Whats the difference between Magnetic & Crystal headphones?

magnetic are either moving coil or moving iron. Google can soon explain how piezos & crystal earpieces work.

NT

Magnetic headphones (like most earbuds) are low-impedance and have DC conductivity. Crystal headphones are high impedance (and are capacitive, kind of like a capacitor microphone in reverse), so have NO DC conductivity. The likely reason to use magnetic is that a DC path to ground is required to correctly bias some amplifier stage.

Absent a DC path to ground, some tube-type equipment outputs hundreds of volts, could be hazardous.

Moving iron headphones were originally in the 1-8k ohm range, modern ones mostly 32 ohms. Crystals are odrers of magnitude higher impedance, much greater efficiency & dire sound quality. A DC path can be added using a resistor or choke.

NT

One works with electromagnetic force, the other works with piezoelectric force.

The first is low impedance and good for low frequencies, it uses current. The other is high impedance and good for high frequencies, it uses voltage.

With a typical 8-Ohm or 32-Ohm output, the crystal headphone is useless.

-Symbol.jpg

I have generally found it useful to give a picture along with an explanatio n - it makes the jargon more grounded, pun intended.

Top picture is a Piezo (crystal) transducer symbol. In the simplest of term s, bend a crystal, it will emit electricity. Apply electricity to a crystal , it will bend. But, as you may see from the symbol, there is no direct con nection between the two poles of the transducer.

A magnetic speaker, whether PM or Field Coil uses a voice-coil that is move d by changing AC voltages applied to the voice-coil. So the two poles are d irectly connected via the voice-coil. Yes, there is DC continuity - and as a rule, magnetic speakers do not like DC.

That the tube tester wants magnetic headphones indicates that it is a low c urrent output device. Given that most tube testers - pretty much a done-dea l after the 60s by way of design improvements - have no formal amplificatio n built in, a magnetic headphone makes more sense. What the "Noise Tester" is measuring is a sample from the anode load resistor and amplifying the ou tput to a speaker (or eye tube) - depending on the manufacturer.

Some testers have settings for this test that more resemble actual operatin g conditions, rather than "full throttle current" as typically done for lif e-test.

The above few lines from "sample" through "Life-test" are quotes.

However, there are all kinds of noise - usually in very small values.

Peter Wieck Melrose Park, PA

In the 1960s, transistor radios and came supplied with crystal earpieces.

.... Phil

Those crystal diode radios we all built when I was a kid needed those earpieces. Had to wind wire on a tube, etc.

Now kids are probably doing SDR instead, at least the nerdy ones.