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How to treat nulls 2
Old 8th April 2014
  #1
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How to treat nulls 2

Hello People!

About two years ago I was very active in the thread How to treat nulls.
This thread will also be about how to treat nulls and I am once again gonna show how I have done it = With Varitunes (V6 &V4) from Svanå (Diffusor.com)

How to treat nulls

The last six months, I have been bouilding a new studio from scratch.
It's a very small studio, just twelve square meters (3x4) on the inside.
I knew from the beginning that it was going to be a big challenge to get the room to sound good because it's so small.
I also new even before measureing that there would be big problems in the base areas with peaks and nulls.

Here is the untreated room.



In the next couple of days I am going to show how I have got rid of both the peak and the null.
It for now!

Swim cool

bREAK
Old 8th April 2014
  #2
Gear Nut
 

12 sq ft? A twin mattress is 20 sq ft. Your room is half the size of a mattress? \

p.s. reminded me playing hide and seek in narnia's wardrobe.
Old 8th April 2014
  #3
nms
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lol. So are we talking 3' x 4'? Or 6' x 2'?
Old 8th April 2014
  #4
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I think it should be in metric......

This is gonna be a intresting threadheh
Old 8th April 2014
  #5
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I'm all ears
Old 8th April 2014
  #6
Gear Maniac
 

I have a similar dip at around 80hz with about the same Q. However I have a much bigger room and some serious treatment. Sorry, but there is not much you can do. You might shave a few db off it, but that's about it.
Old 8th April 2014
  #7
Gear Addict
 

I think it will be a bit problematic with these three guys in your 12 ft² ( 1,1 m²) studio at the same time.
https://www.youtube.com/watch?v=aCxDZRJKkqY

(from 50 sec in English)
Old 8th April 2014
  #8
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Quote:
Originally Posted by Radial185 View Post
I have a similar dip at around 80hz with about the same Q. However I have a much bigger room and some serious treatment. Sorry, but there is not much you can do. You might shave a few db off it, but that's about it.
Dont be so sure about that. I went from the red curve to the black one in the same room using only room treatment and subs (no EQ, DSP, Audyssey or any other processing devices)

How to treat nulls 2-fr-now-vs-early.jpg
Old 8th April 2014
  #9
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Jens Eklund's Avatar
Quote:
Originally Posted by Radial185 View Post
I have a similar dip at around 80hz with about the same Q. However I have a much bigger room and some serious treatment. Sorry, but there is not much you can do. You might shave a few db off it, but that's about it.
Assuming the surface related to the issue can be properly threated (with either a very deep velocity based absorber, or a pressure based absorber), and also assuming that the null is not due to a severe lack of modal support (bad modal distribution) in the frequency range in question; there’s absolutely nothing saying that you cannot fix a null as long as you treat well and on the relevant surfaces. But if due to the floor bounce (first order SBIR cancellation due to the floor); it might be tricky to address unless you can accept a large pressure based absorber on the floor … Other solutions could be to try and partly block/scatter the destructive reflection by adding a panel to the back of the desk, or add subs (positioned on the floor) and cross over to the satellites above the cancellation frequency due to floor related SBIR.
Old 8th April 2014
  #10
Gear Maniac
 

Jens

I have tried all those things till my head felt like it was going to explode if I heard REW test tones one more time. The only thing I haven't tried is a sub.
I did say my null was similar to the OP's, having checked again its more around 120hz or so approximately.

Jim,

That's a impressive improvement, but how much improvement could you achieve without using the sub?? That's the big question, because Im looking for solutions that don't include the extra big expensive of a proper quality sub and crossover etc. In addition , I would guess that a significant null above 80hz, say anywhere from 100-150hz is not really territory for a sub?

I will build acoustic treatment all day and night (and I have!) if that's a chance to work. I cant be Spending $2000 plus on a sub arrangement.

Jim, got any graphs on how you went before you added your sub?

I get around my null by using DIRAC to help with the missing low mid/bass. Not ideal I know. That's all well and fine when using the computer, but if I want to listen to vinyl playback .....No DRC and my null comes up and slaps me on the arse and says hi. I don't like it at all, but I am mentally fried over the course of 18 months trying to fix it. Ill be watching the thread with interest though and I hope the OP can get it improved.
Old 8th April 2014
  #11
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Quote:
Originally Posted by Radial185 View Post
Jim,

That's a impressive improvement, but how much improvement could you achieve without using the sub?? That's the big question, because Im looking for solutions that don't include the extra big expensive of a proper quality sub and crossover etc. In addition , I would guess that a significant null above 80hz, say anywhere from 100-150hz is not really territory for a sub?

