confused by background radiation

A really weird thing is happening with the crystal mic. I do NOT understand this.

The same circuit board taken from another box and put in this box is much noisier. Like, 15-20db noiser. Both boxes are metal or metal-lined, and I’ve checked – repeatedly -the metal lining on this one is grounding.

This is true even with no crystal element attached.

Also, any board put in this box is quieter – less signal. This makes even less sense.

I’m so confused.
 
 


This is part of a collection of posts on building microphones and microphone-related kit, such as mic pre-amps.

presumably the crystal gems would use this kind of microphone

Apparently, I’m really into old-fashioned microphone technologies at the moment, and really, I’m just fine with that. I’ve had this boundary-microphone idea in my head for a while – I even ordered a bunch of parts to build it – and that idea and crystal microphone technologies go together!

Okay, first, crystal microphones were an actual thing. Popular from the mid-1930s through the early 1950s, they were used on-air and in music recording. They’re still in use in certain applications, much like carbon microphones are, but more widely – if you’ve heard of a “piezo buzzer” or “piezo instrument pickup”, that’s exactly the same technology, only applied to a different goal.

The underlying physics: there are crystals which, when flexed, will produce electricity. The charge is positive or negative, depending upon how the flexing is done. Sound waves are enough to do it, which means bing! Microphone technology! This is Neat. And, yes, I have a sample mp3 below.


Hey, that 60s and 70s Skiffy fascination with crystals had to come from somewhere.
(Speak clearly into the pinky ring, Zed.)

It works the other direction, too – current one way will flex the crystal one way, current the other way will flex it back. You can make speakers out of this, and that’s been done. This is also how piezo buzzers work – cycling AC power through a piezo-effect crystal.

I’ve built a couple of piezo-based pickups before, using the Cortado kits, so that seemed like a good place to start. I’m not bothering with a second board-construction write-up; the first one is here, if you’re curious.

But building the carbon microphone driver circuit as an external box made me realise that I should build this mic using an external driver circuit as well, so I can experiment without taking apart the box every time. So I used the housing from a dead laptop power supply I’d recycled a while ago.

The best part was that the AC mains connector slot was almost exactly the right size to hold the XLR connector. I just had to file away a bit at the narrowest points. And, of course, I had to line the whole thing in conductive metal tape, for RF shielding, and ground it.


The Now-Modular Cortado. Piezo lead on the right, XLR to board on the left.


Looks almost professional!


TRS: Tip is outer disc, ring is crystal disc, sleeve is shield ground


Standard balanced XLR mic-level output

This lets me plug in anything crystal or crystal-signal-level-like and use this amplifier on it, just as with the carbon microphone, but for carbon-technology elements. In this case, I’ll be plugging in a piezo disc. But since that’s just the crystal, the real question becomes, what resonates it? What vibrates in the presense of the sound, causing the crystal to flex?

My initial idea for materials involved a lightweight, rigid plastic. I’d also thought briefly about metal, but decided that would be too heavy, and I was right about that. The bad news is, that also turned out to be true for the plastic – it takes too much energy to make it move, so it doesn’t move very much just from soundwaves, and the signal levels were really low.

This is the best I got, using the lightest of the “heavy” plastics. That recording was made talking into a small, clear rigid plastic sheet – I think it’s some sort of acrylic, but I don’t know. It came from Boeing! But does not fly.

I love distant-shortwave-sound of this recording, but that hiss isn’t an added effect – it’s amplifier noise from boosting the signal high enough to hear properly. So, obviously, that won’t work as planned – unless I need exactly this effect, of course.

Still, I’m thinking I could put it in front of a guitar amp or something else VERY LOUD. It’s modular, so there’s no huge reason not to keep it, and I have like 50 of these piezo discs. It also works as a gigantic contact microphone/pickup.

So I started working my way down material weights until I found something too lightweight.


THE HEAVY HEAVY DELRIN SOUND


The thin and tinny base of a styrofoam cup


FAILURES, ALL OF YOU! GET OUT OF MY SIGHT!

