Humner

Fixing ~140hz boomyness in room
« on: June 11, 2017, 08:00:08 PM »
I recently moved into a new place and setup the studio into a bigger room than I had before. After everything was setup I fired up some mixes to compare how the monitors were in the new space and found I still had the same ~140hz boomyness that I had in the old room.

After a little googling, I found this was due to the ceiling height and how the speakers are positioned on the vertical axis which explains why I had the same issue as both ceiling and monitor height is the same between each room.

I couldn't find much in the way of fixes for this. What I normally do is stick an EQ on the mix bus that attempts to null out the 140hz while I mix and then I turn this off before mix down. However I wouldn' mind trying to make up some baffles or some other ideas instead of trying to fix with EQ. Does anyone have any ideas on how I should combat this?

I know GDIY is not exactly the right place for this kind of thing, but I'm curious to hear your thoughts.


Humner

Re: Fixing ~140hz boomyness in room
« Reply #1 on: June 11, 2017, 08:32:21 PM »
I just had a walk around the room with 140hz playing and find that it's greatly reduced when you stand up. It seems like the wave is forming right in the middle of the vertical plane which is where the ears are in sitting position.

Bit of a PITA. I think the only way to solve this will be some kind of overhead baffle.

ruairioflaherty

Re: Fixing ~140hz boomyness in room
« Reply #2 on: June 11, 2017, 09:35:19 PM »
- Can you give us a simple drawing showing your room dimensions and speaker position (in all 3 dimensions)? 
- What model speaker? 
- What are your walls made of?


Humner

Re: Fixing ~140hz boomyness in room
« Reply #3 on: June 11, 2017, 10:17:27 PM »
Heres a quick draw up in Autocad all in millimeters. The dimensions surrounding the monitors are measured to the coil of the woofer. Let me know if anything else may help.

http://www.thraxeh.com/Pics/studio.jpg

Hoping that makes sense. Ceiling height as previously mentioned is 2.4m. Walls are rendered brick.

Monitors are KRK Krok - these in particular http://medias.audiofanzine.com/images/normal/krk-k-rok-145849.jpg

Thanks!

Re: Fixing ~140hz boomyness in room
« Reply #4 on: June 11, 2017, 10:21:46 PM »
- Can you give us a simple drawing showing your room dimensions and speaker position (in all 3 dimensions)? 
- What model speaker? 
- What are your walls made of?

And add to that:

Listening position. You mentioned "halfway between floor and ceiling", the other two ratios would also help.

Beware, that there is an old adage that the only way to really fix EQ problems in a room, is with a D-9. ;D

https://en.wikipedia.org/wiki/Caterpillar_D9

Gene


ruffrecords

Re: Fixing ~140hz boomyness in room
« Reply #5 on: June 12, 2017, 02:20:39 AM »
Because it is a single frequency, you might like to consider a Helmholtz resonator. Basically a box with a hole in it stuffed with absorbent material.

Cheers

Ian
www.customtubeconsoles.com
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ruairioflaherty

Re: Fixing ~140hz boomyness in room
« Reply #6 on: June 12, 2017, 03:59:59 AM »
A few more questions

- Can you add doors and windows to your drawing, or describe?
- What height is the woofer center from floor or ceiling?
- What height are your ears at when listening?

Cheers,
Ruairi

mrclunk

Re: Fixing ~140hz boomyness in room
« Reply #7 on: June 12, 2017, 06:32:55 AM »
Because it is a single frequency, you might like to consider a Helmholtz resonator. Basically a box with a hole in it stuffed with absorbent material.
Handy site for Helmholtz calcs
http://www.acousticmodelling.com/helmholtz.php

Re: Fixing ~140hz boomyness in room
« Reply #8 on: June 12, 2017, 06:54:49 AM »
Just a word of warning on helmholtz absorbers. They are notoriously hard to get right for a few reasons:
- The classical formula doesn't tend to give the same tuning when built (due to losses from the panel vibrating, friction around the holes).
- Getting the right Q takes some trial and error, and there's not a lot you can do after the fact to change tuning.

In terms of approach, I would warn against using highly tuned treatments. Introducing a large hard surfacing (such as the plate of a helmholtz) into a small room, can effectively change the length of that dimension. This means that your absorber is now outside it's optimal range.
Additionally when the room is mostly untreated you will get the the biggest improvement, with least volume loss and expense, with treatments that are more general.

