Are my bass traps reasonable or am i doing something wrong?

[goat76]

Need to first figure out how i can configure that generated graph so it includes only 20..200hz and 1 sec

When you have a friend helping you lift the bass traps, you should do three measurements. One with the bass traps the way you had them before, one with the bass traps with the open side facing into the room, and one without any bass traps in the room. Don't move the microphone, the subwoofer, or anything else.

That way you will have 3 measurements that you can compare to see the effect of what your bass traps are doing to your listening room. The waterfall graph is the easiest one to use for the comparison, and as others have mentioned, you can look at 0-200 Hz for a more detailed view of the bass, but you should also look at what they do to the full spectrum 20 Hz -20 kHz.

Your room has room modes that depend on the width, length, and height. If you use the following "Room Mode Calculator" you will know the directions for each room mode if you point at a specific one and look at the little 3D room. You will see if they go from floor to ceiling in just the corners, or if they stretch between the opposite walls, and so on. That's why none of us, without full knowledge of your room and without a full set of measurements, can for a certain say what your bass traps are doing in your room.

This is the calculator: https://amcoustics.com/tools/amroc

One more thing. If the calculator is somewhat "off" and is not showing the same room modes as your measurements, you must figure out what the big opening to the room is adding to the equation and calculate with that.

 

[slacki]

When you have a friend helping you lift the bass traps

maybe i should clarify that a bit. its not that easy. he lives about 10km away, has to travel by train and bus. so its not easy for me to get those tests.
i made a couple of tests with and without traps, i have them stored and can access them any time with REW or upload them. But next time to make tests is probably when i destroy/un-build(?) the traps. correction: next tests will be when i move the open side facing the room, thats an easy thing i can do by myself. after that i decide if i either uninstall them or keep them, depending on the outcome.

 

[FeddyLost]

I think if you still have wooden boxes, you can check out Helmholtz resonators stuffed with CIB.
They might be useful.

Helmholtz Calculator

 

[Geert]

I think if you still have wooden boxes, you can check out Helmholtz resonators stuffed with CIB.

Wooden tuned bass traps are not a solution for small rooms. And certainly not if you're limited to installing only a few of them. They're also not a valid rookie DIY solution, even when you have experience it can be challenging to get it right.

 

[FeddyLost]

Wooden tuned bass traps are not a solution for small rooms. And certainly not if you're limited to installing only a few of them. They're also not a valid rookie DIY solution, even when you have experience it can be challenging to get it right.

In case TS already have rigid wooden enclosures and would like to remove one or more side walls, he can take drill/hole saw and try to make tuned HH LF absorbers for exact freqs.
There is no cheaper idea of increasing absorption below 100 Hz in such volume.
In case of fault he can always turn this box around and have open CIB again.

 

[Geert]

In case TS already have rigid wooden enclosures and would like to remove one or more side walls, he can take drill/hole saw and try to make tuned HH LF absorbers for exact freqs.

To what frequency are you going to tune them, knowing the room has a lot of different room modes (resonance frequency) and reflections which interact?

What if you can't place the tuned traps at the walls causing the worst room modes?

Did you ever design and built a tuned absorber and measured how well they meet the design and how much they absorb in practice?

Have you ever drill hundreds of holes in plywood?

Just a few references:

• https://www.kissyourears.com/pages/broadband-vs-tuned-absorbers: "broadband absorption is your first go-to point of action in terms of treating your room"
• https://gikacoustics.eu/the-basics-bass-traps-diffusion-panels/: "You can start by treating your corners with GIK Tri-Traps for example. We recommend starting with corners first as this is usually the place where you’ll get the most bang for your buck as far as frequency response and decay time". (GIK Tri-Traps are also broadband absorbers, the 'Range limiter' version with a flexible membrane)
• https://musixon.org/2021/07/02/low-end-acoustics-article/: "Resonance absorbers can take up a lot of space and are much more complex to build and tune accurately. For that reason, most small to medium rooms should rely on the good old open-back panels"

 

[goat76]

In case TS already have rigid wooden enclosures and would like to remove one or more side walls, he can take drill/hole saw and try to make tuned HH LF absorbers for exact freqs.
There is no cheaper idea of increasing absorption below 100 Hz in such volume.
In case of fault he can always turn this box around and have open CIB again.

Good suggestion.

It's probably hard to get it exactly right, but if so, it will work as a tuned bass trap and be more effective for a more narrow and problematic frequency band. And to know which room modes are particularly strong in those corners where the bass traps are placed, OP could use the "Room Mode Calculator" I suggested in my last reply.

 

[Geert]

Since the 'drill some holes and turn the box around if it fails' idea is still being supported despite the reference articles I might as well share a small practical detail; it's not going to work at all.

Opposed to porous absorbers, a Helmholtz resonator needs to be closed (airtight, except for the port holes of course).

 

[FeddyLost]

To what frequency are you going to tune them, knowing the room has a lot of different room modes (resonance frequency) and reflections which interact?

I'd check waterfalls in MLP and suggested location of absorbers. Then I'd try to catch longest tails and subjectively nastiest frequencies into simulated absorption peak.

