Can a sub be placed upside down? - AVS Forum
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post #1 of 29 Old 11-30-2012, 03:38 AM - Thread Starter
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I have 2 Emotive Ultra 12's that I plan on stacking. I have a RCA splitter, 1 female to 2 male. Problem is the splitter can't reach both LFE inputs when stacked normally. The lfe connection is near the top. If I flip the top one upside down, it will reach. The subs are sealed front firing. basically a square with the driver dead center in the front.

Does it matter if a sub is upside down?
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post #2 of 29 Old 11-30-2012, 06:35 AM
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Originally Posted by KidHorn View Post

Does it matter if a sub is upside down?
No. But you'll get better results with the subs spread to smooth room modes.

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post #3 of 29 Old 11-30-2012, 07:26 AM - Thread Starter
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Good to know. I'll stack the two and add a third sub that will be in an opposite corner.
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post #4 of 29 Old 11-30-2012, 09:26 AM
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Originally Posted by KidHorn View Post

Good to know. I'll stack the two and add a third sub that will be in an opposite corner.
The more locations employed the smoother the result.

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post #5 of 29 Old 11-30-2012, 09:35 AM
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Originally Posted by KidHorn View Post

Good to know. I'll stack the two and add a third sub that will be in an opposite corner.

You seem to have missed the point.

As Toole says:

"
Separating the reproduction of low frequencies is a good way to address the room resonance problems in a manner that is independent of the number of reproduction channels.
"
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post #6 of 29 Old 11-30-2012, 12:00 PM - Thread Starter
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Originally Posted by arnyk View Post

You seem to have missed the point.
As Toole says:
"
Separating the reproduction of low frequencies is a good way to address the room resonance problems in a manner that is independent of the number of reproduction channels.
"

I get it. The issue is I have 3 subs on 2 sub channels and am using Audyssey XT32 with dual sub calibration. Dual sub calibration sets the distance for each of the 2 channels. On the channel with 2 subs, in order for the distance to be set properly, the 2 subs need to be the same distance from the primary listening spot. The easiest way to do that is to stack them on top of each other.
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post #7 of 29 Old 11-30-2012, 12:33 PM
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Originally Posted by KidHorn View Post

I get it. The issue is I have 3 subs on 2 sub channels and am using Audyssey XT32 with dual sub calibration. Dual sub calibration sets the distance for each of the 2 channels. On the channel with 2 subs, in order for the distance to be set properly, the 2 subs need to be the same distance from the primary listening spot. The easiest way to do that is to stack them on top of each other.
Do you want to do it the easiest way or the best way? BTW, the importance of the distance from the sub to listener is highly overblown. You're dealing with 14 to 40 foot wavelengths so you can't hear pathway differentials with subs the way you can with mains.

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post #8 of 29 Old 11-30-2012, 03:30 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

Do you want to do it the easiest way or the best way? BTW, the importance of the distance from the sub to listener is highly overblown. You're dealing with 14 to 40 foot wavelengths so you can't hear pathway differentials with subs the way you can with mains.

If the wavelength is 14 feet and one sub is 7 feet closer than the other and both send a monotonic waveform at the frequency that corresponds to a 14 foot wavelength, the subs will be 180 degrees out of phase and cancel each other out. Not a minor issue. This is a worst case scenario, but I wouldn't underestimate the importance of having all the speakers, including the subs, hit you on queue. I'll stick to having subs in two locations instead of 3.
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post #9 of 29 Old 11-30-2012, 07:47 PM
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Originally Posted by KidHorn View Post

If the wavelength is 14 feet and one sub is 7 feet closer than the other and both send a monotonic waveform at the frequency that corresponds to a 14 foot wavelength, the subs will be 180 degrees out of phase and cancel each other out.
No, they won't. That would only happen if said subs were outdoors, or in a perfectly anechoic chamber. In a room of average dimension response is defined more by the relative distances between the subs, boundaries and listening position than the relative positions of the subs and listener alone. The presence of walls and a ceiling changes everything, and the more sub locations the better the result. But hey, don't believe me, I'm just an acoustical engineer.
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post #10 of 29 Old 11-30-2012, 08:01 PM
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Originally Posted by Bill Fitzmaurice View Post

No, they won't. That would only happen if said subs were outdoors, or in a perfectly anechoic chamber. In a room of average dimension response is defined more by the relative distances between the subs, boundaries and listening position than the relative positions of the subs and listener alone. The presence of walls and a ceiling changes everything, and the more sub locations the better the result. But hey, don't believe me, I'm just an acoustical engineer.
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post #11 of 29 Old 12-01-2012, 11:43 AM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

No, they won't. That would only happen if said subs were outdoors, or in a perfectly anechoic chamber. In a room of average dimension response is defined more by the relative distances between the subs, boundaries and listening position than the relative positions of the subs and listener alone. The presence of walls and a ceiling changes everything, and the more sub locations the better the result. But hey, don't believe me, I'm just an acoustical engineer.

