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Discussion Starter · #1 ·
I know running dual Subs will give you a much better FR over more seat or larger area. From what I understand (and I could be very wrong), the real reason of a better FR over more seat is because each sub's difference to each seat is difference, with different wavelength to each seat, so they will smooth out each other and give every seat a better smoother FR.


My question is what about putting the dual at the same wall with about the same distance to the main listener? You know, the most common place that most people put. Both sub at the front wall at about the same distance to each's (like 1/4) side wall with the center channel in between them. So there's distance to the center main seat is about the same.


If someone's main reason (me
) of getting a dual setup is to have a better FR at the main seat (not really care about added db) or to help out a null/dips at the main seat, isn't the relatively same distance of each sub to the main seat will give you pretty much the same FR/dip/null/etc. as running a single sub?


I'm thinking to add another sub because my main seat (center first row) has or feel much lesser bass than the 2nd row seats. Sitting at the 2nd row, I feel very strong bass through the seat. At the front row center seat (my seat), I hardly feel anything there. And I've measured that the main seat has a dip at 40hz. So I was thinking/hoping getting another sub will help out the front row's bass "feel" since the seat is fixed at their current position. Can't move the seat closer or further away the front sub. However, due to the sub size and other factor, the front wall is the only place I could put another sub in. But I second thought about it because of my above question, 2 different sub, but at the same distance to the listening position, will it or won't it help out the FR/null/dip?


I've included a pic of the front wall for you guys to see. If I'm getting another sub, it will be at the right of the center channel. And they will have about the same distance to my main seat.


Thanks in advance guys.

 

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Quote:
Originally Posted by landshark1  /t/1471589/dual-sub-advantage-question#post_23285567



If someone's main reason (me
) of getting a dual setup is to have a better FR at the main seat (not really care about added db) or to help out a null/dips at the main seat, isn't the relatively same distance of each sub to the main seat will give you pretty much the same FR/dip/null/etc. as running a single sub?
It will, and that's why you shouldn't do that. The need to keep the distance from each sub to the LP close to the same is way overblown in some circles. If your room has no room modes, ie., there are no walls or ceiling, then you might find it best to keep the distances from the subs to the LP the same. Otherwise it's of limited, if any, benefit. You'll usually get the best result having two subs as far away from each other as possible, so if one's at the front of the room the other should be at the back.
 

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Discussion Starter · #3 ·
That's for the reply Bill.


That's exactly what I'm afraid of. Spending the money and get disappointed result.



I could squeeze one at the back wall right next to the 2nd row seats in the corner if I really need to. Will there any ill effect, for the 2nd row especially the chair with next to it?


Again, I'm really happy for the PB12-Plus DSP does at the front wall for the 2nd row seats. But quite a bit disappointed at the 1st row and looking for way to bring both row's bass experience closer. At the moment, I would say they are quite different! 2nd row, I could "feel" the bass through the seats. 1st row, I could barely "feel" it.


Also, I noticed Audessey set the sub's distance a little farther away than what it really is, 12' vs 10' real measurement. Will it do anything, good or bad, if I change the distance closer to tape measurement instead of what Audessey said?
 

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Hi Landshark. Based on your build thread it looks like your theater is 15 feet across. That corresponds to a first axial mode (standing wave) of about 38Hz. If your seat is in the center, you'd be sitting right in the null of that wave and would experience a notch right around 40Hz as you mention.


If this is indeed the reason for your null, two subs along the front wall would help a lot, though you might get an additional boost at the second mode of 80Hz (space the subs correctly along the wall and you could likely knock that one out as well).


Just a thought - your null and room dimensions seem to align awfully well to me for this to be coincidence.


Cheers

Chris
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by ETFE  /t/1471589/dual-sub-advantage-question#post_23286313


Hi Landshark. Based on your build thread it looks like your theater is 15 feet across. That corresponds to a first axial mode (standing wave) of about 38Hz. If your seat is in the center, you'd be sitting right in the null of that wave and would experience a notch right around 40Hz as you mention.


If this is indeed the reason for your null, two subs along the front wall would help a lot, though you might get an additional boost at the second mode of 80Hz (space the subs correctly along the wall and you could likely knock that one out as well).


Just a thought - your null and room dimensions seem to align awfully well to me for this to be coincidence.


Cheers

Chris
What does that mean Chris? Are you saying with a 2nd sub at the front wall will help my 40hz null issue? And I'm also having a 80hz issue base on the sub location & room size which will also help by adding a 2nd sub?


