REW results

[Rocko21]

Hi,

I'm working in a home based recording studio, two channel environment. I find it really hard to mix bass correctly. The room is treated but the low end is still a huge challenge.
So, I just used REW to measure it all and would love some advice from you guys.

I have attached a loose schematic of the room itself together with some REW results.

I'm using two Neumann KH310 monitors, which are 3-way speakers regarded as "full range" for nearfield/midfield monitoring. These are posted on speaker stand at ear level (when seated).

In the first three FR measurement - I show the FR result of Left only, Right only and Left+Right. This is done in order of testing for frequency cancellation of one speaker Vs. the other in the low frequency domain.
However, to me it seems that this is not the case. All three measurements show that around ~68 Hz --> There is a huge trough in energy.
So, to better focus on the problem, next measurements are Left channel only.

I also attach the spectogram and waterfall plot for Left only.

Can you help me read the spectogram and waterfall plots? Do those time constants make any sense to you? Could you explain what is considered a quality result for those graphs?
How should I achieve it? Bass traps for ~68 Hz -- does that exist??

Any comment is welcomed.

 

[ddude003]

Hi Rocko, It looks like you missed the room diagram... Which would be helpful... Please post the .mdat file(s) too... For recording you will want pretty flat with little reverb... And yes there are companies like GIK that have or will make Bass traps down below ~68Hz... While you are getting your room squared way, you might also try headphones to get the room out of the equation and see how that sounds... Or mix in the Abbey Road studio with https://www.waves.com/plugins/abbey-road-studio-3

Spectrogram Graph

Everything you would want to know about the spectrogram and then some... Frequency, Energy, Time (in milliseconds)...

Try reducing bass at the monitors themselves... Think about speaker placement and seating... You might try adjusting...

 

[Rocko21]

Yep, sorry.

Room diagram attached.
Notice the two hallways which are problematic. I had added acoustic curtains just on their entrance to avoid air going back and forth.
The two walls (left and right) are not parallel.
At the back of the room their is a massive set of glass windows. Covered with acoustic curtains.

Current acoustic treatment:
GIK 242 as 'clouds' just above my head
GIK bass traps (right side, to units).
GIK bass 244 on left side (no real corner...)
GIK 244x2 on front wall behind monitors
GIK 242 on front wall
GIK 242 on front wall adjacent to 244
GIK 242 on long wall ot the right

All measurements done with this acoustic treatment

 

[ddude003]

Wow... Quite the crazy room... It seems to me that those peaks/dips are caused by room modes... Too much energy boosting or dipping... You might try moving the speakers a few inches to a foot forward into the room... Wider or narrower... And seating... Also it may be worth placing some bass absorbers out into the room as free standing... To see if that makes much difference... I would try a few feet behind your seat and directly aligned with your left and right speaker... Any Bass traps should have a air gap between it and the wall... Have you thought of adding Soffit Bass Traps too... Lastly quash the energy with EQ... You may be able to find a copy of Master Handbook of Acoustics by F. Alton Everest, Ken Pohlmann on the web...

 

[Wayne A. Pflughaupt]

Nice speaker choice!

The Neumannn speakers may well be getting cancellation due to their distance from the floor. The distance between them may also be a factor, especially if the two (speaker to speaker, speaker to floor) are close to the same measurement – which I suspect they are.

You might have better luck with the speakers sitting on the desk.

Alternately, it might be a good idea to high pass the Neumanns and add a subwoofer, properly low-passed, equalized and located. That’s probably a better solution than bass traps. As I understand, bass traps that work as low as your problem is are huge, and it requires a lot of them. There might not be much space in the room left for you!

Your waterfall graphs “look” bad because the levels are so high. Do you really listen at 95 dB?

Here’s some reading on how to better understand time-domain graphs.

Adventures in Waterfalling: Understanding Signal Levels in Time-Domain Graphs

Adventures in Waterfalling Understanding Signal Levels in Time-Domain Graphs Once upon a time in a land far, far away, the capability to generate waterfall graphs was limited to expensive software programs available primarily to professional speaker designers and acoustics engineers...

www.avnirvana.com

Regards,
Wayne

 

[ddude003]

I was going to suggest adding a sub although it is counter intuitive... And those monitors are so nice and dig down, hopefully can just use those... Another solution might be Surkan Gur's (serko70) Virtual Bass Array method...

