One large sub or two small ones?

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.

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.

Craig

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.

chucks0 said:

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.

Click to expand...

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:

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.

Click to expand...

https://routledgetextbooks.com/textbooks/9781138921368/home-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/files/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

Mocs123 said:

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.

Click to expand...

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_Woofers/monolith-FF_Plus.htm
https://www.bkelec.com/HiFi/Sub_Woofers/P12300SB-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:

sunvsmoon said:

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?

Click to expand...

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.