Piezoelectric Mic Evaluation

[John M]

First, I hope these are piezoelectric microphones (photos below). If not, someone please reply as to what kind they are. There has been much discussion about micing an accordion--types of mics, placement of mics, external, internal, etc. By no means am I an expert on this and piezo microphones do not seem to be desired by many folks. However, I thought I would share my experience with the original internal piezo microphones that are in my Excelsior 960 accordion. I do not have any experience with other condenser, dynamic microphones, or other mics for comparison. However, I am very pleased with the sound quality of these piezo microphones (crisp, clear, no distortion); especially when used with the Bose L1 Compact and the TS4 Tonematch with built in selection for accordion preset (thanks to Paul). The sound was O.K. with the Excelsior output going directly to the line level input on the Bose L1, but when going first to the TS4 and then to the L1, the difference in sound quality was incredible. The sound was much richer, less tinny and had a real presence to it. I also liked the touch of reverb I added from the TS4.

This is a description of the mic configuration of my Excelsior. It would be simple to install on anyones accordion. Piezos are not expensive, do not require external power, do not take up much space and all the mics are installed on the treble half of the accordion, Three mics are installed under the GRILL for treble (good placement for all 41 keys) and one mic is mounted on the REED BLOCKS for bass response. I like this installation of the bass mic since it is not installed on the left, bass side, of the accordion. This would involve wires passing through the bellows and that would require tape or secured in some other fashion. After primary gain adjustments with the Bose L1 and TS4, there are two 500K potentiometers for fine tuning/trimming of the bass and treble. Once adjusted, I leave the Bose L1 and TS4 gain settings alone as there is plenty of treble/bass gain adjust with the 500K pots. Any amount of treble/bass blend is available right on the accordion.

These are pics of my 960 and a schematic of the electrical configuration if you would want to build it.

 

[jozz]

looks good

do you have a sound sample of this kit?

 

[John M]

No I don't.  I have never done a sound clip.  I don't think the recording would capture the quality of the sound.  I have listened to many videos of the one mic installation on the reed block.  I thought the accordion sounded "bassy".  With my set up, I like having the two potentiometers right on the accordion for treble and bass adjustment.  I adjust the bass first, to a level where I can start to hear the treble side.  Then I bring in the treble pot to a point where the treble side of the accordion is bright and clear and blends well with the bass side.

John M

 

[kimric]

I have restored a bunch of these at my shop. 

 Here are a couple of tips for getting a decent performance out of them.

 Get a EQ pedal ,Danelectro sells a decent 7 channel model that is about $50. This will allow you to bring down any hot zones in the response and give you a bit of feedback control. 
 
Avoid long cables, the cable will behave like a cap and do odd things to your tone.

Do not use a solid state guitar amp, it will make the mics sound really harsh. Get a bass or keyboard amp. Best option is something like a VHT tube amp and replace the AX7 tube for a AT7 this will drop the volume a little but really improve the tone. Most amps have a line out so you can use the house or the bands amplification for your main volume.

You may want to add a 1k resistor to the + side of each mic to prevent what sound like me in some cases like a odd tone at the and of a loud note being played (might be a weak feedback loop between mics) and a 10 -20 k resistor at the jack on the final output. 
It does not seem to really affect the output in any meaningful way as these things are pretty hot to begin with.

 

[John M]

I have restored a bunch of these at my shop. 

 Here are a couple of tips for getting a decent performance out of them.

 Get a EQ pedal ,Danelectro sells a decent 7 channel model that is about $50. This will allow you to bring down any hot zones in the response and give you a bit of feedback control. 
 
Avoid long cables, the cable will behave like a cap and do odd things to your tone.

Do not use a solid state guitar amp, it will make the mics sound really harsh. Get a bass or keyboard amp. Best option is something like a VHT tube amp and replace the AX7 tube for a AT7 this will drop the volume a little but really improve the tone. Most amps have a line out so you can use the house or the bands amplification for your main volume.

You may want to add a 1k resistor to the + side of each mic to prevent what sound like me in some cases like a odd tone at the and of a loud note being played (might be a weak feedback loop between mics) and a 10 -20 k resistor at the jack on the final output. 
It does not seem to really affect the output in any meaningful way as these things are pretty hot to begin with.

Since you have experience with these, what is a good model "Piezo" mic that you use for replacement?  This will help if I need a replacement.  I don't have much experience with these.

John M.

 

[kimric]

I have restored a bunch of these at my shop. 

 Here are a couple of tips for getting a decent performance out of them.

 Get a EQ pedal ,Danelectro sells a decent 7 channel model that is about $50. This will allow you to bring down any hot zones in the response and give you a bit of feedback control. 
 
Avoid long cables, the cable will behave like a cap and do odd things to your tone.

Do not use a solid state guitar amp, it will make the mics sound really harsh. Get a bass or keyboard amp. Best option is something like a VHT tube amp and replace the AX7 tube for a AT7 this will drop the volume a little but really improve the tone. Most amps have a line out so you can use the house or the bands amplification for your main volume.

