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RE: Understanding Advent Legacy x-over, I have questions...

Posted by seancuster71@gmail.com (P) on March 20, 2025 at 22:04:35

In Reply to: Understanding Advent Legacy x-over, I have questions... posted by walkstoslow on March 20, 2025 at 15:25:12:

Many manufactures run woofers in two-way designs with no crossover this is very very common including Advent. If this is your crossover pictured, then it is a third order crossover on the tweeter and no crossover on the woofer like I said this was common especially speakers in that era. If you could see the back side of the crossover there would be only the speakers' terminals the woofer is driven right off those marked in pink + and yellow - no crossover. The first capacitor is the 6 UF in series with the + then it connects to the 32 UF capacitor also in series with the + in-between the two capacitors you will see the inductor is in parallel contacting the + between the caps and the - at the speaker terminal making a third order crossover for the tweeter. If you do some quick math a 6 UF cap is series, then a .6 MH inductor in parallel followed by a 32 UF cap in series creates a 2500 KHZ crossover for the tweeter.

So, if you want to rebuild the crossover back stock using modern polypropylene capacitors you will run into a few small problems first is electrolytic capacitors have a high ESR value compared to modern poly caps ESR is series resistance. So, just how a resistor can attenuate a tweeters volume more resistance the tweeter plays lower volume less resistance the tweeter plays higher volume.

So, if you switch to modern poly caps with less ESR/resistance your tweeters are going to play slightly higher volume. How much higher maybe a 1/2 dB at most. So, your tweeter will be ever so slightly louder will an increase of 1/2 dB matter? Honestly NO most speakers have around 3 to 5 dB plus or minus variance. So, an increase of 1/2 dB will not be noticeable at all.

With that said I would change the electrolytic to a good poly cap and change that sandcast resistor they are horrible, and they are inductive and degrade sound quality. Use a good non inductive resistor like a mill's resistor sold at parts express that along with good caps will make you and your Advents very happy.

If anyone tells you to put an inductor on the woofer don't do it unless they can provide measurements as proof, it is an improvement if not it is just a guess and not a very good one at that. The designer/manufacture would have used an inductor on the woofer if it needed one. A .8MH inductor in series with your woofer is bad very bad that will start to pull down the woofer's response around 2000 KHZ to 2500 KHZ. which is right around your speakers 2500 KHZ crossover point and a .8 inductor may not sound like a large value but on a woofer with a small voice coil and a considerable amount of voice coil inductance like on the woofer used in you Advents this will cause a huge 6 to 8 dB dip around your crossover frequency of 2500 HZ. Any modification of a crossover without measurements is insane. Thats why all speakers are measured, and all crossovers are designed off those measurements. Sorry but you cannot design or modify a crossover by adding components that do not belong that is insane and then guessing at their value is even crazier. Measurements do not guess unfortunately people do.

And before I forget when you start to search online for 6UF or 32 UF polypropylene capacitors you might find those values don't exist in name brand capacitors or are hard to find so you will more than likely have to buy a 4 UF and a 2 UF to make a 6 UF and a 30 UF and a 2 UF to make the 32 UF if you want name brand caps. Or you could probably find the exact value capacitors on eBay from China but will they be the actual value? probably not.

So, change those caps and change that inductive sandcast resistor to a good non inductive resistor and you and your Advents will be happy.

And the picture of the third order crossover I posted was using your speaker's crossover components value and xsim shows it is a 2500 KHZ crossover point. I googled the crossover point of an Advent Legacy and google says its 2500 KHZ. The crossover pictured does not have the sandcast resistor I don't know why maybe it is the legacy 2 or 3 crossover that might have used a different tweeter. Or it could be an original legacy crossover. Whenever a manufacture buy's speakers in bulk by the thousands they measure them in batches due to the fact there are differences in measurements of a couple dB's. SO, some Advents Legacys might have needed a small 1.3 OHM resistor and other tweeters in different batches did not. And a 1.3 OHM resistor is only going to knock about 1 dB in volume off your tweeter so if you like your highs a little brighter you could try bypassing the resistor with a piece of wire if you like it don't use the resistor when you rebuild if you do not like it then use the resistor when you rebuild but remember to upgrade it to the non-inductive mills resistors.

Hope this helps hope I did not confuse you lets us know how they sound after you rebuild the crossovers.

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