Thursday, December 12, 2013

High-end Soundstages - Part 4

Dedicating enough space exclusively for your loudspeakers on the speaker-end of your listening room is usually the biggest challenge with which audiophiles grapple. Allocating 1/3 to 1/2 of this room for nothing but your speakers pretty much means compromising on using this room for any other purpose. Unfortunately, to get the largest, 3-dimensional soundstage possible this is what you must do. Realistically, however, most people cannot do this or the listening room you use has other compromises. Most people must live in the same space in which they also listen to music so a listening room becomes a multipurpose room. Does this mean that it is impossible to get a good soundstage from such a room? No. Let's see what can be done on a practical level.

If you have been following this series, in Part 1 you saw how monophonic sound progressed into stereophonic sound and then into what is presently called the high-end. From Part 2, you know what happened in the audio industry as the 3-dimensional soundstage developed favor and why rectangular listening rooms are preferred. You also learned how moving speakers influences bass prominence and how the listening room itself influenced the overall sound. From Part 3 you learned how to minimize room bass resonances by mathematically positioning your speakers based on your room dimensions and how high off the floor they should be. You also know that floor rugs are good and that the listening chair ("sweet spot") are about the same distance from the rear wall as the speakers are from the front wall.

In this part, we will explore how to treat your room acoustics so you can achieve the biggest soundstage possible in your listening room regardless of its size or shape. You will also understand better what helps to enhance the size of this soundstage and what to avoid. Here we will address issues above 300Hz, those frequencies where directional imaging cues occur. So with this introduction, let's roll up our sleeves and get to work.

STANDARD SIGNAL SOURCE: At this point, you should be listening to your favorite music in your sweet spot becoming familiar with its new attributes. You may have already noticed a change in the size and shape of the soundstage and maybe not. What we need to do next is all get on the same page and start listening to what readily-available recordings can tell us about what to do next. The first conventional (AKA Red Book or 16 bit/44 KHz) recording that well reveals a soundstage's dimensionality is:


Norah Jones Come Away With Me (Red Book)

If you do not have this recording, you need to buy one now since I refer to it constantly to explain what to listen for in specific passages. While it may be tempting, DO NOT use the MP3 version of this recording in this positioning process since the MP3 compression masks the potential three-dimensionality of an uncompressed Red Book version. However, you should play an MP3 version later to understand the differences and compromises between these two popular digital recording formats.

The Red Book version will suffice to a point but another round of tweaks requires a better signal source. To permit reliable A-B comparisons and assure yourself you are moving in the correct direction, it is best to use the same program material for both positioning rounds. I will use a high-resolution version of this same Norah Jones album and I suggest you purchase the $30 download it here:

Norah Jones Come Away With Me (high resolution)

Download the highest resolution your player/streamer can handle (use the pull-down menu to see what format your streamer can play). This description uses the 24-192 FLAC version. Other similar Red Book and high-res recordings may be used once you better understand how to listen or rather what audible cues to listen for (something else that you should begin to understand as a result of this exercise).

Tweaking is an iterative process, one that takes a lot of time and patience, along with critical listening. As we progress, movements in speaker positions may vary from as much as 4” to as little as ½” with each move making gains in some respects and losing gains in others. The final positions will most likely fall into “your personal preference” category as they should to leverage those strengths you prefer. Allow yourself time to embrace the sound of the relocated speaker and listen to a variety of familiar music after making a location change, typically over several days. You may already be intimately familiar with many different recordings (your personal “favorites”) and I suggest that you listen over and over to those pieces focusing primarily on soundstage width and height during this time, especially the extreme outer edges. Before we begin listening, help your room reveal more of what your stereo can produce by eliminating simple physical impediments, here being first-reflections.

IDENTIFY FIRST REFLECTIONS: First reflections are the surfaces the sound from your speakers strike on the way to your ears. Like balls bouncing off the cushions of a pool table, sound bounces off the surfaces of every object in your listening room. These bouncing sounds arrive at your ears at different times than the direct sound from your speakers. When the level of reflected sound is high, it interferes with the ear-brain interpretation of the location of the direct sound. In other words, reflected sound messes up the soundstage and should be absorbed or redirected to minimize this interference. This is a concept in room treatment called the “live-end, dead-end” or LEDE where the part of the room in which the speakers reside is deadened to absorb these undesired first reflections.

Before we start identifying where these first reflections are, you must remove all furniture from the speaker half of the listening room. Do this now. Doing so allows you to easily identify exactly where on the walls, floor, and ceiling these reflections originate by simple line-of-sight observations. You can return these items to that side of the room later and observe what compromises you have made by re-introducing this furniture near your speakers.

