April 29th 05, 02:30 AM
From a nice DIY Web Page:
>>Ferrite Magnet 604s
As I mentioned on the Home Page, horizontal separation between voice
coil gaps for ferrite magnet Altec Lansing 604 & 904 duplexes is
2.25". This produces 90 degrees of phase shift between the two
driver's acoustic centers at 1500Hz. The supplied passive crossovers
for these units were essentially the same as for the 604-8H, namely
third order high pass and second order low pass sections at 1500Hz with
MF and HF EQ circuitry. Unfortunately, they did not correct for the
phase difference created by the drivers' offset.
So, what about phase correction for the ferrite motor Altec Duplexes,
both the 904 variations and 604-K series? A good question -
unfortunately I didn't have any on-hand to measure, model and listen
to, so the best I can offer is a bit of theory to consider, and leave
the rest up to you.
Toward Phase Correction - the contenders!
The table below shows a good number of contenders for correcting
ferrite duplex phase shift. None of them correct it to zero, but some
are very close indeed! I only included filters that produced a
positive SPL error at crossover of 1.5dB or less. The filters were
modeled in CALSOD using drivers with constant impedance and SPL, but
with the HF acoustic center placed 2.25 inches behind the LF center. <<
>>Ferrite Magnet 604s
As I mentioned on the Home Page, horizontal separation between voice
coil gaps for ferrite magnet Altec Lansing 604 & 904 duplexes is
2.25". This produces 90 degrees of phase shift between the two
driver's acoustic centers at 1500Hz. The supplied passive crossovers
for these units were essentially the same as for the 604-8H, namely
third order high pass and second order low pass sections at 1500Hz with
MF and HF EQ circuitry. Unfortunately, they did not correct for the
phase difference created by the drivers' offset.
So, what about phase correction for the ferrite motor Altec Duplexes,
both the 904 variations and 604-K series? A good question -
unfortunately I didn't have any on-hand to measure, model and listen
to, so the best I can offer is a bit of theory to consider, and leave
the rest up to you.
Toward Phase Correction - the contenders!
The table below shows a good number of contenders for correcting
ferrite duplex phase shift. None of them correct it to zero, but some
are very close indeed! I only included filters that produced a
positive SPL error at crossover of 1.5dB or less. The filters were
modeled in CALSOD using drivers with constant impedance and SPL, but
with the HF acoustic center placed 2.25 inches behind the LF center. <<