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On the Domestication of Car Stereos

7 March 2013 — dan

A reader writes:

I have been rereading some of your stuff concerning speaker building lately and have decided to possibly make it a hobby. A mate and I have a bunch of car audio stuff we pulled out of his car that we would like to turn into a garage/shed powered speaker box. I have been looking on the web and there seems to be about a million different opinions as to various aspects of the build including:

* if we can use the car amp
* if a head deck needs to be involved
* power supply – some say even an old computer PSU can be used some say that the current requirements would be better suited to a car battery with a charger attached (seems a little cumbersome)

So I thought I would send a quick email to great and powerful Tech Master who started me down on this road for some clarification. Help?

Mitch

(Image source: Flickr user Nazly)
Just lever 'em out, and shovel 'em into the house!

Yes, you can make perfectly good household speakers out of car-audio components. Actually, car radio tuners can be better than the home-hi-fi kind, because the extremely variable reception conditions for mobile radio, and the lousy antennas they have to use, mean even quite cheap car stereos often have very good RF sections.

The problem with powering car amplifiers at home is, as you've already discovered, that they can want a lot of current at 12 volts.

First, definitions: You standard "car stereo" has one "head unit" in the dashboard, which combines all of the signal sources - tuner, cassette deck, CD player, line-in socket, memory-card socket for MP3s, whatever - and all of the amplifiers, in one box. These days it probably has four outputs, for two front and two rear speakers. Take such an all-in-one head unit and some speakers and a twelve-volt power supply and hook them all up at home and they'll work the same as they did in the car.

Fancier car audio systems have amplifiers separate from the head unit, and may have multiple head components as well, possibly including a separate satellite-navigation screen, DVD player, et cetera.

A separate car-audio amplifier is basically the same as a separate home hi-fi amplifier: It accepts line-level input, and amplifies it to drive speakers. The input has to come from other components. Fancy car-audio head units may have no amplifiers of their own at all. Again, though, you can run the whole system spread out on a table at home, if you want to and have a suitable power supply.

Standard cheap car-audio amplifiers, like the ones that're built into low-cost one-piece head units, have a maximum output voltage no higher than the 12 volts they run from - 13.8 volts, actually, when the engine's running. Car speakers have a nominal impedance of four ohms - home hi-fi speakers are usually nominally eight ohms - so you can use Ohm's Law to figure out the total possible output current. Ohm's Law says current equals voltage divided by resistance (I = V/R), 13.8 volts divided by four ohms gives 3.45 amps, so that's the most that such an amplifier can output per channel. Each channel is basically its own separate amplifier.

(The "nominal" in "nominal impedance" just means that that's the approximate impedance the speaker presents if you run DC electricity through it. The actual impedance varies quite widely depending on the frequency of the incoming alternating-current music signal, but overall it'll be close enough to the rated nominal impedance for rough-calculation purposes.)

13.8 volts times 3.45 amps is 47.61 watts; an amp with four output channels could therefore output 190 watts, which is more than enough to make the inside of your car very loud, even given the not-so-great efficiency of a lot of car speakers.

(Car-audio equipment of all sorts often has outrageously high "peak music power output" numbers printed on it; this problem may be even worse in car audio than it is in cheap home hi-fi equipment.)

Realistically, to avoid hideous distortion from winding the amp up all the way and to also take into account the rather-less-than-100% efficiency of all amplifiers, a ballpark figure of 25 watts of input power per channel, at the 12 volts you'll probably be running it from at home, is likely to be about the real-world maximum for a basic car-audio head unit. Call it 24 watts for a nice round number of two amps, at 12 volts, per output channel.

More powerful car amplifiers step up their input voltage so they can deliver more volts of output, and the sky's the limit for those. But you can run any amp expecting 12-volt power input from any 12-volt source. As long as you keep the volume low enough that the power supply isn't overloaded, you can probably even run some preposterous multi-kilowatt boom-car amp, at very low volume settings, from a one-amp plugpack.

(This is related to the reason why it's not dangerous to touch both terminals of a car battery that can deliver hundreds of amps into a load with a low enough resistance, like the starter motor. Your body has a far higher resistance, so far less current flows. There are also 12V power supplies with very low output ratings, like say the plugpack for an ancient calculator; you might be able to blow one of those up by just turning on a 12V amp connected to it. You also might be able to damage a 12V amp by plugging an old-style heavyweight unregulated linear power supply into it, because those deliver root-two times their rated voltage when they're unloaded, and seventeen volts might be too much for the amp. All care, no responsibility. Et cetera.)

A PC power supply actually is a pretty good 12V source for running car audio gear at home. It'll be able to deliver a decent number of amps at 12 volts (the yellow wires coming out of standard PC PSUs are +12V), and it should also deal elegantly with overload, and just shut down if you ask for too much current. Modern PSUs may have split 12V rails and other complexities, but an old one out of a superannuated Pentium II box should do nicely for most purposes. Since most home-audio listening happens at only a few watts per channel, unless you want Party Volume of want to hear the music over your power tools, this option should be fine.

A battery charger and car battery will let you run a car amp at maximum power - well, until the battery goes flat because the charger can't keep up with the amplifier load, at any rate. It is as you say not a very elegant solution, though, and the charger may get confused when you turn the amp up and it suddenly sees a strangely high load. And the output from cheap car chargers can be really filthy, noise-wise, too. Car amps generally deal very well with distortion in their incoming power, but you may still hear a whine or ticking noise.

