The piezo fun box

[RMC]

INTRODUCTION

I have different types of drivers from various manufacturers since I like to try a number of things. This simple project is a way for me of letting go some older drivers in good shape as replacements arrive.

Though Piezos are not "noble" and snobbed by some, they're still known drivers, of low-cost that can produce acceptable sound if they are properly accompagnied by a simple crossover network.

Motorola did sell tons of these not only for individuals, but also to some known speaker manufacturers, as well as less known ones, and still counting under other names (back on this later).

Among known manufacturers who used these: Community, Peavey, Fender, Sun (piezo source). They can't be all stupid in my view, though admittedly not high-end drivers, but can still do the job adequately. Motorola Engineers published in the JAES about their invention or discovery in 1975 if I recall correctly, and their specific design is patented. My understanding is they are deemed to be the high-end of piezos.

Motorola's most famous being the KSN 1005A 3 1/2" Super horn tweeter, which I'm tempted to call somewhat of a "poor man's version" (not a copy) of a 2402 for example. JBL Selenium Brazil did make lower cost "copies" of the latter, such as ST200, ST-304, ST-400, and ST-350 (50°X50°), as well as Sammi (China?) HF 200A, and of 2405 as HF 250.

The pair of boxes in the making are low-cost ones for the neighbor's ambience music outside on the deck/near the pool. No pretention of being great high-fi or sound reinforcement cabs. Attracting rave reviews isn't the intent, rather just sound ok in the particular context (e.g. city noise). Simply a fun project.

Btw, the two-way pair of speakers are given to him absolutely free. There's about $60+. of material per box, and my time. The main purpose of the project being to say goodbye to some working drivers that I didn't want to throw away, the same logic applies to other materials in stock such as plywood leftovers from other projects that can be used for smaller box sizes.

Last but not the least, these boxes should sound better than the table radio's bad sound he's projecting when making his pool and deck gatherings. So, in a way its an "investment"...

Of the six piezos I have, 4 of them are 1005 type (2X 100% original Motorola I keep; 1 "semi-original" Motorola given to me- element replaced with OEM?; 1 Asian copy available purchased to make a pair, the latter two going in the neighbor's boxes-see below), plus two KSN 1025A 2X6" mid/high horns, 75W, that are 100% original Motorola. They also made a high-power "Powerline" 400W version of this one. I'm first owner of all originals purchased new. (Back later on Motorola original VS others...).

Since Motorola originals cannot be purchased anymore (with a nuance), contrary to a large number of cheap "copies", I didn't want to give here (see below) "knock-offs" that anyone can easily purchase by themselves, plus for neighbor's use of the boxes it won't make much difference re ambient noise...

If someone wants the latter two 1025 type originals they are available for FREE, packaging included, shipping cost excluded. Since these are light and relatively small, shipment cost should be low, the carton they're in now/for shipping is about 0.25 cubic foot. Tested them today with music, still work ok, good condition. If interested to play with these just let me know by private message or in the thread. Actual ext. dimensions: about 3 X 7.5 X 4" deep. Then 4 of them will be gone, I keep only 2 X1005 originals.

If a person doesn't feel familiar enough "electrically" speaking to play with these, no problem as I can also provide free easy to read technical and simple crossover info on these from Motorola and others, including from a Peavey Loudspeaker Design Engineer. Though many people on the net have their own "recipe" on this, good or bad, I prefer to pass along the real thing from acceptable makers.

In follow-up article, as it comes, I'll describe with some detail the project parameters/tech info. Even if its a low-cost project, to me it's not just a matter of throwing a bunch of components together in a box. There's still some modeling, tweaking and testing work and choices/decisions to be made: e.g. though they don't REQUIRE a crossover, they perform/sound better and accept more power with a simple one... Regards,

Richard

[1audiohack]

Sounds fun.

Piezo’s are crazy things aren’t they? For sure they sound better with a resistor across them and some form of crossover.

Barry.

[RMC]

Hi Barry,

Thanks for dropping in.

Sounds fun? You bet, something different, and outside is somewhat another challenge than building for the comfort of our homes... In this case MANY things to think about e.g. different acoustics, even the presence of many kids who's fingers want to touch everything, pool water flying around, easy carrying as not permanent install, etc. The box itself isn't too different but the context in which it is used IS different, so things need to be "adjusted".

