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Old 13th April 2009, 02:14 PM   #5221
mige0 is offline mige0  Austria
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Hi John, thanks for the informative measurements.
Judging from your plots - there is a distinct qualitative difference regarding the low pass filter effect of the damping material varying with the density of stuffing.

Comparing the curve of no filling with the trace if lightest filling there can be seen a lot of dampening of the peaks but almost *no* low pass filter effect as the green trace touches the red one several times even *above* the main peak

Down from lightest filling to heaviest stuffing the traces go almost in parallel – as if applied a low pass filter with increasingly lower cut off frequency (overlaid by a left shift of the traces in general due to "virtual volume enlargement" / mass coupling respectively).

Would you agree with my observation / analysis?

Michael
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Old 13th April 2009, 02:27 PM   #5222
Telstar is offline Telstar  Italy
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Quote:
Originally posted by john k...
A couple of days ago I said I would post some measurements at the rear of the U-frame with different damping. Here they are.
Very useful for my project, thanks!

Yesterday, I also found this and i'll share it:
link
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Old 13th April 2009, 02:27 PM   #5223
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by Rick Miller



...
Most of the readers of this thread are wanting to have the best sound possible and they are doing the work themselves to have better speakers and a lot of them are using the “no box?design. Other than having no box the only way to have less box acoustic output is to make it as dense and “dead?as possible.
Lead or Gold. Other than that, it's really technically tough to accomplish.
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Old 13th April 2009, 04:19 PM   #5224
dlr is offline dlr  United States
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Quote:
Originally posted by Telstar


Very useful for my project, thanks!

Yesterday, I also found this and i'll share it:
link
I'll just point out that this is unrelated to the damping that John is addressing in his measurements.

Dave
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Old 13th April 2009, 05:19 PM   #5225
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Quote:
Originally posted by mige0
Hi John, thanks for the informative measurements.
Judging from your plots - there is a distinct qualitative difference regarding the low pass filter effect of the damping material varying with the density of stuffing.

Comparing the curve of no filling with the trace if lightest filling there can be seen a lot of dampening of the peaks but almost *no* low pass filter effect as the green trace touches the red one several times even *above* the main peak

Down from lightest filling to heaviest stuffing the traces go almost in parallel – as if applied a low pass filter with increasingly lower cut off frequency (overlaid by a left shift of the traces in general due to "virtual volume enlargement" / mass coupling respectively).

Would you agree with my observation / analysis?

Michael
You have to consider that the resonance can create peaks and dips in the response. The damping plays dual roles: 1) the low pass filter effect and 2) damping resonances. So id the resonances are damped you can see a reduction in the peaks as well as a filling of valleys. Also recognize that as the damping increase the corner frequency of the LP filter shifts down in frequency. If you look at a mean slope I think you will agree that the red trace has a lower Fc that the green as well as being "smoother". The trend continues as the damping is increased.
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Old 13th April 2009, 05:34 PM   #5226
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Here are some additional plots that may be of interest. The black line is the envelope of the input burst. The first is the near field response of the OB system to a shaped 5 cycle burst:

Click the image to open in full size.

Next is the near field response to the same burst for the undamped sealed box:

Click the image to open in full size.


Last is the same sealed box with 4 oz fiberglass fill.

Click the image to open in full size.

The 200 Hz frequency was chosen because the undamped box has a nasty resonance there. Perfect response would be the red plot contained within the black envelope.

I'll point out, without posting a graph, that at 200 Hz the undamped U looks very similar to the OB result because the undamped U has no resonances at 200 Hz.
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Old 13th April 2009, 07:04 PM   #5227
FrankWW is offline FrankWW  Canada
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By the way – his admiration of Dolby (somewhere in the middle of that interview where I stopped continuing reading) is what tells us a lot about his preferences – mere power of industry heroes (one of which he'd like to be / become ?).
So you didn't actually read the interview because you have already made up your mind. Too bad.

Fincham's opinion of Dolby is highly tempered:

<i>"he single-handedly allowed the recording industry to change – even if not always for the better."</i>

Give Fincham credit, his activities certainly led some loudspeaker makers to improve their products.

Your host on this thread probably would agree.

I think you are letting your personal experience colour your view - Taking the particular case and applying it to the general one.

The gold in that interview comes after you stopped reading it and it explains why Geddes might be talking to Fincham.

