Q: How to get rid of room's bass resonance?

[Timur]

Hey there,

I'm in the slow process of setting up my home-studio room and have just begun to thing about acoustic treatment. I already knew that there is audible comb-filtering happening from reflections which should be tameable with some mid/high frequency absorbers and maybe some diffusers. But the most prominent problem that I want to get rid of first is bass resonance and for that I need help from experienced forum members. kfhkh

Yesterday I took a quick and dirty measurement which revealed this:



Noticing the prominent spikes in the 80 and 125 Hz bands I send a sinusoid through my speaker and easily could identify two very outstanding resonances at 75 Hz and 118 Hz. Further testing revealed that the 75 Hz resonance only happens with sound coming out of my left speaker while the 118 Hz resonance happens with both speakers.

I used some internet-calculator to find out that 75 Hz roughly corresponds to my rooms width of 4.60 - 4.70 m, so that may be the culprit, but why does it only happen with one speaker then whose distance from the side walls doesn't seem to be in any natural fraction of 4.60 m.

Even more strange is the 118 Hz resonance which corresponds to about 2.90 m. First I suspected the ceiling to be responsible for that one. The original ceiling height was about 3.30 but it got lowered down in the past (presumably with only air filling the inbetween). But the current height is only 2.79 m and the only connection to 2.90 m I could find is that the upper side of the speakers chassis is 1.45 m away from the ceiling.

1. So where do I start looking for the source of the resonance? What did I miss here?

2. Will simple corner traps help to reduce this kind of problem or do I need sophisticated bass trapping (which is harder to integrate into an apartment full of stuff)?

3. Will EQing with something like a Behringer DEQ2496 help if all other means fail?

4. Can I build/buy any other kind of acoustic treatment that might help with this (I thought about building a floating cloud with at least 10 cm foam-filling)?

Pictures of my room following in the next post

[Timur]

This is the front view of my working place. The backside bass-reflex port is about 35 cm away from the walls, the speakers are angled at 60° towards my listening position. The left speaker (75 Hz resonance) is about 1.97 m away from the left sidewall of my room. Both resonances are most pronounced/loudest in the 1/3 of the room where the speakers stand, remarkably the corners left and right in front of the table/behind the speakers and drop considerably when going towards the breakthrough. The corner behind the table are far less pronounced. Interestingly the line in front of the wardrobe left to the table is almost free of resonances (lower volume). Because of that I thought that maybe the room's deepth in beetween the backside wall and the breakthrough wall might be a problem, but it measures around 3.50 - 3.60 m, so no clear indication for these frequencies.



This is the rearview to the break-through into the adjacent living-room, the corner walls are still standing. Bass resonances mostly only happen within the audio-room, not within the living-room eventhough the speakers point straight through the breaking. There is only a very slight bass boost audible when sticking my head into one of its corners while the resonances are almost omnipresent in the audio-room (dropping in volume the further away I get from the axis of the speakers). Remarkably the ceiling of the living-room is about 5-10 cm lower than the one in the audio-room.



These are pics of the four corners, as you can see there are two windows to the right side of my table, both about 2.20 height and nearly 1.20 wide, adding an additional 20 - 25 cm to the width of the room.

Front left, front right, rear left, rear right (click to enlarge):

[Meef Chaloin]

from the picture it looks like you're closer to the right side wall than the left...that might account for the one speaker problem

[Timur]

Turning down the "Room Control" switch (bass) of my speakers to -2 dB leads to slightly better overall bass response, but the peaks remain. The multiples (like 236 Hz) are far less pronounced.

[Timur]

from the picture it looks like you're closer to the right side wall than the left...that might account for the one speaker problem

I already gave that a deep thought, but I can't come up with a reason since the left speaker that is experiencing the 75 Hz resonance is standing away from both walls in no natural fractions of 75 Hz also it doesn't matter wether the other speaker is turned on or off the 75 Hz resonance remains largely the same.

