polyfill

[bass monkey 10+ year member]

Can putting polyfill in the door panels be used as a sound deadoner? or should i be using a comercialized one like brown bread, or somethin like it?

Click to read more...

 

[more_spl 10+ year member]

i dont think polyfil is a sound deadener. if u wanna keep sound in, use dynamat or brown bread stuff.. polyfil slows the sound waves down to make the box seem "bigger". dont use it in the doors

 

[Mark_ab 5,000+ posts]

In a word, No. Polyfill is meant to break up standing waves so that distortion from backpressure is not present. It does not stop the metal surrounding the speaker (and behind) from resonating. Stick with a sound deadening material.

 

[jlaine 10+ year member]

Originally posted by Mark_ab In a word, No. Polyfill is meant to break up standing waves so that distortion from backpressure is not present. It does not stop the metal surrounding the speaker (and behind) from resonating. Stick with a sound deadening material.

Standing waves inside a subwoofer enclosure is impossible... it primarily is there to slow down compression waves to fool the woofer into thinking it is in a larger enclosure.

Standing waves in a midrange box are completely possible, but the wavelengths of bass waves are so huge that nodes are really impossible.

Elemental designs Edead is on sale right now, check out http://www.edesignaudio.com

 

[MikeofTulsa Moderator]

check out http://www.sounddeadeningmaterial.com good place to get some cheap stuff that works pretty good...good luck

 

[bass monkey 10+ year member]

thanx, but i am still a bit confused...so polyfill shouldnt be used to absorb sound. why do people talk about it so much then? people use polyfill to isulate the inside of their box then? maybe i will try that. right now what i have is the insulation from inside walls in houses. should i replace that with polyfill, or is that basically the same? my box is sealed and about 1.1 square feet that holds a single 10". is that also how peole tune their box? how do yu do that if that isnt how?

 

[Mark_ab 5,000+ posts]

Originally posted by jlaine  

Standing waves inside a subwoofer enclosure is impossible... it primarily is there to slow down compression waves to fool the woofer into thinking it is in a larger enclosure.

 

Standing waves in a midrange box are completely possible, but the wavelengths of bass waves are so huge that nodes are really impossible.

 

Elemental designs Edead is on sale right now, check out http://www.edesignaudio.com

"Standing waves are often a result of reflections of some sort and happen when a sound wave "lingers" in the listening area by being bounced off of reflective surfaces. They can cause frequency cancellations, freq response abnormalities, harshness, distortions, and deceptive location cues in the "Up-front-bass" and imaging department just to name a few. The same principles apply to standing waves that apply to reflections in general. BUT! Standing waves mostly occur INSIDE enclosures,

whereas reflections often occur OUTSIDE enclosures. As with "inside-enclosure" reflections, the rear wave of the speaker tries to disperse into an open area. But, since the air space in the enclosure is finite, the sound wave encounters abnormal airspace resistance AND/OR reflects off the walls. This can cause the sound wave to slow down or simply bounce around in the enclosure until it loses its energy."

"I know there has been some debate lately on the topic "to polyfill or not to polyfill", but I believe strongly that ALL sealed enclosures can realize the benefits of using loosely stuffed polyfill throughout the interior. Polyfill serves to dissipate the rear sound waves of the speaker cones and hinders the chance of reflections and standing waves re-striking the cone. This results in greater detail resolution and the elusive "clean" sub bass, absent of artifacts and "sloppy sound". Polyfill is also known to make subs seem like they are in a bigger enclosure, but I believe the rear wave dissipation character of the stuff is responsible for the phenomenon. I'd like to see someone research the effects of polyfill inside sub enclosures to see if I am right. I believe I am. "

(http://www.elitecaraudio.com/article.php?sid=22 by Audionutz)

That's where I got it from, although I probably wrote down something completely different than he was saying. Ah well.

 

[jlaine 10+ year member]

Originally posted by Mark_ab  

That's where I got it from, although I probably wrote down something completely different than he was saying. Ah well.

No, you copied it correctly, just that his logic is flawed. You can't exactly disperse and intermix a wave that is 30 feet long inside a 1 foot deep box..

The research has been done, for the most part he has been proven completely wrong as far as subwoofers are concerned. Midrange? Sure, but subwoofers, he cannot gain any ground in terms of standing waves.

Extracted from Richard Clark and some of his thoughts:

"Stuffing a box can make it look a little larger. It changes the box interior from a condition called adiabatic to isothermal. This is because the energy that is normally stored in the air spring in the box is converted into heat and lost from the system. Since the air pushes less on the speaker, the speaker "thinks" the box must be larger. The increase in size is really nominal and really doesn't make as much difference as everyone gives it credit for. The actual material used for stuffing doesn't make much difference either. Fiberglass, lambs wool, fiberfill, an old blanket, will all make about the same amout of difference.

As for standing waves the facts here will come as a surprise. The practice of stuffing boxes really came as a result of using woofers into the midrange (400hz to 2khz) in two and three-way home systems. In these systems standing waves were a real problem and serious colorations were the result. In car audio where we never use woofers above 100 hz it is not a problem. A standing wave cannot form inside a box below 100 hz if its longest dimension is less than a couple of feet. Of course this applies even more at 50 or 20 Hz! Actually installers stuff boxes because they have been taught to do so. They rarely understand the physics behind the process and rarely question it because it seems logical. The fact is that an awful lot of boxes get stuffed for no good reason."

I agree with him on this matter, and I do stuff midrange boxes, but I do not stuff subwoofer enclosures, I build them to the right size. I think it will aid you some in terms of box size for a woofer, but will not remedy anything involving a standing wave, as the wave doesn't have the space to interact with anything.

And we do have some factual, documented figures about adding polyfill, done by Tom Nousaine, which can be read here: http://integra.cyberglobe.net/caraudio/resources/fiberfill/

 

[more_spl 10+ year member]

if you put polyfill in the door panels, it would think the panels are bigger than they actually are, just like a box... polyfil WILL NOT, CANNOT NOT, NEVER WILLN'T act as a sound deadener in your door panels.

 

[Mark_ab 5,000+ posts]

Okay, thanks for clearing that up jlaine. Learn something new every day. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif