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Massive bass reverberation

Matias

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I have finally built my long dreamed dedicated listening room, and it has been very challenging getting the acoustics right. The system is set up on the long wall of 5.0 x 4.15 x 3.25 m (Sepmeyer's type B ratio for what it's worth). Windows and door are sealed and with acoustic treatment, walls made of concrete blocks, wood on the floor.

When I started with the empty room the overall decay was crazy high. I could call believers and preach a sermon here like a cathedral's.

So I bought 14 panels of 10 cm depth 120 x 60 cm filled with high density rock wool (64 kg/m3). I ended up with 4 on the front wall and 4 on the back wall, 3 on each side. Plus a nice colorful rug under my recliner chair.

Surely decays above 150 Hz went down a lot and it's comfortable now around 450 ms. Yes, some will say this is still on the high side but I am fine with it for now.

My real problem, and why I am posting this thread, is my massive peak and reverberation around 40 Hz. In the beginning with panels only the bass was muddy as hell and making me crazy.

So after some emails with the great folks from GIK, they suggested I should be adding large columns on the corners to absorb bass. Since they don't have local distribution in my country, and importing would be crazy expensive, I ordered locally 4 of these massive 60 x 60 x 120 cm blocks with lighter density rock wool (32 kg/m3). They are heavy and was hell getting them into the room, where they are stacked 2 and 2 on each front corner. They look like giant fridges each 2.4 m high!

Well of course this reduced the bass decay a lot, but still not enough. It is listenable but somewhat distracting still.

Problem is that I am running out of space to stack more of these giants, let alone the price and trouble getting them in the room.

At the same time there are far smaller and apparently very effective active solution from PSI called AVAA, but they are surely expensive at 5.2k usd a pair.

Back to GIK they also have tuned absorption with their Scopus for 275 usd each (+shipping and customs here).

Moving the speakers around helps to balance the fundamental bass peak around 40 Hz, and EQ does the rest. But decays are not solved by both.

Below a picture from the speaker, the panels and the huge column.

Any ideas how to improve this situation?

room render 09-2022.jpg


IMG_20220916_165608.jpg


rt60 decay-1.jpg
 
Last edited:

abdo123

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It seems like you need some mid-frequency absorption in there.

Anyway air-flow resistivity is CRUCIAL at low frequencies, so you might wanna contact Caruso-Iso bond and see if you can get something with low air flow resistivity or make your own Helmholz resonators.

1663360334657.png
 

fpitas

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I've seen people put absorbers up in the room corners near the ceiling to solve that.

And Massive Bass Reverberation would be a great band name.
 

ppataki

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I have finally built my long dreamed dedicated listening room, and it has been very challenging getting the acoustics right. The system is set up on the long wall of 5.0 x 4.15 x 3.25 m (Sepmeyer's type B ratio for what it's worth). Windows and door are sealed and with acoustic treatment, walls made of concrete blocks, wood on the floor.

When I started with the empty room the overall decay was crazy high. I could call believers and preach a sermon here like a cathedral's.

So I bought 14 panels of 10 cm depth 120 x 60 cm filled with high density rock wool (64 kg/m3). I ended up with 4 on the front wall and 4 on the back wall, 3 on each side. Plus a nice colorful rug under my recliner chair.

Surely decays above 150 Hz went down a lot and it's comfortable now around 450 ms. Yes, some will say this is still on the high side but I am fine with it for now.

My real problem, and why I am posting this thread, is my massive peak and reverberation around 40 Hz. In the beginning with panels only the bass was muddy as hell and making me crazy.

So after some emails with the great folks from GIK, they suggested I should be adding large columns on the corners to absorb bass. Since they don't have local distribution in my country, and importing would be crazy expensive, I ordered locally 4 of these massive 60 x 60 x 120 cm blocks with lighter density rock wool (32 kg/m3). They are heavy and was hell getting them into the room, where they are stacked 2 and 2 on each front corner. They look like giant fridges each 2.4 m high!

Well of course this reduced the bass decay a lot, but still not enough. It is listenable but somewhat distracting still.

Problem is that I am running out of space to stack more of these giants, let alone the price and trouble getting them in the room.

At the same time there are far smaller and apparently very effective active solution from PSI called AAVA, but they are surely expensive at 5.2k usd a pair.

Back to GIK they also have tuned absorption with their Scopus for 275 usd each (+shipping and customs here).

Moving the speakers around helps to balance the fundamental bass peak around 40 Hz, and EQ does the rest. But decays are not solved by both.

Below a picture from the speaker, the panels and the huge column.

Any ideas how to improve this situation?

View attachment 231325

View attachment 231326
Is that ringing also accompanied by a peak in the frequency response?
If yes then you could linearize that with digital room correction filters
That will surely decrease your ringing too
 

Curvature

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It seems like you need some mid-frequency absorption in there.

Anyway air-flow resistivity is CRUCIAL at low frequencies, so you might wanna contact Caruso-Iso bond and see if you can get something with low air flow resistivity or make your own Helmholz resonators.

View attachment 231328
It's not that.