USING A MIRROR: Begin by identifying where the first reflections are in your listening room as observed from your sweet spot and then damping them out. This part is pretty easy but requires some masking tape, a friend, and a mirror (a flat 12” by 12” square will do just fine). All you have to do is move this mirror against the flat wall until you can see one of the speakers and then put tape around that visually-identified area. To identify the areas on these surfaces where first reflections originate (and where sound absorption should be placed in the dead-end of your listening room), do the following:
  1. Sit down at the sweet spot.
  2. Have your friend hold the mirror flat against the left wall.
  3. Move the mirror around on the wall until you see the LEFT speaker.
  4. Put masking tape on the left wall framing the area where you can see any part of the left speaker.
  5. Continue moving the mirror around on the left wall until you can see the RIGHT speaker.
  6. Put masking tape on the left wall framing the area where you can see any part of the right speaker.
  7. Repeat steps 2-6 for the right wall.
  8. Repeat steps 2-6 for the front wall, left side.
  9. Repeat steps 2-6 for the front wall, right side.
  10. Repeat steps 2-6 for the floor.
  11. Repeat steps 2-6 for the ceiling.

If there are multiple seats at the sweet spot, repeat all of these eleven steps for all alternate seating positions.

The taped-off areas on the walls, floor, and ceiling are the locations where sound absorption is necessary. In your decorating decisions for this room, place sound-absorbing panels or hang tapestries at these locations so that the sound is reflected less at these critical points. Hang the tapestries from 1”x2” boards to permit adding acoustic batting behind them. If the first-reflection areas are windows, put soft but heavy curtains on the windows that can be easily raised and lowered. There are many suggestions for both DIY and professional room treatments in the Rives Audio section at http://www.audioasylum.com/forums/rives/bbs.html.

 Use a Mirror to Locate First Reflections in the Dead End

For aesthetic reasons, ceiling treatments are usually the hardest to include in your listening room. You can disguise such a treatment as an indirect-lighting ceiling fixture, especially if there is already a ceiling light nearby. Build an absorber panel as you would for a wall panel (use an Owens-Corning #703 2’x4’x2” fiberglass panel). Frame it at the edges and cover with coordinated cotton fabric. then suspend it uniformly from the ceiling with wires and hooks. Take down the panel. Connect a rope light to the existing ceiling fixture. If the ceiling fixture is not above the absorber, use some plastic self-adhesive electrical channel to help hide the wire from the fixture to above the absorber. Re-hang the absorber. Hide the rope light on top of the absorber and you now have a sound absorbing room light.

If you choose not to build your own panels, you can also buy sound absorbing panels from many sources including a thrifty manufacturer at http://www.readyacoustics.com/diy_acoustic_panels.html.

So far you have taken care of the DE half of the LEDE concept. The LE portion identifies the first reflections in the sweet-spot half of your listening room. Unlike the DE half, the LE half must disperse the sound at these identified locations to randomize their otherwise predictable interference patterns. Use what is called a diffuser to break up these undesired uniform reflection patterns. Identify where this diffuser should be by performing similar steps with the mirror but this time while looking at the back wall from the sweet spot at all listening positions. Tape off the area for the diffuser.

 Use a Mirror to Locate First Reflections in the Live End

DIFFUSERS: In keeping with the Live-End-Dead-End (LEDE) approach to room design, the live end (sweet-spot half) should be reflective and the rear wall is critical in properly contributing to this reflectivity. Here the rear wall should not only reflect sound, it should disperse it in a controlled manner. The human ear is most sensitive those frequencies produced by the human voice (300Hz-6000Hz) so it makes sense to focus on dispersing these frequencies. However, diffusers with a 300Hz cutoff will stick out into the listening room quite far. A good compromise is one octave above the lowest frequency, or a diffuser dispersing sound between the 600Hz-6000Hz range. This LE reflective area identifies the smallest diffuser you should use.

You can buy diffusers in various sizes from many manufacturers such as Overtone Acoustics, but you can also easily make one yourself if you have the time and are so inclined.

 Grid Assembly

Below is a pattern for four heights of 1”x1” square blocks that easily diffuses frequencies within the range of 600Hz-6770Hz. Assembly is simple gluing these blocks to a piece of ½” thick plywood in the positions determined by the number in the table below.

The diffuser below makes one panel 12”x12”. Make multiple panels at least the size of the masked area on the back wall to properly diffuse the sound from the rear wall (a 2’x4’ panel needs 8 of these, 4’x4’ panel needs 16 of these, etc.). These finished panels are very heavy and must be attached to the wall studs for proper support.

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Block Heights: 1=2.823”, 2=5.642” 3=8.465”, 4=11.287”

At this same time, it is best to get whoever is involved in decorating your listening room to understand why things are placed where you have decided to put them. Compromise is the key to a successful relationship and in your listening room such compromises should be weighed against audible effects. Keep your spouse (substitute the appropriate politically-correct term here that describes your relationship) involved in your decorating decisions now instead of having him/her move things around later for aesthetic reasons or otherwise.

Keep to the LEDE plan and you will have a good listening environment, one that can reveal the full potential of your system. In Part 4 of this series, we will describe how to use the Norah Jones signal sources to fine tune the location of your speakers. In this part, I will explain what to listen for in various passages so movements and changes for the good or bad can be correlated.

HOMEWORK: Make sure you have the reference signal sources for Norah Jones album Come Away with Me. Add the absorbers and diffuser to the room now at the appropriate locations and get used to the soundstage with your favorite songs and tracks. This will help you in Part 5 of this series when we start systematically moving things around.

Links to the entire series:
Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7
 
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.

http://www.amazon.com/dp/B00QFIAC3G

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