LSi25 crossover upgrade

[Decker]

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.

[Face]

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

[NJPOLKER]

What all do you plan on doing?

[zingo]

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

[Decker]

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.

[Decker]

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.

[george daniel]

pm Ben,, he did a very good job on a crossover rebuild on some 15's.

[Decker]

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.

[McLoki]

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

[GV#27]

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.

[Decker]

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.

[Face]

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!

[Decker]

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.

[GV#27]

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.

[ben62670]

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

[Face]

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.

[ben62670]

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.

[Face]

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.

[GV#27]

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.

[ben62670]

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.

[GV#27]

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?

[ben62670]

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).

[GV#27]

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.

[GV#27]

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.

[McLoki]

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.

[Decker]

Yes you can switch the phase on the LSi25's.

[dorokusai]

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.

[Face]

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.