Townsend Isolda cable

[SIY]

There seems to be some confusion going on between characteristic impedance and "regular" impedance. Although both are measured in ohms, they are mostly unrelated.

I remember during my grad school days seeing a series of articles in Audio Amateur (the ancestor of my current publisher) by Dick Marsh where he conflated characteristic impedance with impedance when discussing how to run grounds in a preamp. Now at the time, I was teaching an E&M class and wondered a lot if I really understood what I was doing- after all, this was a big name publishing in an excellent magazine and I was a young pup. Then after reading it carefully and running some basic experiments, I realized that either the author didn't know what he was talking about, or he did and put that stuff in to make things seem more black magic-y.

Over the years, I came to the realization that he probably started out completely honestly confused, then later figured out his error (or had it pointed out to him), but then transitioned into encouraging this kind of confusion as part of his black magic hype which made him money. This seems to be an extremely common pattern in fashion audio.

 

[Max Townshend]

Characteristic impedance is irrelevant for the wavelengths involved. You can’t change physics even if your wallet is involved.

I wouldn't bother teaching you basic electricity if there wasn't a profit motive.

From the same paper:

View attachment 23983

Exactly what instruments have you used to make this statement? My Audio Precision analyzer has a bandwidth of 1 Mhz. It can generate signals up to 200 kHz. It has a dynamic range better than any power amplifier by far. Its frequency response is ruler flat. In every way the analyzer exceeds our hearing sensitivity sometimes by massive (orders of magnitude) more sensitivity.

This was written in 1985

 

[Max Townshend]

Then we have this:

View attachment 23984

Spreading the myth that we need impedance matching for audio. We absolutely do not. A power amplifier has impedance very close to zero. Let's assume zero for simplicity. Let's have an 8 ohm speaker. Now, add a speaker wire with 8 ohm resistance/impedance and now you have a voltage divider:

Z1 will be your speaker wire and Z2 will be the speaker. Vin will be the amplifier. If Z1 is 8 ohm as Z2, then it will dissipate half the power the amplifier delivers to the speaker! Same current goes through both resistors so the math dictages power through Z1 is Z1 * I as will Power through Z2= I * Z2.

Raise your hand if you want your speaker wire to throw away half of your power. Good, I don't see any hands raised.

For RF situations or where cables are kilometers long as is with analog telephone we have reflections to worry about so matching impedances are used as you indicate. But for audio, we do not and as such, this is absolutely wrong thing to do. Wire resistance/impedance must be kept to minimum in order to reduce its losses.

In addition to straight losses, speaker impedance varies with frequency. If the wire resistance/impedance is a significant fraction of the speaker impedance, it will server to change its frequency response which again, is a bad thing.

I suggest reading Snow's 1957 Journal of AES paper, Impedance -- Matched or Optimum? Here is the synopsis:
View attachment 23987

View attachment 23988

This dog does not hunt. It didn't in 1957, and doesn't today. Simple, basic understanding of electrical systems and transmission stipulates this.

OK

 

[DonH56]

I missed this one. After a little reading and reflection, I'm glad.

Although, the new 50 GHz TDR we got at work would probably show all sorts of wiggles into a speaker cable.

 

[Max Townshend]

I missed this one. After a little reading and reflection, I'm glad.

Although, the new 50 GHz TDR we got at work would probably show all sorts of wiggles into a speaker cable.

Really good kit. lucky you.
Yes, it will show loads of wiggles, due to strays etc, but the elephant-in the-room will jump out at you!

 

[amirm]

Yes, I agree, but please pay attention as to how you use your gorgeous equipment.
I am demonstrating everything on the most basic equipment. Please try the experiment yourself.

Send me your cable and I am happy to see what it does.

 

[Max Townshend]

Yes, gladly.

What length and where to? Just the cable, terminated with flying leads and separate inductors and Zobels.

 

[amirm]

Yes, gladly.

What length and where to? Just the cable, terminated with flying leads and separate inductors and Zobels.

I will start a conversation and we can take it from there.

 

[Max Townshend]

Great, How do we proceed?

 

[amirm]

Great, How do we proceed?

Check your messages in your Inbox.

 

[Murrayp]

At the risk of embarrassing myself to the world, I have used Max's Isolda speaker cables for some years. I've compared them to various other speaker cables of conventional construction. I prefer these cables. To me there is an audible benefit from cables of this flat construction (I've used three different such designs over the years but I prefer these). The difference of the construction is mainly heard in lock of the sound stage - Max's add apparent extension at both ends- including tightness in the bass that helps things lock together. I doubt the virtues would be noticeable without nearfield listening and a low output impedance (SS) amp or suitable speakers (low extension). Sort of "lowish" impedance amps don't do it for me (eg d'Agostino, very doubtful about any valve amp). Over many years I've often wondered what the cause is but, whatever, I like them. I'm not closed about this and have listened to many speaker cables at all price ranges. Sorry to all the nay sayers here - you do need to listen too - not just assume. So please measure, but please listen too.

