Help! Nulls needing treatment

[NoDad]

I need some help. Below is a REW measurement and as you can see below there’s a big dip 90 – 180 Hz and another around 300 – 450 Hz. These change depending on how far away from the front wall I place the speakers. Which leads me to believe it’s room reflection related.

According to the Wall Bounce calculator 2D Excel file (http://arqen.com/wp-content/media/Wall_Bounce_Calculator_2D.xls) it should work to put absorbers on the front wall. I have never done this before so I need all the help I can get?

What size & thickness should I get?
Will front wall treatment be enough?
Should I get the fabric absorbers or the ones with wood patterns on the front?
Anything else I can do to improve the sound?

My equipment is…
Ascend Sierra LX speakers
Two Aperion Audio Bravus II 8D subwoofers
MiniDSP SHD
Audiophonics Hypex NC502 amplifier

The room is 12’4” x 24’7”. The audio stand contains a TV lift and has a skin of acoustic paneling. I liked the look and thought it might help acoustically. The screen shot below shows the location of the speakers and the subs. There is a 4’ opening to the right (where the 7.48 measurement is listed in the pic below).

Any tips will be greatly appreciated. Thank you.

 

[ppataki]

I will let others comment too but according to my experience, no bass trap will really solve your issue, no matter where you put it and how much. Been there, done that.....

You actually need one or more subwoofer(s) to tame that null - or you need to rearrange the room to see if there are positions where the null is not that wide and deep

Would that be an option for you to consider?

 

[Bjorn]

I will let others comment too but according to my experience, no bass trap will really solve your issue, no matter where you put it and how much. Been there, done that.....

You actually need one or more subwoofer(s) to tame that null - or you need to rearrange the room to see if there are positions where the null is not that wide and deep

Would that be an option for you to consider?

That's not true. Correct treatment will work.
However, for the lowest frequencies (generally below 100 Hz) it requires fairly large area for effective treatment.

Below is a before and after treatment of a 115-120 Hz cancellation with RPG Broadsorbor panels.

Before:

Two panels:

Four panels (slightly better result):

As we can see it didn't take much to treat the nulls at frequencies 115-120 Hz. But if we treating something at for example 60 Hz, it would require a lot more.

It's also important to understand that treatment will always work in the important time domain and also for the whole room. Just focusing on the frequency response will result in a mediocre result at best. That being said, something like DBA or DIRAC Art with multiple subs will also work very well.

 

[Keith_W]

Please read book 2 of the REW eBook. I direct you to section 4.1, "interpreting the frequency response". There is a procedure in there about how to diagnose the cause of nulls in the FR.

There is also a possibility that the null at 110Hz is due to SBIR. If the distance from the front of the woofer to the front wall is about 80cm (quarter of a 110Hz wavelength) it would be highly likely. To diagnose if it's SBIR or not, try pushing the speaker closer to the front wall.

 

[NoDad]

ppataki, thanks for your reply. Aren't the nulls a little high to be covered by additional subs? How high can the crossover be set before the location of the subs become apparent?​

I had the TV & speakers where the right sofa is located, but it didn't work real well. No measurements unfortunately. Not sure what other options there are.

 

[dimedrol]

I will let others comment too but according to my experience, no bass trap will really solve your issue, no matter where you put it and how much. Been there, done that.....

You actually need one or more subwoofer(s) to tame that null - or you need to rearrange the room to see if there are positions where the null is not that wide and deep

Would that be an option for you to consider?

I second that for a typical living room, unless you're willing to turn yours into a recording studio. I am in a very similar situation myself after moving to a new apartment, and I am planning on getting a sub or two to rectify the bass issue, because unfortunately for me, moving the speakers is not an option.

 

[sigbergaudio]

Have you tried pushing the speakers all the way as close to the back wall as they can go?

 

[Geert]

I need some help. Below is a REW measurement and as you can see below there’s a big dip 90 – 180 Hz and another around 300 – 450 Hz. These change depending on how far away from the front wall I place the speakers. Which leads me to believe it’s room reflection related.

That dip between 90 – 180 Hz is to wide to be caused by front wall reflections only. There are 2 effects at work in this frequency range, meaning the absorbers you want to place behind the speakers will only solve part of the problem. So you first need to identify these 2 effects before you can treat them. As an example, one of the effects could be a floor or ceiling reflection or a room mode (you need to do the math and/or measure to be sure).

 

[sigbergaudio]

90-180hz is also so low that it will be hard to realistically treat it with acoustic panels in a normal living room.

