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How to fight room modes with 2 subs?

Smidge

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Any guidance on where to start with 2 subs to overcome room modes? I have only the option to position the subs next to the floorstanders. I have tried corner positions and on the inside of the floorstanders, close to the wall and 0,5m in front of the wall, but I’m still having serious peaks and dips between 60 and 280 hz.

Minidsp SHD is on its way so there will be a lot of options soon.

I was thinking to start crossover the subs at 80 hz, but given the room modes, should I consider moving the crossover up higher? Will 2 subs be better at fighting the room modes above 80 hz than my floorstanders?
I know I can just run Dirac but I rather want to try to improve the starting position before running Dirac. If that would make sense.
 
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hawk01

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in my experience without the use of DSP, dual subs in assymetric positions/locations in the room provide the most even bass response. i have subs located in diagonal opposing walls with one unit slightly snug against the front wall corner, the other slightly pulled out leaning against the rear wall. switching off either subs excite room modes especially in the corners. if you are limited by front location only, try to go for the most assymetric positions. the aesthetic appeal of having them arranged symmetrically does not help one bit in making them sound good.
 
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Smidge

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in my experience without the use of DSP, dual subs in assymetric positions/locations in the room provide the most even bass response.
Thanks, I didn’t consider that yet. I will try some various assymetric positions and measure and compare the outcomes.
 

Descartes

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You should read Todd Welti’s paper
Optimal Configurations for Subwoofers in Rooms Considering Seat to Seat Variation and Low Frequency Efficiency
 

GDK

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When I adjusted the smoothing in REW, I found that it made my room modes magically disappear. Psychoacoustic works particularly well. It really is a powerful program! :D
 

Another Bob

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Congrats on the SHD. It will indeed provide you with tons of flexibility to help with this challenge.

If you put the crossover much above 80Hz you will be able to localize the sounds as coming from the subs. Not a problem if the subs are going to be right next to your main speakers, but that is almost certainly not the best place for them in terms of addressing room modes.

I like to get the best possible response from placement before applying DSP. Remember, dips due to room modes generally cannot be filled in via equalization. I have good luck with the following approach: Measure one sub, i.e., all other speakers turned off. Record its response at all possible/acceptable positions. Look for two positions that have complimentary responses - peaks (or at least flat responses) on one where the other has dips. This is where you want to put your subs. As noted above, it is likely to be an asymmetric configuration. Be open to using different volume settings on the two subs. Good luck!
 

NTK

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Theoretically... Here are the room modes of an example room (dimensions are from the room in this post).

roommodes.PNG


The number on top of each plot is the frequency of the room mode. The first 20 mode frequencies and shapes were calculated.

To NOT excite a mode, place your subwoofer(s) in the white area. To cancel a mode with 2 identical and in-phase subwoofers, put one in the dark red and the other in the dark green areas. To cancel a mode with 2 identical and opposite phase subwoofers, put them both in either the dark red or dark green areas. Or you can sit in the white area and not be affected by that mode.

It is a juggling act to optimize the sub(s) and/or sitting locations to be affected by the fewest modes.
 
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Smidge

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Thank you all very much for your suggestions and advice. It’s exactly what I was hoping for. This weekend I’m going to do various experiments based on your input and I will report back with the outcomes.
 
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Smidge

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After all your suggestions I couldn’t wait any longer and I starting sub lifting and measuring. I will explain my approach. I tested all possible configurations based on the limitations in my room. This resulted in 4 configurations. Although I did test toe-in it didn’t make a significant difference so I left them out for now.
For each configuration I did 3 measurements across the listening area on ear height. The averages are here below:
Sub positions comparison complete.jpg

As you already predicted, the most assymetrical configuration seems to best minimize the dips.

So the “least worst” option is the green line (left sub on side wall + right sub corner. But at the same time, most improvements seem to be irrelevant because of the crossover that will be applied.

do you think the current response is manageble for Dirac? What else would you suggest? I didn’t finish reading everything you recommended me yet...

Tomorrow the SHD arrives so I’m planning to first focus on finding the best delay settings for the subs, since they are no longer positioned symmetrical.
 
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Smidge

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So the SHD is in and connected. But when outputting the SHD to my amp there is a very audible hum (ground loop I suspect) and high pitch noise. Unfortunately my amp doesn’t accept balanced inputs so I’m not sure what to do now...
I tried putting all devices on one powerstrip, and tried both my amp and SHD together into one single wall plug but the problem is the same.

I unplugged all inputs from the SHD so it was only connected via RCA to my amp and the hum and noise is still there.

sorry to go off-topic.

edit: when I connect the SHD to the pre-amp of the integrated amp (line input) the issue is no longer there. So it only happens when the SHD is connected to the power amp stage directly, bypassing the pre-amp. So for now I will have the signal path traveling through 2 pre-amps.
 
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abdo123

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I wanted to ask an off-topic question, can you put a subwoofer under a table? or are frequencies reflective across the entire range?
 
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Smidge

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I’m really happy to show you the outcome. Below you see the end result of optimized sub locations, integration with floorstanders, optimized crossover and delay settings, Dirac Live, and a bit of manual eq’ing:
The result.jpg

It took hours of experimenting but the difference is beyond words. So much more details in the lows, and clarity in the highs.

Thank you all for your advice and suggestions. It really paid off. I guess joining ASR was the best upgrade for my audio experience ever :)
 
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Smidge

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And this is how I ended up placing the subs, that worked best for me in terms of fighting the room modes:
9F56827E-B5AC-4EB9-8C38-5741E803E2B3-min.png

The subs are front firing. The sub on the left side fires to the right. As I mentioned earlier, options to place the subs was very limited.
 

NTK

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I wanted to ask an off-topic question, can you put a subwoofer under a table? or are frequencies reflective across the entire range?
I think the problem is the table may resonate, similar to having a highly nonrigid subwoofer cabinet. I don't think sound (low bass) radiation is a problem. Otherwise down firing subwoofers wouldn't work.
 

sweetchaos

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And this is how I ended up placing the subs, that worked best for me in terms of fighting the room modes:
View attachment 120677
The subs are front firing. The sub on the left side fires to the right. As I mentioned earlier, options to place the subs was very limited.
Very clean look. :)
I love that you've hidden all wires as much as possible.
Nicely done!
Oh yeah, speakers look nice too! ;)
 
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