In a box, when you add stuff or acoustic foam, what relationship does it have with volume? (I assume it reduces it)
Is there a downside to stuffing in terms of sound quality?
Also in relation to this, if you lengthen a port generally what is the result? What if a port is too long, what is the result? Too short result?
Thanks for any help.
Is there a downside to stuffing in terms of sound quality?
Also in relation to this, if you lengthen a port generally what is the result? What if a port is too long, what is the result? Too short result?
Thanks for any help.
When you add something like polyfill it actually slows the sound waves and increases the effective size of the enclosure by up to 25%. In a vented enclosure this also alters the tuning frequency btw.
When you lengthen the port, decrease the port area, or increase the box size (or any combination of the 3) you lower the tuning frequency. The effect this or its reverse will have on the sound depends on the specific driver being used.
When you lengthen the port, decrease the port area, or increase the box size (or any combination of the 3) you lower the tuning frequency. The effect this or its reverse will have on the sound depends on the specific driver being used.
Just the clarify the enclosure fill effect;
Fill damps the oscillation of the driver at resonance, this results in a reduction of the impedance rise at resonance (usually by around half) and a reduction of the "hump" in amplitude response at resonance (by around 3db)
It's the reduction of these 2 things that makes a smaller filled enclosure "sound" like a larger one, however you don't get something for nothing, the larger enclosure will have more bass extension and greater efficiency than the smaller one.
Think of fill as a way to make a driver "behave" nicely in a smaller than optimal enclosure, rather than making the enclosure volume appear larger to the driver (which it doesn't really do)
Fill damps the oscillation of the driver at resonance, this results in a reduction of the impedance rise at resonance (usually by around half) and a reduction of the "hump" in amplitude response at resonance (by around 3db)
It's the reduction of these 2 things that makes a smaller filled enclosure "sound" like a larger one, however you don't get something for nothing, the larger enclosure will have more bass extension and greater efficiency than the smaller one.
Think of fill as a way to make a driver "behave" nicely in a smaller than optimal enclosure, rather than making the enclosure volume appear larger to the driver (which it doesn't really do)
fill generally accepted to reduce standing waves from the sides of the enclosure. The wavelengths of low frequencies are much longer (56.74ft for 20Hz at 24deg c , 25.22ft at 24deg c) so it doesnt really come into play in the same respect unless your box is room sized. My understanding is its normally used for midranges though.
dvdvideo said:
For ported boxes, normally use see two impedance peaks (I call them Tetons). When you add stuffing, you might be able to reduce acoustic high frequency resonance and the the higher frequency impedance peak. If too much stuffing is used it will effect the driver's transient capabilities, and will make the speaker sound somewhat dead. It's possible to use Martin's Mathcad worksheets to get better understanding of the effects on stuffing.
I'm with Bill, but some explanation is needed. Fill DOES make the enclosure seem bigger than it is, even at low frequencies. This is why Q and Fs are reduced.
Waves are not slowed down at all, for if they were their frequency would be reduced. The tiny fibres of the fill vibrate with the acoustic waves and so remove some of the energy from them. This hence produces the effect above as well as reducing the severity of standing waves.
Waves are not slowed down at all, for if they were their frequency would be reduced. The tiny fibres of the fill vibrate with the acoustic waves and so remove some of the energy from them. This hence produces the effect above as well as reducing the severity of standing waves.
Bare said:Geez..
for years I thought "stuffing" with Dacron or ideally VirginLong Hair Wool (insert Media of yer choice) an enclosure was simply a Bodge to try and get some Bass out of a Too Small box...
Instead of buiding an adequate enclosure.
Well, you do get better bass when you reduce the impedance Tetons.
THere is experimental evidence to support both schools of thought - the action of stuffing is perhaps complicated and nonlinear.
I personally favor Volenti's way of thinking. I think substantial reductions in Fc (Fs is a free-air parameter) or Fb, resonant frequencies for sealed and vented boxes, respectively, are caused by uniintentional placement of stuffing too near the driver causing increased mass and damping on the cone.
I personally favor Volenti's way of thinking. I think substantial reductions in Fc (Fs is a free-air parameter) or Fb, resonant frequencies for sealed and vented boxes, respectively, are caused by uniintentional placement of stuffing too near the driver causing increased mass and damping on the cone.
You could refer to this link which goes into some detair of whay a stuffed box looks bigger:
http://www.lungster.com/l/speakers/BassListArchive.html
http://www.lungster.com/l/speakers/BassListArchive.html
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.