L1ability

My box is built to be 20x14.5x14 (lxwxh) wich equals 1.75 cubic feet,..... for my jbl GTO 1.75 is dead on what specs reccomend!

but now, stupid me works in the port area and it turns out to be 1.57 cubic feet!

i totally forgot about this in my design, so i hop on the web and see that polyfill tricks the speaker into thinking its a bigger box, i bought a 1mx1m sheet of double-ply polyfill batten sheet, and i have just glued and stapled it into my box making sure the webbed batten top will hold the fluff down underneath and not come out the port.

after getting back from my local audio place they said polyfill dosent belong in a ported box, and to re-build another box, did 80$ worth of a box just go down the drain? :0

help? lol

t money

iTrader: (5)

that's not a huge difference in sie, see how it sounds first. But the shop is right, poly fill is used in sealed boxes to trick the subwoofer into thinking its in a bigger box than it actually is

Denonite

iTrader: (1)

Polyfill can be used, and does the same thing in ported boxes as well..been using it for 20+ years and have actually done some in depth experiments to prove to myself that it works..but as Tmoney mentioned, your box isn't that much smaller than spec and should still sound fine...you can add about .75 pounds of polyfill and it'll give you approx 10-15% more virtual volume (so your 1.57 cube with poly will make the woofer think it's in a 1.72-1.80 cube box)...that is, if you fell like the box is too small or you just want to experiment. It's cheap and easy to use to adjust a box's tuning as well (sealed and ported).

Destarah

Also, you can regain some space if you are able to move some of the port out of the enclosure ... just a thought

L1ability

i see what you guys are saying, well with that polyfill batten i just glued it down using some super77 and stapled all the edges tight, especially around the port exit, and i gave it a final dusting of super77 to seal the edges of the polyfill sheets.

i lined all the sides inside with about 1" of polyfill, not sure about the weight, but when folded up it was comparable to size with a 1lbs bag of the stuff.

this may sound (and look) stupid, but look at this crudley drawn (and possibly incorrect) idea of what i was thinking when i initially read up on boxxes.... red waves are soundwaves(?)



so if thats how it actually works, using the larger mitre joint in the corner to "fire" the sound waves off of it into the mouth of the port, and hitting the smaller mitre to get it out of the box, would doing this screw up that whole operation (if thats how it actually works)...



would dampening all the internal wall exept the port walls basically make my mitre corner usless? i read to do the mitre thing off kickers website in the box building section...

any input is greatly appreciated

danyman

iTrader: (1)

wouldnt just the fluffy pillow polyfill work better?? just put a screen so it doesnt blow out the port.. thats what i did with my box to get a lower tune.

ohh btw if ur box is 1.57cubes tuned to a certain desired hz adding polyfill will lower the tuning

Denonite

iTrader: (1)

I've always used the pillow stuffing and up to now, i've never had any come out the port..i don't use any glue, mesh or anything else..but you may have to if you use a relatively small amount and it's fairly loose. As danyman mentioned...the tuned frequency will be lowered with the addition of the polyfill..so you may have to adjust your port slightly...listen to it first as tuning is rarely exact and usually not a big factor within +/- 3 hz or so.

Dukk

Conversely, if he tuned the vent using 1.75cuft as the net volume, then the vent is currently too short and tuned too high. Adding some fill may just get it closer to his design.

Denonite

iTrader: (1)

^^yep..., post your box and port specs (dimensions) and we'll be able to advise you better, so you can get that sub as close to what you intended.

zoomer

iTrader: (3)

Just put polyfil in the box. dont worry about the port. 1.57 is 10pct under 1.75 The fill will up that a bit. The rest, well... did you compensate for altitude? barometric pressure? humidity in the air? Production variation in T/S parameters? you get my point.
Listen to it and enjoy!