Q setting for Low Bass PEQ

[Daverich4]

My understanding from reading posts here is that it is not a good idea to try and raise dips in the Low Bass using PEQ. Is there some small amount of correction that would be acceptable? Say, 2-3 dB? Is that enough to make any audible difference? If that amount would help out can someone suggest the amount of Q setting I should use in Roon? Thanks.

 

[janbth]

First some general comments about plots:

• There is a camera icon in the upper left corner. You can use that to produce plots.
• The Y-axis should span about 50 dB. This is conventional and allows us to compare with other measurements.
• Use Var smoothing. 1/6 smoothing is popular for some reason I have never understood. It hides the data in the bass region. Don’t do that! This is especially important if you want to use REW to compute filters, because REW uses the smoothed response as input. (Smoothed input leads to PEQ filters with too low Qs.)

Now to answer your question: Should you use PEQ filters to boost a dip in the response: In general the answer is no, but if you know what you are doing, it may work. It depends on the room modes in your listening room. If there is a dip, there will be a room mode with a frequency at that dip. You will need to separate two cases:

1. The dip is caused by the speaker(s) being located in a null of the mode. Boost OK!
2. The dip is caused by the listening position is located in a null of the mode. Boost not OK!

You'll have to do some work to figure out if it’s 1 or 2 in your setup. (It may be a bit of both, but let’s not complicate things…)

If you have case 1, then go ahead and try to boost. You will probably need to experiment with Q and gain for the PEQ filter.

 

[DVDdoug]

+3dB is double the power and +6dB is 4 times the power. I probably wouldn't go beyond +6dB. Or your woofer or amplifier may distort and that's a clue that you've got too much boost.

As you may know, the problem is standing wave cancelation and although you don't get complete cancelation, if you did have complete cancelation it would take "infinite power" to overcome the infinite wave cancelation.

 

[NTK]

I think a big problem with boosting dips is that if the listener move out of the null position (or there are other listeners outside of the null position [Edit] if the problem is due to the listener being in the null position, not the speaker), they will be hit with a bass peak. And peaks are a lot more audible than dips.

 

[Keith_W]

Well the "rule" that nulls should not be boosted should be taken with a bit of nuance. I see that multiple posters have beaten me to it

One of the considerations is how much headroom you have in your speakers. For that, you look at distortion. This is a display of THD:

Well well, look at that. There is less distortion in your EQ'ed response than in your native response, despite boosting the low frequencies. . I found this a bit difficult to believe so I checked whether it's a real measurement or a simulation. The noise floor in the waterfall graphs are different, so it's a real measurement.

The other reason distortion might be so low is that you are measuring at a very low volume. But I see you are using a UMIK-1, which has a built-in SPL meter, and the nominal volume for the sweep is about 75dB. Is this your normal listening volume? If it's higher than your normal listening volume, you may have some scope to boost those nulls even further

Having said all that, this isn't the best way to look at distortion - for that, you need a stepped sine distortion measurement.

 

[Daverich4]

First some general comments about plots:

• There is a camera icon in the upper left corner. You can use that to produce plots.
• The Y-axis should span about 50 dB. This is conventional and allows us to compare with other measurements.
• Use Var smoothing. 1/6 smoothing is popular for some reason I have never understood. It hides the data in the bass region. Don’t do that! This is especially important if you want to use REW to compute filters, because REW uses the smoothed response as input. (Smoothed input leads to PEQ filters with too low Qs.)

Now to answer your question: Should you use PEQ filters to boost a dip in the response: In general the answer is no, but if you know what you are doing, it may work. It depends on the room modes in your listening room. If there is a dip, there will be a room mode with a frequency at that dip. You will need to separate two cases:

1. The dip is caused by the speaker(s) being located in a null of the mode. Boost OK!
2. The dip is caused by the listening position is located in a null of the mode. Boost not OK!

You'll have to do some work to figure out if it’s 1 or 2 in your setup. (It may be a bit of both, but let’s not complicate things…)

If you have case 1, then go ahead and try to boost. You will probably need to experiment with Q and gain for the PEQ filter.

Thank you for your detailed response. I'm pretty new to REW so appreciate the tips. My dealer assisted in the placement of the speakers. I started choosing the location of the listening position at 1/3 of the way into the room from the back wall. I then attempted to fine tune the position by using Jim Smith's method of using a mic and an RTA to find a location where the RTA frequency response is the smoothest. I ended up slightly closer to the back wall than when I started. From there is there some standard way to answer the question of whether the speakers or the listening position is causing the nulls? Thanks again.

 

[Daverich4]

I think a big problem with boosting dips is that if the listener move out of the null position (or there are other listeners outside of the null position [Edit] if the problem is due to the listener being in the null position, not the speaker), they will be hit with a bass peak. And peaks are a lot more audible than dips.

I'm the only listener so it's only the main listening position that I'm concerned with. I determined the position by using Jim Smith's method with a calibrated microphone and a RTA. That doesn't mean that I did it properly and avoided a null in that location, just that I tried to locate a suitable location.

