Acoustic Diffusion or Absorption?

[Spider27]

Hello,

 

My rear ported speaker has too much bass in my room so just put more space between the wall and speaker. The distance is now 45cm but still have too much bass. I am thinking to put diffuser or absorption but not sure which one would be ideal for this case. I took a quick photo of rear side of speakers and wall for reference.  

 

The room is 3x4m room and the wall showing on the photo is 4m wall facing window.

 

Since I am totally new on acoustic treatment, I watched several videos on Youtube and still confused.. Any feedback or suggestion would be greatly helpful. Thank you in advance.   

 

[Janjuggler]

Hi Spider,

 

You could try some foam placed into the rear port, if you do not have foam some small towels wrapped up.

 

This may be an inexpensive way to first see if there is a difference before buying more expensive treatment.

 

JJ

[joz]

Agreed plug those ports first  

[Spider27]

Thank you. I totally forgot about the option.... Does anyone know Where can I find foam that would fit this rear port ?  The diameter is 11cm so quite big...

[BATMAQN]

4 minutes ago, Spider27 said:

Thank you. I totally forgot about the option.... Does anyone know Where can I find foam that would fit this rear port ?  The diameter is 11cm so quite big...

Have you tried the towels option already did it help?

 

Foam doesn't need to be anything special but Clark rubber or Bunnings will have something to suit you might have to cut it or roll it into a tube.

[Spider27]

1 hour ago, BATMAQN said:

Have you tried the towels option already did it help?

 

Foam doesn't need to be anything special but Clark rubber or Bunnings will have something to suit you might have to cut it or roll it into a tube.

 

2 hours ago, Janjuc said:

Hi Spider,

 

You could try some foam placed into the rear port, if you do not have foam some small towels wrapped up.

 

This may be an inexpensive way to first see if there is a difference before buying more expensive treatment.

 

JJ

 

Yes, I just filled with face towel rolled tight and plug it in and it definitely helped.  Thank you..  Looks quite ugly though. I will try to search for foam that may fit this large port to give a try.  

[Spider27]

Bass definitely tamed by filled the rear port with tightly rolled towel and now much easier to listen. Only downside is that the sound a bit congested and lost a bit of air and soundstage it used to have without the towel... Maybe, the towel was too tight or dense... 

[TOPSHELF]

I've read that paper straws work well filling a port whilst still retaining the sound you are missing with a towel. Maybe a search on the net?

[Al.M]

I never been satisfied plugging the port on speakers as you loose the original sound a fair bit as it becomes a closed design with the bass extension reducing by about 10-20hz depending the on the port freq. If you can’t pull speaker more forward another 10-20cm, try lengthening the port inside with an equal diameter tube by about twice or half which will lower the extension and reduce the bass bump or resonance that may have been designed for.  That way it will more or less retain that open sound.

 

Straws are a vintage method that does the same by retuning the port resonance.

5 hours ago, TOPSHELF said:

I've read that paper straws work well filling a port whilst still retaining the sound you are missing with a towel. Maybe a search on the net?

 

Edited December 23, 2017 by Al.M

[Spider27]

2 minutes ago, Al.M said:

I never been satisfied plugging the port on speakers as you loose the sound a fair bit and it becomes a closed design with the bass extension is reducing by about 10-20hz depending the on the port freq design. If you can’t pull more forward say another 10-20cm, try lengthening the port inside with an equal diameter tube by about twice or half which will lower the extension and reduce the bass bump or resonance that may have been designed for. 

 

Paper straws are a vintage method method that does the same by returning the port resonance.

 

Thank you very much for the suggestion. Do you mean putting same diameter tube towards inner rear port further or extending the rear port towards the wall?

The plastic rear tube port is all the way in so not sure the purpose of putting another tube inside. On the other hand, if it is extending towards wall with extra length of tube connecting from rear port, then it will be even closer to the wall... Have i misunderstood? Sorry... 

[Al.M]

18 minutes ago, Spider27 said:

Thank you very much for the suggestion. Do you mean putting same diameter tube towards inner rear port further or extending the rear port towards the wall?

