Bass traps and diffusers

[kags]

Perfect that’s what I was asking earlier in the thread.
But do the corners need to be floor to ceiling?

If you can go floor-to ceiling, you gain a lot of effectiveness. U would recommend it unless there are other practical reasons why you don’t want to. The tri-corners effectively treat several modes at once.

 

[RoadrunnerOZ]

Do you find tube traps have real-world advantages over non-round velocity absorbers? Particularly for LF issues?

Not unless targeting a specific corner frequency range - however they do have bandwidth greater than Helmholtz absorbers and with clever venting can cover more than one frequency. I have made/used closed at one end tube traps (which mean they’re 1/2 the height of open tubes), made from heavy duty PVC water piping lined with compressed glass pipe liner, opening covered with a cloth sealed into place with a reducer ring, closed end sealed with a cap and sprayed the desired colour using automotive spray lacquer. Feet made from shelf brackets having open end of tube facing down
You can work out the length required from speed of sound and frequency. An open tube is twice the length for the same fundamental frequency but traps more harmonics than a closed one.
http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/opecol.html

 

[RoadrunnerOZ]

You need to find out if there’s a problem after you’ve placed your new wall panels - whatever frequency you find peaking will be related to some dimension(s) in the room. Corners relate to all the possible sound paths - if after treating the wall surfaces you are getting some peaks occurring then you’ll soon know which dimension is the problem.
In your 3 x 3 x 2.2 room you have two major double standing wave problems. Each wall has the same lateral dimension and therefore diagonals as well - these will feed and causes problems to be doubled at their specific resonant frequencies. The next issue is that your ceiling height is approximately 1/2 of the diagonal top to opposing diagonal bottom corner distance - (the longest diagonal on the room eg. left rear wall top to right front wall bottom - there are four of these diags). Therefore you may need to trap at least two corners to kill standing waves and ringing in the room from drums. Corners are pressure zones from floor to ceiling, interrupt one of two corners that interact and you kill the problem. A floor to ceiling open faced absorber in two adjacent corners would certainly help.

 

[kags]

Not unless targeting a specific corner frequency range - however they do have bandwidth greater than Helmholtz absorbers and with clever venting can cover more than one frequency. I have made/used closed at one end tube traps (which mean they’re 1/2 the height of open tubes), made from heavy duty PVC water piping lined with compressed glass pipe liner, opening covered with a cloth sealed into place with a reducer ring, closed end sealed with a cap and sprayed the desired colour using automotive spray lacquer. Feet made from shelf brackets having open end of tube facing down
You can work out the length required from speed of sound and frequency. An open tube is twice the length for the same fundamental frequency but traps more harmonics than a closed one.
http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/opecol.html

Gotcha - tuned cylinders pressure absorbers, rather than the branded Tube Trap velocity absorber. I’ve seen “nested” tubes lik yours that telescope to tune the resonant freq. they are sealed at both ends with a slot cut in the side. I’ve got some math on them from the Everest/ Pohlmann book.

 

[RoadrunnerOZ]

Gotcha - tuned cylinders pressure absorbers, rather than the branded Tube Trap velocity absorber. I’ve seen “nested” tubes lik yours that telescope to tune the resonant freq. they are sealed at both ends with a slot cut in the side. I’ve got some math on them from the Everest/ Pohlmann book.

Yeah - they seem to work really well - cheap to make and easy to tune as well if you want tuneable by using the next size up pipe which slides neatly over the outside of the smaller.
A friend of mine created a didgeridoo from two concentric pvc pipes to change the tuning like a trombone. It’s called a Didjeribone.

 

[JimJhn]

Hey thanks for that photo!

Never saw that done before...what a great idea!

 

[Spencerleehorton]

here are some test results, mic is positioned in the middle and i have done where my ears are and a few inches forward of that listening position and a few inches behind, thats why there is 3 plots.

the bulging panel will be swapped with one of the floor stand ones, dont worry!!!

 

[RoadrunnerOZ]

Ok - seems like you have a cancellation point at around 120Hz. What are the room dimensions and also the distance of the mic from the front wall?

 

[Spencerleehorton]

Room dims are 4m x 3m x 2.2m
And sitting position is 1.5m from front wall

 

[kags]

here are some test results, mic is positioned in the middle and i have done where my ears are and a few inches forward of that listening position and a few inches behind, thats why there is 3 plots.View attachment 119807
View attachment 119808
the bulging panel will be swapped with one of the floor stand ones, dont worry!!!

The 120 Hz is the axial L-R mode so it doesn’t change with listening position. Did you measure decay time or ETC?

 

[RoadrunnerOZ]

Do you have any treatment at the rear of the room - side walls/back wall/ceiling?

 

[Spencerleehorton]

This is behind the mix position

 

[RoadrunnerOZ]

Not much room for treatment where the door opens and where the shelves are.
Your L/R reflections appear to be giving you a null in the centre where you sit. You may need to do more on the side walls.