I will build acoustic treatment all day and night (and I have!) if that's a chance to work. I cant be Spending $2000 plus on a sub arrangement.

Jim, got any graphs on how you went before you added your sub?

I get around my null by using DIRAC to help with the missing low mid/bass. Not ideal I know. That's all well and fine when using the computer, but if I want to listen to vinyl playback .....No DRC and my null comes up and slaps me on the arse and says hi. I don't like it at all, but I am mentally fried over the course of 18 months trying to fix it. Ill be watching the thread with interest though and I hope the OP can get it improved.
Firstly, you don't need to spend $2000 on a sub(s). Mine consists of (2) $100 woofers and a $120 plate amp. I built the cabinet for about $75. Grand total, $300.

The following thread illustrates most of what I did. But it takes place after I had already integrated my sub. Still, might be some worthwhile tidbits there for you.
My Listening Room
Old 8th April 2014
  #12
nms
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Quote:
Originally Posted by Radial185 View Post
I have tried all those things till my head felt like it was going to explode if I heard REW test tones one more time.
You should post up the full details of your room, treatments, measurements in a new thread so it can be solved at least in some degree. Plenty of competent guys kicking around. I'm tackling my first and biggest null at the moment which is 135hz. It's tricky business for sure. There are many places where I'd normally add treatments, but it improves my lowest resonance (length axial mode) while making the 135 hole worse. The front wall to ceiling edge has proven to offer the most improvement so far. To find that hotspot I ran a tone at 135hz and hunted around the room.
Old 9th April 2014
  #13
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What octave smoothing should be used in REW measurement? I sometimes do 1/12, but wonder if that's too much.
Old 9th April 2014
  #14
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Quote:
Originally Posted by seiyafan View Post
What octave smoothing should be used in REW measurement? I sometimes do 1/12, but wonder if that's too much.
I like 1/24th for general purpose. If looking at just the bass, might use no smoothing.

No global answer to your question. Depends what your looking at and what your looking for.
Old 9th April 2014
  #15
Gear Maniac
 

Quote:
Originally Posted by nms View Post
You should post up the full details of your room, treatments, measurements in a new thread so it can be solved at least in some degree. Plenty of competent guys kicking around. I'm tackling my first and biggest null at the moment which is 135hz. It's tricky business for sure. There are many places where I'd normally add treatments, but it improves my lowest resonance (length axial mode) while making the 135 hole worse. The front wall to ceiling edge has proven to offer the most improvement so far. To find that hotspot I ran a tone at 135hz and hunted around the room.
So you would look for a spot in the room where 135hz was cancelling or booming? Are you trying to then treat that spot with velocity based absorbtion or other devices?
Old 9th April 2014
  #16
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bREAK THE NORM's Avatar
 

Quote:
Originally Posted by seiyafan View Post
12 sq ft? A twin mattress is 20 sq ft. Your room is half the size of a mattress? \

p.s. reminded me playing hide and seek in narnia's wardrobe.
Hahaha...

Sorry! Twelve square meters of course (3 x 4 meters) on the inside.
was a bit tired last night

The outside dimension is 3,4 x 4,4 = 14,96 square meters.
The walls are 40cm thick.

In Sweden you can build up to fifteen square without seeking planning permission.
That's why I did not build bigger.




Here are some pictures so you get an idea of how it looks from the outside. We started in October last year.








bREAK
Old 9th April 2014
  #17
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Nice small little box...
Old 9th April 2014
  #18
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Quote:
Originally Posted by Radial185 View Post
Jens

I have tried all those things till my head felt like it was going to explode if I heard REW test tones one more time. The only thing I haven't tried is a sub.
I did say my null was similar to the OP's, having checked again its more around 120hz or so approximately.

Jim,

That's a impressive improvement, but how much improvement could you achieve without using the sub?? That's the big question, because Im looking for solutions that don't include the extra big expensive of a proper quality sub and crossover etc. In addition , I would guess that a significant null above 80hz, say anywhere from 100-150hz is not really territory for a sub?

I will build acoustic treatment all day and night (and I have!) if that's a chance to work. I cant be Spending $2000 plus on a sub arrangement.

Jim, got any graphs on how you went before you added your sub?