You make it sound like the whole thing is a crapshoot where theoretical science doesn't apply. You may be right. From what I remember from my fluid mechanics classes, after you get past the basics, most of the math is based on empirical evidence. Take a lot of data and make an equation that fits. Particularly when dealing with turbulent flows. Trial and error seems to be the best way to see what will sound best.
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post #12 of 29 Old 12-01-2012, 01:46 PM
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Originally Posted by KidHorn View Post

You make it sound like the whole thing is a crapshoot where theoretical science doesn't apply.
Not at all. I was just pointing out that you were using simple math to predict a result that's only accurate when there is one reflective surface to consider, the floor. Each additional boundary added introduces another variable, so while it is possible to mathematically predict the best placement it's not an easy calculation. Rules of thumb as posted by a number of sources, Geddes, Toole and Harman amongst others, are as good a starting point as any.

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post #13 of 29 Old 12-02-2012, 05:52 AM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

Not at all. I was just pointing out that you were using simple math to predict a result that's only accurate when there is one reflective surface to consider, the floor. Each additional boundary added introduces another variable, so while it is possible to mathematically predict the best placement it's not an easy calculation. Rules of thumb as posted by a number of sources, Geddes, Toole and Harman amongst others, are as good a starting point as any.

I would say that if you're taking reflections into account, it would be impossible to mathematically predict the behavior, unless you had a room with very well understood boundary conditions. Which my room doesn't come close to having. My subs are front firing, so the most energy is going to come from a direct pressure wave as opposed to a reflected wave. The direct wave can use applied math to determine the best placement. But hey, since you're an acoustical engineer, you should know this. Where exactly did you get your degree(s) in acoustical engineering? I'm not aware of any university that offers a degree in that. Maybe some offer it as a focal point of study in mechanical engineering and/or physics. I would guess in most cases that the only requirement to being an acoustical engineer is to simply call yourself one, which is unfortunate for those who truly have an academic background in it.
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post #14 of 29 Old 12-02-2012, 06:04 AM
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Originally Posted by KidHorn View Post

My subs are front firing, so the most energy is going to come from a direct pressure wave as opposed to a reflected wave. .
One doesn't have to be an acoustical engineer to know that this is totally incorrect.
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I'm not aware of any university that offers a degree in that. Maybe some offer it as a focal point of study in mechanical engineering and/or physics.
There is much you're not aware of, but since you've decided you'd rather argue than learn I'll just bow out of this thread.

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post #15 of 29 Old 12-02-2012, 07:31 AM
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A quick Google search shows there are several schools offering degrees in acoustics.

Penn State for one, has an multiple graduate degrees available.
http://www.acs.psu.edu/
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post #16 of 29 Old 12-02-2012, 07:32 AM
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Originally Posted by KidHorn View Post

I would say that if you're taking reflections into account, it would be impossible to mathematically predict the behavior, unless you had a room with very well understood boundary conditions. Which my room doesn't come close to having. My subs are front firing, so the most energy is going to come from a direct pressure wave as opposed to a reflected wave. The direct wave can use applied math to determine the best placement. But hey, since you're an acoustical engineer, you should know this. Where exactly did you get your degree(s) in acoustical engineering? I'm not aware of any university that offers a degree in that. Maybe some offer it as a focal point of study in mechanical engineering and/or physics. I would guess in most cases that the only requirement to being an acoustical engineer is to simply call yourself one, which is unfortunate for those who truly have an academic background in it.
Dude, you've managed to alienate one of the finest sources of information on this forum. Check out his website: http://www.billfitzmaurice.com/

And he is absolutely correct... you have much to learn, and a lot of what you say is wrong, especially what I bolded above. A little humility goes a long way.

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post #17 of 29 Old 12-02-2012, 10:44 AM
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Originally Posted by Bill Fitzmaurice View Post

One doesn't have to be an acoustical engineer to know that this is totally incorrect.
There is much you're not aware of, but since you've decided you'd rather argue than learn I'll just bow out of this thread.
Don't do it Yoda. You're better than that and I have abandonment issues. Just don't reply to his posts.