Piezos ARE crazy things, and even then millions were sold, not rocket science though, in fact simple to high-pass, pad down, reduce top end a bit, protect amp from capacitance, just need to know how. Good manufacturers make it easy enough, as well as that Peavey Engineer. Regards,

Richard

[MoD]

I have a pair of motorola 1001 copies. I have put them in old Sanyo sx 170 which were given to me with blown tweeters. I replaced them with those piezos and they are good for use again. Piezos are not match to bass drivers in quality aspect, but speaker now sound decent... I am interested in your piezos because I heard that original motorolas plays bettert han copies. It is shame that those are not same model but I would like to give them a try.

[RMC]

Hi MoD,

Thanks for your post.

RE: "speaker now sound decent" That's exactly my point, decent, ok, correct, no pretention of being high-class. Though I seem to remember seeing somewhere a $3,500. commercial speaker using a piezo?

RE: "heard that original motorolas plays bettert han copies" stay tuned for that because I'll post shortly what I said in a previous post about Motorola VS others, from someone who should know...

Btw there's a small typo I need to correct in my first post, its not model 1025A/B that I give free but rather model 1025A. The B version has beveled edges that mine don't have, rest is same.

The ksn 1001 you have is a small rear mount model VS the larger 1025A model I give away is usually front mounted.

RE: "I am interested in your piezos ... I would like to give them a try." I don't have a problem with that in itself. However, Croatia being very far away from me, one must realize about shipping delays, gear condition on arrival, postal price, etc. when overseas shipment. I cannot guarantee such things, can only do my best re packaging, but overdoing that increases shipping price that YOU have to pay to me at cost to ship.

On the other hand, maybe its your lucky day currency exchange wise, if Croatia has adopted the Euro worth much more than the Canadian $, even more so than USD! Which would further reduce your expense...

Send me a private message I'll explain to you how to do it to minimize your out of pocket money for shipping cost, same principle as I did for the BGW amp and EQ given on this site recently.

RE: "It is shame that those are not same model" (as mine), more sad than shame I understand, but I'd like to hold-on to my pair of original Motorola KSN 1005A, as well as other tweeters I have, for possible future projects and these are somewhat difficult to replace with same... If I ever change my mind on that I'll let you know, but for the time being its the 1025A pair. Regards,

Richard

[RMC]

"Motorola no longer does the piezo's, CTS has taken over the piezo operation. They are still considered to be the premium piezo source, although there have been claims by some that CTS has not been maintaining the quality levels that Motorola did.

Le son, and many of the other sources, were distinctly second tier compared to the original Motorola parts.

Jon Risch" (High Efficiency Speaker Asylum, Forum, May 28, 2002). This should answer MoD's question.

Who is Jon Rish? I checked. Senior Project Engineer, Transducer Engineering Dept. at Peavey, with specialties in Speaker system design, Crossover filter design, Transducer analysis & development; there almost 30 years (Linked In). Education Electrical Engineering, etc. Was granted a few patents in audio.

Peavey used piezos from others in many of its speaker models and its unlikely they just threw these in their boxes without product knowledge and Engineering work.

The relation between Risch's years at Peavey and brand name piezos, is the latter were more widely seen/used in speaker systems years ago, making it quite feasible he was involved then with the drivers, plus its likely he designed himself systems using these. In my view he's a credible source regarding his piezo writings here and others he's written on how to use piezos: crossovers, padding, multiples, etc.


Finally, as mentioned by Risch, CTS took over the piezo business from Motorola, however when CTS ceased making these, then Piezo Source took over Motorola's piezo business in 2005: Eng., rights, designs, mfr line, molds, etc. THEY are NOW considered the premium piezo provider and sell to OEM plus directly online. There is on Piezo source's site a piezo technical document mostly from CTS (2nd half or so more accessible and practical).


More to follow. Regards,

Richard

EDITED for clarity

[RMC]

Hi MoD,

You haven't responded to my post about getting the transaction done for the free pair of original Motorola KSN 1025A piezo 2 X 6" mid/high horns in good condition.

In the meantime I've found out that Crotia's currency isn't the Euro (well known/traded here along with the USD) but rather the Crotian Kuna (seldom seen/traded here), which would make things much more complicated to cover the shipping cost. I assume its the explanation and have to consider you changed your mind about getting these.

Therefore, for the benefit of others, the two piezos ARE still available for free (packaging incl., shipping cost excl.), "while the offer lasts" as they say. If interested, send me a private message or inquire here. Regards,

Richard

[RMC]

EDIT to post # 7:

In order to give folks some idea about shipping cost, I recently sent by Accelerated postal service a BGW amp and EQ from eastern Canada to Nevada, USA which is pretty far from me. The smaller of these two cartons, the EQ one, had a volume of almost one cu. ft. and weight of 4.115 Kg (by Canada Post), shipping cost was 40 something Canadian dollars taxes included. The carton with the two piezos is 0.25 cu. ft. and weight is 1 Kg max. So I suppose shipping cost in North America for e.g. could be about $15 CAD (equivalent to $12 US/10 Euros). I can get a Canada Post shipping quote if one is interested by these.