Yes, my room size is 15' wide x 20' deep.


Thanks a lot for your help my friend.
 

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Quote:
Originally Posted by ETFE  /t/1471589/dual-sub-setup-question-to-help-fight-a-null#post_23286313


Hi Landshark. Based on your build thread it looks like your theater is 15 feet across. That corresponds to a first axial mode (standing wave) of about 38Hz. If your seat is in the center, you'd be sitting right in the null of that wave and would experience a notch right around 40Hz as you mention.
That null would occur mainly at the position lateral to the sub; the further back the lower the depth of that null, while other modes would arise. For instance, that of the reflection off the rear wall. When the OP says 'my main seat (center first row) has or feel much lesser bass than the 2nd row seats' that tells me that the main seat is in a rear wall reflection sourced null, the 2nd row seats are not. If the null is rear wall sourced then another sub in the front of the room won't help with that. A second sub in the back of the room probably would.
 

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Hi Landshark. What we are discussing are nulls or peaks in the bass response caused by standing waves in the room. These are sound waves where the wavelengths fit just perfectly in the room dimensions so certain points in the room always see high pressure or sound levels (peaks) and others see high velocities and low sound levels (nulls). If you know the speed of sound and the dimensions of the room, you can calculate these.


Or, if you do a search on "Harman Room Mode Calculator," you can download an Excel file that will not only calculate this for you but show nice graphics of where the peaks and nulls in your response should be. That (and the papers by Floyd Toole that you can also download from the site) gives a good introduction to room modes.


Bill - I hear what you are saying and normally variations in rows of seating would be caused by length modes, requiring a sub at the back of the room to treat. This is certainly the case in my room - the length is about 27 feet and 20Hz booms like crazy with one sub. Here's why I am thinking differently after looking at Landshark's room dimensions and seating. First of all, 40Hz is spot on what would be expected as a mode in the 15ft dimension and would give a null in the center of the room. This null would not be heard at the rear wall. The second row of seating is very close to the rear wall so you would hear the modes of the 20ft dimension there at about 28Hz and 57Hz. That would certainly come across as more exciting bass in the rear seats. In addition, Landshark moved the front row back from the center of the room so the first row is not really in the null of the 28Hz mode.


I obviously don't know for certain and am trying to be helpful. This makes me feel like the many hours I have spent walking around rooms listening to modes at different frequencies was actually serving a purpose...



Here is a quick test that should give some insight... using either an SPL meter or the SPL meters on either side of your head, play a 40Hz test tone and walk side-to-side and front-to-back in the room. If this is the width mode, as you walk side-to-side, you should hear loud bass at the wall, declining to much softer levels at the seat and then rising again to be loud at the next wall. If it is a length mode, you will have that effect as you move from the front of the room to the back.


Cheers

Chris
 

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Quote:
Originally Posted by ETFE  /t/1471589/dual-sub-setup-question-to-help-fight-a-null#post_23287798



Bill - I hear what you are saying and normally variations in rows of seating would be caused by length modes, requiring a sub at the back of the room to treat. This is certainly the case in my room - the length is about 27 feet and 20Hz booms like crazy with one sub. Here's why I am thinking differently after looking at Landshark's room dimensions and seating. First of all, 40Hz is spot on what would be expected as a mode in the 15ft dimension and would give a null in the center of the room.
When you have a null the first thing you look at is: What's 1/4 wavelength away? If the null is at 40Hz, where 1/4 wavelength is 7 feet, I'd first look at the distance to the rear wall, and then move on to the other potentialities. Also, for the null to be down the center of the room the sub would also have to be in the center of the room. Even then the null frequency would shift, being near 40Hz at the sub, going lower as you move back in the room and the distance from the sub to the walls to the listener grows progressively longer.
 
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What is the advantage/disadvantage of the svs cylindrical sub? I see one on craigslist, an svs pc-13 ultra for $1100. SVS website claims more bass performance per square inch than any other subwoofer. Is this just for small spaces where there is not enough floor space? Seems like the cubic shape has evolved as the standard. What would be a fair price for the mentioned svs sub in "real nice" condition, thanks.
 

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The cylinder sub takes up less floor space and is not as expensive as the wood sub. For similar spec SVS non-cylinder subs, the frequency response on output should be nearly the same. Especially good in a dedicated theater.
 

