I appreciate the responses, however, not having heard the speaker, you might be missing something here. The 3/5a was intended to be used with its grill in place and without any toe-in. This would place the T27 significantly off axis when used in a listening room. See figure 2 here: http://www.stereophile.com/budgetcomponents/361/index10.html
sreten - You're good at graphs. How about showing us an in-room measurement and review which indicates your last statement is correct. This would appear to be a matter of personal taste and much more than simply how the speaker measures on axis. What happens in the dispersion patterns of the drivers would normally be the deciding factor of how the speaker's sound sums at the listener's ears. And whenever you get around to those other questions, I would still appreciate an answer. You seem to be trying to now draw the conversation away from the 3/5a.
Dude................decaf.
Soufiej, Can't you just give up this personal vendetta against Sreten? If you disagree with him or find fault with his posts then fair enough. That's one of the reasons why we are here but I find the tone of your posts disturbing.
Please, people, it's just a forum where people should freely exchange ideas. Hopefully without resulting in this thinly veiled flaming.
Personally I'm just interested in BBC rise and not getting a rise out of someone else.
Soufiej, Can't you just give up this personal vendetta against Sreten? If you disagree with him or find fault with his posts then fair enough. That's one of the reasons why we are here but I find the tone of your posts disturbing.
Please, people, it's just a forum where people should freely exchange ideas. Hopefully without resulting in this thinly veiled flaming.
Personally I'm just interested in BBC rise and not getting a rise out of someone else.
Hi,
At what point have I said or implied that I don't like the LS3/5a ?
This is just getting silly. I'm losing any sensible interest in this.
A person who in not capable of digesting the technical information
in the series of Stereophile articles they keep referencing is one
thing, but then insisting nobody else understands it is another.
/sreten.
At what point have I said or implied that I don't like the LS3/5a ?
This is just getting silly. I'm losing any sensible interest in this.
A person who in not capable of digesting the technical information
in the series of Stereophile articles they keep referencing is one
thing, but then insisting nobody else understands it is another.
/sreten.At what point have I said or suggested I don't understand the technical information? I have merely disputed which graphs are relevant to the discussion. Presenting opinion ("flat is too hot")without any facts to back up that opinion would seem to be a more egregious error. Saying so does not make it so.
From the LS3/5a forum regarding the BBC "dip", "rise" or "curve".
"The only other forum that I know this subject has been discussed is the
Harbeth User Group.
This was first raised on the HUG back in November 2003. This is a copy of
the reply from Alan Shaw on Tuesday 4th November 2003"
----------------------------------------------------------------------------
--
"A very interesting thread this, so here are the facts for your
consideration:
Many years ago I asked Dudley Harwood, my predecessor about the 'BBC dip' or
to be fair 'The Gundry Dip'.
(Gundry senior worked at the BBC but passed away some years ago: Gundry
'junior' works or worked for Dolby Labs)
First take a look at the 'How we hear' pages on the Harbeth web site. Yes,
incomplete but note the huge boost in the ear's *sensitivity* centred around
3.5kHz.
Next, consider that all Harbeth (and probably the vast majority of other
speakers crossover at 3kHz-ish ...... that's a most unfortunate choice of
frequency unless your are *extremely* careful in blending the midrange and
tweeter .... seems that we are, hence the 'Harbeth sound'.
Then, as Harwood stated, there was significant colouration in the 'presence
region' with early conventional plastics ... so reducing the energy in this
high-sensitivity region partly masked the colouration ... and finally ...
BBC monitors were designed for virtually near field use i.e. you could
(probably) reach out and touch them from the studio managers position at the
desk. A little depression in the 1-4kHz region pushed the stereo image
backwards, subjectively, (i.e. the performers seemed to recede a little into
the cabinets) and made the speaker less oppressive to work with. (As a side
issue this image positioning is why a speaker designer should *never* design
a new model as a single, mono speaker and then clone into stereo. I know,
because it is one of the first traps I fell into as a novice some 20 years
ago ... mercifully the product never went into production. Do all the
listening tests in stereo right from the very start of the design coming
together.)
