Building better High sensitivity headphones

Hey Guys! Great discussion!

Just a note; there are two "resistors" to consider...

1- The first is the "series" resistance in an LC tank circuit, which represents the power dissipation in the circulating current, and as noted, the grater this resistance, the grater the losses. In the case of a piezo-resonator (call it a PZR here), the acoustic (sound) radiation is virtually this resistor. So the more efficient this resonator is at producing sound, the greater this "resistance", and inevitably the "lower" the Q, and we would like that.

2a- The second is the input impedance of a device whose output terminal are across a tank resonator. As far as the PZR is concerned, the circulating "current" is the momentum of the vibrating PZR surface, and resonance indeed occurs, As imagined, no dissipation, no series resistance, the impedance at the drive terminal is infinite, and as often touted, purely resistive. I can't find the relation between Q (set by the series resistor) and the output impedance at resonance. But it has to be something like the series resistance multiplied by the Q, or the like (homework for someone). In any event, contrary to the thought that a capacitative element such as a PZR has a purely capacitative input impedance, the input impedance at resonance can be nearly resistive if the piezomechanical coupling efficiency is very high, and such resistance can be relatively low if the aeromechanical coupling efficiency to air is also very high. Perhaps there are but a few PZR devices that can go this route.

So much for the acoustical section of a crystal receiver (CR).

2b.i-Since the only energy source there is in a CR is the RF captured by the RF antenna, one would have to compute said energy from its free space source, which I am not sure how to do at the moment. Microvolts per meter field strength combined with the 377 ohms per square free space impedance is a start. Anyway, getting back to Tanks, there are two here, the latter being the audio tank (PZR or whatever); the former being the RF tank, the wire coil and RF capacitance (often the stray capacitance of the coil winding). Again, there is a series resistor and the output impedance entity which I am getting to. First to dispose of another series resistor, this time that of the RF coil winding. at a megahertz, the "skin effect" of the coil wire is important. Several thinner wires bundled have less RF resistance that a single thick wire of the same DC resistance, so "Litz" wire was born to reduce the RF tank circuit dissipative losses. The H part of the AM radio wave inspires RF circulating current, and we have an energy source available to operate. We choose to impose a nonlinear device, a diode across this tank to get some useful DC or audio energy out of the RF.

2b.ii-Again, the tank output impedance, (Q times something) is relatively high if we want any RF selectivity, otherwise we get all AM stations in our vicinity muddled together. But we take what we can get for now. The diode is operated near cut-off so that its impedance if high, the nonlinear current vs voltage characteristic produced a dc current which varies with the amplitude of the RF H-field, and we have an audio signal thereby. The output impedance of this "Audio" generator has to be somewhere less than the parallel resonance shunt impedance of the RF tank, but greater than the DC resistance of the diode at it operating point. That coves a wide range.... like somewhere between 10,000 ohms and 100 ohms...

2b.iii- To summarize, the general goal is to have on the one hand, an RF tank of sufficient size to capture RF energy out of domestic space that can be converted by a rectifier of conversion impedance similar to the resonant impedance of the RF tank. At the same time, the audio or DC impedance of the rectifier has to be similar to the input impedance of the PZR.

Finally, no one has proposed to try to use some of the available DC to operate an audio amplifier (FET or the like).

Ange

Thanks for jumping in Ange, We are still working on the impedance of a parallel LC at resonance. Yes. we do want minimize losses in both the capacitor and inductor. I think I have a good approximation from another group. Z(tank)~=(2*pi*F*L)^2 / RL/RC) were RL is all loss resistance in the inductor and RC is loss resistance in the capacitor. I start off suggesting Q of 1500 for the capacitor, I have since found info it is much lower. See the last page of this pdf.

So if we do everything very well we may get an inductor with a Q of 1000, and a Q of 400 for our capacitor. Assuming a 240uh L and 100 pf C with the above Qs, that calculates to; Z(tank) = (6.28*1.027Mhz *.00024)^2 / (1.55/3.87) = Oops. The formula looked good until I put in a more lossy capacitor. It may be close but it not right, help!!

