Control Room Nulls

[ONZ]

First post for me so Hi to all,

I have recently converted an outbuilding into a control room.I have some experience, have had some advice, and done some research.
Having run some tests I think I have some issues which I would appreciate some input on. I have too pretty severe nulls ,42hz front to back and 48 hz side to side. The listening position, at first, seemed very bass light ,but having spent a day or two mixing stuff and checking mixes in the real world, things translate better than I expected and I have read that lots of bass traps can take some getting used to.The listening position is very close to the nulls though and I've had to bring the monitors pretty close together and lean in a bit which isn't great.
I thought I'd put a fair bit of bass trapping in. I have 4 RealTraps which are membrane type traps (3 hanging above the desk at a 45 degree angle) and a fourth on a side wall. Speaker wall corners have bass traps (DIY). The top of the back wall (vaulted part) is slated resonator (DIY) which is tuned around 40hz with a 1200mm void behind. The speaker bridge is again homemade 2400x1200x300 with 3 layers of 100mm RW45 with heavy sheets of vinyl between and 100mm gap behind. The sofa on the back wall is also stuffed with absorbent insulation.
I have a drawing with a fair bit of info but am happy to provide more detail. New to this forum and it is telling me that a single pdf is too large to post so here is a link where it can be downloaded (its only 4mb). https://we.tl/t-txvea9bPSi

many thanks

[Gregwor]

Welcome!

Did you take REW tests including a baseline measurement so that we can see what treatment did what? We need to see an mdat of your room. It would also be great to see some real pictures as well as exact placement of speakers and your head in the room.

Thanks!

Greg

[ONZ]

Welcome!

Did you take REW tests including a baseline measurement so that we can see what treatment did what? We need to see an mdat of your room. It would also be great to see some real pictures as well as exact placement of speakers and your head in the room.

Thanks!

Greg

Thanks Greg, I don't have access to the data at the moment but here are some photos which I hope will help.

[DanDan]

Well done, looks well finished. Can you tell me what is between the speakers and the Front Wall? And what distance between the front of the speaker (cone) and the FW.
Speaker and listener locations are a hugely powerful treatment with a very low price. Sitting mid width at often half height we often encounter three first axial nulls.
I would recommend finding optimum speaker and listener locations, but starting with the speakers AT the FW, virtually touching.
https://realtraps.com/art_front-wall.htm

DD

[Soundman2020]

Hi there ONZ, and Welcome to the Forum!

There's quite a few things visible in your photos and description that are "questionable", to put it politely, and likely related to the problems you are experiencing in your room.

As Greg said, we'd need to see the REW data to get a better idea of how the room is behaving right now, and hopefully you have a series of MDAT files, showing the results at various stages in the construction and treatment of the room. Here's a link to a tutorial I wrote a while back on how to set up and use REW for these tests: http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21122 . Hopefully you did all that before, but if not then now is a good time to do so, to make sure you have things calibrated correctly. So to get started, pleas do that, and post the MDAT file so we can take a look.

Based on the dimensions in your PDF sketch, the modal issues for your room are a close match to what you are experiencing: Your 1.0.0 mode is at 42.6 Hz, and your 0.1.0 mode is at 49.2 Hz. The slight discrepancy could be due to any number of valid reasons, but it's safe to say that you have large modal resonance issues at those frequencies, due to lack of bass trapping. It's a small room, so it will need a lot of bass trapping, and there doesn't seem to be much visible in there.

There are also room layout issues that need resolving: more on that later. (Speaker locations, mix position, desk, etc.)

The listening position, at first, seemed very bass light ,but having spent a day or two mixing stuff and checking mixes in the real world, things translate better than I expected

That says more about your mixing skills, than it does about the room! It doesn't mean that the room is "sort of OK": it just means that you are able to mix in a deficient room. That's nice, but you'd be able to mix a lot better in a good room, and your place does have the potential to be good. Even though you managed to mix in there, I'd bet that it was an effort: you really had to concentrate, and try things multiple times to get it right. And there's also the question: How much better could it have been if the room were helping you, not fighting you?

