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Old 7th February 2012, 01:03 AM   #51
sreten is offline sreten  United Kingdom
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Originally Posted by Turbon View Post
Nice slapping sreten...

So give your best shot instead and give the forum the chance of scrutinizing your choice.

Brgds
Hi,

That depends on your target numbers, 4ohm sensitivity, box volume,
Qbox and Fbox, might take a look later based on 2 isobaric B139's.

rgds, sreten,
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Old 7th February 2012, 01:35 AM   #52
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If i had 4 B139s, i'd be doing a pair of one of these TLs (i have the ceilings for the straight ones .

Transmission Line Speakers

Click the image to open in full size.

dave
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Old 7th February 2012, 08:20 AM   #53
sreten is offline sreten  United Kingdom
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Default Reply number two

Quote:
Originally Posted by Turbon View Post
Nice slapping sreten...

So give your best shot instead and give the forum the chance of scrutinizing your choice.

Brgds

Hi,

OK, based on these numbers, 70's version of the driver :
8 ohm, 87dB, 3.0mm Xmax, 25Hz Fs, 0.37 Qts, 164L Vas
the only thing things that change for isobaric are :

a) Senstivity is still 87dB but efficiency wise its an 84dB / watt driver.
b) Impedance halves to 4 ohms
c) Vas halves to 82L
d) moving mass doubles

FWIW sealed box for Q=0.7 isobaric pair is 31L, Fbox = 50Hz (-3dB).
100L gives Qbox = 0.5 critically damped, Fbox = 34Hz (-6dB).
A fair compromise is around Bessel, around Q=0.6 (50L).

The numbers are fair enough and show a single driver needs big boxes.
Pity a lot of the time KEF didn't put them in particularly big boxes.
One trick used is about 1cuft with a series capacitor.

Most noteworthy IMO of the above spec is the 3mm Xmax, 6mm pk to pk.
Its pathetic by subwoofer and decent large woofer standards.

Europe Audio

Just by inspecting this TB 8"x12" woofer you can see its very near equivalent to
two isobaric B139's, 4 ohm, Vas is 70L, Fs 27Hz, Qts 0.34, and "efficiency" 85dB/W.

similarly with this Dayton 10" 4 ohm sub :
http://www.parts-express.com/pdf/295-460s.pdf
though here Qts is somewhat higher.

The reason ? The Tangband has an ~ twice as heavy cone as the
B139 and the Dayton even more, approaching 3 times approximately.

The most eyeopening spec is the Xmax for the two above, 12mm, 24mm pk to pk.

If cone areas are the same that equates to +12dB higher maximum
SPL and if sensitivities are the same (which they nearly are) 16 (!)
times the excursion limited power handling in the low bass.

That doesn't sound right does it ? But that is what the numbers say .....

(Perhaps 12mm is pk to pk, but that is still +6dB and 4 times the power handing.
Cross checking though it seems 12mm one way is doable with the above specs.)

FWIW the Isobarik required wall loading for the bass to be able to
keep up with the rest. I'd make the bass/mid c/o active at least
so bass sensitivity can be adjusted to match the mid /treble.

rgds, sreten.

Playing with the TB sealed you get a Bessel, Q=0.57 in 40L.
Same box vented low at 22Hz also looks very good.
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Last edited by sreten; 7th February 2012 at 08:48 AM.
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Old 14th February 2012, 11:34 PM   #54
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Originally Posted by ingenieus View Post
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

I still have a similar system:
  • Speakers: Linn Isobarik
  • Record deck: Linn LP 12
  • Turntable power supply: Linn Lingo
  • Arm: Linn Ekos
  • Cartridge: Linn Akiva
  • CD player: Rega Planet
  • Phono pre-amplifier: Kinshaw Perception
  • Preamplifier: Exposure XI
  • Power amplifier: (x 3) Exposure Super VIII
  • Power supply: Exposure IX
  • Active Crossover: Exposure V

I love the system, and also use it as part of my TV surround sound setup (Bariks are used for L and R speakers and subwoofer). I also use a Pioneer VSX-LX52 with MK Xenon centre and rear speakers.

I'd be interested to hear how your quest for Isobarik sound works out...
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Old 15th February 2012, 06:45 AM   #55
Colin is offline Colin  United Kingdom
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Speaker Builder magazine had several articles and designs for Isobariks in the late 80s and 90s. Some of them went into the principles and why they thought it worth pursuing.

FWIW, I'd have thought modern driver technology could do better now but it depends how much you want to recreate an old, idiosyncratic loudspeaker of questionable hi-fi merit. Remember, Linn were keen at the time to promote the idea that there was no such thing as stereo image - possibly because their speakers weren't very good at it. And yes, I have heard the original Isobariks.
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Old 15th February 2012, 07:17 AM   #56
Boden is offline Boden  Netherlands
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Quote:
Most noteworthy IMO of the above spec is the 3mm Xmax, 6mm pk to pk.
Its pathetic by subwoofer and decent large woofer standards.
Sreten is fully right.

What is even worse with the B139, of the many ones I happened to own in the early 80ties, not a single one measured a Fo below 32 Hz and some had an Fo as high as 38 Hz. Furthermore, the entire moving assembly was aligned so poorly in some cases they started to distort audibly even slightly above domestic listening levels. A nice thing in the late sities and early seventies, a highly overrated driver afterwards.

Eelco
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Old 18th May 2012, 01:41 PM   #57
Julf is offline Julf  Europe
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Originally Posted by Shaun View Post
The level of knowledge in the audio DIY community is orders of magnitude higher today than it was back then when this speaker was on the market. And the problems that gave digital a bad name then have since been mastered. DIYers even have better and more sophisticated tools available now. I
Agree. I am in the process of "restoring" my DMS briks, and turning them into active ones using 4 hypex nc400 amp modules per box (1 each for the woofers, 1 for the mids and 1 for the tweeters), and a digital crossover.
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Old 19th August 2013, 07:58 AM   #58
Bhu108 is offline Bhu108  United States
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Hi the Briks don't use the T27 tweeters !
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Old 19th August 2013, 08:20 AM   #59
Julf is offline Julf  Europe
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Hi the Briks don't use the T27 tweeters !
I think Stuart mentioned the T27's as a "replacement option".

The original 'bariks used the Scan-Speak D2008, and then the made-for-Linn the Hiquphon D20-LP-1(from 1983) or D20-LP-2 (from 1988). The Hiquphon units are still made, but are not cheap. Not sure about the Scan-Speak.
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Old 19th August 2013, 08:24 AM   #60
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A cheaper alternative of push-pull isobaric principle is a clone of the Totem Mani-2. Read the Stereophile rewiev first...... The original uses Dynaudio woofers, the clone (same box size, slightly different tuning) Hi-Vi D6.8-s. Sensitivity and impedance are pretty low (around 83-84 dB, and 3 ohms), but the bass for the size of the box is astonishing, in-room you can get down to 26-28 Hz.
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