April 18, 2011

Speaker placement guide

Speaker placement often doesn't get the level of attention it deserves. That is a shame because it is free! The difference between good and poor setup here is greater than many expensive upgrades. The most common mistake is simply not taking the time to try different options and pay careful attention to the changes.

One size doesn't fit all

Speaker placement is a juggling challenge where you have to consider the interaction between various factors. The theory offers starting points, but the best option, if there is such a thing, involves a chaotic interaction between various aspects. In other words, I suggest a mix of theory and trial and error with careful listening. The kind of listening that is required for this is not a general listen to "musical engagement" but it's about paying specific attention to the impact of each change.

Specific attention

As you try the different options, listen critically and carefully for the changes. The key is in paying attention to certain cues.

Different rules for different speakers

Many placement guides assume conventional hifi speakers with a small dome tweeter and 4 - 6" mid. However there are different requirements for different speakers. Panel dipoles, open baffles, omnis, horns and waveguide speakers all have different requirements.

1. SBIR - Speaker Boundary Interference Response.

You have 3 distances from the woofer to the floor and the 2 nearest walls. Try to keep each of those different. More >

2. Toe in

Start with the speakers firing direct at your centre listening position. Try angling in or out a little either way. In doing this you are adjusting the tonal balance slightly, and also side wall reflections. Toeing them in a bit more will reduce side wall energy slightly. It will also affect how the sound changes as you move to either side of the centre position. If you toe in with a greater angle, then as you move to the left, the closer speaker is angled further away from you than the farther right speaker. It can make the sweet spot a bit wider. The dispersion of the tweeter is a factor.

3. Speaker distance - lateral

The further apart, the wider the sound stage, but as you get too close to side walls you lose the benefit, so you have to juggle. The closer they are to the walls, the stronger the reflections will be.

4. Speaker distance to listening position

In a small to medium room you have to do what you can to maximise it as you often end up listening too close to get a sound stage developing. I'd think 3m on the diagonal is a good distance. Make it too close and you get a nearfield type of sound where the stage doesn't fully develop. You get less room sound but the lack of a sound stage is unnatural. Make it too far away and the speaker gets swamped by the room.

5. Direct to reverberant ratio

This is the ratio of direct sound from the speaker only (such as you would hear outdoors) to the sound that comes from the room. Nearfield increases direct proportion, placing the speakers in room corners and listening against the back wall is the other undesirable extreme. Every room has a balance in the middle you try to find. You want the sound stage to develop, but also to have a natural balance of room and speaker sound together.

So your task is to put all these things together and find what works in your room. You need a bit of trial and error and some time to listen carefully. It's not a bad idea to break some of the rules, like putting the speakers in the corner, just to hear the extreme version of getting it wrong. If you are stuck in a small room and it's hard to get enough distance from the speakers, then you can push the speakers closer to the wall than ideal, and tame the artifacts that creates with some treatment.

The key is to try things out and to carefully pay specific attention to these things. I've seen a lot of setups where the speakers weren't placed very well. I think it comes down to not trying things out, and not paying attention to the specific issues. When you toe in, pay attention to what happens to the sound as you move laterally (side ways). Also pay attention to the tonal balance, as you will get a change in the treble especially. You probably want to be close to listening directly on axis, so you get the same sound from each speaker. As you adjust the offsets from boundaries, pay attention to the lower midrange area, because you will be adjusting peaks and dips there that come from SBIR. Another step is to get a basic measurement setup and you can actually see it.

Also move forward in front of your listening position and see what happens to the sound stage. Moving closer you get a nearfield sound.

The next step is a little acoustic treatment - that is another adventure!

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