• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Measurements of speaker cables in frequency and time domain

scott wurcer

Major Contributor
Audio Luminary
Technical Expert
Joined
Apr 24, 2019
Messages
1,501
Likes
2,821
I confess I can't recall ever doing this in 50 years of being a "hi-fi bug".

I was at a party where the host was playing the music a little loud through some old valve amps (interfering with folks "chatting up" each other). So someone just pulled the cable off, instant magic smoke.
 

Chrispy

Master Contributor
Forum Donor
Joined
Feb 7, 2020
Messages
7,751
Likes
5,910
Location
PNW
Guys with goofy gear should perhaps be careful if allowing either Costanza or Seinfeld to control the stereo.....
 

scott wurcer

Major Contributor
Audio Luminary
Technical Expert
Joined
Apr 24, 2019
Messages
1,501
Likes
2,821
I made an attempt to measure input impedance of 5m zipcord speaker cable with open end (no termination), with a point-by-point measurement at discrete frequencies and Excel sheet. The result looks quite realistic. There is a dip near 10MHz.

Appreciate the effort, but as I have always said wire threads have only down to go. From the totally inappropriate use of Heaviside's telegrapher's equation to the knee jerk "speaker cables are not transmission lines".
 
OP
pma

pma

Major Contributor
Joined
Feb 23, 2019
Messages
4,591
Likes
10,727
Location
Prague
Finally the last one. Measured input impedance of 10m coaxial speaker cable (not terminated) and corresponding oscillations of one amplifier to which this cable was connected. No magic smoke, only very hot heatsink due to cross-conduction in the output stage. This time, the amplifier was saved by its large heatsink.

10mcoax_open_impedance.png


oscill_amp_10m_coax.JPG

Power amplifier oscillations with the measured cable. The oscillations go away if the cable is terminated by a resistor of some 47 - 200 ohm.

Edit: as my measurement method of cable impedance is simple with not enough resolution, I am adding a simulation of the 10m measured cable. Please note the enormous capacitance at the 1st impedance dip. This is the killer we speak about.

10mcoax_open_impedance_sim.png

Simulation of 10m coax cable input impedance
 
Last edited:

restorer-john

Grand Contributor
Joined
Mar 1, 2018
Messages
12,579
Likes
38,280
Location
Gold Coast, Queensland, Australia
I confess I can't recall ever doing this in 50 years of being a "hi-fi bug".

Parties. Tripping over long speaker cables and pulling them out at high volume. Tube amps go pop. Some transistor amps do too.
 

Thomas savage

Grand Contributor
The Watchman
Forum Donor
Joined
Feb 24, 2016
Messages
10,260
Likes
16,298
Location
uk, taunton
Parties. Tripping over long speaker cables and pulling them out at high volume. Tube amps go pop. Some transistor amps do too.
Wow audiophiles with actual friends and a social life , the good old days , or maybe all just a dream .

Dreaming about parties where someone not only turns up the precious volume knob but the room is filled with people enjoying music and dancing rather than sitting in respectful silence in a trance like state consumed by awe for the equipment and revelling in the safety of solitude.., THEN the wires get ripped out by these ravers and the amps go bang!

Thats like the ' teeth falling out ' dream and the ' walking around school with no trousers ' dream all rolled into one .

Good job @pma , its a shame how the whole ' gotcha ' ' no you didn't ' vibe gets in the way so often.
 

KSTR

Major Contributor
Joined
Sep 6, 2018
Messages
2,690
Likes
6,013
Location
Berlin, Germany
Finally the last one. Measured input impedance of 10m coaxial speaker cable (not terminated) and corresponding oscillations of one amplifier to which this cable was connected. No magic smoke, only very hot heatsink due to cross-conduction in the output stage. This time, the amplifier was saved by its large heatsink.

View attachment 127863

View attachment 127864
Power amplifier oscillations with the measured cable. The oscillations go away if the cable is terminated by a resistor of some 47 - 200 ohm.

