Bunging speaker ports

[Anonymous]

Graham_Thomas: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.

unlike most other hi-fi items, i am thinking that having your audiophile socks run-in would be advantageous...

 

[the record spot]

And washed. Removes, er, colouration apparently.

 

[Anonymous]

Hi Prof - yeah; Andrew hit the nail on the head with his reply.

I must admit I've never experimented with sticking stuff in my ports (so to speak

) so I'm not totally sure what the effect of partially blocking a port would be. If it has the same effect as reducing the diameter of the port, then that would lower the port tuning frequency, which would actually bring the response closer to a sealed box.

Here's a quick example of what happens in a ported enclosure (vs sealed):

Take all of the above with a pinch of salt - it's just an example, and the driver I've used in the model isn't really suited to porting. That said...

The top image shows the low frequency response of a sealed system (red) and a ported (orange). Note how there's more bass around the 20Hz tuning frequency in the ported version, but that the response drops off much faster than the sealed.

The second image shows the displacement of the driver. Note the reduction around the tuning frequency for the ported version. Whilst this isn't a particularly good example, you can see how it would be possible (with a better tuning) to get more low end bass from a ported system, before you run out of excursion.

The third pic shows the speed of the air moving in the port; which increases around the tuning frequency. Port noise can be a problem when the speed of the air is too high. One of the things that increases the air velocity is having a thinner port tube - therefore I do wonder if some of the stuffing ideas may increase the air speed as a result (and thus may create unwanted noise). Well, at least until your floorstander rejects your choice of blockage, and becomes a sock cannon...

the record spot:And washed. Removes, er, colouration apparently.

*LOL* The washing power analogy is not lost on me. Ever notice that, just like washing power, sticking some new gear in your setup makes everything magically better... so... by definition... wasn't the last lot any good?

 

[Coll]

I am new to the forum but would like to comment on the question of speaker bungs.
I have used the type supplied by Monitor Audio and feel it changed the sound too much and did not like the effect.
Andrew Everard suggests using drinking straws which I believe is a very good idea, but would it no be easier to use a very open pore reticulated foam bung made from air filter material which would place a resistance on the air movement but not drastically change the sound.

 

[Dan Turner]

To be honest what you use depends on how much you need to reduce the bass. When I requested some port bungs from Neat they supplied 2 different lengths of foam bungs, but I guess it stands to reason that density as well as quantity of material will affect the degree to which bass output is attenuated.

I've done a lot of experimentation with this and I found that drinking straws > Neat short bungs > Neat long bungs > rolled up socks cut the bass in order or least to most, and it was the socks in combination with some slight position and stand-filling changes that finally got the sound right and cured the bass-excess that I was experiencing, for other people the solution will be different as I'm sure every speaker and room interaction is unique.

 

[Coll]

Just purchased some Monitor Audio RX1s, speakers are only 11cm from rear wall and pleased to say there is no bass boom. What I do feel though is that on some older pop recordings is that too much bass is put in the recording I suppose because in the 60s and 70s hi fi speakers did not reproduce bass as well and in an effort to give strong bass content it was boosted in the recordings. I would be interested to know if this is the case or is it that I have never had speakers that reproduce bass this well before.

 

[CnoEvil]

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.

My goodness Mr E, you weren't half chatty back then!

 

[dannycanham]

A speaker has two enclosures it moves in. 1) Behind it, the box. 2) In front of it, the room.

1) Is set in a closed box design.

2) Can vary.

1) Can also vary if the design has ports and bungs.

A box design tries to create predictability in the way the cone behaves even though the front enclosure can be very different.

The design of the box tries to tune the speaker to a room of particular volume. Usually an average front room size for an average floorstander size. There can be a larger or smaller room size sweet spot depending on design.

There is another factor as when a speaker is close a wall low frequencies radiate differently. Rather than all directions the low frequencies radiate mostly in the forward half of the space around them as well as reacting with their own reflections.

Bunging the ports can help in both cases where the room is smaller than the box design sweet spot and when the speakers are close to a wall....um so yes it provides more flexibility in the environment the speaker is placed in.

I wouldn't worry about bunging ports and damage. Most bunging is done with soft material and speaker boxes can be full of similar material. As long as the material has pleanty of air amongst it (like a spunge, sock or tube) or there is plenty of air between the cone and the bung there is loads and loads of springy air to stop potential damage.

I lightly bung my Spendor S8e's with the foamy substance used to protect hard drives during delivery as my room isn't quite as long as they would like and it works a treat.

 

[dannycanham]

I shouldn't click buttons twice.