 

[kags]

Not much room for treatment where the door opens and where the shelves are.
Your L/R reflections appear to be giving you a null in the centre where you sit. You may need to do more on the side walls.

Rear wall-ceiling corner is a good candidate for a corner trap- could even use 4” panel there, instead of thicker ones. Will help with front-back and side-side issues.

 

[RoadrunnerOZ]

Rear wall-ceiling corner is a good candidate for a corner trap- could even use 4” panel there, instead of thicker ones. Will help with front-back and side-side issues.

Perhaps either
A: two ceiling mounted horizontal 200mm tube traps, one end closed, each 1/2 width with open ends at the corners across the rear wall ceiling above the door
Or B: a single tube both ends open - however if the caps on the closed ends of two separate tubes (as in A above) at the centre are not glued, then they can be removed and replaced with a pipe joiner to see which works best - two traps or one long trap. (3rd option testing with both tubes open with small gap between the ends equal to the joiner spacing)

 

[kags]

Perhaps either
A: two ceiling mounted horizontal 200mm tube traps, one end closed, each 1/2 width with open ends at the corners across the rear wall ceiling above the door
Or B: a single tube both ends open - however if the caps on the closed ends of two separate tubes (as in A above) at the centre are not glued, then they can be removed and replaced with a pipe joiner to see which works best - two traps or one long trap. (3rd option testing with both tubes open with small gap between the ends equal to the joiner spacing)

Regarding the tubes - you mentioned using PVC, but would cardboard concrete forms be effective? Do you line the circumference of the tube or soft fill the tube? I’ve also seen rigid panels inserted across the inside diameter of the tube. Thanks to your suggestions, I’m going to try these in a new room this month.

 

[Spencerleehorton]

I have a long cardboard tube, I think it’s 4 or 5” diameter and about 8’ long.
Do I need to fill it or could I put that up on the rear wall/ceiling?

 

[kags]

I have a long cardboard tube, I think it’s 4 or 5” diameter and about 8’ long.
Do I need to fill it or could I put that up on the rear wall/ceiling?

I don’t think a tube with that diameter will reduce the energy noticeably- something like 20-24 diameter is probably necessary. Maybe OZ can add some insight?

 

[RoadrunnerOZ]

Regarding the tubes - you mentioned using PVC, but would cardboard concrete forms be effective? Do you line the circumference of the tube or soft fill the tube? I’ve also seen rigid panels inserted across the inside diameter of the tube. Thanks to your suggestions, I’m going to try these in a new room this month.

I have a long cardboard tube, I think it’s 4 or 5” diameter and about 8’ long.
Do I need to fill it or could I put that up on the rear wall/ceiling?

Cardboard tubes used for newsprint paper work well. I like the stormwater/pressure pipe as it’s heavy. Cardboard concrete would also work well.
You can’t just use an empty tube, it needs to be loaded with absorbent material but I like to allow an open air column down the tube so the outer lining of glassfibre does not fill the tube completely.
Hollow tube is lined with compressed glass fibreboard, fitted around the circumference of the interior - 25mm board for a 200mm tube. (For 150mm tube I’d use 13mm compressed board).
For this I normally take the 25mm board cut to size then cut slits in the back to allow it to fold round into a tube.
I use PVC pressure pipe and accessories such as caps and joiners. This is thick walled (can’t remember if the size of 200mm is the inside or outside so you need to measure the ID for dimensioning the fibreglass).
For a 200mm ID pipe using 25mm board the inner circumference to calculate board width is based on dia. 200 - (2 x 25) = 150mm - circumference = a 471mm wide board - this may be less due to fold rigidity so a test short piece is advisable. Then slits at say 25mm apart are cut into the back of the board leaving the cloth face continuous facing the inside of the tube. You roll up the board and cellotape it at intervals along its length to keep it rolled up and slide it into the tube - I always try a short piece first to make sure it slides in without jamming - you can cut each holding cellotape just as it is at the tube mouth for a tighter fit if the fibreglass is too loose - you can always cut off one slit section if the fit is too tight.
The open ends need a cloth cover which is held in place using a pipe reducer or an end cap with a disc cut out of the middle - this is a pretty tight fit but looks neat if you’re sandwiching the cloth - the tube outer end may need a little sanding unless you use the end cap with the centre cut out and glue the cloth to the inside face’s outer annulus, the closed ends just use a cap. Joiners are also available. They supply a PVC pipe glue which actually slightly dissolves the PVC and never comes undone so you need to be sure before you glue!!
For cloth ends I’ve used stretch material like they use for pop filters available at any fabric shop.

 

[RoadrunnerOZ]

I don’t think a tube with that diameter will reduce the energy noticeably- something like 20-24 diameter is probably necessary. Maybe OZ can add some insight?

The diameter needs to be really around 200mm or more to be effective. You need a good volume of air to be damped inside the tube to load the area being treated.