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Old 1st March 2015, 07:33 PM   #1
Liliya is offline Liliya  Norway
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Default Measure onJBL123

I have two JBL123A. I hve measured this units with Dayton V2. Every measuring is pretty close to what I can read in the papers from JBL except from Q(ms).
My readings are 1.683 and 1.389. JBL paper says 8.5. Is there anything wrong with my speakers.
Q(es) is 0.589/0.579 and Q(ts) is 0.414/0.431

I hope for comments.

Eivind Stillingen
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Old 2nd March 2015, 07:27 AM   #2
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How old are they?
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Old 2nd March 2015, 07:50 AM   #3
Liliya is offline Liliya  Norway
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I do not know their excact age. They have the grey cone, so I think they are real vintage.

Eivind Stillingen
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Old 2nd March 2015, 09:12 AM   #4
CLS is offline CLS  Taiwan
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What are other parameters? fs for example.

Are the suspensions obviously stiffened?

And I guess the Alnico magnets are probably demagnetized somewhat.
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Old 2nd March 2015, 09:26 AM   #5
Liliya is offline Liliya  Norway
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With Dayton V2 I measured Fs= 26.92 on both elements.

You wrote:

And I guess the Alnico magnets are probably demagnetized somewhat.

What can be done to to this?
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Old 2nd March 2015, 03:46 PM   #6
GM is offline GM  United States
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To best answer your question, I need all of the measured data because right now your averaged numbers don't 'compute' based on your statement that 'Every measuring is pretty close to what I can read in the papers from JBL except from Q(ms).'.

Note that JBL's published specs don't 'compute' either, so I'm trying to figure out which is the most correct set of specs overall.

GM
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Old 2nd March 2015, 07:45 PM   #7
Liliya is offline Liliya  Norway
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Default JBL123A/2213(H)

I got a third JBL123A to day and here are the measure from all three
Attached Files
File Type: zip 1 - JBL123Nr.1 Free air.zip (685.4 KB, 10 views)
File Type: zip 2 - JBL123 Nr.1 V(as).zip (690.0 KB, 1 views)
File Type: zip 3 - JBL123 Nr.2 Free air.zip (685.0 KB, 2 views)
File Type: zip 4 - JBL123 Nr.2 V(as).zip (685.2 KB, 1 views)
File Type: zip 5 - JBL123A NR.3 Freev Air.zip (689.1 KB, 3 views)
File Type: zip 6 - JBL123A NR.3 Measuring V(as)med 90 gram.zip (696.1 KB, 2 views)
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Old 5th March 2015, 12:38 AM   #8
GM is offline GM  United States
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Quote:
Originally Posted by Liliya View Post
And I guess the Alnico magnets are probably demagnetized somewhat.

What can be done to to this?
Assuming you mean, can it be corrected? Yes, they can be drained and re-magnetized if Qes has gone up enough to justify the cost.

GM
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Old 5th March 2015, 12:47 AM   #9
GM is offline GM  United States
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Quote:
Originally Posted by Liliya View Post
I got a third JBL123A to day and here are the measure from all three
Cool! Thanks! I'll go through them as time permits.

GM
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Old 6th March 2015, 10:55 AM   #10
Liliya is offline Liliya  Norway
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Lets take the results from one of my 123A speakers an put it in to this formula:

1/q(ts)= 1/Q(es)+1/Q/ms)

1/0.414 =1/0.589 + 1/Q(ms)

2.41 = 1.69 +1/Q(ms)

2.41-1.69=1/Q(ms)

1/Q(ms) = 0.72

Q(ms) = 1/0.72 = 1.388

Measured value for this unit: 1.389

So, if all the other parameters I have measured the measured Q(ms) is correct.

HOW DO I BRING BACK THE UNIT TO THE CORRECT Q(ms)= 8

I have earlier red that the magnet of this type can loses their Q(ms) value over the years.

Eivind Stillingen
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