I get around my null by using DIRAC to help with the missing low mid/bass. Not ideal I know. That's all well and fine when using the computer, but if I want to listen to vinyl playback .....No DRC and my null comes up and slaps me on the arse and says hi. I don't like it at all, but I am mentally fried over the course of 18 months trying to fix it. Ill be watching the thread with interest though and I hope the OP can get it improved.
The multiple subwoofer approach is also a solution to avoid nulls. Described here: mehlau.net > audio > multisub

Here's the result I got with three subs (two crossed at 140 Hz and one at 80 Hz) in a room. No EQ was applied.


Of course. Frequency response isn't everything and one need some treatment to reduce the decay.
Attached Thumbnails
How to treat nulls 2-three-subs-latest.jpg  
Old 9th April 2014
  #19
nms
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Quote:
Originally Posted by Radial185 View Post
So you would look for a spot in the room where 135hz was cancelling or booming? Are you trying to then treat that spot with velocity based absorbtion or other devices?
I looked for the boundary points it was loudest and targeted them for heavy absorption, thus reducing the energy reflected back at the listening position causing phase cancellation.
I typically just use combinations of Roxul, air gaps, and fluffy fiberglass. A layer of Roxul in front of thick fluffy works a little like a membrane trap.
Old 9th April 2014
  #20
Gear Maniac
 

Quote:
Originally Posted by bwo View Post
The multiple subwoofer approach is also a solution to avoid nulls. Described here: mehlau.net > audio > multisub

Here's the result I got with three subs (two crossed at 140 Hz and one at 80 Hz) in a room. No EQ was applied.


Of course. Frequency response is everything and one need some treatment to reduce the decay.
Very interesting thanks. Do you think you could possibly improve a null somewhat with just one subwoofer set right in he right position?
Old 9th April 2014
  #21
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Quote:
Originally Posted by Radial185 View Post
Very interesting thanks. Do you think you could possibly improve a null somewhat with just one subwoofer set right in he right position?
That's impossible to say anything general about. It depends on the modal distribution in the room, placement and the cause of the null.

Remember that treating low frequency modes normally does require substantial treatment because of the size of the wavelengths. And pressure based traps are far more effective then porous material. Unless one has the possibility of building the traps oneself, the cost can be high. It's almost never sufficient to treat low frequencies nulls with simply some thick porous material.
Old 9th April 2014
  #22
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Quote:
Originally Posted by bREAK THE NORM View Post
.....The last six months, I have been bouilding a new studio from scratch.
It's a very small studio, just twelve square meters (3x4) on the inside.
..... bREAK
Interesting build, bREAK!

Just a couple of questions...
1. The empty room measurement you showed,(post #1) is that one speaker, two speakers, mic in aprox listening point or other position?

2. What kind of walls (from inside-out)? Double gypsum, fluffy and wood?

3. Would you mind show us the waterfall?

Best

Ake
Old 9th April 2014
  #23
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Floor bounce null

Quote:
Originally Posted by Jens Eklund View Post
...... But if due to the floor bounce (first order SBIR cancellation due to the floor); it might be tricky to address unless you can accept a large pressure based absorber on the floor … .
+1

I just wonder, will a large (Lo-Q) HH resonator or "Limp Mass" react fast enough to attenuate the first floor bounce?

And how do we estimate how well it is working, as this happens within the first 10 ms...

The rigid floor is usually untreated (no absorber) for different reasons (cleaning, estethics, psycoacoustics, practical) but often also the ”best” low frequency reflector…

Best

Ake
Old 9th April 2014
  #24
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Quote:
Originally Posted by akebrake View Post
+1

I just wonder, will a large (Lo-Q) HH resonator or "Limp Mass" react fast enough to attenuate the first floor bounce?
Yes.

Quote:
Originally Posted by akebrake View Post
And how do we estimate how well it is working, as this happens within the first 10 ms...
We measure ...

Just see what happens to the FR and possibly the excess group delay -plots.
Old 9th April 2014
  #25
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Quote:
Originally Posted by Jens Eklund View Post
...Just see what happens to the FR and possibly the excess group delay -plots.
Thanks for the prompt reply

Excess group delay… I'll have to practice that ... heh

Ake
Old 10th April 2014
  #26
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bREAK THE NORM's Avatar
 

Okey! let's get this party started
There will be many pictures, hope that's ok guys.

