Help with Monitor 12s passive radiators

Zosimo

Hi all, new to the forum but not to Polk Audio.

Have had my M12s which I bought new in the early 90s. The reason I'm writing is because my 4 year old son destroyed the 12" PR a while back and I had to replace them. However, I couldn't find the originals anywhere at the time and replaced them with a mint set of flat and not coned 12" Polk Audio passive radiators from similar speakers of the time. See pics attached.

Let me cut to the chase with my questions because I am by no means an expert:

1) Have I compromised the sound? If so, how and why?
2) Do Polk sell vintage parts?

thanks!

SeleniumFalcon

Hello, welcome to the Polk forum. Nice clean setup and good photo. Any changes would be in the bass performance of the speakers. Are you able to make any frequency response measurements?
I don't believe Polk has any of the older radiators still available.

Gardenstater

Photo of the original equip. radiator vs the replacement from behind would be interesting. I am told they tuned them by adding different amounts of weight to the spider/cone assembly.

Zosimo

Gardenstater wrote: »

Photo of the original equip. radiator vs the replacement from behind would be interesting. I am told they tuned them by adding different amounts of weight to the spider/cone assembly.

Thanks for your reply. Unfortunately, I don't have the originals anymore as I replaced them a while back , but here are photos of the back of the current PRs. They should be from SDAs if I'm not mistaken.

Zosimo

SeleniumFalcon wrote: »

Hello, welcome to the Polk forum. Nice clean setup and good photo. Any changes would be in the bass performance of the speakers. Are you able to make any frequency response measurements?
I don't believe Polk has any of the older radiators still available.

Thanks. No, can't make any accurate measurements if not from a questionable app from my mobile phone. I really haven't properly used them for a long long time and I have now started to use them again as my main speakers, so I can't make any direct comparisons if not from memory, but I seem to remember them being more bass heavy while now the bass is tighter and less prolonged. Again, this is simply from memory though.

In a way, I actually prefer this sound a bit more these days as my musical tastes have also changed over the years.

Gardenstater

Well thanks I had never seen one of these planar cone PRs from behind. What is the white material? Is it a rigid foamed plastic? Too bad you threw out the old ones. We'll never know now. I have heard it said that the Monitor 12s were a bit boomy. With luck you may have improved them! Do you remember what they looked like from behind? Was there a weight that looked like the head of a carriage bolt?

Zosimo

Gardenstater wrote: »

Well thanks I had never seen one of these planar cone PRs from behind. What is the white material? Is it a rigid foamed plastic? Too bad you threw out the old ones. We'll never know now. I have heard it said that the Monitor 12s were a bit boomy. With luck you may have improved them! Do you remember what they looked like from behind? Was there a weight that looked like the head of a carriage bolt?

Indeed a shame a threw them away. Yes, it seems to be some kind of plastic foam and they are rather light given the size, but I can't remember either the weight of the previous ones or what they looked like from behind.

Re the boomy nature of the 12s, absolutely, they were bass heavy for sure and now that's gone completely, maybe even too much! Again, I really like the sound now, much more balanced. I wonder if anyone else on the forum has tried out this mod.

audioluvr

Zosimo wrote: »

Re the boomy nature of the 12s, absolutely, they were bass heavy for sure and now that's gone completely, maybe even too much! Again, I really like the sound now, much more balanced. I wonder if anyone else on the forum has tried out this mod.

I believe the M12's and the SDA 3.1' s shared the same PR? The ones you installed should work, especially if you like the sound. You can silicone a steel washer or two on the back center to slow them down (lower the bass response).

Zosimo

audioluvr wrote: »

Zosimo wrote: »

You can silicone a steel washer or two on the back center to slow them down (lower the bass response).

Thanks. Yes, have read about this technique elsewhere. So, the heavier I make it the deeper and extended the bass will sound? Does that mean the I'll be lowering the Hz response?You'll have to excuse my ignorance here.

pitdogg2

yes George the SDA passives (most anyways) were Styrofoam with either a soft front panel ( most bubbled badly) or a tuff plastic like material.

To the OP I certainly would not have thrown them away. Depending what was wrong with them we have some pretty incredible folks here who have salvaged many items, not to mention if you found a pair you would have a spare 1 just in case.

