Subwoofer Placement Some Thoughts

[misterdoggy]

I have my Subwoofer to the side as space does not permit it to be much anywhere else.

Someone who sets up Home Theaters recomended to me to put the subwoofer up on a pedestal 12 inches higher and it would sound better.

Now my initial reaction was, "why would they design a subwoofer" low on the ground then" or they could put it in a speaker case higher off the ground like 804S or something if it were to sound better.

Then part 2 was that he was a firm believer that sound should come from the direction where the image is coming from. Of course surround sound is "around" us, but it made me think again about that maybe like the center speaker where voices come from are in front of you the subwoofer might have better effect coming from the front.

I am thinking about playing with this.

[Audiophiliac]

Play with it. This will look weird, but do this: Place the subwoofer in your listening position and as close to your ear height as possible. Then put on some test tones and crawl around the room listening with your head at the level the sub would be. When you find where the tones are loudest without being too "boomy", place your sub there. This might be several spots. I would recommend having it close to the front of the room just to help with localization.

You can take this a step further by playing say a ~40-60Hz tone through your main speakers. Measuring their output level, and then finding the spot where your sub plays the same tone at approx. the same level. This can help the blending of the sub with the other speakers.

Every room is different. So yes, moving a subwoofer 12" in any direction can change its behavior. There are formulas and equations that will tell you what the sound will do, but I think its better to "get your hands (and knees) dirty" and figure it out yourself.

Another "fun" thing to do is play some tones (63, 125,350, etc) and walk around your room and find the peaks and nulls for each frequency. You may find that you can make your system sound better just by moving your speakers 6" forward or backward. Or moving your sofa a foot here or a foot there. Fun stuff.

[misterdoggy]

Audiophiliac

I wasn't talking left and right 12 inches, I was talking about raising it off the ground by 12 inches.

[Karma]

HI doggy,
Before trying to answer your question I must have a starting point. A proper explanation of a complicated subject may out of place here.

So, please let me ask if you understand what is happening to the room modes when you move the sound source? Do you understand room modes?

I'm not trying to be weird or put you on the spot. The answers to these questions may determine whether you are asking us an impossible to answer question. The alternative is to buy some books on acoustics and answer the question for yourself. Acoustics, a subject on which I am not more than an informed amateur, is certainly a facinating subject. Knowledge of it will repay your effort many times over.

If you wish, PM me.

Sparky

[misterdoggy]

Hi Sparky,

Room Modes ? Nope I am ignorant I guess.

I know that you can place the Sub at the listening postion and move around the room until you find the spot it sounds the best and thats the place for the Sub.

The Acoustics in the Room are pretty good, Carpet and drapes, and the ceiling is beamed and lots of objects all over the place ie: sofa, coffee table lots of things to bounce off.

This idea of the sub off the ground 12 inches intrigued me and wondered what the response was going to be.

By the way I sold the Pass Labs X1 for exactly what I paid for it on Audiogon to a guy in England. Although the sound was great, the user unfriendly remote control/ Preamp was overbearing. I bought a Mark Levinson 380S Preamp and its a one button touch to switch back and forth between HT and Stereo. The X1 was a nightmare and didn't work all the time

But inthe end I prefer the Mark Levinson "sound" more realistic.

[Karma]

HI doggy,
Sorry I took so long to get back to you. I have been trying to figure out how to answer your question. I don't know if I can.

Your dealer is not necessarily wrong but not right either. Sub placement is so dependent on the the room and the listening position that pat statements like his are bound to be both right and wrong depending on the situation.

Moving the sub up off the floor will have the same effect as moving the speaker horizontally except the effect is vertical and the room dimension involved is the ceiling distance. The difference will be that the high pressure points (modes) will move up but not change their spacing nor the resonant frequency. This will change the mode position in the vertical direction relative to your listening position but each mode will be just as strong as before. This may be a good thing but without doing a detailed room analysis, it's hard to tell.

Because of the difficulty of getting the sub off the floor, I would exhaust horizontal placement options first.

In my main system, my subs are tower speakers, 5 drivers per tower. They are about 5 feet high. This arrangement has the effect of spreading out the modes over the vertical distributed driver spacing making each vertical mode 1/5 as prominant compared to the equivalent single driver. This is clearly an advantage in smoothing room modes.

But with a single driver sub such as yours or my bedroom systems ASW800's, this advantage in the vertical direction does not exist. However, my ASW800's are dual, stereo subs so I do obtain a smoothing effect in the horizontal modes. But since mine are lined up along one wall, the effect is only valid in the room dimension perpendicular to that wall. The bottom line is I gain a good effect in only one out of three possible mode sets. Remember, the room is three dimensional and modes form based on all three dimensions.

What your dealer may be trying to point out is the floor to ceiling dimension can not be discounted. In this, I agree.

Of course, if the ceiling is peaked, this discussion goes out the window (drapes, please :W ).

Sparky

[caleb]

My limited knowledge leads me to beleive that placement near to a wall and particularly a corner will affect the sound from a sub much more than rasising it by 12 inches.

[jim777]

Look at the very end of this guy's webpage. He is pro in low frequency reproduction (amung other things). Well he is the main researcher for Lexicon. I think he covers room modes in a way one can understand.

http://www.std.com/~griesngr/