Bunging speaker ports

admin_exported

New member
Aug 10, 2019
2,556
2
0
Does bunging speakers ports have any physical/mechanical effects on the driver? If air that is being created by the physical movement of the cone, cannot be dissipated as efficiently due to the port being blocked, what is now happening to this excess air?

Most drivers have a seal between the housing of the driver and the cabinet, so is it entirely safe to effectively form a sealed box enclousre by virtue of bunging?
 
A

Anonymous

Guest
My speakers are infinite baffle, i.e. sealed. Air compresses quite easily so I imagine it does that. If foam bungs are used then I suspect some air escapes through the foam...
 

Andy Clough

New member
Apr 27, 2004
776
0
0
Bunging is a perfectly normal practice for fine-tuning a speaker's bass, and shouldn't cause any problems with the cone. Some manufacturers supply foam bungs with their speakers for customers to experiment with, and I've even used an old pair of rolled-up socks for the purpose in the past with no detrimental effect!
 
A

Anonymous

Guest
Andy Clough:Bunging is a perfectly normal practice for fine-tuning a speaker's bass, and shouldn't cause any problems with the cone. Some manufacturers supply foam bungs with their speakers for customers to experiment with, and I've even used an old pair of rolled-up socks for the purpose in the past with no detrimental effect!

Thanks Andy. Im actually using bungs supplied with my Dynaudio 72SEs (I know you guys werent too crazy about them but they match my Cyrus gear perfectly!).

When the ports are not bunger, the amount of air shifted out of these is immense, and I just wondered what sort of pressures (if any) are exerted on the cone as a result.
 

Andrew Everard

New member
May 30, 2007
1,878
1
0
OK, this is going to be the very simplified version.

Yes, the whole point of using bungs is the effect it has on the driver(s) in the ported enclosure.

Proper bungs use open-cell foam, so they don't block the port tube completely, but rather impede the flow of air in it.

The result is a slight stiffening-up of the movement of the driver, due to the fact the damping effect of the air in the cabinet is increased now it can't move in and out so easily behind the driver.

Blocking the port completely will of course create a sealed box, which could over-damp the drive unit and cause a drastic loss of bass.

And for all the comedy about rolling of socks, the nature of the bung used can make a big difference. So one sock loosely rolled will have less effect than two rolled tightly and thus more efficiently blocking the tube.

If you want to get really geeky about this, try buying a big catering box of old-fashioned drinking straws, and using a bundle of these to fill the port tube. It will have a more subtle damping effect than foam bungs. Or indeed socks.
 
A

Anonymous

Guest
Andrew Everard:

Audiophile straws! quick hide the post before someone smells the opportunity to make a packet! :)
 
T

the record spot

Guest
Andy Clough:
...I've even used an old pair of rolled-up socks for the purpose in the past with no detrimental effect!

And the same here too; money well spent. M&S 100% cotton (black, obviously) did the job extremely well!
 

Andrew Everard

New member
May 30, 2007
1,878
1
0
JAXON5:
Audiophile straws! quick hide the post before someone smells the opportunity to make a packet! :)

No, non-audiophile straws. And people already make them in packets.
 

Andrew Everard

New member
May 30, 2007
1,878
1
0
Nothing old-fashioned about drinking straws per se, but I meant to draw the distinction between the original straight waxed paper/plastic ones and the ones with a concertina section in them allowing them to be angled, or other newfangled kinks.
 

fatboyslimfast

Well-known member
Jan 10, 2008
158
0
18,590
Ah, but you could use the bendy bits (bent at an angle of 90deg) to direct the sound around and bounce it around the listening room, Bose stylee...

Do you think the designers at Bose have drunk a lot of fizzy pop in their time...?
 

fatboyslimfast

Well-known member
Jan 10, 2008
158
0
18,590
Surely you are...? If there are sound vibrations coming through the port, and the straw is directing the vibrations out at a different angle to the original port....

Obviously, most of the sound that is coming out of there are low frequencies which are rather nondirectional, but the theory must be along the right lines?
 
A

Anonymous

Guest
FBSF, check out Helmholz Resonance on Google or Wikipedia.
atb
 

fatboyslimfast

Well-known member
Jan 10, 2008
158
0
18,590
Sorry all, I should have put a smiley at the end of my previous post - there was a hint of friday humour there, but I think I came across all serious!
 