I'd start a search on ebay for both monitor 12 passive or SDA 3.1 Passive radiators. You never know some may pop up. I'm not sure you affected the speaker to terribly with the passives you have used. Even the 12" passives like you have had different weights and stock numbers. SW120 SW121. I've used both on some SDA's that came with one or the other SW120-SW121 and couldn't tell any difference myself.

Personally years back one of the Polk employees stated the reason the passives went to the cone type on the M12-SDA3.1 was they (originals) were no longer available from the supplier.

audioluvr

Zosimo wrote: »

Thanks. Yes, have read about this technique elsewhere. So, the heavier I make it the deeper and extended the bass will sound? Does that mean the I'll be lowering the Hz response?You'll have to excuse my ignorance here.

It lowers the range but affects the top end the most so for example if it is 30-400 Hz with no washer if would be like 25- 325 Hz with one washer. The actual range and spl levels vary greatly based on cabinet volume, number of/size/excursion/efficiency of drivers. Too little and they will sound flabby too much and you may cut out too much of the bottom registers.

Gardenstater

If it's the same as the 3.1tl then you need the SW122. There is a pair of SW121 in slightly rough condition and a probably SW120 on eBay now. What is the date/number on yours. I can't read it:

https://www.ebay.com/itm/154209885418?hash=item23e7a01cea:g:f4MAAOSwpbhfvCHi


https://www.ebay.com/itm/333993116729?_trkparms=aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=20201210111314&meid=779b80e33a244b35bcbf07a046290acd&pid=101195&rk=3&rkt=12&sd=154209885418&itm=333993116729&pmt=0&noa=1&pg=2047675&algv=DefaultOrganic&brand=Polk+Audio&_trksid=p2047675.c101195.m1851

F1nut

Zosimo wrote: »

Hi all, new to the forum but not to Polk Audio.

Have had my M12s which I bought new in the early 90s. The reason I'm writing is because my 4 year old son destroyed the 12" PR a while back and I had to replace them. However, I couldn't find the originals anywhere at the time and replaced them with a mint set of flat and not coned 12" Polk Audio passive radiators from similar speakers of the time. See pics attached.

Let me cut to the chase with my questions because I am by no means an expert:

1) Have I compromised the sound? If so, how and why?
2) Do Polk sell vintage parts?

thanks!

Did you buy your Polk speakers in Italy?

Zosimo

F1nut wrote: »

Zosimo wrote: »

Hi all, new to the forum but not to Polk Audio.

Have had my M12s which I bought new in the early 90s. The reason I'm writing is because my 4 year old son destroyed the 12" PR a while back and I had to replace them. However, I couldn't find the originals anywhere at the time and replaced them with a mint set of flat and not coned 12" Polk Audio passive radiators from similar speakers of the time. See pics attached.

Let me cut to the chase with my questions because I am by no means an expert:

1) Have I compromised the sound? If so, how and why?
2) Do Polk sell vintage parts?

thanks!

Did you buy your Polk speakers in Italy?

Yes, I did. Brand new back in 92 or 93 I think. Why do you ask?

Zosimo

Gardenstater wrote: »

If it's the same as the 3.1tl then you need the SW122. There is a pair of SW121 in slightly rough condition and a probably SW120 on eBay now. What is the date/number on yours. I can't read it:

https://www.ebay.com/itm/154209885418?hash=item23e7a01cea:g:f4MAAOSwpbhfvCHi


https://www.ebay.com/itm/333993116729?_trkparms=aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=20201210111314&meid=779b80e33a244b35bcbf07a046290acd&pid=101195&rk=3&rkt=12&sd=154209885418&itm=333993116729&pmt=0&noa=1&pg=2047675&algv=DefaultOrganic&brand=Polk+Audio&_trksid=p2047675.c101195.m1851

Hey, thanks for the info. Mine are SW121's, while as you say, I'm in need of SW122's.

The ones I have are truly in mint condition and I'm really enjoying the sound at the moment, so I'm going to hang on to these while I scout the internet for SW122's. If I find them great, otherwise happy with what I've got.

Everyone's been really helpful so far and I've got much more understanding now of the situation.

