Re: Acoustic wadding.

In article <6bmdnYnWM7jtqAbZnZ2dnUVZ_o6dnZ2d@xxxxxxxxxxxxx>, "MOSFET" <ntanner@xxxxxxxxxxx> wrote:
What you are calling "acoustic wadding" I think is the same as adding
padding to the walls of a subwoofer enclosure. I have never heard the term
"wadding" before, hmmm. Another common technique is to fill the sub
enclosure with polyfil (the same stuff as in pillows).

Here's the purpose, and I'm going to start at the basics:

Any cone type speaker (including subwoofers) produces soundwaves both
forward and behind. The sound waves produced behind are 180 degrees
out-of-phase with the sound waves produced in front. This makes sense if
you think about it, as the cone moves forward in the front of the sub, it is
moving backwards behind the sub. This produces a sound wave exactly out of
phase. If these two sound waves were allowed to interact, they would cancel
each other out. This is THE MAIN REASON why enclosures are necessary when
building subwoofer systems, to keep the rear sound waves from canceling out
the waves produced by the front. So inside the subwoofer enclosure,
obviously much sound is being created. The purpose of acoustic wadding or
polyfil is to absorb this sound energy. Why is this important? Because if
you don't you can have very strange acoustic phenomena going on in your
enclosure, the main concern being what are called "standing waves". This
can create strong reinforcement (boosts) at certain frequencies and effect
the motion (and sound) of the cone. Also, you can have cancellation effects
going on inside the enclosure which will again affect the motion of the
cone.

Unless the woofer is reproducing up into the midbass region, stuffing is not required.
The bass frequencies do not need to be damped.

Remember, ideally, the subwoofer enclosure should JUST be a volume of air to
act as a kind of a spring for the subwoofer (acoustic suspension). Ported
enclosures are a little different as they utilize a tuned port to emphasize
certain frequency bands (bass reflex) and this port has the effect of
realigning the sound coming out of the port so they are in-phase with what
is being produced by the front of the sub. Ported enclosures can produce
more SOL (they are a little louder) because they are able to utilize some of
the sound energy that is always lost in a sealed enclosure.

A port is not in phase with the drivers output. Below the frequency where they share
output, most all of the lower bass comes out of the port only.

But THE MAIN POINT of any kind of polyfil or "acoustic wadding" or whatever
you want to call it is to try and produce (as close as possible) an anechoic
(no echoes) chamber as echoes CAUSE PROBLEMS (as I already mentioned). I'm
not an engineer so I've probably flubbed a few things, but basically I think
what I have said is correct. I hope this helped.

Thats true, and stuffing can also damp flimsy enclosurers.
There is another effect of course, a very important one. In that stuffed enclosure
the manufacture may have specified a volume, and the stuffing acts to increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very important, FOAM.

greg


MOSFET

"Mike G" <metier@xxxxxxxxxxx> wrote in message
news:449b1d54$0$15591$892e7fe2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I'm a novice as far as audio is concerned, so bear with me.
Have a 12" bass speaker fitted in a homemade infinite baffle cabinet.
Speaker manufacturer recommends cab is filled with acoustic wadding.
Got some wadding. Now I need to know how it should be fitted.
I notice the 3/4" thick stuff I bought is very open and springy. Just
stuffing it in would obviously interfere with the speaker cone, so should
it be cut so it doesn't touch the cone at all, or what?
If someone can point me at a website, or offer any advice.
As an aside what is the effect of having acoustic wadding in a speaker
cabinet?
As opposed to leaving it empty.
TIA.
Mike.


.

Relevant Pages

  • Re: Acoustic wadding.
    ... enclosure with polyfil. ... out-of-phase with the sound waves produced in front. ... subwoofer enclosure, obviously much sound is being created. ... of acoustic wadding or polyfil is to absorb this sound energy. ...
    (rec.audio.car)
  • Re: Acoustic wadding.
    ... Another common technique is to fill the sub enclosure with polyfil ... The sound waves produced behind are 180 degrees out-of-phase with the sound waves produced in front. ... This makes sense if you think about it, as the cone moves forward in the front of the sub, it is moving backwards behind the sub. ... This is THE MAIN REASON why enclosures are necessary when building subwoofer systems, to keep the rear sound waves from canceling out the waves produced by the front. ...
    (rec.audio.car)
  • Re: Acoustic wadding.
    ... What you are calling "acoustic wadding" I think is the same as adding ... padding to the walls of a subwoofer enclosure. ... enclosure with polyfil. ... out-of-phase with the sound waves produced in front. ...
    (rec.audio.car)
  • Re: More stupid buyer tricks
    ... shape, but subwoofer doesn't work - and not in tiny print, either: ... *Speaker enclosure is used and is in great physical condition. ... seller leaves negative feedback: Don't bid on items if you do ... they read the advert then once they get it thay say there is a fault with it ...
    (alt.marketing.online.ebay)
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    ... Auction is for a subwoofer/truck enclosure package. ... shape, but subwoofer doesn't work - and not in tiny print, either: ... seller leaves negative feedback: Don't bid on items if you do ...
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