You may want to add a 1k resistor to the + side of each mic to prevent what sound like me in some cases like a odd tone at the and of a loud note being played (might be a weak feedback loop between mics) and a 10 -20 k resistor at the jack on the final output. 
It does not seem to really affect the output in any meaningful way as these things are pretty hot to begin with.

Since you have experience with these, what is a good model "Piezo" mic that you use for replacement?  This will help if I need a replacement.  I don't have much experience with these.

John M.

There is not a lot still in production, I have enough old ones that I have spares for failed ones. It is important to test the output of the ones you have to see if they all have about the same output level and swap out low or hot ones to get a matched set for each side. This is more important on the right than the left. 
 Many have no names on them so you can't figure out who makes them. There is one that is good and you will find them in the Sano mic systems and they were made by Brush. They are thicker and have a grill that is made of fused sinistered brass. Sometimes even these are not marked.

 

[John M]

I have restored a bunch of these at my shop. 

 Here are a couple of tips for getting a decent performance out of them.

 Get a EQ pedal ,Danelectro sells a decent 7 channel model that is about $50. This will allow you to bring down any hot zones in the response and give you a bit of feedback control. 
 
Avoid long cables, the cable will behave like a cap and do odd things to your tone.

Do not use a solid state guitar amp, it will make the mics sound really harsh. Get a bass or keyboard amp. Best option is something like a VHT tube amp and replace the AX7 tube for a AT7 this will drop the volume a little but really improve the tone. Most amps have a line out so you can use the house or the bands amplification for your main volume.

You may want to add a 1k resistor to the + side of each mic to prevent what sound like me in some cases like a odd tone at the and of a loud note being played (might be a weak feedback loop between mics) and a 10 -20 k resistor at the jack on the final output. 
It does not seem to really affect the output in any meaningful way as these things are pretty hot to begin with.

Since you have experience with these, what is a good model "Piezo" mic that you use for replacement?  This will help if I need a replacement.  I don't have much experience with these.

John M.

There is not a lot still in production, I have enough old ones that I have spares for failed ones. It is important to test the output of the ones you have to see if they all have about the same output level and swap out low or hot ones to get a matched set for each side. This is more important on the right than the left. 
 Many have no names on them so you can't figure out who makes them. There is one that is good and you will find them in the Sano mic systems and they were made by Brush. They are thicker and have a grill that is made of fused sinistered brass. Sometimes even these are not marked.

Thanks for the reply.  I will keep any eye out for them.  Maybe something will show up on ebay or someone will be selling an accordion for parts and mics might be in them.

 

[Ventura]

hello John,
fyi PiezoElectric mics and guitar bridge Piezo pickups do not have a voice coil or magnet, and
require a specialized powered circuit to operate

your Mics are simple Dynamic Mics, similar to any standard hand held
Dynamic Mic, simply made thinner for specialized purposes

the Dynamic Element used in the famous Shure Green Bullet Mic
(for Harmonica players) is still available from the Shure parts dept.
and can be used as a replacement for the large inside the Bellows Mic,

I prefer my Bass Mics mounted inside the left hand action chamber, and
have installed the Shure element (and others) in that configuration
with very good results

More recent Pro Excelsiors (my 960 included) use powered Electret Mics,
they selected a Panasonic model and used them for years..
modern Mic Assemblies for the Accordion have moved to
electret Mics... you do have to replace a battery every so often..
the capsules need a bias voltage to work

the best modern Mic retrofit kits tend to use Sennheiser capsules

thats it in a nutshell

ciao

Ventura

 

[JIM D.]

These mic's are crystal element type. Crystal mic's were used in accordion amplification up to the 90's. The were used for mono & stereo pickups
in all the higher brands of accordions. No longer produced but can be found surplus & used on ebay. I've been saving these (in all sizes ) for 40 years now and use them for repair & installation. Crystal mic's have been the pickup of choice for accordionist's & harmonica performers as they pick
up the sound of vibrating metal reeds better than dynamic's. Shure & Astatic produced crystal models for years as low as $10..00 each. If you find
one today expect to pay from $50.00 to $100.00 USD. The mic's in the photos some how are labeled Piezo's They are Crystal elements NOT PIEZO"S.
Neither are they Dynamic type.
Piezo mic's pick up the sound from the vibrating body of a musical instrument. Crystal mic's pick up the vibrating reed tongues & the vibrating body. You will find these older stereo installations that have 3 or 4 quarter shaped mic's under the treble keyboard & 1 or 2 silver dollar shaped mic's in the bass machine. In later stereo installations the bass mic (usually one) was mounted on the treble reed blocks facing the bass.
Mono pickups have in most cases a single crystal mic' located in the treble section facing the bass side. In 90% of the installations potentiometers were used for volume & tone. The only drawback to a Crystal mic' installation was a problem with feedback. Not a problem today as most newer amps & sound systems have anti feedback.

These older Crystal bass mic's (BA-19) are still the preferred handheld mic' by Harmonica players.

