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Solving Bass Nulls with DSP or not ?

atoprak

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Hello everyone,

I am having a bit of trouble with my setup in my new living room.
I have a pair of Monitor Audio RX6, driven by Creek Audio Evo50 amp. I use Bluesound Node and a Marantz CDP as the source components.
I have also added BK audio XLS 200 subwoofer to mitigate bass null point in my listening room.

Before the addition of the subwoofer I had very tiny bass output on my listening position. The reason is just because of the listening position as it is almost middle of the room ... (just bit close to front wall... ). I also seen that on REW simulation without sub .. and seen some dips around 60h-80hz and 110hz region ... I have added this sub to get bit more low end push and I actually did... now I get decent bass from where I sit but the other places even standup, I get bit boomy sound ... so the balance is not there ...

I am just wondering If I can fix these issues with an addition to miniDSP (with or without dirac) to system or not....

I am also keen on some changes.... may be switching to active speakers .... or event the streaming ones....

What I am looking for is general improvement on balance (with or without sub) and bit more fines .... I am listening on low to mid volumes in general..

Unfortunately changing listening position is not option since both wife factor and the general design of my living room.
Btw... I dont know how but my new Sony TV has a very tiny sub behind the panel which sound very good for the size even on my problematic listening position .. I dont know how but It does.... crazy

What do you think .. which direction should I follow ?

Thank you
 
Last edited:

ppataki

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My 2 cents:
I do have experience with force-correcting bass nulls and to summarize it:
- it is definitely doable, by using adequate EQ or DRC (like Dirac), you can enforce the correction of the dip (even if it is wide and even if it is like -15dB deep) and your frequency response will be flat (or very close to flat)
- but this will potentially introduce elevated amount of ringing (you will see that in the Waterfall diagram, Wavelet diagram and RT60 diagram)
- will the ringing be audible? that depends on the room; in my living room I cannot fully correct my dips since I get killed by the excessive amount of ringing it produces but my friend has a much larger living room (like 70 sqm) and there ringing is barely audible
- this enforced correction will take its toll on your power amp, make sure that you do have enough headroom (every 3dB increase will double the power requirement!)

Also once you corrected your individual channels you might still have to do additional correction after checking the freq. response when both channels are driven.
Both channels can (and do) cause additional cancellations depending on your room - force-correcting that will have an additional amount of ringing, amp load, etc.

Final point is that probably you shall try it and see if you can tolerate the ringing + if your amp can tolerate the elevated power requirements
 

Willem

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Filling in nulls is like filling up a black hole: it demands a lot of power, and even then. So read up on room modes first, and get a Umik-1 measurement microphone to measure actual response with the free REW software. Moving the subwoofer around may help, if you are lucky. The best way to smoothen this response problem is probably to use a second subwoofer in a different location (or even a third or fourth). That other sub will have peaks and dips at different frequencies because it will be located in a different spot in the room, so you will get more but smaller peaks and dips. Such averaging is usually very beneficial. The second sub does not have to be identical or even very large. See here for inspiration: http://archimago.blogspot.com/2020/05/musings-measurements-subwoofers-to.html
 
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DonH56

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Here's a quick overview of room modes: https://www.audiosciencereview.com/forum/index.php?threads/room-modes.25433/
And the Harman calculator: https://www.harman.com/documents/Room Mode Calculator_0.xls
And for reference Todd Welti's subwoofer placement guide: https://www.harman.com/documents/multsubs_0.pdf

Reading the above should help you understand the problem (the nature of the beast).

True nulls caused by a room mode are not really amenable to correction via EQ. They happen because the direct sound, D, is cancelled by the reflected sound R, so D-R=0. If you try to equalize to counter, then you will increase both D and R since you are just amplifying what comes out the speakers. If you increase power by ten (10 dB), then 10D - 1R = 0 for no gain. Except you are now putting out 10x the power, wasting a lot of headroom, and the sound out of the null will be very loud (boomy).

The usual solutions are to (1) move the subwoofer to position it to counter the nulls as best as possible, (2) move the listening position out of the null, (3) add another sub to "drive" the null by countering the reflected wave, or (4) add treatment (e.g. absorbers) to absorb the sound, reducing the null by reducing the reflected wave. The first three depend upon your flexibility in room arrangement and finances. The fourth option is usually impractical because at subwoofer frequencies the treatment depth and area must be very large to absorb enough energy to significantly affect the null (I have done it, with 27 panels 4" to 12" deep in a modest room, but it takes a lot of money, area/volume, and turns the room into something close to an anechoic chamber so sounds very "dead" -- and only gained me about 6~10 dB improvement in a null 20~30 dB deep). I moved the listening position a little, but like many am constrained by the room and the stuff in it, so added subs to counter the null.