You can also, however, plug car speakers into a home hi-fi amplifier. A given volume setting will give you more noise from a four-ohm speaker than from the eight-ohm speakers home amplifiers expect, but pretty much any amp should work fine with four-ohm-nominal speakers; some home speakers actually have six- or four-ohm nominal impedance. Any old mini-system hi-fi amp will do, too, you don't need a fancy expensive one.

Another way car-audio enthusiasts get more noise out of an amplifier is by wiring multiple four-ohm-nominal speaker drivers in parallel. Two 4-ohm drivers in parallel give you a nominal-2-ohm speaker, three in parallel give 1.33 ohms, four in parallel give one ohm, and so on. You have to be careful connecting speakers with very low nominal impedance to most amplifiers; it usually won't cause a problem if keep the volume setting very low, but one-ohm or lower speaker arrays may look like a dead short to any amp that isn't designed, as some car amps are, to drive them.

You can also get small 12V amplifiers intended for use in home and mobile applications, which are descendants of the popular, and distinctive-looking, Sonic Impact T-Amp:

(Image source: Flickr user animakitty)

The modern ones are easy to spot; they all have extruded aluminium cases, often anodised a cheerful colour, and a few chunky controls on the front:

(Image source: Flickr user icoro.photos)

These little amps may be sonically superior to cheap car-audio amplifiers. The radio tuner in a car stereo may have to be good, but car amps can be quite noisy and distorted, because that's not very noticeable in the lousy acoustic environment of the average car. These little units all use similar class-D amplifier chips, which are good for maybe 15 clean output watts per channel or 25 watts flat out. For full power you have to run them from something with at least a five-amp power rating - so, a car electrical system or computer power supply, or a laptop-power-supply-style 12V PSU, which last is what they come with if you buy one with PSU included. Again, though, you can hook up a smaller 12V plugpack if you like, and just keep the volume low.

(Some of these little amps have a USB socket on the front panel, too. In the cheap ones, only have the power pins will be connected, so you can use that socket to charge most phones or MP3 players, but you can't play MP3s off a thumb drive.)

These little amps may or may not sound any better than a cheap car head unit, and all they are is an amplifier - no tuner, CD player or whatever. But they look a lot better indoors than a bare car head unit, and the going rate for one without a power supply is under $US20 delivered.

As I've mentioned before, you can find these amps by searching for "class D" or "class T" (Tripath's trademarked version of class D). You'll find the very cheapest ones if you just search for 12V amps, though. You can get these same chips on little amp-module circuit boards, too, for hobbyists to install in their own enclosures, like a normal sort of amplifier enclosure or powered speakers. The above search is sorted by price, so finds lots of those little modules before it gets to the assembled amplifiers.

Car speakers are a great choice if you want to play with transmission-line speakers, too. The basic transmission-line design has a single widerange driver at one end of a folded tube; here's one under construction:

(Image source: Flickr user Moisturizing Tranquilizers)

A cheap six-by-nine oval car driver with a separate tweeter and/or midrange on a bridge in the middle of it is an excellent low-cost choice for a speaker like this.

Posted in Electricity, Electronics, Hacks, Music. 3 Comments »

Musical interlude

13 February 2013 — dan

And now, two singers whose names started with "Big", and who did not appear to actually need a microphone.

Big Mama Thornton.

Big Maybelle.

That is all. Thank you.

Posted in Music. Leave a Comment »

Bits, batteries and BS

26 January 2013 — dan

A reader writes:

I am a hi-fi person. The kind who likes music to sound as good as possible. I know you are interested in sound too.

I am building the item shown here, which is a Micro ITX system to provide very clean USB signal to a DAC.

It's built around an Intel DN2800MT Marshalltown Mini-ITX motherboard which accepts anything from 8 to 19V DC.

They recommend a battery power source as that clean power helps give better sound. Whether or not you believe in that is another thing. The battery source they suggest is the Red Wine Audio Black Lightning High-Current Battery Power Supply which is $900, costing as much as the entire rest of the system.

I have a problem paying $900 for a battery and charger.

Here's my question. Do you think a standard laptop battery extender (lithium battery plus charger) or similar would work as well? They are a lot cheaper. See for example:

Anker® Astro3 10000mAh Multi-voltage 5V / 9V / 12V 2A External Battery Pack, $US59.99, or HyperJuice 2 External Battery for MacBook/iPad/USB (100Wh), $US299.95. Red Wine Audio specify the battery they use to be "One 12.8V, 10Ah LiFePO4 battery pack". I can get one here with charger for $US159.99. Does that look like a viable solution to you?

I am not an expert in your area so I can't tell whether these provide clean DC power. For example do they use a components that add noise or is it clean DC? I've done a lot of searching and cannot find the answer.

All the best,

Chris

Right off the top: Yes, any other battery with an appropriate voltage and current capacity will work as well as the super-special audiophile one.

Many modern batteries have some circuitry on board to, for instance, cut the battery off before it runs dead flat, or protect against short-circuits. But in normal use, they all deliver DC electricity that's clean as a whistle.

However.

Anybody who seriously claims that running hi-fi gear from a battery instead of wall power will give you...

* Improved dynamics
* Blacker backgrounds
* More natural sounding highs
* Better defined bass
* A larger soundstage
* More holographic imaging

...does not deserve your money, for that battery or for any of their other products.

I would go so far as to say that they do not even deserve the money of Donald Trump, Kim Jong-un, or a professional puppy-drowner.

