Can one build a better (non) LS3/5A speaker based on T27s & B110s? - diyAudio
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Old 1st October 2014, 11:41 AM   #1
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Question Can one build a better (non) LS3/5A speaker based on T27s & B110s?

You can buy a brand new Swiss watch costing thousands of pounds which will be no more and quite possibly less accurate than a digital watch from the far East and costing a few tens of pounds - I spent eight years working for a major UK Jeweller

You can buy a pair of late(ish) second-hand Kef T27s and Kef B110s for less than a hundred pounds.

A pair of BBC LS3/5As will cost you hundreds of pounds on the Bay.

Falcon Acoustics are now manufacturing brand new T27s (144 a pair) and B110s (also 144 a pair) and will sell you a pair of assembled replica LS3/5As with the 15 Ohm FL6/23 crossover for 1,200! A full cabinet kit without speakers but with a crossover will set you back 311.

According to the BBC White Paper (RD1976/29), the LS3/5A cabinet measures 31 cms high by 19 cms wide by 16 cms deep and has a free volume of a little under five litres.

Aside from the obvious requirement that the speaker should accurately reproduce sound, two key BBC design requirements for the LS3/5A were that:
  1. it should be as small as possible consistent with an adequate axial response / frequency characteristic in order to allow use in environments where monitoring on headphones was not satisfactory and yet there wasn't sufficient room for a 'Grade I' monitor - e.g. Outside Broadcast vans.
  2. examples of it should be 100% consistent and interchangeable.
Kef's specification for the B110 suggests a totally enclosed box of five to ten litres should be used.

In a document dated July 1985 describing the construction of a replica LS3/5A, Falcon Acoustics recommended that the depth of the cabinet could usefully be increased from 16 cms to 23cms for a more extended bass.

My question is whether one can build a better sounding small speaker based on the Kef T27 and B110 and if so, what would be its characteristics? I would appreciate it if the discussion could concentrate on just these two drivers and start from the original BBC LS3/5A design. I am interested in hearing views based on the dimensions (e.g. making the cabinet twice as deep -or- twice as deep but triangular), cabinet materials (e.g. braced 25 mm MDF rather than 12 mm birch ply) and (passive) crossover design.
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Old 1st October 2014, 12:51 PM   #2
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Without wanting to immerse myself into the middle of a heated argument, let's see some facts:
Anyone ever experienced the sound of (any derivative) of the LS3/5-s must admit that they deliver some kind of magic, that was typical with many of the british audio products of the 70's and 80's, like the Spendor BC1, Celestion SL6 series, Linn turntables, Naim and Quad amps etc.
Perhaps the most persistently returning piece of that era is the LS3/5, seeing dozens of copies, rebuilds, upgrades with more or less success. Its design principles were simple, possibly the smallest box with accurate vocal and instrumental reproduction, good sense of presence in the recording environment (they were designed as on-site monitoring speakers), but the execution of the idea was rather elaborate:
non-optimal box volume, with elevated upper bass region to compensate the lack of low bass, deliberately "voiced" crossover to correct the driver's (rather uneven) response and many other factors.
In its age it was an excellent product - not many other similarly sized speakers could match its abilities- but then, almost 40 years passed, and while speaker technology has advanced only 10 feet compared to the miles of other areas in electronic design, by today's standards and available drivers, it is a seriously outdated product, posessing mostly nostalgical and "cultic" values.
Again, I am not trying to discourage, or talk anyone out of building an "upgraded" LS 3/5, but for the same money today you can build a much better speaker. The surface treated Bextrene cone of the B 110 is well known for its excellent internal damping, but also fot its "slowness", while the T27 is a simple plastic (Melinex- a derivative of Mylar) dome tweeter. The main trick here (as almost always) is the XO design, which involved a lot of individual listening and tweaking tests, and that's why the end result is still catching a lot of attention in the audiophile community.
But then again, take a similar (altough significantly more costly) example of a recent 2-way 5" woofer 3/4" dome model -like the Sonus Faber Signum- (that I'am listening right now), and you will understand all my caveats. It sits right next to my venerable Rogers LS3/5-s, and.... well really it is no real "race" between the two speakers, the Fabers just simply eat them for breakfast, in all areas.
I am prepared to take all hail coming from LS 3/5 aficionados, but then, do yourself a favour, and get (borrow, steal, build) a decently made similarly sized box with drivers available today (Scan-Speak, SB Acoustics, Vifa), and you will see what I am trying to tell you......
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Old 1st October 2014, 08:08 PM   #3
Lojzek is offline Lojzek  Croatia
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Quote:
Originally Posted by surv1v0r View Post
My question is whether one can build a better sounding small
speaker based on the Kef T27 and B110 and if so, what would
be its characteristics?
According to replacement B110's TS parameters Falcon Acoustics
provides, I believe there is room to improve the performance over
Sterling's LS3/5 speaker

