AudioCircle
Industry Circles => GR Research => Topic started by: Kaiju2189 on 2 Apr 2022, 11:32 am
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I am looking to build a couple of high pass filters like the ones Danny talks about in his Sub integration and bi-amp videos.
Could someone share how to wire these. I think I understand but I would appreciate some expert feedback before I risk any gear.
The design was a capacitor inline with rca connectors to roll off the low frequency to the amp and speakers and a third rca for a full bandwidth signal bypass for the subs.
I have the calculator for the capacitor size needed but could use the help on wiring.
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Heres a basic one i drew for someone else:
(https://www.audiocircle.com/image.php?id=237646&size=large)
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Wow. That goes down as the quickest reply ever. Thanks Hobbs! I am probably missing something. But how do I also wire the bypass that would run to the subs without running through the cap? Thank for helping a newbie.
(https://www.audiocircle.com/image.php?id=239139)
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Here's the insides of that same filter
(https://www.audiocircle.com/image.php?id=239140)
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Thanks Hobbs. Glad I asked. Slightly different than the incorrect way I was going to do it.
Looking forward to seeing some of the potential new designs using the Neo 3 tweeter. Hoping to see another 90+ db sensitive speaker, maybe between the Otica and X MTM. I saw your thread today with a number of designs this morning. Looks like some good ideas are brewing!
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Hi everyone, new here and to DIY (although not to audio),
In my setup - running an integrated amp to a coming pair of GR LGK 2.0 kit speakers in small room - I don't have the option of a filter between pre and power amps.
My question: What value caps should be added to the kit crossover to roll off bass responce at 55-60 hz to cross with small fast sub? And what quality caps are needed? Guess pretty HQ caps since HF will be filtered through = $$$?
Thanks and kind regards
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When putting a high pass filter after the amp, sizes get rediculous.
You're looking at 300uF to roll everything off below ~65Hz
330uF for ~60Hz
360uF for ~55Hz
In which case youll need to purchase 3x 100/110/120uF per speaker. The bundled caps also be so large that you'll want go keep them external from the speaker.
The only way to use a single small cap would be with an electrolytic capacitor. And we really don't recommend that, it will really hamper the speaker's performance.
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The natural -3dB point is 80Hz, which will allow you to get away with 240uF instead.
And Solen does offer a single 240uF capacitor.
https://solen.ca/products/capacitors/fast-capacitors-250v-pa-series-metallized-polypropylene/solen-fast-capacitors-pa24000-240uf-250v-metallized-polypropylene-film/
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Thanks for your swift reply Danny 👍 Much appreciated! Did not expect a reply from the master himself (actually posted in the forum so as not to disturb you good folks at GR Research with what is probably a pretty generic inquiry).
Guess I'll skip the filter then and let them roll off naturally as you designed them and fill out with REL T Zero from 75-80 Hz.
Compliments on your work! - I have been looking for a HQ small speaker both fast on micro dynamics and with a natural tonal balance; pretty hard to find (as you would know) :-) Was considering LS3/5a types but been there done that, natural tonal balance spectacular, but tend to sound artificially slow and dead on the bottom end and dynamics.
Also: My sincere compliments for you sharing your substantial experience and knowledge on your YouTube channel, very inspirational, and confirms what I've experienced myself, without being able to dissect the factors behind it (advantages of bi-wiring being mostly marketing, low mass / small cone movement (tradeoff) sounding more natural, Especially your point on spectral decay makes a whole lot of sense to me after having bought factory speakers for 20+ years in the §6-7k range and typically left unsatisfied with either the (too slow) speed of the woofers messing up micro dynamics and timing OR the tonal balance being too skeletal in fast sounding speakers, more often than not getting one or the other (Harbeth/Dynaudio vs PMC for instance).
Best regards from Copenhagen, Denmark
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Any sufficiently advanced Hobbs is indistinguishable from Danny.
