Any value in adding a second sub if mostly only 2 listeners? - AVS Forum
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post #1 of 23 Old 08-23-2012, 03:43 PM - Thread Starter
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My wife and I sit on the couch next to each other when we watch movies. Is there any point in adding a second sub? Or is a second sub only good for evening the bass response as you move between different areas in the room? I currently have a SVS PB12-plus in a 2700 cubic foot room.

The amazing back story behind my question: my wife really hates the look of speaker stands, and I jokingly said I could get another subwoofer and use them as speaker stands for the left and right speakers. To my surprise, she seriously said that would look better and we should do it. Of course, I haven't really told her the cost of adding a second sub yet, but she sort of knows it is not cheap...

By the way, is there a problem with putting speakers on top of a sub? I've seen a lot of home theater setups like this on AVS, but I wasn't sure.
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post #2 of 23 Old 08-23-2012, 05:16 PM
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Yes. A lot of value in adding a sub. And it is not recommended to put speakers on a sub.

butter and jelly please.
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post #3 of 23 Old 08-24-2012, 12:31 PM - Thread Starter
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Thanks for the reply. How would putting speakers on the sub affect the sound?
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post #4 of 23 Old 08-24-2012, 12:48 PM
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The problem with putting the front L&R speakers on the subs is that the best position for your front L&R speakers won't be the best place for your subs and vice versa.... That's one reason why many ppl on here say that tower speakers with built in powered subs are a waiste.

So other than the placement I don't think it would hurt the sound. You just have to make sure you have no cabinet vibration between the sub and speakers. Also keep in mind that the tweeters of the front speakers should be at seated ear level.

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post #5 of 23 Old 08-24-2012, 01:05 PM
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The Wilson Watt-Puppy was the best selling speaker in the $10,000 + range. The Watt-Puppy had the bass-module right below the mid-range + tweeter module. That might suggest that placing subs below ones speakers isn't such a bad idea after all. YMMV
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post #6 of 23 Old 08-24-2012, 01:53 PM
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Quote:
Originally Posted by beezar View Post

Thanks for the reply. How would putting speakers on the sub affect the sound?

It must depend on the room too though. I've been using my same basement room for 10 years with different speakers, subs, and I've tried all kinds of placements. My favorite configuration by far is my current setup with my speakers sitting on top of the subs.

Do you need a 2nd sub? It depends on what kind of frequency response you are getting now with 1 sub. I know for me I'll never go back to a single sub.
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post #7 of 23 Old 08-24-2012, 02:23 PM
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Originally Posted by spyboy View Post

The Wilson Watt-Puppy was the best selling speaker in the $10,000 + range. The Watt-Puppy had the bass-module right below the mid-range + tweeter module. That might suggest that placing subs below ones speakers isn't such a bad idea after all. YMMV

The Wilson, as superb an offering as it was, can't be compared to typical subwoofer approach.

I believe the two 8 inch drive units (killer piece, but hardly a subwoofer), crossed to the 7" two way at approx 125hz or so. Immediately, knowing that, one can see that blending with the two way top box was clearly the design goal, not mitigating room effects in the modal range.

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post #8 of 23 Old 08-24-2012, 02:45 PM
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Originally Posted by FOH View Post

The Wilson, as superb an offering as it was, can't be compared to typical subwoofer approach.
I believe the two 8 inch drive units (killer piece, but hardly a subwoofer), crossed to the 7" two way at approx 125hz or so. Immediately, knowing that, one can see that blending with the two way top box was clearly the design goal, not mitigating room effects in the modal range.

With the proliferation of subwoofer EQ's (Velodyne SMS-1, Audyssey Multi-EQ XT 32, (Anti-Mode 8033 + Dual Core), SVS AS EQ-1, ARO, PBK, mini DSP, REW + Behringer Feedback Destroyer annd pricier models from Behringer, QSC DSP 30... and the list goes on). Placing subwoofers under ones speakers isn't the big deal it used to be. smile.gif
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post #9 of 23 Old 08-24-2012, 03:24 PM
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I've got no problem with placing them under the mains.

