Front L vs Front R Corner Bass Trap Symmetry?

[anabolique]

Hi everybody,

this is my first post so I hope You wont be too harsh on me if I "misbehave" somehow...its not my intention..

I've heard that symmetry is important but more in the front part... My room is small and I have a double window in the front wall which is a bit off to the left. The result is I that I have less space for front left then for front right superchunk...

In another forum Ethan Whiner said to a guy that its not important for rear bass traps to be of the same size... is that because symmetry is less important at the back ?

[Soundman2020]

Hi "anabolique", and welcome!

In another forum Ethan Whiner said to a guy that its not important for rear bass traps to be of the same size... is that because symmetry is less important at the back ?

Exactly. And also, low frequencies are not directional, so it isn't so necessary to have symmetrical bass trapping.

Of course, if you CAN get the entire room symmetrical, then that would be better, but if not then at least the front half has to be symmetrical.

I've heard that symmetry is important but more in the front part...

Yes! In fact, it is critical. If you want an accurate stereo image and good sound stage, then symmetry is very, very important.

My room is small and I have a double window in the front wall which is a bit off to the left. The result is I that I have less space for front left then for front right superchunk...

Then make them as close as possible, or at the very least make sure they have the same total volume of insulation. Have you considered maybe partly covering one side of the window? If the front of your room is not symmetrical, then your stereo image will suffer. Like I said before, it is not so critical for lows, but still important.

- Stuart -

[anabolique]

Yeah, I get that bass frequencies are omnidirectional, its just that porous absorbers are broadband, so I was wandering about higher frequencies that it affects..


Anyway, situation has changed since my last post, I am starting the search for a new space.
Regarding that, I will search for "normal", rectangular room.. but things like windows and doors that can jeopardize symmetry , I would probably need advices on that..

I dont get, why is rear symmetry of room less important, since speakers emmit (at least at higher frequencies) sound towards the rear wall and their reflections are of bigger concern from rear wall ? Basically, there are no first reflections of the front wall, so why is symmetry more important at the front?

[Soundman2020]

its just that porous absorbers are broadband, so I was wandering about higher frequencies that it affects..

True, but bass traps are often faced with thick plastic or thin paneling, to reflect the highs back into the room while only allowing the lows through.

but things like windows and doors that can jeopardize symmetry ,

They shouldn't, if the room is designed carefully. In other words, if there is a window on the left wall, then leave the section opposite that on the right wall as drywall or something similar, rather than absorption. And if you have a door that is opposite from an absorption panel, then hand a similar absorption panel on the back of the door. etc.

I would probably need advices on that..

That's what we're here for!

I dont get, why is rear symmetry of room less important, since speakers emmit (at least at higher frequencies) sound towards the rear wall and their reflections are of bigger concern from rear wall ?

The first reflections happen in the front part of the room, between you and the speakers, so that is critical for symmetry: for example, of you have first reflections happening on the left side but not the right, then your sense of direction and of tone are all messed up, so both your stereo image and sound-stage, as well as your EQ, is out of whack, and you'll find it really hard to get a decent mix in there. And even if you do manage to make it sound good in the room, it won't sound good anywhere else: Your mixes wont' "translate" to other locations. Since all reflections at the front of the room are well within the Haas time, they mess up your perception of sound greatly: you just are not hearing what the speakers are saying. The reflections interfere with the direct sound, so you are not hearing the same things that is coming out of the speakers: the sound you hear has been distorted, modified, mangled. And since those "front half" reflections are also loud reflections, that puts them inside the 20 dB threshold, so it even messes up your sense of the room response.

But the rear of the room is different: Firstly, it should be treated to attenuate reflections to get them below the 20 dB threshold, and secondly the room should be big enough that reflections form the rear wall arrive at your ears outside the Haas time, so your brain can pick up on the fact that they really are reflections, not part of the direct sound. Reflections form the rear should be diffuse, delayed, and quiet, if the room is designed correctly.

Basically, there are no first reflections of the front wall,

Well, that isn't really true. SBIR, comb filtering, phase cancellation, and other artifacts are absolutely related to reflections off the front wall. That's why soffit-mounting the speakers makes so much sense: it eliminates all of those. So there would be no first-reflections off the front wall in a well designed room with correctly soffited speakers, yes, but if the speakers are on stands, then there are reflections going on at the front wall, and causing major problems.


- Stuart -