piezo transducers

[dave251]

I'm trying to figure out where the anomalies lie with piezo electric pickups. The manufacturers claim "flat frequency response" and "linear response"(I'm assuming this is referring to transient response), but I've never seen any hard numbers, and I've never seen any references to phase shift.

 

We have these specs when it comes to mics, why not pickups?

[Anderton]

That's a good question. I've noticed that piezos tend to sound brighter, and I think that most piezo preamps have some EQ in there somewhere...anyone have a definitive answer?

[dave251]

I wanted to get this back at the top of the posting list...I'd like to know what experiences you recording and live sound engineers have had with these...good, bad...how you set up for them, your opinion of how they sound, and what corrective measures you have come up with for their shortcomings......Thanks, Dave

[derm75yahoo.com]

I have used piezo pickups for both recording and live sound with mixed results on acoustic guitar, cello, violin, and upright bass. For recording, usually the results are not very pleasing. I agree with Craig, they are usually pretty bright/tinny sounding, and also tend to pickup thumpy instrument handling sounds. I have had the best results with bass, probabally because it lacks high end to begin with. Interestingly, I had good results with the semi-hollow acoustic-electric that Gibson makes, I think it is similar to the guitar Dave Matthews plays in concert.

For live sound the results are a little better, again, bass works well, acoustic guitar sounds O.K., cello not so good, violin so-so. Using a mic in addition to a piezo works well live, the piezo helps the instrument cut through, while the mic provides "air" and "warmth". Hope this helps a little.

 

Jeremy Smith

Madison, WI

[neiltrackingstation.com]

I've found that the tinny sound, including varying amounts of harmonic distortion, comes from loading down the element. The lower the impedence, the worse the sound. When I designed a preamp for these pickups, I used a 10 megohm input impedence with volume and EQ after the first stage so it wouldn't affect the pickup itself. They can sound rather nice under these conditions. With a normal amp or mixer input, they sound like shit to me. Neil

[dave251]

Okay, I understand how they sound...I've been working with them for years(or to put it another way, trying to work around them)...I don't hear over response in the upper registers when the piezo is properly buffered...what I do hear is phase shift away from the lower frequencies during the attack transient(the high end comes through first)...

 

I was just wondering if anyone had any hard numbers on the phase anomaly. The same goes for transient response...while overall, they may be responding in a linear fashion as far as voltage output, I hear a compression of the mid-band occurring, with most of the output coming again, in the upper registers...this particular anomaly seems to be more prevalent with the "pressure" transducers, that is, saddle transducers on acoustic guitars.

 

It's not that I'm against these things, quite the contrary, I use them in my guitar designs( www.electrocoustic.com ). I just want to understand the piezo effect better, and just maybe I can improve further upon the tone of my guitars if that happens...so any insight is helpful...thanks.....

 

[This message has been edited by dave@electrocoustic.com (edited 09-14-2000).]

[neiltrackingstation.com]

Dave, you have obviously done some good research and have described 'that characteristic sound' well. I think that the phase shift aggravated or varied, by the pressure of the strings on the saddles. When the string is picked, the pressure increases and slowly decreases. Do you hear the same phase shift on a contact piezo (like the old Barcus-Berry's). It's been a while for me but I seem to remember the compression you talked about, but not the phase shift. Neil

[neiltrackingstation.com]

Dave, my last sentence was referring to contact type, not bridge (pressure) piezos. Neil