They need to go were they need to go. That's driven by two aspects; aesthetic concerns, and measured performance. Typically, even the savvy enthusiast blend those two aspects and split the difference somewhat.

---

Now, regarding subwoofer EQ'ing, I'd recommend that only as the final step. It well understood that both the interactions from the room boundaries, and the room's modal resonance behavior affects a subwoofers response within the room's space. Without the boundaries, most subs would have outstandingly even response. Add the boundaries, all the constructive and destructive interactions take hold,... the room absolutely dominates the response. So, knowing this acoustic interaction causes the response problems, then exploring all possible interactions via experimenting with subwoofer placement is the prudent first step. Finding the combination of subwoofer position, and typically to a much lesser extent listener position, yielding the best workable response is best prior to even beginning the EQ'ing process.


Next comes phase adjustment, experimenting with time domain and how it influences the subsequent response. Then finally, the last step is frequency equalization. As many may guess, yep it's best performed manually, not via DSP ie Audyssey, etc. Now, those types of room correction DSP are nice and powerful solutions that help many achieve great response they would otherwise not get. Great product, especially the two channel varieties, and it get decent results with little effort. There's just better, more predictable results doing it manually. And, it's very easy really.



Good luck

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post #10 of 23 Old 08-24-2012, 05:01 PM
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An Audio/Acoustical Engineer’s Perspective:

First adding a second Sub (identical to the first one) will definitely improve the sound by:

1. Smoothing out the frequency response throughout the room.
2. Cleaning up the sound by reducing the distortion at any given SPL since two units are sharing the load.
3. But most importantly if your preamp/processor/receiver allows True Stereo Subwoofer output/configuration (as opposed to dual mono) you will gain huge improvement in image depth and specificity listening to material that has low frequency stereo info (and a lot of them do).

HOWEVER, you will destroy the sound of the mains by putting them on top of the Subs. This has NOTHING to do with the comment, “best position for your front L&R speakers won't be the best place for your subs and vice versa”. While there is some truth to this, in reality there are bigger issues at hand. In fact for the ultimate sound you want the voicecoil of the subwoofer to be on the exact same plane as the voicecoil of the other drivers in the fronts. The best speakers in the world do this and is why they have the low frequency drivers in the same cabinet (but not the same enclosure) and staggered to be time/phase aligned to the high frequency drivers.

The problem with sitting the satellites right on top of the Sub is that the acoustical energy from the Subs are going to conduct thru the cabinets and modulate the higher frequencies. Stereo image will lose its focus. This is why good speakers such as the aforementioned Wilson Watt-Puppy, while it may appear that the bass drivers are in the same cabinet, are in actuality “acoustically isolated/separated" at a great cost and effort by the engineers so that the energy from the woofers don’t affect the other drivers. For all practical purposes they are in separate “boxes” separated by air. In your case the only way you are going to achieve this is by making sure that there are a few inches of SPACE between the Subwoofer and the mains.

If you can find a way to put the subs as close as possible to the fronts, with their drives in the same plane, without them actually touching, then you have arrived at the best possible scenario. Of course you are going to have to re-run the calibration of all parameters all over again. Also with two subs situated right next to the mains you can get away with a higher crossover frequency between the subs and main (but not too high) for greater mid bass slam and dynamics. Setting up a true Stereo Sub configuration and listening to music, especially live music that has low frequency STEREO INFO CAPTURED by the Recording Engineer is a real treat!

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post #11 of 23 Old 08-24-2012, 07:39 PM
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Quote:
Originally Posted by RanaKabir View Post

An Audio/Acoustical Engineer’s Perspective:
First adding a second Sub (identical to the first one) will definitely improve the sound by:
1. Smoothing out the frequency response throughout the room.
2. Cleaning up the sound by reducing the distortion at any given SPL since two units are sharing the load.
3. But most importantly if your preamp/processor/receiver allows True Stereo Subwoofer output/configuration (as opposed to dual mono) you will gain huge improvement in image depth and specificity listening to material that has low frequency stereo info (and a lot of them do).
HOWEVER, you will destroy the sound of the mains by putting them on top of the Subs. This has NOTHING to do with the comment, “best position for your front L&R speakers won't be the best place for your subs and vice versa”. While there is some truth to this, in reality there are bigger issues at hand. In fact for the ultimate sound you want the voicecoil of the subwoofer to be on the exact same plane as the voicecoil of the other drivers in the fronts. The best speakers in the world do this and is why they have the low frequency drivers in the same cabinet (but not the same enclosure) and staggered to be time/phase aligned to the high frequency drivers.

