LSi25 crossover upgrade

Decker
Decker Posts: 7
edited June 2009 in DIY, Mods & Tweaks
Does anybody have any info on upgrdes that can be done to LSi25 crossovers. This in regards to the mids and tweeter not the woofer.
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  • Face
    Face Posts: 14,340
    edited June 2009
    These should all be similar to the 25.

    http://www.polkaudio.com/forums/showthread.php?t=70357

    http://www.polkaudio.com/forums/showthread.php?t=74096

    http://www.polkaudio.com/forums/showthread.php?t=73233
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • NJPOLKER
    NJPOLKER Posts: 3,474
    edited June 2009
    What all do you plan on doing?
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  • zingo
    zingo Posts: 11,258
    edited June 2009
    Decker wrote: »
    Does anybody have any info on upgrdes that can be done to LSi25 crossovers. This in regards to the mids and tweeter not the woofer.

    Buy new speakers. :p
    Jake
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  • Decker
    Decker Posts: 7
    edited June 2009
    I have a Rotel 1080 hooked up to them and had it a bit to load. I fried one of the resistors and thought this might be a good time to do some upgrades.
    As for new speakers I don't think so.
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  • Decker
    Decker Posts: 7
    edited June 2009
    The thing that I am not sure about is, with the 15's are the subs also run through the Xover or are they separate. The 25's also have a totally different circuit board. Is this just a matter of doing some circuit tracing.
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  • george daniel
    george daniel Posts: 12,096
    edited June 2009
    pm Ben,, he did a very good job on a crossover rebuild on some 15's.
    JC approves....he told me so. (F-1 nut)
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  • Decker
    Decker Posts: 7
    edited June 2009
    I found the schematic for the 15's and it looks like the subs are run off the same circuit board. I guess i will have to do some tracing.
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  • McLoki
    McLoki Posts: 5,231
    edited June 2009
    If you call Polk Customer Service on Monday - they should be able to send you the schematic for the LSi25's. (I had to do that to get the LSiC schematic for my own upgrade)

    Once you get it - forward it on to Dorokusai so he can update the schematic thread....

    Michael
    Mains.............Polk LSi15 (Cherry)
    Center............Polk LSiC (Crossover upgraded)
    Surrounds.......Polk LSi7 (Gloss Black - wood sides removed and crossovers upgraded)
    Subwoofers.....SVS 25-31 CS+ and PC+ (both 20hz tune)
    Pre\Pro...........NAD T163 (Modded with LM4562 opamps)
    Amplifier.........Cinepro 3k6 (6-channel, 500wpc@4ohms)
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  • Systems
    Systems Posts: 14,873
    edited June 2009
    Decker wrote: »
    The thing that I am not sure about is, with the 15's are the subs also run through the Xover or are they separate. The 25's also have a totally different circuit board. Is this just a matter of doing some circuit tracing.
    The woofer in the 15 has a passive crossover (inductor,capacitor)whereas the woofer in the 25 having its own dedicated amp will likely have an active crossover.
    Testing
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  • Decker
    Decker Posts: 7
    edited June 2009
    If I were to keep all the same values of the caps and resistors but upgrade in quality would this be a safe bet for better sound quality?
    I'll be sure to forward the schematic for everybodies future reference.
    Thank you all for the info.
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  • Face
    Face Posts: 14,340
    edited June 2009
    Decker wrote: »
    If I were to keep all the same values of the caps and resistors but upgrade in quality would this be a safe bet for better sound quality?
    Yes.
    I'll be sure to forward the schematic for everybodies future reference.
    Thank you all for the info.
    That would be great, thanks!
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • Decker
    Decker Posts: 7
    edited June 2009
    Here is the schematic for the LSi25's. this is only for the mid's and tweeter.
    I noticed that there is at least I problem with the diagram. R1 is shown to be 2.25 ohms but the parts list shows it as 1.75 ohms. The one that I replaced was 1.75 ohms. I also sent a copy to dorokusai for future reference.
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  • Systems
    Systems Posts: 14,873
    edited June 2009
    The resistor must have been a change in production thats not reflected in the schem.
    The woofers electronic crossover will be integral to the amp thats why it's not included in the drawing.
    Testing
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  • ben62670
    ben62670 Posts: 15,969
    edited June 2009
    I was talking to a guy a while back about doing his LSI25's, and I had suggested putting in a a switch to bypass that huge 500uf cap. What this would do is make the mids run like LSI9's. The switch could easily be thrown to filter the low bass. Also nearly all AVR's/Pre's have XO's built in them. Run the sub signal to the Plate amps on the LSI25's, and set the AVR's XO point to match. The big 500uf cap is the biggest hit to the performance of that speaker.
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • Face
    Face Posts: 14,340
    edited June 2009
    Wow, that's a huge cap. You can either buy a few LARGE Mundorf or Solen caps, or bypass the electrolytic with a small film cap.

