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Emile

Speaker Cabinet FILL - polyfill, fiberglass, etc ...

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Trying to "transplant" a 12" woofer, 14x8" horn (w/ 2" diaphragm) and crossover from a (oops; blasphemy :) ) Yamaha stage monitor into a WAF friendly box.  Planning on a sealed box to keep the size to a minimum - and not concerned about "low bass" since it will be a center speaker :D  Calculated the required volume from the T/S parameters and it's about 2.5 cuft. (Actually does not make sense since the original PORTED monitor only has a 2.0 cuft volume :( ) But; seems "stuffing" is required, especially since I''d like to make the box smaller :) 

 

Lots of reviews on polyfill, fiberglass, denim insulation and others.  Of course there is NO consensus, except that fiberglass seems to be "one of the best" but of course a pain in the azz - OK; hands/arms. And ... polyfill is overrated :) 

 

Any suggestions or comments?

 

Much appreciated.

 

Cheers, Emile

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Per pound fiberglass is the most cost effective if you need a lot of it. However for a small box polyfill from cheap pillows from IKEA, a DIY store or what is nearby is cheaper as you can get a smaller amount than fiberglass. I newer use fiberglass ( and I have spare  insulation in the attic for "free") as polyfill and the like is so much nicer to handle.

 

Avoid covering the crossover with insulation, even if the losses is only a watt or two if well insultated the components can get really hot. My guess is that the horn is padded down with resistors and if they get really hot they can overheat, they can also heat  up the capacitors. For electrolytic caps you can estimate that for every 10 degrees C (roughly 22 F) increase in temperature the lifespan of the cap is halved.

 

There is recycled denim and biodynamic hemp fiber and what not, but dont overdo it.

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What JohnA said or:

- quilt batting at Walmart, Hobby Lobby, or MIchaels

- cut up a cheap foam bed topper from Walmart to line the insides

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Actually there is a consensus, at least over in the DIY speakers and subs world.  For sealed use one pound of Polyfil for each cuft of enclosure.  A 2 cuft box would use 2 pounds of polyfil.  You don't need the expensive Accousti-fil type from PE, a couple of pillows from Walmart or a box of Polyfil will do the job.

 

https://www.walmart.com/ip/Fairfield-10-Pound-Poly-Fil-Premium-Polyester-Fiber-White/20713592?athcpid=20713592&athpgid=athenaItemPage&athcgid=null&athznid=PWVUB&athieid=v0&athstid=CS002&athguid=466001f5-6478cbd4-49b7070152e90bcc&athena=true

 

For ported use open cell foam, I like the egg shell type and glue it to sides.  My Klipsch ported CF-4's used open cell foam sheets 1.5 inches thick and they are folded and loose (not glued) inside the box. I actually use some polyfil in the CF-4's as well, but just a little only in the bottom near to but not blocking the ports.

 

There are a lot of material choices for ported and the denim insulation (from Home Depot, not from JC Pennys ) seems to be the favorite these days. 

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I wonder if there are not two different goals.

 

1)  To reduce / absorb sound bouncing around inside the box, probably above the desired range of the woofer. Acoustic absorption.

 

2)  To increase the effective volume of the box by reducing adiabatic heating.  Absorption of heat.

 

It could be that less material or even different material is needed for 1) than for 2).

 

There is an interesting article showing an effective 40% increase in box volume with fiberglass.  I was surprised. 

 

http://www.pitt.edu/~szekeres/resonant.txt

 

WMcD

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I lined the back of my KG 5.5's with a strip of pink fiberglass and it made a noticeable improvement in the bass. The stuff is horrible to work with though.

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4 hours ago, WMcD said:

interesting article showing an effective 40% increase in box volume with fiberglass

WOW ... my box is getting smaller and smaller :D 

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16 hours ago, Emile said:

WOW ... my box is getting smaller and smaller :D 

You have to be careful.  An air load doesn't have the same effect as a poly load.  Poly load seems to provide extension and smoothness vs punch of air volume.  In my experience anyway.

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OK; thinking of building a box same size as Heresy's.  Because ... :D ... just picked up a set of Heresy I's.  ( @wvu80; for your records $400, condition almost 8/10, raw birch, one blown tweeter diaphragm :( - actually paid $200 and gave him some KG2.5's and 3.2's. ) Playing a piece of classical (Itzhak Perlman, Tchaikovsky's #1) and must say I am really IMPRESSED :D . Nice tonal quality and sound stage. Two hour trip to get them ... seller did not have any front teeth ... dusty/dirty cabinets, etc :)  But think it was money well spend. Now; have to hide them from my wife before she get's back Friday ...no room in front of my KPT-904's :( Oh well; I'll meet her at the door with a glass of wine :D 

Cheers, Emile

IMG_2117.JPG

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