More and larger pictures on Flickr, as usual.

The lighter I got, the more response to sound I got, and the more signal – to a point, of course.

It turns out that the best weight is way closer to the styrofoam cup bottom than to any of the plastics I’d hoped would work out. A pair of thin foam dinner plates did actually rather well – I’d thought it was just one thicker plate, but no, it was two plates! – and I’ll try that again with a better (by which I mean actually shielded) test harness pickup, and plates that don’t have divided food sections.

And also, that styrofoam plate with the last 15mm or so of the “cup” still attached worked pretty darned well, without the echoy effect of a “cup” microphone. Some people want that; I am not one of those people. (But again, modular! And I have 50 of these piezo discs, I could make one anyway.)

This gets closer to the original construction materials used in the original crystal microphones, so really, I have no business being surprised here. I was just hoping that with improvements in crystal technologies that a heavier plate would work. But it’s just not generating enough signal output.

And that’s really kind of putting the kibosh on my whole boundary-microphone idea – at least, using this technology. Nothing strong enough to deal with the requirements of a boundary microphone – they’re quite large – is going to react enough to sound to give a decent amount of signal. Unless there’s some unexpectedly light and strong foam.

At least, not with these discs.

Maybe NASA has something I could, you know, appropriate. And I wonder if I can find that crystal material in, oh, one big giant sheet, and stick that to something strong enough. It has to come from somewhere
 
 


This is part of a collection of posts on building microphones and microphone-related kit, such as mic pre-amps.

the kalamazoo gals: gibson guitar’s erased women

It’s a common story – lots of women enter the workforce during World War II, doing all the jobs normally restricted only to men, before millions had to go off to fight Fascism. Then the war was won, the soldiers came back, the women were forced back out.

But, at least, it was acknowledged, and, at least, some credit was given.

But not at Gibson Guitar. They officially say that they shipped no instruments during World War II at all – not a one. But that’s simply not true. They did – they made and shipped thousands of instruments, with a wartime workforce of women. Some even went with GIs overseas.


Women instrument makers, Gibson Guitars, Kalamazoo, Michigan

Apparently, management decided that people wouldn’t want instruments made by women, so they erased the Kalamazoo Gals from history. When law professor and music journalist John Thomas got a hint there had actually been wartime production, and found out the story, the acoustic department was initially very interested – and then corporate found out he had been digging, and started threatening him for revealing it. It’s fascinating:

Women guitar makers scratched from Gibson history
By Ryan Grimes

Women are constantly being erased from history, including music history. Sometimes more aggressively – and pointlessly – than others. Never forget that.

some days you just gotta write soviet disco, apparently

kawaiilluminatii on Tumblr demanded, and I quote, “YMCA but instead of young man they say comrade and YMCA is USSR,” and liquidcoma threw in a first line. And, of course, I followed up…

…and then I couldn’t stop myself. I tried, I swear, but I kept adding more chunks in a series of reblogs.

The Biggest, Hottest Communist Disco Club of 1978
2016 Crime and the Forces of Evil, I guess?

Comrade! Steel production is down,
I said comrade! Pick yourself off the ground
I said comrade! Seize the factory in town
There’s no need to be a wage slave

Comrade! Marx’s principles show
clearly (Comrade!) There’s no meaning to dough –
it’s all shackles! You must cast them aside
if you want to gain class freedom

(in the video in my head, the five horn hits going into the chorus are red flags popping up –
FLAG FLAG FLAG FLAG FLAG)

The workers rule in the U S S R
The workers rule in the U S S R
We have thrown down our chains, we have taken the reigns,
In the name of the working class!

The workers rule in the U S S R
The workers rule in the U S S R
We have seized control from the capitalists
Private property won’t exist

Comrade! Have the peasants been armed? I ask
Comrade! Have collectives been formed? I ask
Comrade! Are the bourgeois informed?
That their ruling days are over

No one, does it all by themselves
I said no one! or you’ll end up in cells
So come join us! In the U S S R
Be the in-ter-na-tion-al-ist!

