Thank you very much for posting ...
Variing voice coil inductance with excursion Le(x) as described in Fig. 32
seems a rather dominant effect with respect to distorsion in some speakers.
In case of multiway systems i can imagine this effect beeing quite tolerable,
as the inductance component (2 pi f Le) is moderate at low frequencies.
But in fullrange drivers having Le(x) as flat and symmetrical as possible
seems crucial especially if we consider that voltage drive is the common
type of impedance matching between amplifier and speaker, which will cause
Ivc to be modulated by excursion with the amplifier supporting that
in keeping voltage across VC clamps constant ...
Common diagrams used for marketing FR drivers will not reveal quality issues
of the motor design in that respect.
THD measurement using a sliding sine will just measure distorsion near
the rest postition of the driver at HF.
I quickly measured Le around 2,5 Khz yesterday in a motor design i use for a
recent project, making up a series resonant circuit and the VC clamped in
different positions.
-------------------------------------------------------------------------
underhung VC design
NeFeB Magnet
no copper around magnetic gap
no shorting rings
large center hole in pole piece
different drivers of same type
Driver A
Fs.....C......Lvc...Comment
2520 10.00 0.40 3mm out
2580 10.00 0.38 rest position
2600 10.00 0.37 3mm in
Driver B
Fs.....C......Lvc...Comment
2500 10.00 0.41 3mm out
2550 10.00 0.39 rest position
2560 10.00 0.39 3mm in
-------------------------------------------------------------------------
3mm represents Xmax for that particular type of driver and usually
(with overhung design) one would expect Lvc to decrease with the coil moving
outwards, but here seems a slight effect in opposite direction.
However Lvc is quite independent from VC position in the gap, which confirms
me in believing, that this an excellent motor design in that respect.
I appreciate the discussions in here for being really informative and
helpful ...
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Earl,
In the post below, you might find the paper interesting, wrt distortion percepetion :
http://www.diyaudio.com/forums/mult...ver-qts-you-cant-tuna-fish-3.html#post2763851
I experimented with added static 2nd and/or 3rd order distortion (to music signals, up to 5% at 0dBFS) and found it is slightly audible at low SPL volumes, distortion tended to make the sound a bit "richer" (as expected) but also gave a slightly "flatter" stereo depth (for unclear reasons).
- Klaus
Hi Klaus
Was your test blind? Probably not I would guess. Our testing all used multiple screend subjects in a blind test. We did find a slight negative correlation of perception to THD, meaning that people did tend to prefer distortion, but it was a weak correlation. In other non-published studies there was a strong preference for a low order nonlinearity as long as it did not shift to higher orders.
Was your test blind? Probably not I would guess. Our testing all used multiple screend subjects in a blind test. We did find a slight negative correlation of perception to THD, meaning that people did tend to prefer distortion, but it was a weak correlation. In other non-published studies there was a strong preference for a low order nonlinearity as long as it did not shift to higher orders.
Hello Simon,
depending on how good the aircoil is wound, some iron cores
come very close to the aircore if well dimensioned and not
driven into saturation.
Here's some distorsion data comparing an air core inductor
and several iron cores of different shape and material.
http://docs.ts-audio.de/a/ax/svqxmzqwnjaw/ite/it_grundlagen_drosselspule.pdf
I wouldn't bother using e.g. the I-cores from Intertechnik made from
dynamo sheets. Especially the I 96 and I 130 types look quite good.
Of course i wouldn't use iron above midrange, but i guess that's just
personal habit, since even an aircore inductor depends on tight winding
and baked wire seems a good thing too ...
depending on how good the aircoil is wound, some iron cores
come very close to the aircore if well dimensioned and not
driven into saturation.
Here's some distorsion data comparing an air core inductor
and several iron cores of different shape and material.
http://docs.ts-audio.de/a/ax/svqxmzqwnjaw/ite/it_grundlagen_drosselspule.pdf
I wouldn't bother using e.g. the I-cores from Intertechnik made from
dynamo sheets. Especially the I 96 and I 130 types look quite good.
Of course i wouldn't use iron above midrange, but i guess that's just
personal habit, since even an aircore inductor depends on tight winding
and baked wire seems a good thing too ...
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[OT]
I also ran some simpler real-time tests, using the "analog" mode (1% pure 3rd @0dBFS) of the VST-plug "Electri-Q" after upsampling to 96kHz which can be toggled on and off by a click or a key press. I have a special mouse with blocked sensor permanently installed at my listening chair for blind A/B-switching with the utmost minimum possible distraction once I have reached the subconcious deep relaxed state in complete privacy that is required for reasonable audible tests -- a point where many industry/scientific audio blind test utterly fail when it comes to the subtleties, never giving the participants a feeling that they are NOT guinea pigs in a lab-test.
[OT^2]
Electri-Q has a neat feature, allpass filters (2nd Order, adjustable Q). Together with polarity inversion I now can "invert" (phase shift by ~180deg, via a lowish Q) the bass regions independently from the mid/treble. By this I can first adjust -- by switching overall polarity -- my preferred "sound staging", mostly in the "compactness" and "height" of image sources, and when the bass looses punch by this inversion I have the option to regain the bass puch (kick drums).
These things are subtle, but still clearly audible in blind tests to most anyone who has really tried it. I insist on repeaing it as often as I can, because it so easy to try, nowadays.
[/OT^2]
- Klaus
[/OT]
I used Keith Howard's excellent distortion software (albeit only for 16/44 mono files of max 60sec length, so one has some logistics to do by hand to compare full songs in stereo), to be found on his website under "freeware", together with foobar's ABX tool. This should qualify as blind test -- I always strive for blind tested results as much as I can.
I also ran some simpler real-time tests, using the "analog" mode (1% pure 3rd @0dBFS) of the VST-plug "Electri-Q" after upsampling to 96kHz which can be toggled on and off by a click or a key press. I have a special mouse with blocked sensor permanently installed at my listening chair for blind A/B-switching with the utmost minimum possible distraction once I have reached the subconcious deep relaxed state in complete privacy that is required for reasonable audible tests -- a point where many industry/scientific audio blind test utterly fail when it comes to the subtleties, never giving the participants a feeling that they are NOT guinea pigs in a lab-test.
[OT^2]
Electri-Q has a neat feature, allpass filters (2nd Order, adjustable Q). Together with polarity inversion I now can "invert" (phase shift by ~180deg, via a lowish Q) the bass regions independently from the mid/treble. By this I can first adjust -- by switching overall polarity -- my preferred "sound staging", mostly in the "compactness" and "height" of image sources, and when the bass looses punch by this inversion I have the option to regain the bass puch (kick drums).
These things are subtle, but still clearly audible in blind tests to most anyone who has really tried it. I insist on repeaing it as often as I can, because it so easy to try, nowadays.
[/OT^2]
- Klaus
[/OT]
At high SPL (>90dBSPL rms) adrenaline seems to take over, plus my hearing is likely dominated by it's own distortion, so adding a few % doesn't change much. Try narrowband noise, 1kHz with 500Hz bandwith and try yourself at higher SPL (used quality headphones), you'll be surprised. See http://www.davidgriesinger.com/intermod.ppt
The reason I asked is it has always been my feeling that a given percentage distortion (and of given orders) is much more noticeable at higher SPL levels than lower - the higher the SPL the lower the threshold of audibility for distortion - up to a point at least.
My theory on this is that at low SPL you can get away with higher distortion because the distortion products may still be below either the ambient noise floor or our hearing threshold, and thus masked. Bring the SPL up though and the same percentage becomes unmasked.
It's also been my observation that distortion tends to be one of the factors that unconsciously limits how loud we can listen without discomfort or fatigue (again, up to a point) and that a speaker which maintains low distortion to very high SPL levels can be listened to comfortably and without distress at SPL levels considerably higher than a speaker with a more normal level of distortion.
It doesn't necessarily "sound" like distortion is occurring in the higher distortion speaker either - it just sounds "too loud" and uncomfortable to listen to, (maybe "cluttered") even though the lower distortion speaker can play even louder without sounding "too loud". Hope that makes sense.
My thoughts on that are that it may be the "richening" of the sound you mention that is to blame here - the distortion products spread the discrete pockets of spectral energy of the music out over a much wider range of frequencies, and increase the perceived volume for a given SPL, as well as introducing a lot of dissonant frequencies. (Another thought is that over excitation of the sensitive "presence region" by distortion products might also be a factor in making it sound fatiguing)
I know some people are skeptical about the audibility of low levels of distortion, but I think there may be more than one threshold - a higher threshold (on the order of a few percent) where distortion becomes obvious and "sounds like" distortion even at modest SPL's, but also a lower threshold where there isn't an obvious "distortion" sound, but the sound still becomes somewhat cluttered/fatiguing/unpleasant to listen to at higher SPL's.
A failing that, a bit like dynamic range compression in speakers, isn't always obvious until you have a direct comparison with another speaker which performs much better on the same metric, and then it is seen for what it is.
