I guess we are dealing with semantics here. What has been posted as the "response" of the 3/5a including any rising level through the upper frequencies would appear to be not all an "accurate" representation of how the speaker had been designed. Regarding the "subjective response" posted, the following disclaimer is included within the text of the review immediately above the graph.
"Footnote 3: Stereophile's subjective frequency response curves show how the transducer under test sounded to us, rather than how it measured. The vertical scale on each curve is the same, and is scaled so that a barely perceptible audible deviation from flat frequency response is reflected in a barely perceptible visual deviation of the response curve."
I believe the important words here are, " ... how the transducer under test sounded to us, rather than how it measured". This is essentially a representation of what was heard and was drawn out with a crayon rather than any testing gear. The same conclusion was made with the second graph you included which was taken with measuring equipment but is an in-room response.
"Fig.2 Rogers LS3/5a, 1978 sample, spatially averaged, 1/3-octave response in JA's room."
While providing a bit more accuracy than the original subjective graph, this still doesn't indicate the "real" frequency response of the speaker. Possibly I'm not understanding how you DIY'ers measure speakers but I assume the anechoic response is what is intended by the designer and is the only real response curve which matters to the designer. Since the designer can't control the room a consumer will own, the in-room response can measure significantly different than the anechoic response and can measure quite different from room to room.
However, my understanding of the importance of the BBC curve was how it brought to light many aspects of speaker design which are now generally accepted as fact. Until the age of the BBC curve, most speakers strived for flat response out to the highest frequencies possible with contemporary technology. Anechoic chambers didn't exist for the most part and the best measurements were taken in a free field situation. (I still have pictures of the KEF engineers taking measurements of a speaker system mounted on a pole literally out in a field.) While some designers acknowledged the problems of truly flat response in an age of restricted high frequency extension and surface/tape noise (Henry Kloss made subjective demonstrations of the original Advent's tweeter playing back a LP. The demonstartion was done with extension out beyond 17kHz and with the more limited 12kHz response of the actual consumer unit. The choice was made to gently roll off the high frequencies of the Advent's tweeter due to the excessive noise and undesirable information the driver revealed when "full" frequency extension was allowed.), the BBC designs were the first, to my knowledge, which considered in-room response to be the result of subjective measurement and weighed that information when designing thier final product. The purpose of the BBC roll off was to make use of the in-room gain which gave the speaker the subjective sense of (at least) flat response when in actual use. And, remember the 3/5a was specifically designed for monitor use in mobile applications which placed it inside large vans and trucks. The Spendor BC1 showed a more or less similar free field response curve. Its larger enclosure and driver size allowed it to play in larger rooms and at slightly higher SPL's but still gave the "subjective" impression of greater frequency extension where there literally was not such a design.
This is what I have always understood to be one of the important lessons the BBC gave us with the curve. Utilizing nothing much more than their ears, the BBC engineers designed a speaker which sounded correct in an actual room. This had never been attempted before they pulled out their slide rules and Baltic Birch baffles. The low frequency blip gave the sense of a subjectively lower frequency extension than the enclosure allowed (along with the AS enclosure parameters of course)and the high frequency roll off gave the subjective impression of greater high frequency content and extension than what the free field response indicated. Concessions were not made due to the limtations of the associated equipment (as in the Advent design) since the in field monitoring purpose of the 3/5a design most often meant the speaker was being fed a microphone or mixing board output which was capable of much greater extension with far less noise than a commercial LP would allow. Even when given the tape out feed, the BBC monitors were getting better than 15kHz response with minimal noise as Dolby A had been incorporated into most studio decks by the mid 1970's.
