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Adding a subwoofer to a 2 channel DAC without adding an external crossover

gramp

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I'm trying to add my subwoofer to my desk setup. I have an RME ADI-2 DAC. My subwoofer has only 1 XLR input available for use.

Most hifi dacs/preamps only have stereo outputs. Only things like minidsp and some more expensive exotic units actually have dsp and multiple outputs. It's very rare to find and I haven't seen too many.

I don't want to buy a different DAC/amp for this setup. I also don't want to introduce more devices, particularly analog or digital crossovers. So I will run the mains at full range and use the subwoofer's built in crossover to match the mains at full range. The theory is that my mains already sound great, and so I will just try to extend the range further down with the sub.

The difficulty with this setup is that I only have one XLR input of my subwoofer available. I will for sure use XLR to the mains, as they are studio monitors and they don't accept unbalanced connections. This means I have to either split the 2 channel XLR L/R into 3 channel L/R/MonoSum or use the RCA's, sum them, and add an XLR adapter.

This is surprisingly obscure and difficult problem to solve.

I first looked up if it were possible to split my XLR into 3 channels. I could not find any simple device which does this. Analog crossovers will, but I don't want to use a crossover. Probably also some expensive pro audio mixer could do it, but that's super overkill. Also more devices, and cables no thanks..

I looked up cables. You can buy XLR Y splitter cables pretty easily.

I even managed to find a guy who makes XLR summing cables. http://micmodkits.com/other/

So you could in theory make some awful net of split and join cables, but that's also a very very bad idea. See this article.

https://www.prosoundweb.com/why-not-wye/


So I've given up on somehow ripping out a summed mono signal from the XLR's. How about the RCA's?

Again the problem here is I need to sum the rca signal. I also need to add an xlr adapter, which I have. There are several pro audio DI (direct inject) boxes out there which will take 2 rca's and sum them into an XLR balanced mono signal. They are passive devices, so assuming they are built well they should not add any noise to the signal. The problem with all of these is that they produce a microphone level input and not a line level input.

That same guy who makes the XLR cables also makes RCA sum cables. I found a few other companies who make these as well.

Finally, after a long search I stumbled onto this: https://www.sweetwater.com/store/detail/ISOPOD--whirlwind-isopod . This will sum an rca connection, convert it to balanced, and produces line level.

So in the end for this setup I think either the RCA sum cable or this isopod device is exactly what I need. I'm going to try the isopod, as having the ability to convert the signal to balanced could help if I move the sub farther away in the room and need to do a longer cable run.

Am I overlooking something? Does anyone see a reason why this wouldn't work?


If you've successfully integrated a sub into a system using a standard 2 channel hifi dac/amp how did you pull it off?
 
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Jmudrick

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I'm not getting the problem. Currently I output stereo signals from the RME DAC to two powered JBL LSR310s subs via an XLR splitter. Previously I have also output separate L-R signals to each sub via XLR . Both sound good. The only complicated part of the first method is running two additional balanced cables and the splitter.
 
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gramp

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I'm not getting the problem. Currently I'm output stereo signal from the RME DAC to two powered JBL LSR310s subs via an XLR splitter. I have also output separate L-R signals to each sub via XLR . Both sound good. The only complicated part of the first method is running two additional balanced cables and the splitter.

If your subs have 2 inputs, you can run L and R directly into the sub and it's easy. If you have 2 subs with 1 input each and they are positioned well, you can run L to one sub and R to the other. Also easy.

If you have just 1 sub with just 1 input available, you have to sum the left and right signals together yourself. Otherwise you'll only be able to get right or left channel but not both.

I wish the RME would let you separately set Mono on the RCA's and stereo on the XLR's. Unfortunately it doesn't let you operate them separately.
 

pozz

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Dimitri

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Or you could try the completely heretic approach....pick one channel (suggest left ) , feed it to the sub.
If you hate it, continue searching for a solution :)
 
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Blumlein 88

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To do crossovers these are all you need.

https://www.parts-express.com/harrison-labs-fmod-inline-crossover-pair-50-hz-low-pass-rca--266-250

You can get them for different crossover points. A few ways you could arrange this to make it work.

