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Room mode at ~ 82 Hz - Does this make sense?

Odradek

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Hello!

Using this tool I have identified the room modes, and listening subjectively using a tone generator I sort of confirm that the mode at almost 82 Hz is the most offending one (it is the loudest and calls for most attention when sweeping, I can hear a bit at around 41 Hz but my speakers have little output to really excite there).

I know this is all relative since I have not actually measured the freq. response in my room. I intend to buy an Umik-1 from cross spectrum (I'm not sure the additional calibration is really that useful but if I understand correctly it allows for more positioning versatility) but they are currently out of stock. When I get it, I will hopefully make lots of measurements as I have lots of probably stupid ideas I'd like to test!! :D

Anyway what I have been wondering is how I would set up the crossover (I'm hopefully getting 2 small subs and an integrated with high pass filters soon) in order to mitigate this room mode, as they are usually set at about 80 Hz. So what I think is that maybe, if after positioning the subs for most uniform performance this mode is still an issue, I could set the high pass and low pass at slightly different frequencies (80Hz for the low pass and 84Hz for the high pass for example) in order to make a slight dip in response at the middle frequency.

Can anyone please advise if that makes any sense at all? While I have read a lot recently and this page has been great education, I still know very little if anything at all!

As a side note, I think the integrated I would buy can't adjust the high pass slope.

Thanks!
 
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FeddyLost

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could set the high pass and low pass at slightly different frequencies (80Hz for the low pass and 84Hz for the high pass for example) in order to make a slight dip in response at the middle frequency.
Depending on severity of your modal problem and filters' slopes you might need to adjust them even wider, like 77 and 87 Hz.
I'd not do this without measurements because you may get some side effects and pro and contra need to be weighted with any combination.

think the integrated I would buy can't adjust the high pass slope.
Most probably.
I don't know any analogue hi-fi solutions with such option besides dedicated crossovers.

As an option - you can try to use SBIR effect to have deep notch at this frequency.
82 hz it's around 103 cm between woofer and front wall behind the speaker.
 
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Odradek

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Depending on severity of your modal problem and filters' slopes you might need to adjust them even wider, like 77 and 87 Hz.
I'd not do this without measurements because you may get some side effects and pro and contra need to be weighted with any combination.


Most probably.
I don't know any analogue hi-fi solutions with such option besides dedicated crossovers.

As an option - you can try to use SBIR effect to have deep notch at this frequency.
82 hz it's around 103 cm between woofer and front wall behind the speaker.

Thanks! I'm glad that it was not a ridiculous idea :D
Of course I will have to do measurements, I hope I can get the Umik-1 and start soon!

Unfortunately my room is rather small and there are not many placement options, the mains have to be very close to the wall. When I get the subs though, I will put them wherever is necessary!
 

daftcombo

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I have a 80Hz peak due to a room mode at LP, the couch being near the wall. If I move the couch 50cm away from the wall, the peak disappears.
 
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Odradek

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I have a 80Hz peak due to a room mode at LP, the couch being near the wall. If I move the couch 50cm away from the wall, the peak disappears.


I know! walking around the room while playing an 82Hz tone it goes from almost nothing to very loud. I'm not sure now, but I think moving front to back there were 2 loudness peaks and 3 nulls with the nulls being close to the walls and in the middle of the room, and the peaks in between. Unfortunately as I said, due to the small room, WAF, and need to use it for other things besides audio, I really can't move things around too much.

I am negotiating about subs placement XD
 

FeddyLost

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Unfortunately as I said, due to the small room, WAF, and need to use it for other things besides audio, I really can't move things around too much.
I am negotiating about subs placement XD
With such situation I'd definitely plan to insert some kind of EQ in system.
There's no other solution for getting relatively flat bass in small room if your fronts and listening position are close to opposite walls. Real acoustical treatment would help, but WAF-wise it's usually not acceptable and requires a lot of space.
And 82 Hz usually 2-0-0. With subs you'll have 1-0-0 (41 Hz) full scale, so only EQ will help.
In cinema such rise may be beneficial to some degree, but in music it's troublesome.
 
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Odradek

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With such situation I'd definitely plan to insert some kind of EQ in system.
There's no other solution for getting relatively flat bass in small room if your fronts and listening position are close to opposite walls. Real acoustical treatment would help, but WAF-wise it's usually not acceptable and requires a lot of space.
And 82 Hz usually 2-0-0. With subs you'll have 1-0-0 (41 Hz) full scale, so only EQ will help.
In cinema such rise may be beneficial to some degree, but in music it's troublesome.

I watch movies but what I care most about is music. I have 12" foam bass traps but from what I have read I gather they won't have much effect at 82 Hz. I have never actually positioned them in thier optimal locations as I never completely understood if they should be placed where there are peaks or nulls of loudness (was planning to experiment when I get the umik-1), I'm not sure which correspond to peaks in pressure and displacement.

Also, what do you mean that 82 HZ is usually 2-0-0 ?? No clue about what those number mean, if it is too cumbersome to explain would you please refer to where I could learn about it?

Thanks!
 

FeddyLost

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Also, what do you mean that 82 HZ is usually 2-0-0 ??
2nd axial mode (unless your room is 2.1 m (7 ft) long). It's notation from Amroc.
I meant that now most probably your speakers don't play 1st axial mode good enough to make problem with 41 Hz, but any decent subwoofer will do it easily. So, with subwoofer nicely hidden in corner you might have significant 41 Hz pressure at listening place and only EQ will help.
Download REW software and try out room sim. It's very useful for preliminary predictions.
12" foam will not really help below 100-150 Hz.
 

Hipper

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The Amroc site will explain a lot of this:

https://amcoustics.com/articles/roommodes

or go to your Amroc link and then click on the 'More about room modes and this calculator', top right.

I use a Behringer DEQ2496 for adjusting room modes and other bass issues (as well as lots of room treatment). It has ten Parametric EQ filters for just such a purpose as well as a Graphic EQ for adjusting the rest of the frequency response.

There are also various versions of the MinDSP which have crossovers too.
 
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Odradek

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i have a 5dB~ mode at 88hz, -5dB in the EQ and i fixed the problem :D

Nice! do you use subwoofers or you are just eq'ing your main speakers? Unortunately I have no way to apply parametric eq that I know of, the player I'm using right now (clementine) has only graphic eq, I began reading a couple off days ago about getting foobar running on linux but had to run of and haven't followed up
 
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BrokenEnglishGuy

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Nice! do you use subwoofers or you are just eq'ing your main speakers? Unortunately I have no way to apply parametric eq that I know of, the player I'm using right now (clementine) has only graphic eq, I began reading a couple of days ago about getting foobar running on linux but had to run of and haven't followed up
Not subwoofers, i did the EQ to my mains towers :D
 

Jukka

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You need to model it with a proper simulator that will show you total response. Crossovers with specific high&low-pass filters will run into opposite phase which will cancel each other out and create a deep null at the xo point. That is usually countered by inverting the other channel, but you could experiment with that on the room mode. Experimenting with slope steepness can give you good results, but you will need a simulator and dsp with proper functionality. Heck, even a thomann t.racks DSP408 FIR control software will show you that if you run it in demo mode (free download).

If you got any microphone, other than headset, you can try it out with REW. Calibrated mics etc will give you precision, but any cheap mic will give you close enough results for testing.
 
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