Having major problem with speakers

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I recently bought some pa/disco speakers costing me £300 pair [new]
[AC EURO AC115].Even though iI never heard of the name Ac Euro,but the salesman told me they use Eminence drivers;Which is partially true,because
there was no wattage printed on the back or box,so I took out the drivers to see what they are rated at.
Also what puzzled me was,no warranty came with the speakers.

What I found was: 1x Eminence Beta 15,15 inch bass driver.,150w rms,8 ohm

And 1x Motorola/CTS KSN1197A piezo horn driver rated 100w max.With 30 ohm 2w resistor wired on the positive terminal.And CTS KSN1196A 15 Inch x 5 inch abs horn

The cabinet is made from good quality 1 inch plywood,and has 4 round vents in each corner instead of port tubes.
The connection on the back is dual Neutrik jack,and the the internal wire is 12 gauge ofc cable,Trapazoid cabinet,rear panel lagged with fiberglass wadding.
So everything is almost amazing,except for having a piezo and resistor,instead of compression driver and crossover.

I hope you don't get bored to kindly answer my questions;

1. I'm using a 150wrms into 8 ohm,200w rms into 4 ohm amp
Gemini X2 poweramp.I know 150w rms
[unclipped]into a 150w rms speaker drives it cleanly,but i'm worried about blowing up the piezo which is only rated 100 w max,i dread to think what the rms value is,something 50w rms in suspect.But with a resistor of 2w 30 ohm,would this make the piezo able to handle 150w rms.

2. I don't understand why a 2w 30 ohm resistor is used on a piezo,when piezos are supposed to not need a crossover.

3. I have to boost the mid and treble eq on my mixer because otherwise,it sounds muffled,no clear midrange,hardly any treble,just booming bass.The piezo isn't blown,but it is sure much quieter than bass driver output.

4. Would replacing the piezo with a Eminence APT50 Compression horn driver and crossover,improve the awful treble responce,and non-exsistant midrange.

5. Do 15 inch bass drivers,with a freq of 35hz-4khz produce any midrange,such as vocals and warmth and hidden sound effects in the music.

6. Also last but not least,I play mostly drum and bass,reggae,garage. All with very heavy basslines,and nice synith effects.But the electronic effects are hidden in the background,unlike when you boost the mid and treble eqs and you can hear more detail,effects become louder,but can this damage my speakers in the lomg term played at high volume.

I dj in rooms about 6m long,by 5m wide.
My setup is 2x Technics 1210 decks,Gemini ps626 mixer,Gemini x2 poweramp,Ac Euro Ac115 speakers,and PROEL speaker cable and interconnects.
Please help me out,because i'm only a student,with not much money,and djing monthly gives me not much money to earn a living,as well as University costs,and food,etc.
I hope I can answer your questions!!!...

1.The resistor series with the Piezo is to protect your amp against the high capacitance of every piezo driver.It doesn't mean that it will lower the power reaching the piezo!!!At least i would recommand 10R/20W resistor.The impedance of your piezo is around 1000 R.Its capacitance 200-400 pF
Don't be afraid to breake them.In fact it's a reliable technology.Even if sound is .....(censored)


3.Replacing them with good 2'' compression drivers would be a good upgrade.Then go for Eminence or better some Radian.You will have to make a crossover at 800 Hz for both bass and compression,and adjust sensivity of compression with attenuator.

Hope your questions answered... ;)


Joined 2001
Paid Member
The R in series with the piezo is essentially an XO -- a lot of the bad rap piezos get is from being used with no XO. The piezo can be made to sound quite reasonable with a few mods. An XO is one (see below). Others are to disassemble them and treat the cone -- dammar is probably good here. A little bit of damping on the inside of the chamber probably won't hurt. And all the plastic bits need to be damped. I use dust seal.


(cut and paste, most of the below information credited to JON RISCH)
The Parts Express catalog suggests putting a 20-Ohm resister inline with any Piezo tweeter to make it a more stable load for an amp.Will this not also attenuate the tweeter? If so, and if I need further attenuation, can I simply add more resistance? Is there a rule of thumb for how much attenuation I will get with further resistance, or a way to compute this number?