That's the whole story. Anything else you may hear is, I'm sorry to say, not
factual.
Alan Shaw
Harbeth"
From the LS3/5a forum regarding the BBC "dip", "rise" or "curve".
"The only other forum that I know this subject has been discussed is the
Harbeth User Group.
This was first raised on the HUG back in November 2003. This is a copy of
the reply from Alan Shaw on Tuesday 4th November 2003"
----------------------------------------------------------------------------
--
"A very interesting thread this, so here are the facts for your
consideration:
Many years ago I asked Dudley Harwood, my predecessor about the 'BBC dip' or
to be fair 'The Gundry Dip'.
(Gundry senior worked at the BBC but passed away some years ago: Gundry
'junior' works or worked for Dolby Labs)
First take a look at the 'How we hear' pages on the Harbeth web site. Yes,
incomplete but note the huge boost in the ear's *sensitivity* centred around
3.5kHz.
Next, consider that all Harbeth (and probably the vast majority of other
speakers crossover at 3kHz-ish ...... that's a most unfortunate choice of
frequency unless your are *extremely* careful in blending the midrange and
tweeter .... seems that we are, hence the 'Harbeth sound'.
Then, as Harwood stated, there was significant colouration in the 'presence
region' with early conventional plastics ... so reducing the energy in this
high-sensitivity region partly masked the colouration ... and finally ...
BBC monitors were designed for virtually near field use i.e. you could
(probably) reach out and touch them from the studio managers position at the
desk. A little depression in the 1-4kHz region pushed the stereo image
backwards, subjectively, (i.e. the performers seemed to recede a little into
the cabinets) and made the speaker less oppressive to work with. (As a side
issue this image positioning is why a speaker designer should *never* design
a new model as a single, mono speaker and then clone into stereo. I know,
because it is one of the first traps I fell into as a novice some 20 years
ago ... mercifully the product never went into production. Do all the
listening tests in stereo right from the very start of the design coming
together.)
That's the whole story. Anything else you may hear is, I'm sorry to say, not
factual.
Alan Shaw
Harbeth"
More from the forum.
"Alan Shaw has gone on to use this response as the basis of an FAQ on the
current Harbeth website:
----------------------------------------------------------------------------
--
"There is much myth, folklore and misunderstanding about this subject.
The 'BBC dip' is (was) a shallow shelf-down in the acoustic output of some
BBC-designed speaker system of the 1960s-1980s in the 1kHz to 4kHz region.
The LS3/5a does not have this effect, neither in the 15 ohm nor 11 ohm, both
of which are in fact slightly lifted in that region.
According to Harbeth's founder, who worked at the BBC during the time that
this psychoacoustic effect was being explored, the primary benefit this
little dip gave was in masking of defects in the early plastic cone drive
units available in the 1960's. A spin-off benefit was that it appeared to
move the sound stage backwards away from the studio manager who was sitting
rather closer to the speakers in the cramped control room than he would
ideally wish for. (See also Designer's Notebook Chapter 7). The depth of
this depression was set by 'over-equalisation' in the crossover by about 3dB
or so, which is an extreme amount for general home listening. We have never
applied this selective dip but have taken care to carefully contour the
response right across the frequency spectrum for a correctly balanced sound.
Although as numbers, 1kHz and 4kHz sound almost adjacent in an audio
spectrum of 20Hz to 20kHz, the way we perceive energy changes at 1kHz or
4kHz has a very different psychoacoustic effect: lifting the 1kHz region
adds presence (this is used to good effect in the LS3/5a) to the sound, but
the 4kHz region adds 'bite' - a cutting incisiveness which if over-done is
very unpleasant and irritating.
You can explore this effect for yourselves by routing your audio signal
through a graphic equaliser and applying a mild cut in the approx. 1kHz to
4kHz region and a gradual return to flat either side of that."