My background btw is 38 years in power electronics design. Sometimes I think "suspension of disbelief" needs to relate more to my technical views rather than the musical event portrayed.

Presently enjoying Nord n-cores driving B&W 800D3 from DEQX /Roon.

M

 

[Purité Audio]

Keith. The video was made 12 years ago.
High capacitance and low inductance is mandatory for speaker cable to get square root L/C near 8 ohms to eliminate reflections. see
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-14/characteristic-impedance/

SIY It doesn't matter if the PAIR of wires are coiled or not, as there is no net external field, electric or magnetic. The results are identical if coiled or uncoiled. Try it yourself.

Keith. See above. Also, square waves are quite good for analysing the dynamic performance of electrical circuits.

Amir All wires are 10 metres in length, except for the long coil of Monster. The short one is 10m.

Solderdude. The spikes are due to to multiple reflections giving the appearance of rolloff. The results when playing music are shown here

I will be posting a video soon where you can listen to the difference. Quite alarming!

We modelled the class AB transistor amplifier and found it to be stable with zero capacitance and 2 microfarads, but maximum instability with about 10 nanofarads. When my colleague Jack Dinsdale designed the first transformerless transistor amplifier he observed this and so he included the 3 microhenry inductor in series with the output to compensate for this to make the class AB amplifier unconditionally stable. In the 70s, John Farlow of Exposure Elecronics left this inductor out of his designs to make sure you used his widely spaced, high inductance, low capacitance cable for marketing purposes. 3. 5 metres of Exposure/Naim/TQ/DNM etc cable provides the 3 microhenries to stabilise the amplifier. He taught Julian Verica of Naim this trick, hence the proliferation of widely spaced cables with these conditionally stable amplifiers. To allow the use of our high capacitance/low inductance cable (sq rt L/C=8R) with these amplifiers. It works!

Amirm. Yes, the Lodestar AG02601a has a rise time of 0.5 microseconds, but what you have conveniently avoided observing is that the signal is passing through a severely band-limited, normal Cambridge Audio amplifier. The distortion is clearly audible!

Thomas Savage Typical flat-earther comment.

Max Townshend B.E. (Communications)

Max, very nice to see you posting here , welcome to ASR,
Thank you for taking the time to personally respond to my query.
Keith

 

[SIY]

To me there is an audible benefit from cables of this flat construction (I've used three different such designs over the years but I prefer these).

And once again, right here is the reason why claims of audibility need to be substantiated with controlled double-blind listening tests.

I'm glad you're happy with how you've spent your money, but without real listening tests, testimonials (no matter how sincere) have all of the evidentiary worth of the testimonials about alien abductions or homeopathy.

 

[Murrayp]

SIY, fair enough but don't you think there's some room for some subjective support for the product? The only reason I commented here was because I found the discussion rather negative and aggressive toward the maker so I thought I'd add some positive balance from my personal experience. Perhaps this is the wrong forum to state what we like - no room for that - this is Science after all. Said in jest - remember I'm an engineer. I'll look forward to the test results. M

 

[SIY]

SIY, fair enough but don't you think there's some room for some subjective support for the product?

"Subjective" is a term often misused as "totally non-controlled." If your comparisons are sighted, then from the standpoint of understanding reality (you know, the "science" part), then no, there's no value in them. If you can actually hear a difference, not peeking won't change that, and basic controls are absolutely necessary as a sine qua non.

 

[Max Townshend]

I also see this table of measurements:

View attachment 23965
You then say:

How did you get to 8 ohms? I don't know which one of the above is yours but taking the highest one at 88 milliohms/meter, 10 meter length would be 20 meters roundtrip = 0.088 * 20 = 1.76 ohms, not 8 ohms. How did you get to 8 ohms for DC?

You are referring to resistance, R. That is not the issue. It is Zc that is being discussed. In the example above, Zc is 6.1 ohms, which is our new F1 Isolda Fractal cable. The 8 ohms refers to our earlier Isolda cable

 

[sergeauckland]

I just don't understand why characteristic impedance is remotely relevant to loudspeaker cabling. Nothing in a loudspeaker system is impedance matched. The output impedance of the amplifier is essentially zero, the load impedance is anything from 2 ohms to 30+ ohms depending on the loudspeaker and the frequency, and the frequency range is so far away from RF where wavelengths become comparable with cable lengths that it's a nonsense.

I'm reminded of the similar nonsense that used to be spouted back in the late 1960s over 600ohm matching, when low output impedance sending and bridging receiving started becoming popular. Yes, for analogue telephony when cables can be kilometers long, even hundreds of kilometers, impedance matching is a Good Thing. Within a studio or home system, it's totally irrelevant.

S.