What the BBC engineers realized however, was the in-room gain at the frequency limits made for a very different sounding speaker than what the free field measurements suggested. That the 3/5a sounds as if it has flat extension well beyond its design limitations is not in question. As I said, I live with a pair of Roger's monitors as an almost everyday speaker. The speaker doesn't sound rolled off in the highs. Some people might describe the effect as "polite" (which is frequently the overall description of the BBC sound) by today's standards, but that is, in my opinion, due to the in-room response inaccuracies of many of today's commercial speakers. Too many of today's designs tend to have excessive response lifts at both ends in order to sell to an uneducated consumer. (Has anyone heard a mid-priced B&W lately?) The BBC engineers lived with the sound of real music from day to day. They used that sound as their reference. Most consumers in today's speaker maketplace have no idea what live music sounds like and simply compare one speaker to another. The speaker with the best "jump factor" most often wins whether thay are buying for their home or their car system.
I have no argument that the LS3/5a's sound as if they have flat response to at least the limits of my half century old ears when considered subjectively in-room. I do disagree that this repsonse is the result of a rising high frequency response which was designed into the speaker. Quite the contrary. The subjective rise is due to the actual roll off and the resultant in-room gain and is what should be considered an important lesson to be taken from the BBC designs.
That we still talk about and use the BBC "curve" is due to the correctness of what the designers did by ear in the early to mid 1970's. Just as we continue to find Blumlien's work of the 1930's relevant and correct in today's newest technologies, the BBC curve is important becuase of what it should have taught us but is instead what we choose to ignore to our own peril.
In short; flat response sucks!
"Footnote 3: Stereophile's subjective frequency response curves show how the transducer under test sounded to us, rather than how it measured. The vertical scale on each curve is the same, and is scaled so that a barely perceptible audible deviation from flat frequency response is reflected in a barely perceptible visual deviation of the response curve."
I believe the important words here are, " ... how the transducer under test sounded to us, rather than how it measured". This is essentially a representation of what was heard and was drawn out with a crayon rather than any testing gear. The same conclusion was made with the second graph you included which was taken with measuring equipment but is an in-room response.
"Fig.2 Rogers LS3/5a, 1978 sample, spatially averaged, 1/3-octave response in JA's room."
While providing a bit more accuracy than the original subjective graph, this still doesn't indicate the "real" frequency response of the speaker. Possibly I'm not understanding how you DIY'ers measure speakers but I assume the anechoic response is what is intended by the designer and is the only real response curve which matters to the designer. Since the designer can't control the room a consumer will own, the in-room response can measure significantly different than the anechoic response and can measure quite different from room to room.
However, my understanding of the importance of the BBC curve was how it brought to light many aspects of speaker design which are now generally accepted as fact. Until the age of the BBC curve, most speakers strived for flat response out to the highest frequencies possible with contemporary technology. Anechoic chambers didn't exist for the most part and the best measurements were taken in a free field situation. (I still have pictures of the KEF engineers taking measurements of a speaker system mounted on a pole literally out in a field.) While some designers acknowledged the problems of truly flat response in an age of restricted high frequency extension and surface/tape noise (Henry Kloss made subjective demonstrations of the original Advent's tweeter playing back a LP. The demonstartion was done with extension out beyond 17kHz and with the more limited 12kHz response of the actual consumer unit. The choice was made to gently roll off the high frequencies of the Advent's tweeter due to the excessive noise and undesirable information the driver revealed when "full" frequency extension was allowed.), the BBC designs were the first, to my knowledge, which considered in-room response to be the result of subjective measurement and weighed that information when designing thier final product. The purpose of the BBC roll off was to make use of the in-room gain which gave the speaker the subjective sense of (at least) flat response when in actual use. And, remember the 3/5a was specifically designed for monitor use in mobile applications which placed it inside large vans and trucks. The Spendor BC1 showed a more or less similar free field response curve. Its larger enclosure and driver size allowed it to play in larger rooms and at slightly higher SPL's but still gave the "subjective" impression of greater frequency extension where there literally was not such a design.