If I remember right the RME outputs aren't electrically connected. So you could sum whichever you use for the subs and send it right on. For the left and right speakers put an Fmod in each feed to each channel for the appropriate low end roll off. You can find XLR splitter combiners at Amazon or Parts Express or other places. Combine the XLR and send to the sub.

According to page 36 of the RME manual though fed from the same DAC, the RCA, XLR, and Phones have individual driver stages and each can be set at output levels different from the others. Assuming your subs have a hi-pass filter in them, and you use the Fmods for the right and left speakers you can have a full crossover with all the benefits of that.
 
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gramp

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Your solution is in the article you quoted: a summing box. Split the XLR outs and then combine the L and R sub signals using pro equipment.

That's what they advise not to do in the last "Termites in the Woodpile" section. If you want to split 2 channels it's ok. If you want to sum 2 channels, it's also ok.

If you want to split and sum at the same time, you get crosstalk. Using a passive box is no different than using a cable.
 
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gramp

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No bass management is mid grade at best. You can sell it for $800-900 and buy a miniDSP SHD.


I already am planning to get an SHD for my main speaker setup in the living room I don't want to have 2. Also, the shd doesn't have a headphone amp. I suppose you could with the shd use a present which disables xover/dirac and then use a jds atom or something with the rca's though.
 

Senior NEET Engineer

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I already am planning to get an SHD for my main speaker setup in the living room I don't want to have 2. Also, the shd doesn't have a headphone amp. I suppose you could with the shd use a present which disables xover/dirac and then use a jds atom or something with the rca's though.

I had similar requirements and couldn't come up with satisfying all in one compact solution. I use SHD and DX3 Pro for my desktop setup.
 

pozz

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That's what they advise not to do in the last "Termites in the Woodpile" section. If you want to split 2 channels it's ok. If you want to sum 2 channels, it's also ok.

If you want to split and sum at the same time, you get crosstalk. Using a passive box is no different than using a cable.
If the resistor values in the box are high, e.g., 33k, then crosstalk is diminished at the cost of increased noise. This is the cheap way to go about it.

The only way to completely avoid crosstalk is using an active crossover like @jhaider suggested. Otherwise try @Blumlein 88's suggestion.
 
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waynel

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. So I will run the mains at full range and use the subwoofer's built in crossover to match the mains at full range. The theory is that my mains already sound great, and so I will just try to extend the range further down with the sub.

This "theory" is flawed as without bass management your sub may/will deconstructively interfere with your mains at some frequencies while constructively interfering at others. Best to high pass filter the mains while low pass filtering the subs. What monitors and sub are you using. Some studio subs will do the all the filtering for you.
 
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HighImpactAV

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With just using the RME ADI-2 DAC, there will be no way of properly time and phase aligning the speakers with the subwoofer. Unless the subwoofer is much closer than the speakers, you will need to add delay to the speakers.

If you had the RME ADI-2 Pro FS R BE (which is a 4 channel DAC), then you can put headphone 3/4 out in balanced mode and use them as balanced line outputs (page 50 of the manual). You can then use your playback software to set the crossover and delay for mains and subwoofer and use channel 3 for the subwoofer output. If you don't want to time and phase align, you can also use Totalmix to route the left and right to a singe balance headphone output and connect it directly to your subwoofer.
 

msmucr

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If you had the RME ADI-2 Pro FS R BE (which is a 4 channel DAC), then you can put headphone 3/4 out in balanced mode and use them as balanced line outputs (page 50 of the manual). You can then use your playback software to set the crossover and delay for mains and subwoofer and use channel 3 for the subwoofer output. If you don't want to time and phase align, you can also use Totalmix to route the left and right to a singe balance headphone output and connect it directly to your subwoofer.