[RMC]

Since I have three versions of the Motorola KSN 1005A tweeter on hand, one pair original, one semi-original unit and one unit Asian copy to make a pair with the semi, I was interested in knowing with a music listening test, comparing two at the time, how they sounded respectively and versus each other... No crossover, just as it comes "off the shelf".

The original's response has emphasis around 5 khz and some at 15-20 khz, both of which are relatively easy to cure with simple components (resistors and capacitor), more on this later.

The "copy" with no name is the disappointment. Whether compared to the original or semi, it is shy on very high-frequencies, lacking some output there even untreated. Not only less "hissy" than better ones, but also less high-end detail. Will address this issue with the components choice mentioned above.

On the other hand, the copy has more evident emphasis, than the other two, towards the low-end of its spectrum. For example, voices are definitely accentuated vs the other piezos. This one might need a little more correction around the usual 5 khz bump in response. A slight change in resistor value within the High-pass section should take care of that. Finally, the copy's slots directing sound to the horn's throat are of poor design/execution compared to Motorola's original nicely made ones (I opened both piezos to see). I'll try getting another cheap one here, hopefully from another bunch, just to see if its the same or better made.

The semi-original is the pleasant surprise (was keeping it as spare). Globally, its pretty close to the original's sound. Just a tiny bit less output and extreme highs. This one, given to me or taken out of a used speaker cab long ago, is a Motorola identified horn with a non-identified back cover (contrary to original ones) which makes me believe the element may have been changed with a non-OEM. Could be an element from one of the better copies. For example, GRS brand piezo tweeters sold by parts Express claim "Using a 22 mm ceramic piezo element, GRS piezo tweeters follow CTS' original recipe" (Not necessarily Motorola recipe).

Btw I don't recall ever seeing an official sound dispersion spec nor a coverage angle figure for this KSN 1005A horn tweeter. The angle finder tells me 60° should be the nominal number. (2402: 40°)

More to come.

Richard

[RMC]

I've changed course a bit, RE "I'll try getting another cheap one here, hopefully from another bunch, just to see if its the same or better made." from my last post. I ended-up purchasing not one but rather FOUR more low cost piezo 1005A copies for evaluation and testing. Might as well make this a little "educational" by the same token. Plus I've taken many pictures of inside a piezo tweeter, to compare original vs some copies. To be posted soon.

The first copy purchased recently to make a pair with a semi-original, mentioned in my previous post, had too much "mid" emphasis and was lacking some high end. This IS the black sheep among all copies now have, others ARE better.

Because of the poor experience with that first copy, that I opened to see inside and wasn't impressed by the six slots' craftsmanship, I brought along a small flashlight to look deep inside the horn when going to purchase more of these. Quite revealing.

Of the ten or so I looked at, four had serious machining/molding slot issues, like 2-3 or 4 slots partially blocked by halfway done cutting or leftovers. Discarded those. Others had minor similar issues and took home the four best ones seen. Morale: If you're going to buy piezo tweeter copies in a store bring some light with you to check the slots' shape at the bottom of the horn as seen from its mouth. This gives a clue on how well or bad its made and reduces the chances of buying a donkey... My black sheep, after slot corrections, remains the same so it may have a piezo ceramic element or "cone" issue.

The 6 slots are basically the sound's passage way leading to the horn's throat. How can the sound properly enter, go through this passage way and throat plus exit the horn's mouth correctly if the slots located at the beginning are poorly made to start with?

First thing after getting the four copies I opened each driver to check the slots more carefully and the front part of the piezo element (i.e. the "cone"), not the ceramic piezo thing behind it to avoid damaging. But I WILL go there soon with the black sheep tweeter and take pictures, plus hopefully measure the ceramic device VS the GRS mentioned 22 mm...

I corrected slightly with a small very sharp knife the slots incorrectly made, as these should be straight and rectangular shaped. I removed just enough excess plastic to get there, though a few tiny bits remain since too difficult or risky to remove. Too bad I thought about taking pictures only after correcting the first unit of four as it was the worst of the group, with few pretty weird looking slots initially...

Then a listening test of each new unit, no crossover, etc., with music, comparing each first with the black sheep to hear if better (yes, all four are much better sounding), after each new one again VS my semi-original Motorola which is pretty close sound wise to the fully original. The four corrected copies sound the same.

