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Multi-Way Conventional loudspeakers with crossovers

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Old 26th July 2010, 12:59 PM   #6831
Pano is offline Pano  United States
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That's what I was thinking. Also, why not just look at the waveform on a scope or computer?
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Old 26th July 2010, 01:24 PM   #6832
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Originally Posted by panomaniac View Post
That's what I was thinking. Also, why not just look at the waveform on a scope or computer?
That was my point. I have looked at THD at low levels and didn't see anything that would indicate this type of "notch" distortion.
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Old 26th July 2010, 03:12 PM   #6833
mige0 is offline mige0  Austria
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I'm certainly the first to agree that this kind of distortion isn't any significant for the vast majority.
Otherwise it simply would not have been hidden for centuries.

On the other hand we possibly should not classify „significant“ with a mic and a osci at hand – I guess we would be in trouble to debunk more subtle effects that way – you wouldn't do it to demonstrate dither for example, would you?

Also, as much as I'm interested in any flame or snake oil discussion – I don't think its the right time - and also - there will be endless time left for endless discussion about significance AFTER we possibly have traced velocity independent friction down – if thats possible at all.



As for measurement I found that a *relative* approach might work best to begin with.

Looking at the spectra of the trapezoid waveform basically created by VIF, we certainly have it easier to look at changes in the relation of 2nd and higher order distortion correlating with SPL.

Usually (IMO), higher order order distortion comes up with any speaker at low SPL – we should sort out these drivers that come up with higher order distortion at lowest SPL levels to find the most „dynamic“ ones.

As a simple relative measure (not necessarily the best I admit), I have checked at which SPL level higher order distortion overtakes 2nd order.

As this is a mere relative measure, I gained advantage by not doing this acoustically but by direct measurement of the current when feeding the speaker with constant voltage.



A loooot of *if* an *when* – I know...


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Old 26th July 2010, 05:06 PM   #6834
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Originally Posted by mige0 View Post
On the other hand we possibly should not classify „significant“ with a mic and a osci at hand – I guess we would be in trouble to debunk more subtle effects that way – you wouldn't do it to demonstrate dither for example, would you?



Michael
I wouldn't be so quick to dismiss what a mic can pick up. Any mico detail that is in the recording is only there becase a mic picked it up in the first place. And certainly a mic is much, much more sensitive than the ear, regardless of how golden that ear might be.
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Old 26th July 2010, 07:17 PM   #6835
mige0 is offline mige0  Austria
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I have not even tried to do it acoustically - possibly I should have.

My line of thinking was that with electrically measurement we get cleaner signal to analyse as all the noise around - which is at my place around 30-40dB - will be heavily dampened (a speaker will make for a rather bad mic).

Sure - in case of steady signals analysis like THD, we can increase time interval and hence statistically lower noise but IMO its always good to start out with as clean as possible a signal.

A second thought is, that with direct measurement we simply exclude one pretty unknown variable : the mic quality


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Regardless of measurement technique - do you get the rise in higher order distortion at falling SPL as well and what are your conclusions ?


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My crumbly measurements so far can be looked up here:
My open baffle dipole with Beyma TPL-150

and here:
My open baffle dipole with Beyma TPL-150

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Last edited by mige0; 26th July 2010 at 07:31 PM.
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Old 26th July 2010, 07:54 PM   #6836
BudP is offline BudP  United States
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The first two resonances get lowered but also the 3rd and 4th come slightly more alive.
Sorry to come back to this so late Michael. Please look again.

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What I was pointing to was the surface development of the major resonance. If you look carefully you should be able to see the actual steps of resonant activity, as the EnABL'd driver losses energy. The basic shape to the FR is really quite close, with the changes you noted, but the real indication of micro dynamic abilities of the driver are in that stepped reveal of the resonant node, as the amplitude drops. At least in my opinion, this shows that drivers are really very competent in this realm, in every respect, except how they couple with the air.
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Old 26th July 2010, 07:55 PM   #6837
mige0 is offline mige0  Austria
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Just seen that I made my measurement by injecting current and measuring voltage

Another correction :
simus clearly show that with friction its not a morphing into saw-tooth waveform but rather into a trapezoid wave form


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Old 26th July 2010, 08:36 PM   #6838
mige0 is offline mige0  Austria
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Bud, not sure if I'm looking at the same places as you do ?

Here I marked the two areas where I see the major changes:

Click the image to open in full size.


The marked area lower in frequency is considerably smoothed by enABL IMO, wheras the marked area at higher frequency comes slightly alive .

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...but the real indication of micro dynamic abilities of the driver are in that stepped reveal of the resonant node, as the amplitude drops.
This I didn't get - can you give some more explanation?

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Old 26th July 2010, 08:44 PM   #6839
mige0 is offline mige0  Austria
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Ahh I guess I got it now - you are referring to the shape of the resonance that drops in steps originally and which - after enABL treatment - is a smooth rush !

You possibly know we had some similar effects been discussing with looped reflections in the horn honk and wavelet thread..

Well - now I get your point, and I for sure agree that micro details *must* get less masked when you effectively lower looped reflections - or whatever here exactly is involved - by enABL treatment


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Old 26th July 2010, 09:05 PM   #6840
BudP is offline BudP  United States
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You need to roll your cursor on and off of the plot to see the comparison. The red plot is the untreated cone, the blue plot the treated one.

You are looking in the correct places however. My point was that the difference displayed in the waterfall, between the red and blue plots, shows a marked difference in portrayed ringing of the resonance frequency. If you look closely, as you flip between the red and blue plots, you can see a very well defined set of steps, looking much like rice paddies down the side of a hill, in the blue plot. The same stepped portrayal of resonant ringing is not shown on the red plot, yet it is the same driver, test set up and tester involved.

What I am pointing to is that the driver can already perform to this micro level. To me this shows that it is already capable of very fine resolution in the motor and suspension systems and that it has correct damping in the surround. All that is missing from the red plot, untreated driver, is the expression of that micro signal control into the air. Once that coupling obstruction is overcome, the driver shows us what it was already capable of, but was unable to provide as a signal into the surrounding air.

I side with John here, in thinking that the major constraint to improvement in driver micro detail performance is not to be found in the mechanical frictions, though improving them will certainly provide the potential for less distortion to these tiny signals. Where John and I differ is how best to allow those tiny signals to be expressed.

In summation, I think that both the software and microphones are more than capable of displaying these issues. The only fault to be found may be in our lack of experience in recognizing these issues when they are displayed.
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