If SBIR Is At The Same Frecuency As Your Mains what do you end up hearing?

[dasdoing]

It effectively "overlaps" when summed or vector averaged...

Achieving absolutely identical group delay between channels is unnecessary. I'd rather work to have a good enough phase match/coherency and time alignment between all channels. Haven't bothered trying to achieve a perfect-looking step response like what you see in Acourate and Audiolense corrected IRs...

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Currently I use 80Hz 12dB/oct BW HPF for the fronts (ports closed), 60Hz 48dB/oct BW HPF for the surrounds (ports closed), and the sub's own internally fixed 120Hz 12dB/oct LPF (sealed sub). The sub is midpoint the LR channels so no worry of any localization issue.

Not using any FIR for the sub (other than 256 taps each for the most basic linear phase EQ & phase linearization done for the surrounds and mains) which also helps me achieve minimal overall system delay in my MCH setups.

nice. I might try do do this in the future. I am just afraid to waist my time. but I was allready thinking about trying it out

 

[Trdat]

which room mode is the most destructive in your own particular room and listening position and try to position your subwoofers to combat it.

Which brings us to our next question, how do you position the subwoofers to combat axial room mode? well you need two subwoofers, and you need to place each subwoofer at opposite polarities of the mode (check above diagram and below).

These two points were critical in understanding the concept and only the Harman calculator gave me the opportunity to figure out which room modes correlated with my system measurements and although they were not precise it was enough to understand approximately at which frequency these room modes were at. It took me a whole day to understand the above but I still have some questions.

1. When we place sub woofers at opposite polarities do they have to be at the oppsosite ends of the opposing polarities or can it be the next opposing polarity?

2.Most importantl when checking my measurements what am I looking at a peak or null on the frequency response or do we need to look at the waterfall graph to see a long decay rate which will correspond to a room mode? Or even the decay plot or perhaps all help confirm what a room mode is?

3. Agan how do we understand the time domain performace of each room mode, I think this question is similar to the above in that we might suspect a peak but how do we confirm we need to tackle it?

4. Now, we use your above solutions(Subs for first order, Eq for second and absorbers for third) to tackle SBIR or Room modes and I am aware from some of your other posts that your not a fan of more subwoofers or suspicious at least of adding more subwoofers but technically with 4 subwoofers we can tackle all room modes at least first and possibly second order. Place 2 at the first order width(front corner) then another one at the lengths opposing polarity(back) and another at the minus polarity for the height right? You mentioned 2 will tackle all room modes but you need at least 4 subs right?

5. Last question, can we tackle SBIR with the opposing polarity subwoofer technique I am presuming no, only way is to use absorbers or not play that frequency from that speaker like you mentioned?

 

[ernestcarl]

nice. I might try do do this in the future. I am just afraid to waist my time. but I was allready thinking about trying it out

I just now convolve (using A times B trace arithmetic function) from prior unequalized measurements via IR filters generated in rePhase. It allows me create new summed/aligned predictions any time without having to re-measure first. It would be nice if REW's alignment tool actually had a built-in virtual HP/LP filter option for both channels to make the process quicker.

 

[abdo123]

These two points were critical in understanding the concept and only the Harman calculator gave me the opportunity to figure out which room modes correlated with my system measurements and although they were not precise it was enough to understand approximately at which frequency these room modes were at. It took me a whole day to understand the above but I still have some questions.

1. When we place sub woofers at opposite polarities do they have to be at the oppsosite ends of the opposing polarities or can it be the next opposing polarity?

2.Most importantl when checking my measurements what am I looking at a peak or null on the frequency response or do we need to look at the waterfall graph to see a long decay rate which will correspond to a room mode? Or even the decay plot or perhaps all help confirm what a room mode is?

3. Agan how do we understand the time domain performace of each room mode, I think this question is similar to the above in that we might suspect a peak but how do we confirm we need to tackle it?

4. Now, we use your above solutions(Subs for first order, Eq for second and absorbers for third) to tackle SBIR or Room modes and I am aware from some of your other posts that your not a fan of more subwoofers or suspicious at least of adding more subwoofers but technically with 4 subwoofers we can tackle all room modes at least first and possibly second order. Place 2 at the first order width(front corner) then another one at the lengths opposing polarity(back) and another at the minus polarity for the height right? You mentioned 2 will tackle all room modes but you need at least 4 subs right?