----------------------------------------------------------------------------
--
According to Alan Shaw the BBC LS3/5A does not suffer from the "BBC dip" (or
more accurately "Gundry dip" - quite the reverse in fact. The "bump" at
110Hz is a completely separate issue that has been discussed at length over
the years.
Dave.
"Alan Shaw has gone on to use this response as the basis of an FAQ on the
current Harbeth website:
----------------------------------------------------------------------------
--
"There is much myth, folklore and misunderstanding about this subject.
The 'BBC dip' is (was) a shallow shelf-down in the acoustic output of some
BBC-designed speaker system of the 1960s-1980s in the 1kHz to 4kHz region.
The LS3/5a does not have this effect, neither in the 15 ohm nor 11 ohm, both
of which are in fact slightly lifted in that region.
According to Harbeth's founder, who worked at the BBC during the time that
this psychoacoustic effect was being explored, the primary benefit this
little dip gave was in masking of defects in the early plastic cone drive
units available in the 1960's. A spin-off benefit was that it appeared to
move the sound stage backwards away from the studio manager who was sitting
rather closer to the speakers in the cramped control room than he would
ideally wish for. (See also Designer's Notebook Chapter 7). The depth of
this depression was set by 'over-equalisation' in the crossover by about 3dB
or so, which is an extreme amount for general home listening. We have never
applied this selective dip but have taken care to carefully contour the
response right across the frequency spectrum for a correctly balanced sound.
Although as numbers, 1kHz and 4kHz sound almost adjacent in an audio
spectrum of 20Hz to 20kHz, the way we perceive energy changes at 1kHz or
4kHz has a very different psychoacoustic effect: lifting the 1kHz region
adds presence (this is used to good effect in the LS3/5a) to the sound, but
the 4kHz region adds 'bite' - a cutting incisiveness which if over-done is
very unpleasant and irritating.
You can explore this effect for yourselves by routing your audio signal
through a graphic equaliser and applying a mild cut in the approx. 1kHz to
4kHz region and a gradual return to flat either side of that."
----------------------------------------------------------------------------
--
According to Alan Shaw the BBC LS3/5A does not suffer from the "BBC dip" (or
more accurately "Gundry dip" - quite the reverse in fact. The "bump" at
110Hz is a completely separate issue that has been discussed at length over
the years.
Dave.
From the forum.
P.S. I've also re-posted a history of the development of the LS3/5A by Paul
Whatton after he had the opportunity to meet and talk to Jim Finnie about
life in the BBC during the development period of the LS3/5A.
For newer members of this group, Paul Whatton founded this group a long,
long time ago. Paul's father (Maurice Whatton) is listed along with H.D.
Harwood and R. W. Mills as authors of the BBC design report "The design of
the miniature monitoring loudspeaker type LS3/5A" published in October 1976.
Paul has also worked for the BBC.
The following contains some references to other posts within the thread.
Hi Jim,
>commercial considerations had very little influence on the BBC..
the goal was to meet performance targets<
Absolutely! Perhaps the best explanation for its long term standing,
good or bad.
>the BBC sound, so to speak, was probably also the British sound of
that period<
Agreed. Also closely followed in Canada
>the merits or otherwise of veneers - half the participants were of the
view that teak veneers were an unnecessary cosmetic appendage<
Just glad the right side won.
>The sheer scale of the BBC resource of those times defies belief in the present
day. For example, I think they had four (yes, 4) symphony orchestras on the
books, as well as 2-3 full choirs and a raft of smaller groupings. Not only
that, you also need to add the annual Proms concerts which gave the BBC
(engineers) access to live source from some of the best classical performers of
the period. I am sure that someone will say if my numbers are under-estimates!
And of course there was similar access to the
>best of all other music for many decades.
>
>
This bears reprinting. It is the only example of enlightened government
spending of taxpayer monies that I can remember, anywhere. Sadly,
there is no such public repository in NA that can match Aunty's hand bag.
