SpeakerTalk

[hans 67]

Hello all,

some like to know about all the different versions of the LS3/5a.
I do not have heard all the versions (to tell the truth: only 3 recently).
But I follow everything they write and say about it.
Here what I have learned:

1: The 15 Ohm versions have a smoother mid and high. But the bass thumb is stronger, thus the 11 Ohm versions have bass with more grip. Thus a question of taste.

2: The reference cabinet is IT!
I have heard the difference. They play much more easily loud (within the known limits). These are made by Stirling Broadcast.

3: CiCable crossovers are very good but expensive.

The difference between manufactures is small.
And all LS3/5a's are wonderfull!

Greetings, Hans

[terry]

I know very about the LS3/5a. Is it a different crossover design which makes one 11 ohms and one 15 ohms?

[hans 67]

Yes, the crossover makes it a 15 Ohm or a 11 Ohm version. The 15 Ohm uses a transformer for attenuating the tweeter while the 11 Ohm uses resistors. The transformer increases the impedance at higher frequencies.

But:
The early versions had a transformer and used a (selected) B110A. Later on the B110A was replaced by a B110C (has a surround like the B110B but parameters almost like the B110A). When the B110C was introduced then the transformer was skipped and resistors replaced it.

Talking about the 15 Ohm version "means" talking about the version with the B110A!

What is a version with a B110C with a CiCable crossover (transformer is back with the increase in impedance)?

Greetings, Hans

[terry]

[hans 67]

Hello all,

CiCable is a german manufacturer of cables (how surprising) and crossovers. CiCable has a replacement crossover at sale for both the B110A and the B110C versions of the LS3/5a. Yes, 2 different crossovers because the woofer is different. And the tweeter lever is matched to the tweeter level of the original filters. These crossovers are as expensive as a pair of new LS3/5a's!

See: www.cicable.com
Nice pictures of the impedance differences between versions with and without transformer.

Stirling broadcast sells new LS3/5a's with original or CiCable crossover. Both versions (both with the B110C because the B110A is not made any more) can be bought with the original 12 mm cabinet or the better 9 mm cabinet ("reference").

Greetings, Hans

[terry]

Thanks once again Hans
I think that I will have to look more into the details and background of the LS3/5a when I have time.

[MGM]

As for versions of the LS3/5a, I built my own. I was fortunate to purchase two Kef NOS T27s and a pair of the Kef B110 drive units of the version used in the 'BBC no. 1 & 2' LS35as.
The new Falcon Acoustics FL6/23 crossovers were used, and Jerry Bloomfield of Falcon helped me match them to the drivers.
Front baffles and the T27 perforated domes were supplied by Falcon, with Stirling Broadcast supplying the rest of the components.
Two Harbeth LS3/5a cabinets were acquired and the correct terminals for the rear baffle.
Genuine Tygan grilles came from Sid Chaplin, of Traditional Radio Grilles.
The result was the classic LS3/5a sound, and owners of genuine LS3/5as have told me these were the best 'home built ' ones they had heard.
To use a modern expression. I am 'well pleased.'
_________________
M G Miles

[audiolabtower]

Many years ago I got the blueprints for the 3/5a from a friend who worked at the BBC. I got a consortium interested at work and I built around 14 pairs. We got the exact plywood and battens, tygan grill , foam, felt, bitumen pads, etc, the most difficult item was the radio metal core transformers, but we managed to source them and hand wound them to suits the caps. We made our own pcbs, my friend had all the woodworking tools needed for the cabs and veneer. The only thing we could not get was the specially selected B110s. I matched pairs of the ones we bought. We did have a small anechoic chamber at work, but after checking one completed pair it was good enough and I ended up setting the crossover in the remainder on top of my BC1s. Everyone was very well pleased with them, and suitably amazed by the detail and image compared with anything else that size at the time. I now regret not keeping a pair myself but being a perfectionist wanted the correct selected B110s.

The original B110 SP1003 had a neoprene surround which drifted badly in mechanical properties and caused the midrange peak, most now must be out of spec. These are the 15 ohm versions. The replacement had a pvc surround which was much more stable and had better bass performance. Kef did the redesign to get rid of the expensive transformers with their computer equipment and took the impedance down to the so called 11 ohm version to suit modern amplifiers better. Kef supplied kits for all the 11 ohm versions to all the licensees, who therefore only had input on the cabinet.

Unfortunately the selected B110 used in the prototype was right at one end of the production tolerance bell curve, so getting enough units was a real headache, and manufacturers tried hard to sneak enough out just out of spec. Criticism and dissatisfaction with mid range quality in 15 ohm production units within the BBC led to the redesign by Kef. The SP1228 was designed to replicate the prototype original as close as possible while using a superior surround material which would not drift, yet be easily reproducible complete drivers. The transformer taps "set on test" balance was now a resistor ladder network. Frankly I found the 11 ohm version better as long as they were in original thin wall cabinets.

[MGM]

This previous post fascinates me, as it parallels my own build to some extent.
To have the original blueprints must be a big 'Plus.'
I was intrigued by the amount of effort you put in to achieve what you did.

On the thorny issues of selected drive units, 15 ohm compared with 11 ohm, etc. I have to say I wasn't quite so concerned. My reference small speakers are the Harbeth P3ESRs, which to my ears are streets ahead of any LS3/5a.
Consequently, the ultimate performance of my home-built LS3/5as is largely irrelevant as far as I am concerned.
The fact that many listeners have commented on their performance is a plus for me.
In conclusion, the little BBC speaker is a unique design which will continue to interest people.
That must be a good thing...
_________________
M G Miles

[audiolabtower]

I remember the first public demo at the Heathrow Hotel - somewhere I still have the original Rogers brochure for the 3/5 without the "a" yet (they did not have time to produce updated brochures for the show, by then it was superseded by the 3/5a. They were on top of the export monitors, and played Jupiter from the EMI LSO/Previn Planets which was a superb demo recording of the day. Nobody could believe the big speakers were not playing.

[exkefman]