• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Deep mid-bass cancellation Null

Richx200

Active Member
Joined
May 20, 2024
Messages
105
Likes
39
Hi,

I have a real problem with deep mid-bass cancellation null. (see attached) I tried moving/pointing the 2 subs around the room along with moving the mic position; sometimes I would get a little change, but the sub was in an impossible position like in front of a door. From what I have read, this problem cannot be solved with a DSP. Is there any other way I can solve this issue? The wife is a very firm "NO" on bass traps.

This Null is really skewing my room correction results.

Thank you for any help.
 

Attachments

  • Spectrogram Peak Energy.jpg
    Spectrogram Peak Energy.jpg
    93 KB · Views: 185
  • Sub Impulse.jpg
    Sub Impulse.jpg
    147.9 KB · Views: 179
  • SUB SPL.jpg
    SUB SPL.jpg
    89.8 KB · Views: 181
You'll probably have to live with it. I assume more subs are also out of the question.

Does it sound that bad or just measure bad? Usually narrow dips in frequency response aren't as annoying as resonant bumps.

From what I have read, this problem cannot be solved with a DSP.
That's pretty-much true. It takes extreme power and lots of big subs to overcome soundwave cancelation. i.e. a 12dB boost requires 16 times the power.
The wife is a very firm "NO" on bass traps.
There are membrane bass traps that are relatively thin and possibly attractive.
 
Well, at home it works, I have my resonance at 34 Hertz, so I use a high-pass filter that runs at 70 Hertz with an 18 dB slope, good and in addition I have linearized the frequency response up to 150 Hz via REW and everything works wonderfully
 
Firstly I would measure each sub on their own to help find the root cause of the null.

Measure then move the microphone by 1m forward or backwards and remeasure.

If the null remains the same likely cause is SBIR.

If the null changes then you are likely looking at a room mode.

If the null is only present when running both subs then you most likely have a time alignment mis match between the subwoofers.
 
I'm using a special bass trap setup for a similar mode of my own, but for 30Hz instead. The way it works is by the fact that porus bass traps work best when they're in the middle of the wave, and the back of my seat happens to be near the middle, so I have a thick slab of mineral wool acting like a cozy cubby there. It helps by at least 2 dB and is a lot cheaper than getting a second subwoofer. And, it doesn't look totally ugly because I used only the finest fabric from Hobby Lobby. Would something like this work for you?
 
Hi,

I have a real problem with deep mid-bass cancellation null. (see attached) I tried moving/pointing the 2 subs around the room along with moving the mic position; sometimes I would get a little change, but the sub was in an impossible position like in front of a door. From what I have read, this problem cannot be solved with a DSP. Is there any other way I can solve this issue? The wife is a very firm "NO" on bass traps.

This Null is really skewing my room correction results.

Thank you for any help.

Your in-room bass response actually looks pretty good to me. Room correction shouldn't try to fix deep nulls (dip limiting).
 
Does it sound that bad or just measure bad? Usually narrow dips in frequency response aren't as annoying as resonant bumps.

This is a key question IMHO. I've been surprised at how difficult it is for me to detect one or two bass nulls/dips in regular listening when they are very narrow (and not crazy-huge in amplitude).
 
Firstly I would measure each sub on their own to help find the root cause of the null.

Measure then move the microphone by 1m forward or backwards and remeasure.

If the null remains the same likely cause is SBIR.

If the null changes then you are likely looking at a room mode.

If the null is only present when running both subs then you most likely have a time alignment mis match between the subwoofers.
The null can also be due to the listening position. If the listening position is located at a room mode null, relocating the subwoofers will not help much. The solutions are room treatments (can either be passive such as bass traps or active) or near-field subs where you rely on the direct sound from the subs and not from reverberation build-ups.
 
In closed rooms there are 3 Resonances, which we can stimulate to sound with the help of the speakers' energy. If we want to have super fast and nice Bass, we should not stimulate these resonances. I do it with the help of Eqlizator.

Each of us has similar rooms, so there are no miracles.
 

Attachments

  • kor der Box1.jpg
    kor der Box1.jpg
    399.4 KB · Views: 58
  • so kann man das machen.jpg
    so kann man das machen.jpg
    149.1 KB · Views: 59
You'll probably have to live with it. I assume more subs are also out of the question.

Does it sound that bad or just measure bad? Usually narrow dips in frequency response aren't as annoying as resonant bumps.


That's pretty-much true. It takes extreme power and lots of big subs to overcome soundwave cancelation. i.e. a 12dB boost requires 16 times the power.

There are membrane bass traps that are relatively thin and possibly attractive.
After I run ARC, there isn't any bass at all. I have to increase the SVS volume to 0db (max) and then ARC to +5db to hear any bass; in all, that leaves me +5db left. The bass I hear hasn't any timber, just one muddy note.
Your in-room bass response actually looks pretty good to me. Room correction shouldn't try to fix deep nulls (dip limiting).
See Attached
Your in-room bass response actually looks pretty good to me. Room correction shouldn't try to fix deep nulls (dip limiting).
see Attached
Firstly I would measure each sub on their own to help find the root cause of the null.

Measure then move the microphone by 1m forward or backwards and remeasure.

If the null remains the same likely cause is SBIR.

If the null changes then you are likely looking at a room mode.

If the null is only present when running both subs then you most likely have a time alignment mis match between the subwoofers.
Going to try a new approach.
 

Attachments

  • Screenshot (31).png
    Screenshot (31).png
    256.6 KB · Views: 58
Thank you all for your responses.

Going to try to work this out with what I have to work with.

Anthem MRX 1140 ARC Genesis and 2-SVS 13 Ultra with Amp upgrade SVS App.

Wipe all AVR settings, then with quick measure running I'll try :

SVS App Sub; moving subs (can they be moved higher), polarity + -, Phase 0–180, Low Pass Filter 30-200 If I can get good results I'll run ARC and try changing distances.

I'm not sure if any of this will work, is the goal to eliminate the null or mask it?

Does it matter if I take measurements in the room, will it affect the corrections ?

Thank you
 
I have a very deep null around 48hz.

It doesn't show up in the left or right measurements.

It shows up with a test tone playing through both left and right.

The cause is the asymmetrical rear of the room, the left rear is open to the kitchen and other area, so the "reflection" of that range of bass goes 180 degrees out of phase at the listeining position.

I didn't notice it until measured. I still don't notice it with music.

If measuring music, using the RTA function of REW, the hole is there sometimes (mono bass) and is not there at other times (stereo bass).

I could try to chase it down, and correct for it, but other than little experiments to figure it out, I don't worry about it.

Left, Right and Both speakers with mono sourcce (test tone)

1723473577080.png


But with music...

Top is the in-room RTA at the listening position. No hole, or extremely narrorw

Other two traces are the RTA of the left and right channels of the source CD.

Ignore black line, they aren't synchronized, red is peak value, and the in-room matches well with the source.

1723473835145.png
 
Last edited:
I have a very deep null around 48hz.

It doesn't show up in the left or right measurements.

It shows up with a test tone playing through both left and right.

The cause is the asymmetrical rear of the room, the left rear is open to the kitchen and other area, so the "reflection" of that range of bass goes 180 degrees out of phase at the listeining position.

I didn't notice it until measured. I still don't notice it with music.

If measuring music, using the RTA function of REW, the hole is there sometimes (mono bass) and is not there at other times (stereo bass).

I could try to chase it down, and correct for it, but other than little experiments to figure it out, I don't worry about it.

Left, Right and Both speakers with mono sourcce (test tone)

View attachment 386110

But with music...

Top is the in-room RTA at the listening position. No hole, or extremely narrorw

Other two traces are the RTA of the left and right channels of the source CD.

Ignore black line, they aren't synchronized, red is peak value, and the in-room matches well with the source.

View attachment 386111
Have you tried any deep bass music like Techno with this setup?
 
For the last few days I have been working on the Null and I think I have the problem solved. I think the graph looks good, the bass sounds much better, and I have headroom on the subs. The problem is that the settings made by ARC Genesis are inconsistent with the material I used to get rid of the Null.

Floyd Toole's book Sound Reproduction in Chapter 8 page 262 he states: "When measurements are done it is common for some individuals to try equalizing each sub separately and then combine them. Again, disappointment is almost always guaranteed because when the system is in "play" mode all subwoofers are operating simultaneously, and the results of the acoustical summation is unpredictable. The measurement that matters is the one of all subwoofers operating simultaneously. For individually measured subwoofer outputs to sum in a predictable manner ; the measurements must be the transfer function - amplitude and phase - not the steady - state amplitude response. This is the basis of room mode manipulation schemes described in Sect. 8.2.7-."

Arc Genesis didn't follow Toole and produced the these settings:

3db difference between sub 1 and sub 2

SUBWOOFER 1
Subwoofer Crossover Frequency (or Low-Frequency Extension): 80 Hz
High-Pass Frequency: 15 Hz
High-Pass Slope: Flat
Minimum Correction Frequency: 15 Hz
Phase Filter: 120 degrees @ 80 Hz

SUBWOOFER 2
Subwoofer Crossover Frequency (or Low-Frequency Extension): 160 Hz
High-Pass Frequency: 16 Hz
High-Pass Slope: 10th
Minimum Correction Frequency: 15 Hz
Phase Filter: 0 degrees @ 80 Hz

Overall, I would say ARC did a good job, but I don't understand how or why the two subs could be so far apart?
 

Attachments

  • New Position 45 deg Back wall.jpg
    New Position 45 deg Back wall.jpg
    90.4 KB · Views: 38
If you have no automated correction system, I recommend using the free software Multi-Sub Optimizer along with REW to take the required measurements.

Optimize both subs without the mains, using multi sub optimzer.

Then cross over the optimized subs with the mains.

In a third step, you may optimize the combined response. I am using MMM measuring technique and then apply corrections up to approx. 300-400Hz (mainly cutting peaks, no large boosts).

 
Back
Top Bottom