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Discussion Starter · #14 ·

Quote:
Originally Posted by derrickdj1  /t/1471589/dual-sub-setup-question-to-help-fight-a-null#post_23293560


Ever consider a cylinder SVS subwoofer? It may fit where other will not. Just a thought.

Nah.... doesn't like the cylinder sub plus it'll stick out over the seat at the rear corner. I'm sure I'll get another PB12-Plus DSP to smooth out the FR over MLP. Now I'll just need to figure out whether both at the front wall with the center channel in between would work (my preferred location) or I'll have to put the 2nd one at the rear corner. And by rear corner, I supposed they will need to near opposite corner for the best result, correct? (e.g. front right & rear left corner)
 

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During today's measuring effort, using three subwoofers (basically, all on the same wall), turning each on and off and recording the differences, by itself, the left subwoofer had the worse reading of the three and the two on the right corner the best, but despite the poor measurement of the left subwoofer, the addition of the left subwoofer into the sonic mix, raised the left shoulder of the measurement graph by +3dB and smoothed the graph from 25Hz to 45Hz by about -3 dB. But again, when solo, the left subwoofer measurements were absolutely terrible.


The left subwoofer is about four feet out from the left side of the screen wall and the right subwoofer, is out about the same amount. The third or center sub is about a foot from the screen wall and four feet in from the right side wall. I'm sure the room would benefit from a fourth sub but now I'm bumping up against the WAF as this is a living room as opposed to a dedicated theater room.


Today's paramentric change consisted of, in the AVR's main menu, changing Audyssey's recommended distant setting for the center channel from 9.9' to 4.4'. Doing this lowered the bass reading, range of 25Hz to 45Hz, by about -2dB, giving a tighter measurement as I'm now +/- 5dB with no room treatments in what one might characterize as a live room; lot's of {{{reflections.}}}


I don't save measurements other than the last reading from the last secession and the first reading and last reading of the day if the final day's readings are different so I don't have graphs to share and I'm just able to share what today's efforts showed me.......three subs is better than two subs, despite how terrible the reading of one sub might be as it's all a synergistic effort.


Hope the above ramblings help but for your theater, considering the amount of effort you've put forth, I'd seriously consider the addition of a third or fourth sub.


-
 

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Discussion Starter · #16 ·

Quote:
Originally Posted by BeeMan458  /t/1471589/dual-sub-setup-question-to-help-fight-a-null#post_23300429


During today's measuring effort, using three subwoofers (basically, all on the same wall), turning each on and off and recording the differences, by itself, the left subwoofer had the worse reading of the three and the two on the right corner the best, but despite the poor measurement of the left subwoofer, the addition of the left subwoofer into the sonic mix, raised the left shoulder of the measurement graph by +3dB and smoothed the graph from 25Hz to 45Hz by about -3 dB. But again, when solo, the left subwoofer measurements were absolutely terrible.


The left subwoofer is about four feet out from the left side of the screen wall and the right subwoofer, is out about the same amount. The third or center sub is about a foot from the screen wall and four feet in from the right side wall. I'm sure the room would benefit from a fourth sub but now I'm bumping up against the WAF as this is a living room as opposed to a dedicated theater room.


Today's paramentric change consisted of, in the AVR's main menu, changing Audyssey's recommended distant setting for the center channel from 9.9' to 4.4'. Doing this lowered the bass reading, range of 25Hz to 45Hz, by about -2dB, giving a tighter measurement as I'm now +/- 5dB with no room treatments in what one might characterize as a live room; lot's of {{{reflections.}}}


I don't save measurements other than the last reading from the last secession and the first reading and last reading of the day if the final day's readings are different so I don't have graphs to share and I'm just able to share what today's efforts showed me.......three subs is better than two subs, despite how terrible the reading of one sub might be as it's all a synergistic effort.


Hope the above ramblings help but for your theater, considering the amount of effort you've put forth, I'd seriously consider the addition of a third or fourth sub.


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Thanks a lot! Your comment really helps and gave me hope that there's a chance dual sub at the front wall might works versus a front & a back.



Btw, have you tried a single one at the right? You've tried a single left sub and had terrible result (like me). I'm just wondering if a single sub at the right will make any different since you notice/measured adding a single one to the right helps a lot.
 

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I just checked the data record sheet and I didn't try the right sub only. I tried the center sub only and the left sub only but not the right sub. So can't help you there.