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Good stuff- thx
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Thanks for your swift reply Danny 👍 Much appreciated! Did not expect a reply from the master himself (actually posted in the forum so as not to disturb you good folks at GR Research with what is probably a pretty generic inquiry).
Guess I'll skip the filter then and let them roll off naturally as you designed them and fill out with REL T Zero from 75-80 Hz.
Compliments on your work! - I have been looking for a HQ small speaker both fast on micro dynamics and with a natural tonal balance; pretty hard to find (as you would know) :-) Was considering LS3/5a types but been there done that, natural tonal balance spectacular, but tend to sound artificially slow and dead on the bottom end and dynamics.
Also: My sincere compliments for you sharing your substantial experience and knowledge on your YouTube channel, very inspirational, and confirms what I've experienced myself, without being able to dissect the factors behind it (advantages of bi-wiring being mostly marketing, low mass / small cone movement (tradeoff) sounding more natural, Especially your point on spectral decay makes a whole lot of sense to me after having bought factory speakers for 20+ years in the §6-7k range and typically left unsatisfied with either the (too slow) speed of the woofers messing up micro dynamics and timing OR the tonal balance being too skeletal in fast sounding speakers, more often than not getting one or the other (Harbeth/Dynaudio vs PMC for instance).
Best regards from Copenhagen, Denmark
'Guess I'll skip the filter then and let them roll off naturally as you designed them'
Is this what is recommended? No hipass filter on the 2.0 when used with subs. Are you sure you want to do that?
What good reason would there be for not doing it. I don't mean passively, of course.
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The main benefit of a high-pass filter is to give the LGKs better power handling, and has the secondary benefit of cleaning up the mids.
That said, if you can't achieve it by putting a cap between the amp/preamp, (ie using an integrated device) you're going to need a cap that is orders of magnitude larger to achieve the same effect.
For instance, high-passing to a 100KOhm amp will need a 0.015uF for a -3dB of 106Hz or 0.022uF for 76Hz.
On the speaker side, youre going to need a 240uF cap to get a roll off of around 80Hz or 200uF for 100Hz.. at which point it becomes expensive/impractical. It will also take up too much airspace inside of the LGK cabinet.
If your amp has the ability to adjust the bass extension to the speaker, then use that to attenuate the bottom end.
But if you dont have the ability, then there's not likely another realistic option, no?
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I’ve had the LGK 1.0 in my office system for many years. This system has an integrated amp and a sub so no high pass filter. The LGKs roll off naturally and the sub is adjusted accordingly. Since the speakers are only 3ft away, they don’t need much power so not having a hgh pass filter is no big deal.
Would a high pass filter make them sound better in this situation? Possibly. Is one necessary? No. If you want to be able to high pass the LGKs, you will need to replace your integrated with separates. Will it be worth it? For me, in my office system, the answer is no.
My main system does have separates so I can use an inline high pass filter. However, this is not why I have separates in that system. I went to separates for all the other sonic benefits separates bring to the table. The ability to high pass the mains was an added benefit.
Every system choice has tradeoffs. Each person has to decide which tradeoffs work best for them.
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Hobbs, can you share the formula to figure this out?
"For instance, high-passing to a 100KOhm amp will need a 0.015uF for a -3dB of 106Hz or 0.022uF for 76Hz."
-Joe
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Hobbs, can you share the formula to figure this out?
"For instance, high-passing to a 100KOhm amp will need a 0.015uF for a -3dB of 106Hz or 0.022uF for 76Hz."
-Joe
As many times as this question comes up you migkt want to make the link to the calculator a sticky
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Thanks for the suggestion Mike. I tried to be proactive and search for it but after 30 separate links to threads I decided to just ask.
-Joe
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http://www.learningaboutelectronics.com/Articles/High-pass-filter-calculator.php
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As many times as this question comes up you migkt want to make the link to the calculator a sticky
Yeah. On some other forums, they use a single sticky to provide links to some of the most asked questions. This could be one of them.
