Question/s about passive crossover and components?

[Toast_Master]

Hello,

I want to make a 1st order low pass and high pass for a 2 way system, Im going to make it for some simple learning and fun

It involves a 10" mid bass and a high power horn tweeter

I know all the crossover involves is a single capacitor and single inductor of a certain value for a 1st order (unless you series some smaller values to get your target value)

When I find some or read inductor specs they have the reading of resistance of like between 0.1 - 2 ohms, to me that is a lot, which will make my final load over 8 ohms to my amp giving me less power

My questions: How do I, you or manufacturers keep the total load to your specific level of 8 or 4 or whatever you use, because when I measure my current speakers they have a load of 8.0 ohms and they are 2.5 way

When making a passive crossover accurately do you break in the woofer first then measure what the impedance is at the frequency you want to cross then put that impedance value in a crossover calculator?

Im only just starting to learn about frequency impedance

Thanks Cya

[ZilchLab]

DCR is not impedance, though it is a contributor. Impedance varies with frequency.

Manufacturers do not typically adjust impedance in the manner you suggest; it is what it is, and the nominal 8 Ohms spec is often, but not always, the minimum impedance across the frequency spectrum. In lowpass filters, it's usually desirable to minimize the inductor DCR.

Yes, in designing filters, use the actual impedances of the drivers at the target frequency, but ultimately, it's the acoustic crossover performance that counts, i.e. the electrical as combined with the driver(s) frequency response through the crossover region in the final alignment.

[Toast_Master]

Thanks you you clarified what I read, This stuff is interesting

Ive just searched the forums and there have been plenty of people doing what I want to do, and thats use a 10 - 12" driver with a piezo tweeter for a simple 2 way system, but the one thing they all have in common is they didn't want to use crossovers even 1st order, which requires no real extra work and will do wonders in making the project better,

But like them I need a little help,

Im using a 10" woofer and piezo tweeter of sorts, I live in Australia and I am limiting myself to Aussie shops for ease of use,

from what I read if going passive you use parallel crossovers, both units have a nominal impedance of 8 ohms and I'm using 1 of each and want to keep it roughly 8 ohms to the amp,

This brings another question: If I use a parallel type, will that make the nominal load be 4 ohms in practice or does it somehow stay 8 ohms

Or am I expected to use 2 of each in each speaker and then series the 2 tweeters and 2 woofers together to make a 16 ohm then paralell cross them to make a nominal 8 again?

Sorry If im being confusing, its just all this series and parallel stuff with crossovers is new to me

Thanks Cya

[BlueWizard]

Just out of curiosity, why don't you just buy a ready made crossover? Here in the USA, they are about US$20 each, or a simple high-pass filter for less than US$10 each.

Yes, that does add to the cost of the speaker, but it produces a better speaker.

Piezo tweeters typically have an impedance of about 3k ohms (to the best of my memory).

You need a capacitor in series with the piezo to filter out lows, and you need a resistor combination (one series, one parallel) to balance the volume between the woofer and the tweeter. Personally I just use a L-Pad so it is easily adjustable.

Some people, myself included add a parallel resistor across the Piezo terminals to stabilize the impedance. I think I have 10 ohms across mine, but I have mine connected to a 3-way crossover and the crossover assumes that it is working with a roughly 8 ohm speakers.

Which brings up the final point, speaker impedances are all over the place. An 8 ohm speaker is 'nominally' 8 ohms, which means 'sort of' 8 ohms. The impedance across the operating frequency range will drop slightly below 8 ohms and go substantially above. However, I have seen consumer Hi-Fi speakers that drop as low as 3.5 ohms but are still rated as 8 ohm nominal.

If you search the Internet, you will find instructions on how to properly create a crossover, impedance stabilizer, and level control for a piezo tweeter.

steve/bluewizard

[ZilchLab]

Originally posted by Toast_Master
This brings another question: If I use a parallel type, will that make the nominal load be 4 ohms in practice or does it somehow stay 8 ohms

Yes, parallel. Another case wherein all is not what it may seem.

The lowpass filter is high impedance at high frequencies, and the highpass filter is high impedance at low frequencies, so it's only in the crossover region that the actual impedances of both drivers are in parallel, and the system impedance there is the combined impedances of the drivers, which may not be the nominal, and the filters.

Build it and measure the network impedance with the drivers in their final alignment as load.

My message: No textbook or off-the-shelf network is going to perform according to "design" but with ideal drivers. You either have to input all of the variables into crossover modeling software, or empirically optimize a theoretical design using system performance measurements....