This is what I have always understood to be one of the important lessons the BBC gave us with the curve. Utilizing nothing much more than their ears, the BBC engineers designed a speaker which sounded correct in an actual room. This had never been attempted before they pulled out their slide rules and Baltic Birch baffles. The low frequency blip gave the sense of a subjectively lower frequency extension than the enclosure allowed (along with the AS enclosure parameters of course)and the high frequency roll off gave the subjective impression of greater high frequency content and extension than what the free field response indicated. Concessions were not made due to the limtations of the associated equipment (as in the Advent design) since the in field monitoring purpose of the 3/5a design most often meant the speaker was being fed a microphone or mixing board output which was capable of much greater extension with far less noise than a commercial LP would allow. Even when given the tape out feed, the BBC monitors were getting better than 15kHz response with minimal noise as Dolby A had been incorporated into most studio decks by the mid 1970's.
What the BBC engineers realized however, was the in-room gain at the frequency limits made for a very different sounding speaker than what the free field measurements suggested. That the 3/5a sounds as if it has flat extension well beyond its design limitations is not in question. As I said, I live with a pair of Roger's monitors as an almost everyday speaker. The speaker doesn't sound rolled off in the highs. Some people might describe the effect as "polite" (which is frequently the overall description of the BBC sound) by today's standards, but that is, in my opinion, due to the in-room response inaccuracies of many of today's commercial speakers. Too many of today's designs tend to have excessive response lifts at both ends in order to sell to an uneducated consumer. (Has anyone heard a mid-priced B&W lately?) The BBC engineers lived with the sound of real music from day to day. They used that sound as their reference. Most consumers in today's speaker maketplace have no idea what live music sounds like and simply compare one speaker to another. The speaker with the best "jump factor" most often wins whether thay are buying for their home or their car system.
I have no argument that the LS3/5a's sound as if they have flat response to at least the limits of my half century old ears when considered subjectively in-room. I do disagree that this repsonse is the result of a rising high frequency response which was designed into the speaker. Quite the contrary. The subjective rise is due to the actual roll off and the resultant in-room gain and is what should be considered an important lesson to be taken from the BBC designs.
That we still talk about and use the BBC "curve" is due to the correctness of what the designers did by ear in the early to mid 1970's. Just as we continue to find Blumlien's work of the 1930's relevant and correct in today's newest technologies, the BBC curve is important becuase of what it should have taught us but is instead what we choose to ignore to our own peril.
In short; flat response sucks!
I have not read everything in the thread, but I cannot find the explanation that I have heard for the BBC dip. Maybe it is not correct with reagerd to the "BBC dip", but I think it is a relevant explanation to why a speaker should have a small dip somewhere in the midrange:
Assume the normal stereo setup, and the situation where a phantom image is to be produced between the speakers, in the middle. The direct sound from the speakers will then hit the head slightly from the side, which through the HRTF will give a "baffle step" from the head, ie an increase of the higher frequencies. Still the phantom image is straight in front of the listener. This will give the impression of a sllightly too bright sound, which can be compensated for by a dip in the midrange.
I'm not quite sure how the highest treble fits into this line of reasoning, but still.
Assume the normal stereo setup, and the situation where a phantom image is to be produced between the speakers, in the middle. The direct sound from the speakers will then hit the head slightly from the side, which through the HRTF will give a "baffle step" from the head, ie an increase of the higher frequencies. Still the phantom image is straight in front of the listener. This will give the impression of a sllightly too bright sound, which can be compensated for by a dip in the midrange.
I'm not quite sure how the highest treble fits into this line of reasoning, but still.
soufiej said:
Hi,
If you are not familiar with in room curves just say so, don't comment.
In rooms curves correctly interpreted are as "real" as anything else.
I think us Brits ought to know what any reference to BBC terminology
meant in our magazines and articles, we don't need anyone telling us
"oh no you are wrong" this is actually what the BBC meant, or being
told what the BBC considered or didn't, us British hifi nuts know.
Of course that doesn't prevent total misrepresentation abroad.