The important factor here is which physical force is active. Porous broadband absorbers are velocity based. Low frequency absorbers are pressure based. In a real room the absorption coefficient of a porous absorber at 20Hz is 0, particularly an absorber mounted on a wall, where velocity is also 0.

@Matias I'm sorry to say but it looks like GIK sold you mostly useless product as far as the corner traps go. Talk to RPG and use their LF products. Much more expensive but worth it.

Helmholtz resonaters need to be big and are generally too high Q to be effective. You would need several tuned to various overlapping frequencies. The problem area is 30-60Hz, or one octave!

Besides that the graph looks very strange. Are you sure you don't have persistent LF noise?
 
OP
Matias

Matias

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Is that ringing also accompanied by a peak in the frequency response?
If yes then you could linearize that with digital room correction filters
That will surely decrease your ringing too
Yes, bass peak and huge decay are around 40 Hz. And I do use room EQ to flatten the bass (and mids and treble too, as I prefer it). But still bass reverberation is a little distracting.
 

Curvature

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A real room doesn't have a room mode for one continuous octave, it's an artifiact of the R60 view in REW.
It's several modes flattened by EQ, and possibly environmental noise. Unclear at this point exactly what is happening. A single point measurement is limited data.
 
OP
Matias

Matias

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It's not that.

The important factor here is which physical force is active. Porous broadband absorbers are velocity based. Low frequency absorbers are pressure based. In a real room the absorption coefficient of a porous absorber at 20Hz is 0, particularly an absorber mounted on a wall, where velocity is also 0.

@Matias I'm sorry to say but it looks like GIK sold you mostly useless product as far as the corner traps go. Talk to RPG and use their LF products. Much more expensive by worth it.

Helmholtz resonaters need to be big and are generally too high Q to be effective. You would need several tuned to various overlapping frequencies. The problem area is 30-60Hz, or one octave!

Besides that the graph looks very strange. Are you sure you don't have persistent LF noise?
GIK did not sell me anything. They have been really friendly in helping me for free since they could not sell here in my country. That is very noble from them, I have nothing but good will towards them.

The graph I posted is after the huge columns. Before was worst still, believe me, a lot higher decay up to 150 Hz.... Edit: below a measurement without the columns and EQ'ed. Horrible bass decay!

No persistent LF noise. When the room is closed it is dead silent. Plus I live in a very silent street in a residential neighborhood, so as good as it gets.

rt60 decay.jpg
 
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OP
Matias

Matias

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It's several modes flattened by EQ, and possibly environmental noise. Unclear at this point exactly what is happening. A single point measurement is limited data.
That graph is without EQ, raw speaker output in the room, microphone at the MLP.
 

Curvature

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Why? Even if it was 5 meters deep?
The closer sound travels to a wall, the lower the absorption. It is workable but ineffiecient.

In the 1970s some studios used meters of porous material.
 

Curvature

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GIK did not sell me anything. They have been really friendly in helping me for free since they could not sell me here in my country. That is very noble from them, I have nothing but good will towards them.

The graph I posted is after the huge columns. Before was worst still, believe me, a lot higher decay up to 150 Hz....

No persistent LF noise. When the room is closed it is dead silent. Plus I live in a very silent street in a residential neighborhood, so as good as it gets.
Above 100Hz-200Hz the solutions are easy.

Did you actually measure the noise level with nothing playing?
 

kthulhutu

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If you want to target a specific frequency range, tuned absorbers are your best bet.

For dealing with general bass problems, 4 inch panels are too thin. Ideally you need to cover ALL wall boundaries, including not just the corners but the ceiling-wall boundary as well.
 
OP
Matias

Matias

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Above 100Hz-200Hz the solutions are easy.

Did you actually measure the noise level with nothing playing?
No, not yet. Below the measurement if it helps.

If you want to target a specific frequency range, tuned absorbers are your best bet.

For dealing with general bass problems, 4 inch panels are too thin. Ideally you need to cover ALL wall boundaries, including not just the corners but the ceiling-wall boundary as well.
I already think those panels are think and heavy, making them thicker still would be hard. Plus the expense of wasting them and ordering new ones. I would prefer to add stuff than replace right now.
 

Curvature

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No, not yet. Below the measurement if it helps.


I already think those panels are think and heavy, making them thicker still would be hard. Plus the expense of wasting them and ordering new ones. I would prefer to add stuff than replace right now.
Does seem like there is no environmental noise.

I think your problems begin a lot further up. If you look at the clarity ratio there's a nosedive under 250Hz despite all of your current treatment.

You can buy brackets that space your current panels away from the wall, which is very effective if you like further HF absorption, although it doesn't seem necessary.

1663363295448.png
 
OP
Matias

Matias

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Let's focus on the elephant in the room first - the bass. Mids and highs, let alone diffusion, would be icing on the cake.
 

Curvature

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Here's an experiment: use an HPF and filter out all of the lows and mids. Slowly drop the frequency of the knee until you start hearing mud. That will give you a good foundation for a subjective sense of the problem and effectiveness of treatment.

Besides that, congrats on the room. I'm envious of your current set of problems.
No it's not lmao.
Happens when I read inattentively and am too eager to reply.
 
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