The Computer Audiophile site is not as badly contaminated with fluffy anti-reason as the real champions of audiophile insanity. But that's only because those champions are so demented that they speak favourably about the audible advantages of $350 wooden volume knobs, small objects made of exotic materials that you're supposed to place in mystically significant locations on and around your hi-fi equipment, $6500 power cords justified via avant-garde atomic physics, and of course plenty of quantum flapdoodle. (That quantum flapdoodle is sometimes quite hotly defended, too!)

The Computer Audiophile forums could be better, too. This wizard manages to list several ways in which uncontrolled observations cause us to see and hear things that aren't there... and then turns around and say that that's why blind tests are useless!

'Cos the reason why people think audio voodoo works, and then don't think it does on the rare occasions when someone takes the trouble to do a blinded test, is because audio placebos don't stop working just because you've discovered that they don't do anything real. And because blinded tests encourage you to give up those placebos that you previously thought made stuff sound better, you'll then be listening to music through less ridiculously expensive gear that doesn't have those wonderful placebos, and this will make you unhappy.

Or something.

Here's another parade of forum-post explanations for why blinded tests tend not to say what audiophiles want them to.

OK, it's not The Computer Audiophile's fault if people say nutty things on the forums.

But the Audiophile himself chimes in further down that first thread, and doesn't really disagree. And he also posted in this thread, to say that in his experience audio bits read from a solid-state drive sound better than the same bits read from a spinning drive.

(See also, the magnificently deranged concept that there is such a thing as an audiophile SATA cable.)

And here a Computer Audiophile blogger explains that the stress of a blinded test "makes it harder to remain objective".

I now choose my words carefully when I say:

For fuck's sake, people.

As I've written before, these attitudes on my part are not just knee-jerk "scientism" that assumes that empirical testing always beats personal experience. A hard-core attitude like this is foolish, when you're talking about unquantifiable things like "how good that painting is" or "how good that music sounds".

My opinion, rather, arises from the large number of tests done in the course of, for instance, developing lossy compression algorithms, investigating the neurology of hearing, and actually testing weird audiophile claims.

Over and over and over it has been shown that the ear is, if anything, even easier to fool than the eye, and that those who claim a special ability to detect differences in stimuli better than mere modern instrumentation and the scientific method can identify, are mistaken.

And it doesn't matter much what those stimuli are. Dowsers, wine experts, "intuitive healers", audiophiles; they're obviously very different in their scope of activity and the likelihood that their activities will cause misery and disaster, but presuming they're sincere, they're all making analogous mistakes for analogous reasons.

This is not a case of different "schools of thought". This is rationality versus irrationality.

Getting back to audio gear that's alleged to sound better when running from a battery than when running from the mains: The makers of this gear may somehow have managed to screw up their power-supply design so badly that the thing really does run better from battery. But that is the only reason why I am not comfortable in betting my life that they are completely wrong.

In this respect, the choice of battery or mains power is rather like the choice between valve or transistor hi-fi amplifiers. A properly-designed transistor amp should be, and as many blinded tests have demonstrated definitely is, audibly indistinguishable from a properly-designed valve amp.

Valve amps sound better when overdriven into distortion, which is why the "valve sound" is such a big deal for guitar, and other musical-instrument, amplifiers.

But a hi-fi amp should not ever be driven that hard.

Show some golden-eared types a badly-designed valve amp that really does sound different from a transistor one (though not necessarily very different from a badly-designed transistor amp...), however, and at least some of them are sure to want to throw money at you.

This sort of thing happens over and over in the audiophile world. Never mind the pure frauds like expensive audiophile cables that turn out to be made from garden hoses and hot glue. Look, for instance, at this highly-regarded little amplifier, which is actually very badly designed, and atrocious in every way.

I suppose some of this stuff may come from people's memories of early versions of new technologies, which often genuinely were inferior to the highly-developed versions of older technologies available at the same time. Early transistor amplifiers could sound quite audibly lousy, for instance, because early transistors were quantifiably unable to amplify audio as cleanly and linearly as vacuum tubes. See also early audio CDs, many of which sounded if not unarguably worse than top-quality vinyl or reel-to-reel tape, then certainly not as good as you'd expect from the slogan of "perfect sound, forever" and the alarming price of a CD player in 1983.

The lousy sound of transistor amps in 1958 and CDs in 1983, though, have nothing to do with how they sound today.

Let me make perfectly clear, however, that I've got no problem at all with the notion that sound quality can be compromised on the digital side of your DAC - particularly when you're using a general-purpose computer as your audio source. There are plenty of possible software and hardware issues that can cause clearly audible problems with the sound.

To give only one example: If you're running an operating system like Windows that has multiple sound sources, not all of them may even show up in the "mixer" control panel. So even if you mute everything but the source you want and set every relevant volume control to maximum (as the Computer Audiophile FAQ sensibly suggests), there may still be obvious scratchy interference noises from sources that for whatever reason refuse to mute, and for whatever reason are very noisy. Like, say, a microphone input with no mic plugged into it.

And then there's the analogue side of the audio chain, which for the vast majority of PCs and Macs today is the audio hardware built into the motherboard. That hardware is almost certainly going to be built down to a price and thus, in the very cheapest versions, may have gross distortion on the level of this stair-step alias-tastic output:

(Picture courtesy of Practical Devices.)

Onboard audio hardware is also often not very well shielded from the numerous high-frequency RF sources with which it shares the inside of the PC.

But if you're using a quality internal sound card or any sort of half-decent outboard USB DAC, and if there's nothing on the software side on the PC polluting the bits the DAC, then the notion that the signal coming out will be in any way detectable in a blinded test different between different computers, let alone between one computer running from the mains and an identical one running from a battery, is demented.

