Building better High sensitivity headphones

[GregS]

I got a no SCI.PHYSICS.ACOUSTICS
So I changed it.

Here's a page with info using piezoelectric elements, specifically
Kyocera KBT-33-RB-2CN.

The Kyocera data book is
http://www.avx.com/docs/masterpubs/piezo.pdf
KBT-33-RB-2CN data is found on page 20. It's about 35mm in diameter.
The impedance is capacitive, stated as 3k at 1 kHz, and less at higher
frequencies, being about 1 k at 3 kHz.

ALL of those devices have narrowband resonances all over the place. The
response looks like a hedgehog. And they have to be driven with a high-Z
source or it gets worse.

Where is the 107dB SPL measured? Perhaps not at a distance of 1m. Perhaps at
the transducer surface?

Typically the output would be 86 dB at three feet 1 watt.. Add a horn and add
9-10 dB.
They are driving with equivalent 8 ohm .125 watt or 1 VRMS and who knows the
distance.
or complete seal. 1 VRMS draws .00036 watt at 1 kHz roughly. At 300 Hz
very efficient headphone drawing .0001 watt.

Probably, if the transducer is not necessarily intended to couple into air
anyway.

It's still practical to test CR circuits with the radiation from local AM
broadcast stations.
My last venture with a CR such worked OK on WOSU AM radiation, that
transmitter antenna being about two miles east of me. [I used an old 2k-ohm
magnetic headphone set, which also produces enough sound from my old B&K
2203 SLM ac-out port signal to show me whether that SLM was working OK in
the field...]

So what's wrong with using a JFET and a low-efficiency moving coil driver?
It's hard to get efficiency and flat response at the same time.
--scott

I guess its not efficient. The orginal post I think is about crystal radios.
greg

[amdx]

Post by GregS
I got a no SCI.PHYSICS.ACOUSTICS
So I changed it.

Here's a page with info using piezoelectric elements, specifically
Kyocera KBT-33-RB-2CN.

The Kyocera data book is
http://www.avx.com/docs/masterpubs/piezo.pdf
KBT-33-RB-2CN data is found on page 20. It's about 35mm in diameter.
The impedance is capacitive, stated as 3k at 1 kHz, and less at higher
frequencies, being about 1 k at 3 kHz.

ALL of those devices have narrowband resonances all over the place. The
response looks like a hedgehog. And they have to be driven with a high-Z
source or it gets worse.

Where is the 107dB SPL measured? Perhaps not at a distance of 1m. Perhaps at
the transducer surface?

Typically the output would be 86 dB at three feet 1 watt.. Add a horn and add
9-10 dB.
They are driving with equivalent 8 ohm .125 watt or 1 VRMS and who knows the
distance.
or complete seal. 1 VRMS draws .00036 watt at 1 kHz roughly. At 300 Hz
very efficient headphone drawing .0001 watt.

Probably, if the transducer is not necessarily intended to couple into air
anyway.

It's still practical to test CR circuits with the radiation from local AM
broadcast stations.
My last venture with a CR such worked OK on WOSU AM radiation, that
transmitter antenna being about two miles east of me. [I used an old 2k-ohm
magnetic headphone set, which also produces enough sound from my old B&K
2203 SLM ac-out port signal to show me whether that SLM was working OK in
the field...]

So what's wrong with using a JFET and a low-efficiency moving coil driver?
It's hard to get efficiency and flat response at the same time.
--scott

I guess its not efficient. The orginal post I think is about crystal radios.
greg

Yes, headphones for crystal radios.
The object is to use no external power, then hear as many stations as
possible
with a crystal radio. So we want the most sensitive headphones we can get,
also
want high impeadance to prevent loading the resonant circuit.
There are those that receive a strong signal and use that energy to power
an amplifier. The amp is then used to amplify the audio from a weaker
station.
MikeK

[GregS]

Post by amdx

Post by GregS
I got a no SCI.PHYSICS.ACOUSTICS
So I changed it.

Here's a page with info using piezoelectric elements, specifically
Kyocera KBT-33-RB-2CN.

The Kyocera data book is
http://www.avx.com/docs/masterpubs/piezo.pdf
KBT-33-RB-2CN data is found on page 20. It's about 35mm in diameter.
The impedance is capacitive, stated as 3k at 1 kHz, and less at higher
frequencies, being about 1 k at 3 kHz.