/sreten.While I await the outcome of the HiFi News article search, I would think one more point is in order. It has been stated that the "rising" high frequency response (the combined result of in room response and designed in roll off) was corrected in later versions of the speaker. I think this too is possibly a matter of semantics. Yes, high frequency response was altered slightly when the drivers were brought back into line in the late 1980's. But, to change the overall frequency repsonse of the speaker would have violated one of the primary BBC specifications and policies for any of their monitor speakers. As long as the LS3/5 was operating under the "a" designation, the speaker had to allow any one speaker, of any vintage and in this case from any manufacturer, to substitute exactly for any other 3/5a of any vintage and from any manufacturer. Any change in overall frequency response would have necessitated another letter designation. This didn't occur in the lifespan of the 3/5a despite the change in impedance and the later move to bi-wiring. The LS3/5a remained the same speaker sonically throughout its lifespan and retained the same frequency response overall with which it began its existence here on this mortal coil.
What the 1980's revision did was bring the drivers back into a more consistent spec from where they had drifted over the course of fifteen or so years. The autoformer which trimmed the high frequency response of inidividual drivers was also replaced by a resistor which made the impedance change. All reviews of the 15 Ohm version vs. the 11 Ohm version indicate a smoother high frequency response from the newer speaker, but not a different response. (Though I find it interesting to note the real original LS3/5a, which was a one off and had a screwed together front and rear baffle was disqaulified from the LS3/5a Shootout due to its far superior sound compared to any of the commercial products.) While this is making the case for the specifics of the LS3/5a, it goes to the heart of the BBC sound. This specification for interchangeability was consistent throughout the BBC monitor speakers. Until the 3/5a was recently redesigned with new drivers and a new cabinet, and a new letter designation, the BBC liscense did not allow for any revisions of the 3/5a's overall response. To this end, the felt surround on the 3/5a was retained in the 1980's revision despite the better methods known by that time to control cabinet diffraction.
I will obviously allow for correction should the HiFi News articles point to a different conclusion. My copies of the magazine are in the attic and that is not the place I want to be in late July in Texas. But, I think you'll find what I have stated to be the case for this particular example of the BBC sound.
The Spendor BC1 and 2 (not BBC designs) showed sightly different anechoic or free field response curves owing to the more modern flat front baffle design when compared to the antiquated LS3/5a. However, the overall sound still met the general concept of the BBC sound in both models.
What the 1980's revision did was bring the drivers back into a more consistent spec from where they had drifted over the course of fifteen or so years. The autoformer which trimmed the high frequency response of inidividual drivers was also replaced by a resistor which made the impedance change. All reviews of the 15 Ohm version vs. the 11 Ohm version indicate a smoother high frequency response from the newer speaker, but not a different response. (Though I find it interesting to note the real original LS3/5a, which was a one off and had a screwed together front and rear baffle was disqaulified from the LS3/5a Shootout due to its far superior sound compared to any of the commercial products.) While this is making the case for the specifics of the LS3/5a, it goes to the heart of the BBC sound. This specification for interchangeability was consistent throughout the BBC monitor speakers. Until the 3/5a was recently redesigned with new drivers and a new cabinet, and a new letter designation, the BBC liscense did not allow for any revisions of the 3/5a's overall response. To this end, the felt surround on the 3/5a was retained in the 1980's revision despite the better methods known by that time to control cabinet diffraction.
I will obviously allow for correction should the HiFi News articles point to a different conclusion. My copies of the magazine are in the attic and that is not the place I want to be in late July in Texas. But, I think you'll find what I have stated to be the case for this particular example of the BBC sound.
The Spendor BC1 and 2 (not BBC designs) showed sightly different anechoic or free field response curves owing to the more modern flat front baffle design when compared to the antiquated LS3/5a. However, the overall sound still met the general concept of the BBC sound in both models.
As I remember LS3/5(a) FR measurements its not a small dip - its a straight falling FR from the bottom all the way to the crossover point, and tweeter sets in with a bit higher level - this is supposed to give the famous polite sound, and together with the high Qt the experience of more bass, midbass actually
I came to this thread thinking the answer was, "A pay rise significantly below the rate of inflation tied to a unpleasant change in the Conditions of Service".
