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REW help - sub null can't seem to fix

Harris48

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I have tried for days moving and remeasuring moving and remeasuring and can't seem to crack this. It hard to EQ something this dipped. I'd appreciate any thoughts. I set up my seating in this position thinking I can position my subs to negate the null. It's dedicated ht room so all enclosed. My thinking is my main concern is with the 45- 65 drop off and to not be as concerned over 80 becuase I have a RevelC208 and M106 mains that can be crossed over at 80(this could be stupid though). MLP is 9'8" deep and 7'6" from the sides...everything from screen to height speakers and in between has been geared around this seating position. I would like to keep and fix it with subs/treatements. Thanks for any advice you can give. Im new to this whole thing but tried to figure it all out on my own


BEST positioning
Front and rear corners no delay level -30.jpg



Possibly so phase craziness. I've tried the phase switches and inverting in MiniDSP no effect or makes it worse
PHASE Front and rear corners no delay level -30.jpg



These are the top positions there were many worse.
All descent positions.jpg



Room mode cal results

1672695184332.png




Possibly interesting accident - left the door open in the back right corner with the results from the top and it improved the reuslts. Blue is with the door open gold is with it shut

1672695938559.gif
 

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Dumdum

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Use the yellow first trace positions, number 10 in your graphs and take the peaks down with eq assuming your using dsp controlled and it will yield you a flat acoustic response

The phase craziness isn’t crazy it’s just the way you are viewing it, you have delay in the signal chain returning to the mic so it looks like it’s sloping downwards, you need to adjust t zero in rew to make it display as flat…
 
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Harris48

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Thanks @Dumdum. I think I need to learn more about the eq because I could flatten the peaks but the dip between 45-65 remained
 
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Harris48

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I can't EQ this anywhere near flat. 45-65 is still 10 db lower

1672714299077.gif
 

sejarzo

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A null by any other name is still a null, right? No matter how much more power you pump out of a sub at that frequency, the waves still cancel at the measurement point. That's why bass never sounds the same in a home listening room as it does in a concert hall. You can't beat the physics of the situation.
 
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Harris48

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I could have some very bad info but I thought you could use subs to negate the effects of a null. Create a "virtual" sub with two real subs to offset the null. Is this nonsense?
 

suttondesign

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Nulls cannot be meaningfully EQ’d. Bring down the surrounding peaks. It is the best you can do apart from looking for placements which improve things, though in rooms like yours, they tend to just move the nulls and peaks.
 

sejarzo

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I don't know if it is nonsense, but when one has a room that's nearly square, I believe that complicates the issue. Someone who knows more about implementing multiple subs might know better than me.
 

DaveBoswell

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@Harris48 , could you tell us more about the room and setup - dimensions, 1 sub or multiple, if multiple, are the subs a mixture of sealed and ported? The easy answer is to say just get a second sub, a DSP and use MSO to tune the sub frequencies which many are doing, including myself, to great effect. But there may be some quick and dirty approaches depending on your setup.

If 1 sub, then you may be a bit out of luck and are sitting in a null (either length null or width null or both) - you can really only fix this by adding a second (or more) subs and introducing EQ/Delays. If you have 2 subs already, then you could try swapping polarity on one of them. If you have a mixture of sealed and ported subs, then that is almost definitely going to need a DSP that allows for EQ, delays, and all-pass filters which can fine tune phase cancellation issues.
 

DaveBoswell

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And you also may just have two big peaks at 40hz and 80Hz that simply need to be eq'd flat. If you test a wider frequency range (say up to 200-300 Hz) with just the sub alone (bypassing the crossover in your AVR/DAC etc), you would be able to see better the general trend of the FR.
 
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Harris48

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2 subs HSU VTF 3 currently both ports open/ Bic F12 ported
Using miniDSP and REW
Tried the phase switches
Moved many places all over the room just can't find a place that has the 45-65 range

Would 3 or 4 subs help a square room

thanks for the help!
 

DaveBoswell

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Perfect - if you have miniDSP and REW - you've got all you need - then I strongly suggest you download MSO (Multi Sub Optimizer) - after a few hours learning curve it'll do all the heavy lifting for you and can look at thousands of permutations of filter settings, delays, AP filters. etc in less than 5 minutes.

Suggest you watch Jeff Mery's youtube videos first to get your feet wet, the read through the MSO thread on AVS starting around May / June of this year to now as Jeff has put a lot of good additional suggestions on there which are not quite yet in his videos. Here's some sample before and after in my room - I have 2 SVS sealed subs, one in front right corner of a basement room, and one right behind the couch facing the couch with a LPF at 24db/octave slope at 80Hz to minimize localization.

