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Old 29th July 2011, 02:50 PM   #1121
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Sure. I'm leaving for the long weekend soon, so hopefully before I leave. I don't know much about measurement. So I appreciate the help. Hearing what all of you are saying makes me wonder if I botched the whole thing. I thought the FR looked correct (a little messy) but didn't pay much attention to the impulse. What does the impulse even tell you? How controlled the cone is?

Last edited by tuxedocivic; 29th July 2011 at 03:12 PM. Reason: spelling
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Old 29th July 2011, 03:07 PM   #1122
SY is offline SY  United States
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Actually, the impulse is how the frequency response is derived. The impulse response is either measured directly or derived from an MLS response, then Fourier transformed to get frequency response. The inverse can also be done- both time domain and frequency domain have the same information embedded in them.
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Old 29th July 2011, 03:31 PM   #1123
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Quote:
Originally Posted by SY View Post
Actually, the impulse is how the frequency response is derived. The impulse response is either measured directly or derived from an MLS response, then Fourier transformed to get frequency response. The inverse can also be done- both time domain and frequency domain have the same information embedded in them.
While that's true, I think the question could also be more accurately re-framed as "what useful information can be ascertained by looking directly at the impulse response visually instead of transforming it into other representations such as frequency response, cumulative spectral decay, etc" To which I'd say in many occasions, "not much".

Sure, certain types of responses can have nice text book impulse responses that you can interpret somewhat by eye, but as soon as you have "complicated" stuff going on at the high frequency end such as multiple cone resonances, it quickly gets to the point where you can't make much sense of the raw impulse response, or the changes that selective damping may be making.

For studying cone resonances such as those that EnABL is attempting to address I find the most useful measurement by far is cumulative spectral decay, studied in conjunction with the frequency response. (Frequency response by itself is not enough information)

When doing my own driver damping experiments I've found a very good correlation between the sound of resonances, and how they look visually in a CSD, once you get a feel for the correct amplitude and time scales.

Although I look at the impulse response out of interest, when it comes to breaking down driver flaws individually to analyse and address them I don't think visual analysis of the raw impulse response is actually all that useful.

YMMV.
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Last edited by DBMandrake; 29th July 2011 at 03:34 PM.
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Old 29th July 2011, 03:34 PM   #1124
Helmuth is offline Helmuth  Netherlands
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No one mentions the use of phase in thier results, I find it very useful in fine tuning the XO point As you can see in my monitor-xl topic, I plotted the minimum phase a abrupt change in phase is equal to distortion.
So when you got distortion you got abrupt phase shifts.

Here i measure the two way near field to discriminate other influences. And the microphone between the woofer and horn this to have the same travel distance you see a smooth minimum phase bleuline.

Click the image to open in full size.

Here both speakers on mls signal microphone on my listining position so room reflections take place still a very smooth minimum phase 100-10000Hz.

It is a shame people can read the plots I show there then they would know how great it measures. You have to done some measurements and see result before you can compare what I show there.
Click the image to open in full size.
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Old 29th July 2011, 03:38 PM   #1125
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Simon, I'd disagree a bit. Looking at the time domain, it's easier to spot reflections, and from their time, to then make good guesses as to their origin. A simple example is the first floor reflection, which we will usually gate out, but thinks like cabinet cavity resonances, diffraction, reflections transmitted out the cone, and the like can also be spotted, identified, and fixes can be validated.
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Old 29th July 2011, 03:47 PM   #1126
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Simon, I'd disagree a bit. Looking at the time domain, it's easier to spot reflections, and from their time, to then make good guesses as to their origin. A simple example is the first floor reflection, which we will usually gate out, but thinks like cabinet cavity resonances, diffraction, reflections transmitted out the cone, and the like can also be spotted, identified, and fixes can be validated.
I completely agree about using the raw impulse response to find reflections such as floor reflections, baffle edge reflections, cavity back reflections and so on. That's certainly the best use of looking at the raw impulse response, and obviously we need to look at the impulse response at the very least to gate out reflections originating from beyond the confines of the cabinet when taking measurements.

But when applying damping treatments to a cone it's resonances we're trying to control not discrete reflections, and here CSD is king. Although everything you need to know is encoded within the impulse, the best way of "decoding" it visually depends on what you're looking for...

A frequency response graph can't distinguish between resonance induced peaks/dips and reflection induced peaks/dips, whilst a visual impulse response will only show "obvious" resonances, and only be interpretable if there aren't too many different ones occurring at once.

A CSD will pick out and make obvious even the tiniest low level resonance, and allow you to examine every resonance independently and in detail regardless of how many there are at once in the total response. So for damping a cone it's the right tool for the job.
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Old 29th July 2011, 03:53 PM   #1127
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Agreed, for looking at cone phenomena, I'd want to use other measures. Complex impedance (Heyser plots) for sure, frequency response, polar response, waterfall, Wigner. I was being more general- sorry for the poor communication.
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Old 29th July 2011, 08:19 PM   #1128
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I was impressed by how clearly migeO's wavelet graphs showed reflections arising only on the cone. Very much like a set of block prints stamped out in time, showing very discernible patterns repeated.

Bud
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Old 30th July 2011, 11:44 PM   #1129
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Originally Posted by soongsc View Post
I curious as to whether anyone had investigated fiber rubbing in these cases.

Hi,

some thoughts on this, because a woven structure may have
interesting properties.

The friction between the fibres may introduce a large amount of
damping without the mass increase a dampening coat would
introduce on a paper cone e.g.

Furthermore i would expect a weave to have slightly different
wave propagation speed in different directions (anisotropy) which
may contribute to (local) diffusivity, especially since those weaves
don't seem to be spread out axial symmetrically over the membranes
shape.

I imagine it could be tricky to get the amount of damping fairly
independent from the level of excitation ...

Rather slow wave propagation, high damping, diffusivity ...
would be ingredients for a rather "silent" cone material ?

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Last edited by LineArray; 31st July 2011 at 12:01 AM.
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Old 31st July 2011, 02:20 AM   #1130
soongsc is offline soongsc  Taiwan
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It's interesting to discover how different types of data presentation will reveal different information. CSD presented in the traditional means present data within a specific range after the beginning of the sliding window, Wavelet transforms present spectrum within a small sliding window. In practice, if we can get Wavelet Transforms in a better resolution, then we can diagnose problems more associated with the driver.
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