Hello!
I have a pair of speakers with some rather unusual (and somewhat defective) tweeters. They are 25 ohm and replacements are not easily found.
I would like to modify the crossover so that I can install new tweeters. I have a pair of Audax HD 12X9D25 4 ohm tweeters that I would like to use, if possible. Will replacing the tweeters, regardless of crossover modifications, change the overall impedance of the speaker (which is currently 8)?
Overall specs of the entire speaker:
Woofer - 8 ohm
Squawker - 16 ohm
Tweeter - 25 ohm
Overall - 8 ohm
I have the schematic for the crossover but I am unable to figure out what I am supposed to do. All I know that lines 1 and 4 are for the tweeter, and that the lower right part of the schematic is just for an overload warning -circuit.
If anyone would be willing to give me a hand in this, I would really appreciate it. I can also provide photos of the crossover if that is needed.
The schematic (click)
I have a pair of speakers with some rather unusual (and somewhat defective) tweeters. They are 25 ohm and replacements are not easily found.
I would like to modify the crossover so that I can install new tweeters. I have a pair of Audax HD 12X9D25 4 ohm tweeters that I would like to use, if possible. Will replacing the tweeters, regardless of crossover modifications, change the overall impedance of the speaker (which is currently 8)?
Overall specs of the entire speaker:
Woofer - 8 ohm
Squawker - 16 ohm
Tweeter - 25 ohm
Overall - 8 ohm
I have the schematic for the crossover but I am unable to figure out what I am supposed to do. All I know that lines 1 and 4 are for the tweeter, and that the lower right part of the schematic is just for an overload warning -circuit.
If anyone would be willing to give me a hand in this, I would really appreciate it. I can also provide photos of the crossover if that is needed.
The schematic (click)
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The tweeter is connected to the upper most xover part - the cap, inductor to ground, then cap... looks like pins 1 &4. Looks like a series resistor, adjustable before that for level control.
Assuming the amp can drive the load, you only have to take this filter, a "3rd order" or "18dB/octave" and dump the present values into an online crossover calculator widget, and see where the xover frequency comes out.
Next, you put a 4 ohm load in place of the 25 ohm load in the calaculator and dork it until the values are good for the same xover freq and the 4 ohm load.
The indicator lights may not work properly with the changed impedance tweeter, but who cares...
This procedure will get you "in the ballpark".
To do it most properly, you need to run a freq response curve looking at the xover region and try to optimize the values of the HP filter going to the tweeter you are putting in, in light of the acoustic rolloff that you find.
Also, the new tweeter has to go LOW enough to meet the driver below, matching the original tweeter's abilities in that regard. Kinda depends on what that xover freq works out to for the original one.
What type of tweeter is it? Dome? Cone?
How about a jpeg of the speaker?
Hope this helps...
_-_-bear
PS. no matter what, film caps will sound better than electrolytics (look at what is in there now...)
Assuming the amp can drive the load, you only have to take this filter, a "3rd order" or "18dB/octave" and dump the present values into an online crossover calculator widget, and see where the xover frequency comes out.
Next, you put a 4 ohm load in place of the 25 ohm load in the calaculator and dork it until the values are good for the same xover freq and the 4 ohm load.
The indicator lights may not work properly with the changed impedance tweeter, but who cares...
This procedure will get you "in the ballpark".
To do it most properly, you need to run a freq response curve looking at the xover region and try to optimize the values of the HP filter going to the tweeter you are putting in, in light of the acoustic rolloff that you find.
Also, the new tweeter has to go LOW enough to meet the driver below, matching the original tweeter's abilities in that regard. Kinda depends on what that xover freq works out to for the original one.
What type of tweeter is it? Dome? Cone?
How about a jpeg of the speaker?
Hope this helps...
_-_-bear
PS. no matter what, film caps will sound better than electrolytics (look at what is in there now...)
sometimes 8ohm tweeters could be more like 5-6ohm
and the 4ohm, maybe 3.5ohm, or even 5ohm, where it matters most
so you can't say that its half impedance, thus needs twice as big series cap
and obendrin there's the different acoustic rolloff to consider
it's not really that simple
but you could mount it as is, and give it a listen
might not need that much adjustment
and the 4ohm, maybe 3.5ohm, or even 5ohm, where it matters most
so you can't say that its half impedance, thus needs twice as big series cap
and obendrin there's the different acoustic rolloff to consider
it's not really that simple
but you could mount it as is, and give it a listen
might not need that much adjustment
Thank you for your replies. This seems much more complex than I had hoped, I don't fully understand what I am supposed to do. 
I was hoping that there would be an easier solution.
I guess it would be easiest of all to just dump the current mid range and tweeters (and the entire crossover) and replace those with 8 ohm equivalents, and then make a new filter altogether?
There are no electrolytics in the filter, it's all PIO caps. Here's a picture (not mine) of a filter from a slightly different speaker in the same series:
And here's a picture of the speaker itself (also not mine) -
I was hoping that there would be an easier solution.I guess it would be easiest of all to just dump the current mid range and tweeters (and the entire crossover) and replace those with 8 ohm equivalents, and then make a new filter altogether?
There are no electrolytics in the filter, it's all PIO caps. Here's a picture (not mine) of a filter from a slightly different speaker in the same series:
And here's a picture of the speaker itself (also not mine) -
Ok, first step is to just put an ohmeter across the tweeter's terminals, or the wires that run to the tweeter from the xover.
Figure on the DCResistance being a slight bit lower than the ACR, which is the impedance of the tweeter... if it is truly a 25ohm tweeter (very very unusual) then the DCR will be high, over 16 ohms, maybe above 20 ohms...
You do not need to REMOVE the old caps, you can just ADD capacitance across the old caps to arrive at a value suitable for the new tweeters...
BTW, what is wrong with the old tweeters??
The crossover is really simple - caps pass high frequencies, and coils pass low frequencies. So, you have a cap, then a coil to ground, then a cap... each one is a "6dB/octave rolloff" three together = 18dB/octave rolloff.
The caps electrical size sets the LF point that they work, and this depends on the impedance of the load they see - the frequency does. As the frequency goes LOWER the cap looks more and more like a higher impedance (resistance at some frequency), this works to rolloff the driver as the freq goes down.
Similarly the coil *shunts* the LF to ground, as you go lower it looks more and more like just a piece of wire (almost a dead short).
So, when you change from 25 ohms to 4 ohms you need to scale the impedances that the parts in the xover present.
You can see intuitively that if you have a 25 ohm resistance in series with a 25 ohm resistance the power is split equally between the two resistors. So now if you want the same effect at 4 ohms, you then need a 4 ohm in series with a 4 ohm, NOT a 25 ohms and a 4 ohms...
That's where the online calculator comes in - you just figure out the frequency that the existing xover worked at and then plug in the new impedance (4 ohms) and the old frequency and out comes the new values!
The new caps go in parallel to the old and the new inductor goes either in series with the old or else take the place of the old (just unsolder one end, leave it there and solder in the new part...).
That's it...
Figure on the DCResistance being a slight bit lower than the ACR, which is the impedance of the tweeter... if it is truly a 25ohm tweeter (very very unusual) then the DCR will be high, over 16 ohms, maybe above 20 ohms...
You do not need to REMOVE the old caps, you can just ADD capacitance across the old caps to arrive at a value suitable for the new tweeters...
BTW, what is wrong with the old tweeters??
The crossover is really simple - caps pass high frequencies, and coils pass low frequencies. So, you have a cap, then a coil to ground, then a cap... each one is a "6dB/octave rolloff" three together = 18dB/octave rolloff.
The caps electrical size sets the LF point that they work, and this depends on the impedance of the load they see - the frequency does. As the frequency goes LOWER the cap looks more and more like a higher impedance (resistance at some frequency), this works to rolloff the driver as the freq goes down.
Similarly the coil *shunts* the LF to ground, as you go lower it looks more and more like just a piece of wire (almost a dead short).
So, when you change from 25 ohms to 4 ohms you need to scale the impedances that the parts in the xover present.
You can see intuitively that if you have a 25 ohm resistance in series with a 25 ohm resistance the power is split equally between the two resistors. So now if you want the same effect at 4 ohms, you then need a 4 ohm in series with a 4 ohm, NOT a 25 ohms and a 4 ohms...