I have read that lots of bass traps can take some getting used to.

I'm not sure I'd agree with that. Once you mix in a room that has excellent bass response, there shouldn't be much "getting used to it" required! Once you hear a room like that, and experience the clean, tight, smooth, full bass, you'll be able to mix effortlessly. Good bass trapping, properly done, such that you get flat frequency response AND flat time-domain response, should not need much learning or getting used to: it just sounds natural, and right.

The listening position is very close to the nulls though

Which implies that the room is not set up correctly! Please measure from the front wall to the spot where your ears are located at the mix position: not leaning forward or backward.... just sitting up straight at your desk, in the position you originally expected to be. Also measure the height of your ears above the floor at that location.

I've had to bring the monitors pretty close together and lean in a bit which isn't great.

Correct! It isn't great at all! That messes with your sound-stage, and also plays havoc with your psycho-acoustic perception of the sound coming from your speakers. Even though you did manage to mix a bit like that, I'd hazard a guess that the mix didn't sound naturally wide when you listened in other places: it probably sounded "squished up", for want of a better term, with not a lot of depth to it. And you'll end up with a sore neck and back if you try to mix like that every day...

I thought I'd put a fair bit of bass trapping in. I have 4 RealTraps which are membrane type traps (3 hanging above the desk at a 45 degree angle)

Membrane traps only work if you place them at the pressure peak for the problem you are trying to kill. They won't work if you tilt them at a 45° angle, since only a small part of the wave-front will be arriving at the tap face at any given time: the wave-front will sort of "wash over" the trap, reaching it bit by bit at different parts of the trap at different times, so the trap won't ever resonate well. It needs to be flat against the wall, such that all of the wave-front hits it together at the same time. That could be part of your problem, but isn't all of it by any means.

What frequency are those traps tuned to? Membrane traps have a specific frequency at which they absorb, and that must match the frequency of the problem you are trying to solve.

Speaker wall corners have bass traps (DIY).

Are you talking about the small panels across the diagonal of the front corners? They are not big enough, and not in the correct location. There's some activity in the middle of the corners, yes, but the best spot for bass traps is the "tri-corners", where the two walls meet the floor, and the two walls meet the ceiling. That's where things are the most interesting for bass traps. To get the best effect, your traps need to cover the entire room height, from floor to ceiling.

How did you build those traps? What are they made of, and what are the dimensions?

The top of the back wall (vaulted part) is slated resonator (DIY) which is tuned around 40hz with a 1200mm void behind.

Helmholtz resonators are hard to tuned accurately. Here's the predicted tuning for yours (assuming you used something like 19mm thick slats):

ONZ-predicted-slot-tuning.png

Yes, there is a "peak" at around 40 Hz, but I wouldn't call that tuned. The Q is rather low, and the calculator could not even identify the tuning. That might be doing something but only for the 1.0.0 mode. It's not doing anything at all for the 0.1.0 mode, or anything else, and it is also reflecting all other frequencies from the rear wall, straight back to your ears, arriving in less than the Haas time, and at a rather high level, I would presume.

The speaker bridge is again homemade

I'll get to your speaker setup in another post later, but the way you have your speakers and desk set up there is certainly not helping your room acoustics! That will also need fixing...

2400x1200x300 with 3 layers of 100mm RW45 with heavy sheets of vinyl between and 100mm gap behind.

For what purpose? What is the MLV meant to do in there? Where did you get that design from?

The sofa on the back wall is also stuffed with absorbent insulation.

What type of insulation?

In short, the first thing we need to see is the MDAT from how the room is right now, done according to the tutorial I linked you to above, and hopefully additional MDAT files from earlier stages in the treatment process.

There is hope for the room, but the treatment is going to need some modification...


