Thursday, March 8, 2012

Your System's Sound Stage

When building a recording studio, the room in which the final mix is made has a rigorous design approach called the Live-End, Dead-End concept where the half of the room that the primary (front) loudspeakers are placed is acoustically dead (few reflective surfaces) and the other half is acoustically alive (many reflective surfaces). This approach limits the room interaction with the speakers while allowing ambiance at the opposite end of the room. With the possible exception of live recordings, most final mixes are made in this manner.

It would make sense to recreate such a design in your listening room so that you could experience precisely what the mixing engineer and producer had in mind. Or would it?

There is a lot to understanding room resonances and reflections beyond the simple LEDE formula. While an honorable approach, the LEDE approach is not universal and sonic treatment of large rooms should be left to professionals. But for home listening rooms, there are a few basic rules that can be followed to help you get more from your system than you currently do that emulate this LEDE approach.

As mentioned in a previous article on first reflections, the two most problematic conditions (limitations) you impose on your playback system is the position of the speakers and the treatment (or lack thereof) of the walls. Here are a few rules you can use to tweak your speaker position.

Rule 1: Speaker positioning starts low and ends high.

This means that in placing your speakers, listen to the impact moving your speakers around the room has on the bass first. Even small changes in position can have a large impact on the smoothness of the bass response, especially in rectangular rooms with similar dimensions. Resonance peaks are easily calculated from online tools and is a great place to start when evaluating a room. But these programs do not consider furniture, rugs, people, and other absorbing or reflecting surfaces inside of that room. A great little tool for Android smart phones is RTA Pro that transforms your cell phone into an inexpensive room analyzer (I am certain that similar apps exist for the iPhone). Placing the calibrated phone at your listening position can tell you a lot about what happens as you move your speakers around the room.

Rule 2: Eliminate the first reflection from the left/right walls.

As it is in the LEDE approach, reflections from the speaker-half of the room should be controlled (absorbed) as best as you can. One way to do this is with sound absorbing materials and another is with normally appearing room accessories (curtains, tapestries, rugs, etc.). Sit in your primary listening position and have a friend hold a mirror against the flat wall surface and slide it around. Mark with painters tape where the speakers can be seen. This is where sound absorbing materials are needed. Use your best interior designer friend to recommend treatments to match your room style and put these treatments at those marked positions.

Rule 3: Adjust resonances.

Room resonances occur typically at the midpoint along a wall. If you have your speakers in front of a 14-foot long wall, the center of that wall is where a room resonance will occur (the 7-foot point). Again, similar sound absorbing materials work best in helping to eliminate these resonances. Experimentation at this point is the best thing to do along with close monitoring of your results with your RTA application. Remember that the RTA must be in the exact same position in making all measurements (I use a photographic tripod and a reference measured location when making any of my RTA measurements).

Rule 4: Adjust the shape of the sound stage.

Once the bass and room resonances are under control, minor shifts in speaker position will add to the enjoyment of your system. I do this by listening to the impact minor positional shifts has on the size and shape of the sound stage. At this point, I do not consult the RTA program but rather my own psycho acoustical impression. I focus on the far left and right corners and listen to how deep and wide I can get this to be. Even changes of a fraction of an inch can have an impact on the shape of the soundstage. Be patient at this point since small moves can have subtle impacts.

RTA Before Treatment

RTA After Treatment

Once you find the right spot for your speakers, you will know it. In a great system, the sound appears to come from everywhere BUT the speakers. An entire wall of sound is recreated and the better the system, the more stable these psycho acoustic instrument positions will remain stable (not drift left/right, up/down, forward/backward). If your system does not presently do this, try tweaking your speaker positions and see what happens.

Yours for higher fidelity,
Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

My other titles include:

No comments:

Post a Comment

To comment on this blog, you must first be a member. All comments are moderated.

Note: Only a member of this blog may post a comment.