The LS3/5a was designed to sound as much like the real thing as possible, not to sound nice. When you hear your presenters' voices daily in the canteen or newsroom you know what they should sound like. If they don't sound as they should, you change your microphone position (if possible), choose a different microphone (if possible), or tweak the eq. on the desk. You rely on your loudspeakers to be accurate.
The LS3/5a was designed to sound as much like the real thing as possible, not to sound nice. When you hear your presenters' voices daily in the canteen or newsroom you know what they should sound like. If they don't sound as they should, you change your microphone position (if possible), choose a different microphone (if possible), or tweak the eq. on the desk. You rely on your loudspeakers to be accurate.
sreten said:
If you are not familiar with in room curves just say so, don't comment.
In rooms curves correctly interpreted are as "real" as anything else.
I think us Brits ought to know what any reference to BBC terminology
meant in our magazines and articles, we don't need anyone telling us
"oh no you are wrong" this is actually what the BBC meant, or being
told what the BBC considered or didn't, us British hifi nuts know.
Of course that doesn't prevent total misrepresentation abroad.
Sreten
Playing the I'm British I ought to know card is pure hogwash and you know it. Is your post meant as a troll?
Fact 1) There is a significant bass boost in LS3/5a in any version.
Fact 2) The tweeter needs a boost because of diffraction issues.
Fact3) Between the two peaks there must be a dip.
Fac4) Due to driver supply issues and number of taps on the tweeter/woofer crossover with no BBC testing methodology there must be a wide variation in sound from unit to unit.
I don't know what all the fuss is about. The LS3/5A was designed to sound as accurate as possible in the unforgiving environment of a mobile studio/control room, and as a byproduct, works well in the smaller and less regular European style house. It will not work in larger rooms, because of the compromises that design entails. I'm sure many of the copies were slightly different, but they all had to work within the tolerances of the BBC spec to be called LS3/5A, and it was only when the original drivers became unavailable that the spec had to be rewritten. Where's the problem?
I assure you my feathers are smoothed and I thought my response was quite civil. I assumed the bit about what Brits should know was meant to be hysterically funny. How else should/could it be taken? My "political" comments were meant only in jest and a good natured realization of a situation we both share due to our mutual understanding of what government officials mean when they say something. I'm sorry you felt they needed to be removed from the forum.
I get the sense the 3/5a engenders this sort of response quite often. It is a love/hate type of product. I believe I've tried to indicate the fact the BBC "curve" has elements which go beyond the frequency response of the 3/5a and those facts are releveant to what we design, sell and buy in today's market. The 3/5a was hardly the only speaker which employed the curve, as I've noted. The discussion can settle on those qualities which are still valubale lessons today. Or, we can drop the whole issue as the original poster seems to be satisfied with the idea of a BBC "curve" and has placed additional weight on those answers which indicate a British origin.
I get the sense the 3/5a engenders this sort of response quite often. It is a love/hate type of product. I believe I've tried to indicate the fact the BBC "curve" has elements which go beyond the frequency response of the 3/5a and those facts are releveant to what we design, sell and buy in today's market. The 3/5a was hardly the only speaker which employed the curve, as I've noted. The discussion can settle on those qualities which are still valubale lessons today. Or, we can drop the whole issue as the original poster seems to be satisfied with the idea of a BBC "curve" and has placed additional weight on those answers which indicate a British origin.
I have heard of the so called "BBC dip" a number of times before I came into this thread. As speaker designer, as I went through the unofficial web site I grew to love the characteristics of the LS3/5a design. ( the use of elliptical filters and a autotransformer is pretty innovative me thinks) My belief is that it was initially developed by engineers, with ears as their primary tool, to sound as accurate as possible without understanding the theory. I believe the theory has caught up to validate their design after the fact, mainly in regards to baffle step compensation. I think the only fault in the design was trying to specify the crossover design and not the testing to specifications route. Not surprising the problems they had with drivers, as is still bane of most speaker manufacturers today.
infinia said:
Hi,
Sorry if sounded like I was getting a little shirty, but the answer
is no. I suppose its that I find simple contradiction annoying.
