Piezo Film Pickups: How many can be wired together?

by Bart on December 14, 2009

We sell a lot of piezo films, ready for our customers to wire them up as musical instrument pickups. In most applications, a single piezo film pickup is all that’s needed to capture an instrument’s sound. But there are also a lot of situations in which it’s useful to have two or three, and sometimes much larger numbers of piezo film pickups on a single instrument. (For example of an instrument calling for many, think of a xylophone-like instrument in which a pickup is needed on each bar.) The question arises: is it OK to have multiple piezos feeding into a single output? My response to this question, up until recently, has been based on book-learning and not on direct experience. So the other day I finally sat down and did a whole lot of piezo hook-ups in different configurations in order to see first-hand how many piezos you can wire together with good results.

In this posting I’ll first tell you what I learned in terms of numbers, then I’ll describe how I did the tests, and then I’ll provide additional how-to information for hooking up multiple piezos (including ideas for what to do if the number of piezos you need is too large for a single group) .  But first let me review the basic information that was already known before I did my series of tests. The ideal situation is to have a single piezo element operating independently, sending its signal through a cable to its own amplifier input.  It’s also possible to have two or more piezos wired together and going into the same input; however, the more piezos you have in the system, the weaker the signal from each piezo will be.  The question to be answered is, how many separate piezos can you wire together before the loss becomes a problem?

I experimented with both the very small piezo films we sell (piezo “tabs,” they’re sometimes called) and the big 6″ ones.  Here’s a rough summary of what I found.

 RESULTS

 1″ piezo tabs

With the tabs, I was happy to find that you can get away with more pickups in a group than I expected: the signal strength deteriorates as you add more piezos, but not as badly as I had feared. In the chart below, the numbers in the left column are the number of piezos wired together in a group; the comment on the right describes the resulting signal strength and quality.

1          Excellent

2-3       Almost no discernable loss

4-5      Very little loss

6-10    Increasingly noticeable loss, but still functional

10-20   Increasingly serious loss

 Recommendation for multiple piezo tabs: The fewer piezo tabs wired together in a group the better, but anything less than five will be OK in most applications. Depending on your requirements you may be able to work with as many as nine or ten. Use more in a group only if you can accept compromised signal strength and sound quality.

6″ piezo films

With the larger 6″ piezos, the signal strength deteriorated more rapidly as the numbers increased.

            1          Excellent

            2-3       Very little loss

            4-5       Increasingly noticeable loss, but still functional

            5-10     Increasingly serious loss


Recommendation for larger piezo films: The fewer piezos wired together the better, but two or three of the large piezos is probably OK, and you may be able to get away with up to five.  Use more in a group only if you can accept compromised signal strength and sound quality.

2.5″ piezo films

I didn’t test these in-between-sized films, but if you’re working with them you can assume the results will fall somewhere between the larger and smaller ones described above.

TEST SET-UP

Managing such large numbers of temporary hook-ups (up to 20 for the piezo tabs) was slightly chaotic in a fun sort of way. The test set-up was pretty informal. I did the hook-ups using lengths of hook-up wire with alligator clips at the ends. I’ve got a large supply of these convenient little connectors for just this sort of purpose.  I started by hooking up a single piezo film, running its output to an amplifier, and testing it simply by flicking the end, noting the signal strength and tone quality.  I then added a second piezo, and a third, and so forth, testing by flicking after each new one was added.  After I had hooked up and tested twenty of the small piezo tabs, I then went back and tested a single piezo once again, in order to directly compare the full multiple set-up with the single piezo. I did the same for a total of ten of the 6″ piezos.

Something worth noting about this set-up: the hook-up wire I used isn’t shielded.  This means that as I was adding more and more hook-ups, it was to be expected that increasing noise would appear in the system from stray electromagnetic frequencies in the air.  This did occur, especially when I switched on certain lights nearby, but it wasn’t as bad as I feared. In a real installation, of course, you’d use shielded wires.

