Using Roon for Crossover and Subwoofer Integration

I want to use software to perform crossover between main speakers and subwoofers (probably 100Hz 24db/Octave), apply FIR convolution filters for speaker / room correction (generated using REW / rePhase) and be able to vary delay to subwoofers to reduce room modes. Overall budget is up to £1,000.

I understand, from comments by @brian that the simple solution - having 2 DACs, connecting one to main speakers and one to subwoofer, applying filters in Roon to each one and then grouping them) will not work because RAAT will not keep the 2 outputs sufficiently in sync for this purpose.

Have thought of 4 ways to do this.

  1. Use a miniDSP SHD. Crossover would be done in SHD using parametric equaliser. Equalisation would use FIR convolution filter in Roon (SHD does not allow user-generated FIR filters to be loaded). Delay could be in SHD or Roon. Advantage - all in one box. Disadvantage - over budget and paying for Dirac which I don’t want to use.

  2. Use a mini DSP nanoDigi to drive 2 DACs. This uses SPDIF input and output. In theory, DACs driven by SPDIF should (if DAC well designed) stay in sync. Benchmark say that their DACs do this. I already have a Benchmark DAC3 so could buy used DAC2 and be within budget.

  3. Same ideas as (2) but with USB input using miniDSP U_DIO8.

  4. Either (2) or (3) but using same DACs e.g. Topping D50s, Topping DX3 or SMSL M8A.

If anyone has any experience of doing something like this or has used any of the products mentioned I would appreciate your comments - or suggestions for alternatives!

You can also use something like a DSPeaker Anti-Mode 2.0 as crossover to integrate/correct the sub-woofer(s). You can still use a convolution filter in Roon for room correction as the Anti-Mode just controls the sub-woofer(s) (room modes). But you don’t need 4 DAC-channels when you connect the Anti-Mode after the DAC/Roon endpoint.

This way I get a good sub-woofer integration and a system that I can listen to even without Roon.

Thanks for the suggestion. Interesting idea.

Had a look at the manual. I want to be able to roll-off main speakers so that they don’t get low bass. Looks like I would need to Anti-Modes to do this (the manual refers to needing 2 Dual Cores for a 2.2 system). If so, would be expensive (£1,400 total).

Will keep it in mind as one option though …

If this is your goal, keep in mind that when you use an external crossover like the Anti-Modes or others that you will be using the built-in DAC (maybe even ADC) – while I don’t see a problem in doing so for the sub(s), I’m unsure if I would do so for the main speakers – unless you manage to find a pure digital one of course. So maybe Roon as crossover and a high quality 4+ channel DAC might be the cheapest way to go – but giving up the possibility to use the full system without Roon.

PS: There shouldn’t be the need to high-pass filter your main speakers if they are reasonably designed and IMHO lifting the bottom end just a little bit leads to an irregular slope/roll off and makes fitting he sub unnecessary difficult. I’m curious to hear others opinions too. :smiley:

In the case of my system it sounds and measures better if I roll off the main speakers. Although the main speakers should, in theory, roll off smoothly below 100 Hz they are wall mounted and this lifts the bass. When the subwoofers are added this results in a peak in the response in the 80 Hz region. Whilst this can be corrected by equalisation I find that using a crossover (currently implemented in Roon with 2 DACs grouped together using the main DAC (Benchmark DAC3) at 100Hz for the mains and cheap DAC for the subwoofers) with both main and subwoofer rolled off at 24dB/Octave gives a flat overall response. It also means that the power handling of the main speakers is increased because they are not handling much below 100Hz.

I’ve looked at 4 channel DACs and - for the ones I have found - their performance isn’t good enough - certainly not when compared to my current DAC (Benchmark DAC3). I just found this:

What I don’t know is whether it will work with Roon (via USB). Based on things I’ve seen on the forum, together with my experience in trying to use 2 DACs asa an aggregate device under OSX, using Roon with a multichannel DAC can be problematic. I’ll email Okto Reseearch to see if they know whether or not it will work.

As I said: “If they are reasonably designed”. Mine (also wall mounted b.t.w.) are rated to go down to 80 Hz. While feeding full range music to them, as it is intended by the manufacturer, I never noticed anything unusual with them like e.g. big membrane movements or a “plock” sound that indicates that the voice coil has reached it’s physical excursion limit (and I enjoy listening to hip-hop and funk occasionally).
As my primary room mode is at 73 Hz I set the sub-woofer’s crossover to 60 Hz. I saw no need to put more energy in the frequencies above as they were already covered by the primary room mode or the main speakers.

