How to correct a -8db between 100 an 175 hz

[Snarfie]

I'm using mathaudio room EQ an got my self quite a dip -8db dip between a 100 an 175 Hz on my IMF CM2 monitors.

I see more or less as a negative bell curve. Now with a simple eq vst it is quite difficiult to determine the precies bandwith (between 100 and 175Hz). Result could be a uncontrolled bell curve an possible bad clipping.
For now i'm using EasyQ incombination with Mathaudio room EQ running on Foobar2000.

Now i don't know if this is the way to do it so if there are better solution let me know. For now it sound quite good got my self some addional low which sounds in key.

 

[waynel]

Move speakers nearer to rear wall.

 

[Χ Ξ Σ]

If you use REW, it can generate a more accurate set of EQ parameters. It might takes more than one bell curve overlaying to precisely fill that dip. I have tried Mathaudio Room EQ, it is more hassle-free though.

When you have a +6db EQ gian, you might want to set the global gain to -6db so that the peak doesn't go above 0db. Otherwise, If you try a really slow sweep, you might hear some distortion once it sweep through the EQed region.

 

[MRC01]

I've seen deep nulls like that act like a black hole. When it does, EQ (putting more energy into the null freq) becomes ineffective because (1) the null sucks up whatever energy you put into it, and (2) all that extra energy (the big EQ boost) forces the speaker to produce a lot more power at that frequency, which increases distortion. When this happens, I find that room treatment is effective. In this case, narrow band treatments like bass traps or resonators tuned for the problematic frequency.

Also, it's worth testing whether this null is SBIR or LBIR. If it is, you may be able to eliminate it by moving the speakers or listener position.

PS: looks like about 130 Hz, so the 1/2 wavelength distance (where it nulls) is 4.23 feet, so look for speaker or listener 2.12 feet from a wall.

 

[Snarfie]

When you have a +6db EQ gian, you might want to set the global gain to -6db so that the peak doesn't go above 0db. Otherwise, If you try a really slow sweep, you might hear some distortion once it sweep through the EQed region.

As you can see my preferd target curve is flat an compensate up to around +13db but it leaves the deep notche. Mathaudio does not compensate these notches/dips they describe it as follows "Quells resonance peaks of frequency response while leaving the deep notches. Avoids the overcompensation which happens in conventional linearizing room correction systems. " They think it could dammage you speakers.

 

[Snarfie]

Move speakers nearer to rear wall.

They already around 10cm from absorption pannels.

 

[Snarfie]

I've seen deep nulls like that act like a black hole. When it does, EQ (putting more energy into the null freq) becomes ineffective because (1) the null sucks up whatever energy you put into it, and (2) all that extra energy (the big EQ boost) forces the speaker to produce a lot more power at that frequency, which increases distortion. When this happens, I find that room treatment is effective. In this case, narrow band treatments like bass traps or resonators tuned for the problematic frequency.

Also, it's worth testing whether this null is SBIR or LBIR. If it is, you may be able to eliminate it by moving the speakers or listener position.

PS: looks like about 130 Hz, so the 1/2 wavelength distance (where it nulls) is 4.23 feet, so look for speaker or listener 2.12 feet from a wall.

Agreed room treatment is the most elegant solution however i want to try a software solution if possible. I can't move my speakers a lot.

 

[Absolute]

Compensating a cancellation fully could end in audible disaster, if you manage that without blowing the woofer to smithereens that is.
Usually we have these cancellations from the sidewalls/frontwalls/floor/ceiling around the area between 100-300 hz in normal rooms. I find that you quickly end up in a scenario where you compensate for a dip with more energy and then it suddenly sounds awfully muffled.

Not surprising since you change the sound in the whole room with EQ, not only where the microphone happens to be.

 

[Hipper]

If you use REW, it can generate a more accurate set of EQ parameters. It might takes more than one bell curve overlaying to precisely fill that dip. I have tried Mathaudio Room EQ, it is more hassle-free though.

When you have a +6db EQ gian, you might want to set the global gain to -6db so that the peak doesn't go above 0db. Otherwise, If you try a really slow sweep, you might hear some distortion once it sweep through the EQed region.

This is what I did. I used REW to get some filters, concentrating on the 0-300Hz region. I then applied the filters manually to the Parametric EQ of a Behringer DEQ2496. This has ten filters. I measured and applied filters in stereo, that is, both speakers together rather then individual speakers:

Green before EQ. I ran out of filters so that above around 180Hz I would need to use the Graphic EQ.

One problem I had was that when I first used REW values for the filters it didn't remove all of the major 55Hz dip. Therefore I manually removed most of it then measured REW and applied the filters. This worked out better as shown here. And it does sound better too!

 

[Frank Dernie]

I'm using mathaudio room EQ an got my self quite a dip -8db dip between a 100 an 175 Hz on my IMF CM2 monitors.

I see more or less as a negative bell curve. Now with a simple eq vst it is quite difficiult to determine the precies bandwith (between 100 and 175Hz). Result could be a uncontrolled bell curve an possible bad clipping.
For now i'm using EasyQ incombination with Mathaudio room EQ running on Foobar2000.

Now i don't know if this is the way to do it so if there are better solution let me know. For now it sound quite good got my self some addional low which sounds in key.

The only way to reduce nuls is to move the speakers.
The intensity of excitation of the various modes is the position of the excitation, which is only the position of the speaker in the room. If you excite a lot of the modes' harmonics the peaks and troughs will be smaller.
Electronic compensation can cut the peaks but is impractical to boost troughs much, I have never seen one that deep btw.
IME carefully position speakers first makes correction much better as well.

 

[Χ Ξ Σ]

This is what I did. I used REW to get some filters, concentrating on the 0-300Hz region. I then applied the filters manually to the Parametric EQ of a Behringer DEQ2496. This has ten filters. I measured and applied filters in stereo, that is, both speakers together rather then individual speakers:

View attachment 80746

Green before EQ. I ran out of filters so that above around 180Hz I would need to use the Graphic EQ.

One problem I had was that when I first used REW values for the filters it didn't remove all of the major 55Hz dip. Therefore I manually removed most of it then measured REW and applied the filters. This worked out better as shown here. And it does sound better too!

Wait... Are you saying you corrected a subbass null by applying EQ filters without subwoofers? I thought that was not possible. I have to use two subs to achieve that. Is the red curve prediction or measurement?

 

[ernestcarl]

Wait... Are you saying you corrected a subbass null by applying EQ filters without subwoofers? I thought that was not possible. I have to use two subs to achieve that. Is the red curve prediction or measurement?

If the speakers are big enough... still, it's not going to be a solution without its trade-offs.

 

[Hipper]

Wait... Are you saying you corrected a subbass null by applying EQ filters without subwoofers? I thought that was not possible. I have to use two subs to achieve that. Is the red curve prediction or measurement?

Yes. Red is the new measurement after EQ.

My room is highly treated with lots of bass traps. These bass traps reduced a lot of narrow nulls and a few not so wide peaks and nulls but did nothing for this 55Hz dip.

I realise that it is not supposed to be possible, or advisable, to EQ wide dips like this but I had spent a lot of time and effort trying to discover what was going on by:

• speaker and chair positioning
• trying to find where in the room the equivalent peak was by using test tones and SPL meter
• checking gear to make sure there wasn't some fault
• and asking advice.

In the end I just tried adding 5dB at 55Hz on the Behringer to see what happened and the frequency response at 55Hz simply increased by 5dB.

I've no idea what is going on but I now have a flat curve and the 55Hz region is nicely smooth, not only on a graph but as I hear it using test tones.

 

[mlee]

Could be floor bounce due to the monitors bass module not being close enough to the floor. The audibility of floor bounce is debatable, I think Toole and Linkwitz view it as more of a measurement ugly than an issue in practice. If you have a 3 way speaker with bass driver close to the ground maybe you can put it in the same location and do another sweep to see if the Null is different.

 

[Balle Clorin]

I would worry about the treble rise and peak you have also. I would expect this to sound very bright and thin...Does it not .? The frequency trend is far from conventional wisdom regarding a pleasant sound. Different speaker toe in would help. I would also try a completely different positioning . I had a fantastic improvement rearranging from speakers on short wall to long wall...

The speaker also has”inline resistive reflex system” I wonder if this is similar to the PMC transmission line speakers, many of them have an inherent deep cancellation in the range your problem is, sorry ,but trying other speakers may help you pinpoint the problem

Anyway, almost all room and speakers suffer from a dip or valley in the 100-300 range due to boundary effects