Seeking advice on connecting a passive subwoofer, in home studio...

[Ally-007]

Hi all. This is what I want to do: In my home studio, I have a USB audio interface which feeds a pair of small active studio monitors. All straightforward, so far... However, I want to utilize a passive subwoofer that I have, fed by a separate audio amplifier that I also have, (which has a sub out). So I guess what I need is to add some kind of adjustable crossover between the audio interface and the pair of active monitors, to filter out a selected range of lower frequencies coming from the audio interface, and send just those low frequencies to the standalone amp powering the passive subwoofer. The remaining (higher) frequencies will go to the active studio monitors. Is there a ready-made and low-cost crossover unit that would suit this purpose? Would it need to be active or passive? There is one other consideration: the signal connection between audio interface to the active studio monitors is currently balanced. It would be nice if the feed to the active monitors could remain balanced, after adding the crossover device. Thank you for any advice.

 

[rob aylestone]

Do you have spare outputs on the interface? If so, slap on a low pass filter to that path and send it to the sub amp. However, the full range speakers probably need to retain the full range, because dedicated subs don't offer any clarity down the bottom. Probably a 19" rackmount speaker management system - like this cheap chinese copy - might be a simpler way of sorting it.
aliexpress

 

[Ally-007]

Do you have spare outputs on the interface? If so, slap on a low pass filter to that path and send it to the sub amp. However, the full range speakers probably need to retain the full range, because dedicated subs don't offer any clarity down the bottom. Probably a 19" rackmount speaker management system - like this cheap chinese copy - might be a simpler way of sorting it.
aliexpress

Hi Rob. Thanks for your reply. Unfortunately the audio interface only has two outputs: Left and Right (balanced). However, it does have a headphone output. So now, I'm thinking I could run a cable from the headphone output to the AUX-IN on the amp powering the sub. What do you think?

That's interesting what you said about allowing the full range to go into the active monitors. I was thinking that the less low bass frequencies that those small monitors struggle to reproduce, the more clarity I'd get from their 3.5" woofers.

 

[ecc83]

The almost universal setup with an all active system is that the interface feeds the sub first. That has high and low pass (active!) filters in it to send high pass filtered signals to the we'uns. One of the main advantages of a sub is to take the LF 'load' off the monitors so they can play at higher SPLs or/and run with lower distortion.

You also want a good attenuation of the rest of the spectrum feeding the sub else such 'leakage' will degrade the stereo imaging.

I don't know if such a device exist but I shall look. You also of course need a substantial mono power amplifier.

Behringer | Product | CX2310

www.behringer.com

The above seems the only thing suitable I have found so far. You still need a power amp.

Dave.

 

[bouldersoundguy]

Something like the Behringer DCX2496 would do it. It's a digital speaker processor that will take your stereo output and split it as needed, with crossover filters, delay to time align the bands, limiters (more for live sound) etc. It has two input channels and six output channels.

 

[Ally-007]

The almost universal setup with an all active system is that the interface feeds the sub first. That has high and low pass (active!) filters in it to send high pass filtered signals to the we'uns. One of the main advantages of a sub is to take the LF 'load' off the monitors so they can play at higher SPLs or/and run with lower distortion.

You also want a good attenuation of the rest of the spectrum feeding the sub else such 'leakage' will degrade the stereo imaging.

I don't know if such a device exist but I shall look. You also of course need a substantial mono power amplifier.

Behringer | Product | CX2310

www.behringer.com

The above seems the only thing suitable I have found so far. You still need a power amp.

Dave.

Thank you for the suggestions, Dave. Today, I tried connecting the headphone out on the audio interface to the 100W amp powering my 12" passive sub. First impressions are that it works well. I can now hear sound down to around 25Hz, whereas with the two small active monitors alone, I can only hear down to around 45Hz.

I see your point about stereo imaging. Setting the crossover frequency on the amp powering my sub seems to deal with that issue. I may have to dig out my measurement mic to try and optimize the volume and crossover settings on the amp powering the sub, to try to attain a flat-as-possible response curve, when all speakers are in play. Can you (or anyone) suggest a fairly simple and intuitive software for PC (preferably free) that would serve for this?

 

[rob aylestone]

My preference is that the controlled low end of proper monitors is the best quality audio, and the sub is best reserved only for the parts these speakers cant handle. Getting the swap between monitors and the sub is crucial. The old idea that you can put a sub anywhere because we cannot localise bass, is true but only below certain frequencies. On your system, knock up a pulse low bass track and pan the notes left then right at a pitch so you can hear the left right very clearly, then drop that note down pitch by pitch until it starts to come out of the sub. It you can live with the result, all is good.

 

[ecc83]

My preference is that the controlled low end of proper monitors is the best quality audio, and the sub is best reserved only for the parts these speakers cant handle. Getting the swap between monitors and the sub is crucial. The old idea that you can put a sub anywhere because we cannot localise bass, is true but only below certain frequencies. On your system, knock up a pulse low bass track and pan the notes left then right at a pitch so you can hear the left right very clearly, then drop that note down pitch by pitch until it starts to come out of the sub. It you can live with the result, all is good.