Did you ever design and built a tuned absorber and measured how well they meet the design and how much they absorb in practice?

Yes. A lot of work, and mediocre result due to bad design solution (heavy membrane, shallow boxes, corner location). Kind of disappointing experience, but still obviously working.

Have you ever drill hundreds of holes in plywood?

50x120 cm with 10 cm distance means 60 holes per front panel. I'd not call this very problematic. Just some weekend experiment.

Opposed to porous absorbers, a Helmholtz resonator needs to be closed (airtight, except for the port holes of course).

Exactly. Backside shall be glued to architectural wall with sealant.

Anyway, it's just a proposal if TS have time and will for experiments. Maybe a little more education than just throwing out plywood used for existing boxes.

Also, If TS would like to stay with porous absorbers, he can ask guys from Caruso about combination of different materials within given volume. Like 045-040-035-air.

But for getting something correct and EASY(!) below 100Hz in any rectangular room and symmetrical placement I'd still recommend multi-sub configuration if possible.

 

[Flaesh]

for example: http://www.acousticmodelling.com/ml...s32=2&d32=500&v32=3000&s42=2&d42=500&v42=3000

 

[slacki]

It's all in in the graph settings, but I don't have access to REW right now.

Unfortunately i am somehow not able to get 20..200hz in the RT60 Decay. But what i can do, i upload the measurement file. maybe someone with REW is able to tell me, if the bass traps do something "good" to the decay.

sidenote: i changed the volume level a little bit during these measurements as they took couple of hours and i was watching a movie between them. but i guess that does not change anything in the decay

 

[slacki]

and here is the measurement with the closed side (traps) and the open side facing the room

As this looks, guess i disassemble the traps and make a measurement without any wood at all. I will see if i can somehow tape the isobond together.

 

[Geert]

and here is the measurement with the closed side (traps) and the open side facing the room
As this looks, guess i disassemble the traps and make a measurement without any wood at all. I will see if i can somehow tape the isobond together.

You see the traps are leveling out the low end, more specifically doing a great job of improving that huge dip you had around 85Hz. That's a very import frequency band in the low end. EQ-ing won't fix a dip like that.

Who would have thought

 

[slacki]

So you also agree in disassembling them, so they are fully "open" without any wood at all?
Asking because its a heck of work. No idea how many screws i used, but it was a lot.

 

[sam_adams]

So you also agree in disassembling them, so they are fully "open" without any wood at all?
Asking because its a heck of work. No idea how many screws i used, but it was a lot.

To make them more effective without having to come up with a way to keep the material together, cut out large openings in the panels. Crude example follows:

It will reduce the weight and increase the exposed surface area. Do it to the sides and top. You could wrap the box with porous fabric to hide the wood frame.

 

[slacki]

this is even more work than removing the screws. have to remove the isobond, then get a saw and cut the wood, what will produce a lot of sawdust

 

[Geert]

So you also agree in disassembling them, so they are fully "open" without any wood at all?
Asking because its a heck of work. No idea how many screws i used, but it was a lot.

At the side where the traps are near the window, is there still a piece of wall left next to the windows or is the window over the full width of the room? If it's all window I would keep the wooden side of the trap next to the window in place. So you actually end up with a corner made in wood, and 2 open sides facing the room. Glue the panel you remove on top of the side facing the window to make it more rigid. Just wrap a few straps of duck tape around the whole construction to keep the Isobond in place.

 

[slacki]

yes, its all windows. I have a curtain that sits in the corners - its quiet big. when i only remove that one side, i need my colleague because its still too heavy for me alone to lift them up :/
Does the wood do anything when its between the window and the isobond?

 

[goat76]

yes, its all windows. I have a curtain that sits in the corners - its quiet big. when i only remove that one side, i need my colleague because its still too heavy for me alone to lift them up :/
Does the wood do anything when its between the window and the isobond?

Didn't you make any measurements of the room without the bass traps at the same time without moving the microphone or changing any levels, the measurements with and without bass traps don't seem to have been made at the same time. Wasn't your initial idea to get rid of the bass traps altogether?

I think measurements of the room with the bass traps facing to the wall, with the traps facing into the room, with the traps facing to the sides, and without the traps altogether would have given you a more complete picture of all the options you have.

 

[slacki]

Wasn't your initial idea to get rid of the bass traps altogether?

Yes, that would be awesome. But i can also live with the isobond itself, as i can easily move it (if i e.g. need to clean or so). But getting rid of them would be great - and thats what i would do if they do not help improving room acustics - or if i can get the same result with 2 subs.

I think measurements of the room with the bass traps facing to the wall,

thats not that easy. I made 4 measurements with the traps. Then i made 4 without. But that took hours as i can not do that alone. In the meantime i do stuff, watched a movie, changed the volume of the sub etc.
Next thing is that there is a drillions of possible combinations i could measure. E.g. i could place the sub in 4 locations, then remove the upper traps, only left traps, only right traps, measure again 4 times, move the traps so they face the room open/closed, etc. - this is just too much. i made those measurements but they are not 100% accurate, as i changed the volume. but the microphone is always on the same spot.