Yes, it is possible for an audio system to sound better from battery power than from mains, but only if it's got a badly-designed power supply. If "dirty power from a computer motherboard can result in very audible noise and decreased sound quality", so you need to run even your add-on USB card from battery, never mind the DAC, then there is something severely wrong with that USB card, to the degree that it just won't work properly. Anything that can corrupt digital audio data - remember, this is before the signal even gets to the DAC - in an audible way will also corrupt every other kind of data, and this effect will be noticeable in things as simple as sustained data transfer rates.

And then the Computer Audiophile dude goes and uses a "PCIe riser cable" so he can cram a USB controller card into his tiny computer case - but such a cable is completely unshielded!!1!one! You're running the card from battery power but transferring all of the data to and from it through an antenna?!

UPDATE: Damn, a perfectly good snark ruined - Chris pointed out to me almost immediately that the Computer Audiophile picked a riser cable that already does have shielding!

(I'm sure that if he ever thinks of this, he'll immediately hear the difference and wrap the riser cable with earthed foil, or something.)

Sometimes you strike something that's beloved by audiophiles, inexpensive and functional, like the Tripath "class T" amplifiers (which are their trademarked version of a Class D amp). Built amps of this type, and modules from which you can build your own, are all over eBay and other online vendors. The specs of the cheapest ones aren't very good, but just stick a valve up though the casing, decorate your description of the hardware with some real scientific terms that don't actually apply, keep a wall of pseudo-postmodernist babble in reserve in case of hard questions, and the audiophile market will be fine with it.

Usually, though, audiophile snake oil is expensive, and all you get for your money is a placebo.

This woolly-headedness is for some reason acceptable for audiophile hardware, but not for other technology.

"Well, this is where the GPS says I am, but I think the satellites it's looking at right now lack a certain positional air and musicality. Look, you can see the fix jittering. Well, I can, at least; perhaps your eyes aren't as good. I'll wait until it gets dark so I can try some other satellites when the intervening molecules are cooler."

"I'm pretty sure I play Counter-Strike better when my chair's facing east."

"Water boiled from English 230-volt mains power makes better tea than water boiled from US 120-volt. Everyone agrees 120-volt at 50Hz is almost as good, though."

"My calculator's more accurate when I press the keys more firmly."

Most people would consider statements like these as possible symptoms of a formal thought disorder.

But believing some talisman improves your car's power and mileage, or that a magnetic or copper bracelet helps with your arthritis, or that one should always visit one's astrologer before investing any money, or that water has memory, or that bits and electrons have special properties depending on where they came from?

That's fine, according to a lot of people.

We've gotten past this crap. We no longer believe you can revive a drowned person by blowing tobacco smoke up their arse, we no longer believe the brain's only purpose is cooling the blood, and most of us no longer believe planets whistle around in ludicrous epicycles in order to place humanity at the centre of the universe. And no matter what certain alternative-medicine practitioners say, bleach is not a fucking cure-all.

For pity's sake, we have actually achieved the transmutation of base metals into gold. (Though not the way the ancient alchemists or their rather peculiar modern heirs wanted to do it, which is probably just as well.)

If I were you, I'd forget about taking advice from people who insist, in the face of a world of astonishing technology, that it's reasonable to spend large amounts of money on devices that only make sense if the science and engineering that led to all that amazing technology is actually invalid. I find it particularly galling to see this counterfactual thinking applied to powering of a computer; the people who designed and built the hardware in there, including literally billions of transistors operating at billions of clock ticks per second, have not found any mystic benefit to powering the thing from batteries instead of wall power. But when it comes to the handful of transistors and thousands of cycles per second of a piddling audio output, suddenly some occult force arises that's not amenable to the science that puts supercomputers in your pocket and robot probes on distant planets.

Happily, getting superb audio quality out of a PC is a completely solved problem, thanks to boring old science and engineering. It's not even expensive.

The process is:

1: Buy an Asus Xonar DG or something for, like, fifty bucks. Or less.

2: Install it in whatever PC you like.

3: Plug in your headphones and/or ordinary inexpensive hi-fi amplifier and decent speakers.

...and that's it.

If you absolutely must spend more money than that, I suggest you buy from an engineering-first, low-bullshit manufacturer like Headroom or Practical Devices. Those people usually have a bit of audiophile tinsel on offer, like expensive capacitor-upgrade kits that don't fare well in blinded tests, but they also have plenty of claptrap-free products.

Posted in Electronics, Music, Scams. 37 Comments »

More DIY noise

25 August 2012 — dan

Further to yesterday's post about speakers:

(Image source: Flickr user Enrico Salad)

If you're looking for some reading matter to ease you into loudspeaker design and construction, do not buy Vance Dickason's famous, though now out of print, Loudspeaker Design Cookbook. Even getting a pirated PDF of it is not a great idea. This is because the Design Cookbook is for people who already know what they're doing - its subtitle is "Everything you Need to Become a Better Speaker Designer", emphasis mine. You're going to have to learn about Thiele/Small parameters and some other technical stuff at some point if you're building most kinds of multi-driver and ported loudspeaker, but there are several kinds of speaker you can build without doing anything beyond basic arithmetic.

There are a ton of books about speaker design, most of which I've never read, so maybe I'm about to suggest you go in a non-optimal direction. But the best book I have read on the subject is V.A. Capel's An Introduction to Loudspeakers and Enclosure Design, which is also out of print but can still be had cheaply on Amazon and on eBay (there are local Australian and UK sellers!UK sellers!).