Edit: as my measurement method of cable impedance is simple with not enough resolution, I am adding a simulation of the 10m measured cable. Please note the enormous capacitance at the 1st impedance dip. This is the killer we speak about.

View attachment 127870
Simulation of 10m coax cable input impedance
Nice to see a documented real-life example here.

Another take-away we should not forget:
Preamplifier or Headphone amplifiers can and will have the exact same issues. Headphone outputs which have been "optimized" for lowest output resistance by practically omitting any series resistance are especially prone if they don't have a series decoupler for RF frequencies installed -- which one should do anway to avoid RF sneaking into the amp from the output side
 
  • Like
Reactions: pma

scott wurcer

Major Contributor
Audio Luminary
Technical Expert
Joined
Apr 24, 2019
Messages
1,501
Likes
2,821
Thats like the ' teeth falling out ' dream and the ' walking around school with no trousers ' dream all rolled into one .

The number one dream is falling short on credits to graduate. Had the teeth falling out one last night.
 
OP
pma

pma

Major Contributor
Joined
Feb 23, 2019
Messages
4,591
Likes
10,727
Location
Prague
Another take-away we should not forget:
Preamplifier or Headphone amplifiers can and will have the exact same issues. Headphone outputs which have been "optimized" for lowest output resistance by practically omitting any series resistance are especially prone if they don't have a series decoupler for RF frequencies installed -- which one should do anway to avoid RF sneaking into the amp from the output side

Hi Klaus, I tried my headphone amplifier with 0.06 ohm output impedance when loaded with 10m of Tasker C121 cable once with no termination (open end) and secondly with the far end terminated by 50 ohm. I was measuring the 200 kHz square response at the headphone amp output, i.e. the cable input. There was nothing special happening, only that in case of the open cable there is a predictable reflection on the rising edge and some other well damped reflections. The amp has no special anti-RF elements at its output, only it was thoroughly tested with any imaginable load to ensure stability. Yes we would see reflections (in case of the open end cable) with higher amplitude if the amp was even faster.

10mcoaxC121_openend_headampdrive.png

Tasker C121 10m, open end, cable input. Cable driven from headamp with 0.06 output impedance.

10mcoaxC121_50Rend_headampdrive.png

Tasker C121 10m, 50 ohm terminated end, cable input. Cable driven from headamp with 0.06 output impedance.
 

BDWoody

Chief Cat Herder
Moderator
Forum Donor
Joined
Jan 9, 2019
Messages
6,948
Likes
22,625
Location
Mid-Atlantic, USA. (Maryland)
I was at a party where the host was playing the music a little loud through some old valve amps (interfering with folks "chatting up" each other). So someone just pulled the cable off, instant magic smoke.

How was the rest of the party? I bet it got very quiet very fast...I hope the host had a sense of humor about it.
I am thinking this would make for a good SNL skit.
 

KSTR

Major Contributor
Joined
Sep 6, 2018
Messages
2,690
Likes
6,013
Location
Berlin, Germany
Hi Klaus, I tried my headphone amplifier with 0.06 ohm output impedance when loaded with 10m of Tasker C121 cable once with no termination (open end) and secondly with the far end terminated by 50 ohm. I was measuring the 200 kHz square response at the headphone amp output, i.e. the cable input. There was nothing special happening, only that in case of the open cable there is a predictable reflection on the rising edge and some other well damped reflections. The amp has no special anti-RF elements at its output, only it was thoroughly tested with any imaginable load to ensure stability. Yes we would see reflections (in case of the open end cable) with higher amplitude if the amp was even faster.

View attachment 128280
Tasker C121 10m, open end, cable input. Cable driven from headamp with 0.06 output impedance.

View attachment 128281
Tasker C121 10m, 50 ohm terminated end, cable input. Cable driven from headamp with 0.06 output impedance.
Pavel, sure there are designs that handle any amount of real or reflection-generated capacitive load without sustained oscillation, even without any R//L isolation cell.
One just cannot rely it that small signal low current amplifiers are automatically any safer than speaker level amplifiers.
 

