Sub for single-driver desktop speakers

For further discussion of my Arche desktop system with Fostex sub, see

I naively thought a a sub crossover set at - say - 100 hz  - meant that the sub would reproduce the sound below this point, not above it. I should have known better. The Fostex submini 2 comes with a manual with an informative graph (p 12) that shows the output above the crossover point. Even if I set it to the lowest point, 60 hz, there will be audible output up to somewhere in the region 500 to 800 hz!

Even if this is lower than the output below 60 hz, it is very much there, at least to 2-300 hz. I have confirmed this by listening. The sub, playing by itself (speakers muted), offers quite a bit of lower midtone, even (somewhat ghostly) voices. I suspect that this is a general feature of subs, not just this one (dependent on the slope of the filter etc). Therefore, to my ears, the idea that you can place subs almost wherever, since you wont hear where the bass is coming from, is flawed - since you don't just get the deep quite omnidirectional bass, you get higher frequency sound also. Correct me if I am wrong.

Therefore, it is nice to be able to play around with this small sub, easily pushed around on my desktop, so it sounds perfectly in sync - time coherent - with my desktop speakers. This was never easy to do with the big subs I had in my main system. It is also interesting that the new results resemble what I found in my main listening room (regarding front-firing subs).

Namely: 1) get the sub placed and tuned so you dont hear it (you think the bass is coming from the speakers), and then 2) micro-tune the sub - small changes of position - so the time alignment becomes optimal. My result now is in line with what I heard with the big Velodyne DD18 sub in my main system: the sub woofer should be a little bit in front of the speaker driver(s), to "lock in". At that point, at my desktop, I hear added energy, voices sound more coherent. I don't like a sub staring at my face at my desktop, I would rather push it to the back of the table. But it seems that this forwards position, ca 2 cm in front of the plane of the desktop speaker drivers, actually gives the best sound.

The Submini was first placed under my desktop, but the bass integration with the FR2 speakers (on short stands on the desktop) was not optimal. It sounds better on the desktop, firing towards me, more or less in line with the speakers. My goal is not to get the most bass, but the best bass, sounding like it comes from the speakers not the sub itself. The bass now sounds clearer, better articulated and coherent with the midtone and treble. Interesting how "small" things like sub placement can mean big improvements. Ideally the sub should probably stand in between the speakers, but my pc screen makes that impossible. So it now stands to the left of the speakers, and is maybe a bit louder to the left, but not much, provided I tune the sub volume and crossover "just so" (low-moderate) to help the system along. The sub is small and simple, but does a good job now.

The Submini and Arche system now works fine in my home office. Complaints minor.

Fostex PM Submini2 arrived today - very interesting - seems to cure most of the problems with the FR2. Now I get upper bass and deeper middle tone OK. Without much smear or detriment to the FR2. Remains to be seen, how well it can be integrated. FR2 mellowing a bit, over time.

John at Arche will send me a new transformer for the power supply, to get rid of the hum problem.

I changed the DAC from Fiio X3ii to Steinberg UR22, resulting in a bit more smooth sound, with slightly more deep tone, when streaming pcm from Qobuz.

The speakers need break-in, before I can say more, like do I want a sub, or not.

I bought the FR2 speakers, amp and power supply as a package. So the amp is Arche Audio Opus D50A.

What amp are you using?

Update - my Arche linear power supply to the amp - in a separate box - has a bit of hum, and it persists even if I place the supply below the desktop. The hum is from the box itself, not from the speakers (only if I turn speaker volume way up). Maybe I got a faulty unit. Meanwhile, I have bought a Nexa remote control so it is easy to turn it on and off. Although the hum is not so intrusive when I play music, I need full silence in my home office.

Regarding the gap between the low range of the speakers (on paper, 100hz) and the high point of a sub (no higher than 80, or maybe 70) - is there an easy way to measure this? I could use the REW program, or Audacity, I think, but I am looking for some easy-to-use phone app that can tell me about the output in a specific range (like 80-90-100 hz). Ideas welcome.

