A tweeter with a rated impedance of 6 Ohm would be unusual. Usually rated impedance is either 4 Ohm or 8 Ohm as you probably know.
If you have a DMM, try measuring the DC resistance of the tweeter. Then rated impedance is about 1,2 times the DC resistance.
Even if the rated impedance of the tweeter IS 6 Ohm, the result might be passable connecting it to a high-pass filter designed for 8 Ohm impedance. Another factor is the order of the high-pass filter. First order, then the impedance difference (if there is one) is much less problematic. Higher than first, then getting the load impedance to match the component values of the high-pass filter is more important.
There are many members here who will reject anything other than going full tilt in terms of getting frequency response through the cross-over region exactly right.
-Pete
If you have a DMM, try measuring the DC resistance of the tweeter. Then rated impedance is about 1,2 times the DC resistance.
Even if the rated impedance of the tweeter IS 6 Ohm, the result might be passable connecting it to a high-pass filter designed for 8 Ohm impedance. Another factor is the order of the high-pass filter. First order, then the impedance difference (if there is one) is much less problematic. Higher than first, then getting the load impedance to match the component values of the high-pass filter is more important.
There are many members here who will reject anything other than going full tilt in terms of getting frequency response through the cross-over region exactly right.
-Pete
Not that unusual, I have some.
It sounds like this person has an off the shelf XO. Mike, if this is the case and you are panning to use it, then add a 2 ohm resistor in series with the tweeter and be done with it. I will suggest to you that those XO's use book values which, when you get down to it, aren't going to be what your drivers are and aren't going to perform the way you hope. Designing an XO is a long and labourious project with many parts. Tell us more about your project and maybe we can offer advice. Pics help.
Pete, you give every interested speaker newbie a starting point in your sig line. My sig line? Well, you be the judge. 
Perhaps The Heater might gain from this:
http://www.diyaudio.com/forums/mult...designing-crossovers-without-measurement.html
Allen has done a nice job of making it human for those with just enough knowledge to be dangerous.
Perhaps The Heater might gain from this:
http://www.diyaudio.com/forums/mult...designing-crossovers-without-measurement.html
Allen has done a nice job of making it human for those with just enough knowledge to be dangerous.
Hi, Cal, and others who have piped in with help:Thank you!!!!
Here is the application, which may help on you guys' end: car audio.
I know, people will say that things are 4 ohm in car audio. However, I have decided to switch to 8 ohm speakers for a number of reasons, two of which are sound quality to my ear and the fact that there is a lot of power going out and 8 ohms just sounds good on the far end as far as the woofer is concerned. I have a bench set up to test amplifiers before installing them, and all of them run the same small bookshelf Radio Shack MInimus speakers, and they are 8 ohms, and the sound is terrific.
I have no working knowledge of crossovers other than I have used them in home audio speaker building, and they were designed by the company that made my speakers (in my case the old, original Altec Lansing Corporation - yes, I am older than maybe most people posting - as in Voice of the Theater and 604-8G Super Duplex - I own a pair of the latter, purchased new in the 1970's). I have read some threads on this forum about building crossovers, but to be honest, right now I am trying to learn to repair car amplifiers and have my hands full with learning amplifier design/architecture, so crossover theory and design is going to have to wait. I have to read two books and I just got a CD tutorial from a contributor to this forum.
The crossover is something I found through Parts Express. I figure the car audio application does not have to be perfect, and so I was going to pick one of theirs that matches the frequency cutoff of the woofer and the tweeter (going higher than the low end of the tweeter range and lower than the high frequency cutoff for the woofer).
First Order? Second or Third Order? I don't know what this means. I see it discussed in descriptions of crossovers, but in plain terms maybe someone can tell me what it means.
I did read through the first three pages of that link, Cal, for designing crossovers without measurement. However, I would refer to my paragraph above about learning amplifiers right now. I just don't have time to learn and for this application I figured I could just get a pre-made crossover and put it in with an L-Pad to maybe turn down the tweeter if it is too loud.
So if someone can help me with the first/second/third order concept, it sounds from the posts here that I should be OK using a 6 ohm tweeter with an 8 ohm crossover, at least if I install a 2 ohm resistor in one of the wires to the tweeter (I assume it does not matter which one as long as it helps the crossover see more resistance).
I do own a digital multi meter, so I will test the resistance of the tweeter.
I did read enough posts in my search prior to posting this thread that many on this forum feel that the on line crossover calculators are not reliable. Great. I was thinking that would be a good place to start once I begin to try to build my own crossovers.
One last edit. I like a real sharp sound on the high end. That is why I like the old Altec stuff at home because their drivers have plenty of push and you can hear everything. In a car I prefer to install a titanium dome or similar tweeter. The woofer will be a 6.5 inch woofer from Parts Express, made by Dayton. Hope this helps describe what I am doing.
Mike
Here is the application, which may help on you guys' end: car audio.
I know, people will say that things are 4 ohm in car audio. However, I have decided to switch to 8 ohm speakers for a number of reasons, two of which are sound quality to my ear and the fact that there is a lot of power going out and 8 ohms just sounds good on the far end as far as the woofer is concerned. I have a bench set up to test amplifiers before installing them, and all of them run the same small bookshelf Radio Shack MInimus speakers, and they are 8 ohms, and the sound is terrific.
I have no working knowledge of crossovers other than I have used them in home audio speaker building, and they were designed by the company that made my speakers (in my case the old, original Altec Lansing Corporation - yes, I am older than maybe most people posting - as in Voice of the Theater and 604-8G Super Duplex - I own a pair of the latter, purchased new in the 1970's). I have read some threads on this forum about building crossovers, but to be honest, right now I am trying to learn to repair car amplifiers and have my hands full with learning amplifier design/architecture, so crossover theory and design is going to have to wait. I have to read two books and I just got a CD tutorial from a contributor to this forum.