An Introduction to Loudspeakers and Enclosure Design does what it says on the tin, and includes detailed instructions for building one of those single-cheap-driver transmission-line speakers I'm so keen on. If you build it according to the instructions you'll end up with a folded transmission line with ceramic-tile reflectors on the corners; I'm pretty sure just making the reflectors out of wood wouldn't significantly hurt performance.

(Image source: Flickr user Moisturizing Tranquilizers)

You don't have to do all the extra woodwork required to make a transmission-line enclosure, though. A simple sealed box with one driver will do.

(Image source: Flickr user Milestoned); these speakers are the Visaton Solo 100s, one of those short-form kits where you have to make your own boxes.

There's a whole subsection of the audiophile world - both the empirical and the woo-woo side - devoted to single-driver speakers, and such a speaker is a really good option for your first speaker project.

(Image source: Flickr user drosen7900)

A solidly constructed box with a single cheap driver can sound remarkably good, especially if the speakers are close to the listener, even though the response plot reports high treble and low bass are missing, presumed dead, and the midrange response looks like a Worms battlefield.

Loony-audiophile supply houses stand ready to relieve you of extraordinary amounts of money for Fostex or Tannoy drivers...

(Image source: Flickr user drosen7900. More about these speakers here.)

...but now that few people use CRT monitors and TVs, you can build your own computer or hi-fi/home-theatre speakers without even bothering to use magnetically shielded drivers. Any dirt-cheap paper-cone wideranges, or multi-driver round or oval car speakers (which are not strictly speaking single drivers, but can sound good just the same) will do.

And for your first project, all you need is a sealed box, the bigger the better, with one hole in the front that roughly fits a single driver. You will probably need to be able to solder, but not a lot of work is involved, and what work you do have to do can be quite sloppy and still give a perfectly functional result. (Think of it as the Roman Army knife of loudspeakers!)

Oh, and on the subject of very heavy speaker cabinets: What do you do if you've already got some speakers, but you want their cabinets to be less resonant?

(Image source: Flickr user Voxphoto)

Just cast your own speaker stands out of concrete, and bolt the speakers onto them!

Posted in Electronics, Handicrafts, Music. 6 Comments »

DIY noise

24 August 2012 — dan

A commenter on yesterday's post about glass-fibre speaker-box lagging lamented that he can't get loudspeaker kits in the States.

He is wrong. There are definitely speaker-kit sellers in the States. Probably quite a few of them, given the much larger market. (Australian population: 23 million. US population: 314 million.)

I think the biggest name in US speaker kits (do feel free to correct me in the comments) is Parts Express, mostly under their in-house "Dayton" brand. There was a Dayton driver...

...in the kit subwoofer I reviewed.

Parts Express sell everything you need to make speakers of your own design, and have a reasonable selection of kits, too. Their speaker-kit listing is here; prices are quite good, especially given that most of the kits have enclosures that are veneered or otherwise nicely finished.

This super-cheap Parts Express kit comes with only bare plywood boxes, but it's two little 2-way speakers for $US128 with free US delivery! For some reason the kit lacks binding posts and wire, but you can get those for a few bucks more; if you're really pinching pennies, buy those parts on eBay from China.

(Oddly, absolutely nobody seems to sell speaker kits on eBay. I wonder if that's because of the awkwardness of shipping all that wood.)

Note that these little speakers aren't really "bookshelf" speakers, because they have a port on the back, and if you plug the port by pushing it up against a wall, your bass will go away. You certainly can put them on a bookshelf, but you can't push them all the way in like a book.

This Parts Express kit is expensive...

...and regrettably also out of stock, but how can you not want them!?

Back here in Australia, the inventively named "The Loud Speaker Kit", makers of all the kit speakers I've reviewed, is now out of business. I'm not an authority on other Australian speaker-kit places, but I know of a few.

Peninsula Home Theatre have some rather expensive options (their prices are per speaker, not per pair...), but the drivers are high-quality and the boxes are very nicely finished.

Decibel Hi-Fi's omnidirectional kit speakers look fun too, but are a bit expensive.

Danish Sound Technology have kits, but you have to contact them for prices, which is not a good sign.

The Fountek "Signature Series" kits look good for the money, though.

ER Audio has electrostatic-speaker kits, which are all very expensive, but that's because electrostatic loudspeakers are awesome. (They're hideously incompatible with cats and small children, though.)

VAF Research sell kit versions of at least some of their speakers, too, but they're very high-end so their kits cost thousands as well.

At one time or another I think all of the Australian chain electronics stores - Altronics, Dick Smith, Jaycar and possibly even Tandy (Radio Shack in the States, amalgamated with Dick Smith now in Australia) - have offered speaker kits. At the moment I think only Jaycar have them, and they've only got one.

These electronics plus these cabinets give you...

...some very nice European-driver loudspeakers for $AU698 all up, which is quite good value.

You could save a little by only buying the electronics and building your own cabinets. Many "speaker kit" dealers work this way - they sell "short form" kits, giving you everything but the boxes. In Australia, people who sell these kinds of kits include Soundlabs Group and Stones Sound Studio, the latter dealer continuing the proud association between... untidy... Web-site design and audiophile woo-woo. (They also sell the Fountek kits mentioned above.)

Making your own enclosures isn't actually all that hard, by the way; I did it when I was a teenager. If you're a DIYer without a table saw, you just go to a place that sells wood-sheet products and get them to cut some MDF to size for you. Note that they will probably only do cuts all the way across the sheet (or what remains of the sheet after previous cuts), so it can be a bit of a puzzle to get all the parts you want out of the minimum number of sheets. This lets you have unusual finishes on your speakers, though; any material you can use for a kitchen counter, for instance, you can use for a speaker.

