# Can I use this in place of Polyfil? for ported sub box



## GouRiki (Apr 9, 2010)

I have several large pieces of a memory foam mattress pad I cut up awhile ago when I was making something. 

I was wondering if this can be used for the same affect as Polyfill or fiberfill in a sub enclosure. If so, how well would it work compared to Polyfill and fiberfill? 

It is about 1.5" thick.


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## GlasSman (Nov 14, 2006)

No you can't use that stuff.

Get the polyfill or fiberglass insulation which will stay in place much better than polyfill without assistance.


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## minbari (Mar 3, 2011)

I would guess that it is too dense. if you just want to eliminate reflections and resonance in the enclosure, I am sure it would work, but as a poly fill, prolly not.

polyfill is cheap


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## GlasSman (Nov 14, 2006)

Walmart has polyfill for $2 to $3 per bag.


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## GouRiki (Apr 9, 2010)

I just came back from Walmart. Ive used the normal polyfill (it's like $4 for 454g and $9 for 1454g) for sealed boxes. I have a lb in my sealed box right now but I don't really want to use the loose stuff for a ported box. I guess I could make like a mesh "box" inside of the box to hold it along all of the sides right? I have this plastic mesh stuff that would work, I just don't know if it being plastic will affect anything.

Plastic mesh-










Would that work?


Also when I checked walmart, they had three different kinds of batting. I would prefer to use it because I think it'd be easier to just staple it along all of the sides inside the box.

First kind, looks just like the normal loose Polyfill just in sheet form










Second kind, looks exactly like the first except thicker










Third kind, looks thicker than the others but I think its a different material











I know the normal loose polyfill will be cheaper, I'd just like to probably go with the sheet form for ease.

Should I go with one of the battings or just loose polyfill?


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## GouRiki (Apr 9, 2010)

Here's a pic of my ~3 cu ft sealed box with 1lb of polyfill. I just don't really want it loose floating around in a ported box.


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## minbari (Mar 3, 2011)

the quilt batting works good because it is kind of like a sheet. just dont tear it all apart and staple it to the sides of the box.


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## trumpet (Nov 14, 2010)

When I researched this topic for my own use as well as an article I wrote I came to the conclusion that the loose polyfill would be best. The "sheets" were specifically advised as a poor solution because of the density. You want the fibers to vibrate, and it seems logical that they should be loose.


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## GouRiki (Apr 9, 2010)

In the manual where it shows the recommended sq ported box, it says "All sides lined with 1" fiberglass or fiberfill" and for the recommended sealed box it says "Stuffed with loosely packed fiberfill".

Is there a reason JBL wanted it lined along the walls? Even if it was the normal polyfill, if it's lined along the walls, it's basically pretty much be no different than a sheet of polyfill right?

minibari-

Which of those three would you recommend? They never gave a density recommendation so I'm not sure. I doubt it will make a huge difference, but I'd like to make it right the first time.

I forgot to mention this but this will be the second ported box I've made for the w15. The first one has a 6" aero port and when I first put it together, I completely neglected polyfill at first but then I stuffed in an amount through the port and spread it around inside of the box. I'd like the new box to be a little better constructed. I changed the dimensions to fit in my trunk better and designed it as a slot port so while I'm at it, I'd like to also take into account how I have the polyfill.

Thanks for the help so far guys.


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## minbari (Mar 3, 2011)

I would go with the first one you have pictured. the one that is the loosest. 

they prolly want it on the walls because you dont want it getting into the port itself.


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## GouRiki (Apr 9, 2010)

Ah! I just had an idea. 

The quilt batting is thin so I don't know how much I would need to loosely get to the 1 inch thickness. Would it be smart to buy the smallest roll of batting, I'm sure it'd be enough to cover one layer at least, and use that layer as the outer part like a barrier and in between that layer and the walls fill it with the cheaper, loosely packed polyfill to achieve the one inch thickness?


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## minbari (Mar 3, 2011)

could do that or just put multiple layers of the batting. end result should be about the same.


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## quickaudi07 (May 19, 2010)

you could always get some can air glue, and spray the sides of the box, than attach the poly fil to it,


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## TwoDrink (Aug 26, 2009)

You could also just "line all sides with 1-inch *fiberglass*" and be done with it.


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## TwoDrink (Aug 26, 2009)

I always use fiberglass for ported and polyfil for sealed. It has worked for me so far.


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## GouRiki (Apr 9, 2010)

quickaudi07 said:


> you could always get some can air glue, and spray the sides of the box, than attach the poly fil to it,


I've done that before and it just seemed too messy to me and it didn't seem to hold well. I just used the 3m 77 spray glue. A stickier glue would have been better...




TwoDrink said:


> You could also just "line all sides with 1-inch *fiberglass*" and be done with it.


What brand/etc. should I be looking for? I read the pink stuff can be itchy and people would mention, since it's ported, there's always the possibility of the particles coming out through the port. Also, what density should I look for?


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## TwoDrink (Aug 26, 2009)

I use Owens Corning (the pink stuff). Just wear gloves when handling it and don't work in the nude and you should be fine. buy the stuff that's closest to 1" thick (I forgot the R value). It stays together very well. You have to pull it apart to separate it. But I would not line the port with it, just the box.