That's where the online calculator comes in - you just figure out the frequency that the existing xover worked at and then plug in the new impedance (4 ohms) and the old frequency and out comes the new values!
The new caps go in parallel to the old and the new inductor goes either in series with the old or else take the place of the old (just unsolder one end, leave it there and solder in the new part...).
That's it...
How does the sensitivity of the new tweeters compare to that of the old. If the new ones are more sensitive, then you can pad them down with a series resistor, which will also get the impedance closer to the original.
e.g. A 10 ohm resistor drops the level about 10dB, and gets the impedance close enough that you don't have to change anything in the crossover. It won't be perfect, but will get you in the ball-park. Then you can tweak as needed.
e.g. A 10 ohm resistor drops the level about 10dB, and gets the impedance close enough that you don't have to change anything in the crossover. It won't be perfect, but will get you in the ball-park. Then you can tweak as needed.
re:' you only have to take this filter, a "3rd order" or "18dB/octave" and dump the present values into an online crossover calculator widget, and see where the xover frequency comes out..' tried that, unfortunately the schem shows both caps to be equal value, a 3rd order xover has different values. The xover freq is ~ 6KHz, but that's just a WAG. Maybe it's better simply to scale the component values according to their relative DCRs? (Big caveat, without impedance plots, it's all guesswork...)
Idea: If I disconnect the tweeter, and run its wires out of the cabinet... And then connect that to a new cabinet that I make, which contains three 8 ohm tweeters connected in series. Will this work without any modification to the crossover necessary?
The problem is the range of one tweeter, which only goes up to about 9000 Hz. The other one is better but still not great. There's very little overall treble in these speakers, and I like treble. The impedance is indeed 25 ohm. It is stamped on the magnets and I have checked with a multimeter.
Specs: (use Google Translate if you need it)
Tweeter 6???-6-25
Mid range: 20???-1-16
Woofer: 75???-1-8
The problem is the range of one tweeter, which only goes up to about 9000 Hz. The other one is better but still not great. There's very little overall treble in these speakers, and I like treble. The impedance is indeed 25 ohm. It is stamped on the magnets and I have checked with a multimeter.
Specs: (use Google Translate if you need it)
Tweeter 6???-6-25
Mid range: 20???-1-16
Woofer: 75???-1-8
That might sound worse than just connecting the new tweeter without crossover modification, but I've never done it.
Chances are once you figure out what values you need it should be pretty cheap and easy to twist the new parts onto your crossover.
It would be so much easier if you had a way to measure the response of that tweeter with the existing crossover to see the slope and then figure out what parts you needed to give your new tweeter the same slope.
If I was in your position with no measuring equipment, I'd probably add a little capacitance and inductance to the existing high pass filter and try it, swapping in larger values until it sounded right, but to get a perfect match, you're going to have to measure it.
Yes scale up the 2 caps (C2,C7) and down the inductor by the ratio of the measured new and old tweeters DCR's. The crossover calculators would lead to trouble since most practical designs don't use text book alignments.
Also the adj resistor (R1) needs to scaled as well depending on sensitivities and the DCR ratio, but maybe OK just to try nearer to high gain settings. I would be likely to choose a tweeter close to original as possible ie dome horn ie NOT the typical 4 ohm soft dome flat flange types. I tend to doubt the tweeters DCR being near 25 just by looking at present filter values and experience.
Also the adj resistor (R1) needs to scaled as well depending on sensitivities and the DCR ratio, but maybe OK just to try nearer to high gain settings. I would be likely to choose a tweeter close to original as possible ie dome horn ie NOT the typical 4 ohm soft dome flat flange types. I tend to doubt the tweeters DCR being near 25 just by looking at present filter values and experience.
Most of what you guys are saying is going above my head. I'm learning, though. I think.
I have a program (Download Tone) that lets you play a sine wave and you can change it as it plays back by pulling a scroll bar. Well, one of the tweeters stops being audible at about 8000Hz, and the other at about 11000. This is quite noticeable when listening to music as there's just a lot of detail missing from one of the speakers. The tweeters are also not very loud, which I dislike. And they cannot be heard well at all from the sides. I don't like anything about them. But the rest of the speaker is very nice, which is why I would like to replace the tweeters with something else altogether.