Anyway, you get the panels made, then assemble the boxes at home with simple screws 'n' glue and ugly butt joints (proper woodworkers of course use mitre joints). You can jigsaw the holes for the drivers; it doesn't matter if the holes aren't perfectly round, because the driver surround will cover them.

(When I was about 15, I cut my own box panels freehand with a jigsaw from a sheet of super-cheap particle board, and then plugged the gaps where the wood didn't quite touch with Blu-Tack!)

Taking the further step of building your own speakers from scratch isn't that hard, either, especially if you build simple sealed boxes. Doing it entirely yourself is also the only way to get some unusual speaker designs, like corner-loaded horns and transmission lines, at an affordable price.

Transmission lines are one of my favourite loudspeaker types. You make a tall hollow square wooden tube, or reduce the size by folding the tube and putting periscope-type sound-reflecting angled pieces on the corners. The drivers go at the top in the front, there's a port at the bottom at the back, with lagging material all the way down the tube so very little sound actually makes it out of the back. Even if the driver you use is a paper-cone widerange from a junkyard car, the result will often be quite startlingly good, even though the frequency-response plot will look dreadful.

There's no good way to get low bass out of this design without making it really big, though - I once made some folded transmission lines with eight-inch whizzer-cone wideranges in them, and they still didn't have really low bass, but were serious pieces of furniture. So if that matters to you and you don't want the speakers to dominate the room a bit, you'll need a subwoofer as well.

Building your own cabinets also lets you massively over-build the cabinets, for near-zero panel resonance. The easiest way is to use super-thick wood and many braces inside, but you can also make a double-walled design filled with sand, cement or even lead shot, or line the panels with lead sheet. Many super-expensive speakers have cabinets like this, but retailers hate them; do-it-yourself lets you have super-cabinets with affordably-priced drivers in them.

I'm sure some readers know of other speaker-kit outfits; I only mentioned Parts Express in the States, but I'm sure there are more options there and in other countries. I invite people living elsewhere to comment.

And heck, we don't even have to be talking about only kit speakers. Do tell if you know of pre-built speakers that offer similar value for money, like those white-van speakers sold for fair prices on eBay I wrote about a while ago.

Posted in Electronics, Handicrafts, Music. 8 Comments »

Lordy lordy, what a shame

19 June 2012 — dan

I have always had a great enthusiasm for musical jokes.

(Which reminds me, I must brush up my Great Gig in the Sky/Imagine/Bohemian Rhapsody medley again. I leave identification of the points where I graft them together as an exercise for the reader, until I get around to making an MP3.)

If a musical joke involves a pipe organ, so much the better.

Herewith, therefore, I present you with the soundtrack of a swingin' cocktail party for all fifty million inhabitants of a Culture GSV!

Anyone with some experience of organ music will now, of course, know what the inevitable soundtrack will be, when unfortunate events later force the GSV to offload its population and convert most of its mass into engines and weapons...

Posted in Humour, Music. 6 Comments »

The music goes round and round and comes out backwards

16 May 2012 — dan

A reader writes:

Sometimes when I plug in my headphones it seems as if I'm not receiving any vocals. Its still stereo, but I find that the headphone jack isn't completely in. What's going on here? And why does it work so effectively at removing vocals?

Simon

The quick answer: You're hearing the two stereo channels mixed, with one of them out of phase with the other.

I can't for the life of me figure out how this happened, though. In the interminable rambling below I talk about a couple of other crossed connections that can, and often do, happen, but unless there's a bit of wire stuck in the headphone socket or some other such oddity, I don't know how you could have the exact symptoms you report. Unless, of course, what you think you're hearing isn't what's actually happening, which is eminently possible since the ear is as easy to fool as the eye.

Anyway, mixing one stereo channel with an opposite-phase version of the other channel means that any component of the musical mix which is essentially monophonic - in the middle of the stereo "soundstage", the same on both channels - will be cancelled out.

Singing in popular music is, usually, pretty much in mono in the middle of the stereo mix. So mixing one side with a phase-flipped version of the other side will cancel out said singing; all you'll hear of the singer is any stereo reverb or difference in volume between the two sides (a.k.a. panning).

This technique, called Out Of Phase Stereo or OOPS, is used in this simplest form by old and/or cheap karaoke machines that let you "mute" the vocals on normal music, so you don't need a special vocal-less karaoke version of every song.

Simple OOPS doesn't work very well, because vocals are seldom exactly in mono (they usually have some stereo reverb, for instance), and if any other component of the mix - drums, bass, whatever - is also mono, then that'll be muted too. Smarter OOPS vocal-muting tries to identify and mute only the vocals, based on the pitch and possibly even the timbre of the sound.

This weirdness can come about because headphone plugs use TRS (Tip, Ring, Sleeve) connectors. TRS connectors come in a variety of sizes - the big old-fashioned 6.35mm (quarter-inch), the ubiquitous modern 3.5mm (eighth-inch), and the usually unnecessary and irritating 2.5mm (3/32 or 1/10 inch, depending on who you ask). All three-contact audio TRS connectors are, or should be, wired the same way; the tip of the plug is left channel, the ring is right channel, and the sleeve at the base of the plug is a shared ground.

