Townsend Isolda cable

[March Audio]

So you think you have a 12dB increase in noise due to

" a huge amount of added high frequency noise due to the decay of multiple reflections."



If a “long” line is considered to be one at least 1/4 wavelength in length, you can see why all connecting lines in the circuits discussed thusfar have been assumed “short.” For a 60 Hz AC power system, power lines would have to exceed 775 miles in length before the effects of propagation time became significant. Cables connecting an audio amplifier to speakers would have to be over 4.65 miles in length before line reflections would significantly impact a 10 kHz audio signal!

I dont know what you think you have proven but if it contradicts all existing knowledge about the subject then you should doubt your conclusions.

 

[Max Townshend]

But... but... but... HE DID A VIDEO!!!! PROOF!!!!!

OK, so what is wrong with the video that so upsets you?

 

[Max Townshend]

I put the question to James Clerk Maxwell and Oliver Heaviside. Both just laughed.

They laughed because they know and you don't

 

[Max Townshend]

So you think you have a 12dB increase in noise due to

" a huge amount of added high frequency noise due to the decay of multiple reflections."


The lower-case Greek letter “lambda” (λ) represents wavelength, in whatever unit of length used in the velocity figure (if miles per second, then wavelength in miles; if meters per second, then wavelength in meters). Velocity of propagation is usually the speed of light when calculating signal wavelength in open air or in a vacuum, but will be less if the transmission line has a velocity factor less than 1.

If a “long” line is considered to be one at least 1/4 wavelength in length, you can see why all connecting lines in the circuits discussed thusfar have been assumed “short.” For a 60 Hz AC power system, power lines would have to exceed 775 miles in length before the effects of propagation time became significant. Cables connecting an audio amplifier to speakers would have to be over 4.65 miles in length before line reflections would significantly impact a 10 kHz audio signal!

 

[PierreV]

Please don't get us confused with 99% of the high end cable makers where they change the model regularly and they have a range of "Best" cables.

Fair enough and waiting for independent tests as the technical details fly above my head. That being said, for the average customer, if 99% of an industry misbehaves or behaves incoherently, the best policy is probably to abstain.

 

[Max Townshend]

So what mechanism is causing the pink noise differences in the video?

 

[March Audio]

Actually I just watched the video. We have absolutely no information as to the test set up. You could be doing anything. Its totally meaningless as far as demonstrating or proving anything.

It sounds just like you have put a high capacitance in the circuit which has filtered the high frequencies.............


.....remind me, whats the capacitance of your cable?


Oh BTW, what happens when these allegedly massive reflections come back and hit an amp with an output impedance of 3mOhms?

 

[solderdude]

So what mechanism is causing the pink noise differences in the video?

That's the question is it. Before one can answer that there are a few unknowns to 'us'

A: what is the actual level of the signal across the wire compared to the signal level across the amplifier terminals. (this is the biggest question)
B: What is the actual DC resistance of both tested cables.
C: What is the impedance plot of the used speaker or dummy load look like ?
D: What does the spectrum of the signal measured across the wire look like ?

This info needs to be known otherwise the shown signals mean nothing.

Edit: What you are basically doing is 'measuring' a current through a current sensing resistor. Then change the current measuring resistor for one with another value and then compare results that cannot be compared. This part you make audible and then change the cards again by recording this with a camera.
Furthermore the oscilloscope shows the difference between the output of the amp and the load as well as those 2 signals as well.

That's not the correct way to go about this but probably the only way to 'show' differences that are probably too low in level to be clearly audible.

 

[Max Townshend]

Actually I just watched the video. We have absolutely no information as to the test set up. You could be doing anything. Its totally meaningless as far as demonstrating or proving anything.

It sounds just like you have put a high capacitance in the circuit which has filtered the high frequencies.............

 

[Max Townshend]

Here it is again
Here is the latest experiment. The circuit is attached.

