Null at 100Hz - traps or subs?

[post78]

In an apartment studio with a bit of an odd setup, but overall it sounds quite good, minus a low frequency issue.
The room is a large rectangle, sort-of. It is 8'10" high and 14' wide. The length of the entire low frequency space is 27', but at roughly 14', there are partial walls on the left and right sides, leaving a 7' opening in the middle to the rest of the space. I think it's safe to call this a 27' long room for lower frequencies, but I could be mistaken.

I have to sit slightly off center as the right side has a built-in pull out bed space (storage), so I'm shifted a couple feet to the left.
I have 3" Roxul absorbers across the ceiling taking up 7'x4' between the three of them at first reflection points. I have a large round bookshelf full of randomly placed books (about 40 for now, need more!) filling up most of the 7' opening behind me and on those partial walls I've placed 5'x3' diffusers. There will be a large cushy chaise in front of the bookshelf for clients, a set of HEAVY theater drapes that I close while working just behind the bookshelf (quite effective in the vocal range) and a plush 9'x6' rug on the floor, but none of those are in the room right now. I've cut down to the basics to address some LF.

My monitors are Neumann KH 120 A and sit just 1.5' from the front wall... Apartment mixing, yay... I'm roughly 4.5' from the front wall, 6.5' from the left wall, and 7.5' from the right wall.

The response from 400 up is incredibly flat, thanks partially to the monitors and partially to the semi-treatment. The response between 150 and 400 aren't terrible, but will hopefully improve once the couch is in and perhaps when I address the frequencies below it.

I have a 10dB dip at just below 100Hz that I'd like to address. After playing the tone and listening/measuring around the room, I've found a massive build up on JUST the left wall, at the center point (of the 14' length part of the room), and especially where wall meets ceiling.

This is good for me since wall to ceiling is the only viable location for me to install traps.
Will a corner trap along that entire side help reduce the 100Hz null at listening position? If not, I'm afraid I might need to add a pair of subs in different locations to fill the hole, which isn't ideal in an apartment, but I'd do it. The ability to place the subs in better locations with delays and putting a high-pass on the mains might get me there, but I want to address the room first.

I've included a measurement with variable smoothing so we can focus on the lower frequencies. I've also included a couple images made with the room simulator, but the figures don't quite match my measurements. I think the partial walls is having some effect, but that's tricky math for me...

Thanks!

[post78]

I should mention, the back half of the room on the other side of the bookshelf is our living room, so I can't do a lot to that half.

[Soundman2020]

I have to sit slightly off center as the right side has a built-in pull out bed space (storage), so I'm shifted a couple feet to the left.

Then you do not have a usable layout! Sorry. But if your room is not symmetrical, then your mixes won't be either. Your first order of business should be to fix the problem such that you have a symmetrical room. If your left ear and right ear are hearing different acoustic spaces, then your mixes will not be working out well.

Your data looks a bit strange, and I'm inclined to think that your dip is not modal. But I would need the actual REW data file to see if I can figure out what is happening. Please upload it to a file sharing service, such as Dropbox, then post the link here. But you will need to re-do the tests at a higher level. You need to set up the system such that each speaker is producing 80 dBC when played by itself, and therefore both together will produce 86 dBC, which is the "standard" calibration level. Since you did your tests at less than one tenth of that, you might not be triggering all the modes. You also need to do three tests: one with just the L speaker on, one with just the R, and one with both. Do not adjust anything between tests.

Please also post photos of the room, an accurate diagram of the room showing the features you mentioned, and a description of where the mic was for the tests, as well as the make and model of the mic you used.

My monitors are Neumann KH 120 A and sit just 1.5' from the front wall...

Why did you chose that distance? How far are they form the side walls? What is the height of the acoustic axis? What is the toe-in angle? Where is the aim point in the room? How big is your desk, and what is on it? How are the speakers mounted, physically? Please mark all of those locations on your diagram, with the dimensions.

The response from 400 up is incredibly flat, thanks partially to the monitors and partially to the semi-treatment.

... and also to the variable smoothing you have applied in REW!

The response between 150 and 400 aren't terrible, but will hopefully improve once the couch is in

The couch will make some difference, yes, but not as much as you are hoping. Not by a long shot. The couch is far behind you, not in front of you, so it won't do much at all to change the frequency response of the room in the low mids...

I've found a massive build up on JUST the left wall,

Then you have an even bigger problem! Not only are you not located symmetrically in the room, but the room itself is not symmetrical.

If not, I'm afraid I might need to add a pair of subs in different locations to fill the hole,

If the dip is modal, then that would not work. You cannot fill in a modal hole by pumping more energy into it. All you succeed in doing, is making it deeper! Using subs to fill in a dip would work if it is SBIR related, yes, but not for modal issues.

I've also included a couple images made with the room simulator, but the figures don't quite match my measurements.

How did you arrive at the absorption parameters you are indicating in the simulation? Especial a floor that is 30% absorptive...




- Stuart -

[post78]

My monitor levels are set appropriately and the test was ran at 75 dB C-weighted, which is the recommended level and is most definitely loud enough for the room I'm in. I'll upload the file and respond to more of this later tofay. Thanks.

[Soundman2020]

the test was ran at 75 dB C-weighted, which is the recommended level and is most definitely loud enough for the room I'm in.

No. The recommended level is 86 dBC. That's the standard calibration levels for studios, cinemas, and theater systems. I'm not talking about if it is "loud enough for the room you are in". I'm talking about if it is loud enough for proper analysis and calibration. The REW manual talks about 75 dB, but I have no idea why. Perhaps because it was originally meant for home theaters, not studios. If you do not run your tests at a sufficiently high level, you will not get an accurate representation of how the room is behaving, period. So, once again, please set up your system so that each speaker produces 80 dBC using the REW pink noise test signal, which implies that both speakers together will automatically produce the required 86 dBC level. If you have more than two speakers, then you will need to reduce the level of each individual speaker accordingly, such that the total with all speakers playing coherent pink noise, is 85 dBC.


- Stuart -