(This sort of cylindrical plug connector should only be called "TRS" if it has these three contacts. Mono-audio cables with the same sort of plug, like for instance guitar leads, omit the ring contact and should therefore be called just "TS" connectors. Connectors with two ring contacts, as for instance used for stereo headsets with a microphone, should be called "TRRS". Sometimes you'll see any plug of this basic form called a "TRS" plug, though, regardless of how many contacts it actually has.)

Most headphones today have a 3.5mm plug; fancier ones...

...come with a 6.35mm adapter for it, too.

Some headphones mix it up a bit. One of these Sennheisers has a simple 3.5mm TRS plug on both ends of its cable, so you can very easily and cheaply replace the cable if it's damaged...

...but the other has a 3.5mm TRS on one end of its cable, and at the other end the cable splits into a pair of 2.5mm TS plugs, one for each side of the headphones.

If a TRS plug isn't fully inserted, contacts on the plug can touch the wrong contacts in the socket.

(This characteristic makes this shape of plug a bad fit for many applications. I once bodged up a two-voltage power-supply connection for an external SCSI drive box for, of course, my Amiga, using a 6.35mm TRS plug and socket. I avoided the dangers of connecting one voltage to the other's contact and the other voltage to the ground contact by only connecting or disconnecting the power supply when everything was turned off. Or, at least, connecting or disconnecting it really fast.)

A partially-inserted TRS plug could, for instance, leave the tip contact on the plug touching the ring contact of the socket, and the plug's ring contact not touching anything, and the sleeve of the plug still touching the sleeve of the socket, because the sleeve is much longer than the other two contacts. This sort of mis-connection will give you the signal meant for your right ear in your left ear, and no sound from the right side of the headphones.

(The sleeve of the plug is connected to the braided or foil shield of the cable, and any or all metalwork on the plug that is not the tip or ring contact will also be connected to the shield - it's all one big sleeve contact, basically. TRS sockets almost always work the same way; the socket has small tip and ring contacts, but the rest of the socket's metal is all sleeve. This makes it very easy for the sleeve of plug and socket to remain connected when the plug isn't all the way in, and if the plug's a long way out of the socket it also makes it pretty easy for the plug's ring contact to touch the socket sleeve contact.)

I encourage readers, by the way, to try this out yourselves; it's pretty much impossible to hurt your headphones or anything you plug them into by only plugging them in half-way. So do that, especially if you find my interminable blather confusing, or just want to see if you can create Simon's symptoms for yourself.

Another mis-connection could have the plug-tip touching the socket-ring, and plug-ring touching socket-sleeve. Now you'll hear the signal meant for the right side through both ears, but it'll sound weird, because it's out of phase, as mentioned above.

This is because the left and right "drivers" of the headphones (the electromagnetic transducers that actually make the sound) are, with this mis-connection, now wired in series, with the wire going "out" of the left driver that's meant to connect directly to the sleeve contact instead only being able to connect to the sleeve through the right driver and the plug's ring contact, thereby feeding the right driver "backwards".

This causes the right side to be out of phase - when the left driver is moving toward your head, the right one should be too, but now its phase is inverted and it's moving away.

There are two reasons why I'm rabbiting on about this stuff at such outrageous length. The first is that basic audio cabling like this is something that almost everybody has to deal with, and it pays to know what connects to what even if you don't intend to be soldering up any cables of your own - though basic soldering is easy to learn, cheap, and can save you quite a bit of money.

(Just yesterday, I turned a couple of not-that-cheap Apple laptop power supplies, one electrically dead and the other with a fractured and fiendish-to-repair MagSafe plug, into one working power supply with an extra-long cable. Even the dodgiest off-brand MagSafe power supplies are about $US20; a genuine Apple one is $79. With basic soldering skills and equipment, this sort of thing is a literal five-minute job.)

The second reason for this ridiculously large post is that phase problems are actually very common in home audio, and not only among people who fix their own headphones and get one set of Profanity-Allowance-consuming minuscule wires backwards.

People have been creating phase problems ever since the invention of stereo, occasionally by mis-connecting a turntable cartridge, but usually by wiring one of their stereo speakers the right way around (red terminal on the amplifier to red terminal on the speaker, and black to black) and the other the wrong way (red to black, black to red). In this case, each speaker actually is playing the signal that it should be, but one is phase-inverted.

(It doesn't really matter whether you've connected red-to-red or the other way around, as long as both speakers are the same. In theory, having both out of phase with the way they should be, but in phase with each other, could cause an audible difference, but in practice it's only detectable by golden-eared audiophiles who see no need for tiresome things like blinded tests.)

If you've got two working ears, you definitely can hear when stereo has one side out of phase. It's hard to describe, though; it's sort of like having a head cold that's blocked one of your Eustachian tubes but not the other, or how things sound when an air-pressure change has popped only one of your ears. Here's a page that explains this, with nifty audio samples including one (MP3 link) that should sound mono in the first half and out-of-phase pseudo-stereo in the second half.

Out-of-phase audio sounds different on headphones and speakers, because of the basic differences between the two devices. Headphones deliver pretty much pure left-signal to your left ear and right-signal to your right, but each of your ears hears both members of a stereo speaker pair, plus umpteen reflections and resonances from the room you're in.

For this reason, if you're listening to stereo speakers with one side out of phase, there will be strangely little bass, because low-frequency sound has a long enough wavelength that the out-of-phase speakers can mix their sound even if they're separated by a few metres. Higher-pitched centre-mixed components of the music won't cancel as much, though.

Just to make things even more complicated, sometimes it's good to reverse the phase of a subwoofer or surround speakers, to compensate for subwoofer location or the distance of the surround speakers. There's often a hardware switch on a subwoofer or a configuration option on a surround receiver that'll let you do this, or of course you can just switch the wires around or make a crossover RCA cable.

