Dan's Data letters #14
Publication date: 1-Dec-2002.Last modified 03-Dec-2011.
Blow-up sound
Since you've been talking about speakers so much in your letters columns just recently, I thought I would show you these, and ask "How the hell do they work then?" :)
I was thinking, since they're inflatable, it's the sort of thing you can bung in a suitcase and take on holiday with you to plug into an iPod or Minidisc player or something like that. Do you think they are any good? They're a tad on the expensive side, it has to be said. I can get a half decent pair of Altec speakers for half the price.
Ian
Answer:
NXT's FAQ
here may help you out in the how-they-work department.
Distributed mode speaker technology is very interesting, technically, but most products that use it are resolutely low-fi, and I don't imagine these inflatable speakers sound terribly good. I've never heard one, though, so I'm ready to be proved wrong.
Mystery lights
Up here in Brisbane we have traffic lights, just like the rest of the country; and they tend to have red, amber and green lights. This should come as no surprise. It is, however, the physical properties of the lights that intrigue me.
Older lights appear to work much the same way as a torch, that being a bright bulb attached to a reflective backing, covered over with a tinted piece of glass or acrylic. Newer lights look completely different, at close examination being an array of little dots in their respective colour.
Now, me wonders, are these little dots high-intensity LEDs? I wouldn't have thought traffic control would be a suitable task for such devices. There appears to be no dimming of the light source around the edges (as you would expect from a torch-like configuration) and there's no tinted glass to scatter and colour the light.
If you have any idea what these new-fangled traffic lights could be using as a light source, please tell me.
Anthony
Answer:
Yes, they're LED arrays.
LED light propagation is pretty much entirely determined by the profile of the epoxy lens over the die. It can be quite narrow-beam, or quite wide; most of the light does go where it's needed. LEDs work fine as traffic lights, and the absence of a tinted lens is a good thing; the light's already coloured. Another way to think of this is that there's no tinted glass to eat most of the light.
Find more on this subject here.
Peltier power?
At Comdex this year, Thermaltake was showing off this.
My initial thought was, "Wow, what a great product, now I can use a Peltier cooler without having to worry about condensation problems", seeing as how the electronics keep it from ever reaching the dew point. But after thinking for a while I realized that the reason most people use Peltiers to cool their CPUs is so that they can reach insanely cold temperatures. So my question is - if the Peltier isn't being used to its full potential, is it being wasted? Will the CPU actually get colder than it would if it was cooled by a regular heatsink and fan?
Brandon
Answer:
The SubZero4G
does indeed promise to keep a CPU cool, but above the dew point, provided the dew point
is above 26 degrees C. Which it probably is, unless you're in the middle of a rainforest
or a monsoon.
That's not really the problem, though. The problem is that many CPUs will output too much heat for this thing to handle.
The maximum quoted power consumption of the PCI-card controller for the SubZero4G is 73 watts. That's not very high, by Peltier cooling rig standards. Even if you assume all 73 watts is powering the Peltier element, then unless the Peltier is quite amazingly efficient, it'll only be able to move around 60 watts of heat, and will only have a cold-side temperature about 10 degrees C below its hot-side temperature when it's doing that.
So if your CPU outputs more than about 60 watts of heat - a 2.5GHz or higher P4 will, when it's working reasonably hard, and so will a current Athlon XP 2000+ or higher - I imagine this cooler will toast the processor, because the Peltier element just can't move that much heat. And if your CPU outputs about 60 watts, this cooler will only keep it 10 degrees below the temperature of the air inside the case, at best. Here in Sydney, Australia, at this time of year, it's not at all amazing to see day time temperatures of more than 40 degrees Celsius in the shade. It's quite a lot warmer inside computer cases in un-air-conditioned premises.
I'll be interested to see if the SubZero4G can actually handle the heat output of the high-end processors that Thermaltake mention at the beginning of the product page.
Speakers from scratch
I want to build a pair of three-way speakers. Partly because my TV (I think it's from the '80s) has only the built-in single channel speaker, and partly just to see if I can.
I looked at your site and found that speaker kit. I don't really want to build a kit; I want to make my own. Anyway, I want to do three-way, with a sub, a mid-range, and a tweeter (I think).
Can you give me some information on what components to buy and where to get them? Also, could you help me with some instruction on exactly what to do? I priced several pieces on eBay, but I don't know what the difference is between a lot of them. Anth
Answer:
I can't give you specific advice, because there are far too many options. There are,
as you say, lots of online resources; I used to recommend people looking for speaker
design info just buy themselves a book, but I think you can save some money and get
a decent leg-up on the subject on the Web, nowadays. Start from the bass-heavy links
page here, for instance, and
a weekend of page-wandering ought to leave you with a reasonable selection of clues.
