Using piezo tweeters wisely: a "how to"

[Paul C]

OK, Cracker is now testing some bigger horn lens, this 11.5" x 11.5" model by Dayton from Parts Express. The small 6" x 8" horn lens above are a little bright sounding to him. Well, they are made for PA speakers. So, he's testing these right now:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=270-300

 

[crackerkorean]

Ok here are some pics.
And I have to say they sound amazing!!!!!
Nice rich mids and highs that are not too bright

 

[macaltec]

I like the support in that last pic. Nice Atari 2600 game there. Which one is it?

 

[Paul C]

This was a "best case" use of that piezo with his woofer. The Carlson rolled off right where the piezo tweeter rolled in, and the SPL's are apparently close enough for a good blend. No other components were used, just the piezo driver wired parallel to the woofer. Couldn't get any simpler.

Macaltec... do you think he should experiment to see which game cartridge has the best sonic attributes? :scratch2:

You can see in one photo, on the floor in front of the left speaker is one of the smaller horns I had first sent him. You can see the difference in size from that to the largers horn on top of the speaker.

 

[macaltec]

I'll bet some of the more simplistic games would sound better from a purist standpoint . Just my opinion, yours may vary.

 

[crackerkorean]

I guess I need to find several copies of PONG LOL

On the other side I have two because the one pictured is a little taller than the other.

 

[macaltec]

I have joined the ranks of a piezo enthusiast. A brief of background on the project. An Altec Santana II cabinet, Dayton Classic 12" woofer, reworked port, and a new crossover, 12db/octave on the LF with a zobel network and a simple 6db/octave on the HF and an L-pad for level matching (Paul is that right?). I have installed a CTS KSN 1165 mid/tweeter and the crosover is @ 1800hz. I went on recommendation from Paul for the tweeter and am fantastically pleased with the results. Very smooth and detailed. Great imaging and depth as well. I am so pleased with this overall combination (especially the KSN 1165) that I plan to duplicate it in my Altec stonehenge cabinets. This has got to be one of the best sounding set of speakers in my house and I've got alot of speakers but that is for another thread. For the cost versus performance the KSN 1165 has got to be the best bang for the buck for your HF needs. Simply amazing.

 

[Paul C]

Macaltec described it well. He didn't just tear up some Santana's to install these components. He had some perfectly good Santana cabinets with no drivers and wanted to put them into operation now without spending a lot of money, with the idea to later install original type drivers. He really did his homework and found those Dayton Classic woofers for the Santana cabinets. Nice choice! RUBBER surrounds, not foam, and the numbers worked well for his cabinets. All he needed was an inexpensive tweeter that would work in a two way configuration with his woofers.

I have attached the schematic I sent him.

This schematic is similar to the one I use in my living room now with a Speakerlab W1008b (10" woofer) in a 2 cft cabinet. This same schematic could be used with other 6-8 ohm woofers by changing only the capacitor in the zobel network (computed from the woofer's Re and Le).

Macaltec said he did have to dial down the L-pad to match the woofer, even though a look at the SPL's say they should match without. I had to do the same with my Speakerlab woofers. These woofers are rated at 92 db SPL, as are the Daytons. Either the KSN1165a's produce more than 92 db at 2.83v, or these woofers do not produce 92 db at one watt (PE's graph shows 87-88 db). Anyway, it has been my experience that using an L-pad will allow you to get a good tonal balance with these piezo tweeters.

What was neat about using these for Macaltec's boxes, these tweeters fit the tweeter holes in his cabinets. If he wants, later on he can restore these cabinets with original woofers and tweeters. Or he may not want to.

These tweeters coming down smoothly to 1800 hz allows them to be used with many 10", 12", and even some 15" woofers in a two-way configuration with good results. The KSN1165a has the same driver as the KSN1142a in CrackerKorean's horns, only the 1165a has its own small horn lens built on. Like the KSN1142a driver, the 1165 is rated for 100w, with protection up to 400w level. The built in protection circuit gives a "soft compression" effect at high levels and its effect is practically inaudible.

KSN1165a

I have built smaller PA speakers and floor monitors with KSN1165a's that perform very well in these high power applications. They will certainly hold up in a home listening environment. More likely you'll smoke a woofer before you smoke these tweeters!

Mac, since you no longer need those A7's... you have my address.

 

[DaWoofer]

Paul- I thought you might find this interesting in which way 8 of these tweeters were wired together. Switchcraft is the maker of the speaker box. Thats what I was told so I guess they are the ones who wired it.I haven't hooked them up to any source as of yet to see if they work or not. That is my next goal with them. I will let you know when I do. These are what apperears to be very similar to the KSN1001A.

 

[DaWoofer]

I opened up the second matching box and its wired different! Look and see. The first box reads 83 kOhms this boxs reads 170 kOhms. As you can see they used different componants wiring the two. Do you know why that would be. A church had them and claimed they work and were in use. Wouldn't the different Ohms be difficult on the amp. Im gonna need to get them both the same aren't I. Any suggestions?

 

[Paul C]

No, the different ohms had no effect. As far as the amp driving these was concerned, there was no load at all. The impedance was so high there was just no load on the amp.

I have NO idea how the manufacturer computed that impedance, but it is meaningless.

These are hooked up parallel, with a resistor in series with each tweeter.

