CS350LS crossover mod for tweeter

adam2434

I posted a while back that the high freq output of my CS350LS is lower than my LS90's. I can tell this "by ear" as well as the EQ adjustments that my auto calibration mic wants to make for the CS350LS (+5dB at 11kHz).

Eric from customer service told me that they could modify the CS350LS' crossover to better match the LS90s' tweeter output.

Anyone have an opinion on this approach or have a feel for the specifics of what they would do?

I would assume that the inherent freq response of the CS350LS and LS90 tweeter would be very similar, since they are similar tweeters. So, I'm guessing that the tweeter output of the CS350LS is limited by a crossover element with a different value (different size cap or resistor somewhere). I'm thinking that changing this crossover element to the same value as the LS90s' would bring the tweeter output to the same level. I don't know much about crossover design, so I may be over-simplifying.

I plan to talk to Polk more about this, but also wanted to check the opinions of other CP'ers.

Thanks,

Adam

ohskigod

I got the same set up, yeah theres a little difference, but not drastic. If you get the info, keep us posted on the details. Its definitly piqued my interest

mantis

The Ls90's are sweet speakers. A friend of mine has a pair in oak. Good luck with your upgrade although from the last time I listened to the Ls350 with the 90's , I didn't recall a big difference in sound quality. But if this tweak makes a difference , I'll tell my buddy about it.

Dan

adam2434

OK, I'll let you all know what I learn and decide to do.

I've also been wanting to test out a CS400i for comparison. I have one with a blown tweeter, but am having a hard time scaring up a used trilam for it.

What's interesting is that when I got my FX500i, I checked how they match the LS90s by listening to some music using 1 LS90 and 1 FX500i, and found that the high freqs were very similar and a good match - seemingly better than the CS350 that was supposed to be a match for the LS90s.

So now I'm wondering if the CS400i will be closer to the high freq output of the LS90s.

Perhaps Polk designed the CS350 with a tamed-down tweeter output to soften the bright Pro Logic soundtracks of the time and to make voices more natural and less sibilant. Dunno. I have never experienced or measured this difference this with any other speakers I have owned.

Adam

VR3

Trying plugging the CS350 up as a main channel.

Your receiver/preamp could be "dumbing" its signal and flattening the response. My preamp did. (my old NAD)

adam2434

Sid,

That's a reasonable suggestion - it removes a variable. Heck, I can even try that with my receiver totally out of the equation by just using my 2 ch amps and preamp.

However, I do think the lower CS350LS high freq output is real for 2 reasons:

1) Using other speakers (NHT and Athena) with the same electronics, my receiver did not want to boost the high freqs of the center ch.

2) A while back, someone else posted similar observations with their CS350LS.

I'm thinking the CS350LS may be voiced this way by design. Originally, I thought maybe mine was defective, but I have no other observations that would make believe this is true (all the drivers and tweeter are emitting sound, have no visible signs of damage, and do not distort at high volumes, etc.).

Thanks for the input,

Adam

Herfnwolf

I have the same setup with LS/FX surrounds.

I am using a B&K Reference 30 Preamp and I have not noticed the difference in crossover settings but, I will do some testing now that you have brought this up.

What is the expense and method (DIY or factory) for the Polk modification be?Keep us informed

adam2434

Herfnwolf wrote:

I have the same setup with LS/FX surrounds.

I am using a B&K Reference 30 Preamp and I have not noticed the difference in crossover settings but, I will do some testing now that you have brought this up.

What is the expense and method (DIY or factory) for the Polk modification be?Keep us informed

Herfnwolf, it not a difference in crossover settings. It is lower high freq output from the CS350 vs LS90s. The CS350 sounds rolled off on the high end and this is corroborated by the high freq EQ boost (+ 5 dB at 11 kHz) that my receiver wants to put on the center ch from its auto calibration measurements.

I'll post again in a little while to give an update with my learnings from Polk CS.

adam2434

Eric from CS and I have traded a few emails on the question. Here's what I've learned.

A simple crossover mod on the CS350 is not an option because the tweeter does not have a resistor on it, so it can't be brightened-up with a lower value resistor. Interestingly, the LS90s do have a resistor on their tweeter, so they could be dulled-down a little with a higher value resistor. I don't like this option and won't be doing it.

The CS350 and LS90 trilams are not exactly the same. Eric suggested that I try to swap one and see if I like the results, although Polk has never tried this and can't comment on what the results would be. Since apparently the trilams for the LS series are still available from CS, a swap is feasible. I am skeptical that this would do the trick, as I would think that the trilams would be inherently similar in their freq response and efficiency. Also, this seems like a lot of trouble and I don't want to risk effin up one of my trilams in the process. I have not decided if I will try this. Also, this experiment still does not answer my question below.

I'm still waiting on an answer on if my CS350 is functioning properly and if the lower high freq output is normal and part of the design (or an artifact of the design). I have asked this several times in several ways, and have not received a clean answer yet. I'm sure Polk has the data somewhere that would show if the CS350 has rolled-off highs vs the LS90. Sure, this is proprietary Polk data, but all I'm looking for is a yes/no answer.

