Axiom Home Page Forums General Discussion Technical Questions Driver/port orientation-is it supposed to matter?

I have my forward-firing/rear-ported sub sitting directly to the left of my couch and up against a wall. It sits about a third of the way to the front of the room.

Does it matter which way the driver/port faces? Is having the driver face you optimal?

If I fire my sub directly into my couch, I'll have about 5in of clearance to the wall for the port and 2in clearance for the driver to the couch. Is that sufficent breathing room?

I ask only because I see a wide variety of subwoofer designs so it makes the answers to my questions less clear. I'm thinking that driver direction and clearance make a big difference, but there are downward firing subs with not much clearance (between driver and the ground), and the drivers are obviously meant to be fired into the ground. Some of these have phase controls. Why?

For the vast majority of foward firing drivers, I see them oriented with the drivers toward the listeners. Is this because of extensive listening tests, or convention? What does that say about downward firing subs?

If you throw a pebble in a pond, what happens to the ripples? Ok, that is just and example, but it is similar with how the sub frequencies leave the sub. If your system is calibrated correctly, frequencies below around 80hz and below are non-directional, meaning you can't determine where they are coming from....also, a subs frequencies are verrrrry long.

Basically, if there is any difference, it will most likely be non audible to the user.

So interactions of the low frequencies with the environment necessitates the need to alter the phase, and is not necessarily dependent on which way the driver faces relative to the mains?

I guess my experience with my setup is confusing me even more. There is no change sonically if I have my sub positioned so that the driver is firing parallel with my wall (driver facing forward or backward). Even if I shoe horn it into the space so it fires into my couch (perpendicular with the wall) the way the driver faces makes little difference.

BUT, if I rotate the enclosure from any of these positions by 20 degrees or more, in any direction, I need to turn down the trim on my sub by about 2-3db or so.

Guess my placement is not optimal...or I just need another sub to help out.

It can matter which way the drive/port faces both in relation to you and the walls.

If the sub is facing you and very close to your seating, w/o anything blocking it, you may be able to feel the air moving as the sub operates. I found this so distracting I moved the sub behind my futon in my apartment because I couldn’t get it far enough away when in front of my seating.

With your sub near a wall which way the driver faces can have an impact on what room resonances are energized by it. In my experience simply turning the sub 90 degrees when up near the wall has a big impact on It’s frequency response. This in turn will have an impact on how the sub sounds across your entire seating. With the sub out more in the room which way the driver faces should have little impact on how it performs.



I’ve read that as a general rule you should try to keep the port away from the wall by a distance equal to it’s diameter.

Having your sub 2in from the couch is going to effect how it performs. Some acoustical energy is going to absorb right into your couch before it can radiate around the room. So you’re likely going to trade some of the chest pounding feeling for more of a butt shaking feeling. It may cause butt shaking even at higher bass notes which might not feel right.

Cheers,
Dean

Putting the driver too close to a wall can affect the sound, but I do not remember what the recommended distance is. I seem to remember that for down firing subs the suggested distance from the driver to the base plate is 3" or greater.

Thanks guys! Looking over some stuff on the net I get anywhere from 'a few inches' (about 3 in the case of Hsu subs) to 'twice the port diameter' to ranges of 4 - 36 inches.

I guess that is one of the great journeys of home theater/stereo - finding a good place and position for your sub(s)!

If the sub is close to the wall or corner, you will get reinforcement of the signal which can increase your dB readings at certain frequencies. A corner placement while seeming to give you more boom, may not always be the best spot as it will excite all the nodes at all frequencies. The best solution to get a flat response is having multiple subs spread out around the room.

In sub design, if you put the inside opening of a port closer than one port diameter to the nearest wall of the sub, you change the tuning of the sub by changing the port length. I believe what happens is that the air between the port and the wall couples with the air in the port so it acts as part of the port.

I guess it is similar if you put the driver too close to the wall. I believe coupling means that the air moves the same as the driver, in essence becoming part of the driver. Adding mass to the driver changes the drivers parameters and thus its response.

Either way, the distance at which this happens is inches not feet. I would just try the sub in a couple of different orientations and distances to see if you can really hear anything.

I think most sub manufacturers would like that also.

Yep, and once you do it, you will experience the benefits from all seating locations.