One large sub or two small ones? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 34 Old 09-08-2019, 08:26 AM - Thread Starter
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One large sub or two small ones?

I'm just about to pull the plug and buy my first subwoofer. I have decided to get a BKE subwoofer based on the glowing reviews and comments I have seen on the internet. My dilemma is should i get a single monolith plus ff/df or maybe get a P12 300SB-PR to start with and if needed later on get another for a 5.2.2 atmos setup? The only thing that bothers me about the monolith plus is no auto power off function and not 100% which type would be best suited for me (ff or df). size of the monolith doesnt bother me, i would make it fit

My room setup is currently 4x4 meters upstairs with floorboards covered in carpet but will be moving to a similar size room next year with a concrete floor covered in carpet. I would say my usage is 40% movies, 10% music and 50% gaming

There is nowhere close by I can go to demo subs so any help or suggestions would be really appreciated
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post #2 of 34 Old 09-08-2019, 10:08 AM
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Quote:
Originally Posted by sunvsmoon View Post
I'm just about to pull the plug and buy my first subwoofer. I have decided to get a BKE subwoofer based on the glowing reviews and comments I have seen on the internet. My dilemma is should i get a single monolith plus ff/df or maybe get a P12 300SB-PR to start with and if needed later on get another for a 5.2.2 atmos setup? The only thing that bothers me about the monolith plus is no auto power off function and not 100% which type would be best suited for me (ff or df). size of the monolith doesnt bother me, i would make it fit



My room setup is currently 4x4 meters upstairs with floorboards covered in carpet but will be moving to a similar size room next year with a concrete floor covered in carpet. I would say my usage is 40% movies, 10% music and 50% gaming



There is nowhere close by I can go to demo subs so any help or suggestions would be really appreciated


I sure most will agree ( not everyone)that you should buy the best you can afford and add another later if desired! Just makes for a less painful upgrade path!


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post #3 of 34 Old 09-08-2019, 02:33 PM
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I would always recommend buying the best and biggest subwoofer you can afford. It's a key piece in home theater. Adding a second one down the road is icing on the cake. Of course, there are some cases or scenarios where the other is true.
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post #4 of 34 Old 09-08-2019, 03:13 PM
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One argument is it would be better to get two smaller subs over one larger one.

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post #5 of 34 Old 09-08-2019, 03:41 PM - Thread Starter
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I'm after a sub which can handle small clear define details at low to medium volume, not bothered about it being boomy. would the monolith be able to do this or would i be better off with a p12 300sb?

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post #6 of 34 Old 09-08-2019, 06:24 PM
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I would recommend two smaller vs one larger as you get better coverage in the room and less chance of the sound of the bass becoming directional.
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post #7 of 34 Old 09-08-2019, 07:35 PM
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Also, for a true single dedicated subwoofer that will handle all your HT content, I'd also recommend a 15" subwoofer if possible. Again, of course if your room isn't big you can get away with a high quality 12" and potentially add a second one down the road.

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post #8 of 34 Old 09-09-2019, 12:15 PM
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The real answer to your questions is . . . . it depends.

In some rooms, dual subwoofers are needed to achieve a reasonably flat frequency response. Generally, any rectangular shaped room which is sealed from other openings is going to fall into this group. These rooms can be modeled in REW to get an idea of what frequency response looks like with different placement and quantity of subs.

In other rooms, you can get a reasonably flat frequency response from a single sub. I am fortunate enough to have one such room and have a single large subwoofer. Open concept rooms are more likely to be ok with a single sub as the irregular shape of the room makes the bass waves do strange things. Of course this makes it very unpredictable and only a REW measurement and experimentation will let you know for sure.

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post #9 of 34 Old 09-11-2019, 07:32 AM
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I will ALWAYS recommend dual subs over a single. A single sub can only provide ONE "Transfer Function" of bass to a single Listening Position. That single TF can be EQ'd to provide relatively good response at the one single LP, but it will inevitably make every other LP worse. Also, EQ can only be effectively applied to peaks. Nulls are cancellations and adding energy to a cancellation just enhances it.