(FLAG) (FLAG) (FLAG) (FLAG) (FLAG)

The workers rule in the U S S R
The workers rule in the U S S R
We have thrown down our chains, we have taken the reigns,
In the name of the working class!

The workers rule in the U S S R
The workers rule in the U S S R
We have seized control from the capitalists
Private property won’t exist

Comrade! I was once in your shoes
I said Comrade! Down and out with the blues
I felt no one! cared if I would survive
The whole system was just jive and

That’s when someone, came right up to me
And said comrade, there’s solutions you see
There’s a system, in the U S S R
That can start you back on your way

(FLAG) (FLAG) (FLAG) (FLAG) (FLAG)

The workers rule in the U S S R
The workers rule in the U S S R
We have seized control from the capitalists
Private property won’t exist

U S S R! The workers rule in the U S S R
U S S R! The workers rule in the U S S R
Comrade, Comrade, there’s no need to feel down
Comrade, Comrade, pick yourself off the ground

U S S R! The workers rule in the U S S R!
Comrade, Comrade, I was once in your shoes
Comrade, Comrade, down and out with the blues

…aaaaand so on. NOPE AS I WAS WRITING THIS POST I DECIDED I HAD TO GO ADD TWO MORE VERSES AND ARRANGE IT SO IT MAPPED TO THE ORIGINAL SINGLE RELEASED IN 1978.

I’m actually kind of pleased with myself both over making “internationalist” scan, and for extensively paraphrasing Lenin’s letter to the short-lived Bavarian Soviet Republic in a disco song.

But come on, brain, what? XD

(((nazi punks))) fuck off

You might have seen a bunch of (((this))) going around on Twitter. What’s it about?

It’s basically a target. Neo-Nazis and other white supremacists are using it to target Jewish people (specifically) for online harassment, including violent threats and abuse. It’s useful because by default it’s extremely difficult to search for using standard tools – they had to put together a Google Chrome extension, which Google has now pulled – but who knows how many copies were already downloaded and are in use?

So one response is to flood their data streams with bad data, by having everybody put (((and))) around their usernames. I’ve done it, because Nazi punks fuck off is why.

(h/t Vixy of the band Vixy & Tony)

what the hell is wrong with me

There’s a webcomic called Dumbing of Age that I like quite a lot (I have all the books and supported the latest Kickstarter) and search for “tiny baby hand” in today’s strip’s comments and that might explain:

…but, y’know, no promises. XD

some reading and listening material

Two interesting bits I saw online, posted for your enjoyment:

1. The Dark Art of Mastering Music, a neat article on the subtle art of mastering an album, and, linked from that article, you’ll find:

2. Sequential alternating of a song from Metallica’s Death Magnetic track, “That Was Just Your Life,” as released on CD and from elements released for Guitar Hero. To my mind, this comparison actually makes the CD version sound less out of control (and relatively less bad), by not levels matching the vocals against each other. But even this way, you can see how the Loudness War mastering makes everything kind of horrible once you get past the instinctive “loudness is better” first impression.

I mean seriously, look at this. DYNAMIC RANGE WHAT IS DYNAMIC RANGE?

Honestly, what a mess. The CD version of the waveform looks like a sausage. I’ve told the mastering engineers I’ve worked with: don’t do this, I don’t want it. And while I do tend to mix loud (particularly on ragier tracks like Pee Police) I simply do not play this game.

I’m hoping the slow decline of the earbud (and the rise of over-the-ear bluetooth headsets) will bring this – the Loudness War – to an end.

It may only mean something to the music wonks reading, but I don’t even run a compressor on the master bus. I do run a look-ahead limiter, to prevent the occasional spikes – which can result from my lack of over-reliance on compression – from clipping, but that’s a completely different animal. If it’s kicking in enough to notice it doing so, I consider myself to have screwed up the mix and go back and fix it.

