GUIDE FOR SETTING UP YOUR ROOM

[MirrorProfiles]

A quick update! putting the monitors on stands and getting them a little bit closer to the wall has definitely improved the low mid buildup, and it has significantly shifted the SBIR upwards in the frequency spectrum. However, the mode at 123 and the cancellation at 104 Hz have remained the same. I should probably take more acoustic measures, but I'm not sure where to use the bass traps most effectively. As I move around the room, the mode is loudest in the four corners at mid-height and right in the centre of the front and rear walls. I am now considering placing two GIK 244 bass traps directly between the monitors on the wall to reduce the axial mode. The GIK modules have the highest effect at exactly 125 Hz.

Have you tried your room dimensions in Amroc? you can see which frequencies are affected by which boundaries.

If it’s the mode associated with room length, and you have space, leave the front wall reflective and treat the rear wall. 125hz should be possible with absorbers, when you get to below 100hz you need resonance based traps. GIK soffits and monster traps are good, and their scopus panels are good too so long as they’re used right. The 100hz dip could well be another boundary interference dip from the floor, I wouldn’t worry too much about it.

Build up is always highest in corners (and at surfaces generally, corners have several combining), but absorbers aren’t particularly effective. Porous absorbers work best when the wave is moving, and at boundaries the velocity is 0 and pressure is highest. So something with a pressure based element will be most effective in these areas, especially when tackling frequencies below 100hz.

You’ll probably find the positioning to be quite forgiving when placing bass traps. I’d recommend putting your room dimensions in amroc, and then try the panel in a few positions and measure if possible. and always check the time domain, the frequency response doesn’t really show much of what’s going on in the room.

 

[MirrorProfiles]

My room has a huge 130Hz peak, I use REW or ARC to calibrate, I can't listen to my monitors (room) without calibrating anymore, I'm spoiled.

It’s quite normal to have a big peak in that area, especially in most rooms with “normal” ceiling heights. It’s definitely worse in rooms with bigger desks and no cloud, and more so if there are dimensions that are similar or multiples of that (quite common too).

What does the time domain look like?

 

[James Freeman]

What does the time domain look like?

Didn't bother with waterfalls yet but I'm sure it's abysmal. Without correction I can litarally hear the bass notes ring and echo for a second when I pause the music.

 

[TheTrueZoltan!]

@MirrorProfiles Thanks for your tips and advice! One question: I have noticed that the room mode at 123 Hz is particularly pronounced in the corners and in the middle of the front and rear walls, in each case halfway to the ceiling. I already have bass traps hanging in the front corners and the rear wall is covered by a bookshelf. I have now considered hanging bass traps (GIK 244) on the front wall between the monitors to reduce the build-up of the wave there. However, I noticed that you advised leaving the front wall reflective. Can you explain the reason for this?

 

[MirrorProfiles]

Can you explain the reason for this?

For frequencies that low (below the Schroeder frequency), they don’t fire out the speaker like a ray but it’s more like pressure changing at that frequency. This means it can be a bit more forgiving on where you reduce the energy of that frequency - it’s related to the modes of the room.

Keeping the front wall hard means:

- you aren’t overly dampening the room. Our ears hear what’s in front of us and it’ll feel more natural if that surface is reflective. No point making the room dead and uncomfortable to be in unless it’s working effectively.

- the panel is most effective from around 125hz upwards, but generally speaking, it’s more effective higher up and less so in the bass. Low bass comes out of the speaker omnidirectionally, and gradually gets more directional as you go higher in frequency. The panel won’t be too effective for those low frequencies anyway. You can absorb more effectively in other positions in the room.

- The speakers work more efficiently if they can use the energy from that front wall. If you absorb behind it, the speaker works harder so more distortion/less headroom.

You can absolutely try the panel between the speakers, especially if there aren’t other spots you can put a panel easily. Ultimately you have to pick the most sensible compromises. Generally speaking, it won’t be the most effective area to treat and you can find somewhere else in the room that’ll do more good and less bad.

Are you able to try moving the panels off the wall a bit? so there’s a bit of an air gap behind them? Porous absorbers are velocity based and so work most effectively when velocity is high and pressure is low. Right against the wall, velocity is low and pressure is high, so absorbers aren’t going to be their most effective. A lot of rooms have a dip in the low end and then a peak around 120hz-130hz. Ceiling heights and desks etc can all emphasize those more.

Do you have a spectrogram or waterfall plot?

This Axial Mode Calculator can be helpful too: https://carltatzdesign.com/acoustic-tools/

 

[Orvillain]

Worth bearing in mind too, these panels are more effective with an air gap behind them. Don't put them flush against the wall. Try and leave 5cm or so behind them if you can.

 

[Orvillain]

Ah. Ed already said that. Ignore me!

 

[TheTrueZoltan!]

Yep, I know. My panels are already installed with a 5 cm air gap.

 

[TheTrueZoltan!]

[...] Do you have a spectrogram or waterfall plot? [...]

Here are some graphs from a REW measurement I just took. Looks like shit. While the most energy is around 125 Hz, the decay time is worst at around 95 Hz. I guess I need more bass traps.

SPL 1/12 Smoothing

Spectrogram

Waterfall

 

[MirrorProfiles]

I guess I need more bass traps.

Yeah, way more broadband absorption (which hopefully do as much as possible for the low end too) will do wonders for you. It’s not looking too bad at all, it just needs more treatment. Have you got photos of the rest of the room from different angles?

A cloud would help a lot, probably an ideal place to start for biggest gains. The good news is that basically every step you take from here should make a nice improvement to things. DIYing panels is a pretty cheap and effective way of doing it, you can make 6” panels for way less than what GIK would charge.

Maybe longer term I’d really consider the Neumann subwoofer but probably best to get the room more controlled first.

Also it’s worth doing the measurements for L and R seperately if you can be bothered. On the measurement screen there should be an option for sequential channels.

 

[TheTrueZoltan!]

Yeah, way more broadband absorption (which hopefully do as much as possible for the low end too) will do wonders for you. It’s not looking too bad at all, it just needs more treatment. Have you got photos of the rest of the room from different angles? [...]

Here are some photos. I have already contacted the fine folks at GIK to get a little more advice on what panels to buy and where to place them in the room. BTW, the picture above the computer is a DIY panel with 5 cm (yeah, I know, that doesn't do much) of rockwool.

 

[MirrorProfiles]

GIK’s soffit panels are the best thing they make (40cm deep), if you can get a few of those on either side of you they’d be really effective (they may need custom sizes to be able to stack them up but GIK can do that). Putting up a thicker cloud will help a lot too

 

[TheTrueZoltan!]

Fascinating. I have just entered the room data into ChatGPT and asked where in the room absorbers should be placed to be particularly effective against the room mode at 123 Hz and the reverberation time at 95 Hz. Within seconds I had a very detailed and, above all, easy-to-understand explanation as well as a graphical representation of the pressure points. As I had already suspected, the area right in the centre of the front wall is indeed problematic at 123 Hz. In addition, of course, all corners and edges.