ALL of those devices have narrowband resonances all over the place. The
response looks like a hedgehog. And they have to be driven with a high-Z
source or it gets worse.

Where is the 107dB SPL measured? Perhaps not at a distance of 1m. Perhaps at
the transducer surface?

Typically the output would be 86 dB at three feet 1 watt.. Add a horn and add
9-10 dB.
They are driving with equivalent 8 ohm .125 watt or 1 VRMS and who knows the
distance.
or complete seal. 1 VRMS draws .00036 watt at 1 kHz roughly. At 300 Hz
very efficient headphone drawing .0001 watt.

Probably, if the transducer is not necessarily intended to couple into air
anyway.

It's still practical to test CR circuits with the radiation from local AM
broadcast stations.
My last venture with a CR such worked OK on WOSU AM radiation, that
transmitter antenna being about two miles east of me. [I used an old 2k-ohm
magnetic headphone set, which also produces enough sound from my old B&K
2203 SLM ac-out port signal to show me whether that SLM was working OK in
the field...]

So what's wrong with using a JFET and a low-efficiency moving coil driver?
It's hard to get efficiency and flat response at the same time.
--scott

I guess its not efficient. The orginal post I think is about crystal radios.
greg

Yes, headphones for crystal radios.
The object is to use no external power, then hear as many stations as
possible
with a crystal radio. So we want the most sensitive headphones we can get,
also
want high impeadance to prevent loading the resonant circuit.
There are those that receive a strong signal and use that energy to power
an amplifier. The amp is then used to amplify the audio from a weaker
station.
MikeK

I wonder what the highest Z might be. I think 600 ohm nowdays. I don't
know if it would drive a transformer. ??

[amdx]

Post by GregS

Post by amdx

Post by GregS
I got a no SCI.PHYSICS.ACOUSTICS
So I changed it.

Here's a page with info using piezoelectric elements, specifically
Kyocera KBT-33-RB-2CN.

The Kyocera data book is
http://www.avx.com/docs/masterpubs/piezo.pdf
KBT-33-RB-2CN data is found on page 20. It's about 35mm in diameter.
The impedance is capacitive, stated as 3k at 1 kHz, and less at higher
frequencies, being about 1 k at 3 kHz.

ALL of those devices have narrowband resonances all over the place.
The
response looks like a hedgehog. And they have to be driven with a high-Z
source or it gets worse.

Where is the 107dB SPL measured? Perhaps not at a distance of 1m. Perhaps at
the transducer surface?

Typically the output would be 86 dB at three feet 1 watt.. Add a horn
and
add
9-10 dB.
They are driving with equivalent 8 ohm .125 watt or 1 VRMS and who knows the
distance.
or complete seal. 1 VRMS draws .00036 watt at 1 kHz roughly. At 300 Hz
very efficient headphone drawing .0001 watt.

Probably, if the transducer is not necessarily intended to couple into air
anyway.

It's still practical to test CR circuits with the radiation from local AM
broadcast stations.
My last venture with a CR such worked OK on WOSU AM radiation, that
transmitter antenna being about two miles east of me. [I used an old 2k-ohm
magnetic headphone set, which also produces enough sound from my old B&K
2203 SLM ac-out port signal to show me whether that SLM was working OK in
the field...]

So what's wrong with using a JFET and a low-efficiency moving coil driver?
It's hard to get efficiency and flat response at the same time.
--scott

I guess its not efficient. The orginal post I think is about crystal radios.
greg

Yes, headphones for crystal radios.
The object is to use no external power, then hear as many stations as
possible
with a crystal radio. So we want the most sensitive headphones we can get,
also
want high impeadance to prevent loading the resonant circuit.
There are those that receive a strong signal and use that energy to power
an amplifier. The amp is then used to amplify the audio from a weaker
station.
MikeK

I wonder what the highest Z might be. I think 600 ohm nowdays. I don't
know if it would drive a transformer. ??

Yes, a transformer is often put at the detector output and this drives the
headphones.
I see the datasheet for the KBT-33-RB-2CN says 2.8 kohms at 1 khz. These are
often put
two in series (one for each ear) for 5.8 kohms.
MikeK