Subwoofer FAQ’s, answered

Q. What Sub should I buy for music and/or home theatre?

A     There is no single answer to this question.
First of all, you must decide if your main interest is in music or home theater or both. Your budget is the next important factor and then follows the size of your room. Lastly but sometimes very important is the aesthetics factor or the so called “WAF” factor (Wife acceptance factor)

The simple key to a good sub is: the bigger the driver the better and the quality go hand in hand with the weight of the sub.  The basic physics of bass sound is to move air at low frequencies. The more air you want to move (for good bass) the bigger the driver you need. To design a good small sub is a very challenging engineering job and a hot topic nowadays. Velodyne are the most famous for their small subs but they are generally very expensive. Luckily the new kid on the block, M.J. Acoustics, have now changed that, they are super value for money.

NOTE: In choosing a sub for music and/or home theater there are a few things to keep in mind.
For home theater (HT), quality is not that important but quantity is. Home theater is just dialog, effects and lots of “distortion” in the lower frequencies. That is why a big sub woofer is best here. Bass reflex type what their power output advantage over a sealed enclosure sub is the answer if you are a movie fanatic.
In fact the main problem of most, if not all, of that “all in one” systems below the $1500 mark is that their  bass unit is a passive unit with a too small driver, less than 8” which can physically not give enough impact in the bass.  The size of the sub woofer you need is determined by the size of the room and your preferred listing level. In general a bigger room (more than 25 sqm) needs a bigger sub (10” driver and at least a 100w amp) and this is also true for higher listing levels.  An active sub with a 100w rms built-in amp and an 8’’ driver is my minimum recommendation. Small passive subs are definitely out.
For music, a big sub is not needed in fact a well designed small sub with accurate bass is much more important. Bass reproduction for music is very important and most of the times this influence the buyer the most (turn the bass control on your amp completely down and listen how the scale of the music disappears). However “correct” bass is much more important than “lots” of bass. To define correct bass is very difficult and this is also the most difficult to get right in designing a speaker. More bass is also not always the answer. It can tire you out very quickly, especially when it drones. Quality bass is much more important, that is the bass must be tight, well defined and must have bass weight. This is much more enjoyable in the long run. The best music subs are from the sealed enclosure type (not bass reflex). Sealed subs generally go lower and have less distortion than bass reflex subs. Also a subwoofer is important to add fullness to the sound when a lower listing level is preferred to compensate for the human’s ear’s naturally lack of detecting bass at low volumes.

Basically you get 3 types of subs:
1: Using a 5″ or 6″ bass driver inside a box and the bass comes out of a port. Remember when you were a kid you talked into a tube to lower your voice. Well that is the same principle used here. This type is used by the mass market “all in one sub/sat sets” from Sony, Panasonic, Pioneer, JVC, Bose etc. because it’s cheap to make, you only need cheap small drivers that do not need to move a lot of air to fake “bass” sounds. They are the worst sounding subs with a “hollow, drooney, tube like” bass sound. Also, by hiding the driver inside the cabinet they can get away with low cost drivers made of poor quality materials.

2: A much better why is to use a proper 10″,12″ or 15”driver and let it fires into free air and to increase bass “volume” a bass port is also used (bass reflex). However you introduces distortion, typically 10% to 20%. That is OK for Home theater but not ideal for music.

3: The best subs use a 10″, 12″ or 15” driver in a SEALED enclosure to minimize distortion to about 1% (you sacrifice volume a bit). This is an ideal sub for both music and Home theatre. This is expensive to make because the sub’s amp needs to be at least 3 x bigger to move the driver against the trapped air inside the sealed box.

The industry’s real subs from PARADIGM, JAMO and VELODYNE use this last concept at huge cost but now MJ ACOUSTICS has come up with a range of affordable subs using the same concept. For the first time any enthusiast can now afford to better his speakers sound by adding one of these subs without breaking the bank. Also it will keep your other half happy it’s small and beautifully finished in real wood. There are two other important factors that I like about MJ ACOUSTICS subs:
•    Down firing driver:  thus making use of nature’s gravitational force to help pull the driver down on the start and dampened the back movement, ideal for a fast tight bass with out overhang. It also remove the problem to turn  your big driver (on front firing subs) every year at 180 degrees to compensate for the dragging stressing  force on the driver’s rubber surround and voice coil.  Its also fires at right angles to the main speakers drivers making correct phasing and placement in the room less critical.

•    Remote control on some models to control all the main settings on the sub. Note not all CD’s and DVD’s are recorded equal…it depends on the likes of the recording engineer…his personal choice…with a remote you can have your own choice as well…once you used it,  you can never be without it.