But what do I know, they’re the ones actually making a living at this – somehow – while I’m all here with my day job. XD

Collection: Microphone Buildout Projects

Building microphones is fun and seems to be of interest to readers, so here’s a collection post for posts about that! These posts discuss building both microphones, and, when applicable, their matching microphone driver circuits and/or pre-amplifiers.

Building a Carbon Microphone:

Related posts:

Building a Crystal Microphone:

Building a Ribbon Microphone:

Other microphone and preamp customisation/modification posts:

not just a display piece

Laying down timing tracks for the new album, finally. I did four and a half tracks yesterday – this is a quick process. None of these recordings will make it onto the final, but it’s a helpful step.

For the moment, the new microphone is living as a display piece in the corner of the room, on the shelf with all the other microphones. Every time I see it, I consider more places I might actually use it on this album. XD

This whole thing got started by looking up how to fake bullhorn vocals, like I needed for the new single, Pee Police (on Bandcamp, YouTube, and Soundcloud). Universally, people said the best way to do it was use a real bullhorn. I mean yes, I’d wanted to build a carbon microphone for a long time. But in terms of actually doing it, this was the prompt.

If you want a specific sound made by a specific thing, the best way to do it is have that thing. $19 in parts later, I have it!

“Starship on Fire” is so far the most likely track to get some carbon mic vocals in the mix. Since it’s told – sung? – from two different viewpoints at once (past character, present character implied), one of those viewpoints having this kind of effect makes storytelling sense. I will at very least try it, and see how it sounds.

I’m going to use the Korra On the Air icon for all the LJ and Dreamwidth crossposts that mention this microphone forever, aren’t I? Yes. Yes, I am.

It’s a long weekend for a lot of people reading this, so – yay! Go have some fun.

a mic of constant sorrow part iv: once upon a time in a catalogue

The last parts for the carbon microphone arrived yesterday! And once I got back to the Lair, I set about adding them to the circuit and building out the final version. Here’s a quick sample recording I’ll talk about more later.

I’m starting with the previously-discussed circuit, now taken out of the test harness and reassembled on one of the small breadboards. The new isolation transformer on the left – basically the outputs of the original circuit are attached to one side, and new outputs picked up off the other. This serves two purposes: first, it eliminates some kinds of hum noise if they start to crop up, and second, combined with 2K of resistance on the other side, brings the line-level(ish) output down to microphone level.

(These are standards which matter in a studio and … not many other places. XD )

The zig-zag in the resistors doesn’t serve any function purpose other than fitting into a smaller space – ideally, I guess I wouldn’t’ve been making needed values out of collections of other values? But I had what I had.

Signal flow is right to left in this photo. Underneath, at the top and bottom of the board, I’ve built wire rails to connect the components. That probably means I’m not really using the breadboard entirely as intended? I don’t even know. It holds everything in place and that’s definitely what I intended. XD

To house all this, I’m using an “experimenter’s case,” which is basically old-radio-speak for a metal box. XD It has soft metal on two sides, easily drillable and workable, and a hard case. I’m using one side for input, the power lamp, and the on/off switch; the other side is for output, or, as it turned out, outputs.

The carbon element (in the can) is connected to the driver/amplifier circuit via a 1/4″ TRS phone jack – like an old large headphone jack – with the two leads to the carbon element being on tip and ring, and the shielding ground being on the sleeve. (Tip, Ring, Sleeve: T R S.) That socket is on the left in the above photo; the middle component is a small LED, to indicate power on/off, and the right is a BIG CHUNKY POWER SWITCH. I love big chunky power switches. CHONK

For output, I quickly realised that I could have both balanced XLR output at microphone level, and line-level output on a phone plug, if I could find a way to isolate the chassis ground from the phone socket’s sleeve connector.

Normally, both being grounds on the same circuit, they’re connected automatically. Finding one that isn’t already connected is actively difficult! But careful use of electric tape did the job; I drilled the mounting hole larger than it needed to be, and basically lined anyplace the case and the socket would touch. Isolation achieved!