I have a bit of experience here as I have DIY speakers with active crossovers. You mentioned OS/X, do you have a Mac that is currently running the endpoint?

One additional solution is to use a Pro audio interface as a multichannel output for your endpoint. Most of the better of these include SPDIF output that you could route to your DAC3 and get all of the sonic benefits there. Either of the Motu Ultralight AVB/mk4 would allow you to route Channel 1&2 to spdif out and use 2 of analog outs as Channels 3&4 to drive the subs.

Personally I use the Reaper DAW on a Macbook Pro with a Motu AVB for an eight channel DSP. The integrated DACs are just a notch lower performance than the DAC3, but well within transparency. I don’t think you need a full DAW to implement what you’re looking for, just a good interface that can provide a pair of analog outs that are clock synchronized to SPDIF into the DAC3. You can then use the DSP features in Roon Core to implement your convolution on the four channels of audio before transport to the endpoint.

Hi Bob,

That looks like a very useful suggestion.
Presumably the Motu connects to the Mac with USB - is that how you use it?
Does Roon see it as a multichannel device so that parametric and/or convolution filters can be applied to each channel?



Yes it is recognized as multichannel and connected via USB, you can set how many channels Roon will output to in the advanced settings channel layout. You could use the Mix filters in the procedural Eq to map L & R to 3 & 4.

  1. would work but as you say you pay for Dirac…
  2. could work is DACs are identical and actually stay more or less in sync. This is not to critical for subs sot it could work
  3. same as 2

I have spent lots of time experiencing. Filters can be implemented in many ways, hardware, software. The critcial part is downstream : quality of the DAC and the preamp.
With mini DSP product you get an OK quality but will not get access to high end audio (don’t knowing what your amps and speakers are).
I would say

  • either go for <<1000 € setup with nanoDGI or miniDSP 2x4HD, they are great products.
  • OR invest in a good multichannel DAC with preamp connected via USB, and do all processing in software in Roon (USB can stream up to 8 channels). HQPlayer can be a nice addition if your DAC is native DSD.

The Okto DAC8 PRO is in my view today the best bargain, it will certainly outperfom the miniDSP SHD for DAC and preamp functionaiity. It’s around 1000€. Be careful it requires symmetrical amps. A 2nd hand Exasound E28 or E38 works too, can be found at 1500-2000€. Look also at RME products.

One friend had extensive tests with Motu but was disappointed at the end.

Hi Rémi,
Thanks for the suggestions - very helpful.

Amplifiers use Hypex modules (NC122MP with balanced inputs). Speakers are a bit unusual. I wrote about them here.

An alternative approach - which I’ve rejected for now - was to group the DACs using OSX Aggregate Device. This makes multiple DACs look like a multichannel DAC and allows one to be set as master. Unfortunately, Roon doesn’t work with OSX aggregate devices (and this has been a known issue for at least 2 years so I don’t see it being resolved anytime soon). Rogue Amoeba’s software Loopback does work with Roon - see osx aggregate devices - but it doesn’t have any facility to set on DAC as master.

So, I’m going to experiment first with nanoDigi and a good but inexpensive second DAC (Khadas Tone Board. That will let me do crossover in nanoDigi and apply FIR filters (for room correction) in Roon.

After that I might move on to the Okto DAC8 PRO (I can use the nanoDigi in another project) - a used Benchmark DAC2 (which Benchmark confirm would match my DAC3 well for this application) costs nearly as much as the Okto.

When you said that DAC8 “requires symmetrical amps” did you mean balanced inputs?*


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I’m doing the version with the nanoDigi:

Mac mini optical out > nanoDigi (crossover, time delay, EQ) > 2 DACs > active speakers + active sub.

I only crossover the sub and let the speakers play full range. I tried the SHD solution first, but there was no difference in SQ (didn’t use Dirac).

But, beware the mandatory sample rate converter in MiniDSP products that resamples everything to 96 KHz. The nanoDigi sounded strange with 44.1 material, but transparent with 48 and 96 material.

I measured the speakers in-room in REW, and you could clearly see some artifacts in the treble with 44.1 material. This did not happen with the SHD. (User March Audio did measurements of the SRC over on the ASR forum, and showed it was subpar).

In the end, I kept the nanoDigi and just resample everything in Roon to 96 KHz. That bypasses the MiniDSP’s internal SRC.