If the lower high freq level is normal, I don't have to worry about "fixing" it - I just need to decide if I am happy with the sound or want to try something else.

If it is not normal, then I will look deeper into the root cause and try to fix it. Eric suggested some "tired" crossover components a potential.

I just don't like not knowing.

I'll post update #2 when I know more.

Adam

adam2434

Got an answer from Eric in CS today (in quotes below) regarding if the CS350 has an inherently lower high freq output vs. the LS90s.

"Hi, yes there is a slight difference in the response of the center to the L and the R but it should not be that drastic of a difference. It is honestly difficult to say if there is something wrong with the speaker, or if you are very sensitive to that region of sound, in which case you will notice the difference in the output."

So, assuming the difference I'm hearing and measuring is normal (speaker not defective), I would personally characterize it as more than just "slight".

To summarize, there is no crossover mod to brighten up the CS350LS and its high freq output is somewhat lower than LS90s. I still plan to experiment with a CS400i if I can find a trilam for mine, or I may bite the bullet and buy another CS400i.

I'd be curious to learn what other CS350LS/LS90 owners hear. You could try a 2 ch test using the CS350LS as 1 ch, or you could listen in 5 or 7 ch stereo if your receiver/processor has it. In both cases, I hear significantly less shimmer on cymbals and less air in vocals with my ear up to the CS350's tweeter.

Adam

wallstreet

I've got both the 350 and 400i to go with my 90's. I used both extensively in the HT, and I've just about settled on the 400i as the champion. Both centers integrate quite seamlessly with the 90's on the mid to upper octaves of course. Neither centers has near the bass response from the 90's. The 350 has a slight edge on seamless integration, but the performance gains with the 400i won it center stage in the media room. The 350 is still alive and kicking in the bedroom HT with 4 Paradigm reference inwalls.

ohskigod

I like my 350 and had no issues as listed above, but after checking on this thread again, I might try a cs400i for kicks and giggles.

adam2434

Wallstreet,

Did you also notice softer tweeter output from the CS350 vs. your LS90s, and if so, does the CS400i have higher tweeter output, closer to the LS90s?

I should be able to answer the 2nd question in a week or so because I have a CS400i arriving next week.

What did you specifically like about the CS400i?

I'll post my findings on this thread when I get the CS400i.

Adam

wallstreet

adam2434 wrote:

Wallstreet,

Did you also notice softer tweeter output from the CS350 vs. your LS90s, and if so, does the CS400i have higher tweeter output, closer to the LS90s?

I should be able to answer the 2nd question in a week or so because I have a CS400i arriving next week.

What did you specifically like about the CS400i?

I'll post my findings on this thread when I get the CS400i.

Adam

After I calibrated all my speakers with a SPL meter, I didn't notice any softness from the CS350. The 400i goes lower than the 350. As a result, you get more depth to voices, explosions, etc. Also, the 400i has the cascade tapered driver array which the 350 doesn't. The only downside to the 400i is that it's butt ugly. Polk really dropped the cosmetic ball when they came out with these big box centers. The wife objected when the 400i went front and center, but who asked her for her opinion anyways? Their new line closely resembles the old CS350.

adam2434

I've had my CS400i for a few weeks now and thought I'd report back.

The cs400i's high freq output is higher vs the CS350LS. This is obvious by ear and by the fact that my receiver's auto calibration EQ sets the highest freq band flat at +0 dB (same as it sets the LS90s). Recall that it set the highest eq band to +5 dB for the CS350LS. However, I keep the eq off when listening.

It's intereting to me that the high freq EQ settings have always been in line with what my ears have told me. I always felt that my Athenas were on the bright side; the EQ set the highest band to -3 dB. I always felt like my NHTs lacked a little detail; the EQ set the highest band to +3 dB. I always felt my LS90s sounded about right; the EQ set the highest band flat at +0 dB.

I feel like the CS400i blends well with the LS90s and I am going to keep it. It is an ugly black box, but works/looks fine placed on my rack (a stand for a large LCD/DLP TV) which is sitting in front of my projection screen.

I'm going to offer my CS350LS in the flea market before I hit Ebay or Audiogon.

Adam

soiset

Did you ever find out which trilams would work with your 400i?

adam2434

soiset wrote:

Did you ever find out which trilams would work with your 400i?

I'm not sure I understand the question.

Polk no longer carries the trilams, so one would have to find a used one (which is difficult) or buy a replacement silk dome from Polk.

soiset

I was wondering which model numbers you would look for, as NOS or used, that would work with the 400i.

adam2434

Off the top of my head, I'm not sure what the 400i trilam model/part # is. If you have a 400i with a bad tweeter, you could take it out and see. Or, you could contact Polk CS.

I'm pretty sure that a trilam from any of the RTxxxi series with the raised bezel would work.

Good luck, that's a great and popular vintage series, and it's too bad that Polk doesn't carry trilam replacements anymore. The desire for a trilam comes up pretty often here.