Another way would be to use test tones, and our trusty old friends, the ears. I found some sine wave tones on my pc. The FR2 plays tones down to 125hz very loud and clear, no problem. They play a 100hz tone clearly also, providing I turn up the volume (confirming what reviewers have said). Surprisingly, they play 80hz and even 63hz tones also, still clear, at the same louder level. It is only when I play 50hz that they give up, I hear ca nothing. So this would suggest, I think, that the "gap", on paper, between speaker and sub limits may not actually be a problem. My general impression, using subs and main speakers, is that the main speakers should not be cut off at the bottom end, unless there is dire need for it. I think this goes for the FR2 also. Maybe I am too tolerant of "colorations", "doppler effects" and other suspects, but I find that full range speakers should be given a full range signal, to sound best.

Perhaps the ideal, in my context, would be a small sub that has speaker level connections - avoiding crossover/equalizing - that helps the speakers along in the 100 or so hz to ca 60 hz range (or however low it goes). I have some flexibility and can position the sub so it just helps the speakers along, adding some more deep mid and upper bass tone, without disturbing the clarity of the speakers. Positioning + subtle use of sub volume (so it stays "invisible") may do the trick. 

Raised almost to ear height with 19 cm alu stands, plus more break-in, the Arche system now sounds better. Very clear and detailed.

If you need to know, which of your streaming albums should you invest in, on vinyl, this system offers good orientation.

The Gallo Tr2 (also Tr1) is an interesting suggestion , thanks.

A sub should not go high - agree with Atmasphere - just up to 80hz, or if possible, even lower. The lower, the less problems with integrating with the main speakers.

I am not sure, if the gap between the low 100hz end of the speakers, and the top 80hz of the ideal sub, is a real problem. According to John Parks at Arche, the Fr2 system works well with an added sub.

Good to see you are trying the Arche's.

Don't know if they are still in production but years ago I tried/liked a small Gallo sub (TR2) with various widerange single drivers (including 3"-4.5" Japanese drivers).

Also tried it with their little "ball" speakers.

Think the sub's crossover defaulted to 100Hz when using the speaker cable connections (adjustable when using the low level connection).

DeKay

Thanks all for interesting suggestions. Especially to @atmasphere – maybe I hear some Doppler effect, yes. At least, so far, these small speakers sound much better with well-recorded ‘sparse’ music than with high dynamic multi-instrument rock. Like Shelby Lynne: Just a little lovin’ (though I have yet to hear a system where this album sounds bad). However I realize that my initial post may be premature. The FR2 speakers need some weeks to open up, according to reviews.

BTW, these speakers will eventually replace my trusty old Sony SRS-ZX1, that are even smaller than the FR2, and yet go down to 60hz or so. This is due to a C-formed channel at the back that Sony calls a «Mobius duct», leading to the bass port below the single driver. I like this analog domain type of modification, avoiding electronic equalizer glare, but I don’t think Sony ever developed it further. However, even if the Sonys go lower, the FR2s are better from midtone upwards (clearer, more air, space), so I hope they break in, over time.

Another member on this forum bought the MartinLogan Dynamo 800x for his music only system and absolutely loves it. (Can't remember his name). It has the ability to be front or bottom firing, has an app for full control and includes Anthem Room Correction.

https://www.martinlogan.com/en/product/dynamo-800x

I've played with single driver speakers a lot, but not had them be as satisfying as a 2-way or 3-way, depending on the size of the speaker.

To really get the sub to blend its a good idea to keep its output below 80Hz. Otherwise it starts to attract attention to itself- and if it does that, it has to be very close to the main speakers so that all the sound seems to come from the same place. That might mean a sub custom designed to match the main speakers.

I'd also be concerned about having any bass excursion on such a small driver- that causes Doppler effect distortion- so much for 'purity'.

But I understand the idea and the interest- I'm very interested in smaller systems like you might use for desktop or a bedroom. It seems to me though to be successful, the main speaker has to get a bit below 80Hz to really work with most subs (which might be placed in a location considerably different from where the main speakers are).

Radio Shack made a speaker called the Minimus 7 which they claimed goes to 50Hz. Apparently the earlier versions are the most desirable having a better tweeter, and the crossover has to be modified to roll off the woofer in the range of the tweeter. Once this latter bit is done the speaker gets quite smooth with good off axis response. I've not measured it to see if 50Hz is really 'realistic' if you see what I did there 😁 but they image quite well and are surprisingly neutral if you don't push them too hard.

This is what I’d get if it’s in your budget...

https://www.svsound.com/products/3000-micro-subwoofer

More info on the speakers:

http://v2.stereotimes.com/post/arche-audio-fr2-fullrange-desktop-monitors-by-greg-voth