Looking at you plan I would suggest the following:
- If possible move the speakers to the other end of the room. The right speaker has different loading from the wall, so will differ in the low end.
- I would expect to see a dip in your response ~80Hz due to speaker boundary interference. Pushing the speakers against the front wall will push this frequency up to where it is not so damaging. You may get an increase of bass, which you may want to EQ at the amp *
- The problem you mentioned seems to be related to the height mode. Try shifting the speakers up or down 10cm, to drive this mode less. If you want to go the route of an absorber look into Limp Mass Absorbers. They are wide Q, easy to build, and relatively slim. Be sure to face it with 50mm of rockwool/703/foam (ensuring you don't stop the membrane moving), to control the reflection too.

* This one is minimum phase, so okay to do. Don't use EQ to solve modal issues, your settings will only help in one spot.

« Last Edit: June 12, 2017, 07:10:55 AM by thismanysounds »

JohnRoberts

Re: Fixing ~140hz boomyness in room
« Reply #9 on: June 12, 2017, 12:29:26 PM »
And add to that:

Listening position. You mentioned "halfway between floor and ceiling", the other two ratios would also help.

Beware, that there is an old adage that the only way to really fix EQ problems in a room, is with a D-9. ;D

https://en.wikipedia.org/wiki/Caterpillar_D9

Gene
Classic.....  D9 "room EQ" ...  ;D

JR
John Roberts
http://circularscience.com
Tune it, or don't play it...


john12ax7

Re: Fixing ~140hz boomyness in room
« Reply #10 on: June 12, 2017, 04:38:05 PM »
Room EQ Wizard has a nice simulator for these kind of things. In general you want to avoid having the speakers at any half way point in the room.

Raising or lowering the speakers can help, raising them up and then angling down towards your ears is probably easiest. You should also put something that has good absorption at the problem frequency on the ceiling.

Matador

Re: Fixing ~140hz boomyness in room
« Reply #11 on: June 14, 2017, 12:20:20 AM »
You need bass trapping, at least in the corners, and some wide-band diffusion on reflection points visible from the mix position.

Read everything at ethanwiner.com to start off. :)

Humner

Re: Fixing ~140hz boomyness in room
« Reply #12 on: June 14, 2017, 05:50:07 AM »
Thanks for the help everyone. I played around some more this evening. There is a 2500mm long sliding door window on the 5100mm wall with a thick curtain.

my ears are 2100mm from the wall facing forward and 1600mm to the wall from my left. Ears are 1150mm from the ground - this probably doesn't help as its almost exactly halfway between the ceiling and floor.

I had done some testing in my DAW and REW to begin with - generally speaking I'm happy with how the rest of the range performs(and can only get better once I get some broadband and bass trapping in), its the pesky ~140hz that sticks out like a sore thumb.

Haven't make any bass or broadband panels yet as I wanted to get some ideas going first. I played around with speaker height, but this didn't make much difference. Just standing up and shifting my ears away from the center makes the biggest difference.

Also reading about Limp Mass Absorbers as mentioned by "thismanysounds"

ruairioflaherty

Re: Fixing ~140hz boomyness in room
« Reply #13 on: June 14, 2017, 11:25:25 AM »
Doing some quick simulations your 140Hz issue is indeed caused by the floor to ceiling interaction. 

- You can't move your ears up and down much (although I have set up a mix position once on a high stool for a similar issue).
- Raising or lowering speakers and angling will not help much if at all and creates a much smaller sweetspot

The wavelength of 140Hz is somewhere around 8 feet. The ideal place for a velocity based absorber is at the quarter wavelength where we have maximum velocity (or swing), that would put the panel at 2ft from the ceiling and touching the head of a 6ft guy or gal. 

Obviously that's not possible but you'll definitely want to build a 4 inch panel, probably 4' x 4'.  I would mock it up first without frame and cosmetics and have some friends hold it over your head.  Pick a position that's the best compromise between effectiveness and your comfort.

IMO Limp mass absorbers take some work to get right, I've seen them implement incorrectly more than once (at great expense too!).

ruairioflaherty

Re: Fixing ~140hz boomyness in room
« Reply #14 on: June 14, 2017, 11:28:08 AM »
On a separate point the lack of left right symmetry at the mix position will likely cause unpredictable skewing of the stereo image, worse at certain frequencies than others. 

I would suggest another 4 inch panel at the first reflection point on the left and a free standing gobo on the right side to mirror it.  I recently did something similar to help a friend mix at home and it worked out very well, he's been doing some high profile TV work out of his old living room.


Matador

Re: Fixing ~140hz boomyness in room
« Reply #15 on: June 14, 2017, 02:55:50 PM »
Again, in my experience frequencies below 200Hz or so cannot be 'spot-treated', because the wavelength's are essentially the same as the room dimensions. You need broad-band bass absorption that covers the entire room.

