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Need Help - Dips in Room EQ/Acoustics with MiniDSP/REW

ronnzi

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Hello Everyone,

So I just got into more in-depth tuning of my home theater system. I am forced into a lot of compromises since I live in a condo. My entertainment center has to be in the front right corner of a somewhat large and open living room. Moreover, due to furniture (and spousal approval concerns), the only place I’m able to put my dual subs are behind my couch. One is closer to the wall and near a cement pillar which might provide some bass re-enforcement, but the other is behind the couch, more or less in the middle of the room, which I know is a terrible place. Also, one of the main “walls” is ceiling-to-floor windows, though I at least have cloth blinds to somewhat help. I provided pictures of the room for a bit of context, though it doesn’t exactly show how much distance there is after the subs to the back of the room (there is a decent amount).

Here is a list of my components so you have an understanding of what I’m working with:

- Onkyo TX-RZ810 receiver (AccuEq room correction)
- Monoprice Monolith x7 amp (powering all 5 main speakers)
- 2 SVS Prime Pinnacle front towers
- 1 SVS Ultra center
- 2 SVS Prime satellites (ceiling mounted and angled down)
- HSU VTF3-Mk2 and VTF3-HO subs
- MiniDSP 2x4 HD (for subs)
- Jensen ISO-Max ground loop isolation transformers for the 5 main speakers to break a ground loop issue created by my PC

Anyways, utilizing Onkyo’s room correction and REW/MiniDSP to flatten then subs’ responses, this is what I have so far (see the attached graph). I should mention that this graph was taken with all room correction on, in Onkyo’s “ALL CHANNEL” mode since I wanted to see what all the speakers were doing together (I typically use L+R+subs stereo mode when tweaking the subs with MiniDSP). The mains and center are crossed at 80hz, and the surround are crossed at 100hz.

I think I can tweak between 20-30hz further to bring that up a bit, and generally raise the level on the subs to have the lowend raised a bit more, but I’m more concerned about the 80-120hz range, as I’m not sure what is causing that. Is there something I might be able to try with more EQ and minor speaker placement tweaks, or are the responses I’m getting just way too far off.

Any help and guidance would be greatly appreciated. For what it’s worth, I’ve spent a ton of time trying to get the low end smoothed out through EQ already, but perhaps I’m just not doing the best job?
 

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DVDdoug

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You can't always fix a dip because your amplifier and speakers/subs might be putting-out the soundwaves but the waves being canceled by a reflected wave (a standing wave node). i.e. A 3dB boost requires twice the power and a 6dB boost 4 times the power, and of course the speaker needs to handle the power without distortion.

Of course the same thing happens when you try to "extend" the low-end of your speaker/subwoofer... You can exceed the limits of your amplifier and/or speaker. (You can't EQ a 5-inch woofer to put-out bass you can feel.)
 
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ronnzi

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Yeah that makes sense. Most of the deficiencies in my setup are the room, I believe, but I’m trying to figure out which dips/raises are worth treating vs when to leave it alone. I try limiting the amount of
db increase as much as I can obviously, but I’m making so many tweaks in the MiniDSP on top of what REW’s automatic curve already did, that it’s hard to know when I’m going overboard. Just much to learn
 

Eetu

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My guess is that the 100-120Hz dips are caused by front wall SBIR null. Are your tower speakers roughly 70-80cm from the front wall (distance from cabinet front/driver to wall behind)? If it's possible to move them another 30cm away from the wall (closer to listening position) you can shift the SBIR null down in frequency to where your subs take over.

Other option is to move the towers closer to the front wall (only leaving ~10 cm air space). This will shift the SBIR null up in frequency so that you can effectively use absorption panels behind the speakers.

Try it out, remeasure and hopefully you find a solution!
 
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ronnzi

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Thanks for the response! I will have to measure when I get home, but my guess is my fronts are closer to 40-50cm from the front wall. I will do some playing around with the distances and see what happens - thanks for the suggestion!
 

alex-z

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"one of the main “walls” is ceiling-to-floor windows, though I at least have cloth blinds to somewhat help"

Curtains really don't help with windows. You only get a small amount of treble absorption, the glass still has a huge amount of reflected energy. If you want the window to disappear acoustically you would need movable absorption panels mounted on a track.

Your response already looks pretty good. Only thing I would do is place 5.5" absorption panels behind the front speakers, and then move the speakers as close to the wall as possible. That should significantly reduce SBIR in the 100-200Hz region.

Mounting some ceiling panels would also be good if you can get away with it, helps overall decay times.
 
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ronnzi

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Thanks for the response. Right now I’m trying to get away without specific sound proofing treatments besides what is already in the room (rugs, furniture, etc.), but I would love to go down that path in the future, spouse permitting :D I will definitely use the suggestions you’ve made when I get there.

For now, after pulling out the front speakers a little more and repositioning one of the subs, I seem to have improved things a bit. I’m going to keep messing with it, but I think I’m starting to get the hang of using the auto-EQ curves for the subs in REW (hint: averaging multiple seat positions really helped me).
 

Galz

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Doesn't moving the speakers closer to the wall do more harm than good? Wouldn't you then get a boost to bass frequencies below the 1st SBIR frequency and stronger effect of room modes? I am pretty new to this, but sounds like that could be even worse than some SBIR.