Today, someone asked about the maximum length of the wire from the servo subs to the amps. Danny has answered that question already, but it's buried somewhere in this forum. This sticky could provide the link to it.
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Generally speaking the length needs to be 3-4 feet. The longer it gets the less effective the amp is at controlling the subs at higher frequencies.
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Thank you Sir.
-Joe
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Great info in this thread!
I love this forum.
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Thought I would restate a link that Danny had posted on another thread a while back. Simple calculator that’s easy to use.
http://www.pronine.ca/capimp.htm
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Does phase shift become a problem to correct for when using a high pass filter?
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Does phase shift become a problem to correct for when using a high pass filter?
It depends:
https://www.allaboutcircuits.com/technical-articles/understanding-phase-shift-in-analog-circuits/
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After using a variety of series capacitor high-pass filters on my NX-Oticas, I've found I like the sound better without the caps. I get a smoother integration with my OB subs, and the mid to upper bass sounds fuller.
So, for now, I'm leaving them out.
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Does phase shift become a problem to correct for when using a high pass filter?
Phase shift is definitely a problem when using a high pass filter. A single cap is a 45 degree shift at the crossover frequency. Most low pass filters in subwoofers are between 2nd and 4th order, which is a 90-180 degree shift at the crossover frequency. When you have a 45 degree shift one way and a 90 or 180 degree shift the other way, you will need some kind of delay and a polarity reverse to get them to work together properly. I encourage people to leave their main speakers full range.
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After using a variety of series capacitor high-pass filters on my NX-Oticas, I've found I like the sound better without the caps. I get a smoother integration with my OB subs, and the mid to upper bass sounds fuller.
So, for now, I'm leaving them out.
This makes a lot of sense.
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I've tried in-line caps in the past and ultimately just got rid of them. To me it sounds better with the speaker run full range.
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Subset of Passive Line Level XOs (PLLXO): https://www.t-linespeakers.org/tech/filters/passiveHLxo.html
dave
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I've tried in-line caps in the past and ultimately just got rid of them. To me it sounds better with the speaker run full range.
I agree.
Also, in my experience, it is easier to integrate the subs with the mains without the filter. Phase shift, like DannyBadorine has already mentioned, is the main issue. Us REW measuring nuts see it in the measurments.
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If I was doing this for a balanced signal going from pre-amp to amp, using XLRs, then this filter would need two capacitors, right?
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If I was doing this for a balanced signal going from pre-amp to amp, using XLRs, then this filter would need two capacitors, right?
Correct. One cap for each positive and negative legs. Ground leg will remain unchanged.
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If I was doing this for a balanced signal going from pre-amp to amp, using XLRs, then this filter would need two capacitors, right?
You will want to make sure that those caps are matched exactly or you will get some problematic phasing.
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Here's the insides of that same filter
(https://www.audiocircle.com/image.php?id=239140)
Hobbs! I got help from you not long ago with this filter, THANKS! Great.
But now I’m planning to build two Monoblocks with XLR.
And I didn’t check previous post….. :duh: :duh: :duh:
But a drawing would be great.
You do have a great drawing skill. :D
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But a drawing would be great.
You didn’t follow the link i provided. Formulas and a spreadsheet as well.
Here is one of mine… 1st order 240Hz, to biamp Tysen V2.
(https://p10hifi.net/forum/Tysen-PLLXO.jpg)
dave
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Rolling off my nx-otica at ~55hz (3db point) via XLR to amp from my modified schitt fretya + (changed all coupling caps to VCAP ODAM) for 95% of songs it doesn't need it, but when I listen to some really heavy EDM songs with a lot of 20-30hz I will bottom the mid drivers when I am playing quite loud. I just don't want to worry about it. 27k input impedance amp so I used 4 0.1uF VCAP ODAM
I tried sonic caps for fun on the high pass filter, sound was okay but lacked a lot of clarity and punch
Then I tried the miflex pure copper, lot more meat on the bones and better detail across the board
Then I tried VCAP ODAM, without burn in - WOW. FAR better than the above two. VCAP ODAM had everything the pure copper miflex did but added far more details but the biggest thing was the SPACE between notes and THE SOUND STAGE BECAME MASSIVE. I then let 400 hours on them and I about cried at the sound. They sound better with these caps then without them. Using 4 perfectly matched to 0.2% tolerance since doing balanced XLR cables from preamp to amp.