There are also some stereo recordings on which phase reversal is undetectable, because the two channels share nothing at all. Many early stereo rock tracks are like this, and are pretty much intolerable to listen to with headphones because the stereo mix puts each instrument entirely on the left or right channel. Ringo and Paul on the left, John and George on the right. Nobody minded this very much at the time, because almost everyone heard this music in the mono mix, but to make these tracks listenable with headphones you need a fancy headphone amplifier, or music-playing software, that has a "crossfeed" control, to deliberately mix some right into the left and some left into the right.

Out-of-phase mono - the same signal on both sides, but one way round on the left and the other way round on the right - kind of sounds like stereo, because you genuinely are hearing something different on each side. So what I think you, Simon, are hearing from your partially-connected headphones is a mixture of left and right, with one side's waveform inverted, the resultant mono signal being heard one way round on the left side and the other way around on the right. I just can't figure out how you could electro-mechanically get this to happen by only partially plugging in the headphones. I presume there's one contact on plug or socket that's touching two contacts on socket or plug, but I don't know which.

It is, again, entirely possible that you're not perceiving what's going on correctly; psychoacoustic effects can be powerful. But perhaps I'm just insufficiently imaginative. Any ideas (or experiment reports!), commenters?

Posted in Electricity, Electronics, Music. 9 Comments »

Horniness

13 March 2012 — dan

A reader writes:

Why do horns make things louder?

I mean, I accept that they do, on gramophones and megaphones and PA speakers at the train station and brass instruments and so on, but what's actually going on there? Why does the sound of your voice get louder just because you're holding a conical thing in front of your mouth? Is it just making it more... directional?

Dennis

The great problem of audio production, and audio reproduction too, is coupling the sound-producing thing to the sound-transmitting medium, which is usually air.

Air is very light. Most things that make sound are, in comparison, very heavy. The moving parts of loudspeaker drivers, the strings of a violin or piano, the lips of a trumpet-player who's blowing a sort of highly controlled raspberry into the mouthpiece of the instrument; all very very heavy, compared with air. All not good at moving lots of air, which is what you want your sound-making thing to do. Wave a brick around in the air and you'll invest a lot more energy in accelerating and decelerating the brick than you manage to impart to the air.

One way of solving this problem is to make your speaker driver very light too. Electrostatic speakers use a big flat sheet of super-thin plastic as a driver; the sound-producing element in a plasma speaker is made out of ionised air (or other gases, if you're a big wuss who doesn't want ozone poisoning).

Horns are a simpler way of solving, or at least reducing, the coupling problem. When you put a heavy-compared-with-air vibrating object at the small end of a horn, the only air it can move is the air right in front of it at the small end. Moving this air is still pretty easy, but the restricted air's mechanical "impedance" is nonetheless quite a bit higher than it'd be if it were unconfined.

As sound pressure waves move down the horn, the gradually widening shape of the horn (for loudest results, an exponential curve) allows the small amount of higher-pressure air next to the driver to transfer its energy to a large amount of lower-pressure air. The end result is that more of the energy of the driver ends up as sound waves.

A sealed-box loudspeaker has an acoustic efficiency - the amount of the input electrical energy that comes out as sound energy - of about one per cent, at best. Horn speakers can manage thirty per cent without much trouble, and quite a bit more if you design them for loudness rather than fidelity. Take the horn off a phonograph and you'll have to put your ear right next to the diaphragm to hear much of anything, but with a big horn on it, a wind-up phonograph making sound by scraping a needle over a disc of shellac can legitimately be described as quite loud.

(Some phonographs let you remove the horn, or never had a horn in the first place, and allowed you to listen through one or more rubber tubes that went to a headset of some sort - essentially, primordial headphones. This allowed you to listen to your records in privacy, albeit with weird stethoscope-y sound colouration on top of the lousy fidelity of the phonograph system in the first place.)

Outside of Physics Experiment Land, acoustic horn design and implementation has many engineering tricks. For instance, modern horn loudspeakers usually have a horn throat that starts out much smaller than the diaphragm of the actual driver, which may be in its own actual rectangular speaker box stuck on the small end of the horn. There are also horn loudspeakers, like the legendary Klipschorn, that use various workarounds to fold something that acts somewhat like a horn into a speaker that can be mainly built out of flat wooden panels.

Also, the lowest bass frequency a horn can reproduce is determined by the size of the mouth of the horn; that's why public-address and hand-held megaphone speakers always sound tinny. Speakers like the Klipschorn have their horn mouth on the back of the enclosure, and are meant to be shoved into the corner of a room, so the walls behind them can provide a bit more effective horn size. Horn loudspeakers are also deliberately designed to be further away from an ideal horn shape than is strictly necessary, to balance the efficiency of the horn with the hard bass cut-off that a "pure" horn, with a mouth small enough to fit in a room, has at low frequencies.

The old phonograph horns have been reborn, too, as "amplifiers" for MP3 players and cellphones. The phone, MP3 player or ear-bud headphones plug into the small end of a horn, and suddenly the tsss-tsss-tsss of someone else listening to their iPod on the bus turns into actual music.

Some of these devices are very fancy and very expensive, but if you search eBay for "amplifiers" for MP3 players you'll find lots of cheerful-coloured horn doodads among the actual electrical amplifiers. The going rate for a combination iPhone stand and horn "amplifier" now seems to be about two bucks delivered.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Posted in Music, Psycho Science, Science. 1 Comment »

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