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## GouRiki (Apr 9, 2010)

You have to pull it apart to separate it? You can't cut it?

Another options? I can't NOT be able to work in the nude. It's what makes this hobby fun.


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## TwoDrink (Aug 26, 2009)

Yes you can cut it. I mean that it is unlikely to fly apart on its own.


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## Richv72 (May 11, 2012)

Only problem i would see with fiberglass in a ported box is the little particles of fiberglass floating around the car everytime the bass hits.


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## Mlstrass (Apr 22, 2006)

When using spray glue you MUST spray both surfaces. 

My question is why are you putting polyfil in a ported box? I've built around 100 ported boxes and have never used it. Don't think it's really a necessity.


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## GouRiki (Apr 9, 2010)

Mlstrass said:


> When using spray glue you MUST spray both surfaces.
> 
> My question is why are you putting polyfil in a ported box? I've built around 100 ported boxes and have never used it. Don't think it's really a necessity.


From what I understand, basically it's purpose is to simulate a larger box than what you have before using it. If you can build the correct sized enclosure with the space available, I don't see why you would need it but when you can't build that big box, it will help. 

I've heard the difference between using it and not using it in sealed and ported boxes but whether it works or not is not the purpose of my thread. The purpose of this thread was to figure out a more efficient way of using polyfill than what I previously used and hopefully it will help others searching for the information. 

In the case of my sub, I would need to build a slightly over 8 cu ft enclosure tuned to 21Hz to get it flat (not taking into account cabin gain) down to 25hz with a 2db drop at 20hz. I don't know about you, but I don't want an 8 cu ft + box in my car, nor would it be possible. I'm pretty sure I can't fit a 6 cu ft either but I can fit a 3.87 cu ft enclosure tuned to 27Hz. 

In the case where the port volume stays constant, the larger the internal volume of the box, the tuning frequency becomes lower. By using something like polyfill, which when added to the inside of a sub enclosure simulates a larger volume, you can "increase" the internal volume of the enclosure without making the box physically larger, thus lowering the tuning frequency. 


Please correct me if anything above is wrong. I've had a combined 10 hrs of sleep in the past 3 days and right now been up for the past 20hrs


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## stochastic (Jan 24, 2012)

The general rule for stuffing boxes is: Sealed boxes get stuffed with polyfil or other similar product that slows down air speed (such as acoustic wool) thus making sound waves act like they're in a larger box. Ported get lined with an acoustic absorbent material (check here: http://www.bobgolds.com/AbsorptionCoefficients.htm for a list of acoustically absorbent products) to prevent standing waves and ringing at the helmholtz tuning frequency. Transmission lines and quarter wave boxes can utilize both methods in moderation, but the polyfil is the most commonly used.

The memory foam in the original post might be the best 'hack' (not bad sense of the word) as from what I understand memory foam is open celled foam - i.e. foam that absorbs sound. But you'll still want a bigger box.

If you can't build an appropriately tuned ported box, then change box style or change your speakers. Approximating enclosure volumes by building a box half the required size then stuffing it with an approximately even ammount of fill will only result in bad choked bass. To really get it done well you'd need to factor in how much the fill material will slow down the speed of sound depending on how much you've stuffed in the box, then factor in the change of speed through the tuning port, then calculate the helmholtz tuning frequency of the whole system. One more thing to factor in is the change of sound that will result from a stuffed/choked small box rather than a properly designed large box 

Have you considered using an aperiodicly vented enclosure design instead?


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## GouRiki (Apr 9, 2010)

stochastic said:


> Have you considered using an aperiodicly vented enclosure design instead?


I've never heard of an aperiodic ported enclosure, only sealed aperiodic. 

I've already planned out the enclosure just need to piece it together. 3.9 cu feet tuned to 26.5, slot port 14"T x 4" W x 47.5" L. It's a JBL W15GTi MKII.


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## stochastic (Jan 24, 2012)

An aperiodic enclosure is by definition a vented enclosure. The vent is aperiodically dampened - sometimes with a flow restricting substance, sometimes with a flow restricting geometry.

A sealed aperiodic enclosure is not sealed, it's vented.

If you do decide to stuff your box with polyfil don't expect the tuning of it to drop much (maybe one or two Hz).


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## Aaron'z 2.5RS/WRX (Oct 24, 2007)

GouRiki said:


> I've never heard of an aperiodic ported enclosure, only sealed aperiodic.
> 
> .


 
There is no such thing as either.. 


To add to the abovefrom Stochastic

Aperoidic is aperoidic.. 

It's a different alignment than the rest.. 

It can use a sealed box, or it can be mounted ot the cone of the sub, using the cone as the box, doesn't matter... front and back wave have to be seperated just like any other alignment... 

Aperoidic fell off, like Isobaric, when large(and small) small box woofers started coming into thier own... 

AP, like IB, was used to control a lot of larger subs, that you didn't want to build a HUGE box for... prior to there being decent IB subs for the app..


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