JBL Speaker Polarity Reversal

Archived from groups: rec.audio.pro (More info?)

A few weeks ago, I was involved in a discussion about JBL drivers being
negative polarity, with respect to drivers of other brands.

My E-V, Altec and Eminence drivers are positive polarity, while the JBL E
series drivers are negative.

I have my gauss meter out yesterday and discovered that the JBL E series
driver magnetic fields are reversed with reference to the others. All other
drivers show cause the needle of the gauss meter to pull toward "+". The E
series drivers pull the meter toward "-".

One JBL driver that bucks the JBL convention is the 2403 Elliptical Horn
Tweeter. It's magnetic field is positive, like the other brands of drivers.

Now this raises the question as to whether the actual diaphragm movement is
positive. Since I can't easily measure this, one has to assume some things.
If magnet polarities are the determining factor, then I would have to assume
the tweeters are positive, unlike the E-series drivers.

One thing I noticed when I corrected the polarity relationship between the
JBL and the E-Vs is that a dip in white noise spectrum as measured at a
distance of 4' appeared some 40 hz above the Linkwitz--Riley crossover
frequency.

A few months ago, I experimented with reversing the tweeter wiring and
noticed this same anomaly around 5KHz after reversing the wiring.

If the low to mid crossover dip with drivers in phase is any indicator, then
the phase of the tweeter WAS in fact out of phase by 180º before the wiring
reversal added a dip there too.

Does anyone have absolute factual data on the polarity of the JBL 2403
compression tweeter? Because if the magnet polarity is the means by which
JBL polarizes a driver, then the 2403's are positive pressure with positive
voltage on the + terminal.

--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-

Archived from groups: rec.audio.pro (More info?)

"Chris Hornbeck" <chrishornbeckremovethis@att.net> wrote in message
news:l07a21hakan3410le8f0e5mj0jt1ml962l@4ax.com...
> On Wed, 02 Mar 2005 00:17:31 GMT, "Mark & Mary Ann Weiss"
> <mweissX294@earthlink.net> wrote:
>
> >Does anyone have absolute factual data on the polarity of the JBL 2403
> >compression tweeter? Because if the magnet polarity is the means by which
> >JBL polarizes a driver, then the 2403's are positive pressure with
positive
> >voltage on the + terminal.
>
> Can you put your finger tip on the diaphragm? A single-cell
> battery will move the diaphragm enough to feel with your
> finger tip. Try both polarities, and you should have a high enough
> confidence level. If not, ask your wife to help. Women aren't
> just smarter; they feel better too. You've perhaps noticed this...
>
> Good fortune,
>
> Chris Hornbeck

LoL! :-)
'Scuze me while I wipe my coffee off the monitor...

Okay, the reason I can't easily measure this tweeter is because it's a
compression driver with a horn/phase plug sort of configuration. The
diaphragm is inaccessible.

I did some white noise spectrum measurements in the last hour, with the
E-series driver wired red to red on the tweeter and then with the E-series
wired black to red on the tweeter.
Interesting results.. there was a wide squarish-looking notch of about -8dB
from 3kc to 3.6kc with the first wiring arrangement. When I flipped the
midrange driver polarity, the notch went away.
I decided to leave them both wired that way and stop inverting the polarity
to the entire cabinet at the loudspeaker manager/crossover.
A whole lotta' tweakin' goin' on here!


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-

Archived from groups: rec.audio.pro (More info?)

On Wed, 02 Mar 2005 03:22:14 GMT, "Mark & Mary Ann Weiss"
<mweissX294@earthlink.net> wrote:

> it's a compression driver with a horn/phase plug sort of configuration. The
>diaphragm is inaccessible.

The reason I recommend the finger-tip test is that *nothing else*
will really convince you (or me neither/ niether). If you remove the
horn, the diaphragm surface is exposed.

Wacky? Maybe, but this is science! Nothing is too over-the-top.
Like Art, the struggle is all. The truth will out.

Peace, Love, Dopamine,

Chris Hornbeck

Archived from groups: rec.audio.pro (More info?)

