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A (better?) solution for contact mics

 

I bought, at Aliexpress, such an ultrasonic transducer:



Soldered it to a piece of cable - single shielded wire (see pictures) with 6,3 mm plug I had laying around and it is quiet.
In 2 wire cable with shielding mount and an XLR plug there is a faint buzz, eliminated totally when shielding is connected to the outer case (obviously).
No buzz, no hum, just silence. I ran few tests - it seems to have good sensitivity. Easy to handle, to press against a surface. Looks very promising.
Haven't tested it as a hydrophone yet, for the lack of handy stream near by.
 

Link doesn't work. Was it this sensor??



Am Mo., 6. Mai 2024 um 08:12?Uhr schrieb pmfalcman via <pmfalcman=[email protected]>:

I bought, at Aliexpress, such an ultrasonic transducer:



Soldered it to a piece of cable - single shielded wire (see pictures) with 6,3 mm plug I had laying around and it is quiet.
In 2 wire cable with shielding mount and an XLR plug there is a faint buzz, eliminated totally when shielding is connected to the outer case (obviously).
No buzz, no hum, just silence. I ran few tests - it seems to have good sensitivity. Easy to handle, to press against a surface. Looks very promising.
Haven't tested it as a hydrophone yet, for the lack of handy stream near by.

 

Link works for me. Specifications don’t seem to reveal very much. Very curious to hear some sample recordings!
 

Interesting. The listing doesn't say what it's made of or how it works; is it just a piezoelectric element in a housing? Then the "40 kHz" number probably means its resonance is at 40 kHz, so it produces the maximum output power when driven at that frequency.

If it's a piezo element, it'll benefit from a high-impedance buffer like any other contact mic. But it's a nice form factor.
 

Underwood - seems like it. Model designations are somehow similar:
there's 1640?and TR, as well as specs. But this is China... May mean nothing :)
On the other hand, at this price it doesn't hurt to try. I ordered mine totally blind: "let's see if it works".
 

It only says "transceiver" somewhere. It's a piezo after all.
Yes, description suggests that 40 kHz is the resonance frequency.

Oil drum banging & tapping raw recordings. A plastic traffic cone (end of 383 file) and last file - wood planks.
Just what I had at hand.

Straight from the recorder, no edits.
No impedance buffering either.
 

Added also a buffered recording of the same oil drum.
Sounds much better, fuller.
Simple makeshift buffer based on Don Tillman's design, I cobbled together couple years ago.
 

As per usual no shipping to the UK...


On Mon, May 6, 2024, 17:40 pmfalcman <pmfalcman@...> wrote:
Added also a buffered recording of the same oil drum.
Sounds much better, fuller.
Simple makeshift buffer based on Don Tillman's design, I cobbled together couple years ago.

 

I've got good results with Hosa MIT-129. Small passive transformer impendance?converter that works good with piezos.

I combine them with a thomann inline FETAmp, that blocks the P48 to the transformer.


Am Di., 7. Mai 2024 um 00:51?Uhr schrieb Adrian Hicks via <mail=[email protected]>:

As per usual no shipping to the UK...

On Mon, May 6, 2024, 17:40 pmfalcman <pmfalcman@...> wrote:
Added also a buffered recording of the same oil drum.
Sounds much better, fuller.
Simple makeshift buffer based on Don Tillman's design, I cobbled together couple years ago.

 

I will go Jules' piezo preamp route.

Out of curiosity I tried thomman's Millenium DI-e passive DI box as they're supposed to match impedances. But it doesn't seem to do much except effectively only lowering overall signal strenght.
 

On Tue, May 7, 2024 at 12:51 AM, Adrian Hicks wrote:
As per usual no shipping to the UK...
?

I checked registered mail rates to UK.
Since this could be sent as a letter (20 mm thickness max) the cost is relatively reasonable - ~ ?5.

I'll be ordering more soon, can as well cover your needs and then send them over to you.
Just say how many you want and prepare for long wait ? May take a month or longer. One never knows.
 

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Passive DI's are inadequate for piezo transducers; They want to see a very high load impedance, typically > 1Megohm. Passive DI's are about 50 kohms.

Le 07/05/2024 à 19:18, pmfalcman a écrit?:

I will go Jules' piezo preamp route.

Out of curiosity I tried thomman's Millenium DI-e passive DI box as they're supposed to match impedances. But it doesn't seem to do much except effectively only lowering overall signal strenght.

 

"impedance matching" has nothing to do with audio signalling where only voltage needs to be preserved, and power can be ignored.
https://eepower.com/technical-articles/understanding-impedance-matching/#

If a high impedance source needs to be either transformed to a low impedance, to preserve the signal, it would to a lower voltage, or else current buffered to tolerate a low impedance load.
A source impedance can be as low as practically possible and the load as high as practically possible. Only voltage is considered.
Signal transformers with impedance numbers on them are designed for some dBu line levels,? have very high no-load impedance.
The impedance transformation, is the square of the turns ratio.? A 10:1 transformer has a 100 times impedance ratio, and 20dB loss.? Optimum loads may limit usable matching range.
Jensen Transformers has a bunch of circuits and parts available.
 

As I said - I used the DI box just out of curiosity. I had one laying around.
 





Am Mi., 8. Mai 2024 um 07:11?Uhr schrieb pmfalcman via <pmfalcman=[email protected]>:

As I said - I used the DI box just out of curiosity. I had one laying around.

 

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This article is interesting:

The facts are correct, but the analysis is flawed.
The lack of technicity of the author leads him to dubious conclusions.

Le 08/05/2024 à 08:38, underwood a écrit?:





Am Mi., 8. Mai 2024 um 07:11?Uhr schrieb pmfalcman via <pmfalcman=[email protected]>:
As I said - I used the DI box just out of curiosity. I had one laying around.

 

Impedance matching with non-linear transducers such as piezo elements does actually matter.? A piezo changes behavior if it has to source current.

-Scott

On 5/7/24 23:10, c d wrote:
"impedance matching" has nothing to do with audio signalling where only voltage needs to be preserved, and power can be ignored.


If a high impedance source needs to be either transformed to a low impedance, to preserve the signal, it would to a lower voltage, or else current buffered to tolerate a low impedance load.
A source impedance can be as low as practically possible and the load as high as practically possible. Only voltage is considered.
Signal transformers with impedance numbers on them are designed for some dBu line levels,? have very high no-load impedance.
The impedance transformation, is the square of the turns ratio.? A 10:1 transformer has a 100 times impedance ratio, and 20dB loss. Optimum loads may limit usable matching range.
Jensen Transformers has a bunch of circuits and parts available.
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry

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