piezo tweeters

[Mainlander]

The gear you get to work with sometime... I have a couple of Ashton PB15
two way PA speakers that have Motorola / CTS KSN1142 piezo tweeters
(probably mounted on separate horns) and 15" woofers.

The high frequency end of the audio spectrum reproduction is very bright
and sharp. Without knowing very much about the speaker design, I know
that piezotweeters are often used without a crossover and it seems likely
to me that not enough attention has been paid to matching the speakers in
the bin so the tweeter probably has higher sensitivity than the woofer
resulting in the sharp HF tones.

I'm just looking at output EQ and whether the highs can be brought down a
little in a 1/3 octave graphic equaliser or whether the effort would be
better expended on new speakers because cheap tweeters will never sound
as good as the more expensive ones.

[Gidney and Cloyd]

Mainlander wrote:

> ...two way PA speakers that have Motorola / CTS KSN1142 piezo tweeters
> ... piezotweeters are often used without a crossover and it seems likely
> to me that not enough attention has been paid to matching the speakers in
> the bin so the tweeter probably has higher sensitivity than the woofer
> resulting in the sharp HF tones.

The Motorola division that makes the piezo's had an app note
about crossovers to tame the tweet; I'll see if I can dig it up.

[Rob Judd]

Mainlander wrote:
>
> The gear you get to work with sometime... I have a couple of Ashton PB15
> two way PA speakers that have Motorola / CTS KSN1142 piezo tweeters
> (probably mounted on separate horns) and 15" woofers.
>
> The high frequency end of the audio spectrum reproduction is very bright
> and sharp. Without knowing very much about the speaker design, I know
> that piezotweeters are often used without a crossover and it seems likely
> to me that not enough attention has been paid to matching the speakers in
> the bin so the tweeter probably has higher sensitivity than the woofer
> resulting in the sharp HF tones.
>
> I'm just looking at output EQ and whether the highs can be brought down a
> little in a 1/3 octave graphic equaliser or whether the effort would be
> better expended on new speakers because cheap tweeters will never sound
> as good as the more expensive ones.

Those Motorola piezo's are horrible, but you have worse problems. If
you're going straight from a 15" woofer to a tweeter, you're missing the
all-important midrange. The highest your woofer should be doing is about
200Hz. From there to about 2.5kHz isn't being handled by anything.

Rob

[Scott Dorsey]

Mainlander <*@*.*> wrote:
>The gear you get to work with sometime... I have a couple of Ashton PB15
>two way PA speakers that have Motorola / CTS KSN1142 piezo tweeters
>(probably mounted on separate horns) and 15" woofers.

I am terribly sorry.

>The high frequency end of the audio spectrum reproduction is very bright
>and sharp. Without knowing very much about the speaker design, I know
>that piezotweeters are often used without a crossover and it seems likely
>to me that not enough attention has been paid to matching the speakers in
>the bin so the tweeter probably has higher sensitivity than the woofer
>resulting in the sharp HF tones.

Piezo tweeters are high-Z devices that are very capacitive. So, to make
a high pass filter with one, you can use a series resistor and let the
device capacitance be the rest of the filter. So that series resistor
you see in front of it _is_ a first-order crossover. It's about as
effective as any other first-order crossover (like the capacitor in
series with the horn on an Altec A-7).

>I'm just looking at output EQ and whether the highs can be brought down a
>little in a 1/3 octave graphic equaliser or whether the effort would be
>better expended on new speakers because cheap tweeters will never sound
>as good as the more expensive ones.

The real problem with the piezo tweeters is that they have a lot of narrowband
resonances, and you can't easily EQ those out. Get an oscillator and sweep
back and forth in the high end and listen; the response plot looks like a
porcupine, so it'll sound nice and clean until you raise the frequency a
little and it starts to squeal when it hits a resonance. You could try
using a parametric EQ set up as a bunch of notch filters although I don't
know how much good you can really do.

I have never heard any piezo system that I liked, but Marshall Leach has
and he tells me I shouldn't just discard the whole piezo thing out of hand.
I'd suggest replacing your horn assembly with something that will cross over
at about the same place.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

> Piezo tweeters are capacitive. So, to make a high-pass
> fitler, you can use a series resistor and let the tweeter's
> capacitance be the rest of the filter.

