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Old 19-09-2005, 03:22   #16
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Mpemba effect

All things being equal, cold water freezes faster than hot. However, things are not always equal. A curious phenomenon known as the Mpemba effect can, under some very specific (and poorly understood) circumstances, result in hot water freezing faster than cold water. The factors that allow this effect to take place are conduction, evaporation, convection, dissolved gases, and even container shape. Since this is a complex effect, involving a number of variables, the various explanations may be somewhat speculative.
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Old 19-09-2005, 07:10   #17
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Re: Mpemba effect

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All things being equal, cold water freezes faster than hot. However, things are not always equal. A curious phenomenon known as the Mpemba effect can, under some very specific (and poorly understood) circumstances, result in hot water freezing faster than cold water. The factors that allow this effect to take place are conduction, evaporation, convection, dissolved gases, and even container shape. Since this is a complex effect, involving a number of variables, the various explanations may be somewhat speculative.

And here's a link to the effect. I'm still not sold on it at all. The issue came up in a sophomore thermodynamics class I was in. The professor roundly disproved it and left it off as an old wive's tale. My problem is the experiment hasn't been done enough times in an environment without variation. My gut says it's the environmental conditions and initial temperature selection that causes this effect.

Also, don't get caught up thinking throwing hot water into your ice cube trays is going to make them freeze faster or save you power on the boat. You will be losing more, actually, since it took energy to heat that water in the first place, and then the same amount of energy to cool it back to room temperature, and even more to get it down to freezing. This may or may not work under extremely precise conditions. For the vast majority of conditions (like your freezer at home or on the boat) it won't.

http://www.physics.adelaide.edu.au/%...hot_water.html
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Old 19-09-2005, 10:41   #18
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The water comes directly in contact with the rods. The rods contain the radioactive material and, therefore, the radioactive material is not directly in contact with the water, it is contained. They make the rods so that the radioactive material is uniformly distributed so as to not approach a critical mass yet still be concentrated sufficiently so as to generate energy.

The water is not only for cooling it is a good neutron absorber, so much so that you can stand directly over a pool reactor and look at the rods through the water. That is how I saw the beautiful blue from the sodium ionization.

The water is not heavy water necessarily to begin with although random atoms of tritium could happen to be there or be created by the source just as the sun's energy creates tritium in the ocean.
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Old 19-09-2005, 13:35   #19
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Very interesting, but mate, what a deveation from the original post
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Old 22-05-2008, 01:15   #20
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When mixing audio sources into an external amplifier, it is nice to have the input levels fixed and to adjust gain only at the output. I was just reading the manuals for the Standard Horizon GX1500S, GX3000S and GX5000S and thought I would note that they all support setting fixed audio output level for just this purpose.
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Old 22-05-2008, 03:08   #21
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Gee... an old thread revisited AND brought back to the OP topic - can't let that go too far so I will add my 0.02 dollars worth on the hot water freezing thread drift.

I have always understood (but never bothered to really check it out) that the hot water freezing faster "myth" is explained as follows. If standard old tap water is boiled for a few minutes and then left to cool back to room (or tap) temperature, then placed in a freezer along side some unboiled water, the previously boiled water will freeze faster. The explanation being the boiling drives off the dissolved air in the water so the boiled water has slightly less impurities in it (i.e. dissolved air) and therefore will freeze faster. Don't know the truth of this claim so please feel free to shoot holes in it - more thread drift now including guns .

As to mixing speaker outputs into one speaker, another way to achieve this is to use a twin coil / cone speaker. I am not talking a twin cone speaker rather a speaker that two seperate concentric coils each connected to their own cone (also concentric). The result is one physical speaker with two electrically isolated inputs. I probably use one or two a year.
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Old 23-05-2008, 02:45   #22
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I was just reading the manuals for the Standard Horizon GX1500S, GX3000S and GX5000S and thought I would note that they all support setting fixed audio output level for just this purpose.
I may have misread that. The fixed external audio output is listed as part of the VH-310 external handset, not the main radio.... I'm not sure why or how that is.
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Old 23-09-2009, 11:43   #23
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I want to combine the output from two separate devices and input both to one speaker. I have stereo speakers in the cockpit now, and want to hook one of them up to the external speaker jack on my VHF radio (it's about 2" away).