And here is a video.

https://drive.google.com/open?id=1HRRaiVVifHlSKF0A6B0ukfPLy4Enbc26

The Pink noise is from my phone on Audio Tool
The audio is from the Sheffield Lab test disc, only playing the left channel.
The amp driving the cables is a Cambridge amplifier
The second amplifier is a Nobsound Lindsey-Hood class A (an absolute audiophile bargain)
The speaker is a small two-way.
The spectrum display is from a calibrated microphone, 2 inches (50mm) from the middle of the speaker. The analyser is a Behringer Ultracurve Pro DEQ2496 .
The camera is a Cannon G12. The sound you hear, is from the microphone in the camera, positioned about 3 feet away from the speaker and is a little "shrill" sounding due to the appalling acoustics. But you can still hear the difference, even on your phone!
The dummy speaker, is a hard-wired implementation of the dummy load, as represented in the simulations. (a real speaker would be very loud and swamp the other)

The circuit allows input selection to the power amplifier and the two cables under investigation are in parallel, connected to the output terminals.
The two way switch on the right selects the cable.
The object of the experiment is to observe the difference between the voltage on the send end and the receive end of the cable, by amplifying the difference between each end of the ground ("-") wire.
There is a clear difference between the cables, with the Monster exhibiting rising output, commencing at about 500Hz, rising by about 12dB+ at 20khz. In contrast, the Isolda produces a "rolled-off" sound. Further, the Monster sounds a fair bit louder than the Isolda, a bit masked by the AGC in the Canon microphone. If the differences were due to DC resistance, then the Monster should be 75% SOFTER than the Isolda.

In the case of the Isolda, the difference sound is due to the resistance loss only, whereas with the Monster, there is a resistance loss, similar to the Isolda, but with a huge amount of added high frequency noise due to the decay of multiple reflections.

The mathematics, the simulations, the measurements and the listening all concur.

Please try the experiment yourself.

I am pleased to answer any questions.

 

[solderdude]

Thanks for doing this.

Some very important questions that need an aswer but aren't in your post.

A: what is the actual level of the signal across the wire compared to the signal level across the amplifier terminals. (this is the biggest question)

So the answer should have 3 voltages (preferably measured with a continuous signal)
1: the RMS value of the applied voltage to the cable.
2: the RMS value of the voltage across the load.
3: the RMS value of the voltage across the measured wire.

Would be great to see this measured at say ... 50Hz, 1kHz and 10kHz SINEwave.
Maybe include 50kHz as well ?

I know this is all about the 'impulse' which we won't be 'seeing' here but seeing that the impulse in the monster cable is about as 'fast' a a 200kHz sinewave I don't think it is relevant.

What would be fun to see on the video and may be very interesting is to show the input and output of the cable (so not the difference) shifted so they almost are overlaying, just below one another of the following signals. Also not the current in the cable.
Just the voltages.

a 10kHz squarewave, a 50kHz squarewave,
a 10kHz sine and a 50kHz sine.

B: What is the actual DC resistance of both tested cables.
Stating that the Monster would be 75% softer is suspect.
Measuring 75% less at 20Hz for instance does not mean the same as sounding 75% softer at all.
75% = 2.5dB and thus somewhat 'softer'.
I assume you mean the Monster cable has a lower DC resistance than the Isolda.

C: Is your cable fitted with the Zobel and 1.5uH inductors or only 1 inductor in the cable part that is not measured ?

 

[SIY]

Three card monty. Delightful.

 

[March Audio]

So Isolda is 3100pF/m V maybe 50pF/m for typical speaker cable.

so 7m is what 22nF

I will perform some tests tomorrow, but the massive capacitance of your cable is probably acting as a filter.

 

[solderdude]

So Isolda is 3100pF/m V maybe 50pF/m for typical speaker cable.

so 7m is what 22nF

I will perform some tests tomorrow, but the massive capacitance of your cable is probably acting as a filter.

You also need to include 3uH in series.