Some nuggets here, for instance:

Quote:
MALCOLM STEWARD: While you were at KEF you were instrumental in introducing leading-edge computer systems to the design and manufacturing processes and you developed the now well-established Uni-Q driver that has become the company’s sort of USP. Could you tell us more about that? LAURIE FINCHAM: We did find by using computer aided measurement and controlling the processes that we could produce drivers that were extremely consistent so you didn’t have happenstance performance. Having got that consistency you have to ask yourself what you wanted: you could make speakers that were arbitrarily flat but the problem was that they didn’t always sound the way they measured – and this is the perennial problem. It was sort of tacitly understood that the reason was because you needed to look at the response on more than one axis. Now if one were to characterise approaches to design – remember earlier we talked about the BBC and primarily what they did was teach you to put speakers on a stand, move it way from the wall and get very close to the speaker so pretty much the direct sound dominated and that became the design objective for the for the large part of the English school of speaker design. In America they always cleaved more to the idea that the bulk of the sound comes to you through an indirect path – obviously popularised by Bose – but before them there was AR on the East coast who essentially said that if so much of the sound reached the listener that way then one should look at the power response, and certainly the Germans did, while the Scandinavians, who had very live rooms, and they found that with such rooms you couldn’t ignore their contribution so they produced omni-directional speakers such as the Sonab. As inevitably happens with all these things neither side was right and neither side was wrong. It turned out that they were both right and they were both wrong. In a sense we’ve gone full circle. Floyd Toole (formerly at Harman but now retired) really has a handle on this. He’s spent a lifetime figuring out how to listen to speakers and designing them: he concludes that the response of many angles is appropriate and indeed it is but we’re now getting to the point where we’re beginning to understand the set of data to be extended. You can’t guarantee that it’s good but if you were a gambling man you would say that the likelihood that something that measured like this would sound pretty good. And that’s about as far as you can get. As a result of that you can say Yes; on- and off-axis matters, and it matters in different ways. It matters where it comes from and what the relative levels are. It’s not just simple measuring. You have to weight it with psychoacoustic factors. Now, if that is the case, the point about something like Uni-Q, for example, was to say if we can do this we can have a device that has matched directivity and it did and the interesting thing about it was that its response was worse truly on-axis: it was very good everywhere else, in contrast with other speakers that were good on-axis but crap everywhere else. So, there was a steep learning curve: Uni-Q was not a slam-dunk by any stretch of the imagination. If you think that it’s been around for nearly twenty years and it’s only earned a modicum of respectability in that time. KEF has resolved a lot of its problems – edge reflections causing a ragged response, for instance – but it’s still an on-going process: that is how can you effortlessly control directivity? I suppose that what I’m working on now, which is how you can do that interactively…
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Old 13th April 2009, 09:43 PM   #5228
mige0 is offline mige0  Austria
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Quote:
Originally posted by john k...

... If you look at a mean slope I think you will agree that the red trace has a lower Fc that the green as well as being "smoother". The trend continues as the damping is increased.

Yes, I agree on that F-res is lowered and the (fluffy) red curve has gotten smoother - but what I wanted to point at was that we don't see the red and green curve in parallel - indicating a shift in conrner freqeuncy - ig indicating a low pass behaviour.

The low pass behaviour is clearly visible for the denser stuffings for me though.

Michael
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Old 13th April 2009, 09:51 PM   #5229
agent.5 is offline agent.5  United States
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http://htguide.com/forum/showthread.php4?t=33184

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Old 13th April 2009, 10:00 PM   #5230
mige0 is offline mige0  Austria
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Quote:
Originally posted by FrankWW


...I think you are letting your personal experience colour your view

Not exactly – put it that way:
my personal experience *is* my view !

Quote:
Originally posted by FrankWW


Give Fincham credit, his activities certainly led some loudspeaker makers to improve their products.


No problem – many people around this forum did as well... no glorification needed



Quote:
Originally posted by FrankWW


The gold in that interview comes after you stopped reading it and it explains why Geddes might be talking to Fincham.

Some nuggets here, for instance:

Almost anything discussed here earlier

+++++

Please don't take my sidenote personal – my point just was that nobody around has to quote any THX guy to impress someone as they are BS'ing as anybody else in the biz – and certainly Earl's point of view always is appreciated by its own (though not always shared)


Michael
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