Some questions about piezos

[DarkHorseJ27]

I have a few assorted questions about peizos i hope you guys won't mind answering.

 

1. I find peizos to sound thin and tinny compared to soundhole pickups. Is that due to the placements of each pickup?

 

2. I find that peizos typically have more of a "three dimensional" sound compared to soundhole pickups. Is that because they have a wider frequency range.

 

3. The peizo is mounted between the saddle and the top, which is an important connection. Do they perceptibly change the unplugged tone any?

[liko]

I have a few assorted questions about peizos i hope you guys won't mind answering. 1. I find peizos to sound thin and tinny compared to soundhole pickups. Is that due to the placements of each pickup? 2. I find that peizos typically have more of a "three dimensional" sound compared to soundhole pickups. Is that because they have a wider frequency range. 3. The peizo is mounted between the saddle and the top, which is an important connection. Do they perceptibly change the unplugged tone any?

 

 

1. Not really. It's less the location and more how each one works. A soundhole pickup is magnetic; its signal is generated almost solely by the string's disturbance of its magnetic field. With magnetic pickups, the amplitude of the vibration determines not only volume but tone. A piezo, on the other hand, picks up vibration of not only the string, but the entire instrument, because the pickup is mashed between the saddle, which transfers some vibration, and the body, which generates MUCH more. The problem is that much of the vibration in the top does not actually change the pressure between saddle and bridge which is what is converted to a signal.

 

2. The sound is more three-dimensional because the vibrations it picks up are not just from the string; again, the entire body contributes hugely to a piezo signal, not just the string.

 

3. Not really. Though the pickup is pressure-sensitive, it doesn't compress very much as you would expect a pressure-sensitive tool to be. The ratio of the amount the piezo pickup actually changes in thickness to the amount of travel the entire top has at the bridge is on the order of hundreds to 1 in favor of the entire top. In addition, the top is driven more by the change in tension in the strings, which are anchored into the bridge. That anchor point is a far more important piece, even though it's beyond the speaking length.

[seagullplayer77]

Personally, I think piezos sound better than soundhole pickups---at least the cheaper soundhole models. With the piezo, you get the vibration of the whole guitar, not just the vibration of the strings. I suppose it might pick up more high-end than a soundhole pickup would, but I think soundhole pups are kinda mid-heavy and muddy.

As small and thin (about 1/32") as the piezo is, I don't see it making any perceivable difference when the guitar is unplugged. Just my two cents...

[Clif Schlicher]

Well, there's piezos and then there's piezos. Not all of them are under saddle mounts. There are several that mount to the bridge plate or the top itself, such as the K & K Pure Western and the McIntyre Acoustic Feather. There are now some improved USTs as well, such as the Fishman Acoustic Matrix, which have reduced the piezo 'quack' many complain about.

The piezo transducer is a crystal which when bent, even ever so slightly, produces a minute current. As I understand it, when the material is compressed, as under the saddle of a guitar, it can't flex as freely wants and this tends to emphasize some frequencies while diminishing others, leading to the "quackiness" we have all heard about.

Piezos mounted to the bridge plate or the sound board can flex freely, allowing the transducer to produce the full frequency range of the guitar, not only of the sound board or bridge plate, but any reflected vibrations or overtones produced by the guitars construction and tone woods as well. This is also the reason why these transducers are more prone to feedback in noisy venues.

I believe there is a link in the annex to the Doug Young site, where you can hear various pickups in a variety of guitars, all compared against the same guitar into a professional grade mike.

Enjoy the search.

Clif

[Scodiddly]

Piezo pickups are usually heavily influenced by the load impedance they're connected to. Typically a lower impedance input meant for a magnetic input will make a piezo sound thin and "quacky". "Acoustic" inputs and preamps such as a Baggs or Fishman DI will provide an input with a very high impedance, allowing the piezo to sound better.

[Terry Allan Hall]

I have a few assorted questions about peizos i hope you guys won't mind answering. 1. I find peizos to sound thin and tinny compared to soundhole pickups. Is that due to the placements of each pickup? No, if a piezo, whether in the form of a UST or as a SBT is properly installed (not all that often in a factory set-up, unfortunately), it's a very accurate way to amplify the instrument. 2. I find that peizos typically have more of a "three dimensional" sound compared to soundhole pickups. Is that because they have a wider frequency range. Absolutely! 3. The peizo is mounted between the saddle and the top, which is an important connection. Do they perceptibly change the unplugged tone any? Not at all.

 

 

In the 7/07 issue of Acoustic Guitar, there is a Roundtable on this very subject that I think you'll find interesting reading:

 

http://www.acousticguitar.com/article/default.aspx?articleid=7636