>the rises and falls in the frequency responses that have been mentioned were
the result of an almost never ending iterative process
>
It bears repeating, that even with objective tools at hand the
subjective must guide and even over rule the objective during the process.
>here is the real 'rub', the domestic environment barely entered the equation.
>
>
I for one think it's just dandy there was this unintended side effect!
>I think I have two compartments in my brain, one retains a memory of live
(classical) music and the other of reproduction music. For me, the two are
contentedly close, and have been so for many years.
>
Very nicely put.
>In fact, I find that my main contention has for some time been one of
environment, mostly because I cannot control the live arena in the same way as I
can my own home!
>
Meet you on the Holo deck?
>
>I think that the LS3/5A design reflects a strong subjective input which was
gained from live performance and from professional musicians, coupled with the
original design environment brief. They have stood the test of time because they
have taken a tentative step towards bridging the great objective/subjective
divide and they are so tiny - therein lies the real engineering achievement.
>
OK! Paul are you reading this. Time to close up shop! Jim's done it and
all in one paragraph! Nuff said, say no more, can't argue with that!
Marvelous, thanks Jim
P.S. I've also re-posted a history of the development of the LS3/5A by Paul
Whatton after he had the opportunity to meet and talk to Jim Finnie about
life in the BBC during the development period of the LS3/5A.
For newer members of this group, Paul Whatton founded this group a long,
long time ago. Paul's father (Maurice Whatton) is listed along with H.D.
Harwood and R. W. Mills as authors of the BBC design report "The design of
the miniature monitoring loudspeaker type LS3/5A" published in October 1976.
Paul has also worked for the BBC.
The following contains some references to other posts within the thread.
Hi Jim,
>commercial considerations had very little influence on the BBC..
the goal was to meet performance targets<
Absolutely! Perhaps the best explanation for its long term standing,
good or bad.
>the BBC sound, so to speak, was probably also the British sound of
that period<
Agreed. Also closely followed in Canada
>the merits or otherwise of veneers - half the participants were of the
view that teak veneers were an unnecessary cosmetic appendage<
Just glad the right side won.
>The sheer scale of the BBC resource of those times defies belief in the present
day. For example, I think they had four (yes, 4) symphony orchestras on the
books, as well as 2-3 full choirs and a raft of smaller groupings. Not only
that, you also need to add the annual Proms concerts which gave the BBC
(engineers) access to live source from some of the best classical performers of
the period. I am sure that someone will say if my numbers are under-estimates!
And of course there was similar access to the
>best of all other music for many decades.
>
>
This bears reprinting. It is the only example of enlightened government
spending of taxpayer monies that I can remember, anywhere. Sadly,
there is no such public repository in NA that can match Aunty's hand bag.
>the rises and falls in the frequency responses that have been mentioned were
the result of an almost never ending iterative process
>
It bears repeating, that even with objective tools at hand the
subjective must guide and even over rule the objective during the process.
>here is the real 'rub', the domestic environment barely entered the equation.
>
>
I for one think it's just dandy there was this unintended side effect!
>I think I have two compartments in my brain, one retains a memory of live
(classical) music and the other of reproduction music. For me, the two are
contentedly close, and have been so for many years.
>
Very nicely put.
>In fact, I find that my main contention has for some time been one of
environment, mostly because I cannot control the live arena in the same way as I
can my own home!
>
Meet you on the Holo deck?
>
>I think that the LS3/5A design reflects a strong subjective input which was
gained from live performance and from professional musicians, coupled with the
original design environment brief. They have stood the test of time because they
have taken a tentative step towards bridging the great objective/subjective
divide and they are so tiny - therein lies the real engineering achievement.
>
OK! Paul are you reading this. Time to close up shop! Jim's done it and
all in one paragraph! Nuff said, say no more, can't argue with that!
Marvelous, thanks Jim
The last transfer from the 3/5a forum for now. I hope this helps with some misconceptions regarding the process of designing the 3/5a and gets the thread back on target.
RE: [ls35a] Re: LS3/5a response curve
Hi Jim,
Thanks for your detailed response - it's great to hear this sort of
information from someone who was there.
For the newer members of this forum I've reposted below a detailed
description of the development of the LS3/5A by Paul Whatton after a he
visited you back in 2001.
Dave.
During December 2001 I was very fortunate to be invited to visit Jim Finnie.
Jim worked in BBC Research Department at the time of the development of the
LS3/5A and knew personally many of the members of the team that designed it.
Jim provided a fascinating account of the early days of the LS3/5A project
and it is mostly thanks to him that I am able to pass on the following
information.
Paul Whatton
December 2001
BBC Research and the un-tweakable LS3/5A
-----------------------------------------------------------------
To really understand the LS3/5A it is necessary to first place it in the
context of the activities of BBC Research Department at Kingswood Warren
(KW). During 1973/ 74 the department led the world in many aspects of
broadcasting research. It was staffed by an elite of graduate and
post-graduate qualified engineers, recruited from Britain's top universities
including Oxford, Cambridge and Imperial College.
Much like a traditional university, these engineers had a mostly free hand
in what they did and this included Blue Skies research. Cost was not the
prime consideration, their research outcomes were focussed by the philosophy
of absolute excellence in broadcasting. And, much like a university research
culture, the staff were divided into two, the researchers who dreamed up the
bright ideas and the technicians who did the practical work.
Research Department's Audio Section team was headed by Dudley Harwood and
included many now familiar names, in particular, Spencer Hughes who would
later produce loudspeakers under the now famous Spendor brand. Also working
at Research Department at that time was Dave Stebbings, who went on to form
Chartwell.
One of the projects undertaken by Research was the development of a small
high-quality monitoring loudspeaker suitable for use in cramped environments
like outside broadcast vehicles. The BBC had failed to find a commercially
produced loudspeaker that was of sufficiently high quality or consistent
enough to meet their requirements. The project had evolved from the
department's work on 1/8 scale acoustic modelling of studios, which
indicated that it might be feasible to make a small monitor of sufficiently
high quality. This project was to become the LS3/5, later the design was
modified and became the LS3/5A.
The BBC was in a unique position and had several advantages over commercial
manufacturers in the development of loudspeakers. The engineers had access
to a wide range of live music and could easily make comparisons between
reproduced and live sound. Indeed at times live musicians would be hired
specifically for engineering tests.
But the single factor that made it possible to develop the LS3/5 was the
Blue Skies culture of the department which was largely free of the time and
cost constraints of a commercial manufacturer. The team would agonise over
tiny changes and Jim Finnie remembers how some of those involved argued for
the best part of a week over a modification which changed the speaker's
performance by just one dB. At the time the thinking was that a 1dB change
was inaudible. However Research Department had someone with hearing that was
demonstrably so sensitive that he was able to consistently hear changes of
1dB and so they were able to justify these changes. The person with such
acute hearing was probably Ralph Mills who worked in the Design Department
and who is credited on the BBC technical paper describing the LS3/5A.
Thus the LS3/5 evolved through a series of small improvements to become the
LS3/5A. The "a" suffix was added because the changes made the speaker
sufficiently different that it could not be used in a stereo pair with its
older brother. It became the most tweaked loudspeaker in the world. The full
extent of this work can be realised from the huge cost of the LS3/5A
project, estimated at £100,000 in 1975. At today's' prices this represents
an investment in research of about £1,000,000 (US$1,600,000). Clearly no
commercial loudspeaker manufacturer could hope to approach this level of
investment in a project.
Within the limitations of the drive units and cabinet size, the LS3/5A as
developed in Research Department was the ultimate design. Jim Finnie
eloquently described it as being like the point of a pencil, so highly
developed that even very small alterations would push it off the highly
tuned point and degrade the performance.
The Kingswood Warren LS3/5A was un-tweakable!
