SpeakerTalk

[deckard]

Ha! I figured it must have come up, but I've never even heard of a ProKUBE!

A few questions if you don't mind:

Was there a balanced version of each KUBE model?

Was the pro version purely to facilitate XLR connections or was the circuitry different? I was thinking/hoping there may already be points to tap into on the board to achieve balanced connections, as I've read that many unbalanced outputs start out as balanced.

Also, was it "pro" in the sense that it operated at +4 instead of -10?

In lieu of a ProKUBE, what would you recommend: some Jensen transformers or a "properly" made XLR to RCA cable (see wiring diagram #17 on this page: http://www.rane.com/note110.html)?

Thank you!

[deckard]

Since my last post, I had been exploring some options on how to go from balanced to unbalanced, which brought me to a thread over at Audiogon from someone in the same boat. Everyone there was touting using Jensen ISOMAX audiophile transformers. Once I chimed in and described my scenario, it was suggested I give Jensen a call.

The scenario I had was:

- balanced pre out to balanced amp in for HF.
- unbalanced pre out to KUBE. unbalanced variable output of the KUBE to balanced amp input via XLR to RCA cables for LF.

With this setup, I was getting significantly less gain on the LF side, even with the variable output cranked, because of using the XLR to RCA cables.

Well, I was lucky enough to speak with Bill Whitlock of Jensen, who is both very knowledgeable and willing to give thoughts and suggestions about my situation. He observed that the gain mismatch I was getting from using XLR to RCA cables would be best remedied by somehow getting more output from the KUBE. I sent him schematics of the KUBE 200 and he quickly replied, instructing to change out 2 resistors in the variable output circuit for lower values***, which would extend the gain by a few dB (he gave exact specs, but I don't have them handy). He said that I could stick with the RCA to XLR cables the way I had them wired, but suggested that if I got any noise, I should try combining the shield with the black conductor at the RCA end. If no luck there, then I should look into getting a Jensen PI-2RX, etc.

*** Please someone (speakerguru) let me know if this is worth attempting or deserves a slap...

I have yet to do this because I haven't gotten the parts (and I would like some feedback about this from here first), but in the meantime, I figured I'd have a go with another poster's suggestion and just try it for myself using my unbalanced preamp out, non-biamped, to see if it truly messed with the midrange. I hooked it up in this fashion and gave it a go.

I have to say, I really didn't notice any discernible difference in the HF with the KUBE inline. It may be that my gear is just not good enough to expose anything (plus I wasn't exactly in my "normal" listening position while messing with the KUBE), but I went back and forth a few times with connections and I swear I did not hear any detrimental effects on the mids or highs.

One difference I did notice, I have less gain from using the RCA to XLR cables from the KUBE to my amp (same as with the LF when I tried biamping previously). I have to crank the preamp up a bit more, but I thankfully don't have any hiss, buzz or hum. I'm going to live with this setup until I get the parts I need to mod the KUBE for biamping***, or I may just make another set of RCA to XLR cables and forget the balanced preamp output altogether.

Now, as far as using the KUBE...
As we've been discussing here, the whole point of getting one was to see just how well it could extend the low end, because some of us felt we were missing out on the lower octaves. I can say that it does indeed work as advertised, but, as proffski suggested earlier, I think it may be at the expense of overall SPL and some very obvious strain on the woofers.

A few observations:

- With the LF and HF controls set at the center notch (which I assume would be flat), there was a noticeable bass boost when bypassing and un-bypassing the KUBE, so it seems those knob positions are not flat, or the same as bypass. I did not notice anything like this on the HF, but admittedly, I wasn't paying as much attention to it at the time.

- When engaging the KUBE at a decent volume with the LF contour slightly increased and some moderately bass-heavy material, the bottom woofer's movement began to scare me...

- The KUBE seems to not only extend the bass, but also change the tone of the bass, if that makes any sense. I noticed this regardless of whether the LF knob was centered or not. It almost seems like I lose a tiny bit of upper mid-bass as soon as the KUBE is engaged. Maybe this is part of the midrange coloration that people have mentioned?