I have my nx-otica using all vcap ODAM bypassed by dueland pure silver 0.01 on the tweeter and the mid cap bulk cap is the sonicap but with a 0.1uF vcap ODAM over the miflex and then another 0.01 dueland pure silver and the detail, musicality, and soundstage is just utter next level real.
I personally wouldn't use a miflex anymore after hearing the VCAP ODAM.
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my modified schitt freya +
May i ask how you get this thing apart?
Mine broke, but i am stymied trying to get in to look.
dave
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I will be posting a full upgrade video on youtube before long, but long story short
pull off volume nob comes right off just pull hard. Remove the 10mm nut and washer.
Now back edge of the unit, either use a rubber mallet or I just use my fist (make a fist, soft bottom part of your hand) and in both back corners HIT the corner at a 45 angle directing the force from back of the unit towards the front. Do in both back corners. Don't be afraid to give it some force. Then the top will slide about 1" inch forward and you pull the top off. Don't be afraid to give it a good wack. I've opened mine about 4 times now. Easy.
Pro tip when your buttons fall off the front when you take it off, don't worry. Put tape on the holes from the front of the cover so the buttons can be put back in and stuck to the tape as you go to put the top back on. Then when you go to put it back together and then take the tape off the front it's as good as new.
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Thank You!!
:^)
dave
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Here's the insides of that same filter
(https://www.audiocircle.com/image.php?id=239140)
Here’s my version, but I’m getting really bad noise come in through these. I can tell why, since there’s a decent amount of exposed wire, but what can I do to fix this? Thanks!
(https://www.audiocircle.com/image.php?id=244082)
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Can I ask what amp or amps you are using?
Rolling off my nx-otica at ~55hz (3db point) via XLR to amp from my modified schitt fretya + (changed all coupling caps to VCAP ODAM) for 95% of songs it doesn't need it, but when I listen to some really heavy EDM songs with a lot of 20-30hz I will bottom the mid drivers when I am playing quite loud. I just don't want to worry about it. 27k input impedance amp so I used 4 0.1uF VCAP ODAM
I tried sonic caps for fun on the high pass filter, sound was okay but lacked a lot of clarity and punch
Then I tried the miflex pure copper, lot more meat on the bones and better detail across the board
Then I tried VCAP ODAM, without burn in - WOW. FAR better than the above two. VCAP ODAM had everything the pure copper miflex did but added far more details but the biggest thing was the SPACE between notes and THE SOUND STAGE BECAME MASSIVE. I then let 400 hours on them and I about cried at the sound. They sound better with these caps then without them. Using 4 perfectly matched to 0.2% tolerance since doing balanced XLR cables from preamp to amp.
I have my nx-otica using all vcap ODAM bypassed by dueland pure silver 0.01 on the tweeter and the mid cap bulk cap is the sonicap but with a 0.1uF vcap ODAM over the miflex and then another 0.01 dueland pure silver and the detail, musicality, and soundstage is just utter next level real.
I personally wouldn't use a miflex anymore after hearing the VCAP ODAM.
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Here’s my version, but I’m getting really bad noise come in through these. I can tell why, since there’s a decent amount of exposed wire, but what can I do to fix this? Thanks!
(https://www.audiocircle.com/image.php?id=244082)
Any help on this?
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That's really odd, my guess would be either a bad connection somewhere, it's being placed too close to other electrical devices, like a transformer within an amplifier or other electrical device, and it's picking up a lot of electrical noise from it, like an antenna, or it's somehow creating a massive ground loop.