>
> ** There is no "determining factor" involving the magnet or voice coils
at
> all.
>
> JBL simply mark (or used to mark) all their drivers the reverse way to
most
> others.
>
> IOW - it is simply a matter if which terminal gets marked red or + by
> the maker.
>
>
>
> ............. Phil


Maybe so, but in my book there are two ways to make a driver polarize and
that's to orient the magnetic field, or the direction of the voice coil
winding. Whether the left terminal gets marked "+" or "-" is based on the
physics of the driver.

I have conducted some tests this afternoon, using microphones placed as
close as physically possible to the mid driver and the 2403 tweeter horn.
Results were not as cut and dried as earlier tests comparing mid to woofer
phase:

With the high pass filter in-circuit, at 5Kc, tweeter and midrange were
exactly in-phase.
With the high pass jumpered out, at 5Kc, phase of tweeter lagged about 40º.

With the high pass filter in-circuit, at 3Kc, tweeter lagged about 110º.
With the high pass jumpered out, at 3Kc, tweeter was almost 180º out of
phase.

This tends to suggest that tweeter is wired out of phase with mid driver,
but the phase shift with frequency could be an anomaly of the horn-loading.
Measuring a horn-loaded driver is not as straightforward as measuring a
cone-driver.

The bottom line? Mid-field spectral measurements show a smoother response
with the wiring the way it is now--the E-series driver reverse-wired, the
2403, wired normal. I think I'll leave it like that until I find compelling
evidence that another configuration would present better results.


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION • FILM SCANNING • DVD MASTERING • AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-

Archived from groups: rec.audio.pro (More info?)

In article <38nohvF5ecftjU1@individual.net> philallison@tpg.com.au writes:

> ** Totally irrelevant to the marking which is purely by convention.
>
> Whether a cone moves in or out when a source of DC volts is applied matching
> the +/- markings is a completely ARBITRARY decision.
>
> Think it through - it will come to you.

There's a convention (an AES standard, even) for relating microphone
diaphragm movement with the polarity at the terminals - when the
diaphragm moves inward, Pin 2 is supposed to go positive with respect
to Pin 3.

It would seem reasonable that there's a corresponding standard for
loudspeakers also, but nobody has established it.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

Archived from groups: rec.audio.pro (More info?)

"RD Jones" <annonn@juno.com> wrote:
>You should be able to observe the direction of motion by
>loosening the ring radiator mounting and using a 1.5v cell.
>Since the JBL rings and diaphragms can be reverse wired
>during a repair, is it possible something got switched
>around at some point ? The ring design dates to the mid
>50's so I would be surprised if the 2403 wasn't the same
>as the bullet, slot, and earlier eyeball models.

Bill Burton designed the JBL 075 ring radiator in the mid 60's, not the
mid 50's.

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

Archived from groups: rec.audio.pro (More info?)

Harvey Gerst wrote:

> Bill Burton designed the JBL 075 ring radiator in the mid 60's, not
the
> mid 50's.
>
> Harvey Gerst
> Indian Trail Recording Studio
> http://www.ITRstudio.com/

I used the JBL hisory link as my reference,
although I have no way to know if it is correct.

http://www.jblpro.com/pages/history1.htm

'54 does sound like a very early date.

rd

Archived from groups: rec.audio.pro (More info?)

"Chris Hornbeck" <chrishornbeckremovethis@att.net> wrote in message
news:l07a21hakan3410le8f0e5mj0jt1ml962l@4ax.com...
> On Wed, 02 Mar 2005 00:17:31 GMT, "Mark & Mary Ann Weiss"
> <mweissX294@earthlink.net> wrote:
>
>>Does anyone have absolute factual data on the polarity of the JBL 2403
>>compression tweeter? Because if the magnet polarity is the means by which
>>JBL polarizes a driver, then the 2403's are positive pressure with
>>positive
>>voltage on the + terminal.
>
> Can you put your finger tip on the diaphragm? A single-cell
> battery will move the diaphragm enough to feel with your
> finger tip. Try both polarities, and you should have a high enough
> confidence level. If not, ask your wife to help. Women aren't
> just smarter; they feel better too. You've perhaps noticed this...


The magnetic polarity is irrelevant by itself. The combination of the
magnet and polarity of the voice-coil makes the totality of the drive unit
one way or the other.

Unless you are bundling a whole bunch of drivers in a clump....


geoff