Honestly, the four slots corrected copies are close to the semi unit on sound quality, having more balanced sound than the black sheep- less mid more highs. The differences noted were the four copies have I'd say about 2db more output/sensitivity globally, so a little louder, and the very top end of the semi has just a little more detail/sweeter.

So, I'm somewhat surprised by the four copies being better than expected, tested after slots correction. Reason for getting four? Basically to give just a little validity to the sample. Had I got one only and it been differently poor than black sheep then what do you do/think? The other reason being trying to get two more closely matched units for the neighbor's boxes, instead of a pair made of the semi and black sheep, also meaning, if need be, doing identical electrical corrections in X-over. I didn't compare the four units to the fully originals I have as I thought initially that comparison would be unfair.

Bottom line, of the five 1005A copies on-hand, the black sheep will be scrapped on the "dissection table" for "educational" purposes (back later/picture), I'll take any two of the four remaining slots corrected copies for the project mentioned in post # 1, since they look and sound the same, and I'll put the remaining two in the carton with the originals 1025A units, all being given away for free here (excl. ship.), since I don't need them. The1005A do fit in same carton, I checked, and btw according to Piezo Source the 1005A weight is 75 grams and 1025A weight is 130 grams, total drivers weight = 410 grams, adding the pretty small carton weight I don't see how this would reach or exceed one Kg.

Remember, the initial project objective is to reduce driver stock, not increase it. I'll keep only the two 1005A Motorola originals, and the semi-original one as spare just in case... More on the way.

Richard

[RMC]

Was looking today at some well-known speaker forum where Q & A are given about hooking up piezo tweeters and doing crossover, pad, etc. The number of unbelieveable answers given is nothing short of alarming (e.g. use of an 8 ohms 10 W parallel resistor, over heating btw, to pad down such tweeter!!). Even though trying to help in all good faith MANY of the answers seen are plainly WRONG, doing no good or counter productive. These folks have certainly not looked at Motorola, CTS, Piezo Source and Jon Risch's stuff on these issues, but instead give their own "recipes". Hence my previous mention that I prefer to pass along info from credible sources...

Considering the above, as a preview or warning note, lets just say for now that in most cases you'll need only up to four easy to find components: two capacitors and two resistors, no requirement for inductors. One simple "safety" resistor (may also be used to modify response) in series re amp stability vs capacitive nature of piezos (one included in the 1025A), one series capacitor to pad down the tweeter if need be (not really a resistor as seen above), one resistor in parallel to make a load looking like a resistive one (may also be used to modify response), and one series capacitor that acts as a high-pass filter. Simple.

Will discuss the order of these in the signal path and their values further in a future post. Regards,

Richard

EDIT: The logic here being the lower cost driver is dealt with simple lower cost solutions the vast majority of times (e.g. crossover, pad, etc). Otherwise it would sort of defeat the purpose of that purchase. Clever Motorola and other Engineers...

[RMC]

I took 28 pics total, from which I'll post a dozen or so of the more revealing. Mostly grouped by subject or issue for comparison purposes (e.g. copy vs original or before vs after some correction).

First group: Pic 1 Original Motorola nicely made chamber, slots are pretty uniform size, straight and rectangular from top to bottom. Pic 2 "Nice" copy's chamber and slots before correction, small plastic bump above 6 o'clock slot; slots at 4, 8 and 10 o'clock curiously machined/molded at the bottom; slots at 8 & 12 o'clock aren't really straight. Pic 3 A copy's more uniform slots after some corrections and plastic bump removal by me with a sharp blade.

Other pics on the way

EDIT: order of pics came out wrong, damn it, first is #3, second #2 and third #1...So in this post one should look at the pictures from bottom to top.

[RMC]

Second group: Pic 1 Nice Motorola original "cone" on front of piezo ceramic element. Btw it has more play/loose and "suspension" than one from the copies. Pic 2 A copy's cone, sorry pic not as clear as I would have liked.

Other pics on the way

[RMC]

Third group: pic 1 Poor copy's view of the slots seen from horn's mouth with light from the back, light showing slots have a uniformity ussue (a revealing trick), that piezo copy is the one being scrapped for "educational" puposes in some later pictures. Pic 2 Sharp blade corrected slots on a relatively nice copy, again front view with light in the back, this is basically how it should look like, light seen being more uniform.

[RMC]

Fourth group: Pic 1 Copy seen before slots correction, plus molding plastic bump present here under 12 o'clock slot. Pic 2 A copy seen after corrections of the above issues.