5. Last question, can we tackle SBIR with the opposing polarity subwoofer technique I am presuming no, only way is to use absorbers or not play that frequency from that speaker like you mentioned?

1) what do you mean by the opposite end of the opposing polarity? The peaks?

2) the magnitude response (frequency response curve) is fine, whatever makes it simple for you to identify the issue. Doesn’t matter which graph. The waterfall graph might show modal peaks easier but the dips will not show up easier IMO. It’s your call.

3) in the modal region of the room most rooms are minimum phase, meaning that the magnitude response also represents the phase response as well. Phase correction for room modes seem unnecessary or a ‘plus’, not necessarily a requirement for good tonality.

4) there is nothing wrong with more subwoofers, the more the merrier. But keep in mind that you’ll be limited to 80Hz 24 dB/Oct or 100Hz 48 dB/Oct cross-overs if you don’t want to localise them, so you’re lucky if your room is big enough so that they can cover / fix all first order and second order room modes and first order SBIR. For most people their rooms have 2.4-2.5 meter height so the first order mode is smack down at 75-80 Hz and the second order is outside subwoofer range. It’s best to invest 50/50 in subwoofers and treatment.

5) you can make the subwoofers and speakers overlap, like what you currently do I think? I don’t think the compromise is worth it as for me imaging really suffers with any overlap over 100Hz.

 

[ernestcarl]

Btw, once you get that to work the only thing you need to do in order to have "perfect-looking" step response is to implement phase correction of the XO between sub(s) and mains. And that is the only "magic" what Acourate and Audiolense do when integrating subs..

Done something like this and I already was able to create a near "perfect-looking" step -- but the delay is a real problem since I more frequently stream videos now (netflix, amazon prime etc.) than in previous years. I can't recall the last time I bought physical media. Maybe over two years...

 

[Trdat]

1) what do you mean by the opposite end of the opposing polarity? The peaks?

2) the magnitude response (frequency response curve) is fine, whatever makes it simple for you to identify the issue. Doesn’t matter which graph. The waterfall graph might show modal peaks easier but the dips will not show up easier IMO. It’s your call.

3) in the modal region of the room most rooms are minimum phase, meaning that the magnitude response also represents the phase response as well. Phase correction for room modes seem unnecessary or a ‘plus’, not necessarily a requirement for good tonality.

4) there is nothing wrong with more subwoofers, the more the merrier. But keep in mind that you’ll be limited to 80Hz 24 dB/Oct or 100Hz 48 dB/Oct cross-overs if you don’t want to localise them, so you’re lucky if your room is big enough so that they can cover / fix all first order and second order room modes and first order SBIR. For most people their rooms have 2.4-2.5 meter height so the first order mode is smack down at 75-80 Hz and the second order is outside subwoofer range. It’s best to invest 50/50 in subwoofers and treatment.

5) you can make the subwoofers and speakers overlap, like what you currently do I think? I don’t think the compromise is worth it as for me imaging really suffers with any overlap over 100Hz.

1. I just realised a third order mode you recommend using absorbers and not sub woofers but for arguements sake, there is a plus that starts from one end of the room then a minus then plus and another minus. Can I put the sub at the first plus and first minus from the one end of the room? Or does it have to be the minus at the other end of the room? I am guessing as long as there on opposing polarity peaks it will be fine but just checking...

2. Okay great good to know the frequency response will suffice.

3. Ill look into this. But I mostly get what your saying that for room modes no need to dig that deep.

4. So to confirm we can use subwoofer with opposing polarities to tackle first order SBIR or are we just cancelling the frequency with that speaker and using the sub to play it which has less SBIR?

5. I haven't localised my subs yet as they are on the front wall but after putting 2 more subs on the back wall it wasn't as good as I thought, it did make the bass more even but I not only localised it I found bass from the back not that enjoyable perhaps that's what you mean by muddying. Although the back wall is a minus of a first order reflection so I am keen to keep one sub there at low volumes(unless you have a better option) and put the second one on top of my ceiling panel to cover the height mode. This should tackle the first order modes as best as possible then ill use Audiolense for DSP and see what the final response is on REW. Only problem being, is all 4 subs will have to be summed either as mono or stereo(all over the place) meaning each sub will not get the individual frequency correction they need and time alignment for that matter.

