Dual Sub setup question to help fight a null? - AVS Forum
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post #1 of 36 Old 05-06-2013, 03:25 PM - Thread Starter
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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 tongue.gif ) 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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post #2 of 36 Old 05-06-2013, 04:19 PM
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Originally Posted by landshark1 View Post


If someone's main reason (me tongue.gif ) 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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post #3 of 36 Old 05-06-2013, 06:09 PM - Thread Starter
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That's for the reply Bill.

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

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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post #4 of 36 Old 05-06-2013, 07:26 PM
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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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post #5 of 36 Old 05-06-2013, 09:30 PM - Thread Starter
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Originally Posted by ETFE View Post

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. smile.gif
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post #6 of 36 Old 05-06-2013, 09:33 PM - Thread Starter
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Oh, IF I really need to put a 2nd sub at the back corner of the room, and I don't have the space for a PB12-Plus DSP there, would a level down, PB12-NSD helps? Or it'll do more hurts than helps by adding a lesser sub?
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post #7 of 36 Old 05-07-2013, 07:28 AM
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Originally Posted by ETFE View Post

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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post #8 of 36 Old 05-07-2013, 08:53 AM
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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... smile.gif

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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post #9 of 36 Old 05-07-2013, 11:11 AM
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Originally Posted by ETFE View Post


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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post #10 of 36 Old 05-08-2013, 09:29 AM - Thread Starter
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So I guess the back corner is still my best option with a "chance" that front wall might works too.

Thanks again for all your help guys.
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post #11 of 36 Old 05-08-2013, 03:49 PM
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Ever consider a cylinder SVS subwoofer? It may fit where other will not. Just a thought.

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post #12 of 36 Old 05-09-2013, 09:31 PM
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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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post #13 of 36 Old 05-10-2013, 12:58 AM
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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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post #14 of 36 Old 05-10-2013, 11:06 AM - Thread Starter
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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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post #15 of 36 Old 05-10-2013, 11:39 AM
 
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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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post #16 of 36 Old 05-10-2013, 11:55 AM - Thread Starter
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Originally Posted by BeeMan458 View Post

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.

-
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. smile.gif

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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post #17 of 36 Old 05-10-2013, 12:11 PM
 
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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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post #18 of 36 Old 05-10-2013, 12:59 PM
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Originally Posted by BeeMan458 View Post

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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post #19 of 36 Old 05-10-2013, 01:04 PM
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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.
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.

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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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No it's not. Why?
Because the meaurements you get in your room will be completely different than the measurements someone else gets in their own room, even if they're using the same subwoofer.
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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.
General advice to use measurements and to try different placements is fine. However, offering placement advice to someone else, (which is what you were doing), based on the results you found in YOUR room is inappropriate.

More importantly, did you read my other post about not using the CC Distance and using the subwoofer Distance instead?

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post #22 of 36 Old 05-10-2013, 02:10 PM
 
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However, offering placement advice to someone else, (which is what you were doing), based on the results you found in YOUR room is inappropriate.

To you, it's inappropriate and to me, it's a perfectly fine thing to do; encourage others to try what I've found works for our situation. To do what I suggest, does no harm. Currently I'm using the AVR provided level control for the center channel and the gain control on a single sub to steer the graph.......up and down, up and down, up and down.......there's got to be some ginger spice around here somewhere. I encourage everybody to use their level and gain controls; learning how to steer their measurement graphs in this fashion.

It's fun making changes and measuring the room's response to the changes. That's how one gets to know their system and sharing personal experience is part of the hobby. And if a recommendation doesn't work for them, then, they put the subs back in the original location, reset their settings to what they were before and continue scratching their head, wondering why they're not obtaining the results they're wanting.

Reading what others had to post, their personalized comments led me to believe there was a possible phase issue somewhere so I took the time, made phase changes and came to the conclusion, whoops, not in this case. Put everything back the way they were and got on with working some other ideas. No harm, no fowl. Didn't cost zip and no physical damage. Today, I've been playing with this stuff for about four hours and still having fun.

The -20dB null I use to have, has been reduced to -4dB but it's 22Hz across (1/3 octave) and still, no room treatments have been installed.

...

