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« The Soundroom Project Part 5. Absorption Vs. Diffusion. | Main | The Soundroom Project Part 3. Bada Boom on da Bass. »
Tuesday
Jun 18 2013

The Soundroom Project Part 4. Subwoofers, Rear Channels, and Other Things

The second of the four systems in our sound room is a T301 5.2 system (for the uninitiated, 5 is the number of speakers (2 fronts, 1 center, 2 rears) and the 2 is the number of subwoofers, in this case I put one on the fronts and one on the rears).

My House Vs. My Office

In most living room home theater setups, the speakers need to be installed to fit the room and the decor leaving little room for speaker placement variation. To help your ears and eyes decipher the experience together, the center channel should go directly above or below the screen and the fronts should go as wide as is practicable. But to fully enjoy your home theater, careful consideration also has to be taken as to where you place your subwoofer(s) and rear speakers.

My main system at home is a great example of how limiting the compromise between great audio and comfortable living can be. The room is rectangular, but the fronts and center fire into the short dimension of the room, and because we like to be comfortable in our living room, we have a couch and some chairs, a few tables and other stuff that makes living there more comfortable. Also, because we don’t like to sit three feet away from the television, the couch and chairs are against the wall opposite the wall unit my KEF R300 and R200c speakers sit in. This leaves exactly 0” behind the couch for the rear channels. Needless to say in this setup, getting the system to sound spacious and articulate was a challenge.

In the sound room here at KEF I didn’t have any of those problems. I put the furniture in the optimal place for listening and viewing and I had a full 11 feet 3 inches behind my listening/viewing position to place my rear channel speakers. Spaciousness was a given.

At home, after a lot of experimenting I found that the best place under my conditions to place my rear channel speakers was in the rear corners of the room firing almost sideways toward my place on the couch. The rest of the family sort of gets either way too much rear channel or not enough, depending on where they sit, but hey, how many compromises am I expected to make? After all, I’m the audio person in the family, and anyway that’s what remote controls are for.

I over-rode the factory settings on my AV receiver and fiddled with the dimensions a bit until I was able to get some spatiality from the rear channels without them becoming too overwhelming, distracting or unnatural sounding. My personal taste across the frequency spectrum is for the sound to be understated and part of the environment. To me, it’s the difference between going to a small club and hearing a loud band with far too much sound reinforcement, and going to a concert hall and listening to the actual instrument as it was intended to sound.

More than likely your room will not be perfect, but with a little experimentation you can use that imperfection to your benefit. Don’t let your brain trick you into thinking your ears are happy, move things (like furniture and speakers) around a bit and play with the settings on your AV receiver or DSP until you like what you hear.

Subwoofer Placement

I’m not a giant fan of placing subwoofers in corners. Sure they sound louder and boomier, but loud and boomy isn’t necessarily always a good thing. Try it in a corner and then against a flat wall as well. As a rule of thumb, your sub should be placed inside of the front left and right channel speakers so that the apparent source of the low frequencies is the same as the rest of the sound.

You'll invariably find that even a few inches left or right, forward or backward, makes a sizeable difference in your subwoofer’s performance. The easiest way to tell which placement is best is to use a song or soundtrack you're familiar with and repeat it with every new position.

Phasing

Typically, your front subwoofer will be in the same phase as your front speakers, but you should be aware that just because something is in phase at 80Hz doesn’t necessarily mean it is 0° in phase at 100Hz. The phase shift may only be a few degrees, but depending on where you sit relative to the wave, that few degrees makes a difference. If your sub only has a 0°/180° switch, then set your front sub to 0°. If it has a variable control, try adjusting it slightly until you hear strong, smooth, articulate bass. As always, the most important Real Time Analyzers you own are your ears.

A quick description of phase: The best way to easily understand phasing is to visualize your speakers pushing out and pulling in as they produce sound. A speaker that is pushing while another speaker is pulling is out of phase with that speaker. When one speaker pulls and the other pushes, the waves are cancelled, or at the very least diminished. Phasing is particularly noticeable with low frequency energy, but is important at all frequencies.

That being said, don’t be fooled. I’ve heard subs set out of phase with the fronts that sounded really good. That was because they were cancelling (and overpowering) the low frequencies from the front speakers. In cases like this, you may want to try changing your crossover setting. The THX standard crossover is 80Hz. Live sound engineers will use a crossover point around 100Hz or slightly below. If you have small drivers on your fronts you may try going as high as 150Hz. For a more natural and exciting response, I try to set my sub as low as I can, typically in the 80Hz range.

In the KEF sound room, I added a sub to the rear channels for added effect. The sub in the front was placed on the listener’s right, so I placed the sub in the rear on the listener’s left, just to help even the sound out a bit.

The sub in the rear was set out of phase with the sub in the front. To ensure that the signal wasn’t out of phase coming from the source, I checked my rear sub at 0° and 180°. When you have speakers facing each other, always remember that one will be pushing while the other is pulling unless of course they are wired out of phase or your amp/receiver or DSP has changed the phasing.

* * *

There are plenty of do’s and don’ts when setting up your home theater, but the most important rule is that you take the time to experiment with positions and levels in order to ensure you’re getting the most out of your home theater investment.

Jack Sharkey for KEF America

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