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post #18 of 29 Old 12-04-2012, 05:37 AM - Thread Starter
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Originally Posted by craig john View Post

Dude, you've managed to alienate one of the finest sources of information on this forum. Check out his website: http://www.billfitzmaurice.com/
And he is absolutely correct... you have much to learn, and a lot of what you say is wrong, especially what I bolded above. A little humility goes a long way.
Craig

You obviously don't understand yourself. There's no way the initial wave will not be the strongest. It's basic thermodynamics. Every reflection will result in less energy because some of the energy is lost at the boundary.

I'm not saying anyone is right or wrong. What I'm saying is the only way to tell optimal placement is through trial and error. There are way too many variables involved in a real world application.

I've written many computer models that use finite element analysis to model real world behavior. You can only go so far. In order for any model to work you have to setup boundary conditions that in reality will almost never be correct. For a final design, you have to build a real model and collect empirical data. This is true in acoustics, air flow, heat transfer and anything else that involces particle motion and transfer of energy.

But hey, I don't have a website with drawings of subwoofers, I just have college degrees and years of experience modeling things, so what do I know about it.
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Originally Posted by KidHorn View Post

It's basic thermodynamics. Every reflection will result in less energy because some of the energy is lost at the boundary.

FYI, folks here like to discuss sound as if Fluid Dynamics and Thermodynamics, don't apply to acoustics,. Regarding some conversations, it's as if they don't exist at all. Makes for irrational conversations. Good luck.
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post #20 of 29 Old 12-04-2012, 07:41 AM
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Originally Posted by KidHorn View Post

You obviously don't understand yourself. There's no way the initial wave will not be the strongest. It's basic thermodynamics. Every reflection will result in less energy because some of the energy is lost at the boundary.
I'm not saying anyone is right or wrong. What I'm saying is the only way to tell optimal placement is through trial and error. There are way too many variables involved in a real world application.
I've written many computer models that use finite element analysis to model real world behavior. You can only go so far. In order for any model to work you have to setup boundary conditions that in reality will almost never be correct. For a final design, you have to build a real model and collect empirical data. This is true in acoustics, air flow, heat transfer and anything else that involces particle motion and transfer of energy.
But hey, I don't have a website with drawings of subwoofers, I just have college degrees and years of experience modeling things, so what do I know about it.

Perhaps the issue is one of practicality. If you lose 20 percent of the energy at the boundary, that's a decibel, which will affect in-room behavior only slightly. Likely inaudibly. Certainly boundary losses are not sufficient to eliminate the peaks and nulls the everybody has in home-sized rooms.
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post #21 of 29 Old 12-04-2012, 10:53 AM - Thread Starter
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Perhaps the issue is one of practicality. If you lose 20 percent of the energy at the boundary, that's a decibel, which will affect in-room behavior only slightly. Likely inaudibly. Certainly boundary losses are not sufficient to eliminate the peaks and nulls the everybody has in home-sized rooms.

You may be right about the amount lost. I really don't know but from a best way to set things up point of view, I think the best bet is to try to optimize the initial sound waves at first since that is much more achievable than trying to take reflections into account. I think the best overall way is through trial and error. Many suggest doing the sub crawl, which is probably a very good idea, but I'm not sure how well that would work trying to place 3 subs.

I would guess the reflections do get absorbed a decent amount since otherwise the room would sound like an echo chamber. Drywall seems like something that would do OK with sound absorption. Almost certainly better than concrete or wood.
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post #22 of 29 Old 12-04-2012, 11:12 AM
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Originally Posted by KidHorn View Post

You obviously don't understand yourself. There's no way the initial wave will not be the strongest. It's basic thermodynamics. Every reflection will result in less energy because some of the energy is lost at the boundary.

I think what you're missing is how those reflections can interact with one another, ie constructive and destructive interference.
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post #23 of 29 Old 12-04-2012, 11:44 AM - Thread Starter
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I think what you're missing is how those reflections can interact with one another, ie constructive and destructive interference.

I fully understand that. The issue is it would be almost impossible to accurately predict how the reflections would effect The final sound at the end listening position, I have 11 speakers and will have 3 subwoofers in a rectangluar room with a cathedral ceiling and 2 large openings. I also have a 7 foot wide closet jutting into the room. I have 3 area rugs over a maple floor. The only practical way to optimize the sound is to try different placements of the subwoofers. I have to have a starting point and I think the best starting point is to have the 2 subs that will be on a single channel stacked. The reason is that's the best way to have them in sync with one another. Audyssey recommends the same thing. Not stacking, but having the two subs equidistant from the primary listening position. The only way I can have them equidistant is to stack them.

