[dor900]

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 the magnet 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 !

I measured the speakers impedance in a "free field" (in my living room,
not baffled).

Does someone experience with similiar differences between displayed (by

manufacturer) and measured (by the designer) parameters?

Best regards
Halldór K. Júlíusson

[UOSWOTPPNR]

Sounds like your room accoustics are skewing the results. Manufacturers
utilize an anechoic chamber to make precise measurements.



"dor900" wrote in message
ups.com...
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 the magnet 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 !

I measured the speakers impedance in a "free field" (in my living room,
not baffled).

Does someone experience with similiar differences between displayed (by

manufacturer) and measured (by the designer) parameters?

Best regards
Halldór K. Júlíusson

[Rudi Fischer]

"UOSWOTPPNR" wrote:

Sounds like your room accoustics are skewing the results.

No, there's nearly unmeasurable effect of room on
impedance of a free air driver.

Manufacturers
utilize an anechoic chamber to make precise measurements.

Wrong, on TSP the word is *Klippel*.

BTW: Peerless is known for publishing very reliable
data (IME).

Rudi Fischer
--
....and may good music always be with you

[[email protected]]

UOSWOTPPNR wrote:
Sounds like your room accoustics are skewing the results.

No, it doesn't.

Manufacturers utilize an anechoic chamber to make precise
measurements.

Not for Thiele/Small parameters, they don't.

In fact, Small makes no mention of this requirement in his
detailed description of parameter measurement (Small,
"Direct Radiator Loudspeaker System Analysis," JAES
1972 June, Appendix A, "Driver Parameter Measurement")
The only statement that Thiele makes is:

"Now the loudspeaker is suspended in air as far from
reflecting surfaces as is practical"
(Thiele, "Loudspeakers in Vented Boxes: Part II",
JAES 1971 June, reprinted from Proc. IRE Aus.
1961 Aug).

And Thiele references a further work for parameter meas-
urement, which states:

"the speaker is held at least 1 meter away from any
plane surface,"
(Ashley & Swan, "Experimental Determination of
Low-Frequency Loudspeaker Parameters," JAES
1969 Oct.)

Further, with computer-based measurements, anechoic
measurements can be performed without needing an
anechoic chamber. Indeed, the vast majority of meas-
urements these days are NOT done in anechoic chambers
with no loss of accuracy, given appropriate eqiupment and
techniques.

To address the original poster's questions:

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 the magnet 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 !

I measured the speakers impedance in a "free field" (in my living room,
not baffled).

This simply is incapable of accounting for the huge
discrepancy.

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

Not, not by a long shot. Your resonant frequency is off by almost
an octave, and the Qms figure is off by nore than a factor of 4.

Frankly, the most likely explanations are that you either do NOT
have the drivers you think they do, they were assembled using
the wrong suspension parts, they are broken, or you have some
serious calibration issues.

[Scott Dorsey]

Rudi Fischer wrote:
"UOSWOTPPNR" wrote:

Sounds like your room accoustics are skewing the results.

No, there's nearly unmeasurable effect of room on
impedance of a free air driver.

Agreed. I could see SOME difference due to the Fs being a little higher
before the spider is loosened up in break-in, but I can't see a whole octave
difference being realistic.

Are you SURE the driver you have is the same driver you think you have?
Are you sure you did the arithmetic right?

BTW: Peerless is known for publishing very reliable
data (IME).

That's why, if I got those results, I'd go through and make sure I didn't
divide when I should have multiplied or something.

What if you just hook the signal generator up to the thing and sweep back
and forth until you hear the peak? Where is it when you hear it, and how
far off the center of the peak can you sweep before you hear a change in
tone?

Are you driving the speaker with a power amp or with a 600 ohm source?
If the driving impedance is too high, it could affect it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

Scott Dorsey wrote:
Are you SURE the driver you have is the same driver you think you have?
Are you sure you did the arithmetic right?