Sorry, I didn't follow all that, but once we have minimized the losses in our tank then we start loading our tank with three things, the antenna, the detector and the PZR device to get audio. (often a electromechanical speaker). I'd be curious to see a graph of reactance and resistance of a piezo element used as the headphone. We want high impedance to keep the bandwidth of our tank high, for good selectivity. We also want a very efficient device to convert current to sound.

Oh there are those that receive a strong local and use that energy drive an amp to hear more distant stations. Some say it's cheating :-) Also there is FET detector circuit that's suppossed to work well.

schematic at bottom

"amdx" wrote in news:b8b42$4cb83ca1$18ec6dd7$ snipped-for-privacy@KNOLOGY.NET:

First of all, let's be clear on the model, which is a series resistance (Rs) and inductance (L) that is in parallel with a capacitance (C)to form a parallel tank circuit. In other words, the resistive loss is assumed to be entirely in the inductor.

For this situation Q=wL/Rs. Subsitituting your numbers for Q, frequency and inductance yields Rs=1.5 ohms

From here there are several ways to proceed, but the simplest is to perform a series L+Rs to parallel L//Rp transformation.

The reason for doing so is because the capaaitive and inductive reactances vanish at resonance and all that is left is Rp, the impedance at resonance.

For Qs>>>1, the transformation is Rp=Q^2*Rs. For Q=1000, the impedance of the specified tank circuit at resonance is resistive and is 1.5Meg. A p-spice simulation of the specified tank circuit confirms this result.

Putting the equiations together: Q=wL/Rs Q^2=Rp/Rs

Therefore Rp, the impedance of the tank circuit at resonance, is Rp=Q^2*Rs = (wL)^2/Rs

Using your numbers Rp=((6.28x10^6)(0.24x10^-3))^2 /1.5= 1.5Meg

"Angelo Campanella" wrote in news:i99tku$lep$ snipped-for-privacy@news.eternal-september.org:

I disagree with many of your comments, but rather than going through them one by one, let me simply state "my" bottom line. Specifically, when dealing with a purely passive system, such as a crystal radio receiver, one must consider the interacton among all of the components of the system. Like it or not, acoustic transducers are specified in terms of acoustic output per applied volt, with complete disregard for the interaction between transducer impedance and its driving source impedance. Consequently, a higher "pressure per applied volt" sensitivity for a transducer does NOT necessarily translate to higher acoustic output and higher OVERALL system sensitivity when the transducer is installed in a passive system.

s of the system interact. can not

Pretty darn close to the 1.5072 Meg that originally calculated. It's been fun! MikeK Now about those piezos, I may ask for a quote just see what they are thinking.

"amdx" wrote in news:da2aa$4cb8d7dd$4501214e$ snipped-for-privacy@KNOLOGY.NET:

It should be, because it's the same equation.

Rp=(wL)^2/Rs =wLQ (Q=wL/Rs)

That's the good news. The bad news is that the impedance of the tank circuit at resonance is irrelevant bcause the impedance of the tank circuit is not the impedance that is seen by the crystal earphone.

Uzytkownik "Angelo Campanella" napisal w wiadomosci news:i99tku$lep$ snipped-for-privacy@news.eternal-september.org...

You also should know about the field emission of electrons from a transmitting antenna. So the electrons are captured by RF antenna. Of course they flow in form of pulsatile flow combined with the oscillations.

In physics are the two method: the field method and the charge method.

For the electronocs the charge method is better. S*

Electrons are NOT enitted from a transmitting antenna. E/M waves re launxhed from a transmitting antenna.

Waves are received by a reciever's Antenna.

A temporary charge can be found on antenna during each voltage swing. have nothing.

Component interations are based on charge location ad intensiy.

Ange

Uzytkownik "Angelo Campanella" napisal w wiadomosci news:i9duu6$jpa$ snipped-for-privacy@news.eternal-september.org...

E/M waves are in the papers. In antennas are electrons. They flow from (or to) the ground (or chassis) and antennas. In the cristal radio is a diode. Is in such radio the electrons flow?

But what the electrons do?

In transmitting antena the voltage is doubled at the end and the electrons jump off.

Charge is an excess or lack of electrons. The field emission/absorption is a fact. S*

They jump into the tank to make waves.

No, waves from the tank jump off the end of the antenna.

All electrons stay in the tank wire.