That's not correct. Neither ADI-2 DAC nor Pro (AD/DA) has 4 simultaneous balanced outputs, because if you connect HP amp in balanced mode, it will use also your main output DAC. You can use main balanced output and unbalanced headphone output with different signals from computer, no problem with that.
Also no ADI-2 model has TotalMix, that's available only on their other interfaces. BE model is just special black edition of standard model, there are no functional differences.
 

HighImpactAV

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That's not correct. Neither ADI-2 DAC nor Pro (AD/DA) has 4 simultaneous balanced outputs, because if you connect HP amp in balanced mode, it will use also your main output DAC. You can use main balanced output and unbalanced headphone output with different signals from computer, no problem with that.
Also no ADI-2 model has TotalMix, that's available only on their other interfaces. BE model is just special black edition of standard model, there are no functional differences.
You are correct in correcting me :). I thought that TotalMix was necessary for routing the 6 inputs and 8 outputs on the ADI-2 Pro, but I guess it is all through the menu.
 

RayDunzl

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If you've successfully integrated a sub into a system using a standard 2 channel hifi dac/amp how did you pull it off?

At preamp, full range XLR out to amplifiers, and full range stereo RCA out to miniDSP 2x4HD to four subs.

I don't want to buy a different DAC/amp for this setup. I also don't want to introduce more devices, particularly analog or digital crossovers.

Good luck.

I've found that sometimes what you want, what you think you want, what you have, and what you need to accomplish what think you want, don't intersect as desired.
 
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gramp

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So to clarify, here is what I'm actually doing.

I live in a very small apartment. My computer desk is in the living room. I have IK Multimedia MTM iLoud studio monitors at the desk and also my main living room speakers (salk veracity ST) / sub (funk audio) by the TV. I chose these monitors because they have a good range despite being small enough to fit on my desk.

I use the studio monitors for non-music use, but sometimes I also listen to music with them. They are decent ones, but nowhere near the class of my main speakers. Given they are on my desk and pointed at my ears, sometimes from this position I can get better detail since the near field monitors are positioned correctly for my seated position when I'm working at home. The main speakers are setup for the couch area. Also, it's just fun to switch it up sometimes. I also use headphones here a lot, but not all the time.

The main speaker setup is where I spent the most money and try to achieve "perfection". I currently have a minidsp shd in shipping to upgrade that.

My sub actually has 2 xlr inputs. One of them is used by the main system with the current amplifier.

So I thought wouldn't it be cool if I could also use my same subwoofer with the desk and try to add some bass extension to my studio monitors, using the other XLR input and setting a LPF on the sub itself. The funk audio subwoofer uses DSP and lets you separately configure each input. So I can have the desk input using the sub's dsp, and the main input with no filtering because I'll do all my signal processing with the shd at the source. Now I can reuse the same sub for either the desk, or mains and I don't even need to buy an XLR switch or anything like that.

So the goal is to see what I can get away with cheaply and easily to improve upon what I have currently. The goal is not to drop another $1000 or more on exotic devices and cables which may or may not even materially improve things. If I wanted to spend that kind of money on this project, I'd buy better monitors.

I'm also in general suspicious of adding analog or digital crossover devices in the chain. I haven't seen anyone reviewing those and giving measurements. In my opinion if you really want to do any signal processing to your speakers and sub you want to do it at the source *before* your expensive DAC.

Even in the pro audio world, it looks like analog crossovers are going away in favor of digital. One highly regarded model, the Ashly Xr1001 which I was looking at for a while, is still for sale at retailers but appears no longer manufactured by Ashly.

There are super high "audiophile" grade crossover like marchand and bryston. I'd love to see Amirm review some of those and see if they stand up to their reputations. I don't even want to get into that world where a crossover can cost more than your subwoofer. I really don't see what can be the possible appeal of going that route when you can just get an shd.
 
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