Zero Ohms

[Bryson]

Does anyone want to hazard a guess at how this product actually works?:

https://zohms.com

It claims to allow use of any speakers at all without worrying about impedance mismatch, essentially allowing the impedance to drop to effectively "zero ohms" and still working.  It's not powered, totally passive.  It's specifically not a 100v/70v system.  What are they up to?

 

The unpowered and "black box" nature of the product initially set off my snake oil detector, but they're being represented by reputable distributors (over here anyway) so I guess it does actually work....but how?

[sandall]

15 minutes ago, Bryson said:

the unpowered and "black box" nature of the product initially set off my snake oil detector

Mine too.

[DrV]

From the Vietnamese Sailing Club case study: [QUOTE]Standard laws of physics would dictate that the ability to connect 
speakers in this fashion is not feasible.[/QUOTE]

So which particular non-standard laws of physics do they follow instead..?

I'd really like it not to be snake oil as it would be very interesting, but when someone claims to be able to break the laws of physics you have to wonder. Shall we all contribute so that Big Clive can buy one and explain it to us?!

Edited June 2, 2023 by DrV

[mackerr]

I expect it is just a big transformer in the box. The brochure never says no transformer, it say you don’t need 70/100V transformers. It also says “transforming audio”. In 70/100V systems each speaker has a transformer, I think with this there is one large transformer for all the speakers.

Mac

[Keith_]

Well, that is interesting. They explicitly say there is no transformer and the thing handles 4kW, so I think there is not room in their short 2U box for any big power handling passive components. I had a quick look for relevant patents and found this: US20170070195A1.  Is that relevant? If this thing works and is not too pricey, I would be up for using it.

UK distributor:  https://www.dizzyfish.net/

Edited June 3, 2023 by Keith_

[richardash1981]

8 hours ago, Keith_ said:

I had a quick look for relevant patents and found this: US20170070195A1.

That patent (which is Music Group, i.e. Behringer etc.) is a system for doing distributed active speakers - each speaker has it's own Class D power amp, but all are fed down a single cable which carries both DC power and the audio signal. That's the baseline, the patent is for adding a system to allow the amplifiers to be switched off when not in use, but brought on when needed, in the name of saving idle power (which if you starting point is a paging system which runs 24/7 could be a quite a big reduction). I don't think it will be relevant to the original box, which claims to work with ordinary low-impedance passive speakers.

If I was to respond to Bryson's original post and speculate on the way the box works, I would suggest a chopper at work (possibly with some sort of feedback loop to adjust it for different loads). In principal a low duty cycle Pulse Width Modulation (PWM) together with an output filter can be used to provide high current at low voltage from lower current at higher voltage, subject to the frequencies of interest being much lower than the PWM cycle frequency. The distortion numbers being nothing special and the high frequency roll-off on the chart would allow for this, maybe 5% duty cycle PWM at 400kHz - which is more than doable with modern fast electronics. The whole system would be driven by, and so modulated by, the incoming audio, and so sort of "passive" - at least in that the power for the control circuit could be stolen from the incoming audio (rather than a mains input), the way that Stax used to do for electrostatic headphones.

Whether it is a sensible idea I seriously doubt - not least because the speaker cable losses at those very low combined impedance will be astronomical - something we have worked out on here before now!

[Keith_]

Great suggestion, Richard. I had wondered about taking power from the incoming audio (kind of cheating). You point about cable loss seems reasonable: I thought that was the basic reason for 100V line. If for simplicity we just consider resistive loads, then the current, at least for the first few speakers on the line would be enormous and require exceedingly fat cables (https://www.grc.nasa.gov/WWW/k-12/airplane/ohmrpar.html). It seems using that zero ohm thing would have most of the energy going into resistive, rather than inductive load (a very expensive heater). The low duty cycle PWM sounds analogous to a class D amp. Is the theory that current is effectively proportional to pulse width? I don't think I understand it yet, do you mind explaining or pointing me to the theory?  One day I will learn how to read patents!

Edited June 4, 2023 by Keith_

[mnorwood]

According to this article from 2021, the applicable patent number (which doesn't appear to be silkscreened or otherwise printed on the product) is US9479870B2. My electronics know-how is insufficient to tell whether or not it makes sense.

[Keith_]

Thanks mnorwood. So it's just a giant capacitor acting as a sort of flywheel or ballast, with a very basic high-pass filter to compensate. Sheesh!

One of these for an experiment?  https://uk.farnell.com/kemet/als70a203kf100/cap-20000-f-100v-alu-elec-screw/dp/2729166?st=20000 mf capacitor

(legal issues asside, I won't be trying it on any expensive kit)

[sandall]

Ok , so it's a couple of big capacitors in parallel in either the hot or cold leg, with a bit of frequency correction thrown in, rather like the output circuits of most early transistor power amps. If it works, why were (really smart) designers back then quoting minimum loads of 4 or 8 ohms?

[DrV]

Without doing the maths (cos I've forgotten most of the a.c. theory I ever knew, which wasn't much to start with) I suppose the principle is that having a fat capacitor in there limits the current at low frequencies, where the speakers are nearly short circuits, and the speakers themselves limit the current at higher frequencies because they are mainly inductive. (Ignoring all the weird stuff that happens around resonance!). What I would question though, is the assertion that you can comfortably use polarised  electrolytics in such a circuit. When they were used as the output caps of transistor amps that was because the output was sitting at half the supply rail so one end was (usually) +ve w.r.t. the speaker terminal, the other side of the speaker being connected to the -ve rail.

[sandall]

I suspect that 25000uF of non-polarized might be hard to find (& rather large). I was never very happy with the idea that if an electrolytic went short it was going to put 30V DC across my expensive speakers.

[DrV]

35 minutes ago, sandall said:

I suspect that 25000uF of non-polarized might be hard to find (& rather large).

Indeed, but the usual arrangement is to put two in series with opposing polarities (obviously twice the required value).

[richardash1981]

4 hours ago, DrV said:

Indeed, but the usual arrangement is to put two in series with opposing polarities (obviously twice the required value).

The weird thing with this patent is that it shows them in parallel with opposed polarities - which will more or less end up as a short circuit ...

I fear that this story mostly indicates the short-comings of certain Patent systems, and the amazing salability of snake oil ...

At best most of the amplifier voltage swing will be lost across the series element, greatly reducing the available output power to the speakers. At worst, the huge phase shift involved (as the amplifier is now essentially driving a capacitive load with a little series resistance) will cause the driving amplifier to overheat and fail. I'm sure it will invalidate your amplifier warranty quite nicely!

[J Pearce]

My biggest concern with specifying and installing this sort of thing is that if it doesn’t work/breaks and isn’t fixable you’re into a whole world of rewiring.

At least 100V is a standard where you can change/upgrade various components and know they’ll work interchangeably.

For the scenarios this product professes to be ideal, I suspect you’d be better served with distributed amplifiers with CAT6 between them, you could feed analogue audio (with DC power too) or network audio over the CAT6, and it’d be much better future-proofed. There are even POE speakers that work well for paging/BGM type work, and use a standard structured cabling that is easy to reuse/upgrade etc.