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Bass in small bedroom (effects of PSI AVAA, subwoofer and EQ, also passive absorbtion)

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Jan 21, 2020
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#1
Hello,

for some time i´m trying to get a smooth bass response in my small bedroom (14 sqm). I recently tried to throw some money at it and just wanted to share my experiences. I show you the effects of EQ, 2x PSI AVAA and a subwoofer for your amusement. Please note: Everything i say i solely about the situation in my room and i´m not trying to generalize something, so take from it what you want.

Mains: Neumann KH 310
Sub and EQ: Neumann KH 750 DSP

Room dimensions: 3,0m x 4,7m x 2,5m
Listening distance from front wall: 1,8m
Distance to mains: 1,3m (mains are close to the front wall)
There is a big window in the front wall which resonates at will and sometimes messes up the upper bass and midrange
Sub location: at front wall, 75cm from side wall
AVAA locations: front wall upper left corner + back wall upper left corner, note: the AVAA´s sensitivity had to be powered down a bit, they are not working under optimal conditions

Passive absorbtion:
- front wall: 2x corner traps basotect (2m x 0,5m x 0,4m), 1x basotect panel between mains (0,5m x 1m x 0,15m)
- ceiling: 1m x 1m x 0,12m basotect cloud
- side walls: 2x 1m x 0,5m x 0,10m basotect
- back wall: big closet (open) + 2m x 0,5m x 0,15m basotect
- also there is a bed in my bedroom (surprise!)

Frequence response (L + R measured seperately, then averaged, var smoothing), passive absorbtion alsways the same
Black: the best i could get after months of trying (with sub, AVAA and EQ)
Green: Mains only, no sub, no AVAA, no EQ
Red: Mains + sub + EQ, no AVAA

FR AVAA EQ Sub_k.png


What i get from this in my room and under the given circumstances:
- Room EQ is a must, of course, even with some passive absorbtion
- AVAA doesn´t do much about the FR, the biggest effect was around 25 Hz (SBIR null from back wall is almost eaten up by the AVAA)
- Sub is needed to "fill" the grand canyon between 70 and 100 Hz, bass extension to 20 Hz is expected

Additional measurement: Spectrogramm (left channel only, sub + EQ present)
AVAA activated
Spec mAVAA.png


AVAA deactivated:
Spec oAVAA.png


The AVAA reduces the reverberation significantly. I tried some other positions where it had a bigger effect. Also the reduction would be better if the AVAA could work with full power. It has the potential to almost flatten it if you can use it better than me. But for me, this was the best compromise i could get.

All in all i expected a bit more from the AVAA, but i am not disappointed. They do what´s promised but they don´t work wonders. I´m keeping them because it´s definately better/cleaner with them present and it´s hard to get back once you´ve been there...
 
Joined
Mar 27, 2020
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#2
Great post, as simple as it gets.

I have a small room myself (3.5mX3.5m) and have been struggling to achieve a proper bass, I have built 3 big (120cmX60X40) bass traps that didnt even help the bass, ironically, the only thing that really helped is a huge closet that is in the room (240cmX180X60)
eventually i took the multi-subwoofer approach , with some EQ i got incredible bass I never thought was possible achieving in that room.

have you thought about multi sub option?
 
OP
D
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Thread Starter #3
Thanks!

Maybe multi-sub would have been the better strategy. At least as far as the price/performance ratio is concerned, I could of course have bought several subs instead of AVAA, perhaps with a better result. I do not know.

I originally didn't want to buy subs because I was afraid that I would not be able to handle the integration well. Besides, I actually wanted as few additional devices and cables as possible.
So I thought that the AVAA (even if they are very expensive) would be the easiest solution for me. But then I realized that it could not solve my problem between 70 and 100 Hz.
I had then thought about buying two subs, but wanted to start with one first. If I had two, I could place them both on the front wall, each at 25%. But I don't know if that would really bring an improvement. Maybe it also brings the danger that I might get new problems (cancellations)?
Many other installation options (e.g. 4 subs in the middle of each wall) are not possible for me, because the room with bed etc. is already quite full.

How did you set up your subs and what does the reverberation look like?
 

Absolute

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#4
Even here at ASR you will find people who strongly disagree with the science, but here's what it tells us about bass;

- we don't hear "timing" at low frequencies, so integration is all about frequency response. We don't hear phase either.

- We don't hear ringing, we hear sudden peaks and dips.

- Because of math ringing will also "go away" when you EQ a peak.

- Multi-sub is the best way to get good bass in a room.

My suggestion would be to sell those stupidly expensive AVAA's and get 3 or four small sealed subs, download the multi-sub optimizer program (can find all about it at www.minidsp.com) and use whatever minidsp you need for that to work.

Or build a single bass array on the front wall with stupid amounts of porous insulation at the back wall.

Whether the science is all correct or not, it's simpler to try it and see if it works than to keep throwing time, money and energy into a problem that they claim have already been solved for you.
 

q3cpma

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#6
Even here at ASR you will find people who strongly disagree with the science, but here's what it tells us about bass;

- we don't hear "timing" at low frequencies, so integration is all about frequency response. We don't hear phase either.