The recommended resistor is to help protect the amplifier from oscillating due to the raw capacitance that is a piezo driver. Adding resistance in series with a piezo will actually roll off the highs a bit, adding more will roll off the highs noticably. To attenuate a piezo, add a series cap, which creates a voltage divider with the capacitance that is the piezo drive element. Most piezo elements run in the 0.1 to 0.26 uF range, so a cap of the same value as the piezo element will attenuate it 6 dB.

Piezo's can be crossed over, and to great advantage. I have often thought that some of the bad rap piezo drivers have is due to the "you can use them without a crossover" fallacy. Yes, you _can_ use them without a crossover, but just because you can get away with it, does not mean it is optimal.

Since most piezo's are used in inexpensive systems, the cost of adding in "unecessary" components is often never even considered.

How to crossover a piezo:
Add a resistor in parallel, and the driver can be made to look like a current driven device to any outside components, such as a crossover cap. However, to keep costs and power dissipation down, 8 ohms is way too small of a value. The impedance of most piezo's is still quite high at 20KHz, so use a 22 ohm resistor, this makes any series crossover cap smaller and less expensive, and the resistor dissipates less energy. Use of an 8 ohm parallel resistor will also tend to lose you a little bit of output level.

For most piezos, use of a 22 ohm resistor, and a 4-4.7 uF cap will allow the response to be identical to what it was in stock form, but rolls off the lows at 6 dB/oct below 1 kHz or so. This actually increases the power handling of the piezo, as it is voltage limited. Exceed the voltage used to pole (polarize the piezo element during manufacture) the unit, and it will loose sensitivity, and eventually burn out. Most pro grade piezos will handle 35 volt transients, and 28 volts continuous, which are 150 watts and 100 watts into 8 ohms respectively.

Add in a capacitor and 22 ohm resistor, and the power handling could effectively be quadrupled, as the LF voltages are not imposed upon the unit, just the HF voltages.

Piezo's crossed over in this manner don't sound as harsh and spity, and tend to be quite a bit more reliable. Many of the piezo units have a mild peak just before they roll off in the LF, so making the series cap a little smaller can actualy flatten response, and provide even more protection and smoother sound. For the smaller piezo units that cut off at 4-5 kHz, a series cap of 1.5 uF will do the trick, larger units that go down to 3 kHz can use a 2.2 uF, and the large compression driver units meant to be mounted on a horn need about 5 uF, as they do not peak, and any higher would lose the sloping output even more.

Attenuation, HF roll-off AND the crossing over can all be done at the same time. To attenuate, place a cap in between the piezo and the 22 ohm resistor that is shunting across the unit, then if HF roll-off is desired, use a series resistor in this location too. Then the series crossover cap should be in front of the 22 ohm shunt.

Looking from the amp, first the series crossover cap, say 4 uF, then the 22 ohm shunt from hot to ground, then a series cap of about 0.15 uF for 6 dB attenuation, and then a series resistor of about 30-50 ohms to tame the very top end, then the piezo itself.
diyAudio Moderator Emeritus
Joined 2001
Motorola first came out with piezoelectric speakers. CTS bought out Motorola's part of the business. The speakers are still being made in Motorola's plant in Albaquerque, New Mexico where they always were made, so apparently the "buyout" has little affect on the actual production of the speakers themselves.

CTS has an "application note" that goes into crossover principles, among other things. Essentially it says the same thing as Planet 10, but in greater detail.

diyAudio Moderator Emeritus
Joined 2001
The KSN 1197 horn driver, presumably mounted to the 1196 horn, is listed at the CTS website with a sensitivity of 92 dB. They are actually running on much less than a watt, but fitted to an 8 ohm woofer, they will play at 92 dB when you are sending the 8 ohm speaker one watt.

The Eminence woofer is near 100 dB at one watt, so it seems you have a mismatch.

Adding another piezo horn/driver combo in parallel with the existing one will boost your tweeter sensitivity 6 dB-up to near where the Eminence Beta is. That is probably the biggest part of your problem right there, I would guess.

