I parted out a pair of highboys and another pair of lowboys and still have the two
12" woofers from the lowboys. They do not match, one has the magnet bolted on,
otherwise the cone, spider, dust cap and edge look the same except for the edge
on the brown one being heavily coated with sealant. Note that the cone does move
easily even with the heavy coating:
The other pair matched the brown one on the left but without a heavy coating of
sealant.
Front view, the cones look a bit faded and splotchy but not too bad:
The brown one has a crack in the magnet, not sure if it goes all the way though but
the voice coil does not rub:
Note heavy sealant coating, it dripped down the front of the frame:
Just wanted to note these differences anyone else have them and noticed if they
have a heavy coat of sealant?
Measured the T&S parameters of the brown (PLB-A) frame driver:
And of the silver (PLB-B) frame driver:
The first thing that stands out, and others on this forum have mentioned that they are
roughly 12 ohm drivers. I'm not sure what the designer was thinking - a very easy load so
as to not stress the amp?
The next important thing to note is that these woofers do not match very well, one has a
.86% efficiency (91.4dB) and the other .62% (89.9dB) a 1.5 dB difference. Now the weaker
one has a magnet that looks thinner, but checking the Bl product both are 9.7 give or take.
This suggests that the magnetic field strength (B) and voice coils (l) are the same. Looking
further we see that PLB-A has a moving mass of 33.7g and the other 38.5 this is enough to
explain the difference. The Qms value is 3.6 for the A woofer and 2.7 for the B woofer and
given how low these are I'd expect them to have metal voice coil formers perhaps one is
thicker causing the increased weight and lower Qms. One could cut off the dust cap to
see if there is a second cap under the first one - not sure how to account for the weight
difference.
Neither of these drivers make much sense for a vented or acoustic suspension (AC) design.
The Vas is very high suggesting a high compliance suspension which is excellent for an AC
design but completely wrong for a vented one. We want it as high as possible for a
sealed design but we want it roughly equal to the box size or about twice that for a
vented design. Fs is about right for a vented design, but the Qts is high for a vented
design at about .6 ish when it should be closer to .4 for vented. The moving mass is low
for a sealed design being 34 to 38g about half that of the AR3a 12" which is at 70g ish.
I once measured the Fb for this design at about 20 Hz, I'd increase this to 28 Hz so that the
port output and excursion reduction are at a frequency that is more useful to a greater
percentage of music and a better match to the capability of the woofer. The 3" port tube is
about 5.5" long and I found cutting this in half provided roughly a 28 Hz Fb. Mine did not
have any stuffing in the port tubes and that's how it should be.
Simulation of the vented design in one of the box simulators would be a good idea.
This woofer actually makes sense for use in a very big sealed box as are used in Bozak
speakers. Put it in a big box for an Fc of 35 Hz and then the system Qtc will provide strong
bass output down to 35 Hz.
Measured the input impedance of woofer PLB-A in free air also in the .ZMA file for simulation
purposes: .ZMA file is attached as a .TXT file, download it then change the extension back.
12" woofers from the lowboys. They do not match, one has the magnet bolted on,
otherwise the cone, spider, dust cap and edge look the same except for the edge
on the brown one being heavily coated with sealant. Note that the cone does move
easily even with the heavy coating:
The other pair matched the brown one on the left but without a heavy coating of
sealant.
Front view, the cones look a bit faded and splotchy but not too bad:
The brown one has a crack in the magnet, not sure if it goes all the way though but
the voice coil does not rub:
Note heavy sealant coating, it dripped down the front of the frame:
Just wanted to note these differences anyone else have them and noticed if they
have a heavy coat of sealant?
Measured the T&S parameters of the brown (PLB-A) frame driver:
And of the silver (PLB-B) frame driver:
The first thing that stands out, and others on this forum have mentioned that they are
roughly 12 ohm drivers. I'm not sure what the designer was thinking - a very easy load so
as to not stress the amp?
The next important thing to note is that these woofers do not match very well, one has a
.86% efficiency (91.4dB) and the other .62% (89.9dB) a 1.5 dB difference. Now the weaker
one has a magnet that looks thinner, but checking the Bl product both are 9.7 give or take.
This suggests that the magnetic field strength (B) and voice coils (l) are the same. Looking
further we see that PLB-A has a moving mass of 33.7g and the other 38.5 this is enough to
explain the difference. The Qms value is 3.6 for the A woofer and 2.7 for the B woofer and
given how low these are I'd expect them to have metal voice coil formers perhaps one is
thicker causing the increased weight and lower Qms. One could cut off the dust cap to
see if there is a second cap under the first one - not sure how to account for the weight
difference.
Neither of these drivers make much sense for a vented or acoustic suspension (AC) design.
The Vas is very high suggesting a high compliance suspension which is excellent for an AC
design but completely wrong for a vented one. We want it as high as possible for a
sealed design but we want it roughly equal to the box size or about twice that for a
vented design. Fs is about right for a vented design, but the Qts is high for a vented
design at about .6 ish when it should be closer to .4 for vented. The moving mass is low
for a sealed design being 34 to 38g about half that of the AR3a 12" which is at 70g ish.
I once measured the Fb for this design at about 20 Hz, I'd increase this to 28 Hz so that the
port output and excursion reduction are at a frequency that is more useful to a greater
percentage of music and a better match to the capability of the woofer. The 3" port tube is
about 5.5" long and I found cutting this in half provided roughly a 28 Hz Fb. Mine did not
have any stuffing in the port tubes and that's how it should be.
Simulation of the vented design in one of the box simulators would be a good idea.
This woofer actually makes sense for use in a very big sealed box as are used in Bozak
speakers. Put it in a big box for an Fc of 35 Hz and then the system Qtc will provide strong
bass output down to 35 Hz.
Measured the input impedance of woofer PLB-A in free air also in the .ZMA file for simulation
purposes: .ZMA file is attached as a .TXT file, download it then change the extension back.
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