- We don't hear ringing, we hear sudden peaks and dips.

- Because of math ringing will also "go away" when you EQ a peak.

- Multi-sub is the best way to get good bass in a room.

My suggestion would be to sell those stupidly expensive AVAA's and get 3 or four small sealed subs, download the multi-sub optimizer program (can find all about it at www.minidsp.com) and use whatever minidsp you need for that to work.

Or build a single bass array on the front wall with stupid amounts of porous insulation at the back wall.

Whether the science is all correct or not, it's simpler to try it and see if it works than to keep throwing time, money and energy into a problem that they claim have already been solved for you.
We may not hear LF group delay, but decay is another matter. I've not seen any research delving into the subject of its audibility.
 

tecnogadget

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#7
I would like to read some research that supports that ringing is not audible.

I hope I’m not making a mistake, but if we consider ringing and decay almost if not the same thing, it is something you should be able to perceive.
A sustained bass note in the time domain, instead of having natural-correct decay...
 

QMuse

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#8
I would like to read some research that supports that ringing is not audible.

I hope I’m not making a mistake, but if we consider ringing and decay almost if not the same thing, it is something you should be able to perceive.
A sustained bass note in the time domain, instead of having natural-correct decay...
Unlike post-ringing, which gets masked, pre-ringing is indeed audible. You can easilly spot it as waves in front of step response. It usually comes from linear phase filters or too aggressive phase correction.

HF pre-ringing that you see in front of DACs impulse response is not audible.
 

QMuse

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#9
Black response would be perfectly fine if region between 20 and 100Hz is boosted by 5dB, and tat shouldbe be hard to do using EQ.
As you have only 1 sub you may also want to consider having your sub overlapped with mains instead of crossign them in a point, as suggested by Geddes research. For example, you may want sub and mains overlap in 70-110Hz range to help tame that depression in FR.
 
OP
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Thread Starter #10
@QMuse
I will try that!

Also i will measure what happens if i set the AVAA to default sensitivity, and i will try how decay looks when i EQ the 33Hz peak of the "red" graph (probably the difference between AVAA on/off is even smaller then). I´m also getting some new motivation from this public striptease to try out a few more options. I´ll keep you posted if you´re interested.
 

QMuse

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#11
@QMuse
I will try that!

Also i will measure what happens if i set the AVAA to default sensitivity, and i will try how decay looks when i EQ the 33Hz peak of the "red" graph (probably the difference between AVAA on/off is even smaller then). I´m also getting some new motivation from this public striptease to try out a few more options. I´ll keep you posted if you´re interested.
Send me that black measurement via private messaging and I will create filters for your sub (rename .mdat to .txt). Where have you set XO?
 
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#12
Thanks!

Maybe multi-sub would have been the better strategy. At least as far as the price/performance ratio is concerned, I could of course have bought several subs instead of AVAA, perhaps with a better result. I do not know.

I originally didn't want to buy subs because I was afraid that I would not be able to handle the integration well. Besides, I actually wanted as few additional devices and cables as possible.
So I thought that the AVAA (even if they are very expensive) would be the easiest solution for me. But then I realized that it could not solve my problem between 70 and 100 Hz.
I had then thought about buying two subs, but wanted to start with one first. If I had two, I could place them both on the front wall, each at 25%. But I don't know if that would really bring an improvement. Maybe it also brings the danger that I might get new problems (cancellations)?
Many other installation options (e.g. 4 subs in the middle of each wall) are not possible for me, because the room with bed etc. is already quite full.

How did you set up your subs and what does the reverberation look like?
I will measure and make a proper graph that will show how the subwoofers effected the room bass

my setup is with currently with 5 subwoofers, might even make it 7., placement look like this , note that these are not even identical subwoofers.
also the real "magic" happened when i had the subwoofers both in front of my listening position and behind me.
1585397034531.png

its not very ideal, because the subwoofers are very close to each other which means i get the benefit of one big subwoofer rather than 2 separate subwoofers, but i dont really other places i can put them sadly...

I might however, try the Geddes (pretty sure its Geddes ) approuch and place the subwoofers in random places rather then a symmetrical spots and try and see if i get better results.
 

QMuse

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#13
@QMuse
I will try that!

Also i will measure what happens if i set the AVAA to default sensitivity, and i will try how decay looks when i EQ the 33Hz peak of the "red" graph (probably the difference between AVAA on/off is even smaller then). I´m also getting some new motivation from this public striptease to try out a few more options. I´ll keep you posted if you´re interested.
Measure with all speakers playing, using RTA MMM pink noise. Make 2 additional measurements of L and R channel playing separately. Don't apply any smoothing in any of those 3 measurements.

See how RTA MMM is done in this video.

In ideal case your response should follow the violet line. As you can see your responsee is app 5dB shy below 110 Hz, but that it quite easy to correct by adding a few filters to your sub.

FR AVAA EQ Sub_k.png
 
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OP
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Thread Starter #14
@QMuse Thanks very much for your offer! I think i´m good at the moment, though (see below for my reasons). The video and the RTA MMM technique is very useful, i didn´t know that. Thanks for that, too. By the way i like the bass to be quite low, just my personal preference.