Below is what one of our first graphs looked like.

...

Currently being used are two eighteen year old subwoofers with replaced divers and radiators and one current RW-12D with no room treatments added. I'm still working on figuring out how to fill in that middle gap as it's not distance, it's not phase and no room treatments are allowed. Since it's currently only a -4 dB null, I'm considering the addition of a miniDSP.

Unfortunately, some have forgotten how to have fun with this hobby.

-
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post #23 of 36 Old 05-10-2013, 04:14 PM
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Originally Posted by craig john View Post

Because the meaurements you get in your room will be completely different than the measurements someone else gets in their own room, even if they're using the same subwoofer.
General advice to use measurements and to try different placements is fine. However, offering placement advice to someone else, (which is what you were doing), based on the results you found in YOUR room is inappropriate.

More importantly, did you read my other post about not using the CC Distance and using the subwoofer Distance instead?

I read that post with great interest, and it makes good sense to me. I will mentally file that away for future use when I am fiddling with my own stuff.

When I read the OP's question, in my head I play "think like the pros." I guessed that a second sub in the back might be best to solve the problem, so thanks for the validation on that. In my beloved state of West Virginia, we like to say "sometimes, even a blind squirrel finds a nut." rolleyes.gif
+++

Thinking outside the box: Since the OP's original problem was a null in EXACTLY the front/center seat, is there an optimum position to place the single front sub that might give him the best sub sound? If I were guessing, I would say something off-center, maybe facing into the front wall/corner instead of facing front. I would also think a downfiring single sub might not have that front/center null.

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post #24 of 36 Old 05-10-2013, 05:29 PM
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Quote:
Originally Posted by BeeMan458 View Post

To you, it's inappropriate and to me, it's a perfectly fine thing to do; encourage others to try what I've found works for our situation. To do what I suggest, does no harm. Currently I'm using the AVR provided level control for the center channel and the gain control on a single sub to steer the graph.......up and down, up and down, up and down.......there's got to be some ginger spice around here somewhere. I encourage everybody to use their level and gain controls; learning how to steer their measurement graphs in this fashion.

It's fun making changes and measuring the room's response to the changes. That's how one gets to know their system and sharing personal experience is part of the hobby. And if a recommendation doesn't work for them, then, they put the subs back in the original location, reset their settings to what they were before and continue scratching their head, wondering why they're not obtaining the results they're wanting.

Reading what others had to post, their personalized comments led me to believe there was a possible phase issue somewhere so I took the time, made phase changes and came to the conclusion, whoops, not in this case. Put everything back the way they were and got on with working some other ideas. No harm, no fowl. Didn't cost zip and no physical damage. Today, I've been playing with this stuff for about four hours and still having fun.

The -20dB null I use to have, has been reduced to -4dB but it's 22Hz across (1/3 octave) and still, no room treatments have been installed.

...

Below is what one of our first graphs looked like.

...

Currently being used are two eighteen year old subwoofers with replaced divers and radiators and one current RW-12D with no room treatments added. I'm still working on figuring out how to fill in that middle gap as it's not distance, it's not phase and no room treatments are allowed. Since it's currently only a -4 dB null, I'm considering the addition of a miniDSP.

Unfortunately, some have forgotten how to have fun with this hobby.

-
It's great that you've improved your own response. Still, what you done in your room will have little applicability to what someone else can achieve in their room. For example, Landshark's room looks symmetrical and sealed. Your room is asymmetrical and open. The dimensions, acoustics and most importantly the position of the LP in the room are completely different. What works in your space will likely not be the optimal solution in his room. Recommending what you've done... for him... is not at all likely to work.

Wanting to share your experience with others is laudable. However, knowing what to share, and it's applicability to others, makes your sharing much more useful.

In the graphs you've posted, is that the CC and the sub? If so, post the graphs of the L + the sub, the R + the sub and the sub in isolation and each speaker in isolation. This will let us see if the problem is a null in the room or some interaction of the speaker(s) and sub. If it's a room null, then a change of subwoofer placement or listening position will impact it. If it's an interaction of the sub(s) and speaker(s), then a settings change will impact it. Try measuring the response at some other adjacent LP's, left and right of the primary, and front and rear of the LP. Often these nulls are positional and you can "correct" them just by moving the listening/measuring position.

