Condenser sound pickup

[glavni]

Hi all,

I've been researching various types of (sound) pickups for acoustic guitars. The most commonly sound is picked up by piezo transducer (which obviously reacts to sound vibrations) located under the saddle of guitar and further signal is processed by onboard preamp...

I found this one very interesting, but I didn't get how it really works (to be more precise, how it actually pick up the sound)?!

http://mi-si.com/wp-content/uploads/products/motif_manual.pdf

Vendor states that it is "Condenser pickup", and looking at the element which goes under guitar saddle, seems like it's PCB with array of SMD ceramic caps (correct me if I'm wrong).

Does this mean that those caps are actually reacting to sound vibrations picked up from instrument?

I'm trying to compare this with condenser microphones, but their construction include diaphragm made of light and flexible material which vibrates according to sound waves. As diaphragm is actually one of capacitor plates, it's movement changes capacitance... But how those ceramic caps would achieve this?

Regards

[Richard Crowley]

It looks VERY much like a piezoelectric transducer.  I can't imagine how any "condenser" transducer could be created in that form factor or withstand that kind of static load pressure.

Capacitive audio transducers (mostly microphones) typically have air-gap "dielectric" and are quite fragile (to be sensitive to air vibrations).

Piezoelectric audio transducers are also commonly called "ceramic" (in lower-end phonograph pickup cartridges and cheap microphones).

[glavni]

Hmm, interesting...

You claim that those SMD components are actually piezo transducers. I'm disappointed with manufacturer at this point

[tszaboo]

The "Motif Acoustic Guitar Condenser Pickup" looks like just a PCB with 6*7 capacitor on it.
Can someone explain to me how does this work?

[Zero999]

I don't know how this works. My guess is it uses ceramic capacitors, with a piezoelectric dielectric, to pick up the vibrations, hence the name "condenser pick up in" the marketing material.

I can't see any problems with this. Integrating the amplifier into the pick-up would make sense to minimise noise and loading with the cable capacitance.

[Circlotron]

I've been researching various types of (sound) pickups for acoustic guitars.

Have you tried using an air pressure sensor? Not sure what the frequency response would be like but it would certainly handle extremely high sound levels.
https://www.google.com.au/search?q=mpx4100AP&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiwuIPCubvXAhWMpZQKHe1nBJAQ_AUICygC&biw=1371&bih=975

[glavni]

Have you tried using an air pressure sensor? Not sure what the frequency response would be like but it would certainly handle extremely high sound levels.
https://www.google.com.au/search?q=mpx4100AP&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiwuIPCubvXAhWMpZQKHe1nBJAQ_AUICygC&biw=1371&bih=975

No, you think it would be possible?

[Circlotron]

Sound is variations in air pressure so of course it will work.
Whether it has enough sensitivity or suitable frequency response you will have to experiment to see if it works well enough for your particular application.

[Richard Crowley]

The gadget in question does not pick up sound vibrations in the air.
It picks up mechanical vibrations under the bridge.
It is a vibration sensor, not a sound (or air-pressure) sensor.

Perhaps they have found some particular brand/model/value of ceramic SMD capacitor that is microphonic (sensitive to mechanical vibration).
Being microphonic is typically NOT a desirable property in any electronic component except a sound or vibration sensor.
But if they have discovered a particularly microphonic SMD ceramic capacitor, that accident doesn't seem like a very reliable thing to base a product on.
The manufacturer could come along with an "improved" version of that component that is less (or non-) microphonic and they would be out of business.

Or maybe there is actually a vibration/pressure transducer in the form-factor of an SMD capacitor?
In any case, a rather clever design, IMHO.

[Richard Crowley]

Have you tried using an air pressure sensor? Not sure what the frequency response would be like but it would certainly handle extremely high sound levels.

Yes, it would likely be able to handle sound pressure so high that would damage our ears.
But the sensitivity is likely much lower than any kind of transducer designed to be a microphone.
And the frequency response is very likely not only limited but pretty uneven (since that isn't important as a pressure transducer).

[glavni]

Perhaps they have found some particular brand/model/value of ceramic SMD capacitor that is microphonic (sensitive to mechanical vibration).
Being microphonic is typically NOT a desirable property in any electronic component except a sound or vibration sensor.

This sounds like interesting DIY project - test various SMD caps microphonic properties

[Circlotron]

Maybe some kind of accelerometer might work?

[floobydust]

This circuit is really good for playing with capacitor microphonics:
https://www.eevblog.com/forum/projects/gravity-wave-detector-radio-electronics-april-1986/msg1103545/#msg1103545

[glavni]

Maybe some kind of accelerometer might work?

Yes, accelerometers definitely works but with few drawbacks: noise floor of the sensor is audible, high frequency response of the sensor should be higher etc.

I've read an interesting article on this topic:

http://www.analog.com/en/analog-dialogue/articles/mems-accelerometers-as-acoustic-pickups.html

[Buriedcode]

Looks to me, as others have pointed out, that it just uses the piezoelectric effect of ceramic caps.  Note how there are 6 groups, one for each string.

The 'condenser' part is not only because that is the old-school name for a capacitor, but also (because of that) capacitor mics are referred to as condenser mics, its just what the audio industry would call it.  It is probably a lot cheaper to manufacture than a standard piezo strip, its just the cost of the PCB and populating.  Using supercaps as the power source is interesting "charges in 60 seconds" and claims lasts 16 hours.  I'm assuming that is regardless of whether one is using it or not (self discharge? I'm assuming its always 'on').

As for how it sounds, I would have thought, based purely on its placement that it'll sound just like a standard under-saddle pickup, brittle and full of treble.  Some like that sound, I'm not a big fan, but its pretty much the only option for live amplification.
As a side note... I've had some success with wiring an under-saddle pickup in parallel with a soundboard pickup (before the preamp). It seems to have the benefits of both, and reduces the downsides of both. (the 'quack' is gone, and the soundboard pickup isn't as boomy/bassy).