Won't the extent of the SBIR cancellation (at least theoretically) gets reduced as the speakers are further from the wall, as the direct sound amplitude scales with 1/r where r is the distance between you and the speaker, while the reflected energy is 1/d where d is the total distance from speaker to wall to you (which isn't actually a straight line, as it needs to reach you after reflecting off the wall). For example if speaker is 1m from wall and you are 2m from speaker, r=2m and d is at least 4m, so the amplitude after cancelation will be 1/2-1/4=1/4, and the energy will be (1/4^2)/(1/2^2)=1/4, which is a 6db dip (in reality a bit less due to angles from wall making d longer).

Please let me know if I understand anything incorrectly.

I've also seen comments about distance from wall improving imaging, but couldn't find any meaningful explanations why.
 
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ronnzi

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Doesn't moving the speakers closer to the wall do more harm than good? Wouldn't you then get a boost to bass frequencies below the 1st SBIR frequency and stronger effect of room modes? I am pretty new to this, but sounds like that could be even worse than some SBIR.

Won't the extent of the SBIR cancellation (at least theoretically) gets reduced as the speakers are further from the wall, as the direct sound amplitude scales with 1/r where r is the distance between you and the speaker, while the reflected energy is 1/d where d is the total distance from speaker to wall to you (which isn't actually a straight line, as it needs to reach you after reflecting off the wall). For example if speaker is 1m from wall and you are 2m from speaker, r=2m and d is at least 4m, so the amplitude after cancelation will be 1/2-1/4=1/4, and the energy will be (1/4^2)/(1/2^2)=1/4, which is a 6db dip (in reality a bit less due to angles from wall making d longer).

Please let me know if I understand anything incorrectly.

I've also seen comments about distance from wall improving imaging, but couldn't find any meaningful explanations why.

I’m new to this too, but if I read the replies correctly, it’s being suggested that to help the situation I should either (a) move the speakers out further from the wall so that they are at least 70-80cm’s away, or (b) move them closer and then heavily treat the walls behind them with thick (5.5inch) absorption panels.

Someone chime in if my understanding isn’t correct as well. Sounds like these would just be two different ways to try to tackle the reflections, with option (a) probably sounding better, but being less practical depending on the room setup.
 

GimeDsp

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So your measurement really doesn't have the info we need.

1. decide how big of a listening position you want to correct far. you can start with 2 or 3, IE, whole couch.

2. You need to take off all DSP/crossovers from speakers and subs and measure them separately

If either sub or speaker is showing large suck ours or high peaks these need to be fixed with positioning changes without your allowed area.

3. With speakers you want a smooth response on with both from positioning and THEN you can EQ a little in the crossover region to smooth that out before you do anything with the subs.

4. SUBS
Now measure each sub and see what you get.

PROBLEM is because you have BOTH subs in line you will most likely just make things worse. However you may be able to play some tricks like using delay or polarity to smooth things out.

SUB 1
Move from left to right and look for best response from 300hz down with no DSP, crossover, EQ, or open up the Xover to highest point that is non LFE. Look for smooth response with peaks you can hopefully tame down, don't add any EQ to lift anything.

sub 2.
Measure by itself again, look for same thing BUT if you have a hole/dip in sub 1 move sub 2 around to see if you can fill in the missing spot.

After this you can smooth each sub over in the Xover range
Then smooth our peaks in each sub
then you get the smoothest response AND you have smoothed the subs out in the Xover region

Now you can combine subs and mains correlty and you can run any other DSP/correction you like.

You can save these settings and see how it measures up to other automatic programs/etc.

Good luck.
 

MRC01

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You can't always fix a dip because your amplifier and speakers/subs might be putting-out the soundwaves but the waves being canceled by a reflected wave (a standing wave node). ...)
True, you can't fix a deep dip with EQ for the reason you state, it's like pumping energy into a black hole.
But you can fix dip... by rearranging the speakers, listener position, or with room treatments that absorb the problematic frequency when it hits the wall, weakening the reflected wave.
However, a 100 Hz bass tone has a wavelength of about 10 feet, so it passes through a 5 or 6 inch thick panel like it's not even there. You need other kinds of treatments to weaken it, like a bass resonator or trap.
 
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ronnzi

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Aug 20, 2021
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So your measurement really doesn't have the info we need.

1. decide how big of a listening position you want to correct far. you can start with 2 or 3, IE, whole couch.

2. You need to take off all DSP/crossovers from speakers and subs and measure them separately

If either sub or speaker is showing large suck ours or high peaks these need to be fixed with positioning changes without your allowed area.

3. With speakers you want a smooth response on with both from positioning and THEN you can EQ a little in the crossover region to smooth that out before you do anything with the subs.

4. SUBS
Now measure each sub and see what you get.

PROBLEM is because you have BOTH subs in line you will most likely just make things worse. However you may be able to play some tricks like using delay or polarity to smooth things out.

SUB 1
Move from left to right and look for best response from 300hz down with no DSP, crossover, EQ, or open up the Xover to highest point that is non LFE. Look for smooth response with peaks you can hopefully tame down, don't add any EQ to lift anything.

sub 2.
Measure by itself again, look for same thing BUT if you have a hole/dip in sub 1 move sub 2 around to see if you can fill in the missing spot.

After this you can smooth each sub over in the Xover range
Then smooth our peaks in each sub
then you get the smoothest response AND you have smoothed the subs out in the Xover region

Now you can combine subs and mains correlty and you can run any other DSP/correction you like.

You can save these settings and see how it measures up to other automatic programs/etc.

Good luck.

This all makes sense to me - thanks for the response! I’ve done much of this already, but I’ve been learning so rapidly, that at some point when I have the time, I may need to start over from scratch just to make sure I didn’t skip any steps. When I re-do things, I should also save measurements of non-Eq’d positions so I have a better reference as to what the room and placements are doing on their own.

Thanks again.
 
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