frequency modulation of the upper ranges by the bass!! - Page 2 - diyAudio
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Old 27th June 2013, 10:16 PM   #11
jcx is offline jcx  United States
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If there were a sound source on the cone surface, say a small tweeter, then a low frequency vibration of the main cone would cause the tweeter to move back and forth and it would exhibit Doppler distortion.
this is the key - as I said the diaphragm motion is a linear function of the drive signal to a very high degree of accuracy

so the high frequency motion is exactly like "a sound source on the cone surface, say a small tweeter" - by superposition

and the position and velocity of this high frequency "source" is moving with the motion of the diaphragm from the bass - so it is Doppler shifted


the "nonlinearity" causing the FM/PM/Doppler distortion is in the conversion of the linear cone motion into sound - over the varying position/displacement of the cone in the air - the high frequencies have no way to "know" the average position of the cone - they radiate from it wherever it is in its bass driven spatial position/velocity curve

there is no way to separately claim "breakup modes" are shifted and some other cone motion isn't



Rod Elliot gets it right eventually even if his measurements aren't terribly clear - they are measurement and evidence that "naysayers" have to explain

Last edited by jcx; 27th June 2013 at 10:37 PM.
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Old 27th June 2013, 10:48 PM   #12
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None of this matters. If a listener is satisfied with the sound of the music reproduced by a driver and to their ear there are no audible problems.... Then who cares?!?
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Old 27th June 2013, 10:56 PM   #13
chrisb is offline chrisb  Canada
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Originally Posted by silverhairbp View Post
None of this matters. If a listener is satisfied with the sound of the music reproduced by a driver and to their ear there are no audible problems.... Then who cares?!?

well, obviously, some (myself certainly encluded) enjoy the babble more than anything
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Old 27th June 2013, 11:00 PM   #14
jcx is offline jcx  United States
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its nice to get the basic physics of loudspeaker sound production right

builds some confidence when a speaker manufacturer seems to be getting it right


but the question of when Doppler distortion from a single driver becomes audible/objectionable is as the 1st post stated both music level and frequency content related
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Old 28th June 2013, 02:23 AM   #15
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by jcx View Post
the high frequencies have no way to "know" the average position of the cone - they radiate from it wherever it is in its bass driven spatial position/velocity curve
think a bit more about what the cone is moving relative to....

otherwise, we will agree to disagree
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Old 28th June 2013, 03:58 AM   #16
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Quote:
Originally Posted by Bigun View Post
think a bit more about what the cone is moving relative to....
The cone is mving relative to the reception device (ear)

dave
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Old 28th June 2013, 04:41 AM   #17
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Hi Fellas,
There's a good number of very interesting comments being produced but errors are also being made.

1 - The perfect cone is Not rigid. Most driver designers working on bass-wide and wide band classes will have their own flex ratio and mass/transmission formulas.

2 - Signal output transmission modulation variation is Not the sole "nemesis" for/of wide band drivers. Having tested several sub woofs, woofs and bass-mids over the years, the LF signal reception variance is significant in many of these drivers, certainly audible in the many anechoic and music tests we've made. Most of this testing was done prior to the design and production of Markaudio's Woofer No. 6 (EL166) and were instrumental in the formulation of its design.

Historically, the design of most wide-band and full-range driver were based on short stroke designs. I strongly suspect that the issue of modulation has become confused with the LF output limitations of these drivers.

In the case of Markaudio units, many of the Japanese testers (Ozawa San for MJ Magazine, Matsumoto san of Lean Audio, Clarke san etc etc) have cottoned on the benefits of Markaudio's long linear throw, low mass power train design; Observing little of no audible differentiation in musical output on a typical mixed frequency spectrum that includes LF loadings.

Bob Brines himself has made several recent references to the practical application of applying LF gain loads to Markaudio drivers. I believe the reference to Bob's page posted the thread starter should be read in the context of older wide-band and full-range driver operational designs.

To help out, I'd suggest the following guide to getting a good bass response without any "fluffiness' becoming audible:

For single point source projects, work on the basis on only deploying around 50% of the driver's quoted X-max for extended LF loads. Make use of the more efficient box concepts (Pensils being a prime example - Thanks to Dr. Scott) that minimise LF generation losses. Size your project according to your room requirements. Don't expect small drivers to cope well in large room situations.

These sorts of issues are interesting and get guys thinking and debating, but I can see that in some comments, the lack of knowledge on the operational properties of drivers is particularly evident. By all means guys, keep posting while applying more thinking and research time before committing to the "bold" statement.

Any comments that are severely technically in-accurate to the point they mis-lead others, I'll have to delete them, as many folks rely on the Markaudio section for reasonable technical accuracy, to help them learn better and get more from their projects.

Cheers
Mark.

Last edited by markaudio; 28th June 2013 at 09:56 AM. Reason: typo fix
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Old 28th June 2013, 04:56 PM   #18
jcx is offline jcx  United States
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I am just addressing "Doppler" FM, PM distortion from an ideal speaker - assuming for argument that motor/suspension/diaphragm are all "ideal", giving linear, uniform motion of the diaphragm with respect to electrical input- which may not be "ideal" for a full range driver which has to control sensitivity and directivity by clever use/balancing of "non ideal" material parameters

Klippel measures loudspeakers - includes Doppler distortion in their zoo of driver distortion mechanisms - show how to differentiate, recognize "Doppler" in measurement

Quote:
6.8. Symptoms of the Doppler Effect
The harmonic distortion measurement is not useful for detecting the Doppler effect. A single
signal tone can not provide both sufficient displacement and a short wavelength to produce a
significant phase shift. The Doppler effect can be easily detected by performing an
intermodulation measurement with a varying voice tone as illustrated in Table 5. Similar to the
Le(x)-nonlinearity the intermodulation rises by 6dB per octave to higher frequencies. However,
the Doppler effect causes only phase modulation and the value of the amplitude modulation
(AMD) is low. Clearly the Doppler effect can not produce any distortion in the displacement and
in the input current.
http://www.klippel.de/fileadmin/klip...ymptoms_06.pdf


Quote:
The green thin line shows the 2nd order modulation distortion Ld2 according
to IEC 60268 which becomes dominant at higher frequencies due to the Doppler effect.
http://www.klippel.de/fileadmin/klip...Distortion.pdf

Last edited by jcx; 28th June 2013 at 05:05 PM.
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Old 28th June 2013, 05:58 PM   #19
Bigun is offline Bigun  Canada
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I'm glad that Mark is here for us to make great sounding drivers without me needing to wade through the math

Describing it as phase modulation turned on some light bulbs for me (as opposed to Doppler) - I think I can see where phase modulation can arise - the creation of successive peaks of the sound waves can occur when the cone surface is closer or further from the listener and this difference in distance translates to a difference in phase of the peaks. The distance the cone moves however is typically tiny so the phase modulation is also tiny and there are other distortion contributors in any speaker that are more important to pay attention to than this.

Therefore, it seems to me that there is nothing to be concerned about - on the contrary, using a full range driver, means there is no cross-over which means it will have orders of magnitude better phase integrity over multi-way speakers.
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Old 28th June 2013, 06:22 PM   #20
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LISTEN TO THE MUSIC!!!

The rest just doesn't matter if the music is right.
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