Ange

essentially, charge sloshes back and forth in the transmitting antenna element, which causes charge to slosh back-and-forth in the receiving antenna element.

imagine you are holding a +1 coulomb charge and i am holding a -1 coulomb charge in my hand. we both allow movement of our charge up/ down and left/right, but we restrict the movement along the direction of the line that connects the two of us.

since the charges are opposite sign, they attract, but we restrict their motion so that they don't crash into each other.

now if i move my charge up, your charge will follow it up. if i move mine down, yours will follow it down. if i move mine to my left, your charge follows. if i move it up and down repeatedly, your charge follows up and down repeatedly. *that* is an EM wave.

if i move it up and down a million times per second, you can tune in the carrier on an AM radio. if i move it up and down 100 million times per second, you can tune in it on an FM radio. if i move it up and down 500 trillion times per second, you will see it as a blur of orange light.

but electrons are not leaving my hand. i am just waving them around and they have an attractive force on the positive charges in your hand that vary as the relative position varies.

r b-j

element, which causes charge to slosh back-and-forth in the receiving antenna element.

It take place in the original Hertz apparatus. So the receiver must be parallel to transmitter.

coulomb charge in my hand. we both allow movement of our charge up/ down and left/right, but we restrict the movement along the direction of the line that connects the two of us.

their motion so that they don't crash into each other.

mine down, yours will follow it down. if i move mine to my left, your charge follows. if i move it up and down repeatedly, your charge follows up and down repeatedly. *that* is an EM wave.

You described the electrons in the antennas. *that* is rather an electric wave.

the carrier on an AM radio. if i move it up and down 100 million times per second, you can tune in it on an FM radio. if i move it up and down 500 trillion times per second, you will see it as a blur of orange light.

and they have an attractive force on the positive charges in your hand that vary as the relative position varies.

You have a magic force acting between the antennas. In reality the electrons are leaving your hand. Electrons have mass. If your waving (voltage) is intensive they jump off. The father of the radio is Tesla. His radio waves are longitudinal. According him the EM is a myth. S*

Is there any currently produced off the shelf product as good as the ancient "CANS" the military once used?

Most crystal radios nowadays are about scientific demonstration or nostalgia, right? Historically accurate ones are generally extremely durable.

A good modern crystal radio (AM) might be a good thing to pack away in an emergency or survival kit as a backup for extreme (Civil Defense) emergencies where batteries have all run out.

To tune in FM Radio even on headphones would inherently require some sort of power source, correct?

For something like this, photovoltaic cells might actually be worth their high cost, right? (Though access to light might be a weakness.)

I actually had to sleep on a Red Cross cot for two weeks in June of 2008 and I can tell you that lots of people had batteries that were dead when needed, or ran out quickly.

Yes this is the unloaded Q. We have antenna loading and detector/headphone loading. Also to make the numbers worse I have found more realistic numbers for the Qs. I'm a little surprised how low the impedance at resonance is. With a resonant frequency of 1 Mhz.

240uh inductor Q=800 XL= 1507 ohms R=1.884 ohms 105pf capacitor Q=400 XL=1507 ohms R=3.768 ohms Z=2piFl^2/R1+R2 Z=2271652/5.652 Z=411,531 ohms From what I can find out, the Qs I used are high but doable, so this is a high tank impedance for a crystal radio. MikeK

I had about 12 pounds of fresh alkaline cells with me when I spent a couple weeks in a county hurricane shelter, along with two radios and five flashlights. I hd over a month's supply of each medication, and a basic set of tools in my truck in the parking lot. I even took my rolling chair from my computer desk so i didn't have to sit on a folding metal chair or emergency cot all the time. It doubled as a cart to haul my stuff into the shelter, and out when my street was declared safe to return to.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

when i was really little (pre-1965) i had a crystal radio (from Knight- Kit that was a division of Allied Radio) that worked okay for AM radio around Fargo ND. i never did this with a crystal set, but later, when i was a ham radio operator, we had this technique called "slope detection" for FM that used an AM receiver and i did try it once. it sorta worked sorta crappily.

