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How much bass trap/panel am I expecting to have to tame the bass below 500Hz?

Skylinestar

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Here is an RT60 decay graph, played from my left speaker, right speaker and subwoofer together. It seems everything under 500Hz is crazy, exceeding 1 second. (In fact, it is bad with 1Khz and lower.) I can't imagine how a normal house y'all living in has value around 600 milli seconds and lower (based on my readings in various forums).
FYI, the room has concrete walls and floor.
How much panels do I realistically have to place around the room to tame it? To bring 1 second to 500 millisecond seems like a mission impossible?

Screenshot 2025-01-23 135600.jpg
 
It's doable but it might take covering 25% of the room (including ceiling) as a rough rule of thumb.

There are a few types of treatment that really work for bass - membrane, VPR, Helmholtz and binary diffusers. Also, super thick absorptive traps.

Depending on your budget it's possible to really get this under control, your situation isn't really that unusual.

Do you already have all the furniture in the room that you intend to? It works as "natural' acoustic treatment in most cases.
 
Some points to make.

1. Typical rooms have a rising noise floor (EDIT: rising noise floor in the bass region) in the low frequency region. Typical room noise is usually about 35-40dB. Yours seems to be below 25dB which is suspiciously low - it indicates to me that your curve has not been adjusted with an SPL meter. Regardless, if you extend your SPL range down to 0dB you will see your noise floor. Why is it important? Because a rising noise floor can give the appearance of more bass "ringing". So the first thing to do is make sure you are actually looking at bass decay rather than a rising noise floor. A 45 second sweep has about 90dB of noise rejection. Take five 45 second sweeps and average them. That will give you a really clean measurement to look at.

2. The DIN 18041 target for RT60 has varying decay times for room volume and intended application. It is more generous in the bass region. The tolerance can be up to 1 second for very large rooms. If you give me your room dimensions (W, D, H) I can calculate your DIN 18041 for you.

3. Bass does not form reverberant fields in a small room - they form modes. A room mode has the appearance of extended decay. Make sure you do not confuse a mode with decay. Modes can be improved with EQ.

4. The room is not the only source of bass ringing. Don't forget the subwoofer. If the driver itself keeps ringing (as may happen in some poorly designed subwoofers, or if a note is played at the driver's resonance frequency Fs) it will show up in the waterfall plot.

Diagnosis comes before treatment. I am not sure if you have diagnosed the problem correctly.
 
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Quarter wave tubes works really good for resonances down to 20hz if you have the space
Below ~40hz the tube dia has to be at least 35cm

I have found they are a bit more effective then Helmholtz and take up far less space.
Can be layin behind the sofa for ex.
I do have a niffty excel sheet for calculation but it is in Swedish.
1737629679661.png
 
First off, do an RTA measurement of your room with no audio playing to check the noise floor. If you want accurate decay times the measurement needs to be 50-60dB above this at all frequencies.

It is relatively easy to ballpark the absorption area needed for a certain RT60 if you have a rectangular room.


For example, a 20x15x8ft room aiming for .6 second RT60 needs approximately 199sq ft of absorption, with an absorption coefficient of .17.

There are some caveats.

The first being that the Sabine and Eyring formulas are only approximations. They don't apply to low frequencies in small rooms because they are not reverberate fields.


The second is that concrete is a worst case scenario for bass. The transmission loss below 100Hz is significantly higher than a brick or wood/drywall structure, so more energy is trapped and the absorption area needed will rise.

The third is that the absorption coefficient needs to be targeted, if you are using porous absorption it has to be the right thickness and density. The goal is to balance your decay rate, if you treat only mid and high frequencies you will have a room that lacks spacious qualities in music yet has boomy bass.
 
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I do have a niffty excel sheet for calculation but it is in Swedish.

That looks very interesting; I'm doubting between building a Helmholtz resonator or similar to bring down a +-40Hz room mode. Care to post the Excel file itself? I'm Dutch-speaking so most of those Swedish words don't event need translation for me because they look so similar :)

If you just lay the tubes on a level floor do they start rolling around when music plays, i.e. do they need a bit of support to stay in place?
 
@Keith_W and back to front which ain't possible in typical small room so minimum phase close to wall.
@Skylinestar I am much more concern what a hell is happening in highs there? Are you sitting close to the wall behind you or it's actual room problem as there acoustic treatment is rather efficient both absorbers and diffusers.
First fire up REW when you can find time with low ambient noise, set the lv to uper mid 70's so that mods are active but not running wild and things ringing. Do a measurement pass and PEQ the first big bump free by hand the best you can and still not to kill it entirely in RT but in level with similar small ones (room). Put the PEQ in the chain and do another swap. Now let him do EQ to target but be certain to match the SPL levels for it correctly! Put it on and enjoy. You might/should want to ensure normalisation and equal loudness compliance also.
 
Here is an RT60 decay graph, played from my left speaker, right speaker and subwoofer together. It seems everything under 500Hz is crazy, exceeding 1 second. (In fact, it is bad with 1Khz and lower.) I can't imagine how a normal house y'all living in has value around 600 milli seconds and lower (based on my readings in various forums).
FYI, the room has concrete walls and floor.
How much panels do I realistically have to place around the room to tame it? To bring 1 second to 500 millisecond seems like a mission impossible?

