Dear community,

I want to make this thread as straightforward as possible, but it is tough to keep things short when introducing the room I am working in. To set the ball rolling, I will try to focus on the most important things first. I am in the need to "rescue" a studio room that I joined, since I moved to a new city. It's definitely a tough nut. I am not entirely new to room acoustics, but have never been in the role of "designing" a room, neither would I claim being capable of. But I have been working through the master handbook, numerous GS threads and projects - now I feel like I understand a lot of approaches, but none feels like: Yes, let's do it this way. I want to discuss three "strategies" (more vague ideas) and decide on what sounds most promising. Then follow this direction.

The situation is as follows: I joined a musician who renovated most of this project studio room himself. Too bad most of the room layout was already finished/decided, then. Since I am an engineer 80% of my work time, my goal is to get the most out of this space for mixing and smaller recording purposes (essentially overdubs) The location within the city is really good and rent is affordable, so I want to put effort in this room. But I cannot just decide for myself, since we share the room.

Apparently, the typical acoustical treatment mistakes have been made: loads of high/mid absorption, few modal treatment and all but ideal room planning (he built a booth which I don't use because it sounds dull and the booth limits the "control room" position to one narrow spot).

Attached, you can see
- groundplan
- basic visualization (I used the GIK tool).
- measurement + .mdat file
- studio photos

The room measures can be taken from the pictures attached, it is very high and it is basically cubic, but the built in booth makes things a bit more complicated. The ceiling (both the "hard" and the suspended ceiling) is angled maybe 20 degrees. 3 of the 4 walls are gypsom dry board that were angled by the guys who put them in, in the hope of killing room modes (which it did not). This makes the room hard, if not impossible to calculate..

The "glossy" studio pictures show first setups where we mounted my speakers on his just for the first photo session.

My experienced main issues:
- not the 30Hz fundamental mode (probably axial between floor and ceiling), since this one is quite distinct and you can tell when mixing "aha, I know you"
- definitely the 80-100 Hz null and upward comb filters
- the peaks in the 300 Hz region make the room sound very boxy

From where I am now, I have 3 strategies / stages with different levels of effort.

1st: put lots of mineral wool between the speakers and hope for the best
Build a huge frame construction and load it with loosely packed mineral wool for bass absorption and less severe SBIR. The construction would go between the speakers and be about 2.5m high. Additionally tuned perforated panel absorbers covering the lower half of the corner bass traps might help. Though I fear the comb filtering at the LP will simply remain untouched.

2nd: strategy #1 + build a "fake suspended ceiling" over the control room
This would go right above the mixing spot and line up with the roof of the booth. Here, loads of losely packed insulation, angled absorptive panels/reflectors could be used. + Additionally tuned perforated panel absorbers. Regarding location, I would be in the zone of velocity maxima of the fundamental axial, but would this really help things? Has anyone experience in such a "middle" ceiling?

3rd: strategy #1 + Suspend the acutal ceiling (which is already suspended 20cm) of half the room (the area of the control room and the couch) about 1 metre and fill it loosely with insulation. This will have the most impact, but would require lots of persuasion.

The reason I ask before I just try and error is that my colleague, who is not too affiliated with acoustics, does not see the point in spending so much more effort in treatment, since the room is already "okay". Of course we are afraid of spending lots of time and money without knowing about the reward.

What I will definitely do:
- build solid speaker stands
- design back wall (where the couch is located) as a QRD type diffusor with broad wells for LF dispersion
- try tuning helmholtz type absorbers after the basic "rescue" treatment is done

I would greatly appreciate any advice, considering the amount of text and pictures so far and I'll be glad to share any further info you need to chime in.

Julien

No suggestions, anybody? Any thoughts on the measurements? I would be so glad if I could get any advise on how to best treat those dips and peaks in the spectrum..

You need to put alot more bass trapping into the room. You can place more insulation like fluffy or safe n sound behind the existing panels to balance their absorbsion better across the spectrum. Stuffing the existing ceiling is not a bad approach either.

You also have to be sure your speakers and listening location are in the best place.