Q. What is the best sub for my room?

A.      To answer that question requires some background information. You may have noticed similar specifications for the less expensive subs. There is very little in the specifications to justify the cost difference. More than any other performance parameter, what you are buying as you move up in the sub line is power and size and thus more bass volume for HT and bass resolution for music. Unlike video, there are no specifications in subs for resolution. You can hear it, but it is not easily defined. Also remember, bass reproduction is heavily dependent on your room acoustics like soft furnishes or hard furnishes. Soft furnishes and soft carpets absorb a lot of bass whereas hard furnishes and wooden floors reflect bass and can make the bass booming and droning. Also you have to think of the problem in terms of the size of the sub. Even in a small room a bigger sub would sound better, you just have to turn it down slightly, the less volume the better. Fortunately, bass can be eliminated easier than it can be produced. The best solution is to go for a very well designed sub of type 3.

Q. How much power must my sub deliver?

A.     The more the better but that also pushes up the cost.  Individual listening levels vary so greatly that a definitive answer is impossible. At least 100w (RMS) is the norm but this is not always a clear cut because it depends on how thick (strong) the driver’s rubber surrounds are, some needs about 1000 watts just to start moving them. Also remember that subwoofers that move a lot of air and are impressive in a home theater demonstration are usually sloppy and become tiresome during extended music listening. If you are impressed with a home theater demo of a sub, wait a bit. The best subwoofers don’t call attention to themselves but provide the most enjoyment over the long haul.

A FEW TIPS
Hooking up your sub:
There are a few things to remember when hooking up your sub and speakers. Never switch on your amp until everything is finally hooked up. Never unplug or plug in any thing with your amp on, always switch it off first. The amp goes through a protection phase when switched on and will only switch the speaker on after everything is found to be safe. When changing things after this, there is no way the amp can tell if something is wrong or not. There are two ways to connect a sub: 1 by connecting your pre amp output (or “sub out” on your HT receiver) to the low level (line level) input on your sub via a coaxial RCA cable. This is the best way for HT. 2 By connecting your speaker terminals to the high level input (speaker terminals) on the sub via normal speaker wire or best via a NEUTRIK connector like MJ ACOUSTICS subs. This is the best for music because your sub then sees the same signal as your speakers and will work then together with your speakers to enhance the bass.

Sub Placement:
Sub placement in your room is critical, especially for good bass reproduction. To understand the basics of sub placement, it’s important to remember that the lower the frequency, the less directional the sound becomes, until you get to the point where the sound is Omni directional (the point at which the wavelength is longer than the distance between your ears – usually below 120 Hz). In theory the subwoofer can be placed anywhere in the room but for optimal music reproduction the sub should be close to the middle of the front speakers. That is in most cases not practical because your equipment rack is in the way…so start off in the next best location, the front corner of the room.  As the sub gets closer to the walls, the bass will reflect off the walls and can be
reenforced, this tends to give a “stronger” bass (more volume) but the bass become more boomier (“sloppier”) or less controlled also known as less defined. As the sub moves further away from the wall, the bass will “tighten” although this will diminish its bass volume. The secret is to move the box in and out from the wall until the best compromise is achieved. In general also place the sub at a slightly larger distance from the back wall than from the side wall…we talking a few inches here.

Subwoofer settings:
It’s a difficult process trying to get a subwoofer to integrate with the main speakers especially when it comes to music reproduction. Trial and error is the best way to tackle this problem. A sub with remote control on all its setup functions is a great help here (like M.J. ACOUSTICS). Most surround sound receivers give the option of sending the bass information to the main speakers or the subwoofer or both. I’ve found that, if your main speaker is a floor standing speaker then the best result and least distortion is when the setting is on “both” thus sending the bass signal to both the sub and the front speakers.  As a rule of thumb for the initial set up, place the phase switch (if available) at zero, the volume level to around 50% and the crossover to around 20% off the lowest setting.  Tweak the settings from there, until it sounds good to your ears, bass tightness is far more important than bass volume.
Tweaking will be different for each room and each placement position.  A note on my personal preference is to have my Sub’s roll off freq much lower for music than for movies typically at 9 o’clock for music and 3 o’clock for movies. The fact is that there are much more info on movie tracks in the range 60Hz to 150 Hz than below 60 Hz contrary to the general believe and music has a lot of information below 60hz. A remote control with different storing settings is a great advantage here, like some MJ ACOUSTICS subs.

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