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High-pass line filter to relieve main speakers from low frequency

Hi everybody
I recently purchased a subwoofer, KEF Kf92. It has a built in low-pass filter, 24 dB, that can be set from 40-140 Hz. They go with ATC SCM20sl. Their specs are: 80-20 kHz +/- 2 dB, 55-25 kHz : - 6 dB (free standing, which they are, actually: free hanging).
I wonder whether it would be beneficial to insert an high-pass filter before the power amp, consisting of a capacitor with a set point of 65 Hz. This filter might not have a huge impact because the frequency of the ATC SMC20sl rolls off quickly by itself below 80 Hz, apparently by about 12 dB/octave.
My thinking however is: the loudspeakers still receive the complete energy of the low bass from the amp. They might not be able to convert it into sound, but instead convert it into heat and distortion. So a filter will make the life of the amp and speaker easier, since at 33 Hz, only a quarter of the energy is produced.
Do you agree with me?
b_mueller
sd40
40 posts
 
It lools like you guys are looking for an active crossover. Per ocd hifi guy - check out Marchand. - https://www.marchandelec.com/electronic-crossovers.html

Many folk discourage. I have limited knowledge but I believe crossovers cause phase shift. If you have expensive time aligned drivers you may be doing more harm than good.

Marchand has both active and passive crossovers.

On their web site is a paper that discusses why there is no phase shift with a 24dB/octave slope.
I use two of their XM9 active crossovers. The newer one came with a selection of inserts that allow you to choose your crossover point.
hshifi
572 posts
 
Hello,
I have been using the JL Audio CR1 crossover. This is an Audiophile piece of gear. It has XLR and RCA which can be utilized at the same time. Also it has home theater bypass for the subs. It is not cheap. But it is awesome and works with all speakers and subs. It also has a few other features like damping and your choice of roll off. 
terry9
2,333 posts
 
That's right Tom, analogue crossovers introduce phase shift. But, as Sd40 points out, 24 dB crossovers don't; then again, 24dB crossovers do retard the signal by 1 complete cycle at the crossover frequency. Actually, that's an oversimplification and it's more complicated than that, but you get the idea: analogue crossover design is hard.

Then there's the problem with components. You just can't expect $10 parts to sound like $500 parts, and even the most expensive parts are not neutral and will introduce their own sound.

This is the one arena where digital is far superior. Since your speakers fall off sharply, I suspect that your best bet is to not bother with a highpass crossover. But no-one knows until you try it.

IMO
b_mueller OP
45 posts
 
Thank you all, I suppose almost all aspects have been covered by your comments.
Anyway, I bought a set of high-quality capacitors (Duelund JDM Silver Foil, 47 nF) and will insert them at the amp (input impedance 51 KOhm). I will report findings.
b_mueller OP
45 posts
 
I‘ve done it - added a 47 nF Duelund silver cap in line at the power amp‘s input. I soldered between Eichmann bullets plugs and sockets, allowing quick removal. I dislike any modification that adds sockets, wires, soldering points, but there was no space inside the amp. When I used pink noise and measured frequency response in the room, the drop below 60 Hz is steeper, as was predicted for a high pass. Furthermore, the woofer extends much less, indicating less low freq power reaches the chassis.
On sound quality (with KEF Kf92) the effect ist not huge. There is a bit less stress and increased clarity. I will do more comparisons.
https://ibb.co/gFP5Vxw
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