If this doesn't sound good, then I can try moving one and adjusting the phase to compensate for the variance in distance betweeen the 2 and the primary listening position. At this point, I don't think anyone can state with any certainty what the best setup is. Stacking tends to produce a less diffuse sound, but it helps guarantee the subs will be in sync. Spreading them out will likely have a converse effect.
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Originally Posted by KidHorn View Post

The only practical way to optimize the sound is to try different placements of the subwoofers. I have to have a starting point and I think the best starting point is to have the 2 subs that will be on a single channel stacked. The reason is that's the best way to have them in sync with one another. Audyssey recommends the same thing. Not stacking, but having the two subs equidistant from the primary listening position. The only way I can have them equidistant is to stack them.
If this doesn't sound good, then I can try moving one and adjusting the phase to compensate for the variance in distance betweeen the 2 and the primary listening position. At this point, I don't think anyone can state with any certainty what the best setup is. Stacking tends to produce a less diffuse sound, but it helps guarantee the subs will be in sync. Spreading them out will likely have a converse effect.

Some subs come with continuous (0-180) phase controls so you can adjust accordingly. You can also do the real time analyzer game and find a program that works with your microphone. Then of course, there's Anti-Mode, 8033S II which allows one to work with many subs in stereo while working in compliment to XT32.

Warning, doing what I suggest above costs money, time and one ends up with a boatload of additional cables.
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post #25 of 29 Old 12-04-2012, 12:40 PM
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The issue is it would be almost impossible to accurately predict how the reflections would effect The final sound at the end listening position

I don't think anyone is really debating that. As Bill mentioned though:
Quote:
Rules of thumb as posted by a number of sources, Geddes, Toole and Harman amongst others, are as good a starting point as any.

Of course, if you don't want to follow those guidelines, nobody is going to put a gun to your head and force you to.
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Stacking tends to produce a less diffuse sound, but it helps guarantee the subs will be in sync. Spreading them out will likely have a converse effect.

It's not about a "diffuse sound", but modal averaging to smooth the frequency response. In any case, it sounds like you've got your mind made up, and Bill already answered your original question. Good luck!
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post #26 of 29 Old 12-04-2012, 02:18 PM
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Originally Posted by KidHorn View Post

You may be right about the amount lost. I really don't know but from a best way to set things up point of view, I think the best bet is to try to optimize the initial sound waves at first since that is much more achievable than trying to take reflections into account. I think the best overall way is through trial and error. Many suggest doing the sub crawl, which is probably a very good idea, but I'm not sure how well that would work trying to place 3 subs.
I would guess the reflections do get absorbed a decent amount since otherwise the room would sound like an echo chamber. Drywall seems like something that would do OK with sound absorption. Almost certainly better than concrete or wood.

bass will never sound like an echo chamber. If bass was being absorbed significantly, you would not have peaks. While 75 dB plus 75 dB = 78 dB, 75 dB plus even onlty 70 dB equals only 76 dB. Not enough of a variance to even get concerned about. Yet pelple have 20 dB nulls and 10 dB peaks in the bass in real rooms.

If you poke around on these threads you'll find folks with very deep nulls. I mean way over 10 dB deep. Given the reality that you're never talking about just one "reflection" with bass, it'd by highly unlikely to find a place where all the reflections actually cancelled to 0 dB at some frequency. "significant" absorption or loss within the room would eliminate the very problems that people struggle with in real rooms: peaks and nulls. The fact that we can hear and measure peaks and nulls in any room indicates that they are indeed not significantly absorbed or passed through walls, floor, etc.

But really it's the chaos of the modes that occur in the bass that is indeed hard to model in real world rooms. But on the other hand it has been demonstrated pretty effectively to be most simply dealt wih by using multiple sub positions. I mean you could try to absorb all the reflections to keep the cancellations and peaks from occurring, but if you just want to go down to 30 Hz (just over a 37 foot wavelength) to be fully effective each absorber at each reflection point (actually all of every wall plus the ceiling, needs a quarter wavelength, or just over 9 feet, of absorption. Noplace left for equipment and seating in many rooms.