HTH - Don
 
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Dumdum

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What you can and can’t correct depends on what’s causing the issue, but generally speaking you can’t smooth the response for every location… you said it’s good at the listening position, but can be boomy elsewhere, no a dsp won’t correct that for the most part, it can smooth the response at the listening position, but that will then make it different at other locations, some worse, some better

It can also make the crossover better with time alignment if you put the sub in the correct place, but again, that can be very specific location based correction
 

DVDdoug

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The "black hole" problem is the BIG issue. A +6dB boost is 4 times the power and +10dB is 10 times the power. The bass is where you already need power and woofer and efficiency and you can easily end-up driving your amp into clipping or over-driving the speaker.

I believe bass traps are the best solution. Buy absorbing/trapping the reflected bass you smooth-out the nulls AND anti-nulls. (DISCLAIMER - I don't have any treatment and I've never measured my room.)
 

Owl

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I have two rooms that I use with the same speakers. One has bass or corner damping and the other does not. The room shapes are different, and one has hard wood floors and the other carpet. I can definitely say that the bass traps work. Even small speakers will put out some bass frequencies that were absent in the un-damped room.
 

levimax

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I just went through this when I added 2 subs to a full range stereo system. The Todd Welti's article linked above is great as you get the theory and the practical application. From my experience the short answer is you can't fill bass nulls with DSP and more power, room treatments are expensive and aesthetically challenging and often impractical. This leaves multiple subs and DSP as the best solution in most cases. One thing to keep in mind is you don't need the biggest, best, and most expensive subs in a multi-sub system to get a huge improvement in bass response. Several smaller and cheaper subs that you can put into key locations can be very effective
 

Willem

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I agree with Don that for bass traps to be effective at these low frequencies they have to be pretty large. Floyd Tooole has argued this as well. So the most elegant and effective solution is indeed multiple subs (two already make a big difference, and the second one can be quite small), combined with dsp eq using e.g. Multi Sub Optimizer:
 

FeddyLost

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I have added this sub to get bit more low end push and I actually did... now I get decent bass from where I sit but the other places even standup, I get bit boomy sound ... so the balance is not there ...

I am just wondering If I can fix these issues with an addition to miniDSP (with or without dirac) to system or not....
First you need to understand what exactly causes this null/notch/bass deficiency.
If it's some destructive interference (i.e. like subtraction of bass when one your speaker is phased in reverse) then you can make some changes with DSP.
If it's some modal issues (i.e. your listening point is located in modal null or double null) then you can play with subwoofer location/phase/crossover and EQ everything to have "decent" LF responce at LP. Usually it will require heavy EQing the problematic frequency, so it will boom at corresponding modal peaks (i.e. near to wall or in corner).
If you need good LF responce at the multiple places in the room without boominess somewhere, most probably you'll need at least 2 subwoofers and a lot of processing with DSP.
Proper passive room treatment at frequencies below ~150 Hz is definitely not the thing your wife will appreciate. So IMO it's not an option.
Also I'd not recommend you to "fill" modal null by simple EQing it. This requires a lot of power and your listed equipment have some headroom only if your room is small and your SPL is really low.

Personally I see no problem if you have some issues somewhere else but not at main listening position.
Your setup is not a multi-seat home cinema, so I'd leave everything as is unless i.e. your walls rattle and small things fall from dresser in the corner.
 

DVDdoug

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Here is something I'm not sure about, but I'm sure some of the acoustics experts will know...

If you have a null in the middle of the room MIGHT you have an anti-mode at the walls (or ceiling & floors)? If so, I would assume that causes maximum wall vibration and boosting would be very-bad for the neighbors!
 

levimax

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Here is something I'm not sure about, but I'm sure some of the acoustics experts will know...

If you have a null in the middle of the room MIGHT you have an anti-mode at the walls (or ceiling & floors)? If so, I would assume that causes maximum wall vibration and boosting would be very-bad for the neighbors!
I will be interested to hear what the experts say about rattling the wall and bothering the neighbors. Playing around with adding the 2 subs I managed to get decent response at the LP but am amazed if I generate say a steady 30 Hz tone with REW and walk around the room how much variation there is .... you can read about "theory" but actually walking around the room and hearing the modes and anti-modes it is amazing and brings the theory to life.
 
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A

atoprak

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My 2 cents:
I do have experience with force-correcting bass nulls and to summarize it:
- it is definitely doable, by using adequate EQ or DRC (like Dirac), you can enforce the correction of the dip (even if it is wide and even if it is like -15dB deep) and your frequency response will be flat (or very close to flat)
- but this will potentially introduce elevated amount of ringing (you will see that in the Waterfall diagram, Wavelet diagram and RT60 diagram)
- will the ringing be audible? that depends on the room; in my living room I cannot fully correct my dips since I get killed by the excessive amount of ringing it produces but my friend has a much larger living room (like 70 sqm) and there ringing is barely audible
- this enforced correction will take its toll on your power amp, make sure that you do have enough headroom (every 3dB increase will double the power requirement!)

Also once you corrected your individual channels you might still have to do additional correction after checking the freq. response when both channels are driven.
Both channels can (and do) cause additional cancellations depending on your room - force-correcting that will have an additional amount of ringing, amp load, etc.