HOW-TO INFORMATION FOR MULTIPLE-PIEZO INSTALLATIONS

 You can find full information for hooking up single piezo films here.  This is the sheet that comes with the piezo films when you buy them from us.  The basic idea is that you run two wires, called the hot wire and the ground wire, from two terminals on the piezo, through a cable and to the preamplifier. (The preamp is often incorporated into a regular amplifier input.) The shorter the length of cable from the piezo to the preamp, the better. 

In hooking up multiple piezos, you have a choice of whether to join them in series or in parallel. Because of the electrical nature of piezos, series connection yields poor results; parallel is the way to go.  In practice this means: connect the hot lead from each of the piezos in the group to a common wire for the hot side of the output, and connect the ground from each peizo to a common ground wire.

What if the number of piezos you need for an instrument is larger than the number that can work well wired together in a single group? Example: imagine you’re putting pickups on a home-made xylophone with 12 bars, but to prevent signal loss you want to keep the number of piezos grouped together to five or less? The answer is to wire the piezos in two or more smaller groups, and keep the groups electrically “buffered” from one another. In this case, for the twelve piezos needed you might create three groups of four, or perhaps two groups of six.  To buffer the groups from one another, they need to go to separate preamps before their signals are mixed.  If you’re an electrical whiz, you can build miniature op-amps into each circuit before mixing them.  If you’re not an electrical whiz, the easy solution is to send them to separate mixer inputs. This is quite feasible because nowadays there are very compact and affordable mixers on the market with as few as four inputs – you may even be able to affix a mini-mixer to the body of the instrument somehow.  This also has the advantage of giving you separate volume and tone controls for each of the groups. 

Addendum (March 26, 2010): This later post has information on another consideration in multiple piezo installations, phase cancellation.  

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A *New* New Grove Dictionary of Musical Instruments

by Bart on October 28, 2009

The three-volume encyclopedia known as the  New Grove Dictionary of Musical Instruments appeared in 1985, totaling just over 2,700 pages, weighing 12.8 pounds altogether.  That was right around the time I was starting this organization called Experimental Musical Instruments, and I felt it my duty to put up the $350 to purchase it — far and away the most I ever spent on a book, before or since.  I’ve never regretted that $350. 

The musical instruments dictionary took its place in the tradition of Grove’s music encyclopedias beginning with the Dictionary of Music and Musicians edited by Sir George Grove in 1878. (For the latest incarnations, see Oxford Music Online.)  Over the years the Grove’s dictionaries, including many offshoot publications on particular facets of music, have been seen as the foremost and most authoritative scholarly resources in their fields.  The 1985 musical instruments dictionary has been no exception in this respect:  it’s justly regarded as the final and exhaustive word in musical instrument scholarship. Even after a friend’s dog chewed part of the cover off of Volume I of my copy, it remained for me the first place to look for all things instrument-related.  It became less central to my life only more recently with the simplicity and currentness of web searches.  

Word has now come that for the first time in  25 years a new edition of  New Grove Dictionary of Musical Instruments is on the way.  The editor of the new version is the New York instruments scholar Laurence Libin.  “Reflecting advances in scholarship during the past quarter-century,” he recently wrote, “the second edition will encompass a greater range of subjects in more detail, thus serving a larger community of readers worldwide.” In the 1985 edition, most of the articles on conteporary instruments were written by Hugh Davies.  And a very large number of articles it was … I often marveled at what a huge amount of work his contribution represented.  Sadly, Hugh passed away in 2005. 

I’ve seen no date for publication of the new edition … perhaps not surprisingly, since such a work is likely to take a bit of time to prepare.  But it’s something to celebrate.



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Luigi Russolo, Luciano Chessa, and sixteen composers

by Bart on October 28, 2009

Guess what, I got to see and hear the Intonarumori! 