It's just more effective in the real world to "fix" the peaks and nulls by sort-of averaging them out and because our ears aren't using bass to identify direction or reflectiveness or anything else, in part just because our heads are too narrow versus the wavelengths involved, it's no great sin to let go of thoughts of everything being "in phase". The place where phase matters in home audio systems is the crossover range from mains/surrounds to the sub(s), because for everything to "add up" correctly they all have to be in the right relative phase. But our speakers and our subs all introduce phase delays that differ at different frequencies, so it becomes again a mantter of trial and error, preferably with measurements involved, to identify the phase change (read sub channel delay) that causes everything to splice together appropriately. But the measured and experienced level and phase of bass energy in a room, whether it comes from a sub, main speaker or somebody whacking on a bass drum, is dominated (really, dominated, that is not overstating the case at all) by the room modes,, and not by the native frequency content of the sound source.
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post #27 of 29 Old 12-04-2012, 02:55 PM
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You obviously don't understand yourself. There's no way the initial wave will not be the strongest. It's basic thermodynamics. Every reflection will result in less energy because some of the energy is lost at the boundary.

I'm not saying anyone is right or wrong. What I'm saying is the only way to tell optimal placement is through trial and error. There are way too many variables involved in a real world application.

I've written many computer models that use finite element analysis to model real world behavior. You can only go so far. In order for any model to work you have to setup boundary conditions that in reality will almost never be correct. For a final design, you have to build a real model and collect empirical data. This is true in acoustics, air flow, heat transfer and anything else that involces particle motion and transfer of energy.

But hey, I don't have a website with drawings of subwoofers, I just have college degrees and years of experience modeling things, so what do I know about it.
When you place a subwoofer in a room, the room becomes the biggest factor in the reproduction of the bass. Period. Direct wave theory is useless in a room. The wavelengths are so long at bass frequencies that small distance discrepancies are immaterial. It is the modal response of the room that totally dominates. If you get an SPL meter and play a single frequency tone and walk around the room, you can measure the peaks and nulls throughout the room. These peaks and nulls are caused by constructive/destructive interference from the REFLECTED waves off the room boundaries combining, sometimes in-phase, sometimes out-of-phase. The in-phase combinations will add SPL; the out-of-phase combinations will decrease SPL.

With multiple subwoofers placed separately around the room, the peaks and nulls appear at different points in the room and they tend to cancel each other, yielding smoother response.

Here is the baseline response of one of my subwoofers measured outdoors with the mic placed on the ground one meter away from the side of the sub:



Bass frequencies propagate omnidirectionally, so that would be a measurement of the "direct wave" from the subwoofer.

Take that same subwoofer and place it in my room, and this is the response at the listening position:



Place it somewhere else and you get this:



Put 3 of them in the room, all daisy chained off one Subwoofer output, all placed randomly, at different distances to the LP, and EQ'd with Audyssey XT32, and you get this:



The *point* that Bill was trying to make to you was that, when you stack 2 of the subs, you forego an opportunity to spread them out and improve the smoothness of the response in your room. The "direct wave" is inconsequential when you're dealing with bass frequencies. The reflected sound has it's way with the direct sound and produces the final response you *HEAR*, which is the only response that matters. You can blather on about modeling and direct waves and thermodynamics all you want, but this is the only important aspect of optimizing multiple subwoofers.

With that, I will do what Bill did, and bow out of this thread.

You're welcome.

Craig
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post #28 of 29 Old 12-04-2012, 03:10 PM - Thread Starter
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I'm hoping I can get the 2 subs to sound like one and then let audyssey handle everything else.

I have a sub that I bought probably around 1999. It was something like $119 plus maybe $20 shipping. I put it in my bedroom where I never watch TV (My wife's TV domain) and it was awful. I could never tell it was on. Not good in the sense that it blended in, but bad in that it never made a sound. I didn't care since I rarely use it. It was good for putting a lamp on and that was about it. It was in a corner next to a 6' tall entertainment center and a wall. I decided I wanted to see if it worked or not, so I put it in a bedroom in my basement. I was amazed at how good it sounded. It really sounds good. I played a test CD and it can play 10Hz. Or at least I can hear a low frequency rumble when it plays a 10Hz source. It's a 12" ported down firing Dahlquest. It doesn't even have a 3 prong detachable power cord. It has a hardwired two prong cord. Something like you might see on a toaster. I always knew placement was important, but until I did this, I never realized how much of a difference it can make.
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post #29 of 29 Old 12-04-2012, 03:41 PM
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Originally Posted by craig john View Post

You're welcome.

a very informative post which certainly deserves a thank you smile.gif.

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