If you're interested in getting a book, the scare-the-tripes-out-of-yourself standard reference work in this area is Vance Dickason's "Loudspeaker Design Cookbook" (home page here), but it's not a good book for a beginner. I used to recommend V. Capel's "Introduction to Loudspeakers and Enclosure Design" (ISBN 0-85934-201-8), but that's now very hard to find. You can see the main loudspeaker project from that book, though, on this site. It's an interesting single-driver transmission-line design, and a very good choice for someone who's never built a speaker before, but has some basic woodworking skills and tools.
Flash, begone!
How do I stop my browser from asking me to install Flash every 30 seconds?
Why don't I want Flash installed? I hate those Flash ads. I mean I really hate them. They piss me off. A lot. Especially the ones that won't let you turn them off.
So I'd rather give up all legitimate Flash animations and sites, for the rest of time, than see another annoying Flash ad.
The problem? Every time I visit a site with a Flash animation or ad (it seems every 2nd site has a Flash ad nowadays) I get the "install Flash viewer" pop-up from IE. I can answer no (NO! For the love of GOD, NO!!) but on the next page, or the next site, I get the same "install Flash viewer" prompt.
Is there any way to stop being harassed to install the Flash viewer on every page with a Flash ad on it?
Chris
Answer:
There's probably a way to stop it asking, but the way I'd deal with the problem would
be to allow it to install Flash, but use blocker software to intercept the ads.
That way you can still view worthwhile
and educational Flash content.
I haven't tried it, but apparently AdShield will block Flash ads, among other things. The Proximotron can do it, too.
Camera hallucinations
At a party I had recently, we had a big ultraviolet fluoro tube hung up on the wall. This looked totally awesome to the naked eye, but when we took photos with our digital camera (I don't have the camera or the box handy, so I can't tell you what model it is - I think it's a Sony, but I can't find a camera on their website that looks like mine) the fluoro tube showed up a bright pink (see attached photo).
Can you explain why the UV gets interpreted as pink?
Ben
Answer:
That "pink" is magenta with a little bit of cyan in it, which suggests to me that your
camera has a cyan-yellow-green-magenta sensor (see
here for an explanation of what this means), and the incoming light's primarily
tickling the magenta-filtered pixels. The slight cyan tint may be because the light
making it through to the cyan pixels as well - which isn't out of the question, since
cyan is bluish-green and thus closest to the real colour of the blacklight. Or the colour
shift may just be down to the camera's white balance setting.
The reason why the magenta pixels are seeing the light but nothing much else is - leading the camera to think that it's a magenta-coloured light - is, I'd guess, because the magenta pixel filters happen to be highly transparent to near-ultraviolet light as well as their intended frequency range, but the others aren't.
Camera sensors typically have lousy sensitivity to the blue end of the spectrum anyway, but with a bright enough blacklight and a dim enough room, there'll be enough photons to make something happen.
Sonic snake oil, instalment 2938
I read your response [in this column] to one reader's observation on the peculiarities of so-called "audiophiles". Here's another one I came across while looking for a new tone arm for my turntable. The explanations offered here to encourage you to ditch all of your old RCA audio/video cables certainly rewrite a number of sections of my Handbook for Electrical Engineers. Obviously I attended the wrong educational facility.
Aurora
Answer:
Yup, that site's got ticks in most of the audiophile-nonsense boxes, all right, including
the usual assurances that their special connectors will make digital cables better,
too. Mm hm.
To be fair, though, the Eichmann Bullet Plugs are considerably less snake-oily than a lot of audiophile tweak stuff. Never mind the marketing spiel; these probably are quite good connectors, and the RCA compatibility is nice, too. Not that they do anything for the crappiness of the RCA sockets you plug them into, of course.
This page, however, makes it clear (to me) that (in my opinion) this outfit is either bananas or a bunch of card carrying rip-off artists. Either way, they fit nicely into the high-end audio market.
I leave you with this.
When Your Tivo Thinks You're Gay
Liked your recent column. Then this got linked to from Slashdot.
If you haven't already seen it, it's another good reason for database pollution.
pompomtom
Answer:
Yeah, I read
the WSJ
piece. It's entertaining, but it's a complete beat-up; as various Slashdot posters
observed in the comments
for that story, it's not as if PVRs
record stuff-they-think-you-might-like instead of stuff you've told them to record.
You've got to be pretty darn insecure,
IMHO, if you actually get upset
about your Tivo suggesting gladiator movies, musicals and "Will and Grace" reruns to
you when you're just not that kind of guy.
Any interface that's so cluttered with impulse-buy-inducing "suggestions" that it becomes harder to use - Amazon is teetering right on the edge, if you ask me - is a problem even if the suggestions are good, and is a worse problem if they're dumb. But Tivo-type suggestions are just icing on the cake.
"Cryptophis Nigrescens killed my computer"
("...or it might have been Pseudechis Porphyriacus")"My computer was making a strange hissing noise last night and this morning when I turned it on there was a crackling noise and some smoke then nothing, if I bring it in can you fix it?"
A colleague took this technical support call today and has the photographs to prove it. I thought you might appreciate it.
We haven't done a scale count yet, so we're not sure whether it was a small-eyed snake or a young red-bellied black snake.
Rohan
