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Old 15th April 2010, 03:08 AM   #21
TheGimp is offline TheGimp  United States
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I got the FE103s today and I'm trying to measure the Thiele-Small parameters.

I'm not just trying to build a set of speakers, but I'm trying to understand the theory behind the design.

I'm using Audio Tester V2.2 to try to measure the parameters. If I add the 20gm of clay and de-Vas via cabinet I get positive numbers. If I select Vas via cabinet I get a negative number for Vas and 0 for the other parameters.

Some of the results I'm getting appear in the right range (Re, Fs,0, Qms) but others like Vas appear to me to be wrong.

Click the image to open in full size.

Can anyone shed some light on this?

Here is the phase and impedance plot. I ran it on two speakers and got very similar results.

Click the image to open in full size.

Thanks.

Steven
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Old 15th April 2010, 03:10 AM   #22
TheGimp is offline TheGimp  United States
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Quote:
Originally Posted by planet10 View Post
Geddes' research shows a threshold of something like 25%. ie it has to be pretty bad to concern yourself about when attention could be be elsewhere more important.

In his book he has a chapter on distortion. Now after his research he says not to bother reading it...

dave
Doesn't this depend greatly on which harmonics we are talking about. Odd in particular are more noticeable, and higher order harmonics tend to be more harsh?
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Old 15th April 2010, 03:18 AM   #23
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How i interperet Geddes results is that THD measures are measuring the wrong thing... the nature of a dynamic speaker usually means very little above 3rd and monotonic.

dave
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Old 15th April 2010, 03:20 AM   #24
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Quote:
Originally Posted by TheGimp View Post
If I add the 20gm of clay
20 g is probably too much. 10g is what i use, but i should probably make a 5g lump for drivers this small.

dave
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Old 15th April 2010, 03:27 AM   #25
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Quote:
Originally Posted by TheGimp View Post
Doesn't this depend greatly on which harmonics we are talking about. Odd in particular are more noticeable, and higher order harmonics tend to be more harsh?
I agree. 25% THD of odd harmonics would sound like a guitar fuzz pedal....actually 25% of even harmonics would sound like a fuzz pedal too...

25% THD...so a 3:1 ratio of sine to overtones...that only represents something like -6dB for the sum of the harmonics amplitudes. i dont get how that is possibly correct, otherwise i struggle to see how the ear could distinguish the phase problems of a 2 way speaker over a FR type when listening to harmonically rich instruments like sax. Obviously, a full fourier anaylses would need to be done to determine the full extent of the harmonics produced by any given driver, but being natural in nature, they would be less at 5th and 7th than at 3rd harmonics.

I would have believed 2.5% THD or even .25% THD, my experience with amps, although small, showed the onset of audible THD to be somewhere between 0.5 and 1%THD. I by no means have 'golden ears' but i do not have a sunshine halo syndrome afflicted ones either. 25% of THD may only just be annoying for those who blast an personal stereo at full volume(in the days beforee mp3), or for those that have pretty underpowered valve gear, but I CAN hear it way before that. I know this as i measured the THD and commented on audibilty for my thesis in E/EE. by no means is it absolute, as 2nd harmonic THD was not tested.

I think this is more of a case of how much THD is acceptable to the listener, and what type is acceptable (especially if it artificially extends the HF BW of a driver), and not a case of what is strictly audible. Whilst i respect Toole's work, his latest work HAS recieved some justified criticism, though not from me i might add.
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Old 15th April 2010, 03:33 AM   #26
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I tried 5grams and still got way off numbers. Vas was 669.97.

I emailed Uli to see what he says to do, but was hoping someone here had already measured some 100mm speakers and could shed some light on the process.

Thanks.
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Old 15th April 2010, 04:14 AM   #27
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sorry to jack the thread inadvertedly.

Personally i have never used the added weight method to determine Vas. From all i have learned and read, and heard from others, this method is not nearly as reliable. I use the 'test box' or known box method...I cant remember the real name for it. Im sure Planet10 will know it.

Measuring Loudspeaker Driver Parameters

the page shows how to do either test to measure Vas, although i recommend the 'known box' method.

sorry im not much help here.

Good luck
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Old 15th April 2010, 05:07 AM   #28
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I don't know about added mass vrs known box. I use added mass.

I do know that the T/S generated are f(V, weather). If meaured using the same or similar kit the factory specs are reasonable... and the boxes designed with them seem to do what you expect.

The numbers i get are quite different. Attached is data i measured, and that Mark Fenlon measured on the same drivers.

Both sets are equally valid IME.

Someone might say that my measures must be done incorrectly, but my measures have been the "same" as those made by others (including Zaph & MJK)

dave
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File Type: gif Fenlon-FE127-measures.gif (7.2 KB, 323 views)
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Old 15th April 2010, 11:52 AM   #29
TheGimp is offline TheGimp  United States
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Compared to the measurements posted by dave, my measurements are ok, except Cms (off by 3 orders of magnitude) and Vas (off by two orders of magnatude).

How do you mount the speaker when taking these measurements? This might be a factor. I have the speaker setting face up on several towels to isolate it from the workbench. Clip leads are used to make the connections.

What altitude are you at? Since sound velocity effects the measurement this would be a factor. I'm at 1000' which I did not expect to have a great impact.
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Old 15th April 2010, 04:12 PM   #30
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Do note that the measures i posted are for FE127eN not FE103

I'm at 800 ft above sea level.

dave
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