The KW LS3/5A cabinets were hand built by skilled technicians. The
crossovers were hand-built and tweaked by painstaking selection of
components. Every component was bridged and labelled with its value. Where
the crossover schematic required, for example, a 2uF capacitor, two nominal
value 1uF capacitors would selected from a huge stock each of which had been
accurately measured. They would then be put in parallel to ensure the
theoretical value was met to within specification. Significantly the KEF
drive units were highly selected, with 96% of the ex-factory KEF T27
tweeters being rejected!
So as well as being un-tweakable the KW LS3/5A was also labour intensive and
impractical to manufacture! It was at this point that the speaker was handed
over to BBC Design Department with a brief to try to modify it so that
sufficiently high numbers could be produced to meet the BBC needs. Design
Department was very much concerned with nuts and bolts engineering and would
often be tasked with converting the innovative, if sometimes impractical,
output from Kingswood Warren into working equipment.
The relationship between BBC Research and Design departments was not always
an easy one. It would not be an exaggeration to say that some of the
engineers in Research resented the changes imposed on their work by Design
Department. The engineer in charge of this part of the project was Maurice
Whatton who was assisted by Ralph Mills.
Initially it was felt (by Research Department) that the LS3/5A would not
need much work done to it. In practice a number of significant changes were
required in order for the speaker to be manufactured by companies granted a
BBC licence. In particular the tight specification of the drive units was
unworkable and so changes were made to the crossover design in order to
accommodate a wider manufacturing spread. Thus the already complex LS3/5A
crossover printed circuit board became even more crowded.
There are then significant differences between KW LS3/5As, manufactured in-
house by the BBC, hand-built and so highly tweaked when compared with those
that came off the licensees' production lines.
Care should be taken not to confuse these rarest of LS3/5As with the
Chartwell units that were made available as a kit to BBC staff. The
Chartwells were to all intents and purposes, identical to production
speakers. A production LS3/5A can never meet the performance of the in-
house units for the reasons explained above, and this was borne out when Ken
Kessler managed to obtain a pair of KW LS3/5As for use as a reference in the
June 2001 Hi-Fi News Shootout.
For a DIY tweaker, unable to select from a big batch of drive units and
stuck with a production cabinet, the production crossover then holds the
best chances of improved performance by careful selection and matching of
components.
Few LS3/5A enthusiasts can ever hope to hear, let alone own, a pair of KW
LS3/5As built in Research Department in 1974. There were perhaps only 20
pairs ever made. Some, like the pair Ken Kessler borrowed, did escape the
BBC because enthusiastic employees were able to purchase the highly selected
components and make a pair with the help of Research Department's skilled
technicians. But for most, the hope of finding them at an audio jumble or in
the second hand advertisements is just a dream!
RE: [ls35a] Re: LS3/5a response curve
Hi Jim,
Thanks for your detailed response - it's great to hear this sort of
information from someone who was there.
For the newer members of this forum I've reposted below a detailed
description of the development of the LS3/5A by Paul Whatton after a he
visited you back in 2001.
Dave.
During December 2001 I was very fortunate to be invited to visit Jim Finnie.
Jim worked in BBC Research Department at the time of the development of the
LS3/5A and knew personally many of the members of the team that designed it.
Jim provided a fascinating account of the early days of the LS3/5A project
and it is mostly thanks to him that I am able to pass on the following
information.
Paul Whatton
December 2001
BBC Research and the un-tweakable LS3/5A
-----------------------------------------------------------------
To really understand the LS3/5A it is necessary to first place it in the
context of the activities of BBC Research Department at Kingswood Warren
(KW). During 1973/ 74 the department led the world in many aspects of
broadcasting research. It was staffed by an elite of graduate and
post-graduate qualified engineers, recruited from Britain's top universities
including Oxford, Cambridge and Imperial College.