    I'm not sure bypassing the cap altogether would be a good idea, it would probably sound boomy.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • ben62670
    ben62670 Posts: 15,969
    edited June 2009
    Face wrote: »
    Wow, that's a huge cap. You can either buy a few LARGE Mundorf or Solen caps, or bypass the electrolytic with a small film cap.

    I'm not sure bypassing the cap altogether would be a good idea, it would probably sound boomy.

    It would sound like modded 9's with a sub.
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • Face
    Face Posts: 14,340
    edited June 2009
    If LSi25 cabinets are similar to the LSi15, the top portion has less displacement than a LSi9. Plus, the tuning is different(no power port). There would be greater roll off at the bottom end which may throw the speaker's balance off by adding too much upper/mid bass. It's simple to try, easily reverse-able, and best of all, practically free though.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • Systems
    Systems Posts: 14,873
    edited June 2009
    Face wrote: »
    If LSi25 cabinets are similar to the LSi15, the top portion has less displacement than a LSi9.
    Also unlike the 9's cascaded xover with different rolloff points for each woofer, the 25 and 15 are true MTM 's in that the woofers are series connected so cross over at the same frequency.
    Testing
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  • ben62670
    ben62670 Posts: 15,969
    edited June 2009
    My major argument for it is nearly all AVR's/Pre's have XO's. If you are running full range just flip the switch so you are not bypassing the 500uf. It is only a 6db high pass.
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • Systems
    Systems Posts: 14,873
    edited June 2009
    ben62670 wrote: »
    My major argument for it is nearly all AVR's/Pre's have XO's. If you are running full range just flip the switch so you are not bypassing the 500uf. It is only a 6db high pass.
    It would be something worth trying,the only issue might be one of phase.Does the 25's plate amp have adjustable phase?
    Testing
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  • ben62670
    ben62670 Posts: 15,969
    edited June 2009
    GV#27 wrote: »
    It would be something worth trying,the only issue might be one of phase.Does the 25's plate amp have adjustable phase?

    Hopefully the OP can answer that. Here is the spec page.
    http://www.polkaudio.com/homeaudio/lsi/specs.php
    I would think side firing would mess with the phase a bit too(placement dependent).
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • Systems
    Systems Posts: 14,873
    edited June 2009
    ben62670 wrote: »
    It is only a 6db high pass.
    Because of the large value of capacitance it will be operating down low, likely near the natural rolloff of the woofers.So if you combine the 6db for the cap and 12 db for the natural rolloff it's probably closer to being 18db.
    Testing
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  • Systems
    Systems Posts: 14,873
    edited June 2009
    ben62670 wrote: »
    I would think side firing would mess with the phase a bit too(placement dependent).
    IMO no as long as the xover frequency is below 150hz or so.The drivers separation is far less than a wavelength.
    Testing
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  • McLoki
    McLoki Posts: 5,231
    edited June 2009
    GV#27 wrote: »
    Because of the large value of capacitance it will be operating down low, likely near the natural rolloff of the woofers.So if you combine the 6db for the cap and 12 db for the natural rolloff it's probably closer to being 18db.

    supposed to cross over at 80hz.
    Mains.............Polk LSi15 (Cherry)
    Center............Polk LSiC (Crossover upgraded)
    Surrounds.......Polk LSi7 (Gloss Black - wood sides removed and crossovers upgraded)
    Subwoofers.....SVS 25-31 CS+ and PC+ (both 20hz tune)
    Pre\Pro...........NAD T163 (Modded with LM4562 opamps)
    Amplifier.........Cinepro 3k6 (6-channel, 500wpc@4ohms)
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  • Decker
    Decker Posts: 7
    edited June 2009
    Yes you can switch the phase on the LSi25's.
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  • dorokusai
    dorokusai Posts: 25,577
    edited June 2009
    As it was written....

    Ken,

    1.75 ohms is the correct value as stated on the schematic. 2.25 ohms is an older value. If the customer is consistently burning up 1.75 ohm resistors, but not 2.25 ohm resistors, then I'm sure it would be ok to use the 2.25 ohm resistor. There will be slightly less output from the tweeter, but if he's playing them loud enough to blow resistors constantly, he probably won't notice the difference.

    Scott Orth
    Systems Engineer
    Polk Audio, Inc.
    CTC BBQ Amplifier, Sonic Frontiers Line3 Pre-Amplifier and Wadia 581 SACD player. Speakers? Always changing but for now, Mission Argonauts I picked up for $50 bucks, mint.
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  • Face
    Face Posts: 14,340
    edited June 2009
    The change from 1.75ohms to 2.25ohm will only bring the tweeter down 1dB. As Scott mentioned, he probably wouldn't notice a difference.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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