LS90 - crossover configuration
soiset
Posts: 724
My understanding of the LS90 xover config has been that it is a 2.5-way speaker. It has two mid-woofers, and two woofers. Is that the case? If not, just what does "cascade tapered array" mean?
I may very well be a new owner of some LS90's, soon, and I'd like to mimic the original xover config actively, to eliminate intermodulation distortion, etc.
I may very well be a new owner of some LS90's, soon, and I'd like to mimic the original xover config actively, to eliminate intermodulation distortion, etc.
Post edited by soiset on
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Im not familiar with this speaker so I just have the schems to go by.(Are the 4 midbass drivers the same,the schem does not indicate driver model #'s.?)There are 2 versions the original and a revised.The original appears to be more of a 2.5 way with the 3 and 4 th woofers crossed over much lower than in the revised version.My understanding of the LS90 xover config has been that it is a 2.5-way speaker. It has two mid-woofers, and two woofers. Is that the case? If not, just what does "cascade tapered array" mean?
I may very well be a new owner of some LS90's, soon, and I'd like to mimic the original xover config actively, to eliminate intermodulation distortion, etc.
Cascade means that 2 (or more) drivers are used to cover the bass range together but their low pass filters are set at different frequencies with one operating up to the crossover to the tweeter,the other operating in the bass and lower mids only.Testing
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Im not familiar with this speaker so I just have the schems to go by.(Are the 4 midbass drivers the same,the schem does not indicate driver model #'s.?)There are 2 versions the original and a revised.The original appears to be more of a 2.5 way with the 3 and 4 th woofers crossed over much lower than in the revised version.
Cascade means that 2 (or more) drivers are used to cover the bass range together but their low pass filters are set at different frequencies with one operating up to the crossover to the tweeter,the other operating in the bass and lower mids only.
The woofers are all 6.5", and identical. The original version was apparently quite unsatisfactory, and Polk made a "running" change during production to fix what was considered muddy bass and woolly midrange. My assumption was as you say, that the upper two woofers ran from the tweeter all the way down, and the lower two ran from some lower point, probably less than 500 Hz, down. If the original appears to be 2.5-way, what does the revised show, a full 3-way design? -
With its 1mh inductor vs the 4mh in the original, the revised versions midbass #3 and 4 are allowed to operate up to a much higher frequency.Therefore the rev version is closer to being a 2 way.However because of the series connection between drivers # 3 and 4 their levels will be as much as 6db down in comparison to the parrallel connected midbass drivers #1 and 2 .IMO this speaker is a good candidate for removing the passive xover and going active as you have planned.If the original appears to be 2.5-way, what does the revised show, a full 3-way design?Testing
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Anyone know what serial numbers would indicate when the change was made?
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Anyone know what serial numbers would indicate when the change was made?
I found this in an archived thread:The LS90 had a running change early on since the first ones sounded tubby and woolly. The corrected model was much better and is the one to modify. The original can be modified also, but the values used in the crossover were different and you should upgrade the parts with the later values. Easy way to tell: early LS90 models had a 4.0mH coil in position L3 on the crossover while the re-tuned version had a 1.0mH coil there. Other parts were different, too. -
With its 1mh inductor vs the 4mh in the original, the revised versions midbass #3 and 4 are allowed to operate up to a much higher frequency.Therefore the rev version is closer to being a 2 way.However because of the series connection between drivers # 3 and 4 their levels will be as much as 6db down in comparison to the parrallel connected midbass drivers #1 and 2 .IMO this speaker is a good candidate for removing the passive xover and going active as you have planned.
Thanks so much for your help. I suppose the ideal active config would be a 2.5-way, mimicking the revised version, with the lower two drivers operating up to 500-600 Hz. I'd guess that they had cut them off around 200 Hz in the original. -
I found this in an archived thread:
Can you post the link? I can't find it for the life of me. -
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Your welcomeThanks so much for your help.
Without knowing the impedance of the drivers its hard to pin point where the inductor begins to roll off the midbass's response.Interestingly Polks fix in the revised version means that the output of all 4 drivers will be overlapped for a greater portion of their operating range. One would think this would create an excess of output in the mid -upper bass,and lower midrange, the very problem they were trying to fix.I suppose the ideal active config would be a 2.5-way, mimicking the revised version, with the lower two drivers operating up to 500-600 Hz. I'd guess that they had cut them off around 200 Hz in the original.
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The extra woofers in most 2.5 ways Im aware of will roll off in the 300hz range.If I was doing this actively thats the range I would shoot for and I would use atleast a 12db slope to limit the amount of overlap.Testing
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