Craig

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Perfection is not attainable, but if we chase perfection we can catch excellence."

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Quote:
Originally Posted by wvu80 View Post

Since the OP's original problem was a null in EXACTLY the front/center seat, is there an optimum position to place the single front sub that might give him the best sub sound? If I were guessing, I would say something off-center.
Symmetry pleases the eye, but it usually offends the ears where low frequencies are concerned.
Quote:
I would also think a downfiring single sub might not have that front/center null.
Subwoofers radiate omni-directionally. The lows sound the same no matter which way the sub is aimed. Down or rear firing filters above bandwidth harmonics, but does nothing with respect to room modes.

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Quote:
Originally Posted by Bill Fitzmaurice View Post

Symmetry pleases the eye, but it usually offends the ears where low frequencies are concerned.
Bill, if we put that on a T-shirt and sell it to the sub guys on this forum I bet we could make our first million. I'd split it with you. cool.gif

Check out my new sig. Now people will think I'm smart, too. tongue.gif

Symmetry pleases the eye, but it usually offends the ears where low frequencies are concerned. -Yoda Fitzmaurice
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Hello everyone.

I have dual subwoofer setup. Both on the front left and front right corners. Despite dual subs, I have serious null issue at 30Hz. 1/4 wavelength of 30Hz is about 9.5 feet.

My room dimension is about 15' (W) x 27' (L) x 9.5' (H).

I guess the room height is the issue here. What can I do to combat this issue? Placing my subs off the ground? Will stacking one sub on top of another help?

I'm not worried about peaks because I have DSpeaker Antimode to fix those. I'm just worried about this 30Hz null.

Please help. Thanks in advance.
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post #28 of 36 Old 10-11-2013, 12:28 PM
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Quote:
Originally Posted by Skylinestar View Post

Hello everyone.
I have dual subwoofer setup. Both on the front left and front right corners. Despite dual subs, I have serious null issue at 30Hz. 1/4 wavelength of 30Hz is about 9.5 feet. My room dimension is about 15' (W) x 27' (L) x 9.5' (H).
I guess the room height is the issue here.
It would be if your LP was right next to one of them and the distance from your ears to the ceiling was 9.5 feet. Otherwise, no, the problem probably relates to having both of them at the front of the room.

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post #29 of 36 Old 10-11-2013, 12:37 PM
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Quote:
Originally Posted by Skylinestar View Post

Hello everyone.

I have dual subwoofer setup. Both on the front left and front right corners. Despite dual subs, I have serious null issue at 30Hz. 1/4 wavelength of 30Hz is about 9.5 feet.

My room dimension is about 15' (W) x 27' (L) x 9.5' (H).

I guess the room height is the issue here. What can I do to combat this issue? Placing my subs off the ground? Will stacking one sub on top of another help?

I'm not worried about peaks because I have DSpeaker Antimode to fix those. I'm just worried about this 30Hz null.

Please help. Thanks in advance.

Spread your subs in the room and excite room modes from different locations; preferably one each on opposing walls.

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post #30 of 36 Old 10-11-2013, 12:58 PM
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The room simulator here is great for doing these kinds of experiments:
http://www.hometheatershack.com/forums/downloads-area/47460-v5-01-beta-downloads-asio-support.html

If the front-back wall resonance is creating the problem null, you need 1 in front and 1 in back to cancel it out.
If the left-right resonance is creating the problem null, you need 1 on the left and 1 on the right.

Opposing corners can work well to cancel the main nulls on both axes. This can work great to tune for a single seat, and just okay for multiple seats.

For the best seat-to-seat consistency, it's good to have symmetry on both axes.
Front-center and back-center can accomplish that, but you sacrifice a lot in efficiency, compared to corner loading.
4 subs with 1 in each corner is ideal for FR, efficiency, and consistency.

If you don't want to buy 4 subs, experiment with front/back center and opposing corners, to see which works best for you (consistency vs. efficiency).

Based on the practical limitations in your room, due to your main speakers, placing subs in the 1/4 and 3/4 positions on the front and back walls would probably be ideal.
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