Does the sound go away if you touch the outer housing of the full range output, or does get worse?
If it's acting like an antenna, or has to be kept close to powerful transformers then using some copper shielding kits on the inside like you see for guitars may be a good idea to reduce/prevent EMI issues.
https://www.stewmac.com/electronics/shielding/self-adhesive-shielding-kit/?utm_source=google&utm_medium=shopping&utm_campaign=2022-09-gp&gclid=Cj0KCQjwj7CZBhDHARIsAPPWv3d3h9QOx80RGneVEPEByXqoI-8k1tidif-GergTGkJRliAVUdPDJKQaAsMyEALw_wcB
I would also check if it's causing a ground loop. Do both connections exhibit the same noise issue? does it exist if only one connection is made, or is it only with both connections are used that the issue arises?
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Any help on this?
I am kind of wondering if it is a ground connection issue.
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Any help on this?
Those solder joints are horrible. It's probably diode effect from the cold joints causing RF pickup.
1. The leads ends are tinned first.
2. A good mechanical conection is made to the solder tabs before soldering.
3. The ground tabs should be positioned between 2 nuts not compressed between one nut and the plastic case.
4. You need to apply enough heat to allow the solder to flow uniformly without spent solder sticking to the iron when removed.
5. Practice.
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I hadn’t had any issues all weekend. I run my music off of a desktop, but today as soon as I arrived with my work laptop to put in more hours at home the sound started again, so I’m wondering if it’s picking up WiFi noise.
Edit:As soon as I got done working I turned off my work laptop and the issue went away. So it’s definitely causing some signal to be picked up by my filter.
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In my situation I am using a pair of GR-Research OB subs in parallel to Magnepan 2.7 QR speakers and would like to roll off the 1st octave of bass to the Maggies. What would you propose in the scenario where you are running a powered subwoofer using high powered input (speaker level) in parallel with your main speakers?
In the video associated with this thread, Danny specifically says this will not work well due to the necessity of using large value capacitors which smear the sound.
The sound I get running in parallel is good, but I would like to see if it can be improved.
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In my situation I am using a pair of GR-Research OB subs in parallel to Magnepan 2.7 QR speakers and would like to roll off the 1st octave of bass to the Maggies. What would you propose in the scenario where you are running a powered subwoofer using high powered input (speaker level) in parallel with your main speakers?
In the video associated with this thread, Danny specifically says this will not work well due to the necessity of using large value capacitors which smear the sound.
The sound I get running in parallel is good, but I would like to see if it can be improved.
This little coupling cap and by-pass will work if using a separate amplifier for your main speakers. If you are using an integrated amp or receiver then this type of high pass filter system will not work.
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It is not an integrated amp, so if I could run a separate RCA cable to the location where the speakers are I could use the LFE from the sound processor or a simple low pass filter such as this, on the input side of the sub's plate amp.
Running the extra cables is the issue, which is why I run the sub & speaker in parallel.
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I think Danny should upload a specific video explaining the high pass filter and the improvements it brings.
Yesterday I posted on twitter about it, in Spanish, explaining another possibility in case of not using a subwoofer. By filtering out what the KEF Q100's coaxial woofer does not reproduce directly, I get clearer sound and... more bass!!!
https://twitter.com/nauscopio/status/1657767153850892288
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He already has
https://youtu.be/65eFr2rKy3M
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Thank you / Muchas gracias!
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Heres a basic one i drew for someone else:
(https://www.audiocircle.com/image.php?id=237646&size=large)
Would this work for balanced interconnects? If not what would that circuit look like?
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Would this work for balanced interconnects? If not what would that circuit look like?