With dual subs, these issues can be addressed. With two TF's to work with, the second sub can be placed in such a way that it fills in the nulls of the first sub, and the first sub fills in the nulls of the second. This leaves you with only peaks, and peaks can be easily dealt with using EQ. In addition, you get better, more consistent response at more LP's and the EQ is effective over a larger listening area. Finally, you get 3 to 6 dB of additional system "headroom", allowing each sub to be turned down and the whole system to play back with less distortion.

Of course, dual subs take more time and effort to install and get right, but the benefits are absolutely worth the investment.

I would only recommend a single, bigger sub if there is a definite plan in place to add a second identical sub down the road. The only downside to two smaller subs is that you give up some deep extension. (Two identical smaller subs will still have the same LF extension as as single, they'll just have a few dB more output at the lowest frequency they can reproduce). If deep LF extension is important to you, then start with a single larger sub, and plan to add a second down the road.

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post #10 of 34 Old 09-11-2019, 03:09 PM
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If adding dual subs means buying smaller, lessor subs to fit a budget then I would buy just one larger sub. As many before me have said on this forum, always buy the biggest and best single sub you can afford (unless of course you can afford two of them right off the bat). The reason - bass is addictive. If you buy two smaller subs you may outgrow them or you simply may not be happy from the start. Now you have to trade/sell your two smaller subs and purchase two larger ones. This will always cost you more than buying one to start out with and adding a second down the road if you feel it is necessary. I've been through 3 subs in 2 years. It's not cheap to upgrade.
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post #11 of 34 Old 09-11-2019, 07:25 PM
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One other important thing to consider when deciding between 1 large vs 2 small subs.

While a flat frequency response is a nice goal, the reality is that in normal listening, you are unlikely to hear dips and nulls unless they are severe (in width, not height). In my setup, the frequency response at the primary listening position is completely flat with no dips or nulls. All of the secondary listening positions have several peaks and valleys. I know this because I have checked it with REW, but I have never had a single person watch a movie and comment that certain frequencies were missing or louder than others. Instead, they are blown away by the system. Bass in most content is a complex combination of frequencies and narrow nulls really aren't audible, even if you know the nulls exist.

This is why many people recommend getting the single largest sub you can afford now. While you can seldom hear the occasional null in frequency response, you can absolutely hear the difference between a sub that is more powerful than another.
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post #12 of 34 Old 09-11-2019, 09:33 PM
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Quote:
Originally Posted by chucks0 View Post
One other important thing to consider when deciding between 1 large vs 2 small subs.

While a flat frequency response is a nice goal, the reality is that in normal listening, you are unlikely to hear dips and nulls unless they are severe (in width, not height). In my setup, the frequency response at the primary listening position is completely flat with no dips or nulls. All of the secondary listening positions have several peaks and valleys. I know this because I have checked it with REW, but I have never had a single person watch a movie and comment that certain frequencies were missing or louder than others. Instead, they are blown away by the system. Bass in most content is a complex combination of frequencies and narrow nulls really aren't audible, even if you know the nulls exist.

This is why many people recommend getting the single largest sub you can afford now. While you can seldom hear the occasional null in frequency response, you can absolutely hear the difference between a sub that is more powerful than another.
Of course nulls are not audible. They're the absence of sound. You can't "hear" a null. You only know about nulls when you hear the same content being played without the nulls and you hear the missing information. It's not surprising that no one has ever complained about missing notes in your system. The old expression: You don't know what you don't know... (is missing)... applies quite well here.

I have a few discs I use to audition systems... content I know extremely well. If I notice bass notes are missing, (notes I know should be there because I know the content so well), I know the system has some nulls that are making those notes inaudible.

Elimination of nulls actually makes the bass seem louder and more powerful. That's because you get to hear ALL the bass, including the sounds that would have been cancelled by the nulls. In addition, dual, smaller subs will experience 3 to 6 dB of increased headroom, so the max SPL output could be very similar to the larger sub. The only thing the smaller subs give up is some deep LF extension, which is a worthwhile trade-off to get flat FR.

Flat, full bandwidth frequency response is the ultimate goal. The only way to achieve that in the bass is to use multiple displaced subs optimized for flat response.

