more.

Unfortunately, cloning the Keltik would be quite impossible with round woofers. But if anybody has any info on them, I would like to know more. Google turns up little except second-hand ones for sale.
  Reply With Quote
Old 21st July 2011, 04:13 PM   #4
diyAudio Member
 
Join Date: Oct 2005
It will be difficult to reproduce the tonality (or your memory thereof) of the original with modern speaker drivers. But it sure is an interesting project!

Fyi Tang band produces pretty decent oval woofers at a reasonable price. It wou.d be cool to keep the same overal look and feel. Check them out.
I don't have access to winisd at the moment, but i seem to remember that this program can simulate isobarik configuration, also worth checking.
  Reply With Quote
Old 21st July 2011, 04:19 PM   #5
diyAudio Member
 
Join Date: Dec 2004
The Keltik is a right old belter of a speaker, I remember walking into a Hi Fi show in the late 90's thinking there was a live band.

It happened to be a pair of Ketliks, actively driven and fed from an LP12 filling an entire ballroom with sound, very impressive.
  Reply With Quote
Old 21st July 2011, 04:52 PM   #6
diyAudio Member
 
Join Date: Apr 2011
Location: Pretoria
Quote:
Originally Posted by talaerts View Post
It will be difficult to reproduce the tonality (or your memory thereof) of the original with modern speaker drivers.
Matching the original sound is not that important. It was a long time ago. All I can remember is the deep bass and the dynamics. As long as the 2011 (or should that be 2012) version sounds good, I will be happy.

Quote:
Originally Posted by talaerts View Post
Fyi Tang band produces pretty decent oval woofers at a reasonable price. It wou.d be cool to keep the same overal look and feel. Check them out.
They do indeed have something that is a very close match.

Click the image to open in full size.

http://www.tb-speaker.com/detail/1208_03/w8q-1071f.htm

The dimensions are 308 x 214mm.

Click the image to open in full size.

Here is the cutout required for a B139.

Click the image to open in full size.

The dimensions of the hole add up to 300 x 210mm. The KEF datasheet (see below) also gives the second dimension as 210mm, although the first is not stated.

All of a sudden this project looks a whole lot less hypothetical...

EDIT: I have found this driver on sale and the price looks right:
http://www.parts-express.com/pe/show...&FTR=W8Q-1071F

Only one problem - it has an impedance of 4 ohm. This means that each woofer will needs its own amp, or the LF amp will have to be stable at 2 ohm and lower. Did I mention that it will be an active speaker?

Hat tip to talaerts!
Attached Images
File Type: gif B139small.GIF (57.9 KB, 90 views)

Last edited by ingenieus; 21st July 2011 at 05:21 PM.
  Reply With Quote
Old 21st July 2011, 05:51 PM   #7
diyAudio Member
 
Join Date: Apr 2011
Location: Pretoria
I'm pencilling in this unit for the midrange. The only reason at this stage is that it is also from Tang Band. That should count for something.

Click the image to open in full size.

Click the image to open in full size.

http://www.tb-speaker.com/detail/1208_03/w5-704d.htm

Last edited by ingenieus; 21st July 2011 at 05:54 PM.
  Reply With Quote
Old 21st July 2011, 06:58 PM   #8
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
I have taken a pair of isobariks apart... went on an isobarik building run shortly after.

There are no issues building something using the same concepts... you'd have to work to get a system today with the same personality/coloutful sound as these. ie you can do much better.

Personally, i would take the concepts & approach of the Castle-style microTower and add isobarik bass. I do beleive that isobarik does bring more benefit than just allowing use of a box ~1/2 the size. With the wide choice of drivers today thou, one has to carefully consider whether spending 2x as much on a single woofer can get you more.

I wouldn't get stuck on using an oval woofer.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 21st July 2011, 07:55 PM   #9
jerryo is offline jerryo  Isle of Man
diyAudio Member
 
Join Date: Jun 2007
I have owned a pair of DMS Briks for a few years that I bought from a house clearance and paid 50.00 for them; they did have all the tweeters blown and the relevant crossover parts were also fried but with a little patience I took them apart and fixed them. I cannot claim that they are as good as new but they do sound great. What were Linn thinking by putting the crossovers in the cavity between the Isobarik loaded bass drivers?!
Personally I think you should buy the actual drivers used, as they come up on ebay quite frequently; you will have to bite the bullet with the purchase and shipping costs but if you want that sound......! The cabinet is complex but not that bad and could be easily improved upon.
Go for it..............
  Reply With Quote
Old 22nd July 2011, 09:02 AM   #10
diyAudio Member
 
Join Date: Apr 2011
Location: Pretoria
At this stage, the most vexing question for me is just how those midrange enclosures look and how they line up. Any detail that you guys who've been there and done the Isobarik dismantling can fill in the missing gaps, it would be much appreciated.

I still have the Sara's on hand to dismantle and investigate the bass bin construction, which should be similar. Come to think of it, I've done that twice to replace fried woofers. (Start of rant) Naim amplifiers does not have any DC offset protection of any kind. Any relays in the output would degrade the sound quality in some mysterious way. And our world famous amplifiers never break down anyway. (End of rant)
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
21st century tube? Non-Vacuum Trout Tubes / Valves 4 1st February 2009 02:18 PM
PMS plus Avalon clone equals ??? fsammet Multi-Way 9 5th May 2007 07:07 PM
alpheus or PMS? stephen Bishop Multi-Way 0 28th October 2006 03:38 AM
Dantax century Luckyme Multi-Way 0 14th March 2004 03:51 PM


New To Site? Need Help?

All times are GMT. The time now is 09:31 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2