Confusion about subwoofer stuffing

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I'm finishing off a 210L sealed sub. All the reading I've done suggests 1lb/cubic foot of polyfill, and it's invariably described as 'lightly stuffing'.

Problem is when I stuff lightly, without deliberately compressing the polyfill, I only get about 50% of the intended polyfill into the box. To get it all in requires a fair bit of compression, and would be what I'd describe as 'lightly stuffing'.

Am I doing something wrong here? The Nousaine article

Ultimate Polyfill Subwoofer Enclosure Resource [audiojunkies]

seems pretty unequivocal about how much needs to be used to achieve max effective volume, should I just go by weight and stuff in all my 3kg's?

Help much appreciated.


Stuffing is usually done to taste. Following guidance form the manufacturer might get you somewhere close, but you'll have a different listening environment to the one they tested it in. Start with none. See how it sounds. Add some (enough to fill the cabinet without compression). See how that sounds. Add even more (squashing it up quite a bit this time). See how that sounds. You'll find a happy medium somewhere along the line. You might find different aspects of the sound you prefer for different amounts of stuffing, so try half way. It's a very personalised activity, so don't take what the manufacturer says to heart.


You cannot trust anything without the correct assumptions.
e.g. polyfill is polyester, there are quite a few types, e.g.
one type is hollowfill *, the fibres are tubes, not solid, and
its maximum stuffing density is a lot lower than just "fibre",
e.g. another type the fibres are ridged, not smooth, I think
its called Acoustistuff, and this will give again a different
maximum density. Another type used for stuffing is BAF
(bonded acetate fibre). Unless you have exactly the
same type (e.g. fibre size may vary) IMO you cannot
trust any notional density.

Use a half change regimen tpo home in on ideal, i.e.try 50%
and a 100%, then better of the two with 75%, then either
62.5% or 87.5%, you should be pretty near at this point.

rgds, sreten.

* Used e.g. for very lightweight sleeping bags.
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Vance Dickason covers this in detail in his Speaker Cookbook. As I recall, fiberglass was actually the most effective (wear gloves!) and all the materials had to be stuffed pretty densely for maximum effect.

There are two effects:
1) Absorption of upper frequencies from the rear of the cone so they don't radiate through the enclosure walls, port, or back through the cone.
2) Changing the thermodynamic properties of the enclosed air mass from adiabatic to isothermal, making the enclosure behave as though it were slightly larger.

Pillow stuffing is easily accessible, but NOT the most effective for either #1 or #2. And don't block the rear of the driver (or port, if any). Yes, ya gotta get into every tiny nook and cranny.
Thanks guys.

I take it that it doesnt matter how close to the driver it comes as long as it doesnt touch the cone? I was planning to superglue stips of nylon flyscreen across the back of the driver frame to stop any poly getting in there, reckon that ok?
Well, don't block any kind of magnet structure vents. And you don't want to impede direct airflow. I don't have a hard and fast rule, but I'd keep a few inches away. And several diameters away from a port.

I don't know that the poly should get so loose-it should all stick together, you don't really want to be stuffing tiny pieces in there. Flyscreen could change the mechanical Q a bit, depending how open it is.
enclosure lining

I have made many different cabs over the years, mostly true subs of the 6th order BP variety (Coupled cavity) and reflex designs. It is a misconception that just "subs" needed some lining it is far more important for high powered mid range cabs especially dedicated mid range horns, which can literally be filled with lining.

First thing to consider is wood type. MDF has better resonant qualityies than the same thickness birch ply but is much heavier. Ive found MDF needs less lining due to its denser nature. Ply has a more lively sound and can really benefit from lining.

100mm loft insulation seems best and should be applied to 2 or 3 adjacent sides. This is adequate but its also down to trial and error. 100mm seems right and i always use a large staple gun to hold in place every 150mm or so (bit like a buttoned couch).

Dont be tempted to use the stuff contained in plastic as this will rattle and fart like hell.! If building large cabs with shelf ports make sure you dont alter the port dynamics by constricting the throat. If using the cavity slab type stuff remember that it does effect internal volume slightly, but can be good for mid range cone isolation in full range cabs.

One of my best sounding cabs has a couple of old wool jumpers inside!!!

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