- Stuart -

[ONZ]

Well done, looks well finished. Can you tell me what is between the speakers and the Front Wall? And what distance between the front of the speaker (cone) and the FW.
Speaker and listener locations are a hugely powerful treatment with a very low price. Sitting mid width at often half height we often encounter three first axial nulls.
I would recommend finding optimum speaker and listener locations, but starting with the speakers AT the FW, virtually touching.
https://realtraps.com/art_front-wall.htm

DD

If I understand you right between the speakers and the front wall is absorption,50mm RW45 with 25mm air gap then the wall itself.Distance from cone to FW is 54cm to front of absorber (+75mm to wall). Cone to side wall is 94 cm (+75mm to wall) and the listening position (head) to front of FW absorber in 150cm with the room length being 4040cm wall to wall. The rear wall including door is all BAD panel diffuser absorber with a tuned resonator panel above.

I have tried multiple speaker positions starting tight to the wall but where they are seems best, which is actually with the rear of the cabs sitting on the speaker bridge (this is also a bass trap as mentioned) and the front of the cabs sitting on the small ledge of the console giving a tilt.looks and feels all wrong but they image is best here and this is where they sound best.

[Soundman2020]

.looks and feels all wrong but they image is best here and this is where they sound best.

When you do the REW testing I mentioned in my reply above, please do one set of tests with thing set up in that way that you say sounds best, and another set of tests with things set up the way the room was originally designed: speakers in their design locations and angles, mix position at the original design location.

- Stuart -

[Soundman2020]

...front wall is absorption,50mm RW45 with 25mm air gap then the wall itself....
...the listening position (head) to front of FW absorber in 150cm...
... room length being 4040cm wall to wall....

If my math skills are holding up, that places your head about 157.5cm from the front wall, which is about 4% of the room length.... And your room is 40 meters long....

Doesn't sound right... I think you mean the length is 4040 mm, not 4040 cm...

- Stuart -

[ONZ]

...front wall is absorption,50mm RW45 with 25mm air gap then the wall itself....
...the listening position (head) to front of FW absorber in 150cm...
... room length being 4040cm wall to wall....

If my math skills are holding up, that places your head about 157.5cm from the front wall, which is about 4% of the room length.... And your room is 40 meters long....

Doesn't sound right... I think you mean the length is 4040 mm, not 4040 cm...

- Stuart -

Sorry yes 4040 mm.

[DanDan]

I have tried multiple speaker positions starting tight to the wall but where they are seems best, which is actually with the rear of the cabs sitting on the speaker bridge (this is also a bass trap as mentioned) and the front of the cabs sitting on the small ledge of the console giving a tilt.looks and feels all wrong but they image is best here and this is where they sound best.

For years I used the same set of floor standing monitors. Celestion Ditton 66, 18Hz -40K in their day.
Here at soundsound.ie I placed them where they sounded best in my inedequately treated small concrete bunker, aka, Control Room.
Like you I gravitated to a spot where the stereo width and depth were best.
Later as I studied acoustics I discovered that is was lack of bass which was causing this preferred imaging.
It can be a tad humbling when the Science calls out the Art. But it is a better truth.
Now my speakers are almost touching the wall, and some Eq is used to help with the side effects of that. Similarly a bit of honk is taken out.
The final result is real firm bass all the way down, clear natural mids, great imaging.

DD

[ONZ]

Thanks all so much for you input.

There's obviously an awful lot to do which is somewhat overwhelming.I'm not sure that it's not beyond my abilities to provide the measurements required and then address the issues with the help of the forum. I totally understand how much better my workspace will be if I can trust it and I would love to sort it. I need to pick myself off the floor,take a breath and asses my options. I have the added problem of a full diary of bookings making it difficult to find time for analysis not to mention ripping the room apart. One option might be to get professional help and stump up for it, even if just to get accurate measurements. RPG are actually local to me and I believe reputable. I shall post again when I have some more data, thank you again.