More piezo elements under the top = more natural transduction?

[thecelloronin]

Hello all,

I'm considering installing some piezo transducers under the top of my mandocello, like the JJB 220 or K&K Twin. However, I've wondered what could be done with 4-element models–the ones more frequently seen on flat-top acoustic guitars.

I pitched the question to the owner of JJB, and he said while the more elements = more natural sound relationship generally holds true, it may not be so on instruments like mandolins and mandocelli which lack a bridge plate. He expressed concern that the two pairs of elements would be out of balance, as one pair would hit the sweet spot under the bridge feet and the others would be somewhere necessarily slightly less resonant.

What would happen if you put two elements on the "best" spot under the bridge feet, and two more under the "second best" spot (wherever that may be), then soldered one pair to the tip of a stereo jack and the other to the ring? My thinking is that you could then adjust the signals in a device like the Tonebone PZ Pre to get even levels and a wider dynamic range of resonance across the top.

What is the feasibility of this, and has anyone ever experimented with this approach or one like it? Where might you guess the "second best" spot would be on the top?

[almeriastrings]

Hmmm... I'm not so sure. Personally, I have found two transducers more than adequate on mando family instruments, and indeed, on most acoustic guitars. As you increase the number of transducers you also increase the potential for timing and phase incoherence between the units (the transducers do not receive exactly the same signal at exactly the same time - the difference is miniscule, but detectable on precision measuring instruments). There is also the issue of increasing the voltage peaks as the total transducer surface area increases, and this can end up sounding worse, rather than better, as many preamps start to have problems with the large peak-to-peak outputs that result.

[Tavy]

I'm not so sure about that either: consider that as soon as you have 2 or more sound "receiving devices" at differing distances from the source (mics or pickups makes no difference), you will necessarily get some phasing at one frequency or another. For 3 or 4 pickups in a row along a bridge plate the pickups are so close together that it's unlikely to make any difference at any frequency you would notice. The same would probably be true for 3 (or 4) in a row under a single foot bridge. Scatter the pickups further around the top plate and I would expect significant phasing though. Plus as Almeria says, the output from 2 pickups is so strong anyway that you don't really need any more.... so for whatever reason "2" seems to be the optimal number.

[Astro]

Great question. Of course as usual, I have no idea.

But when I got my octave mandolin I asked for a K&K type pick-up to be installed. Instead the luthier suggested I use his preferred pick up because it has "a sensor under each string course to give a fuller sound". I went with his recommendation and indeed it sounds great amplifies. I have the k&K (JBB) type on my mandos and I know its comparing apples to oranges as the octave is much bigger but the octave's pick up is much louder than the mandolin's. When I switch from mando to octave I have to turn the preamp gain knob down.

I have no idea if that relates to this thread or not.

Do piezo's come in different sizes? Anyone tried using lots of nano piezos? Wouldnt it be fun to do that with a "piezo mixing board" to experiment with the blend from all areas of the sound board and use summation and blending to get different tones?

[Tom Wright]

The "sensor under each string course" is an under-saddle type, my favorite.

As to multiple sources and phasing, the phase relationships will be no issue as any array will be too close for differences to exist. K&K has a triple, I believe, as well as double-piezo and single versions.

The first difference would be somewhat more signal, I'd think. The main difference is that a piezo at a given location will hear some resonances but not others. Acoustically you hear the whole mix, so multiple sensors should be more even and accurate. The result is not guaranteed, I'd also think, and a particular location might actually be better than the acoustic sound, at least in the low-mid resonances.

I remember an excellent electric violin from Canada in the 90s (I think) called RAAD. It didn't survive commercially ($6,000 US), but the sound was sweet and acoustic. It used a polymer piezo patch. This type is flexible, and can conform to curved surfaces. I wonder why it didn't catch on?