Much like a traditional university, these engineers had a mostly free hand
in what they did and this included Blue Skies research. Cost was not the
prime consideration, their research outcomes were focussed by the philosophy
of absolute excellence in broadcasting. And, much like a university research
culture, the staff were divided into two, the researchers who dreamed up the
bright ideas and the technicians who did the practical work.
Research Department's Audio Section team was headed by Dudley Harwood and
included many now familiar names, in particular, Spencer Hughes who would
later produce loudspeakers under the now famous Spendor brand. Also working
at Research Department at that time was Dave Stebbings, who went on to form
Chartwell.
One of the projects undertaken by Research was the development of a small
high-quality monitoring loudspeaker suitable for use in cramped environments
like outside broadcast vehicles. The BBC had failed to find a commercially
produced loudspeaker that was of sufficiently high quality or consistent
enough to meet their requirements. The project had evolved from the
department's work on 1/8 scale acoustic modelling of studios, which
indicated that it might be feasible to make a small monitor of sufficiently
high quality. This project was to become the LS3/5, later the design was
modified and became the LS3/5A.
The BBC was in a unique position and had several advantages over commercial
manufacturers in the development of loudspeakers. The engineers had access
to a wide range of live music and could easily make comparisons between
reproduced and live sound. Indeed at times live musicians would be hired
specifically for engineering tests.
But the single factor that made it possible to develop the LS3/5 was the
Blue Skies culture of the department which was largely free of the time and
cost constraints of a commercial manufacturer. The team would agonise over
tiny changes and Jim Finnie remembers how some of those involved argued for
the best part of a week over a modification which changed the speaker's
performance by just one dB. At the time the thinking was that a 1dB change
was inaudible. However Research Department had someone with hearing that was
demonstrably so sensitive that he was able to consistently hear changes of
1dB and so they were able to justify these changes. The person with such
acute hearing was probably Ralph Mills who worked in the Design Department
and who is credited on the BBC technical paper describing the LS3/5A.
Thus the LS3/5 evolved through a series of small improvements to become the
LS3/5A. The "a" suffix was added because the changes made the speaker
sufficiently different that it could not be used in a stereo pair with its
older brother. It became the most tweaked loudspeaker in the world. The full
extent of this work can be realised from the huge cost of the LS3/5A
project, estimated at £100,000 in 1975. At today's' prices this represents
an investment in research of about £1,000,000 (US$1,600,000). Clearly no
commercial loudspeaker manufacturer could hope to approach this level of
investment in a project.
Within the limitations of the drive units and cabinet size, the LS3/5A as
developed in Research Department was the ultimate design. Jim Finnie
eloquently described it as being like the point of a pencil, so highly
developed that even very small alterations would push it off the highly
tuned point and degrade the performance.
The Kingswood Warren LS3/5A was un-tweakable!
The KW LS3/5A cabinets were hand built by skilled technicians. The
crossovers were hand-built and tweaked by painstaking selection of
components. Every component was bridged and labelled with its value. Where
the crossover schematic required, for example, a 2uF capacitor, two nominal
value 1uF capacitors would selected from a huge stock each of which had been
accurately measured. They would then be put in parallel to ensure the
theoretical value was met to within specification. Significantly the KEF
drive units were highly selected, with 96% of the ex-factory KEF T27
tweeters being rejected!
So as well as being un-tweakable the KW LS3/5A was also labour intensive and
impractical to manufacture! It was at this point that the speaker was handed
over to BBC Design Department with a brief to try to modify it so that
sufficiently high numbers could be produced to meet the BBC needs. Design
Department was very much concerned with nuts and bolts engineering and would
often be tasked with converting the innovative, if sometimes impractical,
output from Kingswood Warren into working equipment.
The relationship between BBC Research and Design departments was not always
an easy one. It would not be an exaggeration to say that some of the
engineers in Research resented the changes imposed on their work by Design
Department. The engineer in charge of this part of the project was Maurice
Whatton who was assisted by Ralph Mills.