Zosimo

F1nut wrote: »

Zosimo wrote: »

Hi all, new to the forum but not to Polk Audio.

Have had my M12s which I bought new in the early 90s. The reason I'm writing is because my 4 year old son destroyed the 12" PR a while back and I had to replace them. However, I couldn't find the originals anywhere at the time and replaced them with a mint set of flat and not coned 12" Polk Audio passive radiators from similar speakers of the time. See pics attached.

Let me cut to the chase with my questions because I am by no means an expert:

1) Have I compromised the sound? If so, how and why?
2) Do Polk sell vintage parts?

thanks!

Did you buy your Polk speakers in Italy?

They were such a rare and exotic brand at the time here in Italy and I was so fascinated by the closed cabinet setup. I remember seriously falling in love with them. I was just a teenager at the time and worked an entire summer just to purchase them. Fully intend to never part ways with them

F1nut

Zosimo wrote: »

F1nut wrote: »

Zosimo wrote: »

Hi all, new to the forum but not to Polk Audio.

Have had my M12s which I bought new in the early 90s. The reason I'm writing is because my 4 year old son destroyed the 12" PR a while back and I had to replace them. However, I couldn't find the originals anywhere at the time and replaced them with a mint set of flat and not coned 12" Polk Audio passive radiators from similar speakers of the time. See pics attached.

Let me cut to the chase with my questions because I am by no means an expert:

1) Have I compromised the sound? If so, how and why?
2) Do Polk sell vintage parts?

thanks!

Did you buy your Polk speakers in Italy?

They were such a rare and exotic brand at the time here in Italy and I was so fascinated by the closed cabinet setup. I remember seriously falling in love with them. I was just a teenager at the time and worked an entire summer just to purchase them. Fully intend to never part ways with them

I noted you were in Italy and knew they were an uncommon speaker there, so I was just curious if you purchased them there. Hats off to you for keeping them in such good condition.

If desired, you can experiment with tuning your current PR's by temporarily taping different size weights to the rear of the Styrofoam part. Don't use a tape with too strong of an adhesive as you could damage the Styrofoam. The various weights Polk used were not heavy, so no need to go crazy. Also, make sure the weight is centered.

Edit:
If you haven't already, be sure to epoxy the magnets on your mid-drivers. Info on how to is posted on the forum.

Gardenstater

Zosimo wrote: »

Gardenstater wrote: »

If it's the same as the 3.1tl then you need the SW122. There is a pair of SW121 in slightly rough condition and a probably SW120 on eBay now. What is the date/number on yours. I can't read it:

https://www.ebay.com/itm/154209885418?hash=item23e7a01cea:g:f4MAAOSwpbhfvCHi

https://www.ebay.com/itm/333993116729?_trkparms=aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=20201210111314&meid=779b80e33a244b35bcbf07a046290acd&pid=101195&rk=3&rkt=12&sd=154209885418&itm=333993116729&pmt=0&noa=1&pg=2047675&algv=DefaultOrganic&brand=Polk+Audio&_trksid=p2047675.c101195.m1851

Hey, thanks for the info. Mine are SW121's, while as you say, I'm in need of SW122's.

The ones I have are truly in mint condition and I'm really enjoying the sound at the moment, so I'm going to hang on to these while I scout the internet for SW122's. If I find them great, otherwise happy with what I've got.

Everyone's been really helpful so far and I've got much more understanding now of the situation.

Assuming of course that the Monitor 12 used the same Passive as the 3.1tl. I did some approx. calculations and the cabinet interior volume of the 3.1tl is about 42.5% bigger. Cabinet volume is definitely one of the factors that goes into determining the effective moving mass of the passive that is desired to achieve the desired resonant frequency. That's from some reading I did. Also, the thiele small parameters and number of midwoofer drivers factors in as well. What MW# do your Monitor 12s have? I know it is 4 stereo drivers vs. 4 MW6503 stereo and 1 MW6511 dimensional driver for the 3.1tl.

It looks like, all other factors remaining the same, if you decrease cabinet internal volume, you need more mass for the same target resonant frequency:

https://audiojudgement.com/passive-radiator-speaker-design/



Thanks for giving me the opportunity to learn a little more here.