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Old 23rd October 2012, 07:01 PM   #28381
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Quote:
Originally Posted by Johnloudb View Post
Forgive my ignorance, but what's his avatar?
http://www.analog.com/library/analog...cd/vol25n1.pdf
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Old 23rd October 2012, 07:02 PM   #28382
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Originally Posted by Johnloudb View Post
Forgive my ignorance, but what's his avatar?
AD743/745 die photo.
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Old 23rd October 2012, 07:12 PM   #28383
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Quote:
Originally Posted by gk7 View Post
I dont doubt that you get results with this if you say so, but nevertheless it sounds
rather counter intuitive.
One might argue that where has been an impedance peak in free air (which you now
lower or flatten), might be an impedance minimum once the speaker is mounted
in a ported box.
What is the theory behind that ? How does this work (in contrary to the more
common method of flattening the mounted speaker and frequency network) ?
The theory behind this is called "Self-satisfaction". When you hit the cone, instead of "BOUM BOUM" you hear kock-kock". However, when connected to the amp, you hear no difference.
To hear the difference you need an amp with current drive, high output resistance.
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Old 23rd October 2012, 07:23 PM   #28384
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Quote:
Originally Posted by Wavebourn View Post
The theory behind this is called "Self-satisfaction". When you hit the cone, instead of "BOUM BOUM" you hear kock-kock". However, when connected to the amp, you hear no difference.
To hear the difference you need an amp with current drive, high output resistance.
Not at all. Please, try by yourself, instead of reject things because you don't understand them, or because they are counter-intuitive. Then go back with your results. (You will notice clearly the change, in the acoustic response curve)
I'm often surprised to see the "believe/not believe" position of the hifi people, not a very scientific approach...
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Last edited by Esperado; 23rd October 2012 at 07:48 PM.
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Old 23rd October 2012, 07:26 PM   #28385
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Originally Posted by gk7 View Post
What is the theory behind that ?
It change the Thiele and Small parameters(speakers+motional compensation QTS.)
I was very surprised too the first time i noticed that.
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Last edited by Esperado; 23rd October 2012 at 07:34 PM.
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Old 23rd October 2012, 07:30 PM   #28386
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Quote:
Originally Posted by Esperado View Post
It change the Thiele and Small parameters(speakers+motional compensation.)
I was very surprised too the firt time i noticed that.
...even when shunted by amp's output resistance? No way with my amps. Guaranteed.
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Old 23rd October 2012, 07:47 PM   #28387
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Originally Posted by Esperado View Post
Fibers does-not break ? (with the obvious non linearity ?)
Compression/expansion movement of it does not produce noise ?
Frictional forces do not outweigh the restoring forces ?
I use to damp the back chambers of my drivers with fiberglass, but never tried-it in contact with the membrane.
Many treble units use fibreglass wadding to damp the back chambers. Just try adding a little more so it ju...ust touches the diaphragm. Use the very fine stuff. If it doesn't move the coil off centre, the answers are

No, no & no. But try for yourself.

Not sure why you want the damping material to provide restoring force but you can provide it by this very simple method.
_____________

I'm resisting but .....

Quote:
.. very few of them care to correct the motional impedance at the resonance. Is it easy to do, with an inductance, a cap and a resistance. Do-it with your loudspeaker at free air. (according to its Thiele & Small parameters).
You will object that it will give strange results, when a bass reflex changes the impedance curve near the resonance, as well as the resonance frequency ?
Just try-it, and you will be surprised to see the flatten remains correct.
Are you saying the free air corrected impedance remains corrected even when the unit is used in a bass reflex? Got some curves that show this?
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Old 23rd October 2012, 08:07 PM   #28388
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Originally Posted by Wavebourn View Post
...even when shunted by amp's output resistance? No way with my amps. Guaranteed.
My goodness.
What the hell your amps have to do here ? Even if they are 0 ohms source impedance ?
It is not only a question of damping. It is a question of phases and Q.
You are right on a point, a damped speaker (low impedance amp) will resonate with a lower peak at his FS. It is not the whole story.
Change the coil of a given speaker with an other of the same weight and more turns (i don't know the word in English for 'spires'), no mechanical change, then measure how the Thiele and Small parameters had changed and how different it behave in your vented or closed box, whatever your amp.....
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Last edited by Esperado; 23rd October 2012 at 08:31 PM.
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Old 23rd October 2012, 08:30 PM   #28389
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Originally Posted by kgrlee View Post
Not sure why you want the damping material to provide restoring force but you can provide it by this very simple method.
To remove suspension ring, then reduces fractioning forces...
Thanks a lot for your idea, i will try.
Not easy, need a little compression of the fiber wool in order it follows the membrane displacement, without leaving contact with the membrane....
I wonder too how fiberglass can behave with its own inertia at high frequencies...
Quote:
Originally Posted by kgrlee View Post
...Got some curves that show this?
I will try, but i do not promises. It supposes i can re-find in my cellar some Bruel & Kjaer old sheets, more than 15 years old, if they still exists, go figure...

What i can say is it removes few dbs in the low medium area and a little change too near the FS. Remember this review i published about the "Aeria system".
They wrote
"Those of you, familiar with the 416 Altec, recognize their beautiful transparency between 200 and 800 Hz, but those loudspeakers misses the weight and serious mass impact of a JBL 2215 for example. The Audio Dynamic transducer had found this ideal compromise between impressive sub-basses (it can nail you to the wall) and this desired transparency in the 300-600 Hz area without any side effect of "cardboard " cone."

They tribute-it to the speaker, the would have better tribute-it to the motional impedance compensation, but they do not knew anything about.
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Last edited by Esperado; 23rd October 2012 at 08:33 PM.
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Old 23rd October 2012, 08:39 PM   #28390
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Originally Posted by Esperado View Post
My goodness.
What the hell your amps have to do here ? Even if they are 0 ohms source impedance ?
It is in parallel with both speaker and your "compensating" network. I can do you easily even negative resistance from tube amp.
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