If you look for the blue and white wires, you can see where the TS (mono) phone plug is tapping the raw (line-level) amplified mic signal, just before it’s fed into the isolation transformer.

The transformer is really pretty optional – powered carbon circuit signals are pretty high as microphone signals go, and as I mentioned above, we’re actually reducing that signal to create the balanced XLR output on the other side of the transformer. But it’s nice to have the option of using line level, since it already exists. That’s what built-in sound inputs like on your laptop want, too, so there’s a point to it.

And here’s the whole driver/amplifier circuit, with a battery holder made of velcro.

Is that cheating? Holding the battery down with velcro, I mean. totally cheating I’m hoping it works out – I didn’t have a 9v battery case and it seemed excessive to try ordering one.

That LED power indicator? It’s warm white, left over from another project. I was planning on putting in your typical red LED, but realised that if they’d had a power indicator on one of these in 1932 or whenever, it most certainly would’ve been a little incandescent bulb, and it may and may not have had a colour lens. So I went with warm white, because period accuracy! Sort of.

The neat thing about the way this circuit works – and all carbon microphone driver circuits work – is how it points you right at vacuum tubes, and from there transistors, conceptually. It really, really does.

See, in tubes and transistors – which are both signal amplifiers – the input signal is used to create an amplified copy by controlling how much raw input power is let through, from another source. That’s why tubes were called “valves” originally; it’s because they are valves, electrically controlled, and regulating the flow of electricity from an input, just like the valve on your faucet controls the flow of water from the plumbing.

In this case, exactly the same thing happens yet again. But the input signal is sound pressure (how loud the sound is), which is controlling how much electricity is let through from the battery. And those changes in sound pressure – and therefore electrical flow – make the electrical copy of the sound waves.

Neat, huh?

Anyway, that’s the inside. Let’s look at the case!

I really like how chunky and primitive it looks. This is an old experimenter’s case; I’ve had a box of random cases in which I can build things for a while, and I don’t even know where I got this one, or when. If you saw it on the set of a 1950s television SF show, nobody would give it a second glance.

Always document your builds! You never know what might confuse people later. And by people, I mean yourself, after you’ve come down from the science-related memetic disorder high. I want at least the theoretical possibility of using this amp with other carbon elements, so writing down how the interface works is pretty important!

Except for the glare from the power light, I think this would be the Radio Shack Catalogue photo from, say, 1975:


Good, Better, or Best? Probably “Good.” It is just carbon, after all!


Or maybe this is the catalogue shot? Not sure.

Finally, here’s a test recording I made, using both outputs (phone/line level and XLR/balanced mic level) at once, hooked up to two different inputs on my board. I put both recordings in the same mp3; one’s on the left channel, the other’s on the right. The two tracks should be pretty much identical – being the same signal picked up at two different places on the board – and I wanted to see if that actually happened. Fortunately, it did!

Well, eventually it did. This is actually the second time I tried this, because the first time, I discovered that I’d managed to wire the two outputs up as electrical inverses of each other. Playing the two tracks back at the same time resulted in massive waveform cancellation. Which was hilarious, but also a good indicator; they wouldn’t’ve cancelled so well if they weren’t really similar. 😀


EXTREME WAVEFORM CLOSEUP

So that’s about it for this project! I’ll most likely do something to the ring to control the elastic better. And I’ll probably build a case for the whole kit, like I’ve done before – mics should have cases for protection! – but that’s a separate project.

This has been such a fun build, you have no idea. If you have any interest in this kind of DIY audio, I totally recommend this as a fun, easy project. Particularly if you don’t have studio gear, because you can look up the line level part of the output to damn near anything (including a PA system, I might mention) and it’ll work.

As always, more and bigger pictures on my Flickr account. And if you’re out of work, that’s a great time to listen to the new (NSFW lyrics) single! It’s awesome.

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