Now I KNOW there are them as will say "Ee ALWAYS mentions this!" but what can I do? A few months ago Sound on sound magazine released a very comprehensive set of test tones as a free download. Not looked but I am sure there will something in the ref subs.

The OP's 3.5" "monitors" are going to run out of steam LONG before they get to 'sub' frequencies* and so either the sub will be intruding up in the 80, maybe 150Hz region and effing the imaging or there will be a 'zone of silence' from 100Hz to say 40Hz. And 25Hz? WTF do you have making MUSIC down there?

Integrating a sub woofer with 'full range' speakers is tricky to get right and is best done when ALL the components are from the same stable and designed to work together. An ad hoc, thrown together system MIGHT sound impressive but accurate it won't be. But if one enjoys the sound....who am I to?


Dave.

 

[Ally-007]

My preference is that the controlled low end of proper monitors is the best quality audio, and the sub is best reserved only for the parts these speakers cant handle. Getting the swap between monitors and the sub is crucial. The old idea that you can put a sub anywhere because we cannot localise bass, is true but only below certain frequencies. On your system, knock up a pulse low bass track and pan the notes left then right at a pitch so you can hear the left right very clearly, then drop that note down pitch by pitch until it starts to come out of the sub. It you can live with the result, all is good.

Thank you for the tip, Rob. I did this, and have good L/R separation/distinction even below 50Hz. In real life music production, even the lowest notes I'm likely to record have harmonics well above that level, making L/R distinction even more pronounced. Now I just need to get my head around the methodology of fine-tuning the setup for a flat-as-possible response curve..

 

[Ally-007]

A few months ago Sound on sound magazine released a very comprehensive set of test tones as a free download. Not looked but I am sure there will something in the ref subs.

Thank you for that. The files are still available. I've downloaded them, as they could be useful when calibrating my setup.

 

[Gtoboy]

Small monitors are going to act as a 'crossover' just by being unable to reproduce the lower frequencies. I would not bother with a crossover..

 

[ecc83]

Small monitors are going to act as a 'crossover' just by being unable to reproduce the lower frequencies. I would not bother with a crossover..

Not really since the speakers are still being fed low frequencies which will both compromise their maximum SPL and cause distortion due to unneeded cone excursion.

Subs are NOT all about window rattling! ("Subaru man" excepted)

Dave.

 

[bouldersoundguy]

There may be a good rationale behind the advice not to high pass the monitors, but there's also good reason to do it. One Dave explains above, but there are also the challenges home recordists often have mixing in small spaces where LF interactions in the room cause problems. Since monitor placement needs to account for proper imaging, you have less freedom to place them where it works for LF. By high passing the monitors, you can mitigate the LF/room issues. You can then independently place a sub wherever it sounds best from the listening position.

With or without high passing the monitors, time alignment is something that should be addressed.

 

[ecc83]

There is also the fact that if the small speakers are not filtered, there will be a peak in the response where both they and the sub are reproducing the same frequency (look at any info on passive crossovers) OR! If you ***k up the polarity, a suckout"!

Speakers are NOT simple! (unless you just want to make a bit of exciting noise)

Dave.

 

[bouldersoundguy]

Well, you could tailor the sub's low pass filter to work with the natural rolloff of the monitors, but that's usually a more gradual slope. One of the disadvantages of crossovers is that, even if you align levels/polarity/phase at the crossover frequency, there's going to be a little response variation just either side of that frequency due to the phase sloping in opposite directions.

 

[bouldersoundguy]

Just for fun, I did some quick and dirty frequency response measurements of a few bookshelf speakers I had lying around, NAD 8225 (blue), Electro-Voice S-40 (red) and Mission M71i (yellow). These were done in my living room, so not an acoustically perfect environment, but I tried to place them for minimal room effects (i.e. away from walls, on a stand about a third of the room height high). Distance from mic was about 0.5 m. No settings were changed between measurements. I applied a 1/12 octave smoothing filter to the traces.

Note that boundary effect will substantially increase LF response.

 

[Gtoboy]

So I haven't run into studio monitors that did not have filters built in to their inputs to prevent the sort of nonsense that is being described in the last few posts, My bad for assuming.

 

[bouldersoundguy]

So I haven't run into studio monitors that did not have filters built in to their inputs to prevent the sort of nonsense that is being described in the last few posts, My bad for assuming.

I wouldn't be surprised if active monitors have high pass filters to protect the woofers. But that won't prevent small room LF problems.

 

[markmann]

I use an active sub along with my full freq monitors but I think I could get the same result with a passive + low pass filter.

With my active I can adjust the volume plus it has an adjustable LPF that I can adjust to be below the monitors. I know where to x-over is but I adjust by ear and it works great.