The crossover is something I found through Parts Express. I figure the car audio application does not have to be perfect, and so I was going to pick one of theirs that matches the frequency cutoff of the woofer and the tweeter (going higher than the low end of the tweeter range and lower than the high frequency cutoff for the woofer).
First Order? Second or Third Order? I don't know what this means. I see it discussed in descriptions of crossovers, but in plain terms maybe someone can tell me what it means.
I did read through the first three pages of that link, Cal, for designing crossovers without measurement. However, I would refer to my paragraph above about learning amplifiers right now. I just don't have time to learn and for this application I figured I could just get a pre-made crossover and put it in with an L-Pad to maybe turn down the tweeter if it is too loud.
So if someone can help me with the first/second/third order concept, it sounds from the posts here that I should be OK using a 6 ohm tweeter with an 8 ohm crossover, at least if I install a 2 ohm resistor in one of the wires to the tweeter (I assume it does not matter which one as long as it helps the crossover see more resistance).
I do own a digital multi meter, so I will test the resistance of the tweeter.
I did read enough posts in my search prior to posting this thread that many on this forum feel that the on line crossover calculators are not reliable. Great. I was thinking that would be a good place to start once I begin to try to build my own crossovers.
One last edit. I like a real sharp sound on the high end. That is why I like the old Altec stuff at home because their drivers have plenty of push and you can hear everything. In a car I prefer to install a titanium dome or similar tweeter. The woofer will be a 6.5 inch woofer from Parts Express, made by Dayton. Hope this helps describe what I am doing.
Mike
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Hi Mike,
...ah yes I seem to have a couple of their parts. 604-8H, 416, 421, 802, 808, 288C, 511B, 811B, 1803B, assorted XO's and other goodies, ya I remember them.
Don't count on it, there's plenty of old farts here. I'm 50 and feel like a spring chicken. The young'uns aren't as interested in building things in their disposable society.
I seem to remember that name, let me go check...
...ah yes I seem to have a couple of their parts. 604-8H, 416, 421, 802, 808, 288C, 511B, 811B, 1803B, assorted XO's and other goodies, ya I remember them.
Stick with 2nd order. What that means is there is a 12dB per octave slope (electrical) after the XO point. When you combine a choke coil in series and a capacitor shunt on a woofer you get just that. Same with the tweeter but you reverse the order of components. It's often the best compromise of driver blending, driver separation and power handling for the tweeter.
You can get a premade and it will work to an extent but it will not be ideal as the XO components rely on impedance. When impedance changes, so does the effect the component has on the driver so you can end up with a gap or an overlap or... Just because it says 6Ω doesn't mean it is the same as another that says 6Ω. You may not even need an L-Pad.
No need to. DCR won't tell you anything about impedance other than if it reads about 4Ω DCR, it is a 6Ω tweeter.
OK. Second order.
And what, in plain terms, does it mean when you have a crossover with a certain "db per octave" slope? Is it reducing or enhancing that many db? And I take it this occurs at a certain frequency?
I will hold off on the L-pad until installation and see if I need it. It sounds as though every crossover has potential issues since impedance is variable with transducers.
What then is a first order and third order xover doing?
Maybe I will buy a tweeter that is already rated at 8 ohms if I find something small enough to fit a surface mount application. I assume if I find a 4 ohm tweeter then I would need a 4 ohm resistor in series with the tweeter wires.
And what, in plain terms, does it mean when you have a crossover with a certain "db per octave" slope? Is it reducing or enhancing that many db? And I take it this occurs at a certain frequency?
I will hold off on the L-pad until installation and see if I need it. It sounds as though every crossover has potential issues since impedance is variable with transducers.
What then is a first order and third order xover doing?
Maybe I will buy a tweeter that is already rated at 8 ohms if I find something small enough to fit a surface mount application. I assume if I find a 4 ohm tweeter then I would need a 4 ohm resistor in series with the tweeter wires.
I don't recall previously coming across a tweeter described as 6 Ohm, but last night going through an up-to-date catalog, I very quickly was able to find several called 6 Ohm. So you are correct.
"dB per octave" slope, in a (passive) cross-over network is the stated number of dB of reducing, rolling off, or attenuating. The rolling off or attenuating, for a second order cross-over network, is -6 dB at what is called the crossover frequency. At what frequency the rolling off starts may not be actually known and is of less concern.
The roll-off of first and third order filters (high or low-pass of a two-way cross-over network) equal respectively -6 dB/ octave and -18 dB/ octave.
Connecting a 4 Ohm resistor in-series with a 4 Ohm tweeter is less acceptable than connecting a 2 Ohm resistor in-series with a 6 Ohm tweeter. That is because with the 4 Ohm tweeter sensitivity of the tweeter is reduced -6 dB. The connecting of a resistor in-series with the tweeter makes a voltage divider. In some situations that might be OK, but it depends on the relative rated sensitivities of your combination of tweeter and woofer.
Some of the above may already be obvious to you,
Pete
A 2way crossover is two filters: a high pass to feed the treble driver and a low pass to feed the bass driver. The "mid" portion of the audio signal can be with either or both of the upper and lower halves depending on what crossover frequency you choose.
The half crossover sees the driver and anything else that is attached to the output of that filter.
In a parallel crossover (as opposed to a series crossover, which is much less common) each filter and it's output loading can be considered quite separately from the "other half".
The half crossover sees the driver and anything else that is attached to the output of that filter.
In a parallel crossover (as opposed to a series crossover, which is much less common) each filter and it's output loading can be considered quite separately from the "other half".
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