Balanced is going to be quite different
It will be like this:
(https://www.audiocircle.com/image.php?id=252978&size=xlarge)
Here's one with both channels in the same chassis:
(https://www.audiocircle.com/image.php?id=252979&size=large)
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Balanced is going to be quite different
It will be like this:
(https://www.audiocircle.com/image.php?id=252978&size=xlarge)
Here's one with both channels in the same chassis:
(https://www.audiocircle.com/image.php?id=252979&size=large)
Hobbs. Thanks for this picture. But on which lead do we connect the sub out, if I use rca? XLR looks obvious, but do show us. Thanks
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If you want a full-range RCA out on an XLR bypass:
Positive will be pin 2
Negative will be pin 1
If you want an all RCA filter with both full range and highpass:
(https://www.audiocircle.com/image.php?id=253157&size=xlarge)
Left: input from preamp
Bottom: full range out
Right: high pass out
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hey
just wondering if someone could help me out a little, not super knowledgeable about the technical details here but was looking for some advice on what to frequency i should start my -3db roll off, i have some dynaudio geminis (mtm design with dynaudio 15w75 mid drivers) with with a resonant frequency at 55 (so i thought a roll off at 50hz?)
my amps input impedance is 47k so a .68uf cap would be suitable to do my roll off at 50,
below i have upoaded a image aswell as a link of the drivers specs from the dynaudio site, im just wondering if there is a more suitable point to roll these off based on the specs of the driver, cheers
https://site.diy-loudspeakers.com/images/datasheets/loudspeakers/dynaudio/WOOFERS/DYNAUDIO_15W75.pdf
(https://www.audiocircle.com/image.php?id=254217)
regards
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Are they in a sealed or ported box?
Also keep in mind that your actual crossover point is going to be where the speakers and subs are both 6db down.
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hey
just wondering if someone could help me out a little, not super knowledgeable about the technical details here but was looking for some advice on what to frequency i should start my -3db roll off, i have some dynaudio geminis (mtm design with dynaudio 15w75 mid drivers) with with a resonant frequency at 55 (so i thought a roll off at 50hz?)
my amps input impedance is 47k so a .68uf cap would be suitable to do my roll off at 50,
below i have upoaded a image aswell as a link of the drivers specs from the dynaudio site, im just wondering if there is a more suitable point to roll these off based on the specs of the driver, cheers
https://site.diy-loudspeakers.com/images/datasheets/loudspeakers/dynaudio/WOOFERS/DYNAUDIO_15W75.pdf
(https://www.audiocircle.com/image.php?id=254217)
regards
Actually, you will need 0.068uF for a -3dB at 50Hz (though it's a fairly uncommon value to find high quality caps)
Considering its a ported MTM design, that should be fine with the -6dB around 40Hz.
You can also use 0.047uF for a -3dB around 72Hz, with a -6dB around 55Hz.
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hey
thanks for the quick replies (also thanks for pointing out my error missing the zero on the value, life saver haha)
I've just found the that yes those caps are quite hard to find, (especially in Australia)
if I were to use a 0.047uf with a roll off at -3db around 72hz/-6db at 55db, would that be affecting the speakers natural roll off to much? i just assumed this inline filter idea was more towards rolling off bass the speaker cant produce?
and also, in Australia the decent caps i find here are janzten but the shop doesnt stock values that small, can you please recommend some other good brands i should look into, i know Danny likes the soni platinum/miflex, are there any other caps brands that are also recommended or that have sounded decent used in this apllication?
regards
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Question regarding integrating the sub back in once the filters are built:
I get the cap value is being selected to high pass the power amp and the connected speakers based on both the -3dB point of the speakers and input-Z of the power amp. But , then how do you determine the -6dB point to crossover the subs in? Would that also be a spec from the speaker manufacturer or is there an easy way to approximate that frequency?
thanks
JS
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For a single pole high pass filter, the -6dB point is one octave below the -3dB point. That is why a single pole filter can be both a Butterworth and Linkwitz-Riley filter.
As an example, if the -3dB point is 100Hz, the -6dB point will be 50Hz.
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Ah… makes sense.
So if the cutoff freq were 70hz, the crossover freq for the sub would be 35Hz?
