How To Add Piezo ?

[Growly Lytes]

Hi guys,
I recently got hold of a nice little Motorola tweeter that is Piezo.It works fine.I asked a guitar tech how can it be tested & he said to connect it to the input jack on the bass cab so i tried it & it worked really nicely.
Now i wanna install the tweeter but im not sure how to wire it up.
I have some nice speaker cable like the ones from Monster Cable or some thin wiring that cabinet makers use when putting bass cabs together.Its much thinner.Can i use the thick wire,would it make a difference ?
Also how do i connect the cable....positive to positive on the sleeve ? Im not going to use any crossovers or resistors...its piezo & it sounds good connected raw so now its time to connect it to the cab but how is the question ?
Thanks dudes.

 

[billfitzmaurice]

Without any filtering and using only one you'll likely blow it in short order. Piezos can work well, but only in arrays and with a low pass filter.

 

[sprocket123]

You ll need some buffer preamp too , look at Bartolini PUs : Invalid Link Removed

 

[Growly Lytes]

Can i use some resistors to stop that low-end blowing it up ?
It seems to handle everything o.k when raw but i havent yet pumped it to much.
Resistors , filtering or buffer preamp ? What does a buffer preamp do ?

 

[billfitzmaurice]

Can i use some resistors to stop that low-end blowing it up ?

You need to use at least two piezos, preferably four, vertically aligned, wired series/parallel, with a purpose designed high-pass filter.

 

[bobcruz]

There are a lot of inexpensive bass cabs that use a single piezo with no filter and only a beefy resistor to protect it. I'm not saying it's ideal because I'm sure Bill's recommendation IS ideal, but just that it's been done a lot.

 

[B-string]

The main complaint I personally have had with piezos is without a high pass filter the sharp conduction noise (as the piezo starts conducting with full range audio anyway) is disturbing. I suppose this also presents a load shock to the element as well in high power use.

 

[billfitzmaurice]

There are a lot of inexpensive bass cabs that use a single piezo with no filter and only a beefy resistor to protect it. I'm not saying it's ideal because I'm sure Bill's recommendation IS ideal, but just that it's been done a lot.

Key word: Inexpensive. Net cost to add to a cab: two bucks, tops. Also ubiquitous in cheap PA speakers. The result is bad, but that's not the fault of the piezo, it's the fault of poor implementation.

 

[Growly Lytes]

Why then do the electronic stores that ive rang say it doesnt need anything because it only produces the freq it can handle.Ive asked about 3 stores one was an guitar electrician & he also said it should be o.k.
Ive seen heaps of cabs that dont have any filter or beefy resistors.Lots of cabinets have only one tweeter that sound good.The cabinet i got this Piezo is from was a Fender bass cab.It didnt have anything just wired parallel with the speaker.
Anyway ive asked people that know more then me & im not getting one answer but alot of different ones.So im not getting anywhere at this point.
Il keep researching.

 

[billfitzmaurice]

Why then do the electronic stores that ive rang say it doesnt need anything because it only produces the freq it can handle.Ive asked about 3 stores one was an guitar electrician & he also said it should be o.k.
Ive seen heaps of cabs that dont have any filter or beefy resistors.Lots of cabinets have only one tweeter that sound good.The cabinet i got this Piezo is from was a Fender bass cab.It didnt have anything just wired parallel with the speaker.
Anyway ive asked people that know more then me & im not getting one answer but alot of different ones.So im not getting anywhere at this point.
Il keep researching.

Piezos can be used without a crossover, and most of the time they are. They also can be used singly. The result when you do either is that it sounds bad, and since that's how most do it piezos have gotten a bad rep. If you want them to sound good and not be in danger of blowing you use them as I've described.

 

[will33]

Why then do the electronic stores that ive rang say it doesnt need anything because it only produces the freq it can handle.Ive asked about 3 stores one was an guitar electrician & he also said it should be o.k.
Ive seen heaps of cabs that dont have any filter or beefy resistors.Lots of cabinets have only one tweeter that sound good.The cabinet i got this Piezo is from was a Fender bass cab.It didnt have anything just wired parallel with the speaker.
Anyway ive asked people that know more then me & im not getting one answer but alot of different ones.So im not getting anywhere at this point.
Il keep researching.

Their impedance goes way up below where they play, so they accept very litte power down there and do sort of highpass themselves. If you're set on doing it without a filter, put a 4ohm, 10 watt resistor in line with the + wire. It's to protect the amp more than the piezo. They don't have a voice coil, so I don't think they have any inductance and can sort of make the amp "try to play" upwards of 50khz in frequency, like a dog whistle. Some amps can't handle this, so you put the resistor there so the amp "sees something". I may be wrong about the inductance, but the resistor is more for the amp rather than the tweeter.

 

[billfitzmaurice]

I may be wrong about the inductance, but the resistor is more for the amp rather than the tweeter.