No, the impedance curve shown suggests the error is
very large and very real.

BTW: Peerless is known for publishing very reliable
data (IME).

That's why, if I got those results, I'd go through and make sure I didn't
divide when I should have multiplied or something.

Again, look at the impedance curve he supplied a link to.

Are you driving the speaker with a power amp or with a 600 ohm source?
If the driving impedance is too high, it could affect it.

Nope, it will have very little effect at similar levels of excursion.
The resonant frequency is determined by mechanical, not
electrical, parameters, notably suspension compliance and
moving mass. Neither are dependent upon the method of
electrical excitation. The suspension compliance is non-linear
with respect to excursion, but that is simply a drive level, and
cannot account for a factor of 4 error in compliance.

This "factor of 4" error is suggested by the fact that the Qms
figure is MUCH larger than spec. This further suggests that
the compliance of the driver is around 4 times too low.

[Phil Allison]

"dor900

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 the magnet 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 !

I measured the speakers impedance in a "free field" (in my living room,
not baffled).

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



** This 6.5 inch, pressed steel frame *budget priced* Peerless driver is
famous for not meeting the published Fs figure.

See: http://www.geocities.com/rbrines1/Pa...less_Pipe.html

Running it in for a while will soften the spider and lower the Fs - then
maybe 56 Hz is the norm, not 38Hz.

Luckily, suspension stiffness variations do not have a dramatic effect on a
driver's actual performance when mounted in a tuned box appropriate to its
size.



........ Phil

[Paul Stamler]

"UOSWOTPPNR" wrote in message
.com...
Sounds like your room accoustics are skewing the results. Manufacturers
utilize an anechoic chamber to make precise measurements.

Room acoustics won't affect T/S measurements nearly enough to cause this big
a difference. Either lying magnet-down for a couple of years has drastically
affected the suspension or the published T/S parameters are based on a
woofer that's been broken in. Breaking in a woofer consists of playing
enough bass signal through it to make the woofer move in and out a fair
amount, thereby repeatedly flexing the surround, spider, etc. It
significantly changes the T/S parameters.

One way to break woofers in is to hook them to the secondary of a 6.3V
filament transformer. Leave them hooked up for a couple of days. Preferably
in the garage.

Peace,
Paul

[Rudi Fischer]

"François Yves Le Gal" wrote:
On 18 Jul 2006 14:43:23 -0700, "dor900" wrote:

Does someone experience with similiar differences between displayed (by
manufacturer) and measured (by the designer) parameters?
Peerless DK is well known for changing parts - such as spiders or surrounds
- during the lifetime of their entry level products and not modifying the
published specifications.

Sure you can name at least one example/source
for this claim? Thank you.

IME they may not change model but PartNo.
by doing so.

Rudi Fischer
--
....and may good music always be with you

[Phil Allison]

"Rudi Fischer"


Sure you can name at least one example/source
for this claim? Thank you.


** See: http://www.geocities.com/rbrines1/Pa...less_Pipe.html


Read the WHOLE thread - ****head.




......... Phil

[Rudi Fischer]

wrote:
Rudi Fischer wrote:
"François Yves Le Gal" wrote:

Peerless DK is well known for changing parts - such as spiders or
surrounds - during the lifetime of their entry level products and not
modifying the published specifications.
Sure you can name at least one example/source
for this claim? Thank you.
In examining many thousands of drivers from hundreds of
sources,

Well, our numbers were only about 10% of that.

the phenomenon Mr. Le Gal describes is, quite
unfortunately, all too common.

We too experienced unacceptable deviations (more than
10 times in less than 5 years), but these were french
drivers. They weren't able/willing to fix that, the reason
we switched to scandinavian, were very lucky with
them.

OK, could have been plainly that: Luck.