Dr. Floyd Toole writes:

Quote:
The real problem is standing waves, which cause bass to boom at certain frequencies, to be absent at others, and to be different in different locations in the room. Equalizing a single subwoofer can improve the sound at the microphone location, but nowhere else. A single subwoofer has no ability to reduce seat-to-seat variations or remove peaks and nulls. Multiple subwoofers can do both, presenting an opportunity to attenuate resonances, alleviating the associated pesky peaks and nulls in the standing waves. Chapter 8, p. 215 describes the options for reducing the detrimental effects of room resonances on bass. Some solutions work only in rectangular rooms, reducing the number of active resonances, and creating areas of rooms within which seat-to-seat variations are reduced. In the most advanced solutions, the resonances and seat-to-seat variations are essentially absent. All of the most effective solutions involve multiple subwoofers and these are well explained in Chapter 8.
https://routledgetextbooks.com/textb...me-theatre.php Part 2, Subwoofer Options His book has a lot more information.

Bottom line, if the budget is fixed and no more will ever be spent on subs, then dual, smaller subs will generally sound better than a single, larger sub. OTOH, if the ability exists to buy a second sub down the road, then getting the single larger sub first is a good option with goal being to buy a second, (third and fourth+) down the road.

Here's another paper that explains the benefits of multiple subs:
https://www.harman.com/sites/default...multsubs_0.pdf

If that's not enough, here's another:
https://mehlau.net/audio/multisub_geddes/

Here's an example of what I' describing. The first 2 graphs are the subs in different locations. The first sub is located on the front wall between the CC and RF speakers. It has a wide deep null from about 40 to about 63 Hz.



The second sub is in the rear, right side wall at about 2/3 of the side wall dimension. It has a big null from 25 to 35 Hz.



If you look closely you'll see that were one sub has a null, the other does not. Therefore, they fill in for each other. The following graph is the combined response of the two subs:



The combined response has NO nulls and only a couple of smaller peaks, (Ignore the response above 80 Hz. That is the response of the CC. It is consistent in all 3 graphs and is immaterial to my point.)

The next graph is the subwoofer alone, but with Audyssey Room correction applied.




When a room correction system doesn't have to deal with nulls, and it only has to pull down a few peaks, it can do a great job of providing flat, smooth bass. The sound of flat, smooth bass is full, articulate and powerful.


Craig

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post #13 of 34 Old 09-11-2019, 11:29 PM
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Originally Posted by Dave Ol View Post
.... always buy the biggest and best single sub you can afford (unless of course you can afford two of them right off the bat)
So if someone can afford to buy two of them off the bat, should they buy those.... or pause.... think for a moment..... and wonder why not buy a single subwoofer that costs as much as those two subs that was just about to be purchased?
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post #14 of 34 Old 09-12-2019, 05:44 AM
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Originally Posted by craig john View Post
Bottom line, if the budget is fixed and no more will ever be spent on subs, then dual, smaller subs will generally sound better than a single, larger sub. OTOH, if the ability exists to buy a second sub down the road, then getting the single larger sub first is a good option with goal being to buy a second, (third and fourth+) down the road.
I'm not saying you are wrong or that multiple subwoofers are a bad idea. In rectangular sealed rooms, they are almost a necessity to get a flat response.

The point I was making is that in a lot of cases, the differences in frequency response that show up clearly in a graph are usually not noticeable during actual use. However, the difference between 100db and 110db is very noticeable. In addition, there are many rooms that don't require multiple subs to achieve a flat frequency response. I have one such room and went from 2 smaller subs to 1 large sub and have much better results.

The advice people give to buy the single most powerful sub you can afford today with the hopes of adding a second down the road is a good plan.
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post #15 of 34 Old 09-12-2019, 05:58 AM
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room size has lot to do about this. my office, one 12 inch sealed sub is more than enough and since its my office Im always sitting at my desk. my living room its much, much more complicated. I need 4 huge subs...but who wants to look at 4 huge subs in your family living space...or who has the space... dedicated spaces usually anything goes. if just starting off and can get away with it, get one huge 18in plus sub and put it behind your chair.

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Lots of good advice from more knowledgeable people than I, but here is my two cents:

While the real answer is two large subs , I would go with one large sub vs. two smaller subs. My reasoning is dual subs give you ~ +3db over a single sub. The larger sub will likely be louder and play deeper than a smaller sub, and even after adding a second smaller sub, should still play deeper.

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post #17 of 34 Old 09-12-2019, 07:12 AM
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Quote:
Originally Posted by tojo_m View Post
So if someone can afford to buy two of them off the bat, should they buy those.... or pause.... think for a moment..... and wonder why not buy a single subwoofer that costs as much as those two subs that was just about to be purchased?

Great point. I guess a lot of this would depend on the room response and how sure you are that the sub you are picking is right for you. If it were me, I would go after the one, test it out in my room to make sure I like it before proceeding to a second one.
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post #18 of 34 Old 09-12-2019, 10:15 AM
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Lots of good advice from more knowledgeable people than I, but here is my two cents:

While the real answer is two large subs , I would go with one large sub vs. two smaller subs. My reasoning is dual subs give you ~ +3db over a single sub. The larger sub will likely be louder and play deeper than a smaller sub, and even after adding a second smaller sub, should still play deeper.
When one adds a second identical *driver* to a system, one adds 3 dB of SPL acoustic power. When one *doubles the amplifier power*, one adds 3 dB of SPL acoustic power. When one adds a second, identical subwoofer, one adds a second driver and doubles the amplifier power, which adds 6 dB of SPL acoustic power being driven into the room.

What is achieved in-room will depend on the room and placement. If the 2 identical subs are co-located, (placed immediately next to each other, or stacked one on top the other), the full 6 dB is realized. This is because the bass wavelengths are so long that the two subs "couple" and their waves propagate as one wave. If high SPL is the goal, one can achieve 6 dB of increased output just by using two subs and co-locating them. This is fine if there is only one listening position and it *by chance* happens to have fairly good FR with one sub. I have rarely found that to be the case. EQ can help, but as I previously explained, EQ can't fill in nulls.

However, extra SPL is not the only goal when using dual subs. The other, and far more important goal, (in my opinion and in the knowledge base of some of the most knowledgeable people in the world on this subject), is to smooth out the frequency response and make it more consistent over a larger listening AREA. When the two subs are distributed around the room, they can do what I showed with the graphs I previously posted.

Lets take a look at the subs @sunvsmoon is considering:

https://www.bkelec.com/HiFi/Sub_Woof...th-FF_Plus.htm
https://www.bkelec.com/HiFi/Sub_Woof...2300SB-PR.html

Looking at the spec's, they're both 12" drivers, with one being a PR design and the other using a large flared port. They're both spec'd to an F3 of 20 Hz. One uses a 300 watt amp, the other uses a 500 watt amp. (Please keep in mind that one needs to double the amp power to get a 3dB increase in SPL output, so going from 300 to 500 watts won't even provide 3 dB of increased output, (all else being equal which is not the case here, obviously.) The cabinet sizes are quite a bit different at 50 litres for the smaller one and 95 litres for the larger one.

Still, duals of the smaller subs in this case should provide equal to or slightly MORE total output and just as deep extension, (20 Hz) as a single of the larger sub. More importantly, they'll provide the opportunity for much smoother and more consistent bass response than a single.

This is a no-brainer... dual BKE P12-300SB-PR's is definitely the way to go. Place one in the front and one in the rear, gain-match them, set appropriate Distance/Delay settings, EQ them appropriately, and the final result will be virtually identical SPL capability and extension, with much better FR across more seats.

Of course, if there is the possibility of adding a second Monolith down the road, then starting with one of those is a great idea. Just be prepared to have less than ideal FR until the 2nd sub is added.

Craig


Edit:


Quote:
Originally Posted by sunvsmoon View Post
I'm after a sub which can handle small clear define details at low to medium volume, not bothered about it being boomy.would the monolith be able to do this or would i be better off with a p12 300sb?
The OP is not looking for massive output. He's looking for high sound quality. Dual smaller subs, and the smoother and more consistent FR they can provide, will do a MUCH better job for him than a single larger sub.
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post #19 of 34 Old 09-12-2019, 04:17 PM - Thread Starter
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Thank you for all the detailed replies. I ended up going for a single monolith plus for the time being but will eventually get another one in the next few months when we move house. I think this is the best way forward and now after reading all the comments realise how beneficial running two subs will be.

I should receive my sub tomorrow, is there anything special i need to set on first use or do i just run audyssey and let it configure the sub?
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I wouldnt run audyssey right away so you know what it sounds like before throwing eq/dsp at it. if you use rew, its good to have a baseline

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post #21 of 34 Old 09-12-2019, 07:22 PM
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Quote:
Originally Posted by sunvsmoon View Post
Thank you for all the detailed replies. I ended up going for a single monolith plus for the time being but will eventually get another one in the next few months when we move house. I think this is the best way forward and now after reading all the comments realise how beneficial running two subs will be.

I should receive my sub tomorrow, is there anything special i need to set on first use or do i just run audyssey and let it configure the sub?
Get a mic, download the free Room EQ Wizard software and start measuring your response. You'll be astonished at what you find... and you'll soon realize why 2 subs are (almost) always better than 1.

Lombardi said it:
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post #22 of 34 Old 09-12-2019, 09:33 PM
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Quote:
Originally Posted by craig john View Post
Quote:
Originally Posted by sunvsmoon View Post
Thank you for all the detailed replies. I ended up going for a single monolith plus for the time being but will eventually get another one in the next few months when we move house. I think this is the best way forward and now after reading all the comments realise how beneficial running two subs will be.

I should receive my sub tomorrow, is there anything special i need to set on first use or do i just run audyssey and let it configure the sub?
Get a mic, download the free Room EQ Wizard software and start measuring your response. You'll be astonished at what you find... and you'll soon realize why 2 subs are (almost) always better than 1.
If we are only concerned about a single seating position(let’s say the others don’t care about sound quality), then how strong is the argument for duals vs single? Can’t EQing help get a flat response in just a single seating spot with a single sub?

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post #23 of 34 Old 09-13-2019, 04:12 AM
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Originally Posted by tojo_m View Post
If we are only concerned about a single seating position(let’s say the others don’t care about sound quality), then how strong is the argument for duals vs single? Can’t EQing help get a flat response in just a single seating spot with a single sub?
If you don't care about nulls, and the fact that you'll be missing some content if you have nulls, then a single sub EQ'd to pull down the peaks should be fine. OTOH... please read my posts above.


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post #24 of 34 Old 09-13-2019, 08:26 AM
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If the 2 identical subs are co-located, (placed immediately next to each other, or stacked one on top the other), the full 6 dB is realized.
I see 6db often mentioned, but I either didn't realize or appreciate that the subs would have to be co-located. Is there a general guideline for the additional output if not co-located?

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Here's an example of what I' describing. The first 2 graphs are the subs in different locations. The first sub is located on the front wall between the CC and RF speakers. It has a wide deep null from about 40 to about 63 Hz.

The second sub is in the rear, right side wall at about 2/3 of the side wall dimension. It has a big null from 25 to 35 Hz.

The combined response has NO nulls and only a couple of smaller peaks, (Ignore the response above 80 Hz. That is the response of the CC. It is consistent in all 3 graphs and is immaterial to my point.)
Of course it's room-dependent, but does one typically get much of a smoothing benefit from placing subs on the same wall, some distance apart. Say, on the front wall next to the front left and right speakers?
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post #25 of 34 Old 09-13-2019, 02:51 PM
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I see 6db often mentioned, but I either didn't realize or appreciate that the subs would have to be co-located. Is there a general guideline for the additional output if not co-located?

Of course it's room-dependent, but does one typically get much of a smoothing benefit from placing subs on the same wall, some distance apart. Say, on the front wall next to the front left and right speakers?
Great questions! The answer to both questions is basically the same. This is all about "mutual coupling" of drivers. The general rule for two drivers playing simultaneously to "couple" at a given frequency and result in a 6dB level increase at that frequency is that their cone centers need to be within a 1/4 wavelength of each other. At 80Hz, 1/4 wavelength is about 3 1/2', (1130/80/4). So to couple at 80 Hz, the subs would need to be within 3 1/2' of each other. If they're further apart than that, their wavefronts will propagate separately and there will be two distinct waves that can work synergistically to smooth the FR.

However, as bass frequencies go lower, wavelengths get longer. At 20 Hz, 1/4 wavelength is 14 1/8'. Subs that are 14 1/8' apart will couple at 20 Hz. If the subs are further apart than 14 1/8', their wavefronts will propagate separately and they can work synergistically to smooth the response. In plain English, the bottom line is that the further the subs are apart, the better chance for FR smoothing to lower frequencies. If FR smoothing is the goal, placing the subs as far apart as possible will provide the highest probability for FR smoothing. This is why the Welti paper recommends one sub in front and the other sub in the rear. Alternatively, opposite corners will work quite well.

Once they are separated, there is no hard and fast rule about how much additional SPL or system headroom the 2 subs will provide. At that point, it will depend completely on room acoustics and how the 2 individual responses combine. You could get ZERO, (not likely), or you could get 6 dB or more. It just depends on the distribution of the room modes and how the subs are placed within the room and those modes If the 2 subs raise all the nulls, and still have multiple large peaks, you could actually end up with more than 6 dB, (but not likely.)

I hope that makes it slightly clearer than mud!

Craig
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Last edited by craig john; 09-13-2019 at 02:54 PM.
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post #26 of 34 Old 09-13-2019, 05:37 PM
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Quote:
Originally Posted by craig john View Post
Quote:
Originally Posted by Qwerty123 View Post
I see 6db often mentioned, but I either didn't realize or appreciate that the subs would have to be co-located. Is there a general guideline for the additional output if not co-located?

Of course it's room-dependent, but does one typically get much of a smoothing benefit from placing subs on the same wall, some distance apart. Say, on the front wall next to the front left and right speakers?
Great questions! The answer to both questions is basically the same. This is all about "mutual coupling" of drivers. The general rule for two drivers playing simultaneously to "couple" at a given frequency and result in a 6dB level increase at that frequency is that their cone centers need to be within a 1/4 wavelength of each other. At 80Hz, 1/4 wavelength is about 3 1/2', (1130/80/4). So to couple at 80 Hz, the subs would need to be within 3 1/2' of each other. If they're further apart than that, their wavefronts will propagate separately and there will be two distinct waves that can work synergistically to smooth the FR.

However, as bass frequencies go lower, wavelengths get longer. At 20 Hz, 1/4 wavelength is 14 1/8'. Subs that are 14 1/8' apart will couple at 20 Hz. If the subs are further apart than 14 1/8', their wavefronts will propagate separately and they can work synergistically to smooth the response. In plain English, [IMG class=inlineimg]/forum/images/smilies/wink.gif[/IMG] the bottom line is that the further the subs are apart, the better chance for FR smoothing to lower frequencies. If FR smoothing is the goal, placing the subs as far apart as possible will provide the highest probability for FR smoothing. This is why the Welti paper recommends one sub in front and the other sub in the rear. Alternatively, opposite corners will work quite well.

Once they are separated, there is no hard and fast rule about how much additional SPL or system headroom the 2 subs will provide. At that point, it will depend completely on room acoustics and how the 2 individual responses combine. You could get ZERO, (not likely), or you could get 6 dB or more. It just depends on the distribution of the room modes and how the subs are placed within the room and those modes If the 2 subs raise all the nulls, and still have multiple large peaks, you could actually end up with more than 6 dB, (but not likely.)

I hope that makes it slightly clearer than mud! [IMG class=inlineimg]/forum/images/smilies/biggrin.gif[/IMG]

Craig
Wow! Very succinctly explained. Thank you!

------------------
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post #27 of 34 Old 09-13-2019, 11:57 PM
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Wow! Very succinctly explained. Thank you!
I live in Chandler, too! 😌😁

😎It's just life, dude. We are all gonna die sometime--Might as well try and have a kickass time while we're still here.😜
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post #28 of 34 Old 09-14-2019, 03:27 AM
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I live in Chandler, too! 😌😁
So do my kids and grandkids, (at least one set of them.)

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post #29 of 34 Old 09-14-2019, 03:43 AM
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Learned a lot from Craig. Thanks Craig.

Do it all or don't do it at all.
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post #30 of 34 Old 09-14-2019, 04:10 AM
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@sunvsmoon , did you get your sub? Did you download REW and use the room simulator to help you locate a good spot? Bet soo you will thin about another. I started with 1, then a few months later got a 2nd. A year later got a 3rd, and now I continue working on a BOSS! It never ends, but it sure is fun.
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