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October 15, 2017 / consort3


I am always tweaking this blog. Unfortunately I tend to edit existing posts, so it is worth re-checking pages you are interested in, if you have visited before.

Changelog 5/9/17 link to Booker T Stax Prom on Renaissance to Rock page 13/9/17 Audio woo link on Loudspeaker projects page. Failure of record formats links on Technology page. 2/10/17 Build a better monster link on Orwell festival page. 5/10/17 Sputnik 1 link on Olympus page. 6/10/17 Amelia Earhart link on Aviation mysteries page. 16/10/17 added Good bass from a low Xmax woofer page

October 14, 2017 / consort3

Good bass from a low Xmax woofer

In celebration of 50000 hits, a lot of reads but not much comment, what it is to have the gift of exposition!  Anyway in honouring the occasion, I offer the following.

You cannot get good deep bass from a Woofer with low Xmax, right. Wrong, it can be done and here is a way to do it.  Thiele in 1961 realised that the equivalent circuit of a bass reflex speaker was a fiIter. Filter development is a method of selecting the poles (and possibly zeros) of a transfer function to meet a particular design criterion. Thus was born the scientific way of doing speaker design, Thiele-Small parameters and the concept of alignments, as in aligning filters.

In the old days you looked up alignments in tables . A bass reflex is a forth order filter. I was fascinated by the sixth order alignments which offered bass extension and control of the excursion by adding an external high pass filter. An underdamped second order filter has boost and can compensate for the drop off in frequency response at low frequencies. Because the speaker has to be active, the design has not been popular until recently for sub-woofer use.

The cone excursion on a bass reflex is at a minimum at the box tuning frequency determined by the port.  I realised that if you made the external boost filter peak at the port box tuning frequency , it would minimise the excursion. I did a design which worked well, then I discovered Don Keele’s paper describing the idea scientifically.

The two equations (possibly the 2 simplest equations in the whole of speakerdom!) describing the Keele alignment are these:

Vb=4.1 X Qts2 X Vas


Keele applies  a filter with 6db boost at the port frequency and this is also the -3dB response limit. These are good starting point for a design. The equations are approximations so it is worth checking using a modern computer program. Winisd is an excellent program for this type of design as you can call on a peaking filter and observe the cone excursion. In my case to keep the twin peaks of cone excursion level and below the Xmax limit I had to offset the external filter upwards from 44Hz to 50Hz resulting in a slight drop of response which I corrected by making the boost 8db.

System response showing 44Hz 6dB peak filter and 50Hz 8dB filter:


Cone excursion with the 2 filters


Filter response of the 2 filters


I looked up the damping factor needed for 8db boost in Don Lancasters Active filter cookbook. Fig.3.25 gave me a figure of 0.4. I used the Japanese filter website to come up with a circuit.

However  when I simulated the design I got 4dB boost. So I used a figure of 0.2 as damping factor and got the 8 dB boost and this circuit:


Such a simple circuit to solve all those problems! You do need to drive the speaker with a good power amplifier capable of supplying current at the peak frequency. The low frequencies and small boxes allowed by the technique give a port problem. The long port typically required  is difficult to realise. I am going to use the speaker stand as a port tube.

February 28, 2017 / consort3

Minimalist Duelund crossover

A remarkably cost effective 3 way active circuit is due to Egerton in WW Circuit ideas, Jan 1988. A subsequent analysis by Brian Pollard in WW Feedback July 1988 showed a slight error in Egerton’s analysis but despite that the circuit is adequate. As given the crossover frequencies are 363 Hz and 1.456 kHz. Egerton found he needed a 200pF capacitor across R5 to suppress high frequency oscillation. The midrange filter is a maximally flat type. I haven’t tried this circuit myself as I have only just found it. Such an elegant circuit demands a decent implementation. However the mid-range driver needs to be high quality and ATC domes do not come cheap!  A 2 way design could be made by eliminating the woofer components.

The resistor values given are exact presumably so you can see the relationships. Putting the nearest E24 series values slightly changes the results. I scaled the resistor values to the highest I would be comfortable with. That also gives the lowest capacitor value.

Try R1,2,3,4 &6 as27k, R5 &13 as 16k, R12 10k, R8 68k, R10 39k all Cs 8.2n. If the Cs are made 4.7n the crossover frequencies are 655 and 2.675kHz, which is suitable for the Faital pro 3FE22 I want to try.