View attachment 423207

I think you should ignore the decay times under 100 Hz for now and focus on trimming down the decay times above that range. The "under 100 Hz" needs more complicated solutions or very thick absorption panels, but I also find that that range doesn't tend to get in the way of the music as the energy often falls rapidly under 60 Hz for most tracks.

My room has concrete walls and ceiling, and by just adding three absorption panels (two measuring 1200x600x100 mm and one measuring 1200×975x100 mm) to the room, a lot happened to the decay times down to about 125 Hz which is the specified effectiveness of the acoustic panels I bought. It looks like you may need a few more panels than I need for my room, but I suggest you buy say 4-6 panels to start with and see how it measures, and then take it from there.

The pre-made panels I use have a hard backside so I use them without any air gap to the wall, but if you go with panels that don't have that you can add an air gap of say 100 mm to make them even more effective lower down in the bass region.

Anyway, the GIF picture below shows what only three panels did to the decay times in my normal-sized living room (5.08x4.28x2.59 cm). So again, don't try to solve everything in one go, buy (or make) a few panels at a time, re-measure, and hear what it does to the sound and you will know what the next step should be. The goal is to get the decay times as even as possible besides lowering them overall.

1737636683489.gif
 
That looks very interesting; I'm doubting between building a Helmholtz resonator or similar to bring down a +-40Hz room mode. Care to post the Excel file itself? I'm Dutch-speaking so most of those Swedish words don't event need translation for me because they look so similar :)

If you just lay the tubes on a level floor do they start rolling around when music plays, i.e. do they need a bit of support to stay in place?
I will fix it later today.
Important is to have it adjustable and that you later lock with silicone.
A bit of filling in the tube to lower the speed and over the hole you have a bit of cloth with medium tension.

Cut the tube 20cm shorter then needed, glue a plug or a plate at on end.
Cut a 40cm long tube, cut out a narrow strip on the length so you can press it and it fits in the longer tube, that is your adjustable end piece.

Put some speaker filling in the tube, Very loose (!) and use rubber band o put the top cloth in tension.
Then it is time tune the pipe, at working freq the cloth vibrates.
Last, secure the end pipe and everything else.

You can have tubes laying on the floor, to prevent rolling you can have a square end piece.

They loose a bit of efficiency where there is high pressure as in corners.
 
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Also, super thick absorptive traps.

Depending on your budget it's possible to really get this under control, your situation isn't really that unusual.

Do you already have all the furniture in the room that you intend to? It works as "natural' acoustic treatment in most cases.
How thick are we talking about here? 12"?
I guess that is super thick bass traps at ALL room corners (vertical and horizontal)? That is a lot of money.
Yes.
 
2. The DIN 18041 target for RT60 has varying decay times for room volume and intended application. It is more generous in the bass region. The tolerance can be up to 1 second for very large rooms. If you give me your room dimensions (W, D, H) I can calculate your DIN 18041 for you.
Here's a sketch. It's not actually a closed room. The left and right sides are opened to stairs.

Untitled.jpg
 
How thick are we talking about here? 12"?
I guess that is super thick bass traps at ALL room corners (vertical and horizontal)? That is a lot of money.
Yes.
For very low frequencies 12" is really just scratching the surface.

The issue with porous traps is they only absorb sound to the extent that the air is actually in motion, i.e. they are based on 'velocity'.

At the walls, you have high pressure but low motion of air. Naturally the wall stops the air from moving, right?

For mounting on walls, "pressure" traps are considered better, i.e. VPR or membrane. Or use helmoholtz resonators.
 
I don't know. Doesn't bass penetrate wall like nothing?
It does so by transferring the motion into the wall itself, the air can't go through the wall, that's all. So the pressure is high but at the surface of the wall the velocity is ~zero. This is why foam / fiberglass don't do much against bass when attached to the wall.

However, BAD panels can have a good effect down to 100hz and even below, and they're just perforated sheets with special patterns that go on top of absorptive panels. I have read the book where the math behind this is explained, but it's beyond me.

Having looked more at VPRs again, it seems like you need a 1.0 - 2.5mm thick steel sheet which is rather thick and heavy. (not crazy expensive, maybe $200 for a 4'x8' piece, but probably hard to work with.) So I think if I have one recommendation it's to look into BAD (binary array diffuser) treatments.
 
Here is your RT60 target.

1737690333721.png


Ignore the measurement in red/green. For Acourate's RT60 calculator to work, it needs a graph to be loaded. So it's a random graph. Look at the thick red lines which I highlighted for you - that's the upper/lower RT60 target calculated for your room and the DIN 18041 target.
 
First off, do an RTA measurement of your room with no audio playing to check the noise floor.

I second that. Find your noise floor and make that the bottom of your waterfall. Things will look quite different then, I'm sure.

Besides the waterfall plot, are there other symptoms of excessive bass reverb, like boomy or woolly bass?
 
If we try to be a little realistic here, how many success stories have you guys seen where people have managed to solve the bass problems under 100 Hz in a normal living room?

I think OP should start to focus on the whole area from 100 Hz and upwards, and to solve that he needs as many as possible broadband absorbers that are at least 10 cm thick with air gaps, and even better 15 to 20 cm thick panels.

After he has solved most of the problems with the above mentioned solution, he can then start experimenting with BAD panels and such. But to start with such suggestions, I think it will risk to kill the improving acoustic project before it has even started. Just saying. ;)
 
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