The 118 Hz resonance volume on the other hand changes correspondingly when turning on/off the second speaker (louder with both speakers running).

I checked again and noticed that the 75 Hz resonance remains loudest inside the whole half of the room while the 118 Hz one only remains loudest in the first third.

[Bunky Freaks]

I built eight of those and moved them around in my studio (try and error like) until it sounded fine to me:

http://www.gearslutz.com/board/bass-tra ... traps.html

I also added "wedges" to the two front corners of the room to control bass and sub bass frequencies.

All this treatment helped a lot to free the room from flutter, generally it sounds really good now but it did not entirely flatten the resonances in the bass frequencies (3 peaks between 60 and 140 Hz). These peaks are now broader and less loud, in my case this is acceptable. I consider the room treatment to be done. Better room acoustics would increase costs enormously (aka room-in-room builds without parallel walls).

So I suggest to start with building a set of diy bass traps like in the link i provided or buying similar commercial products if you can spare the cash. Though don't expect wonders in normal "square domestic home studio rooms" regarding the dampening of certain frequency peaks in the bass domain.

[Bunky Freaks]

one small addendum: try to move the whole setup away from the wall into the middle of the room and see if it helps. Monitoring in corners is generally to be avoided due to the building up of standing waves.

[Timur]

Thanks for the hint. I once stumbled upon that thread before, but that was before my room was setup. I am also thinking about the "super chunk" method of building your own cornertraps. But I don't like the idea of handling mineral wool and having it hanging around relatively open in a living-space (even with something in front of it). I prefer foam, but that's expensive. Maybe coldfoam mattresses will do, especially since these come easily at 18 - 25 cm thickness and are very dense.

[Timur]

one small addendum: try to move the whole setup away from the wall into the middle of the room and see if it helps. Monitoring in corners is generally to be avoided due to the building up of standing waves.

Then I wouldn't be able to pass through the room anymore.

[chris vine]

And if you don`t fancy the rectangular bass traps try tubetraps......

here is a DIY link

http://www.teresaudio.com/haven/traps/traps.html

and then you can also get the originals premade at

http://www.acousticsciences.com/tubetrap.htm

+1 on getting yr monitors away from the wall.

[Bunky Freaks]

one small addendum: try to move the whole setup away from the wall into the middle of the room and see if it helps. Monitoring in corners is generally to be avoided due to the building up of standing waves.

Then I wouldn't be able to pass through the room anymore.

That's the price you have to pay if you have a home recording studio, hardly possible without haveing a messy room

If you place your speakers near walls you will always run into problems, there is no way you can avoid this, its as simple as that. Play some music, walk around in your room and compare the frequency response of "near walls" and "middle of the room", this should yield huge differences..

[Bunky Freaks]

Thanks for the hint. I once stumbled upon that thread before, but that was before my room was setup. I am also thinking about the "super chunk" method of building your own cornertraps. But I don't like the idea of handling mineral wool and having it hanging around relatively open in a living-space (even with something in front of it). I prefer foam, but that's expensive. Maybe coldfoam mattresses will do, especially since these come easily at 18 - 25 cm thickness and are very dense.

I used dense stone wool panels to fill the frames, which has larger fibers than glass wool and "should" be fine. anyways I sealed the traps tightly to minimize any health risk...

[Angstrom]

Maybe coldfoam mattresses will do, especially since these come easily at 18 - 25 cm thickness and are very dense.

I think the difference between furniture foams and acoustic foams is that acoustic foams are 'open-cell' , meaning that the sound waves can penetrate the material and get absorbed within the greater surface area in there.
With closed cell foams a greater proportion of the energy just bounces off the surface instead of getting entangled in the material.

I could be wrong here (about bass frequency absorption), but that's my understanding. It's certainly that way for mid-range and high frequency damping.

I've not built a bass trap as my room is too small to take them.

[Moody]

That wooden cabinet next to your left speaker is probably what is resonating.

[djsynchro]

The backside bass-reflex port is about 35 cm away from the walls

That's too close