The resistor is there so that the amp won't oscillate at very high frequencies, where the very low capacitive load of the piezo can present as a dead short. It won't attenuate the piezo at all.

 

[RoadRanger]

A more typical series resistor is 22 ohms 2-5 watts. If yours is labeled a "PowerLine" (which has internal protection) no prob with wiring it as it was wired in the original cab.

Personally I usually put a 1uf cap in series and a 47 ohm 10 watt resistor across the piezo to filter out some of the lows. If you add a series resistor to the piezo it goes between all that and the + of the piezo.


+Input -> 1uf 250V -> 22 Ohm 5 watt -> +Piezo
-Input -> -Piezo
-Input or -Piezo -> 47 Ohm 10 watt -> junction of the 1uf and 22 Ohm resistor

 

[billfitzmaurice]

A more typical series resistor is 22 ohms 2-5 watts. If yours is labeled a "PowerLine" (which has internal protection) no prob with wiring it as it was wired in the original cab.

Personally I usually put a 1uf cap in series and a 47 ohm 10 watt resistor across the piezo to filter out some of the lows. If you add a series resistor to the piezo it goes between all that and the + of the piezo

The issue with piezos is that they lack adequate high pass slope without external filtering. If you're going to filter at all then you might as well do it right, with a 2nd order highpass, which ends up giving a 4th order response when combined with the inherent roll-off of the piezo. A 5.6uf cap and 5mH coil with a 30 ohm dummy load resistor work very well, giving a high Q Chebyshev alignment that not only eliminates potentially damaging low frequencies but also increases sensitivity above the 2kHz corner frequency, extending by a half octave the useful range of the piezos. But the filter alone won't help by much the 28v capacity of the piezo, so at least two must be used series wired to eliminate any possibility of over-powering.

 

[RoadRanger]

You can do anything from connecting it direct to what I suggested above to what Bill suggests above. Anything you add will most likely make it sound a bit better and last a bit longer. I'd at an absolute minimum add a 22 ohm 5 watt series resistor to protect the amp from the nasty load a "bare" piezo presents to it and that also rolls off the piezo a bit at higher frequencies (unless it is a "powerline" which already has such internally). Does it have any writing on it?

 

[Growly Lytes]

You can do anything from connecting it direct to what I suggested above to what Bill suggests above. Anything you add will most likely make it sound a bit better and last a bit longer. I'd at an absolute minimum add a 22 ohm 5 watt series resistor to protect the amp from the nasty load a "bare" piezo presents to it and that also rolls off the piezo a bit at higher frequencies (unless it is a "powerline" which already has such internally). Does it have any writing on it?

Funny it doesnt say Powerline BUT i have another tweeter ive had for years i have taken from an Etone p.a speaker cabinet.This one does say Motorola Powerline on it (il take a pic of both tweeters) BUT it doesnt fit the profile of the cabs.The shape of it is funny & i dont know how i would be able to install it.It doesnt have the horn portion which was a huge horn shaped bit extending out & it was very heavy.The tweeter itself sounds great but i cant see a way to have it sit in the cabinet.
The Motorola that ive got from the Fender cab is made to sit flush with the other speakers.
What is really worring me is " What actually happens when the amp oscillates because of a piezo tweeter ? What is happening & what can the damage be ?

 

[RoadRanger]

What is really worring me is " What actually happens when the amp oscillates because of a piezo tweeter ? What is happening & what can the damage be ?

99.9% of modern bass amps won't have a problem. If it happens it would probably destroy the tweeter pretty darn quick. I'd put an 8 to 50 ohm resistor in series with it "just in case", 5 or more watts. Radioshack should have something suitable.

 

[billfitzmaurice]

99.9% of modern bass amps won't have a problem. If it happens it would probably destroy the tweeter pretty darn quick.

It will blow the amp output transistors. Most good quality amps use bandwidth limiting so that they won't have an issue. Finding out the hard way that yours doesn't isn't worth saving a couple of bucks on a resistor.

 

[Growly Lytes]

Alright i was to busy to take a pic of the tweeters ive got but i had time today.
What about the ohms ?
The cabinet is wired to be 8ohms.All of the tweeters are around 8ohms one is 7ohms.There is a Le Son High EfficencyDome Tweeter , a Motorola Powerline , a Motorola standard Piezo from a Fender cab & one chunky tweeter thats made by a company a long time ago called 'Plessy' in Australia.Ive never seen a tweeter with magnet size like this,its massive but sounds great.
When i test the Motorola Piezo from the Fender cab it sounds good... maybe not great but it passes.Im getting a better sound plain & simple.The other tweeters im to scared to test because they have coils & i get readings of 8ohms or even 7ohms with the Le Son tweeter.Will all of this effect the ohms of the cabinet ?

 

[RoadRanger]

The non-piezo tweeters will smoke if you hook them up without a proper crossover.