Someone explain this bizarre 3-way

[guy48065]

I bought these a few weeks ago at a pawnshop.
The tall towers are the new-old addition, plus I've been using the subs from the system next to them.

They're heavy as all hell and have some unique features. On the sides are slabs of Fountainhead Corian, held on by tension rods that pass all the way through the cabinets to the other side.
Curiosity got the better of me and I decided to finally dissect these speakers.
I laid one on its side and removed the six bolt heads so the slab with the woofer hole could be removed. This is what I found underneath:

I'm baffled, pun intended, by way there are holes in the sealed upper part of the cabinet. The Fountainhead panels are gasketed to the sides so there's no leakage, but I don't understand what purpose the upper holes serve.
Next are the center two holes, each of which contain a heavy weighted column. The upper one is a length of PVC pipe with caps that is filled with some sort of mass... concrete... lead shot... I don't know. The one right below is a cylinder of rock. The length of each of these, plus the pad in the center of the ends, brings them exactly flush with the side of the cabinet. The intention here might be to keep the 1" mdf sides from bowing in as you tighten the tension rods.

The 8 inch woofer is a very solid dual voice coil unit with a cast basket and a vented pole piece. I don't know the make of it because the labels have been removed. I couldn't find a similar one with purple foam surround searching on Google.
The mid-range is an Audax HM170C0, the front tweeter is a Morel MDT32. There's a tweeter at the top of the rear of the cabinet but I didn't want to remove it to see if there was a brand on it. It's a small dome tweeter with a steel mesh grill.

There were no crossover components visible so I looked a little deeper and noticed the bottom of the woofer cabinet wasn't the overall bottom.
Unscrewing the spike feet I found the granite bottom plate removes to expose the crossover compartment.
Here's where things get even stranger:

There are no coils and no resistors used in this three-way system!
There's a bunch of capacitors glued to a PCB and much of the whole thing is covered in black conformal coating.

The woofer appears to be low-passed through a unique scheme where one of the voice coils is directly connected to the binding posts and the second voice coil is connected through electrolytic capacitors OUT OF PHASE--thereby canceling the high frequencies driving the motor by the main voicecoil. The voice coils then acts as a summing junction for these two independent signals.
I followed the wiring and found that the Audax mid-range is run full range. The tweeters have a capacitor on each wire feeding them.
A "balanced" crossover. Intriguing.

In addition to the unique cabinetry and unique crossovers the cones & domes are coated with something that makes them stiffer.

None of this would matter if they sounded like shit... But they sound amazing!

 

[guy48065]

If anyone can give me more information on the design aspects of these, or the drivers used I would really appreciate it.
I would date these as 1985-1990 from what I do know, and what I've been able to find out.

 

[Penelinfi]

The PCB has "Unity Audio" on it by the looks. Perhaps you can find a model number too?

It could also be a DIY job or modification, or maybe a prototype.

 

[restorer-john]

The capacitors will likely have date codes, as will the PVC piping date of manufacture. I doubt they are that old- gold terminals like the ones used are post 2000 IMO.

They look like someone's 'thought bubble' speakers. I hope they were really cheap...

 

[Penelinfi]

Depends what you call really cheap. They look nice enough though I don't doubt that they could probably do with a new crossover.
It's a good looking speaker imo.
I've had a similar style of speaker but with an average cheap cabinet. I actually turned the cheap bottom woofer into a passive radiator with "damping" (switch to short woofer terminals in isolation), because I didn't like the stock sound. And rework crossover. No real frequency measurement but I do work with impedance curve to make sure no odd resonance effects happen.

 

[sam_adams]

This is about some weird DIY speaker? Man, I thought this was something about Aubrey Plaza, Taylor Swift, and some sex-crazed monkeys.

 

[guy48065]

I knew these were Unity Audio because my 40yo sat/sub system is. That's why I obsessed over these & finally brought them home.
It's difficult to find info on Unity Audio, since it never was a big producer, and I don't think ever had an Internet presence. They got some exposure in Stereophile a couple times--one glowing review & one lukewarm (different products, different years).
Through hours of googling, leading down many rabbit-holes, I've finally identified these as a Cerous 6 system.

 

[guy48065]

I still haven't identified the make of the woofer.
I'm still in the dark about the purpose of the masses in the center of the enclosures. A simple brace would have been adequate to keep the sides from bowing in under tension-rod pressure.

 

[holdingpants01]

Nice find! There's possibility that the drivers or at least the woofer is made by them, certainly it's surround looks non factory glued. The crossover is rather exotic as there's none, at least according to them lol. There's some hint in brochure as to what those pipes suppose to achieve. Overall this thing gives DIY vibe but in a good way

 

[kemmler3D]

Fascinating stuff. These were probably pretty pricey when new, and I'm glad to hear they actually sound good. The capacitor-only crossover sounds questionable, so it's impressive that they got it to work. The corian and weighted tubes are really interesting, maybe they're used as weights to modify cabinet resonances...