The problem with sitting the satellites right on top of the Sub is that the acoustical energy from the Subs are going to conduct thru the cabinets and modulate the higher frequencies. Stereo image will lose its focus. This is why good speakers such as the aforementioned Wilson Watt-Puppy, while it may appear that the bass drivers are in the same cabinet, are in actuality “acoustically isolated/separated" at a great cost and effort by the engineers so that the energy from the woofers don’t affect the other drivers. For all practical purposes they are in separate “boxes” separated by air. In your case the only way you are going to achieve this is by making sure that there are a few inches of SPACE between the Subwoofer and the mains.

If you can find a way to put the subs as close as possible to the fronts, with their drives in the same plane, without them actually touching, then you have arrived at the best possible scenario. Of course you are going to have to re-run the calibration of all parameters all over again. Also with two subs situated right next to the mains you can get away with a higher crossover frequency between the subs and main (but not too high) for greater mid bass slam and dynamics. Setting up a true Stereo Sub configuration and listening to music, especially live music that has low frequency STEREO INFO CAPTURED by the Recording Engineer is a real treat!

If you are lisening to a person playing guitar outdoors and take a step toward the guitar player, you change all the relative phases of the various frequencies being produced by the instrument, but unless you are unusual, you do not experience the changed phase relationships as wrong, since they're not. Which is to say that to a significant extent, phase relationships seem to be less important than my rational brain tells me they should.

AFAIK, unless our heads were a couple of feet wide our ears cannot distinguish direction for low frequencies. One sees 80 Hz bandied about a lot but I don't know if that's an 80 Hz low pass, or 80 Hz absolutely. I suspect the former. Clearly different people localize deeper frequencies differently but there is a physiological reason why below some point they cease to be localizable for everybody. As long as what your subs reproduce is below the frequency you can localize it's hard to see how "stereo" bass can be differently enveloping.

IMO, etc etc etc.
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post #12 of 23 Old 08-24-2012, 08:49 PM
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Quote:
Originally Posted by RanaKabir View Post

An Audio/Acoustical Engineer’s Perspective:

confused.gif

Well, I'm uncertain of your credentials or technical savvy within the realm of Audio/Acoustical Engineering, but I do believe you're mistaken on several of your points.

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post #13 of 23 Old 08-24-2012, 09:06 PM
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Originally Posted by FOH View Post

confused.gif
Well, I'm uncertain of your credentials or technical savvy within the realm of Audio/Acoustical Engineering, but I do believe you're mistaken on several of your points.

I agree.

Placing the speakers on the subs is not a bad idea. The only problem is that they might not be in the most optimal place in the room. But two powerful subs like the PB12 Plus will still kick out some monster bass in your listening position with no problem. I'm sure there is no detrimental effects on the sound of the speakers. The only thing you want to be aware of is that if the subs have significant cabinet resonance, it could slowly vibrate your speakers off the subwoofers. Also make sure you try different phases when you calibrate the two subs so you don't actually get a loss of SPL due to cancellation.
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post #14 of 23 Old 08-25-2012, 01:19 PM
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Originally Posted by JHAz View Post

If you are lisening to a person playing guitar outdoors and take a step toward the guitar player, you change all the relative phases of the various frequencies being produced by the instrument, but unless you are unusual, you do not experience the changed phase relationships as wrong, since they're not. Which is to say that to a significant extent, phase relationships seem to be less important than my rational brain tells me they should.
AFAIK, unless our heads were a couple of feet wide our ears cannot distinguish direction for low frequencies. One sees 80 Hz bandied about a lot but I don't know if that's an 80 Hz low pass, or 80 Hz absolutely. I suspect the former. Clearly different people localize deeper frequencies differently but there is a physiological reason why below some point they cease to be localizable for everybody. As long as what your subs reproduce is below the frequency you can localize it's hard to see how "stereo" bass can be differently enveloping.
IMO, etc etc etc.

