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Absolute Polarity, Asymmetric waveforms and clipping effects

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Posted on March 9, 2016 at 14:20:48
BigguyinATL
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Posts: 2997
Joined: April 10, 2002
To study the effects of the audibility of retaining absolute polarity it is useful to have an asymmetrical waveform (see link for examples). But I was thinking about this and was noting that you really have to watch out not to clip the signal within an amplifier in the system - I was going to use headphones for the listening test. If an Asymmetrical waveform clips on the "larger" side signal - the device it is driving is going to see a DC offset voltage - essentially moving the driver out of the center of it's gap causing likely audible distortion. A multi-way loudspeaker high passed devices will go unaffected - but the woofer and its inductor coils will be effected. probably noticeably. If sufficient in amplitude it could damage the loudspeaker. Just think how much a 1.5 volt battery causes a woofer to move.

While playing music, it may be more likely that a woofer is damaged that a tweeter with amplifier clipping! And certainly the audible effect of the clipping will be greater as the woofer (that reproduces the primary fundamentals and overtones of the music we listen to operates non linearly...


"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

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What's the point you're trying to make? Nt, posted on March 11, 2016 at 05:31:39
geoffkait
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Nt

 

Heck if I know... OK, posted on March 11, 2016 at 09:40:01
BigguyinATL
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(1) some folk have the misimpression that clipping is always a harsh high frequency experience. If clipping is resulting in an dc offset driving a woofer's neutral point forward (or backward) in the gap, the observation of the distortion would manifest itself as a much subtle distortion such as a change in timber. And the effect would go away once the clipping conditions alleviates itself.. Tube Amps are not immune either - the DC voltage will saturate the output transformer.

"The DC component is a very sensitive parameter and a small DC bias
can lead to the complete saturation of the magnetic core of the
transformer with the generation of harmonics (distortion of signals).
The order of magnitude of the DC current necessary to saturate the
transformer is the same as that of the transformer no-load current i.e. a few % of the nominal current."

"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

RE: Absolute Polarity, Asymmetric waveforms and clipping effects, posted on March 11, 2016 at 11:46:27
Tony Lauck
Audiophile

Posts: 13629
Location: Vermont
Joined: November 12, 2007
If you are doing any kind of listening test and making adjustments to input signals then you are not hearing the signal, you are hearing the amplifiers and speakers reaction to the signal. Thus, for example, if you have a signal with two sine waves at 25 kHz and 26 kHz and there is no distortion you will hear nothing. But if the amplifier distorts it will create a beat tone at 1 kHz which may be audible. (If you crank the volume up in a clean system you may create similar distortion in your own ears, if you don't smoke your equipment and damage your hearing.)

It is certainly possible for amplifiers to have asymmetric response and different clipping levels for positive and negative signals. This is sometimes easy to see with a sine wave signal and a scope as you increase the volume.

Correctly identifying the cause of small sonic deficiencies can be difficult. One has to have good hearing and training to recognize that something is wrong, but that's not enough to identify the cause. That requires additional knowledge or careful experimentation. In the case of the amplifier polarity scenario, one way to isolate whether the problem was with the amplifier would be to reverse the polarity of the input signal and the speaker wiring (both speakers) and compare the sound with the original input and speaker wiring. This will catch polarity effects with the amplifier, but not the speaker. If the speakers were perfectly symmetric dipoles then perhaps you could turn those around to check for the effects of asymmetric speaker distortion, but obviously this won't work for box speakers.


Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

 

RE: Absolute Polarity, Asymmetric waveforms and clipping effects, posted on April 11, 2016 at 05:41:03
reuben
Audiophile

Posts: 1550
Joined: September 28, 2004
The speaker will see the DC offset with or without clipping.

Dark energy? Ridiculous!
We live in an electric universe.

 

RE: Absolute Polarity, Asymmetric waveforms and clipping effects, posted on April 15, 2016 at 13:51:02
tomservo
Manufacturer

Posts: 6866
Joined: July 4, 2002
" Just think how much a 1.5 volt battery causes a woofer to move. "

Yes but....
Like with a sine wave, it must exist for a period of time before it represents a single frequency (assuming it has no distortion) and not a bandwidth.
The "flat DC" portion only lasts for a very short time and an FFT of the wave-shape would likewise show a wide bandwidth and not DC.
Tom Danley
Danley Sound Labs
Gainesville Ga

 

I should have thought that time / phase coherent speakers, posted on September 27, 2016 at 04:06:51
Timbo in Oz
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June 25, 2014
and simple distant coincident or near coincident recordings would be sufficient.

Because they are and have been for me, for several decades.

It does require that your understand how we 'get' timbre, expression, nuance and interplay.

And, it has SFA to do with 'the harmonics on the continuous tone'.

Why? Because lots of instruments just don't have continuous tones, but we still get timbre and expression from them.


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: I should have thought that time / phase coherent speakers, posted on October 1, 2016 at 16:36:17
geoffkait
Manufacturer

Posts: 9375
Location: northern Virginia
Joined: August 23, 2000
Time or phase coherency is not what were talking about, however, as important as that is. Were also not referring to the phase shift that speaker crossovers mightier might not produce. Abosoute polarity is either correct or it's not. If it's not it's reversed polarity and is 180 degrees from correct polarity. Thus, your speakers can be time and phase coherent but the system can still be out of absolute polarity. An component can be inverted polarity for example.

Another way to look at it is if your system is measured to be in correct polarity using a test CD or record and the source CD or LP is reverse polarity you can correct for that by reversing the + and - at the amp output for both channels or at the speaker.

 

I was commenting on teh requirement for laboratory type asymmetrical test signals to show polarity matters on , posted on October 1, 2016 at 22:23:06
Timbo in Oz
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Location: Canberra - in the ACT - SE Australia
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June 25, 2014
music, and that simple stereo recordings of acoustic music are far more likely to reveal polarity, and pointing out that time and phase coherent speakers ought to be, and IME are essential as well.

I have been using speaker-level absolute polarity switching since the early 1980s. Initially by hand, but since I went with bi-amping in the late 1990s - using a 24V AC powered set of a 4PDT relay per channel, wired at my listening seat. Through speakers with minimal odd-order crossovers.

It seems to have passed you by that I might have some experience of its validity and audibility. Viz.

"Were also not referring to the phase shift that speaker crossovers mightier might not produce. Absolute polarity is either correct or it's not."

I partly disagree - IME IF the speaker isn't capable of letting you hear correct polarity then the issue is moot.

That is, IME it is not consistently audible through speakers that have steep even order crossovers. Yes, where the polarity of the relevant driver has been swapped, as usual.

IME, using time and phase-coherent speakers since the late 1970s, polarity is plainly and consistently audible (per recording) on the sort of recordings I referenced. Simple real stereo (aka 3d image) ones including multi-channel sound-field recordings, whether re-encoded to 2Ch stereo or not.

Further? That polarity switching is of little value - to me - on multiply close-mono-miked mix-downs, variously phased, Eq'd, flanged, delayed, compressed, Aphexed, .... etc, and often made over several weeks of sessions with individual singers and musicians. Bang goes ensemble playing.

Noting that I have a large collection of pop-recordings of this type. And still enjoy all but a handful which I've been too lazy to sell. I did begin to lose interest - in the genre as a whole - somewhere in between disco, punk and hip-hop. :-)! Not solely because of the damage done to the music in such recordings, but because of the shift in values that the recording technology is just one symptom?

Do you understand my points about the cruciality of attacks and decays, and the relative un-importance of 'the overtones on the continuous tone', to our getting timbre, nuance and expression?



Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

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