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

[knotkranky]

Yeah that resonant freq area is a rough one. I find it's usually the floor to cieling that's most of it. Even ceiling to desk or under the desk can cause probs. Corners too, walls not as much. Set your speakers up in a few different spots just to hear what yer room is doing. move the desk out of the way. If it's still a prob, get some nice headphones and amp.

[Moody]

Bring your speakers in front of the desk and try it again.

[nebulae]

nice colors, timur, you very very gay man you! rock on!

[Timur]

Thanks for all answers so far. I found out that the 74/75 Hz resonance is reflections from the left side corners. The reason why the right speaker/corners don't reflect these is most likely because:

a) there's a heavy metal (no pun intended) CD shelf standing in the front right corner

b) the front right corner is 'broken apart' by a wooden box that houses heating pipes

c) the wall from the front right corner to the window is only 35 cm which leaves less surface for reflecting a 4.60 m long wave.

d) the rear right corner has only 53 cm of wall remaining to the breakthrough which again leaves less surface for reflecting the 74/75 Hz wave.

Yeah that resonant freq area is a rough one. I find it's usually the floor to cieling that's most of it.

Yes, after carrying around my speakers and swapping both speakers and channels I conclude that I am fighting the resonance of the room itself for which speaker placement really doesn't seem to matter that much. I just wonder how the frequencies I found relate to the measurements of my room, but most likely it's just more complex than what I thought about or there's something hidden behind the brought down ceiling. I will look for some nice corner traps and use an EQ to get rid of he remaining very specific resonance frequencies.

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...

I will give this a second thought, but foam is still my prefered material. Thanks again for the links and hints.

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.

You are right about middle and high frequencies. The idea of acoustic foam is to kind of 'entangle' the soundwaves within the foam. But that doesn't work with bass frequencies going into wavelengths of several meters. For those you preferably build a 'second wall' (like a wood or fiberglass plate) in front of the room's wall that is detached from the wall with some foam/wool like material. When the bass soundwave reflects/bumps into that second wall the plate is pushed into the foam/wool and thus absorbs the energy much like crush-collapsible zone of a car.

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

To the contrary! Since it's stuffed up with clothes it even absorbs bass frequencies (similiar to what I described to Angstrom). The bass is considerably less pronounced when I'm standing in front of the cabinet or put the speaker in front of it.

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

That's too close

Partly, having speaker so close to the back wall results in generally emphasized bass, but that's not my problem here. I can simply switch the "Room Control" of the speakers to -2 dB to get that right. According to Yamaha atleast about 1.5 m would be ideal. Anyway that wont really help with my specific problem, because even when those resonance frequencies are less pronounced they still exist even when the speaker is far enough away from the wall.

[Timur]

nice colors, timur, you very very gay man you! rock on!

Hehe, hey, it wasn't me who wanted to have half of the kitchen walls in pink while the rest was red. I can tell you it was very difficult to find a combination of pink and red that did not look like candy paper (and left me painting those walls half a dozend times). After two years my lady admitted that the red walls look better than the pink ones and I had to repaint them again.

Here's Mr. Snowman right in front of the formerly pink kitchen wall!

[Moody]

Move your speakers around the cabinet then.

[Timur]

Move your speakers around the cabinet then.

Doesn't help, because the corner behind the cabinet is still reflecting gallore! And don't ask me to put the cabinet into the corner, you don't put century old cabinets into your appartment to hide them into a corner behind the door. It need some room to breath to both sides of it. I'd rather die with style than live without.

[Tone Deft]

there is audible comb-filtering

how can you tell it's comb filtering?

long posts, I didn't read anything about the hardwood floors (nice floors btw), those are great for reflections, get a big huge cushy rug to cover the hardwood.

[Timur]

there is audible comb-filtering

how can you tell it's comb filtering?

Just an uneducated guess, but another guess is that I'm also fighting some standing waves here, cause there's all that fluttering sounds happening when moving my head around.

