Must try MOD - Foam inside the stamped steel baskets - YES!

Gardenstater

I previously mentioned this in a couple of scattered places and didn't open up a dedicated thread. I suppose I didn't want to stick my neck out until there was confirmation from another who has tried it ✔. I've been living with this for almost 6 mos. now and I still continue to be super pleased with the benefits (I think the foam is still breaking in...kidding)! I used Armacell closed cell 1/8" thick foam but this is open to experimentation with perhaps open cell, composite of open cell over closed, felt over closed, felt alone......just keep it relatively thin like maybe 1/4" max(?). Let's get some more people trying this because it is a super rewarding mod and not all that difficult to do.

I won't get super long winded but I posted my initial report over in the other thread "What did you do to your stereo today" on p. 122.

https://forum.polkaudio.com/discussion/184609/what-did-you-do-to-your-stereo-rig-today/p122

Pictures are always worth more than words. I think the benefit of this is 3 fold: 1) Mechanical vibration dampening of the basket, 2) Sound proofing of the basket preventing acoustical into mechanical excitation, and 3) some amount of reflection attenuation of backwave reflections that would come back and hit the back of the cone. 3) is last but not least because when I did just one speaker initially I had to rebalance with whitenoise by lowering the unmodded speaker's channel by 0.4dB to compensate. I believe that is due to the reduction in reflected backwave which comes out as audible sPL through the cone. That has to be distorted due to time delays and phase differences and varying transmission/reflection for different frequencies.

Anyway, Merry Christmas and let's have fun with this mod. I'll add pictures when I find them.

Initial sizing on a spare driver I had. Settled on 1-1/4" x 1-5/16" but not super critical as long as you don't block the basket windows. You can even trim the windows with an Xacto knife after install:







Completed driver with the Armacell inside of the spokes and the section between spokes near the spider. I cut off the 3 vestigial tabs with a dremel cut off wheel - be careful not to get metal dust inside the driver:

SIHAB

now you've done it. I haven't even done the outside of the baskets
yet but have some sonic barrier laying around. Why not try the
inside too!

xschop

You guys are late to the game lol...




Seriously, this was Gstater's idea and I will be doing the same for all the stamped steel baskets. Been listening for quite awhile now (5B's are done) to all my familiar favorites and can vouch that the lower sax notes and even vibraphone notes are cleaned up that much more. Sleeper mod as they say.

Have to add I am using 0.090 thick open cell PVA foam with a thin layer of Power grab. They are 1.25 x 1.25" and only on the frame uprights.

VR3

I would be careful with putting anything to thick

You also want to keep it off the spider and surround

Toolfan66

My only issue with this mod is if you end up not liking it, it would be a major pain to reverse, if at all possible to reverse. Also doing 16 drivers doesn’t sound like fun at all..

I’m glad you like your findings, and having fun doing it..

Gardenstater

I think that's a valid concern for sure. Probably applies to a lot of the mods that we do. I took the no guts no glory attitude and I had the Vandersteen midrange driver patent I had read as my *spurs*, if you will and it gave me confidence in the theory at least.

I wouldn't blame those with the large multi driver vintage speakers not wanting to plunge right in.

Those with the 4's, 5's, and 7's......go for it don't be a chicken lol. But seriously, I feel that with the Armacell PSA adhesive, it is sticky but I told myself that I can probably scrape the foam out with my fingernails if need be. But I'm never going back.

Pick some songs that you want to use as your test songs before and after. I like ones where there are low level details or similar voices (or instruments) in timbre or pitch or overdubs that are subtle. I'll throw 4 out:

Mercy Street by Peter Gabriel from "So"
Cousin Dupree by Steely Dan from "Two Against Nature"
Telegraph Road by Dire Straits from "Love Over Gold"
I Talk to the Wind by King Crimson from "In the Court of the Crimson King"

Gardenstater

VR3 wrote: »

I would be careful with putting anything to thick

You also want to keep it off the spider and surround

Indeed. In my first 2 pics I tried to show how I left clearances at both the spider and the surround. Actually, that part of the spider is inactive so you could butt some thin foam right up against it. You can even see the adhesive excess from Polk there and it isn't a problem. The size I gave should work out just fine too. I think the 1-1/4" was the dimension of concern.

I chose to keep it thin on the theory that the internal basket area, although not closed obviously, might just diminish transient response if it were reduced too much. How much is too much I do not know. Also, I didn't want to hinder pressure wave transmission through the basket windows.

F1nut

Do either of you have BH5 squares mounted in the speakers you are adding the basket foam to?

xschop

I'm using 6x6x 1/2" open-cell foam product by Soundcoat. BH 5 or not, this mod is reducing backwaves from cone. I initially listened to a few tracks of Sade (her voice is toughest to get right in these vintage Polks)
The last bit of hollowness is gone.

I listened to a few of my favorite G Washington Jr. tracks and could clearly hear that the last bit of resonance that was masking his reed growl was also gone.