If your not using the booth, tear it down, and re-purpose the materials as movable gobos for some isolation when tracking.

As a final measure you can use eq to help chop a couple db off some peaks, and shorten decay.
Boggy on speaker location

Speaker placement methods


How to find the listen position

Finding the sweet spot in the room

Jens outlines basics of treatment including pictures, with links about resonators

Advice Wanted: Best Option(s) for Additional Bass-Trapping

Can you put treatment on the back wall? I think your idea with the ceiling is a good one. If you can manage to do that, expand the corner traps, and put thick panels on the rear wall I think that should make a huge difference.

It's a bit odd to have that L shape there. I agree that the booth is not ideal for the mix environment but it sounds like you are not at liberty to change it.

Do you have a left and right measurement?

The null around 74.5hz looks like SBIR with strong reflection from ceiling.

The 1-0-0 peak at 31.0hz can be reined with an EQ after treatment.

Thank you Kyle,

I will have a read through the monitor placement articles - I measured about 6 different setups already (distances, spacings of the monitors) and found this one to be the best regardign frequency response. Though I don't like the speakers spread out like this, but I will get used.

So the idea is that more bass trapping will "simply" even out things a bit more? Would you give a direction whether to tune traps or simply use lots of insulation to have more massive absorbers? I want to build tuned perforated panels and place them in front of the bass traps just to test if they have any effect.

@ thethrillfactor : Yes there are a lot of left/right only measurements in my ever growing archive ;-) But I did three new measurements today to compare L/R + LR as things are right now, I will post them:

Thank you again.

Yes bass trapping will even things out more. Tuned traps make sense where their reflective surfaces won't cause comb filtering (ie reflect things away from listening position) and are located where that particular frequency is an issue (ie where it is high pressure).

The effect of placing a perf panel in front of a broadband bass trap will be to narrow the effective range of the trap.

You may want to consider something like this instead.

-

Avare use 20% open area to make LF absorber that reflects highs.

Small Room: maximise fluffy insulation?

Can you post MDAT?

Thanks Kyle,

I imagined the perforated panels to be mounted on the lower half (1m high from ground) of the bass traps to tackle resonances of high SPL at this position. But those perforations are much lower than 20% to work --> see my examplary calculation attached for 127 Hz.
> hole diameter 4mm
> hole spacing 65mm
>> perforation 0,29%
> panel thickness 5mm
> airspace 58mm
>> design frequency 127 Hz

I assumed it would not reflect too much from "down there" (lower front part of the bass traps) into the LP and cause more comb filtering at the LP than the surrounding walls cause anyway, but I might be wrong. Regarding wave length, those perforated panels (dimensions 100x68x6cm) would not reflect anything below 344 Hz right?


Aside from that, when reading through the BBC doc referrenced in the post you sent, another question occurs: in the broad band absorbers they present, does the hard back of the panels make a difference?! The bbc measurements did not show measurements of panels without wood backings. All the broad band panels I built don't have that hard back, the back simply is made of a thicker fabric "fleece" than on the front side. Never thought about that!

yes sure, I will post it now.

@ thethrillfactor , here is the mdat file. I don't understand why the measurement of the right speaker only was not saved, the .mdat only contains L+R and L... I will scan through the other measurements and hopefully find it, if not, I will do another scan tomorrow monday morning... too bad!!

L+R is really not that helpful for this type of analysis unless its a subwoofer.

Separate is always best.

My wifi is down so i can't look up my reference (build it like the pros) where it states the bandwidth of a dampened vs non damped resonator. Acousticmodelling.com has a graphic readout showing the curve, it might be worth double checking.

Assuming 127hz is a problem at the location your talking about a perf panel can be good. What i like about the concept in the link is it lets you have broadband bass Absorbsion, a wider effective range. It depends on if 127hz is the only remaining peak you need to tackle, and how much depth you would have for a broadband alternative.

Hard backs do make a difference, tho i do not know exactly how they compare to non hard backed, all other things equal. It's optional not necessary, and depends which methods suit your needs better. I appologize i don't have a better understanding there, maybe someone will chime in.

Your chart looks good, tho i only speak English (stupid american) so i had a bit of difficulty reading it.