Final point is that probably you shall try it and see if you can tolerate the ringing + if your amp can tolerate the elevated power requirements

Yes... but It seems that the outcome is not certain and I have to try this ...
Try and error is fine.. but I need that equipment which my friend or neighbour dose not ... so ... I have to buy them....

If I hear that kind of ringing or strain on amp, all this investment will be vanished... If I knew/certain about a decent improvement on the sound, I am can order right away ..
 
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atoprak

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Filling in nulls is like filling up a black hole: it demands a lot of power, and even then. So read up on room modes first, and get a Umik-1 measurement microphone to measure actual response with the free REW software. Moving the subwoofer around may help, if you are lucky. The best way to smoothen this response problem is probably to use a second subwoofer in a different location (or even a third or fourth). That other sub will have peaks and dips at different frequencies because it will be located in a different spot in the room, so you will get more but smaller peaks and dips. Such averaging is usually very beneficial. The second sub does not have to be identical or even very large. See here for inspiration: http://archimago.blogspot.com/2020/05/musings-measurements-subwoofers-to.html

Instead of second sub, I would prefer no sub solution .. but .. I understand and know that this is highly unlikely will be the case...
Second sub is a big deal for me as I need to convince house hold about this :)
 

Willem

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It only needs a small and affordable sub like the BK Gemini, somewhere in a discreet corner. In the end, you cannot escape the laws of physics.
 
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atoprak

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Here's a quick overview of room modes: https://www.audiosciencereview.com/forum/index.php?threads/room-modes.25433/
And the Harman calculator: https://www.harman.com/documents/Room Mode Calculator_0.xls
And for reference Todd Welti's subwoofer placement guide: https://www.harman.com/documents/multsubs_0.pdf

Reading the above should help you understand the problem (the nature of the beast).

True nulls caused by a room mode are not really amenable to correction via EQ. They happen because the direct sound, D, is cancelled by the reflected sound R, so D-R=0. If you try to equalize to counter, then you will increase both D and R since you are just amplifying what comes out the speakers. If you increase power by ten (10 dB), then 10D - 1R = 0 for no gain. Except you are now putting out 10x the power, wasting a lot of headroom, and the sound out of the null will be very loud (boomy).

The usual solutions are to (1) move the subwoofer to position it to counter the nulls as best as possible, (2) move the listening position out of the null, (3) add another sub to "drive" the null by countering the reflected wave, or (4) add treatment (e.g. absorbers) to absorb the sound, reducing the null by reducing the reflected wave. The first three depend upon your flexibility in room arrangement and finances. The fourth option is usually impractical because at subwoofer frequencies the treatment depth and area must be very large to absorb enough energy to significantly affect the null (I have done it, with 27 panels 4" to 12" deep in a modest room, but it takes a lot of money, area/volume, and turns the room into something close to an anechoic chamber so sounds very "dead" -- and only gained me about 6~10 dB improvement in a null 20~30 dB deep). I moved the listening position a little, but like many am constrained by the room and the stuff in it, so added subs to counter the null.

HTH - Don

Thumbs up...
I agree and I know (I believe) what my problem is ... This is all about listening position and the shape of the room (so the system setup)..This is evident in REW simulation as well.. so I am more or less sure about the problem.... i.e. If I walk in the room and get closer to rear wall, I get what I want from these speakers event without a sub (not a fan of subs ! ) ...

there are two weird / unknowns to me ...

First, what happens when I stand up right at my listening position. If I standup .. everything is fine... the bass changes like night & day ...
Second my TV ... I really dont understand how it sound like without getting effected by the room that much ... I dont know what Sony does ... but sometime I ask my sell all these and buy a sound bar with similar tech ... or this high tech (HT09) surround system with all room correction magic...

these two makes me crazy ...
 
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atoprak

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The "black hole" problem is the BIG issue. A +6dB boost is 4 times the power and +10dB is 10 times the power. The bass is where you already need power and woofer and efficiency and you can easily end-up driving your amp into clipping or over-driving the speaker.

I believe bass traps are the best solution. Buy absorbing/trapping the reflected bass you smooth-out the nulls AND anti-nulls. (DISCLAIMER - I don't have any treatment and I've never measured my room.)

Would be my first choice but If had a separate listening room... living room wife factor ... killers. :(
 
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atoprak

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so I'd leave everything as is unless i.e. your walls rattle and small things fall from dresser in the corner.

That sometimes happen… I mean in some cases, even If the overall sound is not that laud, I hear my kitchen window (almost 30ft away from the listening position )rattling or receive some complaint about the very low end noise from the ones at the first floor.
 
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I don't have good news for you either. I have the same problem as you, sitting in the middle of the room and have huge dip between 40 and 60hz. Take a look at my EQ
Untitled.png


However, this 12dB boost doesn't do miracles. It only mitigates the dip for 6dBs

21.jpg
 
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