Agreed, but note that there is a coherency to the relative phases of the various frequencies coming from any live instrument. It isn’t like everything below a certain frequency, say below 80Hz, is coming from a source 10 feet away. (Please note I picked 80Hz somewhat randomly because like you said it is “bandied about a lot”, I personally use 40Hz in my system.) As a recording and reproduction engineer I would always prefer to capture the original signal and play the reproduction to be as identical to the source as possible.

I again agree/understand the principles and of wavelengths involved and why one SHOULDN’T be able to locate a low frequency source or hear any difference between a Stereo and a mono (or dual mono) setup but, and this is a big BUT, one can. I and my colleagues have tested/verified this in many setups, including my own. With two identical systems meticulously set up with identical equipment, volume matching, etc. Stereo subs re-create the original acoustic space of the recording with a deeper, wider soundstage much better EVERY TIME. The performance is palpable as if you are at the original venue. This is readily apparent if you were at the original recording session and experienced the original event and therefore familiar with the original space. It is like night and day.

I became aware of this in a recording studio nearly thirty years ago listening to a recording I had just made and was playing it back using a pair of the original B&W 801s (the ones with the big 15” woofer). When I switched the sound over to the close field monitors (smaller B&Ws hooked up with a single Velodyne ULD-15 subwoofer) the soundfield OF THE VENUE collapsed. This has led to a lifetime of study since that shouldn’t have happened. The crossover was at 50Hz and otherwise very identical (both systems were “full up” at 20Hz and sloped -3 at 17 Hz. In later years I ran into this problem in my home when I switched from a pair of KEF 107/2 to a pair of Magnepan 3.1As with a sub crossed over at 45 Hz. The Maggies actually threw a deeper soundstage than the KEF’s on its own, BUT playing Mussorgsky: Pictures at an Exhibition (Dorian Recordings) the KEFs simply blew the Maggie setup away. The KEF’s were full up at 20Hz so in essence has built in subs (stereo). This led to me to drag another Velodyne ULD-15 from the store (used to be a KEF and Velodyne Dealer) and hook two of them up in Stereo mode with the Maggies (starting with the voice coil on the same plane as the Planar diaphragms and then correcting for delays inherent to the “laggy” servo in the Subs) and viola, the huge hall acoustics returned. From then on ALL my Studio and Consumer System that I have designed incorporate either full range speaker that are full up at 20Hz or Dual Subs in Stereo mode. I have hundreds of initially skeptical clients that have changed their minds once they have heard the difference.

There IS low frequency info that the brain “hears” and localizes, perhaps thru bone conduction. It is there for anyone to experiment and verify. Be aware that if the recording is essentially mono at low frequencies as is the case for engineers who mix for 5.1 with the .1 channel having mono info then you won’t hear what I am talking about. But if the engineer was careful to capture the original subsonic info in Stereo, as in good musical performances, boy what a treat! Also be aware that this is not so apparent if your system/room has limited resolution. I am an Energy Physicist/Engineer and a musician with a passion for high-audio. While I am NOT wealthy, I have been fortunate to own & play with very hi-resolution equipment all my life which makes this very clear to hear/experience. You will not hear this difference using mass market Chinese equipment that couldn’t image properly even if your life depended on it.

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post #15 of 23 Old 08-25-2012, 01:32 PM
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Originally Posted by FOH View Post

confused.gif
Well, I'm uncertain of your credentials or technical savvy within the realm of Audio/Acoustical Engineering, but I do believe you're mistaken on several of your points.

Well, I am always willing to learn from my mistakes, so, could you please be so kind to enlighten me as to precisely where/how I am mistaken? Thanks.

My Credentials/Tech Savvies can be had on the web. You can start with ENDSEnergy.com where I am utilizing my Energy Physics background for Human Salvation (I am the smiling guy who is the CTO & Chairman of the Board). From there you can look me up on LinkedIn where you will find pointers to SOME of my other Electrical Engineering/Chip Manufacturing and Audio Consulting Ventures.