BBC LS3/5a loudspeaker Stirling Measurements | Stereophile.com

in the sense of having more bass extension(reflex loading) and voicing
the speaker for flatter midrange FR. It remains unknown which version
would sound better, the original or DIY version. I would bet on DIY.
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Old 1st October 2014, 09:03 PM   #4
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Don't fall into the trap of assuming that a thicker cabinet would be an improvement. Read the BBC published paper by Harwood where he shows that thinner walls with heavier damping (a greater damping to mass ratio) is the only way to reduce cabinet resonances.

I think you could do better than the LS3/5a today, but primarily if you used better current drivers. The B110 SP1003 was good but not especially consistent. The T27 is not a very good tweeter. I thought the first several units I measured were defective. There are plenty of tweeters with higher sensitivity, smoother response, greater extension and lower distortion near resonance.

More cabinet volume would help and attention to cabinet diffraction would improve system response smoothness, especially if a grille isn't required.

David S.
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Old 1st October 2014, 09:22 PM   #5
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I believe I recall reading that a slight bump was built in at 120 hz to fool the ear
into believing the bass went a little lower. This might explain why the box volume
isn't quite as large as that recomended by KEF.
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Old 1st October 2014, 10:16 PM   #6
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Quote:
Originally Posted by speaker dave View Post
Don't fall into the trap of assuming that a thicker cabinet would be an improvement. Read the BBC published paper by Harwood where he shows that thinner walls with heavier damping (a greater damping to mass ratio) is the only way to reduce cabinet resonances.
I was under the impression that thick and thin wall cabs solve the inherent resonance problems in different ways but with hopefully similar results.


Thin walls with heavy damping deal with the resonant frequency by lowering it to below audible levels. Very much like correctly matching tone arm mass with cartridge compliance when it comes to turntables.

Thick-walled stiff cabs on the other hand raise the resonances to frequencies which are easier to kill by whatever other means.

Could be wrong, it's been many years since I read the BBC papers.
I seem to remember settling for the thick&stiff approach as it seemed easier to implement. Basically you can just completely over-engineer one of those, always erring well on the safe side while the thin-wall approach requires careful tuning and thus a lot of prototyping to work as intended.
Of course once you've got it right they are a lot cheaper to produce in numbers.
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Old 1st October 2014, 10:32 PM   #7
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We beat this to death on several threads a year or so ago. I really recommend the Harwood paper as it makes a clear and compelling case.

Cabinet resonance Q is the key factor. Damping is the only cure for a high Q resonance. Making the cabinet stiffer or the walls heavier will only assure that any damping applied will be less effective. Q is only lowered if the ratio of damping mass to wall mass is increased (thin walls and lots of damping). If panel resonance Q is reduced then tuning of resonances isn't needed (they are damped).

Raising the resonances will inherently make it more difficult to treat them.

I had a pair of LS5/1a years ago. They had thin plywood walls and heavy felt pads adhered to the walls. They really had a different sound when your rapped on them: Subdued and non-resonant.

The BBC knew what they were doing.
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Old 1st October 2014, 11:56 PM   #8
raul_77 is offline raul_77  Europe
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Seems that you search some as a 'clone'. Perhaps as this?:

http://www.china-hifi-audio.com/en/j...rs-pair-p-1077

http://www.positive-feedback.com/Issue47/jungson.htm

Last edited by raul_77; 1st October 2014 at 11:59 PM.
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Old 2nd October 2014, 12:14 AM   #9
sreten is offline sreten  United Kingdom
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Hi,

One things for certain, you can't use the LS3/5A x/o
with most of the versions of the B110, and the
simpler KEF x/o's work best with various versions.

An updated LS3/5A homage :
Continuum, Pr

rgds, sreten.
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Old 2nd October 2014, 01:03 AM   #10
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Quote:
Originally Posted by speaker dave View Post
Raising the resonances will inherently make it more difficult to treat them.
But also make them less likely to get excited -- less energy available to do it.

dave
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