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-   -   vented subwoofer vs room issues? (http://www.diyaudio.com/forums/subwoofers/8662-vented-subwoofer-vs-room-issues.html)

Ilianh 14th December 2002 03:39 PM

vented subwoofer vs room issues?
 
I got this 10" woofer and made a vented subwoofer out of it..


When i run it, it sounds loud and tight in some parts of the room, in other parts i barely can hear it...

then i tested something else, using the same box, i filled it with polyfill, took out the vent, and closed the hole so no air could leak, and the sound was not as loud, but it was present all over the room, and it was a bit tighter/better...

i was wondering, is my vented deisgn bad? should i recalculate?
or should i try using some kind of air resists on the vent, like some fabric or something.

any web sites talking about vented vs room positioning and issues ?

ive heard vented woofers in the past, wich could do that "room filling" sound.

any help would be apreciated.

Bylie 14th December 2002 03:46 PM

I suppose you have favorite listening position. >hat you now should do is put the subwoofer on that position and play some bass tones. Now you should walk around the room and try to find a place where the bass sounds best, this is the place the subwoofer should be placed.

Ilianh 14th December 2002 03:49 PM

yes, that will work if you are the only one in the room :)

theres 2 couches in my living room, and when watching movies people will fight to have the bassy-place ;) and then :smash:


why does a closed baffle fills a room? and not a vented?

im trying to find sites on that subject sine a couple of days..

Bylie 14th December 2002 04:06 PM

Thinking logically, it's probably because with a vented box you have two points from where the sound originates, this is not a problem as you will get more sound but the problems begin when these two soundsources are interfering with eachother creating dips and spikes all over the place.
With a sealed box you have only one soundsource so the only interference that can happen is with the reflections of the room, the downside is that it will not sound as loud and most of the time doesn't go that deep which is rather important in HT (clean bass is important too imho, too many people forget that, not the ones here though :)).

Think of it as pond and a rock, when you have two stones of 20kg's each and you let them fall in the water the ripples will interfere with each other and the reflections of the side. When you then have one stone of 40kg and let it fall it will provide a clean ripple that only will have interference because of the reflections of the side of the pond.

Maybe a sealed box with a larger driver is the solution.

Ilianh 14th December 2002 04:46 PM

i was thinking of using a bit bigger box and 2 of the same drivers in a closed box, as those drivers are cheap ;)

or what about installing 2 ports ?


or as ive said before, acoustic resist's on the port

roddyama 14th December 2002 04:56 PM

Ilianh,

The port probably gave you another half octave of bass extension. Not having been in your living room, I would guess that you have room modes in that last half octave that are not excited when the port is blocked. The question is, do you miss that low bass when you run the closed box?

Rodd Yamashita

Ilianh 14th December 2002 05:44 PM

well the whole bass is like 3 db lower, the low bass is there, but around 3 db lower than with the vent...

the box is preety big too... 2.8 cu ft

pinkmouse 14th December 2002 05:58 PM

Ilainh

I would tend to agree with Rodd, the problem is more likely to be due to room modes excited by the lower response of theported box than interference problems, due to the long wavelengths of the sounds involved.

Of course, you could always build another sub and run a pair...:D :D

roddyama 14th December 2002 08:13 PM

Quote:

Originally posted by Ilianh
well the whole bass is like 3 db lower, the low bass is there, but around 3 db lower than with the vent...

the box is preety big too... 2.8 cu ft

Ilianh,

The port will contribute to the total output of the sub well up to 2X the fs of the driver. That means you will hear the loss of the ports output all the way into the mid-bass region. Your box, at 2.8cu.ft., is not a large box by most standards.

I would first try Bylieís suggestion and start moving the sub around until I found a place where the standing waves are minimized at the listenerís position(s). If that didnít work, I would go with Alís suggestion of stereo subs (actually, I would do this first. It does affect the image). The next step is room filters, bass traps or absorbing panels, to try and tame the standing waves in the room.

Hope this helps,
Rodd Yamashita


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