Its one thing understanding the development of speaker design,
quite another knowing about who, what, when and how these
things happened. Just seemed to me someone was inventing
their own version of history and in the process ignoring several
posts from different people (who happened to be Brits) all more
or less giving the same version of history regarding one point.
Going back to the original question, ignoring the much more used
term BBC dip (around 3Khz), BBC "rise" as a term is not common
(as the googling post amply demonstrates), and if it actually means
anything it relates to the early (deliberately) overbright LS3/5a's.
/sreten.
Then I ask that the person who should understand the BBC's policies better than any foreigner possibly could to explain something to me that I apparently do not understand.
If the "early" version, as you call it, of the LS3/5a had this rising response (which I don't believe you've proved is in the design itself, merely in the subjective and in-room curves), and that response was altered in later versions, why was no letter designation made to reflect the dissimilar response curves? It is a well known fact, even on this side of the pond, that any 3/5a must have the ability to substitute for any other 3/5a. That would seem impossible if two speakers have different frequency response curves.
If the "early" version, as you call it, of the LS3/5a had this rising response (which I don't believe you've proved is in the design itself, merely in the subjective and in-room curves), and that response was altered in later versions, why was no letter designation made to reflect the dissimilar response curves? It is a well known fact, even on this side of the pond, that any 3/5a must have the ability to substitute for any other 3/5a. That would seem impossible if two speakers have different frequency response curves.
Taken from "A Little Legend, The BBC LS3/5A.Trevor Butler. January 1989. HiFi News and Record Review." It can be found on the Unofficial LS3/5a web site.
"Therefore KEF was able to offer matched components to the manufacturing licensees even though the company does not manufacture the speaker in its entirety themselves. It so happens that all three current licensees use the KEF matched parts. At the end of a day it has to be said that KEF did a superb job. They were issued with a BBC LS3/%a reference unit (no. 6) of 1975 vintage and produced a set of 1988 parts which sounded so similar that they were within Grade I limits, and could be made much more consistently. Hence LS3/5A remains.
...
It would perhaps have been simpler in the long term for the BBC to have completely re-designed the speaker, and to have produced a LS3/5B, but they did not want nor could they afford this option, since some three and a half thousand of the existing design were in use up and down the country. And design change had to produce similar results and the same response because future models would end up alongside existing ones. Even today, when a batch is taken to a location, it does not matter whether some are from one generation and some from another - they should all be capable of matching as stereo pairs. That in essence is the whole purpose of the design, consistency through production and during use, anywhere. To sum up, then, the recent changes have offered no enhancements in terms of specification, simply a means to provide better consistency in production to maintain the speaker's standard. This is now back on 'median' and so may sound a little different from those latter 'older models' of just pre-Christmas 1987, but will sound the same as earlier production runs.
...
So an LS3/5A circa1977/78 will not in any particular way be better or worse than one from 1983 or now. The consensus of opinion from those who understand balance, is that the system is the same and offers the same qualities as it always has in terms of its tonal characteristics.
In detail, the latest models are now marginally smoother because irregularities of the high treble have been sorted out, and the coloration has been reduced by a small degree with the new surround, but not so as to affect the tonal balance, because the perception of localized coloration is all part of the balance of the loudspeaker system and its equalization. So if the tonal coloration was reduced to an extent in, say, the 1kHz region where it was noticeable, it could highlight coloration’s elsewhere.
The new design offers only, in real terms, a better consistency, executed by KEF to maintain the standard. No enhancement in terms of the specification was made although commentators say the loudspeaker now sounds a little better because it is back on the median. Essentially it produces the same sound. This has been backed by tests carried out at the BBC and with manufacturers, with regard to the units stereo capability."
