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Sealing subwoofer port questions

17K views 44 replies 13 participants last post by  JohnRael 
#1 ·
In another thread I mentioned how my subwoofer can get boomy at times, and sealing the ports was suggested... but unsure what is the best material to use for this.

I found some thick foam (used for blocking drafts under doors) in my spare room, but it probably won't be an exact fit for the ports. Is that good enough?

Or would thinner foam be better? I may have some shipping foam around here somewhere ... sort of thin though.

Is the idea to block the port completely or just semi-block it a little bit? And is there a chance of the subwoofer breaking by sealing the ports?
 
#2 ·
And is there a chance of the subwoofer breaking by sealing the ports?
yes!

I recently asked svs about blocking my port on the pb2000 as an experiment and got a definite NO!
 
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#10 ·
I blocked the ports on my two tiny SW012 subs in my secondary room and much much prefer the sound; seems tighter and improved the frequency response by flattening it out when I tested using test tones and an SPL meter.

I used the thinnest foam that these guys were selling and cut it to a sorta/kinda round shape with a razor and stuffed it in there.

http://www.foam-futon.com/
 
#12 ·
I used the thinnest foam that these guys were selling and cut it to a sorta/kinda round shape with a razor and stuffed it in there.

http://www.foam-futon.com/
I'll check my basement and see what, if any, foam I have lying around. I think I have something similar from a shipping package I got a while ago, just not sure where I put it.

I know I have the doorstop type of foam... sort of thick and not an exact fit.

Not sure if the idea is to have a complete blockage of the port, or if a little bit is good enough.
 
#17 ·
What kind of sub do you have?
This will help, to give you more informative answers.


What I strongly suggest, is to post here
http://www.avsforum.com/forum/113-subwoofers-bass-transducers/


I hang around speakers and movie review for the most.
Some hang around subs/amps/... and so long.
The above link, will be the place to get members with most knowledge about subs, to give you the most educated answer:)


Ray
 
#18 ·
What kind of sub do you have?
This will help, to give you more informative answers.


Ray
I forget, but think I asked about my sub a while ago over there... got no replies.

Don't think my model will be of much help, as I can't find any real info on it, manufacturer out of business, and company that took them over has no info (I wrote them)... can't find anyone else who has even owned the thing before.

Anyway, it's a signet SP-100.

A google search primarily shows some guy selling one on a Canadian site, a couple of pics of the sub, myself asking questions about it, and some guy selling its bigger brother:
http://forum.polkaudio.com/discussion/65704/fs-signet-sp200-ii-15-inch-powered-subwoofer
 
#21 ·
As a loudspeaker engineer, I'd generally say totally blocking the ports should not harm the driver. However, a couple things can be going on:
1) Port can provide a path for heat to vent, from the sub and/or the amp. This would only be a problem if constantly driven near full power.
2) In SVS case, they may be applying some kind of boost to match the tuning, and blocking a port could lead to excessive boost at frequencies the box is not then set up for. And/or see #1.
3) Blocking the port can lead to more speaker excursion, depending a lot on the port tuning and what music is being fed in. A port sharply reduces woofer motion around the tuning frequency, so blocking the port will increase excursion around these frequencies. Below the tuning frequency, however, the port becomes a leak and it is like the woofer is in free air, moving like crazy. By contrast the sealed box loads the woofer and reduces the excursion.
Sealed boxes generally have better time response, i.e. starting and stopping when the music does. Ported setups tend to "ring" more, which may or may not be audible depending on specifics of the box, the room, and your sensitivity.

Unless you are blasting at full volume continuously, experiment! Just be cautious with the volume knob. Block one port, then both. You need a hard seal, loose foam is a joke. Temporarily maybe a ton of duct tape could serve for initial experimentation purposes, maybe over a piece of Masonite.

I would NOT assume the boominess is due to your sub. It's definitely possible, depending not the driver and box and tuning. But it is also quite possible that your sub + room and mains + room are interacting with the crossover settings to create too much bass. That is rather harder to track down without some sets of measurement, but as a wild try you could set the main speaker crossover significantly higher. It is also possible your main speakers are actually the boomy ones (what are they?)
 
#24 ·
That is rather harder to track down without some sets of measurement, but as a wild try you could set the main speaker crossover significantly higher. It is also possible your main speakers are actually the boomy ones (what are they?)
Canton 701DCs.... doubtful they are the culprit, as I was running them without a sub for some time (and also as large at one time)... not boomy. The more I have the sub do, the boomier it gets.

Of course it could be an interaction with sub + speakers that makes things all boomy, but besides just lowering the crossover to like 20-30, not sure how to get around that... and that probably isn't such a good idea.
 
#23 ·
I've always used socks.

No harm in sealing the ports. I don't know how you could damage a driver by sealing up its port. It's usually the other way around, porting a sealed cab and not applying a HPF, high pass filter.
 
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