Isolda (incl. 3uH) is acting as a low pass filter around 620kHz (lumped filter) @ -3dB
The monster cable being much lower in capacitance and about equal in inductance (as the 3uH inductor) should be well into the MHz but the evidence says the generic cable starts to drop off below 200kHz.


Where is the skin effect in these equations ? Above 20kHz that should become visible. Flat conductors have a low resistance due to the skin effect as the surface is large.

 

[March Audio]

aahh missed the added inductance.

The big give away here is the assertion that the monster cable exhibits a rising output. I have never measured this in any set-up. Never seen anyone comment on the such like.

 

[solderdude]

I think he means the voltage across the wire is rising with frequency.
This means the voltage across the load is decreasing.

The 6dB and 12dB numbers he uses to describe how much the HF rises compared to the lower frequencies.

The important part however is still a mystery as till now he did not mention the absolute levels of the voltage across the wire and the voltage the amp is putting out.


Let's see it this way... assume the difference between 50Hz and 20kHz is 12dB and the resistance over which this is measured is 0.01 Ohm.
The load will be approx 8Ohm and will be perhaps 10 Ohm at 20kHz.

The ratio between the impedance and cable = factor 800
The rise in the resistance of the monster cable = factor 4 so at 20khz the factor is brought down to 200 which means the resistance rises to 0.04 Ohm

This means that the voltage drop at the end of the cable is double (2 lengths of wire).
Simple calculus brings us to the following values:

8/(8+0.02) = 0.9975 = -0.02dB for the isolda.
8/(8+0.08) = 0.99 = - 0.086dB for the monster cable.

So at 20kHz the Isolda will play 0.06dB louder.... very audible indeed.

Its why I insist on knowing the actual voltage levels.
In reality the connectors used will also add some differences... but I think this is what we are talking about here.
At 200kHz the Isolda will become measurably 'better' but who cares ?

 

[March Audio]

I think he means the voltage across the wire is rising with frequency.
This means the voltage across the load is decreasing.

The 6dB and 12dB numbers he uses to describe how much the HF rises compared to the lower frequencies.

The important part however is still a mistery as till now he did not mention the absolute levels of the voltage across the wire and the voltage the amp is putting out.

Either way the same applies. I have never measured a 12 dB loss across a cable to a speaker. Anyone else?

.....now where did all that treble go..........


Yes, it would be the obvious and essential thing to do, measure input and output voltages

 

[Max Townshend]

Three card monty. Delightful.

Takes one to know one.

 

[March Audio]

Well I have just hooked up my B&W CM5 S2 test speakers to my headphone amp (it was on the bench) via about 3m of very ordinary generic and typical speaker zip type cable. It might be 1.5mm2 csa. I will document this and repeat more carefully tomorrow when I have time, pics etc.

Set 80 Hz 100mV sine at the amp output. Measured 99.7 mV at the speaker terminals. thats -0.02dB

Set 20kHz 100mV sine at the amp output. Measured 98.6mV at the speaker terminals. thats -0.1dB.

Just as expected.

...and yes tomorrow I will use white/pink noise and measure on an FFT just to be sure.

 

[solderdude]

The fun part would be if you could use an 8 Ohm cable made up from 6 lengths of 50 Ohm.
I would suggest to connect 3 mantles to the - of the amp and the core to the + and from the other 3 the core to the - and the mantle to the +
All 6 in parallel.
When Max is right the attenuation will be 0.02dB for both 80Hz and 20kHz.

That would validate his claims but completely invalidate the audibility of it.

Then we are all on the same page and while Max may be correct and the frequency response is better this way (due to reflections and not skin effect ?) then one can argue how audible a 0.08dB drop is at 20kHz.
I am sure audiophiles with hearing up to 100kHz (MQA users ?) will appreciate the difference.

Thanks for trying this... am at work a.t.m. so can't do it now ... and don't have enough 50 or 75 Ohm coax anyway.