 

[JIM D.]

Jazz;
If you want a sound sample go to youtube and listen to the late Art Van Damme's recordings. Art always used Crystal mic' equipped Excelsior's in his performances.

 

[Ventura]

first they had carbon mics... very limited frequency response
next came crystal... literally a Rochelle Salt chunk with wires attached
inside the capsule.. these has aweful and uncontrollable feedback issues
and were the cheapest elements for experimenters to buy (dime a dozen)
look inside a few... the ones with magnets and a structure similar
to a tiny speaker in looks are Dynamic.. it is a magnet and wound coil
combination.. Decent Bass and Midrange reasonably resistant to feedback

you can also tell them apart with an Ohmmeter

Electret mics have clean 20-20000- htz response and can be built highly
directional for feedback control

Astatic's bullet shaped Mics did have Crystal elements... most
have not survived as Moisture eventually makes the salt crystal dissapear
(commonly used during WW2) the capsule itself was Pot metal, with a low
profile pyramid shaped front with perforations (quite unique)

Shure's Green Bullet has ALWAYS been a dynamic mic element
the specifications have never changed and they are still made

Hohner also produced a similar shaped harmonica mic. i never
has a chance to butcher a Hohner Mic so i can't say what they used

 

[John M]

Thanks for your input guys.
--Jim, I took the photos of my Excelsior. I thought those were Piezo mics and therefore named the files that way. I didn't realize there was a difference between Crystal mics and Piezo mics. I thought a Piezo was a crystal mic.
Do these crystal mics have a short life? Do they deteriorate with time and have reduced output?

John M.

 

[JIM D.]

I have Crystal mic's taken from accordions up to 70 years old. They work just fine. The way to ruin a Crystal mic' is to drop it or give it a
hard blow that then breaks the Crystal element.

 

[Ventura]

Salt Crystals can certainly be fractured, and obviously Salt
can be liquefied with Water... Humidity is attracted to Salt
and over time can cause a rochelle crystal to appear to evaporate,
then when you open the capsule there is nothing but the two inside
leads attached to nothing and a small amount of white stuff
coating the metal on one end

Quarts crystals are far more rugged and also used in Electronics.. however
they work differently and so were never used for audio applications
(you place Quarts under pressure and it gives off a very very steady
frequency current which you can then use in timing applications
like Watches and frequency applications like a CB radio

Rochelle crystals produce a current ONLY when they are excited,
which the sound waves from your voice or reeds input their
energy which is converted into an electrical signal by the crystal

Old Phonograph players that had those flip back and forth needles
(one for 78, one side for 33.1/3 or 45) were fitted on crystal cartridges
and worked in a similar fashion to the Mics. You may also recall that soon
enough in the 1960 most all Phonograph manufacturers abandoned Crystal
in favor of the Moving Coil (ie:copper coil and magnet structure) and the
slide in or on phono needles.. you may also recall the vast improvement in sound.

Crystal Mics were pretty much abandoned by the industry in the 1960's
as well.. bear in mind all the energy in an audio crystal device is produced
as a by product of the vibrations the device captures and processes, and the
structure of a Crystal is much more efficient in higher frequencies, while
low frequencies barely get picked-up around 100 Htz

the Moving Coil design has energy stored (basically) in the magnet
around which the voice coil is delicately suspended and as a result
moves freely and reacts to the slightest vibration, producing a useable
signal with little waste of energy

again, one can easily sort crystal from magnetic coil with an ohmmeter...
the impedence across the leads is about 1 MegOhm on crystal Mics elements
it is between 500 to 750 ohms normally on Dynamic elements

 

[John M]

Once again--Thanks fellas. There is a lot of good information in this thread I started. Interesting--I started this thread on Jan. 20th of this year and received replies at that time. However, this thread was resurrected this past week by Ventura with good input from Jim D. I am now "straightened" out on my thinking on crystal mics and also learned about dynamic mics. This forum is great!

John M.

 

[boxplayer4000]

This is an interesting thread. An expert, in his book of microphone use that I read, said a microphone should be thought of as an extra ear and placed accordingly. It sounds logical and simple and the writer was not in favour of microphones being actually attached to the instrument at all as his logic said that you do not press your ear up against something to hear it better.
Another expert (there's lots of them about) I know (well established in the music scene in high volume situations) doesn't use mics at all simply because of feedback and that's why he uses a totally digital accordion.
Perhaps the crystal microphones discussed earlier have had their day, although I say thanks to JohnM at the head of the thread for the microphone circuit diagram.
I understand that there are similarities between speakers and microphones (one produces sound waves from and electric signal and the other produces an electric signal from sound waves). Some modern earphones are extremely good and at reproducing sound and are very modestly priced. My question is, could earphone elements be turned into microphones?

 

[jozz]

yes they can, in fact you can more or less plug your 3.5mm headphones in your PC mic input and it will "work"

pickup and results will be poor, though

 

[boxplayer4000]

They would need some resistors or capacitors added to match impedances (like the circuit diagram at the head of this thread).