Acoustic Treatment Primer

A few pertinent quotes:

Quote
The most common application of bass traps in recording studios and control rooms is to minimize standing waves and acoustic interference which skew the room's low frequency response. (See the sidebar, Why They're Called Standing Waves.) As you can see in Figure 1 below, acoustic interference occurs inside a room when sound waves bounce off the floor, walls, and ceiling, and collide with each other and with waves still coming from the loudspeaker or other sound source. Left untreated, this creates severe peaks and dips in the frequency response that change as you move around in the room. At the listening position, there might be near-total cancellation centered at, say, 100 Hz, while in the back of the room, 100 Hz is boosted by 2 dB but 70 Hz is partially canceled.

The only way to get rid of these peaks and dips is to avoid, or at least reduce, the reflections that cause them. This is done by applying treatment that absorbs low frequencies to the corners, walls, and other surfaces so the surfaces do not reflect the waves back into the room. A device that absorbs low frequencies is called a bass trap. Although it may seem counter-intuitive, adding bass traps to a room usually increases the amount of bass produced by loudspeakers and musical instruments. When the cancellations caused by reflections are reduced, the most noticeable effect is increasing the bass level and making the low frequency response more uniform. As with listening rooms, bass traps are also useful in studio recording rooms for the same reasons - to flatten the response of instruments captured by microphones and, with large studios, to improve the acoustics by reducing the low frequency reverb decay time which makes the music sound more clear.

Another common misconception is that equalization can be used to counter the effects of acoustic problems. But since every location in the room responds differently, no single EQ curve can give a flat response everywhere. Over a physical span of just a few inches the frequency response can vary significantly. Even if you aim to correct the response only where you sit, there's a bigger problem: It's impossible to counter very large cancellations. If acoustic interference causes a 25 dB dip at 60 Hz, adding that much boost with an equalizer to compensate will reduce the available volume (headroom) by the same amount. Such an extreme boost will increase low frequency distortion in the loudspeakers too. And at other room locations where 60 Hz is already too loud, applying EQ boost will make the problem much worse. Even if EQ could successfully raise a null, the large high-Q boost needed will create electrical ringing at that frequency. Likewise, EQ cut to reduce a peak will not reduce the peak's acoustic ringing. EQ cannot always help at higher frequencies either. If a room has ringing tones that continue after the sound source stops, EQ might make the ringing a little softer but it will still be present. However, equalization can help a little to tame low frequency peaks (only) caused by natural room resonance, as opposed to peaks and nulls due to acoustic interference, if used in moderation.


john12ax7

Re: Fixing ~140hz boomyness in room
« Reply #16 on: June 14, 2017, 04:24:48 PM »
I would agree that treating the whole room is the way to go. But since this is a floor to ceiling mode problem you do want to address it specifically. Treating the vertical room corners is a good idea, but more important would be the corner intersections of the ceiling and walls, and also the floor and walls. These might be more practical spots for thick absorption than the ceiling or floor itself.

Also read up on VPR absorbers, it's a German patent but seems to be DIY friendly if you can get the right materials. Essentially a big metal plate resting on 4" basotect foam. Highly effective at treating bass problems.


chefducuisine

Re: Fixing ~140hz boomyness in room New
« Reply #17 on: June 18, 2017, 12:06:29 PM »
Also read up on VPR absorbers, it's a German patent but seems to be DIY friendly if you can get the right materials. Essentially a big metal plate resting on 4" basotect foam. Highly effective at treating bass problems.

Jepp - much easier to implement as getting an Helmholtz-Absorber right.

Basically a VPR is a damped resonator with a fairly low Q.

You should pay attention to the following:
- size should be 2x1m (smaller sheets are not as effective)
- the metal plate should have a thickness of 0.8 - 1mm
- Basotect needs to be glued to the backside and cover the whole area without any gaps. Thickness should be at least 10 cm.
- the VPR needs to be mounted with as less fixing points as possible to allow the metal plate to 'swing' freely.
- ideal position in the room is an upper corner.
- If you are not creating a frame, watch your fingers when mounting.

Here is a link for a final product of the VPR (German only, but you can easily understand the important topics):
http://www.renz-solutions.de/fileadmin/user_upload/Datenblatt_VPR.pdf

Edit:
Perhaps Jens reads this.
He has more experience with VPR - DIY and could add a few things that need to be considered. I remember this was a huge topic in the German (Frank's) forum...
« Last Edit: June 18, 2017, 12:10:11 PM by chefducuisine »