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post #16 of 23 Old 08-25-2012, 01:52 PM
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Originally Posted by flickhtguru View Post

The problem with putting the front L&R speakers on the subs is that the best position for your front L&R speakers won't be the best place for your subs and vice versa.... That's one reason why many ppl on here say that tower speakers with built in powered subs are a waiste.
So other than the placement I don't think it would hurt the sound. You just have to make sure you have no cabinet vibration between the sub and speakers. Also keep in mind that the tweeters of the front speakers should be at seated ear level.

In my room, the speakers and subs in the same position IS the best option, SO this really depends on the room. I also have my 2 bookshelf speakers sitting on top of my subs and there are no issues.

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post #17 of 23 Old 08-25-2012, 01:53 PM
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Originally Posted by shadyJ View Post

I agree.
Placing the speakers on the subs is not a bad idea. The only problem is that they might not be in the most optimal place in the room. But two powerful subs like the PB12 Plus will still kick out some monster bass in your listening position with no problem. I'm sure there is no detrimental effects on the sound of the speakers. The only thing you want to be aware of is that if the subs have significant cabinet resonance, it could slowly vibrate your speakers off the subwoofers. Also make sure you try different phases when you calibrate the two subs so you don't actually get a loss of SPL due to cancellation.

Putting any speaker directly on top of a Subwoofer to use the Sub as a speaker stand is a VERY BAD idea. You don't have to take my word for it. Call the Wilson guys or ANY reputable Speaker manufacturer. (No, don’t call your local BestBuy guy; they are not aware of the Energy Physics involved.)

Here is Wilson Audio’s Contact Info:
Wilson Audio Specialties
2233 Mountain Vista Lane
Provo, Utah 84606 USA
Telephone: (801) 377-2233
Fax: (801) 377-2282
Email: was@wilsonaudio.com

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post #18 of 23 Old 08-25-2012, 03:48 PM
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Wilson Audio speakers aren't for those who are chiefly interested in performance, so I am not about to take their word about anything regarding speaker design. Perhaps they can teach me a thing or two about selling speakers to people with more money than sense. I would admit that in a perfect world you wouldn't want to place speakers right on top of subwoofers, for reasons of cabinet vibrations, and also simply to have that much less surface for nearby reflections, but I am sure the aural consequences of either are insignificant. There is no real reason not to do it unless, as I said above, the sub cabinet is poorly braced and is prone to vibrations. I doubt the subs that the OP is contemplating has that problem.

Also, you, as an engineer, ought to understand the limited usefulness of anecdotal evidence in the matter of audio perception, yet that is all you have provided us thus far to back your point. I'd love to see you correctly pick out a properly calibrated monophonic sub system and a properly calibrated stereophonic in a blind test.
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post #19 of 23 Old 08-26-2012, 11:48 AM
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Originally Posted by shadyJ View Post

Wilson Audio speakers aren't for those who are chiefly interested in performance, so I am not about to take their word about anything regarding speaker design. Perhaps they can teach me a thing or two about selling speakers to people with more money than sense. I would admit that in a perfect world you wouldn't want to place speakers right on top of subwoofers, for reasons of cabinet vibrations, and also simply to have that much less surface for nearby reflections, but I am sure the aural consequences of either are insignificant. There is no real reason not to do it unless, as I said above, the sub cabinet is poorly braced and is prone to vibrations. I doubt the subs that the OP is contemplating has that problem.
Also, you, as an engineer, ought to understand the limited usefulness of anecdotal evidence in the matter of audio perception, yet that is all you have provided us thus far to back your point. I'd love to see you correctly pick out a properly calibrated monophonic sub system and a properly calibrated stereophonic in a blind test.


I didn’t specifically want you call Wilson. I picked Wilson since it was bought up by another member in this thread. You can call ANY knowledgeable engineer in any good speaker company.

I didn't know that, "Wilson Audio speakers aren't for those who are chiefly interested in performance". I will have to have a serious talk with every acoustical engineer and audio journalists that I know who revere them precisely for their performance characteristics.

I am afraid that the aural consequences ARE significant. I and the engineers that I work with can hear this. Just because you cannot doesn’t mean it’s not there, the same as a blind man who cannot see the rainbow, doesn’t mean it’s not there.