Based on today's measurements, you might benefit putting both subs on the right. One sub about four feet from the right wall and one sub about four feet out from the screen wall as that gave us the best two sub reading. A sort of right corner loaded subwoofer triangle.
 

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Quote:
Originally Posted by BeeMan458  /t/1471589/dual-sub-setup-question-to-help-fight-a-null#post_23300429


During today's measuring effort, using three subwoofers (basically, all on the same wall), turning each on and off and recording the differences, by itself, the left subwoofer had the worse reading of the three and the two on the right corner the best, but despite the poor measurement of the left subwoofer, the addition of the left subwoofer into the sonic mix, raised the left shoulder of the measurement graph by +3dB and smoothed the graph from 25Hz to 45Hz by about -3 dB. But again, when solo, the left subwoofer measurements were absolutely terrible.


The left subwoofer is about four feet out from the left side of the screen wall and the right subwoofer, is out about the same amount. The third or center sub is about a foot from the screen wall and four feet in from the right side wall. I'm sure the room would benefit from a fourth sub but now I'm bumping up against the WAF as this is a living room as opposed to a dedicated theater room.


Today's paramentric change consisted of, in the AVR's main menu, changing Audyssey's recommended distant setting for the center channel from 9.9' to 4.4'. Doing this lowered the bass reading, range of 25Hz to 45Hz, by about -2dB, giving a tighter measurement as I'm now +/- 5dB with no room treatments in what one might characterize as a live room; lot's of {{{reflections.}}}


I don't save measurements other than the last reading from the last secession and the first reading and last reading of the day if the final day's readings are different so I don't have graphs to share and I'm just able to share what today's efforts showed me.......three subs is better than two subs, despite how terrible the reading of one sub might be as it's all a synergistic effort.


Hope the above ramblings help but for your theater, considering the amount of effort you've put forth, I'd seriously consider the addition of a third or fourth sub.


-
I know you don't like taking advice, and the only "proof" you'll accept is the proof you get from your measurements. Nonetheless, I'll throw this out there... changing the Distance setting of the CC speaker in isolation is the wrong approach. While it may change the bass response vis-a-vis that specific speaker/subwoofer interaction, it also mis-times the CC with the rest of the speakers. Sounds that pan through the front soundstage will be particularly affected as will any sounds that are shared across the front stage.


While you may get better bass response when playing JUST the CC and subwoofer, you'll screw things up when all the speakers are active. The "precedence effect" of having the CC arrive mis-timed will screw up directionality and imaging, as well as dialogue intelligibility. (Google "precedence effect" if you want to understand how this works.)


If you want to impact the interaction of the subwoofer with the speakers, you are much better off changing the subwoofer Distance in isolation because its' Distance setting interacts similarly with ALL the speakers, not just one specific speaker.


Do whatever you want, but you need to understand ALL the implications of the "parametric" changes you make.


Good luck.


Craig
 

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Quote:
Originally Posted by BeeMan458  /t/1471589/dual-sub-setup-question-to-help-fight-a-null#post_23300556


I just checked the data record sheet and I didn't try the right sub only. I tried the center sub only and the left sub only but not the right sub. So can't help you there.


Based on today's measurements, you might benefit putting both subs on the right. One sub about four feet from the right wall and one sub about four feet out from the screen wall as that gave us the best two sub reading. A sort of right corner loaded subwoofer triangle.
The measurements you get in YOUR room will be useless in anyone else's room. Giving advice based on your own results in YOUR room is inappropriate.


Landshark, the only way to know how to get the best results in YOUR room is to measure the results in YOUR room. You can't transplant BeeMan's results to your room. It doesn't work that way. In general, you'll get the best results with one sub in the front and one in the rear. Dual subs on the front wall probably won't work any better than a single sub on the front wall, except that you'll get 3 to 6 dB of increased headroom. Nonetheless, no one can say for sure what the results will be unless they measure the results in YOUR room.


Craig
 

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Quote:
Originally Posted by craig john  /t/1471589/dual-sub-setup-question-to-help-fight-a-null#post_23300772


The measurements you get in YOUR room will be useless in anyone else's room. Giving advice based on your own results in YOUR room is inappropriate.

No it's not. Why? First, the advice is based on disclosure of this working in my room and is a recommendation based on personal experience and second, other than time, moving one's sub around in their room causes no physical or fiscal harm and during the measuring process, gives the individual a better understanding of their room's acoustics.
 
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