I need help with my LS90's

Trevorson · January 27

I recently acquired a pair of LS90s and I am now realizing they need more work then I initially thought.

As some information to help with my scenario, the person I purchased them from was very nice and friendly. They were more then willing to let me listen to them before purchasing. i already own a cs350 center, some ls/fx surrounds and even recently purchased a pair of ls70's for a family member, so I am pretty familiar with the sound of these speakers. The speakers sounded as if they had no issues. When I took a glance at the drivers they looked good.

Well I guess in the heat of the moment, somehow, I did not realize one of the woofers had been replaced. Trust me, I am very very embarrassed about this. After some further inspection, I realized that the replacement woofer is a 7010, rather then the 7100s these speakers are supposed to have. I have no clue how bad this is, if at all.

Another issue I quickly realized, when I use the pink noise built into my receiver the tweeter of the speaker with the replaced woofer has a staticky crackle to it. The static goes away when changing the volume. This static is only ever noticeable when using pink noise and I know its not my receiver. I was thinking this might be due to the odd woofer not "playing" well with the components of the speaker, but I really would not know for sure.

Although I just created an account and this is my first time posting, I have been around these forums quite a bit. There seems to be quite a few LS enthusiasts that are very knowledgeable about this lineup of speakers and I am certain someone could lead me in the right direction. If you made it this far, thank you very much for your time and consideration.

I will try and upload a picture of the odd woofer below.

Best regards,

Trevor

SeleniumFalcon · January 28

Hi Trevor,
Welcome to Polk's forum. Congratulations on your new speakers. I've asked a friend, at Polk, about the different woofer issue you have and he'll be able to note whatever differences there might be. I'll let you know as soon as I hear from him. In general terms differences tend to be the electrical and mechanical characteristics of each woofer model. Things like the DC resistance of the voice coil, the compliance of the suspension and other parameters that determine what the overall tuning of the complete system should be.

Trevorson · January 28

Hello SeleniumFalcon,
Thanks, so far it is a pleasure to be here! Thank you very much for going out of your way to help me out here, I am very appreciative. It is nice to know I will be hearing the knowledge of someone working at Polk. I will also try my best to remember that the different electrical and mechanical characteristics of a driver, rather than just the measurements and performance of said driver, could potentially effect the characteristics of a speaker. That is some very nice insight.

On a side note, assuming that the black cable of the ls90s is the negative and white is the positive, the odd woofer seems to be wired in reverse. I am starting to think that may be the issue for the static I am experiencing. But before making that assumption and running more tests I am going to wait for your response just to play it safe.

ken brydson · January 28

Hey @Trevorson

Far from an expert here but I ran a 7.1 LS HT for many years until I had to downsize. IIRC the difference between the original driver (with the embossed lightning dustcap) and the replacement is that the replacement had a bucking magnet to shield the speaker from old school CRT TV's. The specs are the same and I ran a couple of replacements for a long time without issue.

I'm not sure if the reverse wiring would cause the static you describe but more likely a phase issue. If it persists, try turning the suspect driver 180 degrees and see if that helps. Sometimes an aging spider can sag and cause distortion/ static.

Good luck and welcome to Club Polk!

SeleniumFalcon · January 29

I've heard back from my friend at Polk and the LS90 uses four MW7100 and the MW7010 was used in the RT12 which used 2 of them. He is going to check with the transducer prototyping technician and ask what the differences are between the two. I might take a day or so to hear back.

Trevorson · January 29

Hi @ken brydson

It is nice to now know i can @ people directly, hopefully I did it right.

Hmm, a 7.1 LS setup sounds both awesome and interesting. If you don't mind me asking Ken, I am very curious on the specifics off that setup, from what you used as the LCR all the way down to the sub you used. I am very curious on what sub will blend well with these speakers, especially since I do not plan on running any speakers full range. Did you use specific speakers based on your room and circumstances or did you say screw it and throw 7 ls90s around the room and call it a day?

Thank you for the feedback on using the 7010 as a replacement woofer. After looking around the forums a bit I have found a good amount of people that would agree with you, Ken. That coupled with your experience of running a 7.1 LS HT, which is actually a goal of mine right now, I am starting to feel content with having the 7010 as a replacement woofer in my 90s.

Your feedback on the weird static I have been experiencing is very informative, although I must ask if you can elaborate a bit more. By the "suspect driver" I would imagine you would mean the driver that is clearly making the static noise, even if that driver is the tweeter, correct? The reason I am asking that question, when the answear seems very straight forward, is that the 7010 woofer is actually turned so the sticker is parallel with left side of the cabinet. That has been throwing me off a bit, I thought maybe someone had just made a mistake while installing it. I would assume that the sticker and connections downward would be the 'normal' configuration. Also wouldn't turning the driver effect the placement of sound? Sorry if I am asking too many questions, I do not mean to waste your time I just like to ensure that I am doing absolutely everything correctly. I am the type of person that likes to triple check everything

That little fact of the magnet shielding the woofer from old CRT's is pretty cool to know. I now do remember about hearing of CRT's causing interference with audio equipment.

Thanks again Ken. It is always nice to hear and learn from other peoples experiences.

