Crossover experts in here?

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Beo_Jean Posted: Thu, Mar 29 2018 11:45 PM

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To follow up the noise problem in my midranges in the Beovox M70 (one side more noticeable than the other) 

You can follow the first part of the discussion here:

https://archivedforum2.beoworld.org/forums/t/30587.aspx  

I think the low volume resonance problem might be due to the introduction of low frequency in the midrange that sounds like a very annoying kind of whisper with bass voices or bass guitar notes.

I now question the changes to the crossover. As you can see in the photo, I used electrolytics, as originally, for the woofer and the filler and chose films for the midrange and tweeter.

I am far from being an expert in crossovers but according to my readings, we cannot replace electrolytics by films thinking to improve the crossover original design without taking into account the ESR and other characteristics of the original capacitors. 

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I wonder if, by wishing to do well, I would not have decreased the resistance of the circuit of the midrange by replacing the electrolytics to films and thus increased by a few dB the low frequencies, which can reach the midrange? Do you have facts or factual theories proving my mistake?

Which part of the schematic is actually the high pass filter for the midrange?

Thanks in advance everyone!

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Beo_Jean replied on Fri, Mar 30 2018 2:05 PM

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Schematic...

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Keri replied on Sat, Oct 20 2018 5:59 PM

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Hi Beo_Jean

I suspect that you are right.. it is all too easy to make things worse by putting in "better" components such as capacitors without taking into account all of the factors of the entire circuit.

We are dealing with Bang & Olufsen, with a fanatical devotion to High Fidelity after all. They didn't choose components based entirely on lowest possible price.  The original capacitors were both of high quality, and were part of the original circuit design. Changing significantly from their original characteristics without altering the rest of the circuit is not likely to improve sound and is more likely to affect some aspect badly. This applies within the Beocenter (or Beomaster) as well as the speakers.

As an extreme contrast, if replacing any components in something like a Crosley, it would be difficult to make things sound worse, sometimes even by hitting things with a hammer!

I also experimented with crossover capacitors on B&O and my best advice is to check the originals for value and ESR. If the values are within 10-20% of specification and the ESR is similar to a new cap of similar type and value it would probably be best to leave them alone! 

Unlike the non-polarized capacitors inside the Beocenter or Beomaster, speaker crossover capacitors have a relatively easy life with much cooler temperatures, no DC bias and usually run nowhere near their limit, unless of course you're running at max volume on a system closely matched to the speaker's capacity.

So far as a high pass filter, wouldn't it be in series with the affected driver?

Good Luck!

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Beo_Jean replied on Sun, Oct 21 2018 9:49 PM

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Hi Keri and thank you for taking the time to answer my concern.

The problem wasn't the crossover but a very odd and unusual problem actually and explained right here.

https://archivedforum2.beoworld.org/forums/p/30587/243597.aspx#243597

If you ever come across buying Beovox M series having those ITT midranges, check this out!

Regards