Scott, you seem to be succumbing to the getting-things-backward syndrome that's
been affecting me and a lot of other people the last week or so.

Sticking a resistor in series with a capacitor produces (with respect to the
voltage across the capacitor) a low-pass filter.

[P Stamler]

Bill's right. A series resistor with a piezo produces a low-pass filter.

The way to put a crossover on a piezo is to shunt it with an 8-ohm resistor,
then design a crossover like you would for any 8-ohm tweeter. That will
slightly mitigate the awful sound of the piezo (by keeping bass frequencies out
of it), but only slightly. You still have the sharp resonances and the high
distortion to deal with, not to mention the inbuilt problem of a 15" 2-way
system.

So ditch the things and get a decent set of speakers. These are not worth the
effort to (slightly) improve.

Peace,
Paul

[Greg Bianchini]

Mainlander <*@*.*> wrote in message news:<MPG.19a9a68b9c6f1406989b87@news.paradise.net.nz>...
> The gear you get to work with sometime... I have a couple of Ashton PB15
> two way PA speakers that have Motorola / CTS KSN1142 piezo tweeters
> (probably mounted on separate horns) and 15" woofers.
>
> The high frequency end of the audio spectrum reproduction is very bright
> and sharp. Without knowing very much about the speaker design, I know
> that piezotweeters are often used without a crossover and it seems likely
> to me that not enough attention has been paid to matching the speakers in
> the bin so the tweeter probably has higher sensitivity than the woofer
> resulting in the sharp HF tones.
>
> I'm just looking at output EQ and whether the highs can be brought down a
> little in a 1/3 octave graphic equaliser or whether the effort would be
> better expended on new speakers because cheap tweeters will never sound
> as good as the more expensive ones.

Piezo tweeters usually have a risen in the mid treble, which is where
they have the most trouble. I've heard of people whose taste I respect
getting very good results using a transformer loading based crossover
with the 1142. There's a schematic out there somewhere if you search
hard enough. It just depends how much of a tinkerer you are. I've
gotten piezos to sound very good in the past. They can sound much like
a good ribbon tweeter if well implemented, believe it or not. (And yes
all you cynics, I know the fryin' bacon sound very well.)

The first and easiest thing to do is wrap up the horn with some
bitumen sound dead sheet, or similar stuff. The effect is not subtle
with a cheap plastic horn.

If it is still too loud, parallel an 8 ohm power resistor across the
terminals and solder a ~3.3uF cap in series with the +. Adjust to
taste.

I'd also bet that part of what you are hearing is dustcap breakup from
the cheap 15 at about the same range that the piezo sounds its worst.
It wouldn't hurt to slap some dammar (picture) varnish or latex rubber
on there.

Greg Bianchini

[BOB URZ]

Mainlander wrote:

> The gear you get to work with sometime... I have a couple of Ashton PB15
> two way PA speakers that have Motorola / CTS KSN1142 piezo tweeters
> (probably mounted on separate horns) and 15" woofers.
>
> The high frequency end of the audio spectrum reproduction is very bright
> and sharp. Without knowing very much about the speaker design, I know
> that piezotweeters are often used without a crossover and it seems likely
> to me that not enough attention has been paid to matching the speakers in
> the bin so the tweeter probably has higher sensitivity than the woofer
> resulting in the sharp HF tones.
>
> I'm just looking at output EQ and whether the highs can be brought down a
> little in a 1/3 octave graphic equaliser or whether the effort would be
> better expended on new speakers because cheap tweeters will never sound
> as good as the more expensive ones.

Well, you have a more entry level set of speakers, Nothing wrong with that,
but what they are is what they are. A least you have a piezo mid range horn,
In the old days, people would do the same set up with just 3 square tweeters.

And they die at 4K or so.

The KSN1142a is good down to 1.8 k which may be a bit optimistic.
They would usually be crossed over over around 2 to 2.5K.
And that's assuming a horn that can couple those frequencies to the air.
A piezo is highly capacitive and even at its rated frequencies the load
is not the same as a voice coiled driver. Even with a real crossover, its
not a high end device. and there are problems running a 15" woofer
much past 1000 HZ or so. Yea, it will work but there are
two problems. A 15" woofer starts to beam due to its pistonic size after
around the 1000 hz point. That leads to some inconsistency in the 1000 to
2500 HZ range or whatever your crossover is at.

http://www.cosmos2000.org/audio/lspeaker.htm

The other problem is cone mass. A heavier woofer cone has more mass and
cannot react as quickly to the midrange frequencies. So even though it works,
it probably sounds a little muddy in the mid range compared to a similar
speaker with a real horn crossed over at 1000 HZ or so.

