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Forum index » Science and Technology » Physics » Acoustics
Thiele - Small parameters
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dor900
science forum beginner


Joined: 11 Jul 2006
Posts: 2

PostPosted: Tue Jul 11, 2006 5:50 pm    Post subject: Thiele - Small parameters Reply with quote
Hi all

I am working on a vented box loudspeaker design, based on Peerless
850122 woofers and Vifa PL27TG35-06 tweeters. I purchased the drivers
some 2 or 3 years ago and they have been lying on their back during
that time.

The parameters displayed on the manufacturer webside (
http://www.tymphany.com/datasheet/printview.php?id=194 ) were promising
with e.g. a low value of fs = 38 Hz. When I measured the impedance of
the woofers I got different results (see.
http://www.hi.is/~ohh1/imp-plot.jpg ). The fs was as high as 63 Hz and
Qms = 12,9 !

The speakers where in a free field (not in a baffle) when I measured
the impedance. When these values are transformed from free field to
baffled the difference is only about 7%.

Does someone experience with similiar differences between displayed (by
manufacturer) and measured (by the designer) parameters?

Please comment if you have some.

Best regards
Halldór K. Júlíusson
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bert stoltenborg
science forum addict


Joined: 16 May 2005
Posts: 52

PostPosted: Fri Jul 14, 2006 8:11 pm    Post subject: Re: Thiele - Small parameters Reply with quote
Both speakers deviated that much from the manufacturers specs?
Have you been measuring in a very cold environment? Some rubber
surrounds get large changes when used around or below zero degrees
Celsius.
Lying on the back shouldn't alter speakers that much.
There is always some tolerance in spekers TSP due to temperature and
humidity factors

dor900 wrote:
Quote:
Hi all

I am working on a vented box loudspeaker design, based on Peerless
850122 woofers and Vifa PL27TG35-06 tweeters. I purchased the drivers
some 2 or 3 years ago and they have been lying on their back during
that time.

The parameters displayed on the manufacturer webside (
http://www.tymphany.com/datasheet/printview.php?id=194 ) were promising
with e.g. a low value of fs = 38 Hz. When I measured the impedance of
the woofers I got different results (see.
http://www.hi.is/~ohh1/imp-plot.jpg ). The fs was as high as 63 Hz and
Qms = 12,9 !

The speakers where in a free field (not in a baffle) when I measured
the impedance. When these values are transformed from free field to
baffled the difference is only about 7%.

Does someone experience with similiar differences between displayed (by
manufacturer) and measured (by the designer) parameters?

Please comment if you have some.

Best regards
Halldór K. Júlíusson
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dor900
science forum beginner


Joined: 11 Jul 2006
Posts: 2

PostPosted: Tue Jul 18, 2006 4:08 pm    Post subject: Re: Thiele - Small parameters Reply with quote
bert stoltenborg wrote:
Quote:
Both speakers deviated that much from the manufacturers specs?
Yes, that can be seen in my figure as both drivers are plotted there.

They are quite consistent.

Quote:
Have you been measuring in a very cold environment? Some rubber
surrounds get large changes when used around or below zero degrees
Celsius.
No, I measured at room temperature (even though I am living in Iceland

Smile
I even tried some "burn in" for several hours with no change in TSP (at
least I know that is a myth now).

Quote:
Lying on the back shouldn't alter speakers that much.
There is always some tolerance in spekers TSP due to temperature and
humidity factors
True, I expected some, say, 10% difference between my measurement and

data from the manufacturer but not something like 65% !!! As I am
unable to figure out why this great difference is I thought maybe it
had affected the drivers in some way to keep them lying on the magnet
for such a long time.


Thank you for your reply.
Halldór KJ
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