I didn't exactly say I was hearing it, just wondering whether hissing noise I'd heard (with a woofer making big excursions while very inadequate for radiating infra bass) could have been Barkhausen.
If so, a small mid driver in open air driven by something like a big 10Hz sinewave could be a way to hear it. No FSAF or Distortion Isolation needed, physics takes care of taking out the applied tone.
I think the idea is to have a well-defined place to control and linearize the eddy currents in the dedicated shorting rings/caps.
I think I've read about a segmented magnetic circuit somewhere in Purifi papers/patents/blog, maybe @lrisbo might want to comment?
@lrisbo
JBL is using a unique motor design with copper and steel lamination at the magnet gap in their 1500AL and 1501AL drivers.
https://www.audioheritage.org/html/projectmay/technology/1500al.htm
source: https://adeogroup.it/sites/default/..._synthesis_informazioni_tecniche_k2_s9900.pdf
The pdf document is also attached herein.
source: https://www.audioheritage.org/vbulletin/showthread.php?33557-1501al-2
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If high levels are required to generate loadsa Barkhausen, it might be masked by music. Keantoken, you are right that familiarity with a particular distortion in in listening tests makes it easier to hear them later. see eg appendix of
Intermodulation Distortion Listening Tests
Are large LF sine waves the best to avoid masking of Barkhausen noise ?
I think all that is needed is high excursion, level could be low if your driver is small. Perhaps this doesn't matter as the barkhausen is also quiet then. Perhaps for practical testing it's more comfortable to do with small speaker at 80db than big system blasting 120db 😀
The Barkhausen noise can be plainly audible when sweeping - heard it on underhung woofers (a lot of iron around the coil).
In the past I have found that woofers with foam surrounds would make a "faint swooshing" sound that was clearly audible with large excursions on low sinewaves and woofers with rubber surrounds were much more quiet under the same conditions. I assumed that there was something to do with the light weight of the foam being a better radiator of high frequencies but never knew if the sound came from bending the foam or something else.
That is an interesting observation since bending most types of foam will result in a noise. I wonder if age is a large factor since foam surrounds can still be working even when they are very delicate and liable to go at any moment.
Can you link to some sound files? With details please.
Are you saying Barkhausen in mainly in the steel (iron)? From this discussion, the impression I got was that it was in the permanent magnet materials.
Also a short voice coil would probably cause the least 'change' to the magnetic system especially at 'zero crossings'.
Same here, I am a bit puzzled...
Furthermore, in my experience these puffing, hissing or whatever weird sounds with overly large excursions are more due to high air pressures in small cavities with small air paths than anything else.
This is my take on all this:
It is all about iron noise, both Barkhausen and Hysteresis. It is all about flip flopping of magnetic domains as the Voice Coil field passes past through the B-Field.
To a degree shorting rings help reduce mid-range Iron noise. Shorting rings do little to help long excursion low frequency iron noise.
Real time, to the ear and microphone iron noise sounds like crackling and popping noise.
On a single tone FFT it looks like periodic bursts of noise.
On a Frequency Response done with a tone sweep it looks like “Noise Floor”
On a Level and Distortion Plot the software looks at a particular frequency “F” at a point in time and takes the level of “2F” noise or whatever it is, a single blade of grass is all it takes and uses that number to calculate H2. It is not necessarily a real harmonic but whatever the level of noise that happens to be at frequency F2. The same is true for H3, H4 and the rest.
So if the noise is reduced by 15dB’s so is the "Distortion".
See the attached H2 demo plot as an example.
It says Distortion but looks like noise to me.
Thanks DT
It is all about iron noise, both Barkhausen and Hysteresis. It is all about flip flopping of magnetic domains as the Voice Coil field passes past through the B-Field.
To a degree shorting rings help reduce mid-range Iron noise. Shorting rings do little to help long excursion low frequency iron noise.
Real time, to the ear and microphone iron noise sounds like crackling and popping noise.
On a single tone FFT it looks like periodic bursts of noise.
On a Frequency Response done with a tone sweep it looks like “Noise Floor”
On a Level and Distortion Plot the software looks at a particular frequency “F” at a point in time and takes the level of “2F” noise or whatever it is, a single blade of grass is all it takes and uses that number to calculate H2. It is not necessarily a real harmonic but whatever the level of noise that happens to be at frequency F2. The same is true for H3, H4 and the rest.
So if the noise is reduced by 15dB’s so is the "Distortion".
See the attached H2 demo plot as an example.
It says Distortion but looks like noise to me.
Thanks DT
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Got links to sound bytes? The examples posted so far suggest 'swishy wooshy' so difficult to distinguish from noise.
The comparison is sorta similar to Quantisation Noise (or Q. Distortion if you prefer)
Badly dithered : crackly noise BAD
Properly dithered : swishy or wooshy (depending on the dithering algorithm) INNOCUOUS
The steel in the polepiece causes distortion of the same kind as is in steel crossover inductors. In measurements I haven't seen this differentiated in any way from any kind of distortion coming from the magnet itself. Maybe they are just very similar?
Isn't all signals a varying DC? 🙂
So is what we hear an induced added signal to the drive signal that flows through the "motor" or is it the physical thing itself that vibrates and emits noise?
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So is what we hear an induced added signal to the drive signal that flows through the "motor" or is it the physical thing itself that vibrates and emits noise?
//
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The magnet flux contains Barkhausen events and adds to the force caused by the voicecoil current (with modification depending on drive impedance). Magnetostriction is unlikely because the measurements show wideband noise whereas noise originating from the motor would be mainly coming out through various box and construction resonances.
Focal have introduced a pair of large 3 and 3½ way speakers with "current drive" amplification-
https://www.focal.com/technologies/remote-amplification-in-current-mode
https://www.focal.com/technologies/remote-amplification-in-current-mode
Now you can.
Not likely to find place in sight
Moreover, you need to pick up the two cabinets with the 13" woofer