[Tone Deft]

just busting your balls a bit. I think people usually go with 'standing waves' and 'interference patterns', comb filters are a process, not a result, IMO. I see them when I do a sample slip in a digital signal. dunno, this is a case where I wish a real DSP head could chime in, I can see how a reflection cancelling the original would be a comb filter, never heard it described that way, it just struck me as odd.


maybe you've seen this demonstration of standing waves
http://www.youtube.com/watch?v=MPcJbb5Qfj0

at low frequencies the spaces between peaks (lots of sand) and troughs (no sand) is large, at high frequencies it's smaller, so moving your head around you notice changes in lows much more than changes in highs.

think of that demo above as a slice in space of what's happening in your space. but I'm sure you already know that, you're The Timur after all!!

[Timur]

I think people usually go with 'standing waves' and 'interference patterns', comb filters are a process, not a result, IMO.

So let's say: There is comb filtering happening?!

at low frequencies the spaces between peaks (lots of sand) and troughs (no sand) is large, at high frequencies it's smaller, so moving your head around you notice changes in lows much more than changes in highs.

Unfortunately I notice those easily upto 10 kHz and higher. I wish my ears were as bad as my room or vice versa.

think of that demo above as a slice in space of what's happening in your space. but I'm sure you already know that, you're The Timur after all!!

Yep, and I had a physics class in school, too!

[Tone Deft]

I think people usually go with 'standing waves' and 'interference patterns', comb filters are a process, not a result, IMO.

So let's say: There is comb filtering happening?!

I like that.

at low frequencies the spaces between peaks (lots of sand) and troughs (no sand) is large, at high frequencies it's smaller, so moving your head around you notice changes in lows much more than changes in highs.

Unfortunately I notice those easily upto 10 kHz and higher. I wish my ears were as bad as my room or vice versa.

the wavelength of 10kHz is ~3.5cm, makes sense.

think of that demo above as a slice in space of what's happening in your space. but I'm sure you already know that, you're The Timur after all!!

Yep, and I had a physics class in school, too!

yeah, I just love that demonstration because you can literally SEE what's going on. I go to concerts and stuff with that video in mind, funny when you notice nodes in a room, or I'm just a dork like that, bobbing my head in and out of sweet/dead spots.


anyway, throw a big cushy rug on the floor.

you can also play with monitor placement. I know to tune a studio they'll grab an SPL meter and walk around and move the subwoofer until the readings are pretty mellow, same can go with monitors, where they are, where they're pointed.

[Khazul]

just busting your balls a bit. I think people usually go with 'standing waves' and 'interference patterns', comb filters are a process, not a result, IMO. I see them when I do a sample slip in a digital signal. dunno, this is a case where I wish a real DSP head could chime in, I can see how a reflection cancelling the original would be a comb filter, never heard it described that way, it just struck me as odd.

Comb filters are made by tiny fixed delays that cause alternate cancellation and boosting of frequencies in multiples of the inverse delay time - effectively its articially induced interference patterns.

As sound take a finate time to travel through air - thats also like a delay - muliple paths take different times - so the same effect can result.

Clap you hands in a room, if you can pick up flutter echos then it will probably also suffer from nasty combing in places as well.

Usually its audiable as a result of primary reflection - ie monitor wall/desk/ceiling to you - ie a single bounce with minimal attenuation. It often comes from a shallow reflection from a hard surface - plaster and glass are especialy bad.


Timur -

BTW - the 75Hz or so is likely the second harmonic (for an approx 4.6m dimension), the 125Hz band (ie the 118 you mention) will probably cover the 3rd harmonic.

Whats the room length - ive extracted 3.3m, 4.6m so far... whats the other dimension and current height?

[Tone Deft]

Khazul, have a cookie. check wikipedia or google your explanation is awkward.

[Khazul]

Which bit?

My maths for this stuf is about 25 years old, but its easy to visualize it - overlay a pair of sine waves of the same wavelength, but displace one of them along X axis (time), and mentally picture the result of adding the Y offsets.