@ thethrillfactor , here are the measurements: left, right and both speakers.

Sorry for the low quality photo, but I broke my phone this morning and had to use the built in cam of my laptop. I put the distances on the "measurement setup" photo. To say one thing beforehand: I know the stereo triangle is not done right in this setup, but if I bring the speakers further to the rear wall, I get almost equal distances to the side walls too, which causes new comb filtering again..

It is really strange how the signals of L + R speakers combine

The .mdat file is attached. I'd be very happy for things I overlooked/not thought of with the speaker placement right now.

@ Kyle P. Gushue , good idea! But maybe it's worth a try to build a perforated panel and just see/measure the effect it has. It's probably the inferior method to simply putting in more massive insulation/making the bass traps larger. But I want to know. I will do the build as soon as I get the materials, maybe this week! It can be hard to get wood and stuff during lockdown...

PS: if it helps I can prepare an english version of my treatment calculator.

Nice place, looks like you're busy.

I'd try to find out if the 30 Hz mode is the 1-0-0 or 0-0-1 (floor-ceiling) mode. Judging from your pics, it's a rather tall room so it may be the 0-0-1 mode and you'd need to get your treatment up the ceiling. I don't think it's the 1-0-0 or 0-1-0 mode because 30 Hz is around 5,50 m and your room is smaller than that.

Also, I'd do a measurement without the desk and especially the monitor in the way.

Skip diffusion on the rear wall and play with bass trapping. Get something that has dimensional stability and that you can slap on the wall in 10 cm increments. Caruso ISO-BOND comes to mind.

Schöne Grüße nach Köln.

A couple of observations:

1) Your left and right measurement is clipping around 28-31hz so need to measure at lower level(75db is fine), but turn down input not the output.

If 28-31hz modal peak is really +10db in your space, then the only way to remedy is a fine tuned EQ at the modal peak.

2) Your measured vs calculated modal values are different so whatever you want to build that is tuned must be confirmed.

3) The Left speaker nulls in low end are SBIR and modal reflections and lack of modal support. The nulls at 369hz, 461hz, 1khz are SBIR.

The right speaker null at 386hz is SBIR.

Thank you very much, @ thethrillfactor ,

Could you clarify for me where the clipping occurs? (--> see picture below)
I think the level are higher than needed, but normally, REW stops the measurement if clipping occurs, no?

The modal 30Hz is definitely +10 dB and ironically is the one thing acoustically, that hardly bothers me, because it is so distinct, you can tell every time. But I fear it is pushing the harmonics too, so it should be treated.

2) Regarding my calculation you are right, this was just exemplary for the perforated panels idea and referring to an older speaker setup. I will need to calculate again.

3) It confuses me, that the nulls are so deep in the left speaker and not in the right. Is SBIR at the left speaker side more severe due to the wall up to the ceiling (whereas on the right side, the wall is only about 2.5m and then there's the ceiling of the booth)?

Tonight I will analyse the measurements again thanks to your help!

Here is the L + R combination, but I don't see the clipping. What am I missing?

I also think it is the 0-0-1, but there are some very strange nulls (I hear when walking/climbing) the room. from my ear, the mode sounds like a diagonal from lower corner to opposite upper corner..

when engaging this mode, the whole room feels like "shaking", which also confuses me a bit, because aren't gypsum board walls also good for LF absorption..?

Danke und zurück :-)

Don't think it's that because composite modes are higher up than their individual modes, and that would mean your 1-0-0 and 0-0-1 modes would need to be lower than 30 Hz but the room I don't think is big enough for that.

Click the distortion tab and look for distortion or strong second/third harmonic activity.

In the low end its usually some clipping/distortion at the input.

You can also study the noise rating for the space. If you are trying to setup a control room that meets the ITU-R BS.1116-1 standard the NR at 1khz should be an NR of 10 or 15 Max.

Thanks again for the explanation, that is distotion pretty obviously! The 30 Hz mode is so strong, that must have been it.

Well when you normalize it against the fundamental and mask the harmonics is not as bad as it looks(around 5% distortion).