There are three "groups" of CTS/Motorola piezo drivers:

The KSN1165a, KSN1142a, and one more, a 2x6 horn that I don't remember the number, all have the built in "Powerline" protection circuit mentioned earlier. These had a low end rolloff of 1800 hz.

Also in this "Powerline" series was the KSN1188a, which replaced the older KSN1086 (which lacked the Powerline protection circuit). This is a very large driver that goes down to 800 hz. It is very smooth, with some minor dips and humps that are far less than many well thought of drivers. For making a 2-way with a large woofer, 12" or 15", this is ideal.

In the second group are the various other 1800 hz drivers, KSN1025a (2" x 6" horn), and others, had an internal 22 ohm resistor, but no other protection.

The third group is comprised of various drivers with a low end rolloff of 4000 hz. This group includes the KSN1005a (which are what you have) and the similar KSN1001a (same but rear mount), KSN1016 (2" x 5" horn), KSN1038, KSN1041 all had the same 4000 hz driver. These had no internal components, just the driver mechanism.

BTW, while the 1005 was, and still is very common, the 1001 is pretty rare. So much easier to front mount.

Piezo drivers act like a very small lossy capacitor. In the audio range they have an impedance of about 1000 ohms. Up around 40 khz they drop as low as 4 ohms. And as frequency goes even higher, the impedance continues to drop. This extremely low impedance can cause some amplifiers to oscillate. Or if the amp picks up RF, it can cook the tweeter... I have seen this myself. It is really fun at a gig to see smoke coming out of the PA tweeters.

To prevent this, the 1800 hz drivers and the Powerline series have an internal resistor in series with the driver. This resistor is for protection of the amplifier, not the tweeter.

The various 4000 hz drivers can use a series resistor to protect the amp, just as you see on your tweeter arrays. Each tweeter has its own resistor. CTS recommended 20 ohms to 50 ohms. I have done listening tests, shorting around the series resistor, and you just cannot tell, either in level or tone quality. It makes absolutely no difference in the audio range. Putting 50 ohms in series with 1000 ohms is insignificant.

Again, this resistor is not for protection of the tweeter, and will not pad the tweeter at all, regardless of what you read in some catalogs. Whoever wrote those catalogs did not read, or completely misunderstood CTS's own paper on the subject.

If you want to use a 1005 or other 4khz driver with crossover and L-pad, put the resistor between the 8 ohm parallel resistor and the piezo tweeter.

 

[DaWoofer]

Wow Paul, I want to thank you again. They really added some sparkle to the Heresys. The Heresys sound dull and flat without this array. I have a 2230b powering them running off of the Art 311. Sometimes ya just don't know what your missing until you have it and take it away. The 15 in. W-Bins on bottom running off the Art 311, the Heresys running by themselves and the array on top. The signal is being split off the 2275 wich runs the Heresys. It might sound confusing or not, but it sure "sounds" good to the ear. Much, much better than just a set a Heresys. I use to think the Heresys were great speakers by themselves. Now I know there can be much inprovement to be had on many speakers. Specially since these lacked so much now that I realize it.

 

[Paul C]

Isn't the ART 311 a great little unit? I have one I use with my PA gear. The thing I like about it is the 1/4" inputs/outputs, making it easy to convert to RCA via adapters.

And it sure solves a lot of crossover problems.

 

[dc270]

Piezo File/ Info

Found this old file, maybe it'll help too! Sorry for the size, dont know how to reduce it!

 

[Paul C]

Excellent!

 

[Troy]

Sense i took up deejaying i'v had 3 set's of speakers. Out of the three, one set had a 1 1/2 screw Pizeo driver (which screwed onto the horn). It was the worst sounding horn i'v ever had, no matter how i adjusted my EQ'S it was harsh and nasty sound. I would avoid pizeo for all cost now. I did how ever spend the 75 EACH on new 1 1/2 compression drivers for those speakers, and the sound was great after that.

 

[Dan ʕ•ᴥ•ʔ]

Sense i took up deejaying i'v had 3 set's of speakers. Out of the three, one set had a 1 1/2 screw Pizeo driver (which screwed onto the horn). It was the worst sounding horn i'v ever had, no matter how i adjusted my EQ'S it was harsh and nasty sound. I would avoid pizeo for all cost now. I did how ever spend the 75 EACH on new 1 1/2 compression drivers for those speakers, and the sound was great after that.

Sorry, you can't judge the piezo design as a whole on your one encounter. You could have said the same for dynamic compression drivers, since many of them will etch glass.

 

[bowtie427ss]

Sorry, you can't judge the piezo design as a whole on your one encounter. You could have said the same for dynamic compression drivers, since many of them will etch glass.

Very well put!

A piezo element simply doesn't have the physical and mechanical properties to be an effective substitute for a compression driver.

It's all about application, and as the title of the thread suggests, "using piezos wisely"

just my .02

 

[macaltec]

Sense i took up deejaying i'v had 3 set's of speakers. Out of the three, one set had a 1 1/2 screw Pizeo driver (which screwed onto the horn). It was the worst sounding horn i'v ever had, no matter how i adjusted my EQ'S it was harsh and nasty sound. I would avoid pizeo for all cost now. I did how ever spend the 75 EACH on new 1 1/2 compression drivers for those speakers, and the sound was great after that.

You most likely encountered a setup with inadequate crossovers in place. That is what this thread is about. How to use them properly and with good results.

 

[Paul C]

Or, as likely, you had an encounter with cheap imitations made by someone other than CTS/Motorola. I warned about this early in the thread.