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Thiele Small Parameters vs. Real World.
Thiele Small Parameters vs. Real World.
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Old 9th February 2018, 06:24 AM   #1
globalplayer is offline globalplayer  Germany
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Default Thiele Small Parameters vs. Real World.

Afaik the Thiele Small parameters define the speaker`s "behaviour" at the resonance frequency only. These are so called small signal parameters.

Now how is the behaviour of the speaker at high power levels compared to low/small signal levels?
Which parameters are likely to shift and in which direction?

Has anyone any experience or insight into the matter?
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Old 9th February 2018, 12:00 PM   #2
Ron E is offline Ron E  United States
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Cms increases (most box designs are surprisingly insensitive to this) reducing Fs and increasing Vas
Re increases

Things get weird as things get nonlinear. TS parameters assume linear behavior so only approximately apply.
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Old 9th February 2018, 12:50 PM   #3
scottjoplin is offline scottjoplin  Wales
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I was looking at distortion measurements at differing SPLs made by Linkwitz and their high degree of non-linearity. Best possibly to accept that the small signal parameters are of very limited use in the real world
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Old 9th February 2018, 01:25 PM   #4
Keruskerfuerst is offline Keruskerfuerst  Germany
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Quote:
Afaik the Thiele Small parameters define the speaker`s "behaviour" at the resonance frequency only.
I donīt think so.
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Old 9th February 2018, 01:25 PM   #5
Sonce is offline Sonce  Macedonia
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Quote:
Originally Posted by scottjoplin View Post
Best possibly to accept that the small signal parameters are of very limited use in the real world
Most of the time we are listening at about 1 W power to the speakers, so small signal parameters rules in the real world of your home.
Sound reinforcement is different animal, of course.
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Old 9th February 2018, 03:04 PM   #6
scottjoplin is offline scottjoplin  Wales
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True, my real world is about there
@ global, I've just realised this is in the subwoofer forum, does your question specifically relate to subwoofers?
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Old 9th February 2018, 03:35 PM   #7
Sabbelbacke is offline Sabbelbacke  Germany
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@globalplayer
Take a look into what Klippel published - he has a lot of research and work done on the behaviour of transducers @high power. Lots to read up there
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Old 9th February 2018, 03:37 PM   #8
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by globalplayer View Post
Now how is the behaviour of the speaker at high power levels compared to low/small signal levels? Which parameters are likely to shift and in which direction?

Has anyone any experience or insight into the matter?
All of the basic parameters (Vas, Qes, Qms, Fs) will shift as the cone changes position, and Re will shift (increase as power input increases) . As to how much they shift (within the driver's linear range of operation) will depend on the driver's design.

Having said that, I've gotten into the practice of doing dynamic linearity tests on my builds - basically testing how they perform with short sine sweeps at different levels, up to the point that distortion reaches 10% in the passband. Even the cheap Dayton PA310 holds up quite well, with any significant non-linear changes having more to do with the box design than the driver.
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Old 10th February 2018, 09:03 AM   #9
globalplayer is offline globalplayer  Germany
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Thanks for the answers so far.


Quote:
Originally Posted by scottjoplin View Post
True, my real world is about there
@ global, I've just realised this is in the subwoofer forum, does your question specifically relate to subwoofers?
Speakers in general but with main emphasis on subs.


Quote:
Originally Posted by Sabbelbacke View Post
@globalplayer
Take a look into what Klippel published - he has a lot of research and work done on the behaviour of transducers @high power. Lots to read up there
Thanks for the hint. Will do. Funny name, btw .


Quote:
Originally Posted by Brian Steele View Post
I've gotten into the practice of doing dynamic linearity tests on my builds - basically testing how they perform with short sine sweeps at different levels, up to the point that distortion reaches 10% in the passband.
Good idea. I might have to do the same or something similar.
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Last edited by globalplayer; 10th February 2018 at 09:07 AM.
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Old 10th February 2018, 09:58 AM   #10
scottjoplin is offline scottjoplin  Wales
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Subs are more likely to be used at higher level, I presume also there are more non-linearities due to there being more of everything?
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