The plastic rear tube port is all the way in so not sure the purpose of putting another tube inside. On the other hand, if it is extending towards wall with extra length of tube connecting from rear port, then it will be even closer to the wall... Have i misunderstood? Sorry... 

Lengthening the port on any bass reflex design speaker will generally ask the woofer within the given cabinet volume to try to go lower and flatten out or negative the bass freq response. Can experiment externally and if it works and you want neater look go inside and do same. For  example, original tube is 50 internal diameter by 100mm long, so try same internal diameter tube, but 150 or 200mm length if there is room inside. Even something like an empty toilet roll may work but keep the tube join tight with no major air leaks. If you like it eventually use PVC plumbing pipe off cut, don’t glue it just tight fit with masking tape so you can return it to normal. If there is not enough room inside you can do L shape pipe bend up.

 

The port tube should just pop out from the back.

Edited December 23, 2017 by Al.M

[Spider27]

5 minutes ago, Al.M said:

Lengthening the port on any bass reflex design speaker will generally ask the woofer within the given cabinet volume to try to go lower and flatten out or negative the bass freq response. Can experiment externally and if it works and ou want neater look go inside and do same. For  example, tube is 50 internal diameter by 100mm long, so try same internal diameter tube, 150 or 200mm length if there is room inside. Even something like an empty toilet roll may work, but eventually PVC plumbing pipe off cut.

 

The rear port is 10cm diameter large. and quite deep. And it already has tube all the way in (just 1cm apart from front faceplate) so there is no further room if I understood you correctly   

[Satanica]

All things considered I think you have to do some drastic measures. This includes measuring, EQ and possibly subwoofer(s) and acoustic treatment. Good luck. 

Edited December 23, 2017 by Satanica

[Al.M]

22 minutes ago, Spider27 said:

 

The rear port is 10cm diameter large. and quite deep. And it already has tube all the way in (just 1cm apart from front faceplate) so there is no further room if I understood you correctly   

Ok looks like not much room inside. Can still add further length just outside and 90 or 100mm diameter sewer pipe off is needed.

 

Alternatively you can create your own port diameter say 50-75mm and play with the length and use polystyrene foam off cuts to make a gasket inside the existing port and see what that does. 

 

This is total guess work and it may all be too much effort as you may not know what is going on. There are online speaker port calculators that can give you a general idea of what the changes may do. The problem is we don’t know the woofer parameters. But generally if you reduce the current 10cm diameter port to say 5cm and keep same length the box tuning port freq will go down. The current likely port freq might be say 40hz. So a 5 x 5cm port would in theory take it down to 30hz. Too narrow a port may cause air rush noise so 7cm diameter may be needed. The boominess in the room from current speaker port interaction is likely to be around say 60-80hz so by sending the port tuning freq lower should reduce the boominess.

http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL Port lenth 1.htm

Edited December 23, 2017 by Al.M

[Spider27]

2 minutes ago, Al.M said:

Ok looks like not much room inside. Can still add further length just outside and 90 or 100 sewer pipe off is needed.

 

Alternatively you can create your own port diameter say 50-75mm and play with the length and use polystyrene foam off cuts to make a gasket inside the existing port and see what that does. 

 

This is total guess work and it may all be too much effort as you may not know what is going on. There are online speaker port calculators that can give you a general idea of what the changes may do. The problem is we don’t know the woofer parameters. But generally if you reduce the current 10cm diameter port to say 5cm and keep same length the box tuning port freq will go down. The current likely port freq might be say 40hz. So a 5 x 5cm port would in theory take it down to 30hz. Too narrow a port may cause air rush noise so 7cm diameter may be needed. The boominess in the room from current speaker port interaction is likely to be around say 60-80hz so by sending the port tuning freq lower should reduce the boominess.

http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL Port lenth 1.htm

 

Thank you very much. It is quite a bit of work and I might try foam bung first.  The face towel that I used is very dense & tight and hard to get the air flowing in and out. I will try foam bung to see if it makes better by allowing air moving in and out a bit more.  If not, then will play with pipe option. Again, thank you very much for those suggestions.  

[Al.M]

2 minutes ago, Spider27 said:

 

Thank you very much. It is quite a bit of work and I might try foam bung first.  The face towel that I used is very dense & tight and hard to get the air flowing in and out. I will try foam bung to see if it makes better by allowing air moving in and out a bit more.  If not, then will play with pipe option. Again, thank you very much for those suggestions.  