Except that the studio measures 4m on the long side and 3m on the short side, the ceiling has a slope measuring 2.5m on the higher long side and 2.2m on the lower long side. (This is all inside dimensions).

The studio's timber frame is 45x145mm. (Apart from the floor that has 45x195mm timber)
In the frame, it is standard isoveer into both walls, the ceiling and the floor.
It is 22mm wood panel on the outside and on the inside it is one layer of 12mm OSB-board (only to the walls) and then one layer of 12mm gypsum to walls and the ceiling.(Outside ceiling standard plywood and clay tiles)
The floor has one layer of 22mm floor-chipboard and then one layer of 22mm floor-gypsum.


Finished house from the outside.






After a lot of work it looked like this inside. (Wallpaper and a very thin cheap carpet that is only a few millimeters)

Rear wall.





This is where the first measurement is done with one Yamaha HS80M.
Mic is where my listening Position is.
Moving the mic forward a half meter or back up to two meters, made no difference. It was just as bad with the only difference that the peak and the null moved.

Front wall



Here are all the measurements without treatment.

No smoothing



1/48 octave smothing



RT60 = T30



Waterfall



Here is also the REW File of the untreated room if anyone wants to take a look:

http:///jonathanojeda.com/studiobilder/bTNuntreated2014.mdat


OK, lets continue...
As you can understand I felt like this .
But it was almost exactly the same problems as I had in my old studio (but even worse) so I had an idea where I would start.

I started to build a broadband absorber in the front wall and two absorbers for the sidewalls to take care of the early reflections.
The front wall is covered with pillows (Foam) from two old sofas and also some standard rockwool.
In front of that I have put two frames/screens with very thick fiberglass.
These kind of screens are normaly used as sound absorbing screens on office locations between desks.
I use the same ones as side absorbers.

It looked and measured like this:









As you can see it helped alot in the RT but almost nothing in the low freq.







I will continue tomorrow to show how I have managed to get +/- 4db from 35Hz - 20K on twelve square meters

bREAK
Old 10th April 2014
  #27
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bREAK THE NORM:
RT measurements are not valid in small room since there's no real diffuse field. Forget the RTs and look at ETC measurements of each speaker instead. You should also look at the waterfall up till about 400 Hz.
Old 11th April 2014
  #28
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Quote:
Originally Posted by jim1961 View Post
Dont be so sure about that. I went from the red curve to the black one in the same room using only room treatment and subs (no EQ, DSP, Audyssey or any other processing devices)

Attachment 393782
Interesting Jim, I have followed your thread from the start so Im well aware of your journey. I don't want to hijack the thread but I thought the following information might be of relevance. Certainly for me, I think I will try it as Im certain my null is due to sitting at the half width of the room.



--- Side-wall-to-side-wall first-order axial room mode:
A bass null is likely to be audible (nulls tend to be easier to overlook/ignore than bass peaks)
Left-right speakers or left-right subwoofers will be out of polarity for this room mode so will not excite it, assuming mono bass typical of two-channel recordings. Also, the typical two-channel listening seat located 1/2 way between the side walls will place the ears in or near a null for this room mode. That means the bass frequency response is likely to be weak at this room mode frequency and would be smoother if one uses one subwoofer located off center, or two subwoofers located on the same side of the room to excite this room mode.

Source- http://forums.audioreview.com/speake...aves-2461.html

So given I have only the one sub sitting around not being used at the moment, there seems hope that a single sub, positioned correctly could improve the null in my situation.
Old 11th April 2014
  #29
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Quote:
Originally Posted by bwo View Post
bREAK THE NORM:
RT measurements are not valid in small room since there's no real diffuse field. Forget the RTs and look at ETC measurements of each speaker instead. You should also look at the waterfall up till about 400 Hz.
BWO:

The waterfalls that I have posted are zoomed in on the biggest problem frequencies. Thought it was the most relevant and interesting to see as this is where the biggest difference will be in terms of frequency when I post my final result. Just open the REW-file if you want to see more of the untreated measurement

Regarding RT:

The RT curve in the old thread (How to treat nulls) was highly debated and that room was only 15 square meter. What is the difference between a room that is 12 or 15 square meters when it comes to the diffuse field? Would like to know more about this and thanks for pointing this out!
(I'm certainly no acoustician so I have plenty left to learn)

bREAK
Old 11th April 2014
  #30
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Have not had a chance to post the end result today = Coming soon ....
Will also make a new video soon
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