Is there a way to measure polyfill accurately?

VR3

I was wanting to use Polyfill (just for giggles) instead of the fiber glass inside my speakers currently - and I was wondering what was the best and most effective way to go about measureing it...

Thanks...

Jstas

Double posting it tonight, huh?


Anyhoo, grab a rubbermaid bin or something and weight it on a scale. Write down that weight. Now add the amount of polyfil you want to use. Write down that weight. Subtract the weight of the bin from the total weight of bin + polyfil. That's how much polyfil you have.

VR3

Dangit! My connection is screwy lately... so slow and booting me like crazy!

Thanks - would a regular scale work fine (kind you weigh yourself) - I'm figuring this is under 1 pound...

Thanks... sorry for the double post

audiobliss

Yeah...just reach in grab a handful...that should work fine.

This post inspired by Sid's equally irrelevant posts in my 'Physics Question' thread.

:rolleyes:

Jstas

Dunno. Most bathroom scales aren't that accurate I would think. You could try it. I can't promise results though.

Don't they sell polyfil in bags that are listed in volume but have weight listed also? Like 2 liters of polyfil (38 grams) or some silly stuff like that?

BTW, easy place to find conversion tools and calculators: http://www.math.com

Jstas

Oh yeah. Don't go and get raped by the audio stores selling polyfil. It's the same stuff as what you can get in the arts/crafts and fabric stores for 1/5th what an audio/video store will sell it for.

All polyfil is is spun polyester. Sometimes nylon but usually polyester.

pitdogg2

Reported Aniced1984

mhardy6647

Personally (and FWIW, knowing no one's looking for my 2 cents!) I think stuffing loudspeakers is like seasoning in cooking.
Stuff to taste (i.e., stuff, listen, stuff - or de-stuff, listen again, repeat as needed).

pitdogg2

I might tend to agree Doc if I was more smarter. I have noticed that some speakers are stuffed to the gills, while others are just a smidgen or two. My SDA1 signatures are stuffed. The roll is very tight and leaves a impression from the back of the speaker magnets. Now since I am not the first owner who's to say that someone along the line of owners didn't put more in ? It is one long sheet rolled up and sits tightly in the chambers. On the other hand I have seen SDA2.3TL's that have a small 1.5" dacron sheet rolled up that barely will stay up behind the midwoofers. If you owned a set like that would you put more in to the point like my own speakers, stuffed in tightly to impress upon the magnets?

Jstas

It kinda doesn't work that way. Most people don't really understand how/why it works correctly but I don't really want to get into explaining it right now.

EndersShadow

Jstas wrote: »

Oh yeah. Don't go and get raped by the audio stores selling polyfil. It's the same stuff as what you can get in the arts/crafts and fabric stores for 1/5th what an audio/video store will sell it for.

All polyfil is is spun polyester. Sometimes nylon but usually polyester.

Buy cheap walmart 5$ pillows and tear em up and use that.... even cheaper hehehe.....

pitdogg2

Jstas wrote: »

It kinda doesn't work that way. Most people don't really understand how/why it works correctly but I don't really want to get into explaining it right now.

well stop back when you have time inquiring minds would like to have you spill knowledge. Yes my good friend owns a upholstery business I get mine from him it is EVEN cheaper than the craft stores. who in my area charge 5.00 a foot and it is not as thick as the 1.5" that Polk used. All the craft stores in my area only stock 1/2" dacron.

Moose68Bash

mhardy6647 wrote: »

Personally (and FWIW, knowing no one's looking for my 2 cents!) I think stuffing loudspeakers is like seasoning in cooking.
Stuff to taste (i.e., stuff, listen, stuff - or de-stuff, listen again, repeat as needed).

I agree with @mhardy6647.

However, when I used Acousta-Stuff in my SDA SRS 1.2tl speakers, I purchased a 5# bag from Parts Express.

In the product information about Acousta-Stuf, the following advice is given about the amount to use:

"Most sealed and vented enclosures require 1/2 lb. of damping material per cubic foot of enclosure. For best results it is recommended to loosely fill the material throughout the enclosure."