[Toast_Master]

Thanks but I wont Buy a pre-built crossover, I'm doing this to learn and have fun building it and Im keeping it simple for a 1st project of this nature,

what I have learned is piezo tweeters are very high impedance across there working range and after a certain level, 30 - 100khz they drop as low as 1 ohm and present problems to amps that run them

What I have read is to parallel an 8 ohm resister to stabilize the impedance, then before this paralleled 8 ohm resister is an 8 ohm L-pad,

Is this L-pad an attenuator of some sorts? to lower the piezo's efficiency, what is this L-pad what component is this

To make it easier for you to help me, Im going to use the
KSN1141A Piezo Tweeter and I'm going to 1st order highpass it at approx 2khz

So to make this usable and not so bad, im going to need some help from you guys I will try and understand to the best I can

So can someone help me with The L-pad and the circuit as a whole

I have a slight Idea of circuit order, the 1st order high pass, then the 8 ohm L-pad then the paralleled 8 ohm resister, is there more I need to add

Thanks Cya

[PeteMcK]

http://www.diyaudio.com/wiki/index.php?page=piezoXO

[BlueWizard]

An L-Pad is a constant impedance volume control for your tweeter.

In my case I have a 12" woofer, 3x9 mid-horn, and a 3x3 Piezo tweeter. The Tweeter is noticeably louder than the mid-horn, so I turn down the L-Pad until the relative volumes match.

An L-Pad always presents a constant load to the amp or to the crossover network regardless of where it is set. At full volume, you have a 600 ohm resistance in parallel with the amp and the tweeter. 600 ohms is substantially large enough to be effectively out of the circuit.

When the L-Pad is turned all the way down, the amp sees an 8 ohm load, and the tweeter is effectively out of the circuit. Thus maintaining a constant 8 ohm load to the amp/crossover across the full range of adjustment.

Because you will calculate your crossover frequency based on a known speaker load, you have to know what that load is.

You can put any resistor in parallel with the Piezo and use that resistor load to calculate your crossover components. Though, certainly some equivalent loads will produce ridiculous numbers for capacitors and coils.

I would say a capacitor connected to the L-Pad would insure stable cross over frequencies and limit the signal level to the piezo. I think the Piezo you picked has some built-in protection circuit to keep dangerous signal levels off of it, but it doesn't hurt to be cautions.

If you read the article linked to above by Peter, the Piezo page indicates that it is not necessary to terminate the piezo with an 8 ohm resistor. To some extent that is a waste of power. You could terminate the piezo with a 15 to 25 ohm power resistor and use a 16 ohm L-Pad, I think that would work fine.

16 ohm L-Pad
http://www.partsexpress.com/pe/showd...number=260-254

I think even with the 10" woofer, the piezo is still going to be too loud and will definitely need an L-Pad to bring it down.

One other reason to put a resistor in parallel with the Piezo it that to the amp, unless I am mistaken, the Pieze looks like a capacitor which complicates matters.

Probably not much help, but there it is.

Here is a link to a Parts Express 3-way project that uses a 3x7 Piezo horn, and an attached link to the crossover network.

Golden Boy Speaker Project -
http://www.partsexpress.com/projects...oys/driver.cfm

Golden Boy Crossover-
http://www.partsexpress.com/projects.../crossover.jpg

You are only concerned with the upper section. The 20 ohm and 33 ohm resistor present a stable 53 ohm resistive load to the .22 uF capacitor/crossover. The 20 ohm and 33 ohm also lower the signal to the piezo tweeter by about 38% (leaving 62% to the tweeter).

A combination like this allows for all the necessary considerations, but I still personally prefer an L-Pad so I have a full range of setting for Tweeter volume.

Steve/bluewizard

[Toast_Master]

I have read your helpful posts and Im going to consider them very much, It seems not complicated at all to improve a piezo tweeter with little effort, ok, can I generalize this info and use it as is because I have no way of measuring impedance at frequency's in piezo,

another question:

should or can I use a High pass on the woofer in the passive crossover?

A simple 1st order one is all I want to use so I get more power handling from it, and so I can tune it higher so I get more spl without the risk of increasing excursion at lower frequencies if there present in the music,

I ask that because I never see them in speaker designs of passive crossovers on this site or in pre made ones, Are they not required because of what?

Thanks so far for all your input,

Thanks Cya

[AndrewT]

KEF are famous for adding a high pass to their speaker crossovers to improve their sound.
There will be others adopting this for at least some of their models.