I put back in another set of 6502's that have the same butyl mat damping and phase-plugged, but without the foam inserts and the masking of his reed growl returned. This is not fake news.

Toolfan66

I disagree on the Sade statement, she has been one of my favorites to play on my Polks for years..

Also I don’t see where anyone said it was fake news.

Gardenstater

Yessir. BH5 6" x 6" kindly donated to me by @Moose68Bash. It was a gamechanger. I forget what I posted initially as my reaction......something like hearing vocalists taking a breath or something of that nature. Just first thing that came to mind.

This is bigger than that in my opinion.

xschop

Toolfan66 wrote: »

I disagree on the Sade statement, she has been one of my favorites to play on my Polks for years..

Also I don’t see where anyone said it was fake news.

That's called a euphamism. On the 5Bs at higher volume her voice has/had a slight hollow sound.

F1nut

Sade is sublime on my SDA's. Perhaps if one's gear and/or room is lively this foam idea might be of benefit, but I can say from personal experience that too much damping of the backwaves sucks the life out of the music.

VR3

@treitz3 we experienced music suck out with foam first hand!

Gardenstater

Try it before you make assumptions is all I can say. Here is the Vandersteen patent which got me thinking about this. That guy knows his s**t. I am willing to admit that some distortion can sound pleasant to some people with some systems and some rooms but in my opinion what the patent says about the backwave being reflected back at the cone and some of it transmitting through and some of it even being reflected again perhaps multiple times is out of phase time delayed undesireable sound.

Just for info., my room has a lot of DIY sound treatments and the reverb time is quite moderately low although I don't have the instruments to measure it. My experience is that voices are now distinctly separable and the same goes for instruments that are of similar volume and timbre. This only catches a small fraction of the backwave that is reflected back at the cone. I can only imagine what Vandersteen's design might sound like, although it is not applicable to a passive radiator system but a 3-way with a dedicated midrange. This small amount of foam doesn't stop or impede the sound waves pressurizing the cabinet and activating the PR, only helps with the internal reflections.

https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=5073948A&KC=A&FT=D&ND=3&date=19911217&DB=EPODOC&locale=en_EP

Toolfan66

Back when I was a fish around these parts it was brought up to dampen the inside of your speakers, I had zero experience in doing upgrades, let alone SDA’s, and taking speakers apart, but I have never been afraid to try working on things.

Well I had found a set of 1.2’s just 5 minutes from my house, and I went with ideas from these pages, and I believe at the time Mike had pushed the idea to line the inside of the speakers, so I was all in.

I invested in enough BH5 for the back walls, and I believe Sonic Barrier for the side walls, I can tell you I had fun doing it, and it looked awesome, but as soon as I fired them up I was horrified, I couldn’t pull it out fast enough, I was super disappointed. I had sucked the music out of the music!!

Out of all the mods I have tried, this was the worst one, and a biggest waste of money I have done, you could say I took one for the team. Needless to say it was a learning lesson.

Not comparing what you are doing, this just brought up that time frame shortly after I had joined here. Very thankful for the things I have learned along the way from many good people here, especially Jesse, Ray, Ivan, and Trey. Even though Mike no longer comes around these parts he was a huge help in me modifying my Jolida JD9..

Okay enough of my story telling.

Enjoy your mods, enjoy the music..

xschop

I believe people have a misconception about viscoelastic polymers (foam) as it relates to open-cell vs. closed cell. The open-cell variety will displace almost the same amount of airspace as closed-cell depending on cell structure, material, pour size, etc.

The open-cell catches and dissipates the backwaves a little more efficiently is the only difference. Too much of anything is a detriment to any system. Same concept applies here, don't suffocate your enclosures and transducers.

Again, Mr. Polk said to experiment.

Merry Christmas

Gardenstater

xschop wrote: »

I believe people have a misconception about viscoelastic polymers (foam) as it relates to open-cell vs. closed cell. The open-cell variety will displace almost the same amount of airspace as closed-cell depending on cell structure, material, pour size, etc.

The open-cell catches and dissipates the backwaves a little more efficiently is the only difference. Too much of anything is a detriment to any system. Same concept applies here, don't suffocate your enclosures and transducers.

Again, Mr. Polk said to experiment.

Merry Christmas

Merry Christmas!

So true. I actually tried very hard online to come up with NRC data for closed cell foam vs open cell foam. No dice. I guess since it isn't as effective for sound *absorption* nobody is doing the testing or at least I didn't find it. I found data for lots of typical architectural construction materials however. The testing in question is ASTM C 423 and for those interested here is a test report for some cork panels:

https://www.calibamboo.com/content/downloads/sound_absorption/cork_wall_tile_astm_423_laboratory_test_results.pdf

The info. I did find generally stated that closed cell was better for sound *proofing* vs open cell and better at vibration dampening.

Wool felt NRC data is a bit hard to find but I did find for 3mm, 5mm, 8mm, 10mm (no data!) at the fitzfelt site: 0.10, 0.20, 0.35, ??

