SpeakerTalk

[surv1v0r]

I have acquired a pair of speakers based on the KefKit 3, they are in pretty shabby cabinets and were cheap as a result; all the drivers seem to be in excellent (undamaged) condition and the speakers sound good. I would like (need) to build something smaller that would sound good and based on the T27 tweeter and B110 bass/mid-range units from these speakers. The LS3/5a seemed the obvious choice but people (including my audiophile neighbour who owned a pair) suggest that they lack bass and are somewhat tiring to listen to. Falcon Acoustics who specialise in the LS3/5a suggest that a slightly larger cabinet would make better use of the B110 & T27.

On the basis of these points I have had a look at the P Atkinson Mini-Line Transmission Line speaker design as published in the November 1978 issue of HiFi News & Record Review. It seems to have potential in that the speakers are an acceptable sort of size, were designed my someone who is reputed to have known what he was doing, are extensively braced and use my B110. Sadly however, they were designed with Isophon KK8 tweeters - I am using the T27 tweeters which I happen to have readily available.

I would very much like any advice I can get on passive crossovers I could use with this design. If I knew how to calculate the various values I could perhaps modify the Kef DN12 crossovers from the DIY KefKit 3 speakers. Alternatively (and much more expensively) I could build crossovers based on the Kef recommendations for the T27 & B110. A final and almost certainly unsuitable idea would be to use Falcon Acoustics LS3/5a crossovers. Can anyone help with advice and/or a suitable crossover design please?

For what it is worth, the baffle dimensions of the Mini-Line are 46 cms high X 22.5 cms wide, the T27 are SP1032s, the B110s are SP1003s and I am aiming for crossover at 3,500 Hz (as advised by Kef).

Many thanks.

[SaSi]

IMHO, regarding the mid/high section of the DN12 crossover, you can definitely use that on a TL design. The B110 will be working in a sealed sub-enclosure and should cross to the T27 in the same way it usually does.

I will dare make the step to make an educated guess that there should be no difference in the low/mid section as well, since the sealed enclosure of the Concerto/KEFKIT3 is a different loading of the B139 in the low end of it's spectrum against the TL loading. It just has to do with the resonance point and cutoff frequency rather than crossing it to the B110 which happens upper in frequency.

I would feel pretty safe to use the DN12 crossover and the TL loading of the B139. To err on the safe side, I would make the B110 loading sub-enclosure internal volume according to KEFKIT3 specs, i.e. what your current loudspeakers have. More or less should be in the 5-10lt range, most likely closer to 7lt.

[surv1v0r]

The Atkinson Mini-Line Transmission Line speaker doesn't place the B110 in a sealed sub-enclosure, it is at one end of a 120 cms transmission line the other end of which ends in an open port at the bottom of the cabinet.

I don't know how to include images on this forum but you should be able to see the cabinet details at http://www.scribd.com/doc/96518880/Atkinson-Mini-TL-HFN-Nov78

[habrune]

I've build several versions of the B110A /T27 combi:
In a closed cabinet 5 L with LS3/5a XO: High Q bass somewhat loud, not so deep, indeed somewhat tiring, but good mids, on level with overall response;
In a closed 8L cabinet with KEF CS1a XO, better dampened bass, but somewhat recessed mids by this XO (could listen years to this combi)
tried earlier (more simple) versions of this XO in the same closed 8L box: earlier versions gave more jagged responses (less smooth), but 'had something nice to listen to', but not in the long run;
I've build a concrete pillar, open on top (see avatar), also with CS1a XO, bass goes down to 42 Hz, but with 2 problems: drive units too far apart, and the same CS1a recessed mids)
9L bass reflex enclosure, same performance!! (down to 42 Hz);
The Atkinson Mini Line: more complex to build, but with the same result, bass down to 42 Hz. I could not discover any gain w.r. to the simple 9L bass reflex enclosure. I tried the design version with a Peerless tweeter (not KK8) but was relieved when I applied the more complex kef CS1a XO with the T27: Smooth, clean response, no design errors. The enclosure is appealing, nice dimensions. On the other hand: I could not recognise the specific TL sound, maybe the enclosure is too small for that, with a too short undampened duct.
If you wish to reach the really deep TL bass regions, I advise the DALINE by Robert Fris. I tried those, they really went deep into the 30 Hz regions. (B110A/T27/CS1A). This is my winner for this combi, 9L BR = second. (the earliest lab version of the LS3/5a was a 5L BR enclosure!) (Hm, yes but abandoned...)

For a first XO-trial you could use the components of the DN-12 XO: 2x5uF and the yellow taped 0,25mH coil for the T27 T-filter section; and the 1mH series coil (the one in the B110 section) with the 7uF cap to null for the B110A mid. If You bridge the B110A with a 2mH, 16uF and 10 Ohm (these three in series) you have the early Cresta2 DN13 SP1017 XO, designed for the B110A/T27 2-way. (Cresta has 0,8 mH instead of 1mH).
Without the 2mH/16uF/10Ohm your mids will be too loud; you also will have to restrict the T27 somewhat by putting a resistor (try 1.5, 2.2, 3.3 Ohms) before the first 5uF (as seen from the terminals).

[surv1v0r]

[habrune]

Hi surv1v0r,

I have to admit I skipped the complex building instructions. Way too much work. I build them from 18mm ply (outside) and 6mm inside, and glued (the carefully cut to size) panels cold on the sides. Glue is strong enough (ever tried to take an glued box apart? it breaks but not on the glued joints), and the design has a lot of struts and small oblique panels to hold all the panels together.

If you look at figure 'Inner case complete', you see on the surface of the left side of the box that the inner duct panels are let in into the sides. To do so, you have to cut out 6 mm broad 'canals' that will give room for the inner panels (= the slots). This way you complete the inner case. Next you glue panels 6mm ply to this inner box, this will cover the ugly sight of the slots. This is meant with: build the inner core first, then the outer case. A lot of work! So I skipped it.

Sorry I can't inform you about the exact measures, I rebuild the design, keeping the inner measures exactly the same as the Original.