Cf.: https://www.parts-express.com/acousta-stuf-polyfill-speaker-cabinet-damping-material-5-lb-bag--260-330

Of course, in "stuffing" speakers with a passive radiator, you don't want to put any fill behind the radiator.

pitdogg2

I would think the loose stuff would be even more susceptible to falling down behind the passive.

mhardy6647

Even though, in principle, stuffing an enclosure (which, in essence, makes the enclosure feel bigger to a speaker driver by dissipating the back wave energy as heat) is straightforward, in practice it's largely art and - sort of like wires and other cults of the arcane in this hobby - there are adherents to all sorts of idiosyncratic belief systems related to appropriate materials, volumes, and placement.

For example, transmission lines (and some other, similar enclosure morphologies) are said by some folks to absolutely require long-fiber wool for best results.

Mind you, I'm not (for a change!) making a judgment; just seemed like something worth adding to this thread

ken brydson

Youz guys do realize this is a 12 year old thread dredged up with a spam post, right?

mhardy6647

well -- now -- yeah.

but, you've gotta admit, it's an interesting topic.

pitdogg2

ken brydson wrote: »

Youz guys do realize this is a 12 year old thread dredged up with a spam post, right?

Yea whatcha point

I just figured why it's here why not

ptrooper

His comment is gone,,,your reporting must have scared him off lol

pitdogg2 wrote: »

Reported Aniced1984

pitdogg2

Mods remove them.

pkquat

Jstas wrote: »

It kinda doesn't work that way. Most people don't really understand how/why it works correctly but I don't really want to get into explaining it right now.

pitdogg2 wrote: »

well stop back when you have time inquiring minds would like to have you spill knowledge.

I'm curious too. My experience has been the rolls did a little bit of dampening as well for MW's and tweeters. Although rolls / sheets seamed more tightly packed their rolled form performed similar to the fluffy stuff for cabinet volume and effect on bass.

A 2cents find as well. Doubling the polyfill in 5jr+'s, 1 roll behind the tweeter and 1 behind the MW, helped the bass and IMO gave a fuller sound.

Jstas

OK, so first, a couple things about polyfill.

- It's sold by weight so if you buy a 10 pound box/bag of it, it's 10 pounds of spun polyester.
- There is another weight rating for it and it has to do with how thick the strands are, like speaker wire has a gauge. Typically, you want a lighter weight because you can get a higher density which is important.
- You only really see the higher weights in batting because it's used as insulation, stuffing for stuff like padded quilts and seat cushions. The loose stuff in bags is typically for stuffing toys, pillows, etc.
- You can buy it in loose bundles or rolled batting. Either way, it will do the same thing in a speaker enclosure.

Stuffing a speaker box, should you?

Quick answer: you can but you probably shouldn't. It's honestly a band-aid in most cases.

Long answer:

Look, I don't care what your "ears tell you", stuffing a speaker that didn't have polyfill in it prior to your bright idea is going to hurt performance. Now, with that out of the way, here's why.

First, how polyfill works.

Polyester is a very smooth, reflective surface. So is the alternate, spun nylon. Nylon is also more rigid and you don't see it as much in speakers because it's more apt to damage motor structures. But because of that smoothness, it's very reflective. Reflective is also deflective. It does two things, a physical difference and an audible difference.

The physical is the most important. A speaker enclosure is essentially an air spring. It creates a vacuum when the driver moves out of the basket and it creates a high pressure pocket when the driver moves into the basket. The vacuum keeps the driver from over-excursion damage, the pressure pocket keeps the driver from being able to bottom out. When you stuff a speaker with polyfill, it essentially slows down the air movement in the enclosure because it is diffuse. The multiple fibers in random arrangement will make the air bounce off them and in all directions. This slows the air movement down and creates turbulence. So every time the driver moves in or out, the air movement is slowed by the polyfill. The effect this creates is that it makes the enclosure behave like a larger enclosure. We'll get to what that does in a minute. It makes it behave like a large enclosure by slowing the air movement. Slow the air, you slow the backwave as well. It takes longer to reach the walls of the enclosure. When it does that, it can actually reduce how fast the pressure or vacuum is built up in the enclosure. That can affect how far your driver extends and whether it bottoms out or not. Not a big deal, right? Well, no, it is.