 

[Rocko21]

Dear Ddude003 and Wayne - I really want to thank you for the great suggestions. You are providing me some great advice...

Please do read on.

So, yesterday you got me going through the same line of "add a sub woofer" on floor level. So I went into testing that concept.
The theoretical advantage behind adding a single sub-woofer creating all the lowest end (instead of 2 top monitors) is based on this:
* The sub can be put on the floor, which breaks the symmetry problem. The "distance between the tops is equal to the distance between each other or the distance to the front walls". Symmetry creates standing waves.
* The sub and tops may benefit from different locations. tops require symmetric, ear level distance from listener. That might not be ideal for the low frequency which might benefit from being positioned next to the wall, corner or on the floor.
* Some subs come with different EQ, phase and DSP controls
* Two tops speakers might cancel out each other (tend to more than a single sub). This effect becomes more severe at low frequencies.

But - how can one be sure this will work in his/her setting?? So, I came up with the "Rocko method".
I took one KH310 monitor and and placed it on the floor. Low-cut it (30 Hz) and High-cut it (90 Hz) with my RME soundcrad.
Then placed the other monitor at the original place (on its stand) and low-cut it at 90Hz.
Shortly speaking - I created a sub and single monitor simulation without running out and spending money on an unknown territory.

The results are shocking. See the attached graph.
The red line represents the "Sub+Top" measurement. Notice that the 60-70 Hz dip has completely disappeared. The FR line is quite flat.
Compare that to the huge dip shown in the orange line, which is the result of original positioning.

I plan to work on this topic more, come up with more insights and update here, but again - thank for the great, great, great support and suggestions.

(I will address long reverb times and 95 db measurements issues later on).

 

[ddude003]

Hey Rocko, Good job so far!!!
Here is a resource I usually refer to for a wealth of information regarding absorber/trap placement... http://arqen.com/bass-traps-101/placement-guide/
And here is a resource regarding room modes... https://amcoustics.com/tools/amroc
If you haven't watched "Surkan Gur Virtual Bass Array" youtube video it is well worth the 18mins... Google is your frenemy...

If you go down the multi-sub rabbit hole this paper by Todd Welti might be interesting... https://www.harman.com/documents/multsubs_0.pdf

"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." -Walt Disney-

 

[Rocko21]

Thank you for the links. Very interesting.
Many thanks to Wayne for the Waterfall articles/ I've read all three and now better understand the difference between "Decay Rate" and "Decay Speed". I also better understand the relation to SPL level.

So, here is a waterfall plot taken at a lower SPL. [ Left speaker only on speaker stand, microphone at sitting position, 90 [deg] ]

My understanding:
1. massive room mode at ~30 Hz. This is due to the length of the room (6 meters).
2. A 'null' at ~62 Hz. I guess this is a phase reversed response to the first room mode.
3. Another one at 126 (3rd harmonic)
4. Another one at 164.

Say I wanne "kill" that 30 Hz room mode... Is there any acoustical solution for cancelling out this mode? Helmholtz resonator? Absorption? GIK turbo trap or the like?
Or maybe I better just filter out anything lower than 30 Hz on my set-up and deal with the "easier to handle" higher room modes??

I had also added my sitting position within the room. I'm bound to be in the corner due to that door which opens into the room.
Notice that this schematic is ideal and my room is far from that (walls are not parallel, etc.)

 

[ddude003]

It will only costs you some of your time to see what a high pass at ~30 Hz would sound like... Use your ears... More Absorption/trapping and/or adding sub(s) will cost $$$... Frankly more Absorption/trapping is best to a point... Other than the GIK 242 clouds, do you have any other bass traps up high, in corners? You have a lot of surface area in that room... How much of that surface area is actually covered with absorption/trapping?

And another interesting read... https://ethanwiner.com/basstrap_myths.htm