Regards,

Trevor

Trevorson · January 29

Hi @ken brydson

Hmm, a 7.1 LS HT sounds both awesome and interesting. If you don't mind, I must ask the specifics of this setup. Did you use the 350LS for the center or one of the LS towers? Did you happen to find a sub that blended really well with all the all the speakers? that is something I am especially curious about since I do not plan on running any of the speakers full range. Did you happen to ever run any of the speakers full range? From specs and prior knowledge, I would imagine the speakers would not hold up to well.

I have looked around the forums a good bit so far and it seems a good amount of people would agree with you, Ken. I am starting to feel a lot more content with using the 7010 woofer in my 90s.

The information you provided on the aging and potential sagging of the spider is very informative. I would imagine by the "suspect driver" you would mean the driver that is clearly making the static noise, even if that driver is the tweeter, correct? The reason I am asking that question, when the asnwear seems very straight forward, is that the 7010, the replacement woofer, has the sticker and connections facing the left side of the enclosure. Initially I thought someone had just made a mistake. Would you also be able to tell me if my experience of changing volume, up or down, ridding the static is consistent with the sagging of the spider?

Trevorson · January 29

Its nice to hear back from you @SeleniumFalcon

That's good to know. I was considering pulling out the drivers to check if they all are 7100's. That surely does save me some time. Its nice to know a little more about the RT12's too. I have heard good things about that speaker.

Take your time, don't worry about this too much. I already consider you and your friend over at Polk awesome for taking the time out your days to try and assist me.

Trevorson · February 2

Sorry for the double response to Ken. I'm not 100% sure what happened there. I edited that post because I mentioned Ken wrong but after editing it disappeared completely, for me atleast, so I just rewrote it. Maybe I didn't notice it but I swear even the next day when I checked this thread it still was not there but now it is. Kinda weird. I actually find that pretty embarrassing now but whatever.

Trevorson · February 2

Update on my scenario-

I swapped the tweeter from my working LS90 with the tweeter that's been giving me trouble and that confirmed that their is certainly something wrong with said tweeter. I took kens' advice and reoriented the tweeter. Since the tweeter has 3 screws in a triangle orientation I was not able to get the tweeter completely upside down. I still tried every orientation that was possible. I still experienced static in every orientation. Weird enough, I only get the static sound past -36db and so on. The range is set from -80db to 20db.

bcwsrt · February 2

Vanilla. It happens.

Trevorson · February 2

I gotcha Brian.

Trevorson · February 2

I wonder if Ken is fed up with my excessive typing. Haha. It looks like he has been active since I mentioned him.

SeleniumFalcon · February 3

I've not heard anything from Polk about the differences between the MW7100 and the MW7010 drivers. I'll send another email to the technician.
The tweeter would need to be replaced, I'll check my old parts guide for the correct part number so you can search for it.

SeleniumFalcon · February 5

The part number for the tweeter is SL6000.

pitdogg2 · February 5

https://www.ebay.com/itm/296169958825?

SeleniumFalcon · February 5

Well done!

SeleniumFalcon · February 6

The response from the technical department:

I don’t have the parameters for the MW7010 and the MW7100. Just the build of materials and it looks like the only difference between the two is that the MW7010 is shielded with a bucking magnet and cup while the MW7100 isn’t. I hope this helps you out.

SeleniumFalcon · February 7

A second engineering source found this information:

Could only find the MW7100:
Re: (DC resistance) 6.5 ohms, 5% tolerance
Fs (resonant frequency): 37Hz, 10% tolerance
BL: 5.9 T-m 5% tolerance
Qts: 0.59 15% tolerance
SPL (dB re 1W@1m) 86dB 1.5dB tolerance
Sd: 141.03cm2
Mass: 16.3g

Trevorson · March 4

This is a lot of good information. I am very sorry I took so long to reply. I totally forgot the forums existed.

After I realized that the one tweeter was causing the issues I looked around the forums a bit to see if anyone else had the issue as well as what models would work properly if i got a replacement. I couldn't wait so I ordered one for a good price off eBay and ever since it has worked well and i don't have any issues any more. I actually did get an sl6000 pulled from an ls70. It was assembled roughly a year before mine were. Funny enough it is obviously more shiny than the ones that came with my 90s. Now i just have to swap the less shiny tweeter from my tower with the matte tweeter in my 350 center so the LCR goes from really shiny to kinda shiny to matte. Haha just kidding, kinda. I almost actually want to do that but the purist in me wont allow it. I always wondered why the tweeters in the towers have a shiny finish where as the center and surrounds have a matte finish.

Trevorson · March 4

@SeleniumFalcon Hearing the info you provided straight from a Polk technician is exactly what I need to sleep at night! Although it does not all mean a lot to me,yet, the specs you provided from the second engineering source are very nice to have handy. I will most likely write that down somewhere for future reference. Thank you so very much for helping out a novice like myself.

After hearing this, I would believe the 'odd' woofer is certainly an adequate replacement to continue using, but I also would also imagine you are a lot more experienced and would have a more meaningful opinion than mine. Now if you don't mind me asking, do you believe, given what you heard from your sources at Polk, that the different model woofer would be adequate to continue using?

pitdogg2 · March 4

I actually did get an sl6000 pulled from an ls70. It was assembled roughly a year before mine were. Funny enough it is obviously more shiny than the ones that came with my 90s.

That is not unusual. It all has to do with how the metal was vapor deposited upon the dome. Some of the tri-laminated domes could be 3 different colors, near black, gold or silver.

Trevorson · March 4

That is very interesting. Thank you for sharing.

I need help with my LS90's

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