Downfiring Subwoofer Placement?

I have a Yamaha downfiring sub.Because it's downfiring and pumps out the bass in all directions should it be placed away from a wall closer to the center of the room?Thanks.

 

Some subs are "voivced" so that they should be placed in a corner. Your best bet is to follow the placement recommendation in the user's manual. If the user's manual doesn't have a recommendation, you'll have to go by trial and error. The sub's output will be reinforced by the walls if you put it in a corner.

 

Try it in a spot along a golden rectangle proportion from a corner. The Cardas site recommends this for speaker placement, so it should work for subs too. Have the ratios of distance from the two adjoining walls be 1 to 1.618. Anywhere along that diagonal is a golden rectangle from the corner, then you can place it closer to or farther from the corner as you like as long as it's along that diagonal.

 

My antique RH Labs subwoofer is also downfiring, and I like putting it between the speakers, and having the center of the voice coil of the sub line up an inch or two behind the drivers of my speakers. The bass tends to act as a "center fill" that way to the bass from the speakers.

Worth a try for a few songs....

 

No (well, maybe, but not because it's downfiring).

In a perfect room (no peaks or dips in the frequency response in the subwoofer's bandwidth), you should be able to measure from any physical side of the subwoofer and get exactly the same response. You should also be able to orient the subwoofer in any direction and measure the same output.

The problem is (even if the subwoofer is perfect) we listen to music in imperfect rooms. Even bass notes reflect, since sounds of all frequencies have a wavefront (the first compression of the air in the direction of your ears, followed by subsequent compression/rarefractions of the air), and this wavefront travels at the speed of sound. Unfortunately, higher frequencies are more-easily reflected by common building materials than lower frequencies (a few feet of concrete is just about the only thing that readily reflects bass frequencies).

Still, floor, ceiling, and wall reflections combine to increase subwoofer output in most rooms, and more of these reflections means more modes are excited, often leading to flatter frequency response. When you move a downfiring subwoofer out from walls, (keeping the floor in the equation), you are lowering its output (and decreasing its headroom) and probably changing its frequency response by changing the modes that it excites.

Pre-determining where a subwoofer should go, using some byzantine mathematical formula or between-R&L doctrine, nearly always results in imperfect placement because it does not take into account the most important part of subwoofer design - the room into which it will be placed.

Yes, subwoofer placement is a big subject. Yes, experimentation (and measurement) is the key.

 

Bass notes are non-directional so subs should be the least sensitive to placement, although some are designed for corners and such.

 

This is true in a reflection free zone, however after the first reflections in the room start to interfere with the constant sound of the perfect subwoofer, peaks and dips occur as a result of alternative reinforcement and cancellation of certain frequencies with wavelengths related to the rooms dimensions and your chosen placement. Some of the peaks can be enormous. You just have to experiment with your room's responses to find the best placement.

Cardas recommendations are an excellent starting point.

 

The only sure-fire way to correctly place a sub is to do a frequency sweep (test patterns on various audio cds). Using a Radioshack SPL meter, note the level at each different frequency. What you'll notice is that certain frequencies are non-existent and others are abnormally loud. If you graph it out, you'll see where your problem areas are.

Start with the sub in a corner as this has the best potential to have the most room modes excited. It will also have some serious drop outs. Do your frequency sweep and determine whether this is what you can live with. (That will depend on what type of music you listen to.) If you don't like what you see, move the sub to a mid-wall location and repeat the sweep. If the result is more to your liking, then you are on to something. Repeat the move/measure process as many times as necessary to find the 'best' general location for the sub.

Now it is time to fine tune. Moving the sub even a few inches can have a great impact on the frequency curve at the listening position. Keep at it until you have the flattest response possible. Please also keep in mind that a perfectly flat response in-room is nearly impossible. You simply have to choose what you can live with.

The process is painstaking and time-consuming, but it is ultimately worth it. FWIW, the ultimate placement of the sub-woofer, based on this technique, will invariable result in the lowest possible placement for WAF.

David