A

Anonymous

Guest
Andrew Everard:
JAXON5:
Audiophile straws! quick hide the post before someone smells the opportunity to make a packet! :)

No, non-audiophile straws. And people already make them in packets.

Ouch!!
 
A

Anonymous

Guest
Some info for the interested geeks out there


In a ported (or vented) box, the air mass in the port/vent is effectively isolated from the air in the rest of the enclosure, except for the inside opening of the port/vent tube. This air has mass and inertia, so has its own resonant frequency, which can largely be tuned independantly of the enclosure.

At high frequencies, the inertia of the air in the port is too high for it to respond to the air mass in the enclosure, so it behaves like a sealed box.

At the resonant frequency, the air mass in the port reacts against the air in the enclosure, and vibrates out of phase with it. This results in the air in the port being in phase with the front of the speaker driver, thus increasing output. This also means that the movement of the bass cone is greatly damped at this frequency (as the air in the box is 'bouncing' against the out of phase port air mass). This is why the cone can appear to not move at all, but with loads of air movement happening in the port. I remember seeing a great video of ported box putting out a candle flame!

At frequencies below the port tuning, the port air mass has insufficient inertia to bounce back, and so the rear pressure wave from the bass driver leaks from the port, out of phase with the wave created from the front of the driver, thus canceling out the bass.

For this reason, a ported system will exhibit more bass around the tuning frequency, but will then typically have a fourth order roll off (24dB/octave). A sealed system won't gain the extra bass, but won't suffer from the canceling effect, thus exhibits a second order roll off (12dB/octave).

This can mean you actually get more very low bass on a sealed system (as the roll off slope is shallower). However, it's likely this bass is so low (in both frequency and amplitude) that it wouldn't be much use to you (too quiet to be heard, and below the frequencies of the recording you're playing).

Stuffing (or sealing) a ported system shouldn't cause any problems, but unless there was a very good reason, I'd usually avoid doing it unless the manufacturer had specifically provided instructions to do so (a ported system isn't just a sealed system with hole).

There. That should've bored everyone to tears!
 

PJPro

New member
Jan 21, 2008
274
0
0
Not at all. I'm impressed! Dunno what you're on about but impressed nonetheless.
 

professorhat

Well-known member
Dec 28, 2007
991
21
18,895
I'm also impressed, well explained as well! One question on this though:
sploo:Stuffing (or sealing) a ported system shouldn't cause any problems, but unless there was a very good reason, I'd usually avoid doing it unless the manufacturer had specifically provided instructions to do so (a ported system isn't just a sealed system with hole)
Why would a manufacturer create a port and then tell you to bung it? This isn't a sarcastic question in case anyone is thinking the worst of me, just a genuine enquiry. Is it just to provide flexibility on the environment the speaker is placed in?
 

Andrew Everard

New member
May 30, 2007
1,878
1
0
Yes, Prof, it is. Some speakers are supplied with bungs, but again these don't completely block the port, being made of an open-cell foam.
 
T

the record spot

Guest
chebby:
Probably most effective with rear ported boxes that have to be used very near a wall or corners. I did this with a pair of Monitor Audio Bronze BR1's on Atacama stands. They were about 10 inches away from a rear wall (and one close to a corner) so it was necessary and extremely effective to use the (provided in the box) foam bungs. It really tidied up the bass and removed all 'boomy' moments. My current Rega R3's are about a foot from the wall and have front facing ports. They don't boom at all so no need for bunging.

The bass from the Missions I have is noticeably different if you cover up the bung, without the bass is good, but stand in between the speakers and it's very bass heavy - reall thump-thump, so that;s what the neighbours downstairs would get. If we had any. We live in a bungalow. Which is handy...!
 
A

Anonymous

Guest
You need to be careful with the choice of sock too - cotton removes microphony doesn't it, so a mix or synthetic would be creating potential static.

I have 5 pairs of audiophile socks (still in their original boxes) available for sale if required. £20 each sock or £38 a pair.......Choice of colour too to match your decor. One pair have Homer Simpson on them.
 

ASK THE COMMUNITY

TRENDING THREADS

Latest posts