 

[solderdude]

The test results of Max T. seem to indicate the frequency response is wider (in the upper extension) for his cable compared to 'normal' cables.
That roll-off doesn't seem to be caused by cable capacitance. At 10m length there is 30nF of capacitance and 3uH of extra inductance.
Normal L/C filter freq. would be at around 500kHz.
What is seen from the scope shots is that 'normal' cable shows a roll-off (much lower C but higher L) where the high capacity cable doesn't.
A 10m 'normal' cable would be around 10uH and 2nF probably and around 1MHz.
Yet, the normal cable seems to roll-off and the high capacitance one does not.
This is not what one would expect.

From what I can see is that at 10m cable length the 'roll-off' (lets leave it in the middle where it comes from) is around 50kHz (-1dB).
One would expect a 3m cable (which is more of an audiophile length) would be around 150kHz (-1dB) and don't think this will be audible as no source nor recording nor transducers nor ears will be sensitive to that.

I also cannot see nor have I seen compelling evidence that it matters for bass frequencies and midrange.
The nulling I did once many years ago with 'normal' cables also showed high frequencies to differ in the null tester.
This seemed to come from the phase being different because of the length of wire. Once I corrected for the length it nulled fine again and all differences with speakers and music seemed to correlate to the impedance variations of the speaker ... so Resistance related.
After that I gave up.
All this was triggered by the 8 Ohm/m carbon cable from Dynaudio at that time.
They made it 8 Ohm by having a conductive isolator and a center wire (coax) that had some resistance.
When you loaded say 100m of cable with an 8 Ohm resistor you would measure 8 Ohm resistive, but at the end of the cable the output level was way less than at the input (L-Pad principle). When you cut the cable to 1m (and clamped on the proper connectors) and load it with 8 Ohm you still saw 8 Ohm resistance.

This won't be the case here. 100 m + 8Ohm load at the end would give 9.7Ohm DC reading and at 1 m 8.008 Ohm.

As said... I can't see this do anything for low frequencies when 2 cables have the same DC resistance.

 

[solderdude]

@amirm As I don't have the Isolda cable I can't do any comparisons so I have this 'theory' that would be easy to put to the test.

Assuming the high capacitance (and low inductance) is the reason for the improvements (regardless of theory) and other manufacturers exist that have high capacitance cables it occurred to me that maybe the rather high capacitance effect alone could be easily tested.

I would like to see the following test:
Generic (low resistance) cable with similar length as the Isolda with on the cable input 1x 3.3uH inductor (should be air wound and plenty of wire thickness to protect your amps) on the hot end of the cable and on the output of the cable a capacitor with about the same value as the measured capacitance of the isolda - measured (or estimated) capacitance of the generic cable.
After all the Isolda cable is just a very long stretched capacitor in essence that connects the amp to the speaker.

Just another reason to go active folks... no 'debatable' speaker cable lengths messing up fidelity.

The theory behind this test is to see whether that high capacitance is the reason or the waveguide theory is valid after all despite the theory saying the wavelengths are too short for this.
I can't see DC being improved by a wave guide nor say 100Hz for that matter.
But what I can 'imagine' is that when using a bandwidth limited 10kHz squarewave (which the output of any amplifier is) still has a lot of ultrasonics with a lot of energy well up to 100kHz for instance. We are clearly 'looking' above 50kHz here so the amp used should at least reach this.

At the end of the cable such a signal will be greeted by a capacitance of say 27nF or so (10m cable) which will have an impedance of around 50Ohm which is lower than the 'about 200 Ohm'. When this is in parallel with a speaker it will be lower.
Even better .. use the same Zobel as Towshend uses (10 Ohm + 0.22uF which is about 16 Ohm around 100kHz) and it becomes around 8 Ohm there.
No reason to 'reflect' anything there any more.
The extra capacitance will effectively short higher harmonics of say 1MHz or higher when present.

Another experiment could be to not even use the 3.3uH inductor and extra capacitor but only used the Zobel at the end of the cable ?

I assume mr. Townshend already has done these experiments and got better results with his (quite different geometry) cable.
In that case geometry is what matters.
When the same effect is achieved with just the Zobel network or the extra inductor + capacitor + Zobel then every handy DIY-er or handy business man can make 2 'cable interface boxes' and make any cable 'directional'.

I find the results Townshend got 'intriguing' enough to be tested by a third party and made more public.
When indeed Townshend's theory is true (reflections and geometry) then there is reasonable doubt that this matters in speaker cables.

 

[solderdude]

I just don't understand why characteristic impedance is remotely relevant to loudspeaker cabling. Nothing in a loudspeaker system is impedance matched.

S.

I would agree with this and can't see it being important for audio frequencies either but the 'technical evidence' he presented does appear to point in the direction of his theory. He seems to have technical evidence.
I don't think his nulling tests are proof of the audibilty as one can shoot some holes in there.
Nulling long interconnects will also show differences in the upper treble due to phase shifts and the nulling process which cannot discriminate between phase and amplitude differences yet the waveform will not have altered, just the different length is the culprit (80ns delay in 10m) will measurably roll-off treble while measuring FR at 10m won't show any roll-off.

I think testing/comparing the cable is not wasted time... in the interest of science at least.