I don't think the 3mm Armacell would beat out wool felt so NRC < 0.10 probably. This is better absorption than the steel baskets however lol (0.0 - 0.10). Here's some typical building materials:

http://www.nrcratings.com/nrc.html

@Toolfan66 Thanks for that story. It shows that less is more definitely applies and just because we can dream something up doesn't mean it will work out the way we envisioned. I have learned a lot from people here as well. I've been lucky so far with all the mods I've attempted partially because of them.

Gardenstater

I'm sneaking into everybody's house and doing this to your speakers. And if the toilet paper is the wrong way I'm fixing that too! 😁

Merry Christmas!





https://www.youtube.com/watch?v=5nwIYXqH3RQ

xschop

Lol. Santa's slippin', I still haven't gotten the 16uf Black Dragon caps that I asked for.

Gardenstater

I'm not saying this is what happened but if those things get dropped in the snow and the elves are drunk, they aren't easy to discern from reindeer droppings........

xschop

Hopefully he doesn't consider the uber-mods naughty. I may never know what potential the XS-0198's could have achieved...

Gardenstater

That's too cool.......but some people have to update their "uber's" in their signatures until they get up to speed lol

xschop

In the mean time I've now completed 2 sets of 6502's, I set of 6510s, and all four 6516's. I still have almost half the 99 cent foam sheet left.

gmcman

With regards to the open cell inside the metal baskets, would this be similar to dynamat on the outside of the basket?

Assuming the concept is to stop or reduce the metal basket from ringing or vibrating.

Unless the open cell foam breaks up the sound wave more than a flat piece of metal, in which case the foam could keep the wave from reflecting back into the cone.

Definitely an interesting idea.

Gardenstater

gmcman wrote: »

With regards to the open cell inside the metal baskets, would this be similar to dynamat on the outside of the basket?

Assuming the concept is to stop or reduce the metal basket from ringing or vibrating.

I used closed cell 1/8" (3mm) and put it on the spokes and the basket area between the spokes as well. Rob used 2mm open cell (we think it is open cell) and just put it on the spokes. When I came up with the idea after reading the Vandersteen patent (see post above^^), my main goal was reducing the reflections off the interior structures of the basket that could end up bouncing around and coming back at the back of the cone and getting transmitted through (some might get reflected multiple times though) as out of phase, time delayed distortions. I think a side benefit is that there is some amount of additional vibration dampening of the basket but no where what you get with the dynamat which is designed specifically for that. I think closed cell is more dense and does a better job of soundproofing although the PowerGrab adhesive that Rob used might offset the open cell being less of a soundproofing/dampening material. Sorry if that is long winded.

gmcman wrote: »

Unless the open cell foam breaks up the sound wave more than a flat piece of metal, in which case the foam could keep the wave from reflecting back into the cone.

Definitely an interesting idea.

The foam is being used primarily for that purpose, to absorb some of the backwave that would've been reflected off of the basket structure. Open cell probably is a tad more effective than closed cell for that, for the same thickness of material and coverage area.

motorstereo

Many years ago I tried using foam strips (not armacell) on the spokes of my 2.3s. I didn't notice much of a change if any at all. But I was disappointed a few months later when I opened up the 2.3s and saw that the strips had come loose. Some were in the bottom of the cab and some were in various states of coming loose. Perhaps the glue is better on the armacell but I'm taking a hard pass on ever trying that mod.

I did do strips of bh5 on my 1.2tls back walls last year and that is a worthwhile mod. The glue on the backside of that stuff is no joke. There's no moving those strips once they're pressed into place

Gardenstater

motorstereo did you put the foam on the *inside* of the spokes? What foam did you use? I should have mentioned that I cleaned the inside of my baskets with a cotton swab dipped in Everclear, followed by a dry swab, prior to applying the Armacell. The PSA on the Armacell is almost as sticky as the BH5.

As far as not noticing a change I can't really understand that, however I will say that even if I were deaf I would've noticed a change on my sPL meter because when I modded only one speaker I had 0.4dB less from that speaker measured with whitenoise, and I had to balance the other channel down by that amount.

motorstereo

Thankfully no I did not put the foam on the inside of the spokes. I cleaned them first using lacquer thinner and used foam weatherstripping quite similar to what I've had stuck on some of my door frames for decades. So my thinking was it should be fine for this application.
I'm highly doubtful I'd be able to hear a .4 db change perhaps not even 40 years ago. Kudos to you for having such acute hearing and hopefully the armacell has a much better grip and stays in place for your mod.

VR3

Fwiw, having Sean's 1.2tl here, even cleaning the cabinet walls, black hole 5 was coming off after a month. I ripped it back off and used power grab to reattach and even two months later was super secure

Gardenstater

VR3 good thing you caught that before they went down under! I was worried about that happening with my BH5 so, even though it was wood ( ) I wiped it down with a lint free towel soaked in Everclear 195. So far mine are still stuck good but thanks and I will have to keep my eye on that!