Could also try a foam bung with a hole in it which is basically what I have suggested, a different diameter and length port of sorts.

[Spider27]

32 minutes ago, Al.M said:

Could also try a foam bung with a hole in it which is basically what I have suggested, a different diameter and length port of sorts.

Good idea. I will try that, too.  Thank you for the suggestion...

Edited December 23, 2017 by Spider27

[PicoWattson]

Second AI.Ms suggestion, but looks like you don't have that option. Would avoid foam but as TOPSHELF suggested  pack the port tight with drinking straws, and then you have the option of pulling them in a bundle past the rear face to effectively lengthen the port. I have done this successfully many times over the decades. 

[Spider27]

6 minutes ago, PicoWattson said:

Second AI.Ms suggestion, but looks like you don't have that option. Would avoid foam but as TOPSHELF suggested  pack the port tight with drinking straws, and then you have the option of pulling them in a bundle past the rear face to effectively lengthen the port. I have done this successfully many times over the decades. 

 

Thank you for the suggestion.. I will try this tomorrow when I get some straw. I might need  lots of them since the port is large. There are many different size of straw. Do I go for very thin straw or large straws like the ones that we get from McDonald's ?  

 

 

[andyr]

Can I suggest you need to do one of 2 things to solve your bass problem:

1. buy some sealed speakers, or
2. move your ported speakers way more out into the room - like, say 1.2m distance between the back of the cabinet and the front wall.

 

Andy

 

[Spider27]

4 minutes ago, andyr said:

Can I suggest you need to do one of 2 things to solve your bass problem:

1. buy some sealed speakers, or
2. move your ported speakers way more out into the room - like, say 1.2m distance between the back of the cabinet and the front wall.

 

Andy

 

 

Thank you for those suggestions.   

 

1. i am currently shopping for bookshelf speakers with front ported or small enough so does not give overwhelming bass but meantime, might need to stick to what I got.

 

2. 1.2m is way too far that I cannot afford in my current set up.

 

 

[andyr]

7 minutes ago, Spider27 said:

 

Thank you for those suggestions.   

 

1. i am currently shopping for bookshelf speakers with front ported or small enough so does not give overwhelming bass but meantime, might need to stick to what I got.

 

Sorry, S - you currently have quite large stand mounts (even though they are ported).  Buying ported bookshelf speakers will mean:

• they will produce much less bass (coz they're smaller) - so you'll need to add a sub to get a decent sound, but
• you'll still have a problem, as they're ported.

Why not buy some sealed stand mounts?

 

7 minutes ago, Spider27 said:

 

2. 1.2m is way too far that I cannot afford in my current set up.

 

 

Then rear-ported speakers are not for you?

 

Andy

 

[Al.M]

Or try rolling a flat square sheet of mattress like foam forming a plug or hole. For example, a 3cm thick x 15cm long x 31cm rolled circumference and adjust to suit sound, which gives a roughly 4cm hole and 15cm length tube.

[Spider27]

1 minute ago, Al.M said:

Or try rolling a flat square sheet of mattress like foam forming a plug or hole. For example, a 3cm thick x 15cm long x 31cm rolled circumference and adjust to suit sound, which gives a roughly 4cm hole and 15cm length tube.

You read my mind.  I just ordered 2cm thick x 15cm wide and 1m long foam sheets. I guess that it would be enough for both rear ports to cover.

 

I will also try straw ideas too to see if it makes any difference. Just wondering how big the straw might be ideal size... 

[Spider27]

11 minutes ago, andyr said:

 

Sorry, S - you currently have quite large stand mounts (even though they are ported).  Buying ported bookshelf speakers will mean:

• they will produce much less bass (coz they're smaller) - so you'll need to add a sub to get a decent sound, but
• you'll still have a problem, as they're ported.

Why not buy some sealed stand mounts?

 

Then rear-ported speakers are not for you?

 

Andy

 

Any particular sealed stand mount that you may recommend?    I thought that ported speaker produce more bass than sealed. Isn't it?

Edited December 23, 2017 by Spider27