The circuit appears to be a minimalist form of the State variable filter.  The tweeter circuit unusually uses differentiators and an op amp is saved by combining the summing functions. Rod Elliots adjustable version  of the filter (an analogue DCX2496!) is explained here:

The circuit seems pretty close to a Duelund crossover. John K has an analysis of the Duelund here:

There is also a good analysis by Linkwitz on his site. The other John K used a Dayton RS52 in one of his designs, which might be an appropriate mid-range unit. However it would need a notch filter to get rid of the breakup spike. Talking of the RS52 this project uses it:

Although the designer does not mention it, the crossover looks “Duelundish” to me!

Using Ltspice, I summed the outputs in simulation by using a simple mixer circuit. That showed that the polarity of the mid had to be inverted as Pollard had noticed, also that the mid out was 3db more than normal which could be compensated by the mid amplifier of course.

An easier way to sum the outputs is to use Plot settings/Add trace then in the “expressions to add” window, add the woofer and tweeter outputs (+sign) and subtract the middle output. This shows an underdamped response. Reference to Don Lancasters Active Filter cookbook which has a good section on State variable filters showed that R5 could be tweaked to vary the damping . With R5 at 7.1k the mid response is a plateau but 4.4dB above nominal.


With R1,2,3,4 & 6 as 13k, R5 9.1k R12 3.6k R13 6.2k R8 47k and R10 27k also all Cs 10n you get crossover frequencies at 447 and 3.57k suitable for the venerated ATC mid dome. If R5 is made 12k you get the plateau response with a 4.4dB lift.


There is a good discussion on the Duelund here particularly post 26 by Jon Marsh

Jons piece plus my sims showed that the mid output should be below the woofer and tweeter outputs. To get a level sum on the original circuit, I found it easier to raise the woofer and tweeter levels by raising R2 & R6 to 18k and making R5 9k. Mid in and out of phase plot with this mod:


I am sufficiently intrigued by this circuit that I am going to try it with a HiVi TM1a mid/tweeter combination plus my long suffering CP168. Crossover points would be 1.4K and 5.5K

A 4 way Duelund!

The above site has a helpful application to work out values for a passive Duelund circuit. To emulate the Egerton circuit, I used an A factor of 2.3 and got this:


With this outcome:


Another useful Htguide thread on a derivative of John K’s RS52 design:

The electronic filter slopes are also the target acoustic slopes, but the drive units will not perfectly convert their electric inputs to acoustic outputs. It is the amount of tweaking needed, the less the better, which will determine the success of this filter topology.

Pdf of original article:


A tone control based on similar filtering techniques:

February 6, 2017 / consort3

Darlington Part 4, more thoughts

I developed the amp a few years ago and was surprised how good the transient performance of such a simple design was. I think that performance is partly due to the current drive of the output stage.

The concept makes a virtue of a potential problem. Baxandall pointed out that Transistor Cbc  would slow the response. In this case it acts as a free Cdom stabilising the Vas, which is the output stage.

I needed 800 ohm base stopper resistors to make the simulated design work, but they were not needed for the real world (except for the anomalous ST TIP142).  I suspect that this is why the real world high frequency distortion was better than 0.1%, whereas the simulated distortion was 0.5%. More work needed to match the simulated to the real results but I leave that to the experts.

It was revealing to look at the op-amp output when the amplifier was giving a full output 20kHz triangle wave. There is a dead band which transitions in 1 to 2uS so you will be blissfully unaware of any problem. The ramps show that the darlingtons have good linearity.

However I was not 100% happy with the voltage regulators as a band-aid fix for the quiescent current with supply voltage variation problem. Hence the design never made it to a dedicated PCB layout from the Veroboard prototype. Nor did I formally post it to Diyaudio. I developed it until it was good enough for my own domestic use, but would not regard it as a “production” design. However the prototype has been happily working for several years so I offer the following ideas which I have not tried for you to experiment with.

The main issue was the quiescent current variation with supply volts. A way around this is to have 2 current setting pots, one for each of the upper and lower halves of the output stage.  The current defining resistor is eliminated. Also the voltage regulators are removed. When setting the currents a resistive load is required. R13,14,30 and 31 to be 250 ohm preset pots. R10 and R28 are removed as well as the regulator components.

The current stability would also be improved by defining the op amp voltages with zeners. To lower the self heating effects of the NE5534, the voltage of these would be 12 rather than 15V. R2,3,21 and 22 are now 12V zeners. Also R4,9 ,23,and 27 are 330 ohm.