what we did was position the received FM signal on one of the two slopes (a.k.a. "transistion region" between passband and stopband) of the selectivity filter (a piezo-crystal lattice network) where the slope seemed linear. this means that the desired signal was quite attenuated because it was on the slope and there was potentially an interference signal that could end up right in the middle of the passband of the selectivity filter that could potentially blow your desired FM signal away.

do you understand how positioning the FM signal on the slope of the selectivity filter of an AM receiver might work?

so an unpowered AM crystal receiver could conceivably pick up an FM signal.

and one could design a crystal receiver to have two adjacent passbands very close to each other that somehow went up and down with a two- ganged variable capacitor. the right down-slope of the lower passband would be aligned with the left up-slope of the higher passband. both would have a crystal rectifier on the output and the headphones would be wired in between the two.

r b-j

snipped-for-privacy@k22g2000yqh.googlegroups.com...

there are definitely issues regarding polarization of the EM wave and the position of the antennae. for two simple dipole antennae, it's best that they be parallel.

r

sure, in the antenna element (of either transmitter or receiver), which is of metal or some conductive material, there is wave motion of electrons back and forth.

i have a *fundamental* physical force (one of the four fundamental forces, which, if you choose, you may call "magic" since we really don't know the cause of the force).

oh, a few electrons are leaving my hand now as i type. in fact, because of quantum mechanics, i s'pose there is some non-zero probability that some electron "orbiting" some atom in my hand is hanging out somewhere around Mars, but i would not say that reality is likely.

consider the charge-to-mass ratio of electrons.

maybe a few do (but the waving would have to be just unreal to overcome their attachment to the object they are attached to). nonetheless. this has nothing to do with what is causing the charge that you are holding in your hand to move around. what is causing the charge in your hand to move when the charge in my hand moves is the fundamental EM force that opposite charges attract (as well as like charges repel).

well, reality could be a myth. maybe none of you are real and this experience i am having typing into a computer is just an illusion and my brain (such as it is) is in some mad scientist's laboratory (in a reality where there is no EM) and this mad scientist is just providing stimulus to my consciousness that i am reacting to.

but if reality is what it appears to be, i think Coulomb (who preceded Tesla by a little bit) established that, in reality, these charged objects influence these other charged objects, even though we cannot see anything of substance between the objects.

r b-j

signal.

If you google on "FM crystal set" you'll find umpteen using Slope Detection, and a bunch more using Ratio and Foster-Sealy detectors.

.............. Zim

"robert bristow-johnson" wrote news: snipped-for-privacy@j18g2000yqd.googlegroups.com...

the poster you're responding to sensibly?

I am not fluent with PC.

the position of the antennae. for two simple dipole antennae, it's best that they be parallel.

Electric waves are not polarized. The dipole is like the two loudspeakers. The two waves are "coupled".

which is of metal or some conductive material, there is wave motion of electrons back and forth.

In each real wave must be the drift. "" More generally, the Stokes drift velocity is the difference between the average Lagrangian flow velocity of a fluid parcel, and the average Eulerian flow velocity of the fluid at a fixed position. This nonlinear phenomenon is named after George Gabriel Stokes, who derived expressions for this drift in his 1847 study of water waves."

forces, which, if you choose, you may call "magic" since we really don't know the cause of the force).

Step by step the cause will be know.

because of quantum mechanics, i s'pose there is some non-zero probability that some electron "orbiting" some atom in my hand is hanging out somewhere around Mars, but i would not say that reality is likely.

The field emission is not visible. But if the voltage is high enough the sparks are reality.

It is very high. For this reason the "c" is so high.

overcome their attachment to the object they are attached to). nonetheless. this has nothing to do with what is causing the charge that you are holding in your hand to move around. what is causing the charge in your hand to move when the charge in my hand moves is the fundamental EM force that opposite charges attract (as well as like charges repel).

experience i am having typing into a computer is just an illusion and my brain (such as it is) is in some mad scientist's laboratory (in a reality where there is no EM) and this mad scientist is just providing stimulus to my consciousness that i am reacting to.

Tesla by a little bit) established that, in reality, these charged objects influence these other charged objects, even though we cannot see anything of substance between the objects.

In space is ISM. Rare plazma plus dust. Ions are medium for acoustic waves and electrons for electric. The same is in conductor. The are also acoustic and electric. S*

r b-j