After writing my post yesterday i realized how little effect the AVAA made and that the biggest effect was around the 25hz-mark. So today i tried another option and placed both AVAAs at the back wall. This gave me the opportunity to optimize my passive absorbtion on the front wall as well. Both actions led to a better outcome than yesterday. Below you see:

- Black: The black one from yesterday for reference
- Pink: a new average made with new AVAA position, optimized absorbtion and optimized EQ (added EQs on 200Hz and 110 Hz). I tried the RTA MMM method for this, thats why the response above 300 Hz is flatter, too. I know you can´t really compare the two graphs because of different measurement techniques, but there it is, anyway. The better response aorund 80hz is partly because of better passive absorbtion and partly because of measurement method.
- Green: Left channel only, single measurement (no RTA MMM), AVAA active
- Red: Same, AVAA inactive, additional EQ at 32Hz (around additional -6db) to compensate the effect of the AVAA and almost match the level of the green graph

FR AVAA EQ Sub2.png


Spectrogramm for the "Green" FR (AVAA active):
Spec mAVAA2.png


Spectrogramm for the "Red" FR (AVAA inactive, almost the same level around 32 Hz)
Spec oAVAA2.png


What i learned:
- If was wrong to think i already tried out every position - the last position for the AVAA is much better.
- 2x AVAA at back wall almost completely kill the 25Hz-SBIR cancellation.
- The AVAA reduce the decay time, even if the level is the same.
- A graph made with RTA MMM looks much better and puts my mind at ease.

For the moment i can rest the case, i think.
 

QMuse

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#15
@QMuse Thanks very much for your offer! I think i´m good at the moment, though (see below for my reasons). The video and the RTA MMM technique is very useful, i didn´t know that. Thanks for that, too. By the way i like the bass to be quite low, just my personal preference.

After writing my post yesterday i realized how little effect the AVAA made and that the biggest effect was around the 25hz-mark. So today i tried another option and placed both AVAAs at the back wall. This gave me the opportunity to optimize my passive absorbtion on the front wall as well. Both actions led to a better outcome than yesterday. Below you see:

- Black: The black one from yesterday for reference
- Pink: a new average made with new AVAA position, optimized absorbtion and optimized EQ (added EQs on 200Hz and 110 Hz). I tried the RTA MMM method for this, thats why the response above 300 Hz is flatter, too. I know you can´t really compare the two graphs because of different measurement techniques, but there it is, anyway. The better response aorund 80hz is partly because of better passive absorbtion and partly because of measurement method.
- Green: Left channel only, single measurement (no RTA MMM), AVAA active
- Red: Same, AVAA inactive, additional EQ at 32Hz (around additional -6db) to compensate the effect of the AVAA and almost match the level of the green graph

View attachment 56097

Spectrogramm for the "Green" FR (AVAA active):
View attachment 56098

Spectrogramm for the "Red" FR (AVAA inactive, almost the same level around 32 Hz)
View attachment 56099

What i learned:
- If was wrong to think i already tried out every position - the last position for the AVAA is much better.
- 2x AVAA at back wall almost completely kill the 25Hz-SBIR cancellation.
- The AVAA reduce the decay time, even if the level is the same.
- A graph made with RTA MMM looks much better and puts my mind at ease.

For the moment i can rest the case, i think.
Response below 100Hz should be measured with all speakers playing (2 mains+sub), above app 100Hz directivity starts to play so it is each speaker for itself.
 
OP
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Thread Starter #16
Yes, but in my room there is only a small difference between measuring L+R+Sub vs. ((L+Sub) + (R+Sub))/2 below 100 Hz.
I really like doing the RTA MMM thing - so much more fun.
 

QMuse

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#17
Yes, but in my room there is only a small difference between measuring L+R+Sub vs. ((L+Sub) + (R+Sub))/2 below 100 Hz.
That is not how LF summation works. :)

As sub is doing all the LF work it is true you won't have much difference in the joint speaker measurement but L+R+sub MMM RTA measurement will give you best picture what you are hearing below 100Hz. You can further adjust sub based on that measurrement if necessary.

I really like doing the RTA MMM thing - so much more fun.
Yup, it's fun. :)
 

QMuse

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#19
It is highly dependent on the loudspeaker and the room characteristics, and the individual preferences of the listener. There is no "ideal case".

www.youtube.com/watch?v=aRJJ8XJAT54
www.aes.org/e-lib/browse.cfm?elib=17042

View attachment 56140
While "ideal" may not be the ideal word that violet line follows 10dB fall over 20-20000 range which, according to Toole & Olive research was preferred by most of the listeners in blind tests.

The response you get without room EQ wtih your speakers in your room will vary greatly but that line is one of the most popular EQ target lines as there is some serious research done to support it. Of course, not all of us prefer the same LF to HF ratio so we will modify that curve slightly but it is definitely a good place to start as room EQ target.

P.S. I really see no need in linking AES papers that have been linked and quoted at least 300 times on this forum.
 
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