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Some time ago, I sent away to Motorola and got a stack of flyers for their various models since then. I do not have the 1197 driver, but I do have the 1086 driver flyer. This might well be similar.

This 1086 driver is designed to play through an ElectroVoice horn. I wonder if the KSN 1196 horn is not similar to the ElectroVoice.

At any rate, I thought I would include the frequency response chart for the 1086 in case they are similar.

Note: the measurements were conducted, for some reason, with 2.83 V, (1 watt for an 8 ohm speaker) at a distance of one half meter, instead of one meter which it normally is. Therefore, the reading will be 6 dB higher than normal.

In other words, this speaker is playing around 94 dB, not 100 dB, for most of it's range, (except above 10,000 Hz).

If such a speaker were mated to your Eminence Beta 15's, they would indeed be shy in the midrange/treble area. Unless they were hooked up in parallel with a second driver/horn combo.


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diyAudio Moderator Emeritus
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Finally, I just want to add that a DJ friend of mine has a 3 cubic foot ported box with a single Eminence Kappa 15 in it. He has TWO KSN 1165A's hooked up in parallel, to increase the sensitivity to match the Eminence 15. He has two of these enclosures, each one with one Eminence and two KSN 1165A's in it. The KSN 1165A is quite inexpensive.

He says it works quite well.

I know your enclosure already has the cutout for the larger horn, but I just hought I would pass that along.
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Joined 2001
Well, Bull, I did some research.

The AC Euro 115 website gives the dimensions of the cabinet. Assuming it is one inch thich plywood, the internal volume should be something around 2.2 cubic feet.

The AC Euro site did not give frequency response charts.

The Eminence site gave the chart for the Beta 15. It is below. You will see a huge peak at 2,000 Hz.

I ran the parameters for the Beta in a closed and a ported box, tuned to 50 Hz-most PA systems are tuned to about that.

The blue line is the lower frequency response for a closed box of 2.2 cubic ft.

The red line is the response for the 2.2 cubic ft. box tuned to 50 Hz.

As you can see, there is a pronounced hump in the response around 100 Hz. When you add it to the huge peak at 2,000 Hz that the Eminence gives, you have a reaponse with two pronounced peaks, one in the midbass and one in the treble. The midrange will suffer in comparison.

Here is the response for the Eminence. Only the response above 200 need be noticed here-the bass is not important in this graph.


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diyAudio Moderator Emeritus
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And here is the graph of the bass range, in both sealed and vented boxes.

When added to the Eminence graph, you see you have a pronounced valley in the response centered on 500 Hz-right smack in the midrange.


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I've just thought i could replace the CTS KSN1197A piezo driver rated 100w max with a CTS KSN1188A rated 400w max and over[which is a Powerline piezo driver with built in PTC resistor and Tungsten bulb]The frequency responce is amazing 800hz-20khz,sens 1w/1m 93 db.
Also the CTS KSN1141 can be considered,as it is a Powerline piezo driver with bulit in protection circuit,rated 400w max and over[because PTC resistor draws current,and to avoid the drop in db,it runs though a tungsten bulb].I've have been told this effect is simular to a level compressor.
They are quite cheap to buy each. £22 each for the CTS KSN1197A,
Which would cost me £44 + the two 20w 20 ohm resistors needed.
Or £10 each for the CTS KSN1188A.
Which would cost me £20 and no extra resistors would be needed,because the more expensive one, is a mid/treble piezo.
OK but how about the phase/polar response of the speaker?

May be getting horrible,as if there were no
existant imaging and depth in recordings.

But if you only want to moove people...
OK,go for it!!!

Customers WON'T hear any difference,anyway.

Sorry,but if you search for the best, ?

Don't put more than one piezzo tweeter on it.
But I guess some 2'' RADIAN would do extremely
better :)
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I aam not sure, for various reasons, that a change of piezo horns is going to solve your problem. Nevertheless, I do have the flyer for the 1141A, so the next two replies will be the flyer reprinted, both sides, in it's entirety.