I have a similar sub config as you here's my before and after (bottom chart measured this morning after some tuning over the last few days). And the after is PEQ only, no delays or other tricks as I am using an older DSP and deciding if it's worth upgrading:

Before seat to seat response from Main Listening Position, Right seat and left seat:
1672722559427.png



And then after some work in MSO to find a good balance between EQ and minimizing headroom reduction (you have to be careful you get both subs working together as much as possible), this is the predicted response (the magenta and light blue lines are showing the sum of the EQ filters to be applied to each of the subs):
1672722682812.png



And then this is what I measure in REW when I was done. This is a combine measurement of Subs together with the Right Front speaker which is being crossover at 80Hz. You can see the results are really good for all 3 seats, and are reasonably close to what MSO predicted between 15Hz and 100Hz.
1672722960777.png



And it sounds amazing - by far and away the best I have ever been able to get my subs working together.
 

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DaveBoswell

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BTW I had another look at your room mode calc sheet - confirmed your real issue not that you have nulls at 45-50Hz, it's you have large peaks at 40 and 80Hz becuse you length and width modes are stacking on top of each other right where your seating position is. You should be able to tame these with aggressive EQ using the EQ tool in REW if you want to skip the MSO step - only problem is this will only be optimized for one seat. MSO will figure out how to get a bunch of seats in a an area to have the least seat-to-seat variation.
 

DonH56

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You can usually "fix" a null with multiple subs but EQ alone will not get you there. As previously mentioned, a null occurs because sound waves cancel (combine destructively) at the listening position. Basically direct sound D and reflected sound R subtract: D - R = 0 (null output). If you EQ to increase the amplitude by A, the reflection is also amplified, for no net improvement: AxD - AxR = 0 (still null). You can move the seating position or position the subs to counter the null, but trial and error can be frustrating.

Check out this paper by Todd Welti: https://www.harman.com/documents/multsubs_0.pdf

Then look into something like MSO (multisub optimizer) as mentioned above: https://www.andyc.diy-audio-engineering.org/mso/html/

HTH - Don
 
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Harris48

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Ahhhh I watched the wrong Jeff Mery videos. I quit after the REW ones! haha. Thanks for the advice apparently I've been working harder not smarter

your room looks great...I hope I can get that close
 

ppataki

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I have tried for days moving and remeasuring moving and remeasuring and can't seem to crack this. It hard to EQ something this dipped. I'd appreciate any thoughts. I set up my seating in this position thinking I can position my subs to negate the null. It's dedicated ht room so all enclosed. My thinking is my main concern is with the 45- 65 drop off and to not be as concerned over 80 becuase I have a RevelC208 and M106 mains that can be crossed over at 80(this could be stupid though). MLP is 9'8" deep and 7'6" from the sides...everything from screen to height speakers and in between has been geared around this seating position. I would like to keep and fix it with subs/treatements. Thanks for any advice you can give. Im new to this whole thing but tried to figure it all out on my own


BEST positioning
View attachment 254304


Possibly so phase craziness. I've tried the phase switches and inverting in MiniDSP no effect or makes it worse
View attachment 254305


These are the top positions there were many worse.
View attachment 254306


Room mode cal results

View attachment 254308



Possibly interesting accident - left the door open in the back right corner with the results from the top and it improved the reuslts. Blue is with the door open gold is with it shut

View attachment 254310

Can you please post your mdat file here?
Cheers
 

audiofooled

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2 subs HSU VTF 3 currently both ports open/ Bic F12 ported
Using miniDSP and REW
Tried the phase switches
Moved many places all over the room just can't find a place that has the 45-65 range

Would 3 or 4 subs help a square room

thanks for the help!

Start here https://amcoustics.com/tools/amroc?l=14.8&w=15.1&h=8.11&ft=true&r60=0.6

Read this https://www.audiosciencereview.com/forum/index.php?threads/analytical-analysis-room-gain.23211/

Plug the ports and don't put subs in the corners. That's where the strongest modes are, hence the difference when you open a door.

I hope this helps.
 

ppataki

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@ppataki - Couldn't figure out how to directly post the MDAT file so here is a drive link. You want the actual file right not just the jpegs of the results? Thanks.
MDAT file

@audiofooled interesting thanks.
Thank you @Harris48

In fact your dip can indeed be corrected (not fully but to an acceptable level IMHO) with EQ

Here is the simulation using no boosting, target level = 69dB (1/12 smoothing)

1672766468876.png


And the simulation with some boosting applied, same target curve:

1672766505920.png


I attach the measurement with the simulation included and the convolution wav files that you can use in a convolver to test how they sound
If you cannot use a convolver you can also check out the EQ filters that were used if you open your measurement (BL FR corners level -30) and click on the EQ button

Please find the files here:

Using multiple subs and MSO is probably a better solution but you can also try this, it won't hurt ;)
I hope this helps
 
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