Actually, I saw recreations of sixteen of the Intonarumori as reconstructed, based on the best surviving evidence and descriptions, by the contempory composer Luciano Chessa, in performance in San Francisco a couple of weeks ago.  Some background: The Italian Futurist composer, painter and thinker Luigi Russolo ((1885 – 1947) put forth in 1913 a theory of music based on the idea that it was incumbant upon musicians of the time to leave behind the pastoral past and embrace the clangorous sound world of the machine age.  In keeping with this idea, he created and concertized with a series of noise-instruments which he called Intonarumori. The original instruments are no longer extant.  The current presentation included performance of a recently uncovered 1916 composition for the instruments, plus compositions by fourteen contemporary composers including the project’s director, Luciano Chessa. 

The instruments lined up on stage are a most intriguing sight – sixteen boxes with sound horns protruding in front, cranks and levers from on top and behind.  Some of the instruments produce recognizable pitch with a fair degree of pitch control and accuracy; others less so.  The sounds do indeed show a close affinity to modern industrial sounds – not so much the loud aggressive sounds Russolo’s writings might seem to suggest, but the quieter, richly textural hummings and scruffings of every day machines and appliances, as brought forward in various moods by the dozen-plus composers.

Under the name Metal + Machine + Manifesto, the show travels to New York for Performa  09 on November 11, and to Milan in December.



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How to build a driftwood xylophone

by Bart on October 3, 2009

Hey, people, I’ve recently joined with Joyce Kouffman (percussionist and everything-elsist) in a video demonstrating how to make a xylophone using pieces of driftwood we found at Drake’s Beach in Northern California. You can view it here or on YouTube.  The video was produced by David LaFontaine and Janine Warner of Artesian Media.  

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Aurelio, the SVARAM Workshop, Prof. Klaus Fessman, Singing Stones

by Bart on October 2, 2009

 I had an inspiring and most enjoyable visit recently with Aurelio, director of the Svaram musical instruments workshop. The workshop is located in the town of Auroville in India’s state of Tamil Nadu. Auroville is an “ideal township devoted to an experiment in human unity,” an international community devoted to lifelong learning and spiritual awareness, founded in 1968 with the blessings of UNESCO and the Indian government.  Aurelio, an Austrian by birth, arrived there 1985.  Having long experience in creative instrument making, he began some projects which led to the formation of an instrument-making workshop in the community. He trained young workers from the region who in time coalesced into the workshop’s core group of craftspeople. They now make instruments of many sorts both traditional and original, and new designs are always in the making. There’s an emphasis on keeping the instruments approachable and making the music accessible to all.

 

Through the early years, the workshop survived in part through a series of grants from the community and other sources. Over time, it has become increasingly self-sufficient. While the workshop has always been driven by a spirit of creativity, Aurelio recognizes that it’s time to think increasingly in enterprising terms and project collaborations. To that end, they are developing product lines for both local and international markets, and are happy to enter constructive dialogues and take commissions.

 

klangsteineA change of scene: some years ago the German pianist/composer Professor Klaus Fessmann of Mozarteum Salzburg, found himself moving beyond his classical training, seeking more organic musical forms. He was drawn to the idea of sounding stone. By cutting suitable types of stone to a particular comb-like form he found he could draw a clear tone from the stone with the friction of a moistened finger, creating an instrument he called Klangsteine, or Sound Stones. Visiting Auroville, he met Aurelio.  Fortuitously, a particular type of granite local to Auroville proved to produce the best tone that Professor Fessmann had yet found for the Singing Stones. With the workshop and skilled workforce in place there, as well as the ideal stone, it was agreed that Auroville was the place for manufacturing the instrument. Hannes Fessmann, son of Klaus, visits regularly there to oversee the process and conduct new experiments. And so it is that if you now go to the Svaram website,you’ll find the singing stones among the instruments under development displayed there. You can also see and hear them at the Klangsteine web site (text in German).