Does this still apply if the speakers are sealed?
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The input to the amp impedance does not change, so the frequency response of the high pass filter does not change no matter what speaker load is on the amplifier.
Now, if the response of the speaker is not flat in that frequency range, it is a combination of the responses. That is why there is an electrical frequency response and an acoustic frequency response when they are combined for the total acoustical frequency response.
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Thanks for that
To be specific, I'm asking about where to set the crossover frequency on the sub
For instance:
If Amp input Z is 10k Ohms
& desired high-pass cutoff (-3db) down on the monitor is say 80Hz
...so cap is .2uF.
All good, but ...to blend at the 6dB down point, you just set the crossover frequency at 40Hz?
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Depends on the amp.
The A370XLR3 servo amp has an 80Hz low pass filter setting and it is -6dB down. There is also an 50Hz setting on the amp at -6db down. If other mode is needed when the AVR mode and external low pass is needed at different frequencies. That is according to the spec sheet for those amps.
In that case the high pass filter -3dB point would be 160Hz at -3dB for a 80Hz -6dB point for the main speakers. For a 10K Ohm input impedance, the series connected input cap would be 1000pF or 1nF in value. You want two matched caps to make sure the channels are both the same.
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Hello, can i use Danny roll-off filter between DAC and integrated amplifier, in my case Marantz PM6007?
I dont understand why he claims it doesnt work.
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I dont understand why he claims it doesnt work.
The filter will only affect the DAC and the other sources on the integrated will be unfiltered.
If it's a tube DAC with output capacitor then adding another series cap may not work as expected. But if it's all solid state DAC then the filter should work as expected, but only on the DAC.
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Hello, can i use Danny roll-off filter between DAC and integrated amplifier, in my case Marantz PM6007?
I dont understand why he claims it doesnt work.
You can, but it will roll off the bottom end across the board.
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The filter will only affect the DAC and the other sources on the integrated will be unfiltered.
If it's a tube DAC with output capacitor then adding another series cap may not work as expected. But if it's all solid state DAC then the filter should work as expected, but only on the DAC.
Thank you.
The DAC is a solid state and is the only source i use.
Just want to add two active bass sections and cut bookshelfs for better presentation, but dont want to use DSP or commercial active cross.
At final, the Danny's solution will work in my case, right?
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You have to take the unfiltered signal for the active bass from the DAC before it's filtered, using RCA splitter cable.
You can't use the subwoofer output jacks from the Marantz to your active bass because the highpass filter already peeled out the bass, like Danny said above.
So then, if you take bass signal from DAC with no delay, but your Marantz DSP amp converts all analog inputs to digital for DSP before amplification then the amp might be adding a delay which makes the active bass and main speakers out of acoustic alignment, causing blur through freq band they overlap.
If the Marantz has a pure analog signal path including volume control, etc, then it won't add delay and it should work. But if it's typical of modern receivers and DSP integrateds where analog inputs are digitized and every signal goes through DSP then it might not work.
Fun to try, can't hurt.
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One issue with connecting the sub directly to the DAC is that unless the volume can be controlled digitally via the source, the sub will remain at a constant volume and will need to be independently adjusted up or down any time the integrated amp is adjusted.
You will also need to know the input impedance for the integrated amplifier as a whole, and I'm not sure how available that information is.
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My main amp is a DIY 300B, the input stage is a WE437@ but instead of a grid leak (which is a resistor to ground before the input tube), I'm using a grid choke instead, no coupling cap and inline grid stopper of 100 ohms. The DCR of the grid choke is 1.3K ohm, but it's AC impedance is 500 Meg ohm. I'm using a modified Dahlquist Low pass active, high pass passive crossover. If I use 1.3K the calcs say if I use a 1.5uf cap, my freq of roll off is just a tick over 80hz. I assume it's the DCR that needs to be used in this case, rather than a conventional "input impedance, as I have no way of physically measuring it, and there are no "specs" for this DIY amp