Head_Unit

Major Contributor
Forum Donor
Joined
Aug 27, 2018
Messages
1,341
Likes
688
With class D the intention is to filter all HF anyway so it does not matter there. class-D amplifiers are bandwidth limited anyway while one can build analog amps with >100kHz bandwidths.

GBW
What are the highest bandwidth Class D amps out there? I saw one test of I forget which, bandwidth much higher than usual but not like 500k or anything. In Class AB huge bandwidth was a thing...doesn't seem so as much any more? Maybe because it typically used a lot of feedback?
 

Andysu

Major Contributor
Joined
Dec 7, 2019
Messages
2,885
Likes
1,478
Excellent thought.

It's boring to listen to dummy loads.

How about a test of these electrical microvariations as shown in the response of a speaker in a room taken at the listening position?
that was what i was precisely thinking doing it, you know doing it, trying see if i can use the THX monitor with amp return connected to length cable connected to JBL hf horn in certain way so i can see some sort of result of interest with simply frequency sweep. the test has been on my list for few years, but i have Cats to feed and look after which is far more important than some tom holman THX cinema and dolby lab for movies or music listening, if you get the understanding of my meaning? but i see if i can make effort as this, been one of the curiosities on my mind for a while.
 

egellings

Major Contributor
Joined
Feb 6, 2020
Messages
4,005
Likes
3,245
I think that cables may make a difference in sound, but the effect, if any, is microscopic, and I am not willing to spend a lot of money for so little benefit, if any.
 

Chrispy

Master Contributor
Forum Donor
Joined
Feb 7, 2020
Messages
7,751
Likes
5,910
Location
PNW
What are the highest bandwidth Class D amps out there? I saw one test of I forget which, bandwidth much higher than usual but not like 500k or anything. In Class AB huge bandwidth was a thing...doesn't seem so as much any more? Maybe because it typically used a lot of feedback?
Why is that particularly important?
 

Head_Unit

Major Contributor
Forum Donor
Joined
Aug 27, 2018
Messages
1,341
Likes
688
Why is that particularly important?
Why is what? The bandwidth? Or the feedback? I tend to believe designers who don't like gobs of feedback, because it's nice for steady state but music is not steady state. In some sense feedback should operate at the speed of light but in physical devices...my electrical engineering education was not in that area.
 

Chrispy

Master Contributor
Forum Donor
Joined
Feb 7, 2020
Messages
7,751
Likes
5,910
Location
PNW
Why is what? The bandwidth? Or the feedback? I tend to believe designers who don't like gobs of feedback, because it's nice for steady state but music is not steady state. In some sense feedback should operate at the speed of light but in physical devices...my electrical engineering education was not in that area.
The bandwidth to start.

ps or perhaps the range of the bandwidth as to what is actually meaningful....
 

Andysu

Major Contributor
Joined
Dec 7, 2019
Messages
2,885
Likes
1,478
it is possible highly possible that my Cat, Bear as been doing some chewing on the HF horn speaker cables for L C as signal SPL looks odd in the room while on the THX monitor the sound levels are equal as that is how the THX professional works with short amp return cables and the longer ones going out to the THX speakers.
Bear is a very clever Cat, i do not underestimate him. he has managed to raid the cat food box and pull out 5 packets of cat wet food, last night. so between him and Magic they have eaten and be fed late tonight. you can see Bear sniffing out the JBL 2445 CD, he is plotting. he has managed to get behind the projection screen so many times now, more times, than he has had wet cat food meals. Bear is shifty Kitty Cat.

i may have to take the projection screen down and check the HF horn L C cables, i still get good sound, only its few dB less and i have to compensate with amplifier. Bear is a very clever Snowshoe Cat.

169417711_10159056364895149_5256226429022205055_n.jpg
264188655_10159564714885149_2478385935675884114_n.jpg
169562100_10159056366115149_1514796056143266570_n.jpg
 
Top Bottom