If your VC is designed to stay in a certain spot in the motor structure, it can extend past that sweet spot from the over excursion in either direction. At high volume levels, there is a possibility that you can send the VC out, past the ends of the pole piece in the motor structure. That can cause the driver to actually overheat because if the VC goes past the magnetic field then you effectively reduce the VC's size for the magnet to act on so you can momentarily decrease the resistance while increasing the load on the part of the VC that is still in the magnetic field. You're doing it at the driver's peak as well. Because of that, the driver is not operating at it's highest control potential and you are relying more on the surround and spider to control the movement. That taxes those parts more than normal and can wear them out sooner. If they wear out and lose their control capability, you can actually blow the driver because the VC being extended past the pole piece can either impact the pole piece and seize or it can tear the cone/spider/tinsel leads.

Also, when you stuff a speaker, you move and vibrate the fibers of the polyfill with the driver movement. When that happens, they can eventually fatigue and if the fill is too close to the driver, the motor structure venting can clog up and cause overheating. It can also cause physical failure by making small holes in the control structures that can be stretched out and expanded under even just normal use. Yes, I am not making this up. But, over-stuffing can also slow air movement enough that even a venting system on the driver that isn't clogged isn't moving enough heat out of the motor structure to be efficient. It's more pronounced in, say, a subwoofer where the forces are much larger than what you would find in a full-range speaker. However, overdrive your full range speakers and stuffing a speaker can become an issue.

Now, the sound stuff. We already know what polyfill does physically to the enclosure. So that artificial expansion of the enclosure space will do a few things. We'll go over the positive later. The negative is that it can dampen response and cause the resonance of the enclosure to change. The problem with that is it can cause things to rattle that previously did not rattle. It can also cause the driver to hit it's resonance points and kill efficiency which can cause audible distortion. That's typically found in a sealed enclosure.

In ported enclosures, it can reduce port flow velocity which can hamper low-end frequency response by changing the port tuning. Typically, you want the port to be tuned to compliment the driver at it's peak efficiency point. That requires length and width calculations. It can also cause port noise or even cause the driver to suck the air column in the port back into the port because the air spring behind the driver is weaker. That makes noises like blowing across a bottle neck. I've actually heard these noises.

Jstas

So why SHOULD you stuff a speaker?

Well, compromise.

As we said the fill makes an enclosure behave like it's larger than it is. When you have a small package/footprint restriction, like in a car trunk, stuffing a sub box can vastly improve response. It's not nearly as good as if you built your enclosure correctly. Sometimes that's not an option, though so you band-aid with a wad of fill.

One of the reasons you will see it in tower speakers is because it can be used to slow air around stuff like bracing. Air will move like water and around a sharp edge/corner it will create eddys that create high pressure pockets. That can make the enclosure seem smaller than it is. So if you stick some fill or batting around the bracing spots, it will tame the effect by not allowing the high pressure pockets to develop. But speaker engineers know this and will compensate for it in design of not just the enclosures but also with crossovers.

Another reason it is used is to tame resonances. We've all see the oddballs speakers from like Bang and Olufsen or the cheapy plastic enclosures for computer speakers or HTiBs or Best Buy specials with the plastic or other kind of composite or metallic enclosures. They tend to ring like bells at lower frequencies. So stuffing the enclosure with some polyfill tames that. But, again, it's a big compromise. Then again, those teeny speakers or the crazy designs are compromises as well.

Yet another reason is poor cabinet materials. Using something like particle board can be troublesome because it can start to separate under constant abuse of a driver. So lining the enclosure with batting can knock that down a bunch.

