Perforated plate or porous absorber behind speakers against SBIR? and: Plate resonator against dip at 80Hz?

[DJBonoBobo]

Hello!
Inspired by a Neumann advertising video in which absorbers from "greenacoustics" are used, I am considering using them to improve my listening room. At the moment I'm still using old, temporary Basotect absorbers. I would like to replace them with a good solution. It is important to me that it is harmless to health, since I sleep and work in the room and often spend about 20 hours a day there. They are filled with Caruso ISO Bond. This is how they look:

And in the video:

Here are the measurements of the three absorber types, that "greenacoustics" offers, overlaid - DE-BASS is a plate resonator tuned to 80Hz, DE-MITTER ist a perforated plate absorber tuned to 160Hz, BB-STANDARD is a porous absorber (10cm Caruso ISO Bond). As you can see, according to their published measurements they seemingly work well together:

Here I have overlaid the measurement curves of the absorber types plus the isobar diagram of the KH310 and my current frequency response. I don´t know how well you can see it, but maybe you can see i have still problems with a dip around 80Hz (despite using 2 subs and 2 AVAAs already), and the FR is pretty uneven up to 1000Hz. From 600Hz downwards, the directivity of the KH310 starts getting more wide.

In the descriptions from Greenacoustics and also in the Neumann video, it is always recommended that the standard absorber should be at the top and the DE-MITTER or DE-BASS at the bottom.

I now have the following questions:
- Is it possible that the 80Hz-resonator helps with my 80Hz-dip?
- What should i place directly behind the speakers? The DE-MITTER or the DE-STANDARD? Beware that at the moment i already use 10cm Basotect behind the speakers - i guess there will be not much difference between 10cm ISO Bond (10000kpa) and 10cm Basotect (14000kpa).
- Will the DE-MITTER still work well if it is placed below the speakers (like in the Neumann-video)?

Right now my temporary setup looks like that:

 

[FeddyLost]

There are 2 questions with such setup.
1) are you sure it's SBIR
2) isn't easier to put speakers as close to the wall as possible and then EQ exscessive LF?

 

[DJBonoBobo]

1) No, not 100% sure. It just seemed logical to me.
2) The speakers are already as close as possible. 10cm from the wall, and there is a 10cm basotect absorber already between them and the wall. Closer ist not possible because of the footplate of the stands.

BTW i ordered 2 of the DE-MITTER and 2 of the BB-Standard. I´ll check them out. I guess i will just try what everyone is suggesting, first, and put the DE-MITTER at the bottom. I´m curious how much of a difference this will make compared to the 10cm basotect behind the speakers and the 25cm basotect below the speakers that i already have.

 

[abdo123]

Basotect is one of the best materials (and most expensive too) for sound absorption.

Seems like a waste to throw them away.

 

[DJBonoBobo]

Basotect is one of the best materials (and most expensive too) for sound absorption.

Seems like a waste to throw them away.

I wont. I think i´ll buy some wooden frames for them and place them somewhere else.
I´m hoping to get a better result in the area between 100-300 Hz with the new absorbers.

 

[DJBonoBobo]

This is what BASF is publishing for Basotect:
It´s main advantage is that the absorbtion is very linear. But below 400Hz it does not look very effective. I don´t know how much those graphs can be compared to the ones i posted above, though.

 

[abdo123]

How thick are the green accoustics triple combo panels?

Their website is down atm.

 

[DJBonoBobo]

How thick are the green accoustics triple combo panels?

Their website is down atm.

Standard: 10cm
DE-MITTER and DE-BASS: 15cm

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[abdo123]

If you have a dedicated space and you don’t switch speakers often i would just build a baffle wall from porous material. Should be way more effective.

 

[FeddyLost]

It just seemed logical to me

80 Hz is around 1 m ... 10 cm from wall, even including speaker depth, can't induce such low notch.

 

[DJBonoBobo]

80 Hz is around 1 m ... 10 cm from wall, even including speaker depth, can't induce such low notch.

Ah, you mean the 80Hz dip - no, i don´t think that´s SBIR. I think the 80Hz-thing is mainly the ceiling height + ear height almost exactly in the vertical middle of the room. I don´t know how to handle this correctly.

 

[DJBonoBobo]

If you have a dedicated space and you don’t switch speakers often i would just build a baffle wall from porous material. Should be way more effective.

Sadly i am not able to do that properly. I have at least three left hands... ;-)

 

[FeddyLost]

I think the 80Hz-thing is mainly the ceiling height + ear height almost exactly in the vertical middle of the room. I don´t know how to handle this correctly.

Is your ceiling only 220 cm high?
You can change height of your listening place and/or speakers according to REW Room sim.
It's the cheapest way.
Treating the ceiling with a lot of absorbers, effective at 80 Hz will not be easy/cheap at all.

