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Old 18th March 2017, 11:00 PM   #11
Ron E is offline Ron E  United States
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Show the data, otherwise people are interpreting the question rather than the data.
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Old 19th March 2017, 03:13 AM   #12
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Thanks to everyone who has commented on this issue.. your inputs are very much appreciated.

Quote:
Originally Posted by Ron E View Post
Show the data, otherwise people are interpreting the question rather than the data.
Good idea, Ron. Taking the previous comments into account, let me collect another set, and see what I find.. I'll take two series of readings on the same LS - first, with only minimal disturbance (rested overnight) and a second, after knocking it gently on the table a dozen times, at various orientations. Not very repeatable, but from what I've seen it should be enough perturbation to produce the effect in question.

Give me an hour or two to get this done, and I will report back. BTW - who here knows how to create charts in LibreOffice Calc? That's something else I need to know.
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Old 19th March 2017, 04:58 AM   #13
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First round of new data, from the 4" bare driver. Readings are taken with the driver resting on the magnet structure, with the VC directed upwards.

Bare 3" driver - after 24 hrs. rest.

(Hz - impedance)

20 - 6.79
25 - 6.92
31.5 - 7.16
40 - 7.57
50 - 8.36
63 - 10.34
71 - 12.66
80 - 15.17
100 - 13.66
113 - 10.87
126 - 9.37
159 - 7.73
180 - 7.36
193 - 7.22

It will be interesting to see how this compares to the next set. This is a limited set, spanning 20Hz - 200Hz, so one decade. But it seems as if there's a significant peak in this range (take a look at 80 Hz area) so it's useful.
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Old 19th March 2017, 06:50 AM   #14
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A little more info on the driver. It's not actually 4" (102mm) more like 3.5" (89mm)

3.0" / 76mm shielded magnet structure, 3.5" / 89.0mm cone, black rubber surround, composite cone (yellow in color, has woven pattern), mass 22oz / 620gm. Marked: "55-1500 "8 Ω" "MADE IN TAIWAN" on the back side of the magnetic shield. Seems to be of middle-range quality.. better than total crapola, but not anything hi-flying. Serviceable item?

ETA: Found it in the MCM catalog. They call it a 4" driver, and it's near the bottom of p.3 in this PDF.

Last edited by legendre; 19th March 2017 at 07:18 AM.
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Old 19th March 2017, 07:21 AM   #15
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Old 19th March 2017, 08:06 AM   #16
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And here's the second set.. notice that there is missing data point from each set (got bad data and just ignored it, trends are clear, doesn't affect the results).

Bare 4" driver - after moderate disturbance.. pushed & pulled the cone, rapped the structure on the tabletop many times at multiple angles, etc.

20 - 6.90
25 - 7.05
31.5 - 7.29
40 - 7.80
50 - 8.73
63 - 11.1
71 - 13.47
80 - 15.7
100 - 13.0
113 - 10.6
126 - 9.21
143 - 8.23
159 - 7.74
180 - 7.34
200 - 7.14

And imagine that, now they are tracking - quite well, really! So next, I need to run sets using the original 2-way KLH speaks, and see what those yield.

What's this about - hard to believe it's break-in, being that the driver has almost zero time on it, as far as playing real music.

Last edited by legendre; 19th March 2017 at 08:10 AM.
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Old 19th March 2017, 09:50 AM   #17
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Pardon all the quips..

Actually, there is a notable deviation @ 71HZ. The readings are 12.66V & 13.47V, a difference of R801, or about 8/10 of an ohm, almost 10% of a 8R driver.
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Old 19th March 2017, 10:48 AM   #18
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Puzzling. Speaker ought to return to static status unconditionally, AFAIK. Can we assume the speaker plays OK?

Long ago, there was parameter of interest called something like "blocked voice coil impedance" which reflected impedance in the absence of back-EMF.

Could it be some faulty capacitors inside the crossover? Esp if crossover is low and electrolytic used.

Deteriorating insulation on VC in a waterfront atmosphere?

When I was at Bell Labs, the standard in our department was the KLH 6. Possibly "Bicycle Built for Two" will sound better if you play it on one. The KLH model you mention might be "KLH" in name only, as a brand but not related to the old company.

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Last edited by bentoronto; 19th March 2017 at 10:57 AM.
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Old 19th March 2017, 12:06 PM   #19
Ron E is offline Ron E  United States
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Looks like suspension creep, as someone else said already.

Same thing would happen if you blasted the driver with 20 Hz to near xmax between measurements. The spider in a speaker is not terribly linear. It gets stiffer with excursion, but perhaps paradoxically the resonant frequency goes down as you increase amplitude. It remains lower for a while after the stimulus, then typically "recovers" after a time. For the high frequency differences, the operating point may have shifted a bit and your signal isn't strong enough to move it back.

Graphing in libre office or excel is quite easy, put your data in columns, then select it and click a button and follow a couple prompts. For graphing data, use a scatter plot, then you can later doubleclick the axis and choose a log scale.
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Old 20th March 2017, 01:39 AM   #20
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@Ron E

Quote:
Originally Posted by Ron E View Post
Looks like suspension creep, as someone else said already.
Interesting. This 'creep' factor is new to me, which isn't so surprising - I don't know squat about LS physics. But I have noticed that it seems to take forever for some of the readings to stabilize.. and in fact, I've had to make a number of arbitrary calls on when to log the reading, as settling time wasn't part of the original measurement spec.

I need to learn more about susp. creep, it seems that it might be a factor in this case.

@bentoronto

Quote:
Originally Posted by bentoronto View Post
Puzzling. Speaker ought to return to static status unconditionally, AFAIK. Can we assume the speaker plays OK?
Heh.. 'No', as it's never been put to use. But 'Yes', as it appears to be NIB - never used.

Quote:
Long ago, there was parameter of interest called something like "blocked voice coil impedance" which reflected impedance in the absence of back-EMF.
How is this done? Is the goal to immobilize the cone / voice coil such that it remains in-place, rather than oscillating as intended? In short, to make the vc & magnet behave more like a fixed inductor?

Quote:
Could it be some faulty capacitors inside the crossover? Esp if crossover is low and electrolytic used.
In the case of this 4" (3.5") bare driver, there are no crossover components. It's bare, on the bench, cone facing upwards.

Quote:
Deteriorating insulation on VC in a waterfront atmosphere?
Not recently, I'm far inland (St. Paul, MN, USA)

Quote:
The KLH model you mention might be "KLH" in name only, as a brand but not related to the old company.
Yes, the model I'll test next is the 'KLH' bookshelf LS. The model number is given, above. It's more like a satellite speaker for a HT system, but to me it's a bookshelf. It was this pair that had the greatest deviation in the readings. The woofer is maybe 3" and the tweeter like 3/4"?

@ All

Thanks so much for your input on this. I'll run a similar test on the KLH's now, and see what I see. As with the previous sets, I will try to find a low-freq impedance peak, and center the measurements around that.

Last edited by legendre; 20th March 2017 at 01:43 AM.
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