My idea was to use 4 diodes, one on each of the 4 wires coming to my speaker (2 from the VHF and 2 from the CD player). I thought they would work as "check valves" to ensure that no power from the CD player's output would make its way into the speaker jack on the VHF and fry it. A friend of mine who knows a lot more about electronics and me told me that won't work. But he didn't think a very simple circuit with one transistor would work. He said what I needed to find/make was essentially a very small "amplifier" (but with no gain). It would work is a solid-state mixer to combine the signals.

Then if I'm listening to music a radio transmission comes in, I can hear it mixed in over top of the music. If it's important and I want to reply, I'll turn off the CD player. No extra holes required in the fiberglass, and no 3rd speaker to install.

Has anyone done this? Can anyone point me in the direction of a circuit diagram? I don't mind building it, if I have plans.

Thanks for any help,

Craig
if im understanding the original post you want to have the stereo as the primary signal but transferring over to the vhf during communications. this can be accomplished using a couple of dualpole dual throw relays having the stereo set to normally on the vhf to normally off. the downside to this i can see would be that if there were any squelch chatter it would be switching back and forth quite frequently and annoyingly. i did this same sort of setup on my boat but for use with a highpower amp, if im sailling then the speakers are driven by the cplayer headunit if my engine is running thus charging the batteries the relays kick on the amplifier. works quite well for me.
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Old 23-09-2009, 14:26   #24
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Back in my glory days when I was in Aviation electronics in the Marines, (30 years ago), all the sound went to an impedance matching network with a single output to the pilots helmet. I beleive mini relays were used to assign importance to which signal they wanted.

After my days there I worked on old Leadwing motorcycles. The first Goldwings didn't come with radio systems and there were a lot of after market companies that made a little box that went between the radio, tape deck, and CB which cut the sound whenever the CB was receivng a signal. These are designed to filter out the noise from a motorcycle so I think they would work the best on a boat. To find this you'll need to find an old timer that was in that industry back in the mid 70's to late 80's. After the 80's it was all about dirt bikes and the old thungs were forgotten.

The other thought I have is cell phone companies still sell a kit to put your cell phone over the car speakers. You could adapt one of those.

You might also check with the custom CB shops. they should have or could build something for you.

Also keep in mind that you can't just switch over to a different source for input. When your CB kicks in and your stereo cuts out you have to have a load on your stereo equal to your speakers.
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Old 23-09-2009, 15:32   #25
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all you need is an on-on switch. wire the stereo to one side, the VHF to the other side and the common to the speaker. You could mount this switch in the speaker housing probably. you cant run them both with this though. Although maybe you could run the stereo on mono if it has load protection (most do now days)
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Old 23-09-2009, 15:41   #26
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with a manual on - on switch you would physically have to switch the signal from stereo to vhf. i think what craig was looking for was something that automatically switched the signal for him.
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Old 23-09-2009, 17:18   #27
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A possible over-the-counter approach. This works for all kinds of gadgets..

JL Audio CleanSweep - OEM Interface Car Audio

and another nifty device....

http://www.ps-engineering.com/docs/PMA4000_DS.pdf

Actually, anyone handy in digital electronics might come up with a small circuit using a 4016 quad bi-lateral switch IC and a little gain control/impedance matching circuit for very little parts cost. It would fit in a box the size of a pack of smokes.
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Old 23-09-2009, 17:25   #28
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craig was looking for was something that automatically switched the signal for him.

Oh, OK, he did say he would turn the CD player off if he wanted to respond, I figured he could hear his current radio speaker..... he says 2" away.... which doesnt make sense... why would he need another speaker at all? But he's going through alot to avoid buying a little 2" speaker in housing!
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Old 24-09-2009, 10:26   #29
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After extensive research I've found that all the over the counter switch solutions are highly expensive. Most are designed for PA or intercom and those which are 12v are amp switchers(might work) or designed for aircraft. Either way, home built is the only economical way and not really THAT complex (for someone with electronics experience). Good Luck!
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Old 24-09-2009, 11:03   #30
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VHF Interface

Is this the sort of thing you are looking for

http://www.marine-audio.com/Products/VHF-Extension-Speakers-&-Interfaces/External-VHF-Speaker-~-Audio-Interface.htm
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