I know that this manufacturer of speakers is a bit of a "gamble". Everything is hand-made and they say that every driver they make measure somewhat differently due to this.
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Most of what you guys are saying is going above my head. I'm learning, though. I think.
I have a program (Download latest version of DeCap) that lets you play a sine wave and you can change it as it plays back by pulling a scroll bar. Well, one of the tweeters stops being audible at about 8000Hz, and the other at about 11000. This is quite noticeable when listening to music as there's just a lot of detail missing from one of the speakers. The tweeters are also not very loud, which I dislike. And they cannot be heard well at all from the sides. I don't like anything about them. But the rest of the speaker is very nice, which is why I would like to replace the tweeters with something else altogether.
I wonder if perhaps the capacitors are electrolytic? I can't tell from the crossover photo what type they are, but if they are electrolytic, it might just be that the caps are giving up.
You could try, just for fun, order a couple of cheap poly caps and replace the ones you have to see if that clears the problem up.
Try this: Pop the old tweeter out and wire up your new one to it's leads and run that sine sweep program and see if it still sounds like it's rolling off early.
the specs, sort of via google translate:
The effective working range of frequencies Гц Hz 5000 .. 25 000
Characteristic level of sensitivity, not less Дб Db 91 91
Operating power Вт Tues 2 2
Frequency response Дб Db 12
Total harmonic distortion in summing up the power, the corresponding sound pressure level at frequencies above 1000 Hz % % 2 2
Rated electrical resistance Ом Ohm 25 25
Limiting noise (passport) power Вт Tues 6 6
Limiting long-term power Вт Tues 8 8
Вт Tues 10 10
Гц Hz 3000+600-1300 +600-1300 3000
Overall dimensions мм mm 100x100x35 100x100x35
Масса Weight г g 1000 1000
So from this it seems they want to xover at 5kHz... top freq claimed is 25kHz...
So, almost any tweeter will sub in, once you adjust the xover... of course running in at 5kHz. is a bit high, given the midrange, but a redesign of the speaker is not on the table..
YES, you can take a different tweeter and place it on top, once the internal tweeter is disabled, preferably by removing the wire to or from the ADJUSTING LEVEL CONTROL for the tweeter.
Then it would be fine to put the new tweeter on top with a dedicated xover and box or whatever you want to hold it up... connect the wires to the INCOMING wires at the back of the speaker... NOT inside to the xover... (unless this monster is self powered...)
Testing the old tweeters is a good idea.
They may be fried, or not... using a sweep, keep the LEVELS LOW. Both for your ears and for your tweeters...
_-_-bear
The effective working range of frequencies Гц Hz 5000 .. 25 000
Characteristic level of sensitivity, not less Дб Db 91 91
Operating power Вт Tues 2 2
Frequency response Дб Db 12
Total harmonic distortion in summing up the power, the corresponding sound pressure level at frequencies above 1000 Hz % % 2 2
Rated electrical resistance Ом Ohm 25 25
Limiting noise (passport) power Вт Tues 6 6
Limiting long-term power Вт Tues 8 8
Вт Tues 10 10
Гц Hz 3000+600-1300 +600-1300 3000
Overall dimensions мм mm 100x100x35 100x100x35
Масса Weight г g 1000 1000
So from this it seems they want to xover at 5kHz... top freq claimed is 25kHz...
So, almost any tweeter will sub in, once you adjust the xover... of course running in at 5kHz. is a bit high, given the midrange, but a redesign of the speaker is not on the table..
YES, you can take a different tweeter and place it on top, once the internal tweeter is disabled, preferably by removing the wire to or from the ADJUSTING LEVEL CONTROL for the tweeter.
Then it would be fine to put the new tweeter on top with a dedicated xover and box or whatever you want to hold it up... connect the wires to the INCOMING wires at the back of the speaker... NOT inside to the xover... (unless this monster is self powered...)
Testing the old tweeters is a good idea.
They may be fried, or not... using a sweep, keep the LEVELS LOW. Both for your ears and for your tweeters...
_-_-bear
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