So far, I think the KUBE on the 105/3 is a nice option if you want to get a little more oomph, but only at low to moderate volumes. For "critical" listening or filling the house with music, I would be wary of using it for fear of damage. IMO, the KUBE tries to make the 105/3 woofers do something for which they were not designed.

clubsport911 - Does what I described sound anything like your experience?

zaktech - Not sure I can say I can't live without the KUBE, because I still absolutely love these speakers even without the LF extension, but we'll see what happens after I get the biamp connections sorted.

[speakerguru]

[speakerguru]

[proffski]

Absolutely!

Cone / voice coil move further and perhaps into nonlinear region, result distortion.
Voice coil overheats and either thermal compression happens at the expense of dynamic contrast or it destroys itself.
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

[deckard]

Thanks for the replies.... I completely understand the requirements for producing more bass, I'm just not sure the woofers can (or should) take it, now that I've seen them in action.
I've seen 8" subs move like this, but they were designed with long-throw coils, which AFAIK these don't have.

speakerguru - Diagram 17 in the chart on the Rane page is for a Balanced male XLR to an Unbalanced RCA. This is the cable I am using. Aside from the drop in gain I described, it's working great. Am I missing something?

[speakerguru]

[clubsport911]

I feel that these last few posts sum up the conundrum of the Kube. All things being equal, I would have thought the 105/3's produce "more bass" than they do.

They are not small in stature, have 2 x 8" drivers, a port to swallow a small child and were designed by one of the finest manufacturers on the planet

However, as owners know only too well, lower registers are muted below 50hz.... Enter stage left Kube200 (much applause).

However from the last 6 months studying bandpass designs, cavity coupled bass and so on, I now have changed my understanding and expectations.

These speakers whilst looking large, are in terms of active bass volume, small. The CCB whilst being impressively accurate does not help as much as Kef imagined (hence perhaps why it dropped out of fashion in favour of the reflex design and never really caught on.. ?)

So, I feel that the Kube can only ever be a halfway house. The drivers do not have massive excursion . Neither are they designed for super high powers (no multiple layer windings, no double spider, simple voice coil former) so when used with the extra bass signal of the equaliser, must surely run into compression earlier.

I've not heard the Kube but Zacktech has, and he has heard my system as well. Clearly his had more bass but there were other differences in the system that are worthy of discussion but are off topic.

I have even wired in my av sub and spent ages setting it up to crossover in the right place. Even then, I was not convinced !

At this moment, I'm learning to enjoy the 105/3 "au naturel" . What is there is very articulate, tuneful and accurate (no boom). My old mission 765's (modified with high spec Vifa aluminium drivers, reflex) produced bass in far higher qty and they went a lot lower but the drivers were much more modern than the kefs and the port was tuned to ~30hz. The 65 litre cabinet helped...

Put simply, the Kube seems to push the design to the limit and knowing how I like my music at realistic volumes, I wonder if this is the right solution ?

I'd be interested to know how you set up works bi-amped with the Kube

Cheers !

[zaktech]

@deckard.. Bi-amp and the tone of the bass remains unchanged. The HF and mid range also remains unchanged, provided the Kube is only connected to the LF amp. The Kube without isolation to LF amplification is a bit of a compromise, but isolated to LF it is simply sublime. I play music very loud and I have not yet pushed the bass drivers to their limits even though I have the LF adjuster on the Kube permenantly set to max. Zak .

[vistisen]

[speakerguru]

There you go. I told you not many were made. Check out the hand typed label on the back - s/n 1026. (i.e. number 26)

[deckard]

Looks like the front panel comes off, possibly allowing you to adjust the selectable contour "presets"? I take it this was made specifically for the 107's, which likely means it wouldn't be best for the 105/3's?

[speakerguru]

Probably not, because the Kube 200 took care of that.

[deckard]

[speakerguru]