6. I have about 16 panels RT60 is all between 200 and 500ms and group delay 50ms at listening position so bass is good(from what I understand from measurements) just want to utilise all my subs as best as I could without like you said muddying the image.

 

[abdo123]

1. With the graph that I showed it explains that dealing with first order room mode also deals with third order room mode, moving forward please make it very clear what are you referring to. In other words third order of what? When I said third order is dealt with with absorption I meant SBIR not room modes.

4) just to be clear, the subwoofers will ALWAYS be in phase or at the same polarity (the knob at the back), it’s their physical location in respect to that particular mode that should be out of phase. No you cannot use that particular method for SBIR, but you can have a crossover that is higher than (or at) the first order speaker SBIR so the subwoofer(s) can play that tone instead. That’s what I have been explaining for a while now. If your room is too small for that then speaker first order SBIR will always be an issue.
Please moving forward so I’m not further confused I don’t want to discuss any subwoofer SBIR, just shove them to a wall. I know that was the initial purpose of your thread but my brain can only handle so much.

5) correction for each individual sub is not completely necessary, EQing the global inputs is fine. But having delays for each one is relevant, since they’re likely not going to be equal distance from you. Perhaps a possible upgrade in the future.

6) I shared with you the crossovers parameters necessary not to muddy the image (in my experience). Feel free to experiment with them. As for now I have a question for you. What are your current crossovers and how did you come up with them?

 

[Trdat]

1. With the graph that I showed it explains that dealing with first order room mode also deals with third order room mode, moving forward please make it very clear what are you referring to. In other words third order of what? When I said third order is dealt with with absorption I meant SBIR not room modes.

4) just to be clear, the subwoofers will ALWAYS be in phase or at the same polarity (the knob at the back), it’s their physical location in respect to that particular mode that should be out of phase. No you cannot use that particular method for SBIR, but you can have a crossover that is higher than (or at) the first order speaker SBIR so the subwoofer(s) can play that tone instead. That’s what I have been explaining for a while now. If your room is too small for that then speaker first order SBIR will always be an issue.
Please moving forward so I’m not further confused I don’t want to discuss any subwoofer SBIR, just shove them to a wall. I know that was the initial purpose of your thread but my brain can only handle so much.

5) correction for each individual sub is not completely necessary, EQing the global inputs is fine. But having delays for each one is relevant, since they’re likely not going to be equal distance from you. Perhaps a possible upgrade in the future.

6) I shared with you the crossovers parameters necessary not to muddy the image (in my experience). Feel free to experiment with them. As for now I have a question for you. What are your current crossovers and how did you come up with them?

I have read about SBIR and room modes for about 3 years and I can finally say with your simple but effective presentation I understand it and now know why we pretty much put subs in corners for room modes that is. SBIR was simple enough to understand like you said just shove them in corner and get the subs to play the SBIR frequency but now I have the added benefit of being able to utilise my extra subs to alleviate first and second room modes which are at times again just in corners but also in a few other positions which I will eperiment with.

Yes, time alignment is necessary because the music I listen to needs coherent bass - less revereberation and as two subs will be placed asymmetrically. So I can always add a minidsp in between my DAC and sub amps to individually time align, mind you my set up is a triamp with Audiolense. I just enjoy the minimul distortion with all my well measured gear but I doubt the minidsp will add any flaws/extra distortion to the subs.

I will definitely be experimenting with your lower crossover points and its respectable high pass configuration, easy for me to do with Audiolense. It's time for experimenting and seeing if I can relieve room modes which on paper is possible, not muddy the sound(which you are correct with 4 subs the potential is there, I noticed after adding them to the back) and see if the extra subs are really worth it. So far two quality subs at the front were superb with my overlapping technique at the cost of still having some modes present.

Lastly the Harman room mode calculator really helps to figure out where to put subs and absorbers accordingly.

 

[gelv]

This might be a stupid OT question but would the null be bigger or deeper the higher spl or the bigger the woofer size is?
Apologies if this is considered necro posting

 

[Flaesh]

Regarding subwoofers on opposite walls: