[Ultralight]

Curious.

If you were setting two subs up in a room, where is the default starting position would you put the two subs?  Two corners? Right beside the speakers?  Behind? More towards the center of the room?

And secondly, has anyone ever LIFTED a sub off the ground?  I put mine on top of a 18" concrete block just for kicks and it sounded faster/cleaner/less tubby.  The bass extension was still there, but it sounded more musical.

Thanks,
UL

[Phil A]

Depends on the room and the design of the subs (forward, downward firing, etc.) and your goals (use of the subs).  Many may work in opposite corners.  If the sub is designed to be on the ground, then that's where it should be.  In an old place where I had thick carpet, I put a ceramic tile under the (downward firing) subs to make the bass faster, cleaner and less tubby.  What type of subs do you have?

[JLM]

Recommend reading Floyd E. Toole's "Sound Reproduction".

He explains that in a small (residential sized) room, lower frequencies (below roughly 140 Hz) act in waves.  Now think of a bathtub with 4 inches of water and moving your hand back and forth (like a woofer) along the length of the tub.  The created waves move to the end and bounce back.  As one wave meets another it adds (doubles the peak), subtracts (neutralizes), or just plain messes both up.  In audio terms the frequency response would be by up to +/- 20 dB.  So Toole recommends subs at opposite ends of the room (if you only using 2).  He also tested one on the floor and another higher up.  Keep in mind that bass sound waves are big (1120 feet/second divided by the involved frequency) so a 28 Hz sound wave is 40 feet long.

There was a special subwoofer from Spatial Computer called "Black Hole" (6 moons reviewed it, not sure it's still available, $1295).  It had a microphone that sensed bass and directed the sub to generate the opposite signal to help even out the room response.

[SteveRB]

Individual Parametric EQ controls can help tune each sub to tame peaks and smooth overall response. You need a basic mic and testing software or you can really make of mess of things.

Is this for stereo music or home theatre?

[Ultralight]

You guys (all three of you) are just amazing.  Ask a question, and boom! three responses in short order.

THANKS!!

To reply:

1. This is for 2 channel music. 

2. Subs are dual opposing 8 inch sealed cabinet so it is a dipole. 

The possibilities in placement is pretty vast in addition to location.  After figuring out location, there are still:

a. Direction of the dipole.  Side to side, front to back, angled?   This one is a curious one to me. 
b. Height off the ground. I find that the sub is 'cleaner' when lifted off the ground.

Thanks!

UL

[Phil A]

For setting up system, I use a one third octave RTA (also have one built in the iPhone with the Parts Express microphone as the microphone in the iPhone is not good for that purpose but have not had time to play with it).  My subs in the main and two back-up systems are Rels (all old ones) so they have a separate hi level input, crossover and volume control.  I have two Rel Storm IIIs in the main system (one of them gets used for home theater along with a Dayton Audio Titanic Mark III), a Rel Strata III on one back-up system that is just for music and a Rel Q150 in another that gets used both for music and home theater.  Rives Audio has some resources and sells (or used to) a $21 test disc that is made to use with the old Radio Shack analog SPL meter that compensates for the microphone deficiencies.

[Phil A]

Just read that Rives Audio closed January 2, 2015.

[milford3]

To lift my two subs off the floor I use IsoAcoustics.

http://www.isoacoustics.com/index.php

[werd]

Subs on the ground in forward position close to the speakers is a failed concept imo. I have never been able to make a sub work properly when on the ground in the vicinity of the main speakers.  They always sounded boomy even in the best position. Get the sub up, higher than the lowest driver on your mains and the sub will integrate with low frequency resolution. Basically get the sub to walk with the mains. It is better.

Subs used to provide room ambience can be used on the ground behind the listener.  Behind on the ground loads the room and allows me to get a sense of the room size in both lenght and width. This helps wih PRAT immensely. 

My strategy is forward subs are to be lifted for resolution and rear subs on the floor for PRAT. That is how I use my 2 Nola subs.

[JLM]

Depending on your speakers, you may already have 2 deep bass sources, in which case the other two (subs) should be in opposite corners.  One suggestion is to locate one 12 inches from the corner, one 19 inches from the corner, one 31 inches from the corner, and one 51 inches from the corner (to stagger them 1.6 times the distance from the next).  And yes, one up high (and one out of phase with the rest) might be helpful.  Experiment.  In your room with your gear you are you're own best expert.

[werd]

The thing forgotten with low freq. extension using any driver (sub or mains) is the beaming low frequency signal. Bass drivers will beam. If they didn't there would be nothing but muddled-bass in the sweet spot. Putting subs on the floor even in the best position loses that beaming quality. You want subs to beam in the sweet spot. Your sub won't beam if it is on the floor.  The closer to the floor the more it loses the beam quality and turns on the omni bass directional bass features of the sub. This plays havoc with resolution in the sweet spot. That omni bass quality is useful but it can't be in the sweet spot because it doesn't integrate with the mains, at all ever.  So a raised sub allows for a higher Xover setting for low frequency turnoff. Start with the highest setting on the raised sub and turn back. Probably to somewhere between 100hz and 200hz setting on the sub. 

[JLM]

The thing forgotten with low freq. extension using any driver (sub or mains) is the beaming low frequency signal. Bass drivers will beam. If they didn't there would be nothing but muddled-bass in the sweet spot. Putting subs on the floor even in the best position loses that beaming quality. You want subs to beam in the sweet spot. Your sub won't beam if it is on the floor.  The closer to the floor the more it loses the beam quality and turns on the omni bass directional bass features of the sub. This plays havoc with resolution in the sweet spot. That omni bass quality is useful but it can't be in the sweet spot because it doesn't integrate with the mains, at all ever.  So a raised sub allows for a higher Xover setting for low frequency turnoff. Start with the highest setting on the raised sub and turn back. Probably to somewhere between 100hz and 200hz setting on the sub.

The term subwoofer gets overused/overextended (mostly nowadays by iPod and desktop listeners).  Note that the THX standard calls for an 80 Hz crossover to a subwoofer.  The word implies below a woofer and even small 2-way speakers intended for in-room use are typically rated down to around 70 Hz.  Below 80 Hz sound waves are at least 14 feet long, speed of sound divided by the frequency (1130 feet per second divided by 80 Hz) and are therefore omni-directional.

Speakers with single/small woofers (less than 6 inch diameter) can suffer from lack of mid-bass "body" (feel or presence) in which case something like the Hsu MBM-12 MK2 mid-bass module with a rated frequency response of 50 - 250 Hz can be beneficial.  Keep in mind that middle C is 256 Hz and lower C is 128 Hz (find a piano to hear what that sounds like - nothing like what I'd call "sub-bass").