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Yes, that makes sense to me and it is my observation, too (now that I have speakers that can be considered pretty low distortion). It might be a question of time scale as well. I'm the type of guy who listens to one or two CD's in one go, without moving (or even opening my eyes) during the whole time, let alone change of playback volume... which I set to a level low enough so as to never have the feeling of congested hearing after such a listening session. For a song or two I can listen to much louder levels (like I did for the experiements) but I seldom enjoy it. I just don't like the experience of the ear's compression trying to protect itself (maybe my stapedius reflex isn't in proper shape anymore, need to have that tested).
When trying to identify speaker distortion at high SPL I tend to use professional musician's ear plugs which give a broadband 20dB attenuation, something I learned during my days as a active musician and club sound engineer.
Unfortunately for me I do enjoy loud music.
Only certain songs though. I tend to have fairly long listening sessions of an hour or two but at a moderate volume level, but then for one or two songs here or there I will really turn it up. (Or at least I did, when I had bigger speakers than I currently do)Good idea. I'm not suggesting its a good thing to listen very loud for a long period of time, in fact I think that speakers that have very low distortion and high SPL headroom can actually be dangerous for your hearing in the sense that you can end up listening a lot louder than you otherwise would without even realising it, as the "turn it down" reflex isn't nearly as strong as it is when there is more distortion.
If I'm trying to get a quick idea of what a speaker sounds like pushed near its limits I'll sometimes listen to it with my ears mostly blocked, or from a couple of rooms away in the house - both of which is enough to drop the SPL level enough that any distortion noticed is probably the speakers rather than your own ears - all it takes is a tiny spec of wax touching the ear drum and you can get significantly audible IM distortion even at moderate to loud levels, and there is certainly some degree of inherent distortion of your ears at high volume levels even if they're in perfect condition.
I have been wanting to get a pair of broadband attenuation ear plugs as you describe, both for quick high SPL "stress testing" of speakers, but also for going to the movies!
Despite liking loud music I find the sound in some cinemas so loud and harsh sounding that I either spend half the movie with my fingers partly in my ears or if I remember them I wear my iPod ear buds as a poor mans attenuation ear plug...Regarding my comments about distortion perhaps causing excessive stimulation in the presence region, I just stumbled across the following story:
Cover Your Ears! - ScienceNOW
"Some sounds are excruciating. Take fingernails squeaking on a chalkboard. The noise makes many people shudder, but researchers never knew exactly why. A new study finds that there are two factors at work: the knowledge of where the sound is coming from and the unfortunate design of our ear canals."
"More surprisingly, they found that the frequencies responsible for making a sound unpleasant were commonly found in human speech, which ranges from 150 to 7000 hertz (Hz). The offending frequencies were in the range of 2000 to 4000 Hz. Removing those made the sounds much easier to listen to. Deleting the tonal parts of the sound entirely also made listeners perceive the sound as more pleasant, whereas removing other frequencies or the noisy, scraping parts of the sound made little difference."
So basically the frequencies between 2Khz and 4Khz are what make blackboard scratching noises unbearable to some people. (including me) Rather interesting - I think most of us are probably aware of how sensitive the ear is in that range, but its interesting to see a scientific study that shows that a certain frequency range can be so strongly perceived as unpleasant.
Certainly I find flatness of frequency response through that region absolutely critical, even a small 1dB bump or spike can be enough to make some recordings unlistenable, so perhaps strong distortion products falling between 2-4Khz in a song which otherwise doesn't have much content in that region could indeed sound harsh ?
Another thought occurs to me - some people find blackboard scratching unbearable, while other people don't seem to mind it so much, so I wonder whether the sensitivity to response peaks (or distortion products) in the presence region varies from person to person ? A speaker with a peak in that region might sound harsh and unlistenable to some, yet "bright" and "present" to others.
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Simon, try those custom fit ones, IHMO the best and really worth the money (I'm using the 25dB variant). The simpler and cheaper universal fit models (from various makers) are OK, too, for a starting point, but I found my right ear canal to have a non-standard shape so those never gave a tight and comfortable fit.
I wish I had been using good plugs earlier in my life when I started to play in rock bands, to avoid the non-recoverable damages in the upper midrange that I have to live with now.
Funny thing, since I started to use these pro plugs I also go to the movies more often, like you I usually can't stand the SPL levels that seem to be common today.
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If I am understanding the graph shown here correctly:
FINEMET MAGAMP
For all drive fields varying between 25 and 75 A/m, the field strength would not change from 1.2 T. Is this correct?
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