Initially it was felt (by Research Department) that the LS3/5A would not
need much work done to it. In practice a number of significant changes were
required in order for the speaker to be manufactured by companies granted a
BBC licence. In particular the tight specification of the drive units was
unworkable and so changes were made to the crossover design in order to
accommodate a wider manufacturing spread. Thus the already complex LS3/5A
crossover printed circuit board became even more crowded.
There are then significant differences between KW LS3/5As, manufactured in-
house by the BBC, hand-built and so highly tweaked when compared with those
that came off the licensees' production lines.
Care should be taken not to confuse these rarest of LS3/5As with the
Chartwell units that were made available as a kit to BBC staff. The
Chartwells were to all intents and purposes, identical to production
speakers. A production LS3/5A can never meet the performance of the in-
house units for the reasons explained above, and this was borne out when Ken
Kessler managed to obtain a pair of KW LS3/5As for use as a reference in the
June 2001 Hi-Fi News Shootout.
For a DIY tweaker, unable to select from a big batch of drive units and
stuck with a production cabinet, the production crossover then holds the
best chances of improved performance by careful selection and matching of
components.
Few LS3/5A enthusiasts can ever hope to hear, let alone own, a pair of KW
LS3/5As built in Research Department in 1974. There were perhaps only 20
pairs ever made. Some, like the pair Ken Kessler borrowed, did escape the
BBC because enthusiastic employees were able to purchase the highly selected
components and make a pair with the help of Research Department's skilled
technicians. But for most, the hope of finding them at an audio jumble or in
the second hand advertisements is just a dream!
sreten said:
Hi,
Well it may news to you but not anyone familiar with in-room
averaged responses as taken by HiFi-Choice and Stereophile.
It is true. Text book flat response = smooth in-room roll-off.
I don't really see how you can believe this. Maybe if you'd be so kind to explain how the HF is attenuated with a direct microphone reading, with the reflected sound down at least 10-20 dB.
Dont forget tha we are not just talking for a mic reading on tweeter axis over to the listening position (maybe 3m away) in a real living room. They average many positions over a wide window centered on ear hight at listening position. This means mixing many off axis readings. Its this mean average of power inroom response and not absorption that shows the HF droop.
I could maybe see a HF rolloff for the pair of speakers if they moved the mic too far off the sweet spot and if the tweeter had poor dispersion qualities at 5-15 KHz and were more than 3 dB off between the pair. But I think this is not the case here. Maybe a link could lessen the handwaving excercises. Sorry if I'm a bother, I really would like to understand this HF attenuation in the room average response thing.
Footnote 2: I average 120 individual 1/3-octave response measurements---six in each of 20 microphone positions---for the left and right speakers in an approximate 3' by 8' region centered on the listening position. The analyzer is an Audio Control Industrial SA-3050A, and the test signal is pink noise at an approximate 80dB spl.---JA
This is from stereophile. As you see there are rally many off axis positions.
This is from stereophile. As you see there are rally many off axis positions.
I was hoping that there was an app. note or some discussion regarding differences between measurements of in room avg vs anechoic swept. There must be a correction factor for the avg room response using the Audio Control Industrial SA-3050A if they are repeatable.
So the speakers are placed 8' apart with the microphone at some fixed level and then being moved to 20 locations within a grid 8'x3' some distance from the center line. Is my understanding correct? If so this seems reasonable.
So using a pink noise as a source is agreeable, using white noise, it can be easy to burn HF drivers during extended measurements. But there is a correction factor as well as accuracy of the filter shape to account for using a pink noise generator. As well as the time avg function of the power measurement. Still struggling to understand. Little help please?
So the speakers are placed 8' apart with the microphone at some fixed level and then being moved to 20 locations within a grid 8'x3' some distance from the center line. Is my understanding correct? If so this seems reasonable.
So using a pink noise as a source is agreeable, using white noise, it can be easy to burn HF drivers during extended measurements. But there is a correction factor as well as accuracy of the filter shape to account for using a pink noise generator. As well as the time avg function of the power measurement. Still struggling to understand. Little help please?
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