So, what they are is what they are. A little crossover work might help a
little,
but don't expect miracles.

here are a few links:
http://www.ctscorp.com/components/Datasheets/PIE_Speaker_Application_Note.pdf

http://www.ctscorp.com/components/piezoelectric/piezoelectric_speakers.htm
http://www.diyaudio.com/forums/showthread.php?threadid=3005&highlight=piezo
http://www.diyaudio.com/forums/showthread.php?threadid=8352

BOB





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[info@freewire.net]

tweety

On Sun, 17 Aug 2003 13:50:22 +1200, Mainlander <*@*.*> wrote:

>The gear you get to work with sometime... I have a couple of Ashton PB15
>two way PA speakers that have Motorola / CTS KSN1142 piezo tweeters
>(probably mounted on separate horns) and 15" woofers.
>
>The high frequency end of the audio spectrum reproduction is very bright
>and sharp. Without knowing very much about the speaker design, I know
>that piezotweeters are often used without a crossover and it seems likely
>to me that not enough attention has been paid to matching the speakers in
>the bin so the tweeter probably has higher sensitivity than the woofer
>resulting in the sharp HF tones.
>
>I'm just looking at output EQ and whether the highs can be brought down a
>little in a 1/3 octave graphic equaliser or whether the effort would be
>better expended on new speakers because cheap tweeters will never sound
>as good as the more expensive ones.

[Scott Dorsey]

In article <vjv2ic2b4rf0ac@corp.supernews.com>,
William Sommerwerck <williams@nwlink.com> wrote:
>> Piezo tweeters are capacitive. So, to make a high-pass
>> fitler, you can use a series resistor and let the tweeter's
>> capacitance be the rest of the filter.
>
>Scott, you seem to be succumbing to the getting-things-backward syndrome that's
>been affecting me and a lot of other people the last week or so.
>
>Sticking a resistor in series with a capacitor produces (with respect to the
>voltage across the capacitor) a low-pass filter.

Sorry, too little sleep. I meant shunt and not series. If you check the
back, you will find a shunt resistor. There is a really nifty Motorola
app note about these things which is probably on their web site.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

I'm don't think a shunt resistor would produce a high-pass response. If the amp
has no trouble driving the shunt, then there's no resistance-reactance
interaction to alter the response.

I suspect the shunt is to make the impedance of the tweeter look essentially
resistive -- an ultra-crude Zobel network.

The Motorola tweeter was probably intended to be used without a crossover. To
get a high-pass response, you'd hang the tweeter across the resistor in an RC
high-pass network. If the network's impedance is much lower than the tweeter's
impedance (the tweeter is basically a small capacitor, so that would be easily
done), the tweeter would have little effect on the RC high-pass response. QED.

Jon Dahlquist is a friend. If you guys insist, I'll ask him how he handled the
piezo tweeter in the DQ-10.


Scott Dorsey wrote...

> William Sommerwerck wrote:

>>> Piezo tweeters are capacitive. So, to make a high-pass
>>> fitler, you can use a series resistor and let the tweeter's
>>> capacitance be the rest of the filter.

>> Sticking a resistor in series with a capacitor produces (with
>> respect to the voltage across the capacitor) a low-pass filter.

> Sorry, too little sleep. I meant shunt and not series. If you check the
> back, you will find a shunt resistor. There is a really nifty Motorola
> app note about these things which is probably on their web site.

[Gidney and Cloyd]

We, Gidney and Cloyd, wrote:

> The Motorola division that makes the piezo's had an app note
> about crossovers to tame the tweet; I'll see if I can dig it up.

The appnote I was thinking of was written by Jon Bost, but
I can't find a copy of it ... maybe on a cold disk somewhere.

The Moto ceramics division was sold to http://www.ctscorp.com/.

Did find bookmark for http://members.misty.com/don/pzfix.html.