Totem Acoustic KIN Sub?
 

[Update: This post is really less about the Totem unit and more about how best to hook up a sub-woofer (for $1K or less). Any advice on the methods and questions outlined below (given the constraints of my integrated amp) would be greatly appreciated!]


Has anybody tried this compact but application-flexible sub-woofer?

I have a set of old, but beloved, Beovox M 70's driven by a new Yamaha A-S501 integrated amp (line-level sub out with 100 Hz low-pass, but no separable, line-level pre-amp out/power-amp in). I'm straining the M 70's in my now-larger living room, so adding a sub-woofer may be the most cost-effective improvement. This one is highly recommended by my dealer, I can actually afford it, and it can also be hooked up several different ways.

I plan to route both speaker-level cables from the amp to the sub-woofer and then connect the main speakers to it's dual, speaker-level outputs. This should off-load the low base from the M 70's, allowing them to perform better at higher levels, while still getting good base response from the sub-woofer.

An alternative would be to connect the sub-woofer to the sub out of the amp and leave the main speakers connected directly to the amp, but this appears to have several disadvantages:
1) The M 70's will still get hit with the low base, making it harder for them to produce clean upper base/mid-range.
2) The 100 Hz crossover in the amp may not be ideal, and I'm not sure that the sub's crossover can be bypassed. If not, the two crossovers in series may not play well together.
3) If the sub's crossover can be bypassed, then I wonder if that also bypasses the (essential!) phase control on the sub. (This is the sort of detail that should be fully covered in the manual but is not.)
4) There's also the question of whether the amp's sub out comes off the pre-amp after the volume control. (Again, this should be covered in the manual but is not. Maybe it's standard?) If not, that would certainly make adjustment of the sub's volume necessary every time the amp's volume is adjusted -- a major pain.

Any comments or suggestions would be most welcome! -- Clark2

Group Delay Paradox:

Having now read the treatise on adding a sub-woofer by the Soundoctor (courtesy of JL Audio's Help Center), I'm puzzled by this essential statement: "The typical group delay through a modern, sealed box subwoofer, is perhaps 8 to 15 millisecond." (If I understand correctly, this delay is relative to the sound coming out of the main speakers, in the absence of some kind of digital delay inserted there by a HT processor.) What is the physical origin of this delay? Is it, perhaps, the time it takes the big voice coil in the sub to get moving?

Whatever the cause of this delay in the sub, how is it qualitatively different from that in the main speakers? In my case, at least, these units also have large internal woofers in sealed enclosures? Wouldn't their group delay in the base range be similar to that of the sub? If so, I'm already living with a group delay in these internal woofers, relative to the mid-range and highs; so how does adding a sub-woofer make this any worse?

I must be missing some essential factor here... -- Clark2

Modern subs have digital electronic crossovers that add approximately 10 mSec of delay by themselves.

The rest of the delay is simply due to the acoustic response of the sub itself.

This delay is relative to the electronic signal that drives them.

You are correct in that like for like a big sealed woofer in a floorstanding speaker would have the same group delay as a sub that was designed identically.

However most subs are designed to go much lower in frequency than the woofers in a floorstander, so they generate more delay.

Make sense?

Does that mean that the high-pass out from the sub (in the speaker-level connection outlined above) would experience a similar cross-over delay (which might tend to moderate the relative delay between sub and mains)?

And would the digital hocus-pocus in the sub's cross-over then compromise the fidelity of the highs going on to the mains (sampling rate and/or resolution insufficiency that wouldn't affect the low base)?

Yep, sure does. Thanks a lot for the clarification!

I guess there's not much I can do about it, without spending lots more $$, short of putting the sub under my listening chair (not really practical in the same speaker-level wiring scheme). -- Clark2

Hey, W9TR -- The option of moving the sub much closer to the listening position than the mains still intrigues and would be feasible in my living room. I could string a line-level cable from the sub out temporarily, of course, but anything permanent that would pass the "wife test" would have to be wireless.

I looked at JL's Jlink, but its specified latency is 14 ms -- equivalent to ~16 ft of distance -- negating the purpose. Is there anything else out there in the way of a real-time modulation/demodulation system that doesn't involve A-to-D followed by D-to-A conversion, which I assume is responsible for the long latency? -- Clark2

Not that I am aware of. You could look for a sub without any active eq or room correction and see what their group delay is.

You can always experiment with sub placement but usually you’ll want to place a sub in a location with two boundaries - wall and floor.

If you have a sub that will move a lot of air, at least a 12” driver and/or passive radiatior combo you may get enough output to get a satisfactory result with a mid-room placement.

UPDATE: Here's what I pried out of Totem Acoustic tech support re. the KIN Sub:

1) "The Kin sub does NOT incorporate a high pass filter [in its speaker pass-through] as we feel the added filters disrupt the main loudspeakers overall balance."

2) "The [sub-woofer cross-over] slope is a 12 octave design."

3) "If the subwoofer is in line with your front loudspeakers and your RCA interconnect is less than 10Ft there shouldn’t be any time delay in relation to your front loudspeakers.... It's not a DSP crossover network."

Sounds to me as though these guys are trying to ease integration with conventional main speakers in the absence of an external crossover with variable time delay. I read the above as (1) there's no advantage to using the speaker-level connection over the line-level sub-out connection, (2) the slope is as good a match to my Beovox M-70's as any, and (3) there's probably no need to move the sub closer to the listening location.

Totem also makes several larger sub-woofers, some with "passive radiators," but I don't know yet if these also have the same cross-over described above...

What's with these "passive radiators" anyhow? Is this somehow different from having a ported, as opposed to sealed, cabinet? Can they still maintain smooth frequency and phase response, yet radiate more acoustic power, this way? -- Clark2

Last post I wrote,

>>...but I don't know yet if these also have the same cross-over described above...<<

Here's a final answer from Totem Acoustic:

"...the KIN - STORM AND THUNDER II all share these same characteristics."

So if the KIN doesn't produce enough bass to balance the old Beovox M 70's, I guess I could try the Storm Sub. I still don't understand these "passive radiators" though. Can anyone explain? -- Clark2

Totem Acoustic KIN Sub?
 

Passive radiators have mass and compliance and so function in the same way as the port in a ported loudspeaker.

The air in the port has mass and compliance and can be used to tune the bass response of the system.

The ported or passive radiator system has a 4th order response -24 dB/Octave as compared to a sealed box system which has a -12 dB/Octave response.

The advantage of a passive radiator is its large radiating surface area and ability to operate in a smaller enclosure.

Tom

Thanks again, Tom, for your clear analysis --

I've heard it argued that ported subs suffer in comparison to sealed ones in terms of frequency and phase response. (Or maybe this is more of a problem of matching subs with ported mains?) Can I conclude that passive-radiator subs suffer the same issues (if any), or is there some other improvement besides efficiency to be had this way?

-- Clark2