[John Flynn]

I think less is more. The single element piezo that came with my Rigel is great, as is the twin element K&K in my Mendel octave. I have not liked undersaddle or in-saddle pickups. I had a Fishman M200 on a mandolin I used to have and I currently have a B-Band on my Martin guitar. I just don't care for the sound of them as much. Maybe it's personal taste.

[Astro]

I think it might depend on the under saddle pick-up. I have played some on guitars with them that sound terrible. On the other hand my Breedlove concert solo has them (LR Baggs Element "active") and sounds great plugged in. Not piezo-ey at all. And my octave with under saddle pick ups (no idea what it is but its "passive") sounds very good too. Maybe they have figured something out and gotten better lately ?

[pops1]

For my sound take, the under saddle in guitar or individual pickups in the saddle of a mandolin sound all the same. You can put them in any instrument and have the same sound. Pickups on the bridge plate or under the top of a mandolin sound more like the instrument. There is a distinct sound that comes from under the saddle pickups and a much more acoustic sound from under the top or on the bridge plate of instruments. Under the saddle will not feedback as easily so with louder playing this may be an advantage, but to me sacrificing sound quality for some volume.

[Tom Wright]

For my sound take, the under saddle in guitar or individual pickups in the saddle of a mandolin sound all the same. You can put them in any instrument and have the same sound. Pickups on the bridge plate or under the top of a mandolin sound more like the instrument. There is a distinct sound that comes from under the saddle pickups and a much more acoustic sound from under the top or on the bridge plate of instruments. Under the saddle will not feedback as easily so with louder playing this may be an advantage, but to me sacrificing sound quality for some volume.

I agree mainly, in the way I hear undersaddle pickups used in performance. Especially the guitar players (I hear on recorded shows) seem to apply no appropriate EQ, making them sound toylike and synthetic. More recent installations sound darn good---the Taylors with the Fishman preamp can sound really nice. I think the Baggs undersaddle in Drew Emmitt's Nugget sounds good, ditto Don Stiernberg's.

I have a Headway (HE4) in a Buchanan, and with most or all treble rolled off, a mild mid cut is sufficient. It definitely hears the wood as tapping on the top is quite loud. It also feeds back, another indication it is "acoustic". Covering the soundhole controls that well, though.

I played a gig with a pretty loud country band (using my magnetic-pickup mando), and the guitar player switched to mandolin for a tune. He plugged his inexpensive mandolin with Fishman bridge pickup straight into his Deluxe Reverb, and it sounded fine (if somewhat harsh), and plenty loud.

[Mandobart]

My take on under saddle transducers (UST) vs soundboard mounted transducers (SBT):
Recall the nature of the piezoelectric effect. A piezoelectric material produces a small millivolt signal when subjected to strain (vibrations in the case of an acoustic stringed instrument). A soundboard mounted transducer is only subject to any strain when the instrument is played. An undersaddle transducer is always under strain due to the load imposed by the string tension exerting downward force on the saddle. So UST's are already biased toward saturation and therefore easy to overdrive into distortion. This makes quack, harshness, etc. more likely on UST's. Also, the slot and saddle preparation are paramount to getting good plugged in sound. SBT's are more forgiving. There may be an optimal sweet spot that varies with each instrument, but you don't have to do anything special to mount an SBT.

[mandroid]

Pickups 'hear ' what they're attached to, a microphone out in front responds to sound waves in the air..
like you would hear, naturally..


test the pickup locations placing them on top, to find the 'sweet spots'

then have them installed under those spots inside.

wont be 100% 'natural', but as good as your chosen pickup can do..

[Jim]

I have installed double piezo p/u with one under each bridge foot and had good results and installed single p/u more or less between the bridge feet with roughly the same results. Quite usable in loud venues but not as good as a microphone. I use your basic 12 mm ceramic/ brass discs.

[Br1ck]

I have to think that a company like K&K has tried every combination of size and number of piezos in every instrument they hope to equip. I'd go with what they sell for any given instrument.