The thermal feedback would be more consistent if the Thermistors were bonded to solder tags and the tags used as the power transistor mounting washers. Nelson Pass uses tagged thermistors in his designs which gave me the idea.

Lastly a R-C filter at the input to limit the bandwidth both for TIM and radio interference reasons would be worth fitting. Put 470pF caps across R1 and R20

I just discovered the reason for the anomalous ST TIP142. The zeptobars website has photos of the silicon dies used for various devices. One of these for the 2STD1665 gave a clue that the device would be fast (too fast for owner!) If you look up the spec for the device it is fast. Curiously ST do not make speed claims for the similar planar base island TIP142

November 3, 2016 / consort3

Some History of technology

Where it began, for our purposes, little known Elizabethan physician Gilbert

Stephen Gray, the discoverer of electrical conduction

Thought Morse invented the Telegraph? Francis Ronalds invented it in 1816. Unfortunately no-one wanted it.

It has been 150 years since Maxwell presented his equations:

The history of Maxwells equations

My friend has summarised them here:

Maxwells Equ

Heaviside’s conflict with Preece “Theory versus practice”


A worthy biography of Heaviside is “Oliver Heaviside”   by Paul Nahin

Another book on Heaviside

Another 150th anniversary George Boole. Boole like Heaviside was self -taught.

There is more to Boole than Boolean

Interesting article about a contemporary of Maxwell and Boole, namely Babbage

More detail on the invention

Article about Babbages friend, the first programmer, Ada–augusta-ada-lovelace/id/7225

Great piece on Ada and Babbage by Wolfram

Impressive comic book of the Ada/Babbage story

Another contemporary British invention, the Bessemer process

A quartet of Victorian engineers beginning with B

I had to make it a quintet of people beginning with B. Thomas Bayes came up with Bayes’ Theorem, a basic law of probability governing how to modify one’s beliefs when new evidence arrives. Are you Bayesian or Boolean?

In the Boolean worldview, the world is organised into basic situations such as Sydney being north of Melbourne. Such situations are facts. Truth is correspondence to facts. That is, if a belief matches a fact, it is objectively true; if not, it is objectively false. If you and I disagree, one of us must be right, the other wrong; and if I know I’m right, then I know you’re wrong. Totally wrong.

In the Bayesian worldview, beliefs are not simply true or false, but more or less probable. That is, we can be more or less confident that they are true, given how they relate to our other beliefs and how confident we are in them. If you and I disagree about the cause of climate change, it is not a matter of me being wholly right and you being wholly wrong, but about the differing levels of confidence we have in a range of hypotheses. Dare I say it, shades of grey!

Good explantion of Bayes Theorem

Another question, are you Babylonian or Balkan in your Philosophy? Feynman used to say that there were two kinds of Physicists, the Babylonians and the Greeks. He was referring to the opposing philosophies of those ancient civilizations. The Babylonians made western civilization’s first great strides in understanding numbers and equations, and in geometry.
Yet it was the later Greeks – in particular Thales, Pythagoras, and Euclid – whom we credit with inventing Mathematics. This is because the Babylonians cared only whether or not a method of calculation worked – that is, adequately described a real physical situation – and not whether it was exact, or fitted into any greater logical system. Thales and his Greek followers, on the other hand, invented the idea of theorem and proof – and required that for a statement to be considered thorough, it had to be an exact logical consequence of a system of explicitly stated axioms or assumptions. To put it simply, the Babylonians focused on phenomena, the Greeks on the underlying order.”
Nevertheless, the existence of Babylonian method has actually a deep sense: axiomatic approach can be formulated only if satisfactory number of facts, needed for the generalization, is accumulated.

Interesting reflections on Feynman:

Comments on the Feynman minority report of the shuttle disaster, interesting blog BTW

Feynman’s Minority Report and Top-Down Design | The Multidisciplinarian

More on Feynman:

How ARM happened

More on the history of ARM

Arm 25th anniversary

350 years of scientific publishing. The Royal Society

Contemporary work showing interest in Science from the nobility

How technology developed from the enlightenment

A good summary of the basics of electronics:

Germanium is making a comeback:

The hacker hacked

The history of spreadsheets or the first killer app:

Unsung computing hero Douglas Englebart

The engineering approach to innovation in science

More on this idea

Review of TRIZ for dummies

How to engineer serendipity

Divisions of time

Talking astronomy, where Jocelyn Bell discovered the Quasar. She, Lise Meitner and Rosalind Franklin are more famous female scientists than if they were Nobel Laureates:

Talking of Rosalind Franklin here is the story of the how the structure of DNA was discovered:

More on Crick

Lest I be accused of eurocentrism in the history of science

Sorry its creeping back in. Horrocks

Restoring the balance, Martin Bernal and Black Athena

More balance, Sanskrit and the periodic table

Erdos and the Egyptian fraction problem:

Computers can lead to experiments not being repeatable:

The future of the professions

Philosophy and work/life balance

Lord Nuffields philanthropy

Babylonian maths more advanced than we previously thought:

On the other hand:

The clock on most computers started theoretically on 1st Jan  1970. Someone has worked out when the clock on the Anti-Kythera mechanism started, for solar eclipses it is 12 May 205BC.


The age of enlightenment has become the age of entanglement

Newtons recipe for the Philosophers stone

The extraordinary career of William Dampier

Richard Hakluyt and his early travel book

The silicon revolution started at  Shockley Semiconductor in April 1956 at Santa Clara which was the year Shockley got the Nobel prize for Physics for inventing the transistor. However by 1957 a number of staff he had recruited left to join Fairchild. More here:

How Silicon Valley got the name in 1971:

Unfortunately, all those manufacturing plants in Silicon Valley have left a toxic legacy in the groundwater.

The is/ ought problem

The above was written by Enlightenment philosopher David Hume who may have got some of his ideas from Buddism

The friendship between Hume and Adam Smith

More on Buddism:

Salvation by algorithm!

A scientific look at religon

Smartphones and social media are supposed to connect us. What happens when we are so constantly connected that forget how to be alone?

How information technology affects capitalism:

Maths lessons 4000 years ago in Babylon:

The beginnings of modern philosophy?

The continuation of Greek Philosophy

Scientists solve Prince Ruperts drops mystery:

Genetically engineered Petunia history

November 3, 2016 / consort3

Shakespeare Scrapbook

Another alliterative professor (see 741) was Ephraim Everitt who came up with the radical idea that Shakespeare had written more plays and suggested some. His idea was pooh-poohed at the time but these days there is more of an academic consensus that the bard wrote Edward III. Everitt also reckoned that the manuscript of Edmund Ironside was in Shakespeare’s own hand.

Well this is interesting. Kims FFP technique produced the following table:


Which shows Edward III to be more like Marlowe than Shakespeare. Also interesting is that the  Henry VI part 2 and 3 plays are grouped with Marlowe, possible collaboration when they were both working for Stanley, but part 1 is elsewhere, possibly Nashe had some involvement. Dido, Queen of Carthage is also in the same area, might Shakespeare be the collaborator with Marlowe back in 1587. So keen is Shakespeare on the story of Dido, the Queen of Carthage,  that he mentions her four times in The Tempest, twice in Titus Andronicus, and once each in The Merchant of Venice2 Henry VI, Antony and CleopatraHamlet, and Romeo and Juliet.

One issue I have with Kims FFP technique is the spelling or lack of consistency in Shakespeares time:

Co-author with Marlowe of Henry VI ?

More statistical text analysis

Another play to add to the canon?

Amazing what people can derive from a few lines of Shakespeare

Shakespeare Hackfest

Shakespeare as it would have been pronounced in 1600

Translate your text to Shakespearean dialogue!

Cumberbatch does Hamlet

Not a lot of people know that Shakespeare translated Hamlet from the original Klingon. For too long, readers throughout the Federation have been exposed to The Tragedy of Khamlet, Son of the Emperor of Qo’nos, that classic work of Klingon™ literature, only through inadequate and misleading English translations. Now at last, thanks to the tireless efforts of the Klingon Language Institute, this powerful drama by the legendary Klingon playwright, Wil’yam Shex’pir, can be appreciated in the elegance and glory of its original tongue. khamcov

Talking Sci-Fi I realised I had just missed towel day:

I have an obscure connection with Douglas Adams and it’s not that I once drove a Ford Prefect! There is a related obscure connection between Adams and the renaissance in that Douglas lived in the same small village as William Byrd, the medieval composer.

Consorts conjectures The absence of information about the ‘lost years’ of the Bard has led me to make some informed guesses about those lost years.