 

[DJBonoBobo]

Is your ceiling only 220 cm high?
You can change height of your listening place and/or speakers according to REW Room sim.
It's the cheapest way.
Treating the ceiling with a lot of absorbers, effective at 80 Hz will not be easy/cheap at all.

No, 250cm. But my ears are at around 123cm - and i can´t change that because that´s the only ergonomic height for me.

 

[DVDdoug]

I'm not a acoustics expert but 80Hz has a wavelength of 14 feet so it's probably the room as a whole and that's best handled with bass traps.

I assume the "80Hz resonator" is classified as a bass trap and I know there are tuned traps, but I think most bass traps handle a wider range of frequencies so they don't have to be tuned. By absorbing the bass that would otherwise be reflected, they smooth-out both the standing wave nodes (dips-cancelation) and anti-nodes (bumps-reinforcement) for smoother overall bass. ...I have no idea how many traps, or how much area, you need to cover.

If you haven't read enough already... RealTraps has quite a bit of information. And they want to sell you stuff and/or their services.

 

[abdo123]

I'm not a acoustics expert but 80Hz has a wavelength of 14 feet so it's probably the room as a whole and that's best handled with bass traps.

I assume the "80Hz resonator" is classified as a bass trap and I know there are tuned traps, but I think most bass traps handle a wider range of frequencies so they don't have to be tuned. By absorbing the bass that would otherwise be reflected, they smooth-out both the standing wave nodes (dips-cancelation) and anti-nodes (bumps-reinforcement) for smoother overall bass. ...I have no idea how many traps, or how much area, you need to cover.

If you haven't read enough already... RealTraps has quite a bit of information. And they want to sell you stuff and/or their services.

Keep in mind that if you want to treat 80Hz with traditional porous material you would need something at least 40 cm thick and the surface area requirements are not off the table.

That’s why (15cm thick) tuned membranes exist, i think it’s quite a smart thing to do to design products the way they do so they can actually synergise with each other. But you’re looking at 60% of the room covered with 15 cm panels vs 20-25% of the room covered with 40 cm panels.

Both solutions are valid for different circumstances.

 

[abdo123]

No, 250cm. But my ears are at around 123cm - and i can´t change that because that´s the only ergonomic height for me.

Then there is no way you’re suffering any consequences from the height mode around 80Hz because you’re sitting right at the middle.

But you can adjust the speakers’ height (and toe them up/down) so the SBIR is within a range manageable with porous material.

 

[DJBonoBobo]

I bought 2x DE-MITTER and 2x BB-Standard a ran some tests. Please note, this is not a proper review because i am not qualified to do everything correctly. I made this for myself, and you can do with it what you want. I don´t know how these absorbers will behave in your room.

Always left speaker only without sub and without DSP, 1 sweep at around 1.66m distance from speaker at LP. Var smoothing.

Here are a few examples of what i tried so far.

1. "Baseline" (black): Almost no front absorbers. I forgot to make one completely without.

2. DE-MITTER behind the speakers (stuffed to the corners) - blue line

3. A little bit of basotect behind the measured speaker - green line (a bit worse than the DE-MITTER, but not as much as i expected)

4. BB-STANDARD behind the speaker instead of basotect - turquiose (practically the same result as Basotect)

5. Best result i could achieve so far with added basotect wedges on the sides and a BB Standard in the middle - green line (blue is from No 2 above)
The one in the middle is not doing very much to the FR, but without it i had i little bit of flutter echo when clapping my hands.

And some more tests i made at another day - i forgot to switch the AVAAs on, so there is some deviation in the bass compared to No 1-5 - please ignore everything below 100 Hz.

6. Sort of clean looking, but bad measuring (basotect wedges in the corners, BB-Standard on top of DE-MITTER, like seen in the Neumann video):

7. Same without the wedges (red line; blue is No 6)

8. The other way round (green line; red is No 7) - big difference between 300-500Hz, the rest almost the same.

What i learned:
- The wrong absorbtion can actually hurt the FR and make it worse, even when using very thick material like Basotect. At least in my case. I honestly did not know that. I always thought you can´t do much wrong when using thick porous absorbers.
- The measurements of the manufacturer don´t reflect what the products are doing in my room. I´m not saying they are wrong, but they did not behave like i expected. Looking at the measurements i thought the BB Standard should have been more effective between 300-500Hz, but it is not.
- 10cm Caruso ISO Bond seem to do more or less the same as 10cm Basotect.
- To me at least it seems impossible to know what the absorbers will do unless i measure by myself.
- I am optimistic getting a slightly better result in the end compared to my previous, messy and temporary setup with less, but more carefully selected and placed absorbers.