 

[Penelinfi]

Would be great to get these measured as the marketing does seem interesting.

The holes in the upper cabinet probably reduce pressure on the MDF part; maybe a resistive sink with that tiny air gap between the MDF and stone.
The two masses seem to have a blue damping material on the ends; being "massive" to prevent resonance or perhaps transfer of resonance. Maybe like a tuned mass damper on a building?

All in all seems to be a way to introduce a lossy cabinet while also maintaining a stiff and heavy cabinet.

 

[Matt_Holland]

Did they get the patent on the crossover? Marketing suggests they have created a brick wall filter from just capacitors. Sounds like absolute BS.

 

[guy48065]

Did they get the patent on the crossover? Marketing suggests they have created a brick wall filter from just capacitors. Sounds like absolute BS.

I couldn't Google any patents in his name.
I agree the marketing is deep in the BS swamp but in this case I wouldn't assume it's all lies. Bob is a smart guy with a career in acoustics and materials. Google his older brother Michael Grost if you wanna see what gene pool he emerged from.

 

[Matt_Holland]

I couldn't Google any patents in his name.
I agree the marketing is deep in the BS swamp but in this case I wouldn't assume it's all lies. Bob is a smart guy with a career in acoustics and materials. Google his older brother Michael Grost if you wanna see what gene pool he emerged from.

There is a series filter topology where two drivers are connected in series with a cap across one of the drivers. It doesn’t fully roll off either driver (due to the shunt resistance of one of the driver’s VC) but it does separate them by about 6-8dB. Its useful if you have two identical drivers playing the same frequency range and want reduce a little the spacing cancellation effects. I wonder if something similar is used here.

 

[guy48065]

The holes in the upper cabinet probably reduce pressure on the MDF part; maybe a resistive sink with that tiny air gap between the MDF and stone.
...

I was thinking about this and at first I didn't think it likely that the tiny gasketed space between the mdf & corian could make any difference in anything. Then I switched from thinking volume to pressure & vibration. As the midrange pressurizes the box the walls move outward microscopically. Now if you cut holes in the sides and let that pressure out into a second space outside the box, couldn't that pressure then push back on the walls - - canceling the tendency to move outward?
An elegant alternative to making the box infinitely thick & heavy to keep vibration down.
Is this the "fluid coupled enclosure" mentioned in the lit?

 

[CedarX]

I was thinking about this and at first I didn't think it likely that the tiny gasketed space between the mdf & corian could make any difference in anything. Then I switched from thinking volume to pressure & vibration. As the midrange pressurizes the box the walls move outward microscopically. Now if you cut holes in the sides and let that pressure out into a second space outside the box, couldn't that pressure then push back on the walls - - canceling the tendency to move outward?
An elegant alternative to making the box infinitely thick & heavy to keep vibration down.
Is this the "fluid coupled enclosure" mentioned in the lit?

That may also explain the two columns in the center of the enclosure: they “brace” the corian slabs together, but the (wood) cabinet, at mid-height, is free to float/vibrate in between the slabs?

 

[ldarieut]

I thought at first it was some sort of crazy diy job where the builder covered a botched baffle on the side with corian.
The metal rods will introduce some ringing, so the concrete pipe from side to side are a way to minimize that, and adding some rigidity, that would be my guess.

 

[Ze Frog]

It's an interesting concept, I stumbled across this type of crossover when heavily into D.I.Y. it's basically allowing a full signal to first driver and then passing where the frequency will be -6dB down to the next driver and so on. The idea is, with perfectly matched drivers regarding frequency, impedance, sensitivity etc etc that it's almost sound quality wise like having effectively no crossover. This would however need really careful driver matching and there are very limited combinations you could use this way, each driver would require a very smooth roll-off slope without any horrible peaks.

I should imagine with some extremely careful thought this can be a rather effective method. Arguably far harder work than simply going the regular route.

 

[Ze Frog]

Did they get the patent on the crossover? Marketing suggests they have created a brick wall filter from just capacitors. Sounds like absolute BS.

While 'brick wall' is maybe a stretch, you could actually make a very steep slope. I'd imagine though these are more likely not too steep of a slope, otherwise the box would be full of capacitor's and little else. This method is known, albeit little, but it can actually work provided extremely carefully spec of driver's used. It's a method I seem to remember seeing in someone's D.I.Y open baffle build a good while back.

 

[guy48065]

Agreed in so far as good drivers are needed, with good power handling due to the slow rolloff.
All 3 drivers here are 90dB/W sensitivity so are loudness matched.
Having no low pass means all drivers are in parallel beyond their respective cut-in frequency and that presents a crazy low impedance...albeit a simple one with no coils in the crossover.