************************************************
Is it not possible we are merely debating a measurement taken with varying techniques? All anechoic measurements I can find show the gentle response roll off which I've suggested occurring around the 15kHz range.
http://www.stereophile.com/standloudspeakers/361/index6.html
http://www.stereophile.com/standloudspeakers/361/index7.html
http://www.stereophile.com/standloudspeakers/361/index10.html
While the in-room measurements reflect the slightly rising top end which can be seen in other graphs. I do think we can safely discard the "subjective" response for our purposes other than to say the speaker sounds somewhat different in-room than it measures in a non-reflective environment. Just as we would expect. No?
There are other possible explanations for the variance shown in different graphs. The 3/5a was meant to be used with its Tygan grill in place. This grill has an obvious effect on the response of the speaker as does the protective cover over the T-27 tweeter. Since it is not noted whether the measurements were generally taken with the grill in place, should we not assume this could possibly explain away some differences in how the speaker measured?
Finally, does any of this bickering further the discussion of the BBC "curve"? I fall back on my understanding of what the term means and think the in-room high frequency response is but a part of what we should take away from the lessons of the 3/5a. To me the idea that the 3/5a was seminal to speaker design boils down to the many lessons this speaker can teach us. While the actual theory might not have been fully fleshed out by the BBC engineers, it is obvious they understood the concepts. I find it difficult to believe the conceptualization of the problem and the resulting solution did not contribute to the theory's proof as the mathematics became more powerful with the aid of computers. Many of the engineers who worked on the 3/5a project, and other similar BBC designs, went on to make landmark contributions to speaker design and have become legends in their own right. It is the idea that much of what the BBC engineers accomplished with their ears and their slide rules led us to a better understanding of speaker design theory. That is what still makes the BBC curve important to us today.
"Therefore KEF was able to offer matched components to the manufacturing licensees even though the company does not manufacture the speaker in its entirety themselves. It so happens that all three current licensees use the KEF matched parts. At the end of a day it has to be said that KEF did a superb job. They were issued with a BBC LS3/%a reference unit (no. 6) of 1975 vintage and produced a set of 1988 parts which sounded so similar that they were within Grade I limits, and could be made much more consistently. Hence LS3/5A remains.
...
It would perhaps have been simpler in the long term for the BBC to have completely re-designed the speaker, and to have produced a LS3/5B, but they did not want nor could they afford this option, since some three and a half thousand of the existing design were in use up and down the country. And design change had to produce similar results and the same response because future models would end up alongside existing ones. Even today, when a batch is taken to a location, it does not matter whether some are from one generation and some from another - they should all be capable of matching as stereo pairs. That in essence is the whole purpose of the design, consistency through production and during use, anywhere. To sum up, then, the recent changes have offered no enhancements in terms of specification, simply a means to provide better consistency in production to maintain the speaker's standard. This is now back on 'median' and so may sound a little different from those latter 'older models' of just pre-Christmas 1987, but will sound the same as earlier production runs.
...
So an LS3/5A circa1977/78 will not in any particular way be better or worse than one from 1983 or now. The consensus of opinion from those who understand balance, is that the system is the same and offers the same qualities as it always has in terms of its tonal characteristics.
In detail, the latest models are now marginally smoother because irregularities of the high treble have been sorted out, and the coloration has been reduced by a small degree with the new surround, but not so as to affect the tonal balance, because the perception of localized coloration is all part of the balance of the loudspeaker system and its equalization. So if the tonal coloration was reduced to an extent in, say, the 1kHz region where it was noticeable, it could highlight coloration’s elsewhere.
The new design offers only, in real terms, a better consistency, executed by KEF to maintain the standard. No enhancement in terms of the specification was made although commentators say the loudspeaker now sounds a little better because it is back on the median. Essentially it produces the same sound. This has been backed by tests carried out at the BBC and with manufacturers, with regard to the units stereo capability."