 

 

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EMG Select Pickups?

by Bart on October 2, 2009

 Hey, does anybody know where we can source EMG Select guitar pickups at wholesale prices for sale in the Experimental Musical Instruments catalog? It turns out that this information is strangely elusive (details below). If you have leads on this, please let us know.

 

In case you’re curious, here is background information on my question.

 

We sell a couple of different kinds of magnetic pickups, chosen because they’re types you can’t get anywhere else, and likely to be of particular use to people who like to design and build their own instruments. But it has occurred to me it could also be worthwhile to carry a basic, sturdy, affordable guitar pickup – one that could be equally useful for non-guitar applications. That description nicely fits the Select line of pickups sold under the EMG name. These were designed and originally produced in the early days of the EMG company. But when you contact EMG now, they don’t want to talk about those Select pickups. They’ve moved on to producing more elegant (and higher-priced) pickups, and they no longer manufacture the Select line. Yet the Select pickups are still available from various outlets, so it’s clear that someone is still making them. Apparently there is a licensing agreement that allows I-don’t-know-who to manufacture them and imprint them with the EMG name, even as EMG strives to distance itself from its earlier product. In the current packaging for the Select, it’s indicated that they’re made in Korea, but no further contact information is given. So far, various attempts I’ve made to track down a connection have not yielded results.

 

Meanwhile, I love these totally unfancy Select pickups for what they are. They’re solid as a rock, thoroughly dependable, and remarkably inexpensive. Unlike many guitar pickups, they do not have separate pole pieces, and this means that the pickup functions equally well regardless of the spacing of the strings or other sounding elements above it. The signal strength is respectable and the sound is your basic, unadorned magnetic pickup sound.

 

So if you have any sourcing suggestions for tracking down a wholesaler, please be in touch.

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Kalimba Tines Follow-up

by Bart on September 28, 2009

In the previous post I raised the question of what might be the mathematical relationship between length and pitch in kalimba tines and similar vibrating bodies.  (I had to add a bunch of specific limitations to make the situation mathematically manageable; you can see the details in the original post preceding this one.)  Based on empirical observation, I speculated parenthetically that there might be an inverse-squared relationship (e.g., halving the length would quadruple the frequency). Phill Styles, of the physics department at North Carolina State University, sent this comment:

The square root of the length applies when and only when the bar/rod is so rigid clamped that there is no motion at the point and no slope/bending.  In a kalimba, the bar/rod rests on a stop, where most people measure from, and then continues to a poor clamp.  Because of this the conditions on the bar are not uniform as you mentioned so it doesn’t come out just right.  Not bad tho in some cases.  Easy to understand in the treatment given in “The Physics of Musical Instruments,” second edition pg.64 case b.  The book is written by Fletcher and Rossing.,  USBN 0-387-98374-0. A great book. 

 

… And this fits well with my observations, in which the relevent factor appeared to be just a bit  little less than what the inverse-squared factor would have been. A less-than-perfect immobility/rigidity at the mounting nicely accounts for this “just a bit less.”  Thanks to Phill for this, as well as to Tom Rossing and Neville Fletcher.   

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Pitch/Length Relationship for Simple Kalimba Tines

by Bart on September 9, 2009

 A couple of times people have asked me what the mathematical relationship is between length and pitch in kalimba tines and other sorts of plucked rods held at one end.  My answer has always been “I don’t know.” I’ve never run across this information myself, and I’ve often wondered. 

I wasn’t able to intuit my way to a physical analysis of the situation which would point the way to a formula, so I recently tested the question empirically. That’s a fancy way of saying that I spent a few minutes in my shop setting up rods of different lengths and noting what pitches they produced, looking for a consistent relationship between length and pitch. 

Here, in brief, is what I found:

 

Given a rod or tine of length L, to make it produce a tone an octave higher, it should be shortened to approx .685L.   For an octave below, lengthen to approx  1.460L. 