“Also, you, as an engineer, ought to understand the limited usefulness of anecdotal evidence”, that is precisely why I didn’t offer any. EVERYTHING that comes out of my mind is meticulously experimented/tested/verified by I and my team of engineers. I have no choice since companies/customers pay me handsomely for this. I have NEVER passed on anecdotal evidence since that is blasphemy for a Scientist.

“I'd love to see you correctly pick out a properly calibrated monophonic sub system and a properly calibrated stereophonic in a blind test” Anytime, anyplace, since that IS how I arrived at the principle in the first place, which I have used in hundreds (if not thousands) of installations with positive results.

It appears that YOU are the one using anecdotal evidence since HAD you tried this for yourself using material that has Stereo Subsonic info (and high resolution equipment set up properly in a room) you too would have heard the difference. Every truly high-end system that images like crazy uses Stereo Subwoofers. Again, you don’t have to take my word for it. There are hundreds of experienced Audio engineer/Psychoacoustic Scientists that I have talked to that know this to be a fact.

It is also possible your ear/brain mechanism simply doesn’t have the capability. In that case you should accept the fact of life that just because you can’t do something doesn’t mean some else can’t. I kind of get the feeling you are one of those fellows who are in the “grapes are sour” camp. These people tend to scoff at anything they can’t afford, experience or understand.

My dear friend, if you can’t trust your fellow human beings who are offering you new information (to at least go out and try to find out for yourself), how are you going to learn something new?

Very curious, what kind of equipment (make/models) are you using to arive at your conclusions??
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Beezar, there are 2 types of people in this world. Type A buys a Ferrari and never drives it. Type B, buys a Ferrari, and drives it to the liquor store.
I am type B.

As a practical engineer, I say get the 2nd sub and don't worry too much about using them as speaker stands, you can always place a towel or something in between to absorb vibration. More important is that your speakers are in the proper position/height. You will have twice the output capability (+3db) with 2 than with a single sub assuming all things equal.
The most important factor is room placement. The only sure way is to get the 2nd one and test them both out and see how they sound. As for the wife and cost of sub, that I leave to you.
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post #22 of 23 Old 09-12-2012, 06:05 AM
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I would not even hesitate to use your subs as speaker stands assuming the subs are quality and well braced. I use my PB13s as speaker stands for my bookshelf speakers and have had zero issues. The sound is wonderful. Before going with multiple subs, I was using speaker stands and I simply cannot tell the difference between that and using my subs as stands. Whatever vibration is there must be minimal as the speakers never move. For all practical purposes, using your subs as speaker stands should be a non issue.

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post #23 of 23 Old 09-12-2012, 06:35 AM
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A well-designed subwoofer will not exhibit huge external cabinet vibrations, so blu-tac or some similar treatment to keep the bookshelf speaker on top should be sufficient to keep that speaker in place. Sonically, it may not be the best place though.

Alignment of the voice coils of drivers in a multi-way system has been used to provide phase coherency between those drivers. When you add a subwoofer, which is powered by its own amplifier, the situation changes in regards to phase coherency. Since all the drivers in that multi-way system receive the signal from their amplifier at the same time, the voice coil alignment technique works. Since the subwoofer has a different amplifier and electronic network, there is a different group delay, which causes the subwoofer to emit sound at (quite possibly) many milliseconds later than the bookshelf system. So, achieving phase coherency is not as simple as setting the bookshelf speaker "in the right spot" on top of the sub.

A reasonable approach would be to:

1. Place the subs where their interaction with the room is most agreeable. If you have a spectrum analysis software program (REW, etc.), then use it to find the smoothest response that minimizes room modes.

2. Position the bookshelf speakers in the position where playing a tone at the crossover frequency (which would be played by both sub and main), reversing the speaker cable leads on the bookshelf speaker ( + & - ) to place it out of phase with the sub, and seeing what position of the bookshelf speaker results in zero (or lowest possible) output of that tone. This cancellation of sound means that proper phase has been established between the sub & main speakers.

3. Finally, use any built-in room correction in your AVR/processor to further smooth out any frequency response irregularities, etc. at the listening position.

Hope this helps,

Lee

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