Chris Roger's DIY Transmission Lines

[Richard]

Hi tl lovers,

Yes, those are the ones I have Dave, and there's an A4 mag reprint to go with the Badger Sound booklet. (Not being picky but to avoid confusion I'd re-label that first pdf as HFA73 or similar )

To try and put these in order, this is the diy magazine progression (any others?). They are the 70's B139 ones started by Dr Bailey and ending when big boxes went out of fashion. Then, bleak years through the 80's til the 4th from HFN towards the end of the Kan era. There were mods and drive unit substitutions, notably adding the super tweeter to the Baileys and a choice of tweeters accomodated by the Pro9 xover attenuators.

1) Wireless World TL May 1972 Dr A R Bailey - mag reprint - Kef B139, B110, T27, xover DN12 or Radford BD25/1, MD9/2, TD3/2 xover FN10

2) Hi Fi Answers/Cambridge R50 Aug 73 Chris J Rogers - mag reprint and update - Kef B139, B110, T27, ITT STC 4001G xover Cambridge R50

3) Hi Fi News & Record Review April 1976 P Atkinson Kef B139, B110, 2 Coles 3000, Kef T27, Coles 4001K

4) Practical Hi Fi and Audio Pro9TL Oct Nov 76 Chris J Rogers - mag reprint and Badger Sound booklet - Kef B139, Peerless KO40MRF doped, Audax HD12.9 D25 xover Falcon

5) Hi Fi News & Record Review July 91 Richard McDonald - mag reprint - Volt BM220.2 bass, Elac 25DT30 treble.

[Wieslaw Lipowski]

I believe there is one and only project that can be called PRO9 TL, as per Richard:

"Practical Hi Fi and Audio Pro9TL Oct Nov 76 Chris J Rogers - mag reprint and Badger Sound booklet - Kef B139, Peerless KO40MRF doped, Audax HD12.9 D25, xover Falcon"

Originally other tweeters were also welcome - Seas HD 87 and Isophon KK8.

[Scottmoose]

That's about right I think for the '70s publications.

What interests me about these CR designs is that from the text, or at least the way I read it, he was trying to go for a purely aperiodic line, unlike most of the other contemporary TLs, and (possibly) quite close to what Bailey might have originally intentended, if not actually fully achieved. Some of the assumtions in the text are shaky -particularly regarding the taper. The comment 'the quarter wavelength is not as critical as was first thought' is revealing, and gives an interesting historical angle on TL design and development in this era.

[Richard]

Hi Scot

Yes, the Pro9s are quite dry, without an obvious boost, just extension. I've built 2 pairs and they both gave good bass in several different rooms. By comparison I well remember listening to a pair of IMF50s in the late 70's which had so much at one f that I literally had to leave the room feeling sick.

I understand what you mean about approximations reading the text. The line, yes, the isothermal stuffing, the drive unit tolerance. There seems to be so much tolerance in this system and yet it still gives a bass like no other. So, inaccurate possibly, but still having less error than other systems in practice?

That's only the theory though and when you come to build and tune a pair the fun starts. I am lucky to have met a friend of Chris Rogers, another Chris, who sat in with him on the first Pro9 listening and tweaking sessions. They were fine tuned by ear in a domestic room.

He came round a couple of years ago and we've kept in touch since. We had a listen to mine and he rightly pointed me in the direction of removing a little stuffing from the line. (My room is quite large and dry with concrete floor etc and I use CD.) Then there's the xover etc. A look at other diy projects today such as IPL gives an insight.

[Scottmoose]

Well, the resulting system should be sonically accurate as it's near aperiodic -it's just that some of the premices it's based upon are less so. That's more of an issue for pure QWRs and semi-resonant lines though. You can still see the mild effects in ~non-resonant lines though.

One of the major assumptions made 30 years back was that it was the damping in a TL that lowered the speed of sound and ergo, the cabinet 1st mode. What was not appreciated is the effect that the mild taper they gave the line for convenience made on the FR, even in lines stuffed to near aperiodic levels. It surprises me a little that no-one appeared to have bothered making comparative measures of various unstuffed line geometaries and noting the effects.

For interest, attached are two FR plots. I didn't stuff them because it's easier to pick out the differences like this. Same driver used in both, same 80in length. One is a straight line, with a CSA=3Sd (simply as a convenient measure of CSA). The only difference with the 2nd line is that it's tapered in a 2:1 ratio (which CR used for the cabinet under discussion here). Note even with this mild taper the reduction of Fc, and of the harmonic modes.

[Richard]

What I'm getting at is that bass is so hard to reproduce in a domestic room, that, even with errors, the TL seems to be ahead. I heard a pair of PMC at a dealers a while back and immediately felt at home, whatever the exact line design. It may just be that my aural perceptions are now permanently damaged

[Roy Lewis]

Hello

A friend of mine built a pair of Pro 9's, they were good for their day, but let down by the peerless midrange, they sound like look. The small back enclosure really strangles the mids compared with the open bass. He is in the process of changing all that now.

What ever happened to Chris Rogers, also Carl Anthony, they were amongst the most prominent reviewers, etc, in the 70-80's ???

Roy

[John T]

Does anyone remember the original Dalines? The design was published in HFN in (I think) the late '60's or early '70's.

The original article is here:
http://www.tech-diy.com/daline.htm

It's a pity it's unreadable but the drawings give the general idea.

I built a pair and they still reside, submerged, in the cupboard under the stairs! They were pretty compact - c. 90mm h x 35mm w x16mm d. They used three drivers; KEF B110 (bass/mid) and STC 4001G supertweeter - I've forgotten the number of the unit used for the upper mid range but I think it was KEF's original tweeter soon to be superseded by the T27. It featured a Mylar(?) cone approx 40mm.

The originality of this design was that the line was located across the cabinet rather than front to back. It was also meant to be used tight against the rear wall.

[MJKing]

Thanks Dave,

Martin

[Richard]

Hi Roy

Did he use the original doped paper mids or the later polyprops? I built my first in 77 with paper mids and the second pair in 91 with polyprop as the paper had been discontinued.

The polyprops sounded poor and I swapped them for similar size paper Scanspeak 8640 units in enclosures made from lengths of cardboard carpet tubes. They worked well until Falcon managed to get some NOS paper units and doped a pair. Maybe he has the correct units and still doesn't like them in which case then yes try others. I'll gladly buy his originals if they are paper as spares.

Don't know where Chris went and my friend hasn't seen him in ages. Came across one of his Sirac amps a while back too, remember them?