[...]
IME they may not change model but PartNo.
by doing so.
Your estimation is wrong, simple as that. They may, in fact,
do anything they please. This is especially so since many if
not most of the components are sourced from any number of
Far East sources, and there is often little or no control of
manufacturing and inventory processes or any monitoring
of incoming parts before assembly.

I have to confess that my estimations (especially
regarding this manufacturer) date from the late
nineties - so I'm really sorry to hear that!

[...]
Rudi Fischer
--
....and may good music always be with you

[[email protected]]

Rudi Fischer wrote:
wrote:
Rudi Fischer wrote:
"François Yves Le Gal" wrote:
Peerless DK is well known for changing parts - such as spiders or
surrounds - during the lifetime of their entry level products and not
modifying the published specifications.
Sure you can name at least one example/source
for this claim? Thank you.
In examining many thousands of drivers from hundreds of
sources,
the phenomenon Mr. Le Gal describes is, quite
unfortunately, all too common.

We too experienced unacceptable deviations (more than
10 times in less than 5 years),

Oh, so you DO have some examples.

but these were french
drivers. They weren't able/willing to fix that, the reason
we switched to scandinavian, were very lucky with
them.

And many (most?) of those "Scandanavian" companies
are now run by whom? Using parts made where?

[Rudi Fischer]

wrote:
Rudi Fischer wrote:
"François Yves Le Gal" wrote:

Peerless DK is well known for changing parts - such as spiders or
surrounds - during the lifetime of their entry level products and not
modifying the published specifications.
[...]
We too experienced unacceptable deviations (more than
10 times in less than 5 years),
Oh, so you DO have some examples.

As mentioned befo Until '97 definitely no Peerless
(or SE*S, Sc*nSpeak, Dyn*udio).

Vif*? - Oh, uh, well...

And many (most?) of those "Scandanavian" companies
are now run by whom? Using parts made where?

Being out of this business for some time I had to
guess that your questions imply that this holding is
now korean or chinese. And
http://www.tymphany.com/company_loca...irections.html
shows that my guess was - regrettably - right, at
least partially.

OK, sure enough this explains Mr. Le Gals expressed
opinion and - considering their more recent drivers - I
stand corrected.

Rudi Fischer
--
....and may good music always be with you

[James Lehman]

The one thing that I have found to have the most effect on the free air
resonance of a given driver is its temperature and the ambient temperature
of the air in the room. If you don't believe me, try measuring it after its
been in the fridge for a while and then let it warm up near a heater or in
the sun and measure it again.

James. )


"dor900" wrote in message
ups.com...
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 the magnet 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 !

I measured the speakers impedance in a "free field" (in my living room,
not baffled).

Does someone experience with similiar differences between displayed (by

manufacturer) and measured (by the designer) parameters?

Best regards
Halldór K. Júlíusson

[Mr.T]

"James Lehman" wrote in message
. ..
The one thing that I have found to have the most effect on the free air
resonance of a given driver is its temperature and the ambient temperature
of the air in the room. If you don't believe me, try measuring it after
its
been in the fridge for a while and then let it warm up near a heater or in
the sun and measure it again.

Which is why measurements are always made at a specified temperature. (often
20degC.)

MrT.

[Rudi Fischer]

"François Yves Le Gal" wrote:
"Rudi Fischer" wrote:

We too experienced unacceptable deviations (more than
10 times in less than 5 years), but these were french
drivers. They weren't able/willing to fix that, the reason
we switched to scandinavian, were very lucky with
them.
From which company? Some French manufacturers such as PHL or Atohm turn out
outstanding drivers with excellent QC while others such as Davis or what's
left of Audax - OTOH, the AAC versions seem OK - don't really seem to care
about QC.

Yes, these were Audax. Mostly HDA-Series plus
some early paper-cones - from gluing problems
causing high distortion to one charge with insufficiant
magnetization. That finally did it. Not forgetting the
tweeters with missing/leaking FF...

*Sorry* for my doubts referring to Peerless.

Rudi Fischer
--
....and may good music always be with you