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Using Capacitors as high pass filter

John_Dikeman

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A while ago on youtube I saw a video that said you could put specific capacitors in line with speakers to create a high pass filter. I can't find that video anymore.
Anyone know more about this?
I just got a subwoofer which I'm running off an Arcam A18 FMJ integrated amp and would like to spare my Focal Aria 906's of their sub 80hz workload.

Thanks!
 

MusicNBeer

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It won't work unfortunately. The impedance of a woofer, regardless of box design type, has one or more resonance peaks. The cap will add a series impedance to this, giving an output frequency response in the lower bass that looks like the impedance curve.

It could only remotely work, and not well, if you start attenuating at several hundred Hz, well above the woofer resonance area.
 

solderdude

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It can be done passively but the impedance of the speaker must be known, a steep (12 or 18dB/oct) filter can be calculated with impedance correction in it for that specific speaker.

As MusicNBeer mentioned...a single cap is not going to work well.
 
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John_Dikeman

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OK, thanks for the info.
I'm sure this is very searchable, but can you recommend an inexpensive external crossover? Or some other solution?
 

pjug

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Using just a cap is the same thing you get with the internal high-pass option in some subwoofers. You can simulate the response if you trace the frequency response and impedance curves in VituixCAD, and then add a series capacitor to see the change in response.

It isn't the best solution, though, as others said. You can get a miniDSP 2x4 for <$100 to do a proper crossover with the speakers and sub if you are just using one input. I assume the Arcam integrated will have plenty of gain to deal with the low output of the miniDSP 2x4. If you need multiple inputs then you are kind of stuck because I don't think the Arcam has a breakout between pre and power amps. In that case the capacitor might be your best solution unless you are willing to get a new power amp (you could still use the Arcam as a pre-amp).
 

pjug

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Something like this?
The schematic shows it’s a capacitor in series with an inductor in parallel. No idea how well it works.
I have played around with these. They do give a 12dB rolloff, but that comes with some peaking and you have to be careful about impedance dips.
 

solderdude

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It would be even better to create a 12dB/oct or 18dB/oct line level filter.
Calculated towards the filter of the sub.
 

pjug

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It would be even better to create a 12dB/oct or 18dB/oct line level filter.
Calculated towards the filter of the sub.
And you can buy the Fmod 12dB if you don't want to make it. The problem is you usually don't know the input impedance of the amp and so the end result is a little unpredictable. Also Fmods are $30 a pair, MiniDSP 2x4 $105 (or $95 without case). Also, I see that the MiniDSP 2x4 revB has 2V output. I wish I had that one instead of RevA.
 

Chrise36

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Input impedance according to the manual is 47k ohms. A simple cap filter will cost less than 10$ for a pair.
 

pjug

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Input impedance according to the manual is 47k ohms. A simple cap filter will cost less than 10$ for a pair.
Plus connectors, plus shielding, plus time, and it might not be pretty compared to Fmods. But still it might be the way to go. But anyway a filter on the input is not an option if the OP wants to use multiple sources with the Arcam.
 

Chrise36

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Plus connectors, plus shielding, plus time, and it might not be pretty compared to Fmods. But still it might be the way to go. But anyway a filter on the input is not an option if the OP wants to use multiple sources with the Arcam.
If the rec out selector works independently from what is heard it is possible.
 

raindance

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Plus connectors, plus shielding, plus time, and it might not be pretty compared to Fmods. But still it might be the way to go. But anyway a filter on the input is not an option if the OP wants to use multiple sources with the Arcam.
Plus it would be silly to high pass the source and then have no bass to send the sub...

I'd suggest measuring to see what you're getting in room with and without the ports plugged in the 906's to get an idea of where to set the subwoofer crossover (measure without the sub to see what is happening).

In my room, plugging the ports of my speakers lessens the overlap with the sub, (which is set to about 50 Hz) to the point where I get fairly flat bass. Different speakers, but the idea could be helpful.

I wouldn't worry about relieving them of power below a random frequency unless you listen very loud or have significant acoustic issues in room.
 
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John_Dikeman

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Plus it would be silly to high pass the source and then have no bass to send the sub...

I'd suggest measuring to see what you're getting in room with and without the ports plugged in the 906's to get an idea of where to set the subwoofer crossover (measure without the sub to see what is happening).

In my room, plugging the ports of my speakers lessens the overlap with the sub, (which is set to about 50 Hz) to the point where I get fairly flat bass. Different speakers, but the idea could be helpful.

I wouldn't worry about relieving them of power below a random frequency unless you listen very loud or have significant acoustic issues in room.

I was thinking of doing it as people on the internet say that freeing up your main speakers from playing those lower sounds helps their performance with everything else. However, no I don't listen at super loud volumes. Is it a non issue?
 

Chrise36

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I was thinking of doing it as people on the internet say that freeing up your main speakers from playing those lower sounds helps their performance with everything else. However, no I don't listen at super loud volumes. Is it a non issue?
Most of the time it helps clearing the distortion if you cross above 80hz. You can try with pc software first how you like the sound of the mains with different high pass frequencies.
 

raindance

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I was thinking of doing it as people on the internet say that freeing up your main speakers from playing those lower sounds helps their performance with everything else. However, no I don't listen at super loud volumes. Is it a non issue?
If you don't have a huge bass issue, then I wouldn't be too concerned. You can't guess at it though, you need to measure. Your speakers are generally well behaved, so integrating the sub as best you can will take a bit of work, but will be worth it. If you choose to add a crossover later, that is up to you, but it is more challenging with a receiver than with separates if you can't separate the preamp from the power amp.

In my case, I found too much audible degradation using a low cost DSP unit to make up for any advantages gained doing the crossover properly. Maybe I am just lazy :)

The tape loop won't be a solution for a crossover, FYI. It would not be not volume controlled.
 

Chrise36

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The power amp seems to be separated in processor mode although the pre amp does not seem to be still active in that mode. The tape loop seems to be fixed output so in that case an extra volume control would be needed unless the sub has such capability.
 
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John_Dikeman

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If you don't have a huge bass issue, then I wouldn't be too concerned. You can't guess at it though, you need to measure. Your speakers are generally well behaved, so integrating the sub as best you can will take a bit of work, but will be worth it. If you choose to add a crossover later, that is up to you, but it is more challenging with a receiver than with separates if you can't separate the preamp from the power amp.

In my case, I found too much audible degradation using a low cost DSP unit to make up for any advantages gained doing the crossover properly. Maybe I am just lazy :)

The tape loop won't be a solution for a crossover, FYI. It would not be not volume controlled.
I did find an anti-mode 8033 cheap locally, should arrive tomorrow. Ah, but I guess that only calibrates it to the room, I should still measure it to get it in sync with the speakers. I am still a bit confused though if calibration is largely just the gain why is it so necessary to measure it as opposed to doing it by ear?
(Sorry, I am a completely new to this, but I'm here to learn!)

Initially I just used a bass frequency track and tried to match the gain so it made a seamless transition between the sub and the speakers.
I also tried comparing the different settings, 25 hz or 20 hz, with or without a port plug to see what had the flattest response. Again, just by ear, but as one of the test tracks i tried mentioned, we all have different hearing, so if it sounds flat to me, maybe that's better than being objectively flat? (heresy again?)

I spent quite some time making subtle changes while listening to different tracks of music as well. I feel like I have it at a setting now where I can't tell the difference between the sub and the speakers and I just notice a big difference when it's turned off.
 
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