Hi all,
I have a strange 2nd order crossover that I can't quite connect to the literature.
It has a inductor and capacitor on the high pass side but only an inductor on the low pass side.
In other words the tweeter side resembles this diagram:
Whereas the woofer side resembles a first order crossover like the lower of this:
The crossover cover is marked specifically with 12db ( or 2nd) order.
I am replacing the electrolytic non polar capacitors with metalised film caps and wanted to play with the various online calculators but am finding this difficult to get my head around.
Can anyone explain this to me please?
I have a strange 2nd order crossover that I can't quite connect to the literature.
It has a inductor and capacitor on the high pass side but only an inductor on the low pass side.
In other words the tweeter side resembles this diagram:
Whereas the woofer side resembles a first order crossover like the lower of this:
The crossover cover is marked specifically with 12db ( or 2nd) order.
I am replacing the electrolytic non polar capacitors with metalised film caps and wanted to play with the various online calculators but am finding this difficult to get my head around.
Can anyone explain this to me please?
It's a fairly standard low-cost (which doesn't necessarily mean poor performing) crossover configuration; asymmetrical 2nd order high pass with 1st order low pass. The 2nd order electrical on the tweeter gives it a little more protection and provides a bit of delay which will help line things up.
A point worth noting, if you don't already know, is that acoustical crossover slopes are usually different to the nominal electrical slopes because of the natural driver rolloffs and impedance variations. It's actually quite rare for them to be the same, which is why crossover calculators are usually of limited value as they assume the driver response and impedance are flat. So, for example, a 2nd order electrical crossover may actually provide, say, a 4th order acoustic slope depending on what the driver is doing.
If all you're doing is replacing the electrolytic, then you don't really need to alter the values per se, just swap like-for-like with your choice of MKT / MKP / FF. However, keep in mind that the ESR of the film / FF caps will almost certainly be lower than the electrolytic which may alter the balance a bit; if you end up with a bit too much on the top end, you may need to add a low-value series resistor into the circuit to balance things out. Depends on the original cap, but this isn't a difficult task.
A point worth noting, if you don't already know, is that acoustical crossover slopes are usually different to the nominal electrical slopes because of the natural driver rolloffs and impedance variations. It's actually quite rare for them to be the same, which is why crossover calculators are usually of limited value as they assume the driver response and impedance are flat. So, for example, a 2nd order electrical crossover may actually provide, say, a 4th order acoustic slope depending on what the driver is doing.
If all you're doing is replacing the electrolytic, then you don't really need to alter the values per se, just swap like-for-like with your choice of MKT / MKP / FF. However, keep in mind that the ESR of the film / FF caps will almost certainly be lower than the electrolytic which may alter the balance a bit; if you end up with a bit too much on the top end, you may need to add a low-value series resistor into the circuit to balance things out. Depends on the original cap, but this isn't a difficult task.
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Thanks for the explanation Scott, I had considered adding a capacitor to the woofer side to make it a 2nd order filter but in consideration of your remarks on the difference between acoustic and and electrical filter slopes I will take the view that the manufacturer knew best when designing the thing.
The speakers are MB Quart QM100.03 KX car coaxial speakers. Old but high quality in their day and I got a pair cheap as the electrolytic in one of the crossovers had let go.
Do you think it would be worth experimenting?
The speakers are MB Quart QM100.03 KX car coaxial speakers. Old but high quality in their day and I got a pair cheap as the electrolytic in one of the crossovers had let go.
Do you think it would be worth experimenting?
Providing you're prepared to add a bit of series R if it becomes necessary, no reason why not. I'm not a component obsessive, but shifting to a film cap from an electrolytic will probably be worth doing with the aforementioned caveat in mind. I wouldn't bother spending a packet though, if you want a brand associated with audio, a standard MKP like a Solen Fast Cap, ClarityCap SA, Jantzen Cross Cap or equivalent should be fine.
Actually "Strange second order" is a proper XO terminolgy.
It is used to describe a first order electrical with a resistance in the return path, one of the more experienced speaker builders on the forum once advised me to use inductors with small wire size to increase resistance in the return path when making 2nd order electrical for tweeters for instance. Some optimised XOs combine this function with the Zoble network and minmise component count
It is used to describe a first order electrical with a resistance in the return path, one of the more experienced speaker builders on the forum once advised me to use inductors with small wire size to increase resistance in the return path when making 2nd order electrical for tweeters for instance. Some optimised XOs combine this function with the Zoble network and minmise component count
I've replaced the blown cap with some "audio grade" polyester film caps from an electronic's supplier here in London and I have tosay that it sounds much, much better than the original electrolytic non polar.
Female voices in particular sound much less harsh.
If the tweeter level has changed, the new smothness makes it sound less strident than with the old cap.
I think I will have to change the other one too, bought a capacitor tester to match these with too... 😀
Mylar (polyester) is OK & certainly should improve on a couple of shot bipolars. It's what Harbeth use, and JBL used it for years too in their big systems.
You were right Scott, since I replaced the capacitors the tweeter level is too high
It isn’t apparent with all music or at low volumes but it is at high volumes with well recorded stuff.
What sort of value of resistor would I look to be adding in series with the tweeter and what sort of attenuation would the Values give?
It isn’t apparent with all music or at low volumes but it is at high volumes with well recorded stuff.
What sort of value of resistor would I look to be adding in series with the tweeter and what sort of attenuation would the Values give?