************************************************
Is it not possible we are merely debating a measurement taken with varying techniques? All anechoic measurements I can find show the gentle response roll off which I've suggested occurring around the 15kHz range.
http://www.stereophile.com/standloudspeakers/361/index6.html
http://www.stereophile.com/standloudspeakers/361/index7.html
http://www.stereophile.com/standloudspeakers/361/index10.html
While the in-room measurements reflect the slightly rising top end which can be seen in other graphs. I do think we can safely discard the "subjective" response for our purposes other than to say the speaker sounds somewhat different in-room than it measures in a non-reflective environment. Just as we would expect. No?
There are other possible explanations for the variance shown in different graphs. The 3/5a was meant to be used with its Tygan grill in place. This grill has an obvious effect on the response of the speaker as does the protective cover over the T-27 tweeter. Since it is not noted whether the measurements were generally taken with the grill in place, should we not assume this could possibly explain away some differences in how the speaker measured?
Finally, does any of this bickering further the discussion of the BBC "curve"? I fall back on my understanding of what the term means and think the in-room high frequency response is but a part of what we should take away from the lessons of the 3/5a. To me the idea that the 3/5a was seminal to speaker design boils down to the many lessons this speaker can teach us. While the actual theory might not have been fully fleshed out by the BBC engineers, it is obvious they understood the concepts. I find it difficult to believe the conceptualization of the problem and the resulting solution did not contribute to the theory's proof as the mathematics became more powerful with the aid of computers. Many of the engineers who worked on the 3/5a project, and other similar BBC designs, went on to make landmark contributions to speaker design and have become legends in their own right. It is the idea that much of what the BBC engineers accomplished with their ears and their slide rules led us to a better understanding of speaker design theory. That is what still makes the BBC curve important to us today.
Hello
There is an article by John Kreskov on his web site, " www.musicanddesign.com " ( go to the old one ) under " mesurments ", called " The effect of voice coil impedance variation on passive system response ". He says " the so called BBC dip observed in low level measurements may tend to flatten out at elevated levels where the ear is less sensitive in this criical area ". Basically he states that this may help in an effort to retain tonal balance as the playback SPL level varies. Worth a read to add to this debate !
Roy
There is an article by John Kreskov on his web site, " www.musicanddesign.com " ( go to the old one ) under " mesurments ", called " The effect of voice coil impedance variation on passive system response ". He says " the so called BBC dip observed in low level measurements may tend to flatten out at elevated levels where the ear is less sensitive in this criical area ". Basically he states that this may help in an effort to retain tonal balance as the playback SPL level varies. Worth a read to add to this debate !
Roy
Thanks for the post Roy. That would make the BBC engineers even smarter than I had previously imagined.
"However, it should be noted that the response irregularities with signal level shown here are in the imediate region of the crossover. Typically in a two or three way system the crossover to the tweeter is in the 2k Hz to 4k Hz region where the ear is extremely sensitive, particularly at lower SPL levels. Thus designing a crossover with a so called BBC dip observed in low level measurements may tend to flatten out at elevated SPL levels where the ear is less sensitive in this critical area. Thus there is the potential for the behavior show here to actually be used to advantage in passive crossover design in an effort to retain tonal balance as the playback SPL level varies. Regardless of whether or not such benefits can be realized, the important observation here is that the designer must be cognizant of these effect if the crossover design is to prove sucessful."
"However, it should be noted that the response irregularities with signal level shown here are in the imediate region of the crossover. Typically in a two or three way system the crossover to the tweeter is in the 2k Hz to 4k Hz region where the ear is extremely sensitive, particularly at lower SPL levels. Thus designing a crossover with a so called BBC dip observed in low level measurements may tend to flatten out at elevated SPL levels where the ear is less sensitive in this critical area. Thus there is the potential for the behavior show here to actually be used to advantage in passive crossover design in an effort to retain tonal balance as the playback SPL level varies. Regardless of whether or not such benefits can be realized, the important observation here is that the designer must be cognizant of these effect if the crossover design is to prove sucessful."
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