One more thing that you can have happen is standing waves. Sound travels down a surface which is why you see odd designs of mounting baffles. That's designed to control stuff like off-axis response, reflections and even port noise. It can happen on the inside of an enclosure as well. That's fine, usually, because it doesn't really impact stuff since lots of companies make enclosures with very few hard corners inside anymore. That's because gradual corners let the sound waves disperse as they cancel each other out. But, when you have a square enclosure, like in a subwoofer box, you can get those sound waves traveling down the interior and then they hit an abrupt wall which also has a wave on it. The stronger those waves, the bigger the air pocket they can create. That creates an eddy in that corner which, again, can cause the enclosure to seem smaller. But it can also reflect air and sound back towards the driver which under high-power/extreme situations can cause distortion. Lining the inside with a bit of polyfill can eliminate that.

One last thing is that in subwoofers with high power and an enclosure that has a reasonable WAF rating, the driver can perform too well and overpower the enclosure. Especially in ported enclosures. If the driver is moving enough air, it can create port flow problems. Not just the low-frequency hum of port noise but also with port velocity. Air can only move so fast in a confined space, like a port. The port also slows the air down. So if your port is long enough, the air entering the port from the inside of the enclosure can be moving significantly faster than the air at the other end of the port. What happens then is that the faster moving air runs into the slower air and it's like Black Friday Walmart crowd. The air cavitates and then the flow doesn't work at all and you get this port farting noise. Doing things like Polk's Power Port to smooth all that flow out can help a bunch because it helps maintain velocity and flow at the port mouth by smoothing the transition from high pressure port flow to atmosphere. But in lieu of something like that, polyfill can be used to slow the air in the enclosure enough that you can maintain the proper volume of air to be moved in the port but drop the velocity enough so that you aren't exceeding the dynamic limitations of the column of air in the port.

So there are benefits and drawbacks. Stuffing can seem to improve bass response but more often than not, all it did was change the tuning frequency and drop efficiency of the speaker system (i.e.: drivers, enclosures and crossovers). It can be damaging if not done correctly too. So you want to pay attention to what you are doing.

Polyfil can degrade over time too. It gets dirty or filled with dust and even mold/mildew. That can weigh it down and it can change how it behaves in the enclosure. So sometimes, when you over stuff, you compress the old junk with the new stuff and it can seem like there was an improvement. Well, there was but that's because the original performance was so degraded that it restored most of what was missing. What should be done is the old stuff removed completely and replaced with new stuff.

As far as stuffing with a passive radiator, I honestly wouldn't unless you are willing to fiddle with the weighting of the PR. The weighting is like port tuning and if you change the airflow in the enclosure with stuffing, you can affect how the PR moves because the stuffing changes the air flow and pressure levels acting on the PR. Some are stuffed from the factory and that's designed into it. So if you feel that over-stuffing improved performance, it might mean that you need to replace the stuffing. Adding to it might mostly solve the problem but can cause others as well.

So feel free to experiment. They are your speakers. Just be aware that there's a bunch going on here to be considerate of.

Also, stuffing has been going on for decades. Before polyfill was available, manufacturers used fiberglass insulation.

Viking64

txcoastal1

^^^ Let me assume that you're one of those pet owners that resembles their animals

Viking64

Close.

pitdogg2

Great stuff John. Some I did know but all in all more knowledge is never a bad thing.

Thanks

Viking64

pitdogg2 wrote: »

Great stuff
Thanks

Great STUFF???

machone

How can you type that much!!!!

Jstas

machone wrote: »

How can you type that much!!!!

This is completely uncalled for and why I don't post much anymore. I go through all this effort to help some people out because I can. Then I get mocked and dumped on because I took some time out of a lunch break to provide an answer with complete thoughts formed with proper grammar, spelling and punctuation. All because it's beyond your comprehension that someone can form a complete answer and explain complex concepts with a keyboard.

pitdogg2

machone wrote: »

How can you type that much!!!!

John is an IT pro, putting simple words together is a cake walk. In his day in day out job he strings together lines and lines of gibberish that we all depend on these days on planet earth.