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diyAudio Moderator Emeritus
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Here is the other side. The flyer really wasn't in that bad a shape. My scanner stinks. It's a parallel port job, (my older computer doesn't have a USB connection), and I bought it for under $39 including shipping. I would have returned the damn thing but the shipping charges would be half as much as the cost of the unit. So I'm stuck with it. It's slow as molasses, and as you can see, it puts smudges on the copy where none exist on the original.


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Yes Nar , I agree with you . A good 2" driver will change the sound in better . But ( I suposed ) that drivers will cost 200-350$ or more plus crossover network ( 40 $) .

Another thing :
It is worth to put a good 2" driver with a only 150W RMS speaker ? I guess , it would be need a 8 - 10 dB damping for driver for matching with bass speaker.

About "phase/polar response of the speaker" make a test with 4 piezo and we talk about later. It would the cheapest way to solve the problem. If somebody spent no more 300-400$ for a loudspeaker pair it would be better to sell this lodspeakers and buy something better instead to tweaking .

Regards !
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Djdan might be right. You might want to consider a different box entirely.

I am not convinced that a new piezo driver would necessarily solve your situation. Don't forget that they are all made by the same company, Motorola, and they are largely geared for PA work.

Please look at the graph for the Eminence Beta. If you want to double check, here is the link:

It would appear that huge peak at 2000 Hz plus a substantial hump at 100 Hz is leaving your midrange, (where most of the music is located), de-emphasized compared to the other ranges! If this is true, then this problem must be dealt with before you go changing piezo tweeters.

Remember that middle A on the piano is 440 Hz-piano manufacturers really slugged it out over this-and that is right in the middle of the de-emphasized area.

Question A: You say that you have four holes in the box. Could you please give me the diameter of those holes? It would help me find out to which frequency your box is tuned. Is there any tube attached to them, or are they simply holes in the wall? There is nothing wrong if they are simply holes-I have seen many PA cabinets tuned that way. Of course, a hole in a 1 inch wall counts as a 1" long port in the computer program.

Question B: Is there any crossover components attached to the Eminence woofer in your cabinet? If so, can you please give the values of the components? It could be that the manufacturer took the 10 dB peak at 2000 Hz out in the crossover. If not, then it is still there and will definitely affect the sound.

1. Yes the 4 holes measure 3 inches,and they at each corncer of the cabinet,the baffle board is 1 inch thick laminated plywood.

2. No crossover,except a 2w 30 ohm resistor on the positive terminal of the piezo horn driver.

3.The internal wiring is not soldered to the drivers,but it uses spade clips,the bass cable is 12 gauge ofc,and the treble cable is 16 gauge ofc.

4. Twin i/4 inch jack socket at back,connectors made by Neutrik
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Among other questions, we have an new enigma here: just what is the cutoff of your horn?

The 1196 horn accepts a driver with a 1 3/8" threaded piece. Motorola makes three horn drivers with 1 3/8" threaded pieces:

A) The 1188A, rated 800 to 20,000 Hz, presumably when mated with the proper horn
B) The 1142A, rated 1,800 to 20,000, also presumably when mated with the proper horn
C) The 1197A, rated 3,500 to 20,000, also when mated to the proper horn.

The larger the horn, the lower the cutoff. You should be able to get good performance down to 3,500 Hz with just a 2" square horn. There should be no need for a giant 15" by 5" horn if you are only going down to 3,500 Hz.

Yet, the 1197A is mated with the giant 1196 horn, which can go down to 800 Hz with other Motorolas horn drivers.

Nobody is telling us if the 1197A driver will go down to 800 Hz when matched with the large 1196 horn. Of course, a horn driver with a number like 1197A implies a match with a horn numbered 1196, but the specs seem to indicate otherwise. Why, oh why, would they list the 1197A horn driver as being useful down to 3,500 Hz if it is designed to go down to 800 Hz when matched to an 1196 horn?

There is no Email address to the CTS Automotive Division, which apparently handles the piezoelectric speakers for CTS. I will give them a quick call and see what they say tomorrow, assuming they are open. It is Columbus Day over here-they possibly could be closed.
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