 

[Daverich4]

Well the "rule" that nulls should not be boosted should be taken with a bit of nuance. I see that multiple posters have beaten me to it

One of the considerations is how much headroom you have in your speakers. For that, you look at distortion. This is a display of THD:

View attachment 520829

Well well, look at that. There is less distortion in your EQ'ed response than in your native response, despite boosting the low frequencies. . I found this a bit difficult to believe so I checked whether it's a real measurement or a simulation. The noise floor in the waterfall graphs are different, so it's a real measurement.

The other reason distortion might be so low is that you are measuring at a very low volume. But I see you are using a UMIK-1, which has a built-in SPL meter, and the nominal volume for the sweep is about 75dB. Is this your normal listening volume? If it's higher than your normal listening volume, you may have some scope to boost those nulls even further

Having said all that, this isn't the best way to look at distortion - for that, you need a stepped sine distortion measurement.

Thank you for the response. Yes, around 75dB is the level I listen to most of the time with exceptions for when I'm home alone and it might go up to around 80dB. I'm not a fan of the higher levels some people listen to.

 

[janbth]

From there is there some standard way to answer the question of whether the speakers or the listening position is causing the nulls?

You could try to map out the standing wave patterns of the modes in your room. Check out Amroc:
https://amcoustics.com/tools/amroc
This is a useful tool to visualize how the modes look like.

If the goal is to find the best location for your speakers, there are also boundary effects to consider. These can also cause peaks and dips in the response. Try to search for ‘SBIR’ or ‘Allison effect’.

 

[Torin Krell]

Of course optimizing speaker and sub placement, listening position, and room treatment are the first steps. Then IMHO using PEQ to lower peaks before considering boosting dips is the prudent approach. For my powered subs raising their input level and simply lowering a peak instead of boosting 2 dips worked much better and did not push against the subs build in DSP optimized low end rolloff.

 

[OCA]

My understanding from reading posts here is that it is not a good idea to try and raise dips in the Low Bass using PEQ. Is there some small amount of correction that would be acceptable? Say, 2-3 dB? Is that enough to make any audible difference? If that amount would help out can someone suggest the amount of Q setting I should use in Roon? Thanks.

Here are three key factors to keep in mind when boosting bass frequencies:

Filter type: Make sure the filter is minimum phase. Applying a linear phase filter to fix low-frequency room modes can lead to serious issues, as it breaks causality (Roon’s PEQ filters are minimum phase).
Distortion risk: Check whether the level of boost introduces distortion at the highest volumes you plan to use. Excessive boosting can push your system beyond its limits.
Room nulls: Determine whether you’re dealing with a deep room null. These are usually non-minimum phase and shouldn’t be corrected. Identifying them is tricky. You may need ARMA modeling to find zeros near the unit circle, or use a method that measures how much the phase deviates from minimum phase at the frequency in question.

 

[Daverich4]

You could try to map out the standing wave patterns of the modes in your room. Check out Amroc:
https://amcoustics.com/tools/amroc
This is a useful tool to visualize how the modes look like.

If the goal is to find the best location for your speakers, there are also boundary effects to consider. These can also cause peaks and dips in the response. Try to search for ‘SBIR’ or ‘Allison effect’.

Thanks, you’ve been very helpful. I can see how to set up the room information in the link you provided but it’s going to take some time to work out what it’s telling me. I think the speakers are in a pretty good location, at least it took some time to get them dialed in but I’ll look up the terms you provided to learn more about it.

 

[Daverich4]

Here are three key factors to keep in mind when boosting bass frequencies:

Filter type: Make sure the filter is minimum phase. Applying a linear phase filter to fix low-frequency room modes can lead to serious issues, as it breaks causality (Roon’s PEQ filters are minimum phase).
Distortion risk: Check whether the level of boost introduces distortion at the highest volumes you plan to use. Excessive boosting can push your system beyond its limits.
Room nulls: Determine whether you’re dealing with a deep room null. These are usually non-minimum phase and shouldn’t be corrected. Identifying them is tricky. You may need ARMA modeling to find zeros near the unit circle, or use a method that measures how much the phase deviates from minimum phase at the frequency in question.

I appreciate the help. I would use Roon to do the PEQ. Keith_W gave me some tips about checking Distortion earlier in this thread so that’s also something I’ll be paying attention to. Thanks.

 

[Daverich4]

Of course optimizing speaker and sub placement, listening position, and room treatment are the first steps. Then IMHO using PEQ to lower peaks before considering boosting dips is the prudent approach. For my powered subs raising their input level and simply lowering a peak instead of boosting 2 dips worked much better and did not push against the subs build in DSP optimized low end rolloff.

I could add a pair of subs if that would be helpful. It’s a dedicated room which means they can go anywhere. I’ve looked at the information Harman has about sub placement as well as being willing to do the sub crawl. Still trying to get my head wrapped around some of this.