1578 Shakespeare leaves school early due to his father’s financial downfall and becomes teaching assistant at a noble house. He develops playwriting and acting skills teaching children. The noble house could have been the Stanley family place at Lathom. I think he could have developed into Stanleys Poet as it was fashionable then for noble people to have your own tame poet. When Stanley formed his own acting troupe in 1587 Shakespeare would have been in a good position to join the troupe. Stanley was  a lawyer and he might have doubled as Stanleys scrivener..

1582 Aged 18, he marries Anne Hathaway and they have a child (this is known)

1585 After his twins are born moves to London. Possibly with Stanley at his London base (Cannon Row).

1587 He becomes so useful to acting company that he is invited to join, writing plays from scratch.

One more alliterative professor Hildegard Hammerschmidt-Hummel and Shakespeares portraits

A history channel documentary covered this (50 mins in)

Modern re-creation of Shakespeares portrait

The lack of evidence of Shakespeares life has led to some notorious forgeries:

These are extensively covered by yet another alliterative Professor, Samuel Schoenbaum’s in Shakespeares lives. Schoenbaum dominated Shakespeares studies and was intolerant of others views, yet with so little factual evidence there is only speculation. Ian Wilson in “Shakespeare the evidence” has a convincing argument that Shakespeare was under the patronage of Ferdinando Stanley.

The worldwide following of Shakespeare

Another attempt to rewrite the Bard

Where did Shakespearean Londoners go when they wanted a day out? To Brentford Staines or Ware according to Middleton and Dekkers Roaring girl of 1612. In Jacobean times the Thames was tidal up to Staines, so they would go up river on a flood tide and back downriver on an ebb tide. The journey to Ware was more difficult up the River Lea. Edmund Spenser described the river in his epic poem The Faerie Queene as “the wanton Lea that oft doth lose his way”. The Lea could confuse travellers with its twisting, splitting course.

Parody of “Shall I compare thee to a summers day”

Discussing memorable Shakespeare lines with a friend and he remembered “What news on the Rialto” from the Merchant of Venice. This had resonances with me as I am restoring a Reliant Rialto car! Another line from the same play he remembered was “Do  cream and mantle like a standing pond”

The poisons, potions and charms of Shakespeare

On the 400th anniversary this seems apposite:

Which is Shakespeares most popular play:

Interesting that King Lear does not appear in the top ten in the US but is popular in the UK, perhaps we have more ageing thespians.

Shakespeare web-comic

There is a link between the rythym of  Rap music and iambic pentameter which I have only just realised, thanks to Lenny Henry.

Restoration of Religious paintings John Shakespeare supposedly whitewashed

Hi tech version of the Tempest:

I recommend the BBC comedy series Upstart Crow by Ben Elton.

Not alliterative but Oxford professors CS Lewis, Tolkien and Lewis Carroll turned Christianity, Anglo Saxon and mathematics into successful works of fiction.

Cornish influence on medieval Theatre:

I mentioned Douglas Adams towel day another literary anniversary celebrates Joyces controversial Ulysses. All I know is that Allan Sherman rhymes it with Sissies!

November 1, 2016 / consort3

80 years of BBC TV

On Nov 2 1936 the BBC started TV broadcasts from Alexandra Palace. There were 2 systems the Baird and the Marconi-EMI and both systems were tried, the Marconi system winning. That decision was made in March 1937. On May 12th 1937 the first British outside broadcast was made, the Coronation of George VI. You could buy these sets at launch:
By September 1938 KB and Philips sets were also available
These were household names back until the 1980’s, when Sony, Hitachi (GEC) Toshiba(Rank), Panasonic, Sanyo(Philips/Pye) and Tatung (Decca)  took over. The bracketed make is the factory that the Japanese took over. Pedants will point out that Tatung was from Taiwan. Funny how the Japanese made a success of TV production in the UK when the Brits could not.
A BBC programme covers the start up:
The Baird work was not wasted as the flying spot Telecine became a useful piece of kit.
The 1953 coronation of the present Queen provided a major boost for TV. A lot of the population finding a place to view a TV set. My father in law built a DIY one for the occasion.

Here is the history straight from the horses mouth:

German experiments with early TV

Yet another great engineer beginning with B, Blumlein gets a posthumous Grammy award for inventing stereo, but his inventions  helped establish Television.

Another great engineer beginning with B was Walter Bruch who invented the PAL colour TV system

Aug 14 2017 is the 50th anniversary of the Marine offences act (hello Sailor!) which outlawed the Pirate radio stations: