Tuesday, 22 September 2009

Microphone placement problem

When covering an auditorium to listen to the congregation the rule of thumb is that the distance between microphone is 3 times the distance from the sound source.

This ensure a 12db level difference between adjacent microphones and thus eliminates phase cancellation distortion problems.

If two microphones are picking up the same sound source from different locations, some phase cancellation or summing may be occurring.

Phase cancellation happens when two microphones are receiving the same soundwave but with opposite pressure zones (that is,180 degrees out of phase).

The areas coloured above will suffer degradation due to the soundwaves being out of phase.

The solution is to have the microphones spaced wider, or closer to the sound source depending on what is most practical for the circumstances.

Monday, 23 March 2009

Please do not ask me how I am.

Please do not ask me how I am.

Life is hard,
It has been a struggle to be with you today,
Please do not ask me how I am.

Say it is good to see me,
Ask me how I like to meeting, but
Please do not ask me how I am.

If I think about how I am
I will remember
and retreat back into my shell, so
Please do not ask me how I am.

Wednesday, 21 May 2008

Loch Garry Communications Installation, Project Cancelled?

The ELF (Extremely Low Frequency) facility in America, which became operational in 1989, was a means of communicating with a submerged submarine. Due to the wavelength being so low it uses the subsoil as the antenna.

In order for the UK to maintain it's independent nuclear deterrent, it would need a system independent of other governments.

UK ground based ELF transmitting antenna would need to be in areas with geological remnants of long gone, eroded mountain ranges, like in Scotland.
GlenGarry Forrest in Scotland was intended as a location for a Royal Navy ELF transmitter for communication with the Trident nuclear submarines.

It was reported to be using 72hz, this must have been a deception as this frequency would clash with the American system and would be unusable.
To be technical here: the USA system is listed as being on 76hz, but in reality it uses 80hz for a data '0' and 72hz for a data'1'.

This project was canceled as the expenses contra efficiency was too high and after a political debate was the Glen Garry ELF communication station turned into history. Or so they said.

Having found the frequency 'error' in what little documentation that I could find I started to wonder if there was some kind of coverup.

Then I came across the part of a report shown below.

This seems to add credence to the existence of the Glen Garry installation.
As can be seen on the capture below.
There is room for the USA at 72-80hz, the Russian ZEV version at 81-84hz, and the UK centered on 87hz , perhaps Glen Garry lives.

This is all supposition for now, some checking with my ELF receiver and spectrum analyser is the next step.
A visit to LochGarry would be interesting, but the antenna feeds would look like power distribution lines, with the ground terminations looking like more power equipment.

Tuesday, 13 May 2008

Rising from the ashes of obsoletism

My dear old PC, 1998 vintage Aptiva, has been suffering under the weight of Windows XP.
She take a long time to load and is slow.
The latest software update from Microsoft has taken its toll, we now have continuous BIOS restarts.
Apparently a problem of compatibility with my aging BIOS.

So what can a boy do, I have already upgrade the memory to the max, a glorious 256Mb.

I have been aware of the Open Source software of Linux, tried before but could not understand enough to get it going.

This time I found Ubuntu 8.04 (Hardy Heron), it says that everything is on the CD, and it is free.

Downloaded the disk to another PC, then after saving my lifes work to a memory stick, I ran format /s on the Aptiva hard drive, loaded the CD, and installed without any problems.

Firefox is included, plus some other Open Source office type stuff.
Other versions, like Edubuntu, contains a large number of educational applications.
And Xubuntu is intended for users with less-powerful computers.

So the old Aptiva has risen from the ashes of obsoletism to live another day.

Tuesday, 25 March 2008


As part of a bible study I took a tangential look at purple.

In the New Testament there is mention of Lydia who was a seller in purple dye, obviously rich as she had a house big enough to hold Christian meetings.

Where did this wealth come from?

The Greek word for her occupation is porphuropolis from a compound of porphura (the purple fish, a species of shell fish or mussel ) and poleo (to barter, to sell)

This snail lives in the central and western parts of the Mediterranean Sea. It was known since ancient times as a source for purple dye and also as a popular food “Tyrian Purple,” the purple dye of the ancients mentioned in texts dating back to about 1600 B.C., was produced from the mucus of the hypobranchial gland of various species of marine mollusks, notably Murex. It took some 12,000 shellfish to extract 1.5 grams of the pure dye. One gram of pure purple dye was worth ten or twenty grams of gold.

Legend credits its discovery to Tyrian Herakles, or rather to his dog, whose mouth was stained purple from chewing on snails along the Levantine coast.
Tyrian Heracles and the nymph Tyrus were walking along the beach when Heracles' dog, who was accompanying them, devoured a murex snail and gained a beautiful purple color around its mouth.
Tyrus told Heracles she would never accept him as her lover until he gave her a robe of that same colour.
So Heracles gathered many murex shells, extracted the dye from them, and dyed the first garment of the colour later called Tyrian purple.
The murex shell appears on the very earliest Tyrian coins and then reappears again on coins in Imperial Roman times.
These marine snails still live along Tyre's shores deep among the rocks and sunken archeological remains.

According to Aristotle and Pliny the Elder, the snails were gathered at the beginning of autumn or winter and kept alive in basket-work containers until a huge quantity had been collected, as each shell only produced a single drop of dye.
Το extract the dye the smaller shells were crushed with stones; the larger ones were pierced and a tiny gland (known as the anthos or flower) was removed from the neck of the mollusc.
The milky fluid from this was put into brine, a little vinegar was added and it was left in the sun where the colour gradually changed from yellowish to a deep purplish red. It was then either diluted or concentrated further by boiling it down.

Dye extraction is no longer a viable commercial venture in this way, dyes are made by chemical means.

Monday, 3 March 2008

It took how long?

"I have found the fittings for that old wooden curtain pole, will you fit it over the lounge door please?" She asked.
Six screws, how long can that take I thought, easy. "Of course I will dear." I replied.
So out came the tape measure, "How high dear?" well after some thought 90inches was too high so we settled on 84inches plus the width of the pole.
So I measured and then measured again to get it right, even got out the long spirit level.
Found some wall plugs, 6mm drill it said.
I will use my big electric drill, Walter I call it, (DeWalt DW566K), that won't wobble and I will get a good clean hole.
Drilled the first hole, I use a little blue thingy to stop the dust going everywhere, that was easy I thought, I will be drinking coffee in 10minutes time.
The fittings need 3 holes each side, so I drilled the other 5.
Now for the plugs. Oh dear! They were loose, very loose and getting looser, I had drilled into some very soft mortar.
Find some fatter plugs, of I went to hunt for them, eventually found some in a box in my bedroom of all places, but they were still loose also.
I know I have some special impregnated pads for jobs like this, so went off to find them.
Found them in a box out in the workshop, soon to be the utility room (where will I go then?).
So I soaked the pads and fitted the larger plugs, screwed in the six screws.
Then I fitted the pole and it looks good.
But 2hours for six screws! It had better stay there or it will be fire wood.

Sunday, 20 January 2008

Déjà vu and the spiral of time

I believe it was Charles Dickens who said:
"We have all some experience of a feeling, that comes over us occasionally, of what we are saying and doing having been said and done before, in a remote time – of our having been surrounded, dim ages ago, by the same faces, objects, and circumstances – of our knowing perfectly what will be said next, as if we suddenly remember it!"

I was pondering the idea of seeing the future and was reminded of what my old friend said to me.
"Think of our travel through time as a spiral, like the grooves of a record. We may see across to other grooves, but time ways they are far off."
As we can see forward and backward, as we see across grooves maybe we get a feeling of déjà vu. Life may look like a set of furrow in a field, but as a spiral they are connected.

Further we may have the same vision again and again as the record rotates, and depending on the angle of view we can see more or less of the detail in each furrow, and the time order can be distorted as we look over our shoulder at an inner furrow.
As we get closer to the centre what do we see? Is it more of the future, or just more.

Maybe life is a spiral such that we may get tantalizingly close but never meet, or maybe we will.

And then one has to ask if a traumatic event can force a jump to the next groove or possibly a bounce back.

So should we look? Should we seek coincidences? And what will we gain?

I think to marvel at how we can perceive such things is fascination enough in itself.