Another issue is that the nanoDigi can only delay channels up to 9 ms, whereas the SHD can delay channels up to 30 ms. This is relevant since group delay in the bass octaves is very often 20-40 ms in my experience.

This means with the nanoDigi, you cannot time align the sub though you can of course phase align the system at the crossover region, which is the most important. (Time coherence over time consistent drivers in the bass).

A final issue is that the SHD works as Roon endpoint through Volumio, so no need for a Mac/PC in the chain and using its optical out.

With the SHD, you do pay for more than just Dirac. But the nanodigi solution is just way cheaper and sounds good.

PS. I am eyeing the Okto Dac8 as well…but right now, I cannot fault the setup (apart perhaps from not being able to play DSD and MQA, which is meh when you get to have tight, deep, and even bass response). If I can do it all in Roon including time delay and crossover with the Okto, then I will prob shift to that.

I have tested miniDSP products in several occasion, and was lucky also to test the Okto DAC8Pro. The DAC and volume control section of the DAC8PRO is far superior. Doing all DSP processing in Roon makes sense as you already have a plaform, and simple filters are “cheap” to implement. You can fast prototype a multichannel system using the procedural EQ / module, the issue this that there ais ony one choice of filter and they are not Linkwitz-Riley. But going with Rephase and .cfg files with Roon Convolution engine and Spekaer setup offers an infinite number of possibilities. PCM up to 384kHz should be no pb, if you want to output 4-6-8 channels of DSD you probably need to add a powerful PC and HQPlayer.

Right, I would like to try that out. One other reason I chose naoDigi, though, was the ability to use the Mac system output in the same setup for streaming SoundCloud. Could also be done with the SHD with Volumio as AirPlay endpoint.

When you uses 2 x DAC (Benchmark for main speaker and cheaper for subwoofer), do you have delay thats concerning?

I like this method of integration of DAC as it seems cost effective without revamp the system, just not sure how effective this is

Did u moved on to other solution like the Okto DAC8?

What’s the benefit of having dedicated channels for the subs vs just y-ing them in with the left and right channels?

Hi Bob, hope this note finds you well.

I am looking to experiment on Digital XO’s (with either Acourate or Audiolense) for a 2.2 system. I have been trying to get a Motu Ultralite mk5, but it is not possible at the moment. The vendor is offering an Ultralite AVB, which looks pretty similar, but one drawback is that I cannot control the analogue outputs with the main volume knob (it only controls mains 1 and 2). I will be using Roon, so this “limitation” may not be relevant.
I have read several of your posts and it seems you have mastered something similar and I was hoping you would answer some questions I have:

  1. What do you use for dsp and FIR filters?
  2. Any positive/negative experience on the AVB that you can share?
  3. I have read some issues with the AVB and macOS, does it work for you as expected?
  4. Do you know if the AVB will work by routing the channels directly using Roon (and not reaper as you do)

Thanks in advance for the help.-

I run Roon DSP for an active 3 way crossover atm.
You need to be a little careful, but everything works exceptional well.
Sound quality is exceptional.

Signal path:

NUC Rock > RPI4 Ubuntu Bridge > Motu Ultralite MK5 > Purifi amps.
I use variable gain on the amplifiers to set my maximum gain required, and then utilise Roons software volume contol for all SPL control.

Roon’s volume control is 100% transparent and has been measured accordingly.

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I don’t think you will regret substituting the AVB in place of the Ultralite. They are nearly identical. The only thing I don’t like about the AVB is it doesn’t auto on from power loss, you have to push the on button. Don’t know if the Ultralite does this.

I primarily use Reaper because I like to fiddle with other audio plugins like the exceptionally good FabFilters ProQ linear phase EQ. I find that much music I listen to needs a little remastering EQ for my personal taste. It’s certainly not required for an active crossover system.

Currently I use FIR filters I built by hand using REW and rePhase. I have a license for Audiolense XR, but I have to find a PC to build some filters with it and I just haven’t had the time lately to devote to it.

I can’t say for sure the AVB will work directly with RoonBridge, but it looks like grizaudio has an Ultralite working with RPI Bridge and I believe the USB Audio Class 2 support should be the same for both.

If you can get a return period for the AVB I’d go ahead and pull the trigger on it. It’s very transparent and the software support is great.

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Yep no issues using Ubuntu server 21.10, and Roon bridge. Class compliant device (Motu) works perfectly.

FYI, Ropieee doesn’t work with the Motu ultralite in my setup.

I get clock lock but no audio with procedural mix routing.