 

From this, a bit of math tells us that the semitone-up would be at 0.9699L, and the semitone down would be 1.0320L. You can arrive at other intervals in 12-tone equal temperament by repeatedly applying the semitone-up or semitone-down factor.

 

BUT WAIT!  Please don’t take these observations as gospel, or at least please do read the following notes before working with them.

First keep in mind that these numbers only work for uniform rods or tines. They won’t work if the tines are irregularly shaped – say, thicker at the far end — or if you’re comparing two tines of different thickness or diameter.  Also, the tines shouldn’t be significantly bent over at the end. 

Second, I should mention that my testing set-up and observations weren’t all that precise, and my results weren’t perfectly consistent. The octave-up factor ranged from about .67 to .69.  (I notice that these results are fairly close to the the square root of 1/2 at .7071, which sugggests the possibility of an inverse-squared relationship between length and pitch, but I’m just speculating here.) 

 

I’m wondering if anyone reading this has performed similar experiments. Or, whether have any readers come across or come up with a theoretical formula for this relationship.  This news page isn’t currently set up for reader comments are present, so if you can add to the discussion, please email me at emi@windworld.com.    

 

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Online Payments — I think We’re Good Now

by Bart on September 9, 2009

Here’s what I hope will be my last posting concerning online payments for visitors to our catalog: We’re now able to take all major credit cards as well as PayPal.  Most people’s payments, both within and without the U.S.,  seem to be coming through OK. So if you had any earlier trouble with payment in our online catalog, please don’t hesitate to give it another try (click the catalog button above to get into the catalog).  Remember too that you can always order offline if you prefer … info here.

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Pop Guns

by Bart on September 3, 2009

A few years ago Phil Dadson and I put out a book on plosive aerophones and how to make them. Plosive aerophones is the generic term for things like slap tubes, udu drums, and other instruments in which a body of air is excited by percussion or other sudden  agitation. Sometime after the book was printed, I had a sudden realization: we forgot to include POP GUNS!  Too bad, because pop guns do qualify as plosives, and their sound is one of my favorites. 

As it happens, I did include a section on pop guns, in an earlier book, Funny Noises for the Connoisseur. So if you want the full story of popguns, that’s where to look.  But for a quick start, a short primer on the topic follows here.

Here’s a sketch showing the essentials of a pop gun.

pop-gun-diagram

The idea is to have a tube with a cork lodged in one end. From the other end the player pushes a snug-fitting plunger forward. This compresses the air and forces the cork to pop out, producing the popping sound.

Notice that two corks are needed, the popping cork and the plunger cork. Both have the truncated cone shape, with the large end a little larger than the inside tube diameter, and the small end a little smaller. The plunger cork serves as the piston-plug on the end of the plunger, fitting the inside of the tube closely so as to push the air through. To get that fit, stick the cork in one end of the tube as far as it will go. Cut off the portion that is still sticking out and discard. Sand the cork remaining in the tube flush with the tube end, and then remove it from the tube (push it out from the other side by poking through with a narrow stick or dowel).

At the end where the popping cork is to be inserted, use a rat tail file or similar tool to bevel the tube edges inward. Even if you do a somewhat sloppy job of this, it seems to help the popping effect.

The string that you can see in the drawing prevents the popping cork from flying away and getting lost. It also lets you pull the cork back into popping position simply by pulling the plunger back. The string length should be a little less than the tube length.

The drawing should tell you everything else you need to know. And to give you an idea of the sound you’re after, here’s recording of pop music.

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A pop gun can produce a variety of tones, depending on how firmly the popping cork is seated, how rapidly you move the plunger, and how far you draw the plunger back before starting the forward thrust.

Another sound I get a kick out of, closely related to pop gun pops, is suction pops (think of the sound of a cork being pulled out of a bottle). Maybe in another post I’ll talk more about them.  Suction pop devices are less variable and more predictable in their sound, and it’s possible to tune suction poppers to definite pitches.   

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