 

[NoDad]

Thank you all for your replies.
The speakers were 57 cm from the front wall and 78 from the side walls. I just tried moving the speakers close to the wall. The measurement is ...

Wow, I didn't think it would make such a difference. It does look better. Is the dip at around 120 HZ narrow enough to be ignored. Will this affect the depth of the music stage? Will the TV stand between the speakers cause any issues?

By the way, all the measurements are made without any EQ. I figured I'd try to make it as good as possible before messing with EQ.

 

[sigbergaudio]

Thank you all for your replies.
The speakers were 57 cm from the front wall and 78 from the side walls. I just tried moving the speakers close to the wall. The measurement is ...
View attachment 493520
Wow, I didn't think it would make such a difference. It does look better. Is the dip at around 120 HZ narrow enough to be ignored. Will this affect the depth of the music stage? Will the TV stand between the speakers cause any issues?

By the way, all the measurements are made without any EQ. I figured I'd try to make it as good as possible before messing with EQ.

The 120hz is narrow enough to be ignored. It will likely not directly affect the depth of the music stage, but you may get an experience of slightly reduced soundstage due to the fact that the speakers are further away from you. The TV stand will not cause any meaningful issues.

What you may experience is that you get too much bass if the speakers aren't designed to account for the potential boundary reinforcement from the wall. This is why more speaker manufacturers should design speakers to be placed close to the wall.

 

[Bjorn]

90-180hz is also so low that it will be hard to realistically treat it with acoustic panels in a normal living room.

Seriously? Pure nonsense.

 

[Bjorn]

Thank you all for your replies.
The speakers were 57 cm from the front wall and 78 from the side walls. I just tried moving the speakers close to the wall. The measurement is ...
View attachment 493520
Wow, I didn't think it would make such a difference. It does look better. Is the dip at around 120 HZ narrow enough to be ignored. Will this affect the depth of the music stage? Will the TV stand between the speakers cause any issues?

By the way, all the measurements are made without any EQ. I figured I'd try to make it as good as possible before messing with EQ.

While you avoid SBIR with such a placement, you will have specular reflections with very high gain and you will also likely have stronger resonances in lower midrange and part of the bass frequencies. So you still need treatment for a great result.

 

[NoDad]

Just listened and no affect on the stage, but I'll listen some more. The speakers are delivered with foam plugs to be used close to the wall. I'm going to find them and see if there's a difference.

 

[NoDad]

Bjorn, what kind of treatments are we talking about? Similar to what I initially planned? I mean, front wall absorbers?

 

[Keith_W]

Wow, I didn't think it would make such a difference. It does look better. Is the dip at around 120 HZ narrow enough to be ignored. Will this affect the depth of the music stage? Will the TV stand between the speakers cause any issues?

Once again, read Book 2 of the REW eBook. There is a section in there about ERB and psychoacoustic smoothing and how it will help you determine if a dip is audible or not.

 

[Bjorn]

Bjorn, what kind of treatments are we talking about? Similar to what I initially planned? I mean, front wall absorbers?

Depends on what you can do aesthtically etc. But I would recommend at least one absorber of minimum 120x60 cm on each inside of the speaker. It should address at least down to 200 Hz area. You need to disregard measuring data from most companies at these are quite misleading. RPG Broadsorbor with both 3" and 4" will work great, but not sure if you can buy those were you live. With other absorbers, they generally need to be twice as thick for the same low frequency absorption. DIY is also an option of course.

You have strong specular reflection from nearest sidewalls and ceiling. This is also very important to treat. Not sure though you can treat the sidewalls considering the windows on one side. A movable absorber could be an option there.

 

[Flaesh]

Wow

Can you upload .mdat?

 

[NoDad]

Sorry about the disappearance. I caught the flu and have been down for the count. Anyway, I have done some more speaker moving and testing. I have two sets of speakers, the Ascend Sierra LX mentioned above. I also own a pair of Harbeth 30.1. After lots of moving and testing yesterday and today I have finally settled on using the Harbeth speakers. The speakers (the center of the front) are now sitting 67 cm from the front wall and 79 cm from the side walls. There's still some dips, but not as deep as before. Attached is the mdat file.

 

[NoDad]

Once again, read Book 2 of the REW eBook. There is a section in there about ERB and psychoacoustic smoothing and how it will help you determine if a dip is audible or not.

Thanks for the tip. I had looked at it before, but apparently not reading it properly. I plan to finish it tonight.