Sunday, December 15, 2013

High-end Soundstages - Part 5

Listening rooms sound best when speakers are properly positioned but the room itself plays an integral and synergistic part in your system’s ability to perform at its peak. In Part 5 of this series we will make sure speaker wiring is proper and then take a snapshot of your system’s uniformity.

If you have been following this series, in Part 1 you saw how monophonic sound progressed into stereophonic sound and from there 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 roughly how high off the floor they should be. You also know that floor rugs are good and that your listening chair (a.k.a. the "sweet spot") are about the same distance from the rear wall as the speakers are from the front wall. In Part 4 you identified the locations of first reflections in your room and hung sound absorbers and diffusers in the appropriate places.

I presume that you have done all of your homework assigned in Part 4 and purchased the two versions of source material you will need to follow these tuning instructions.  So with this introduction, make sure your ears are REALLY clean (I am serious about this) and let’s get down to business.

SPEAKER WIRE ELECTRICAL PHASING: The sound from any single speaker regardless of its position in a room will always appear to come from the centerline of that speaker. When in proper electrical phase (+ signal from the amplifier reaches the + terminal of the speakers, that is to say the speaker wiring is proper) phantom sound should also appear from directly in between your speakers. To test that your speakers are wired in correct electrical phase:
  1. Sit in the sweet spot
  2. Play track twelve (Nightingale) on the Red Book version of the Norah Jones album
  3. See if Norah’s voice emanates from in between your speakers
If it does, your speakers are in correct electrical phase; if not, one of the speaker wires must be reversed. To remedy this issue, recheck the polarity from amplifier-to-speaker on both channels and correct the improper wiring connection.

SPEAKER WIRE ABSOLUTE PHASING: As you listen to any signal source whose speakers have correct electrical phase, the sound will also appear to come from either slightly forward or slightly behind your speakers. The correct orientation is slightly behind your speakers. To test for correct absolute phase:
  1. Sit in your sweet spot
  2. Put on track twelve again of the Norah Jones album
  3. See if the sound of the introductory guitar and Norah’s voice comes from slightly behind your speakers
If they do, the absolute phase of your speaker wires is correct. If not, the absolute phase of your speaker wires is incorrect. To remedy this issue, swap the wire polarities at BOTH speakers regardless of their current orientation (move the wire that is now on the + terminal to the terminal, and move the wire that is now on the terminal to the + terminal on both speakers).

Improper absolute electrical phase is a result of one of your pieces of gear (amp, preamp, CD player) internally inverting the phase. Without placing blame, the easiest way to resolve this issue is to correct the problem at the speaker terminals. Now that you are certain the proper electrical and absolute phases are correct, listen to your favorite reference recordings to verify these two phases.

PLANES OF ADJUSTMENT: There are a total of five planes of adjustment you can make to properly aligning your speakers. The three adjustment planes most people are familiar with are:
  • left/right (moves your speakers towards or away from the side walls)
  • front/back (moves them towards or away from the front wall), and
  • up/down (raises or lowers them from the floor)

These three adjustment planes get your speakers in that part of the room where the bass (here defined as those frequencies under 300Hz) is smooth and the soundstage (frequencies above 300Hz) is decent. Moving them from this point may improve the soundstage at the expense of bass smoothness, a compromise only you can decide which is better or worse.

But to fully appreciate the front-to-back dimensionality possible with just two loudspeakers, the last two planes of adjustment are used to fine tune them while minimally impacting bass smoothness. These last two planes are:
  • toe in/out (twisting the speakers toward or away from the sweet spot), and
  • pitch back/forth (raising or lowering the front of the speakers)

This does not mean you shouldn’t move your speakers. On the contrary, mathematical models should be used only as guidelines or starting points and typically fall short of peak performance when applying them to real-world situations, especially when it comes to rooms in homes. Walls assumed to be plumb, square, and completely flat are most likely tilted, cocked, and warped. So the first step in determining where to go is to move your speakers from this starting point.

TRACKING CHANGES: Smart phones and tablets are great communication and productivity tools and most of them can easily become inexpensive audio analyzers. A good Android tablet/cell phone app for observing your system’s response is available here and a good iPhone/iPad app is available here. You can measure the relative smoothness of your system at your sweet spot by playing a quality pink noise signal through your system. Ten minutes of high-quality pink noise is available for free here that you can play in your CD player or music streamer.

Although your tablets/smart phones are not built to the same standards as a professional RTA and calibrated microphone, they are far better to use than by trusting your ears alone. Use the instructions provided with the app to calibrate your tablet’s/cell phone’s built-in microphone to the software and you should have a pretty decent way of preserving the actual results of your efforts.
Some devices, such as the Samsung Galaxy S III from AT&T, have built-in filters that skew low-frequency readings (those under 300Hz) and should be ignored. However, relative changes between measurements will remain reasonably valid. The picture below shows two RTA measurements made before and after moving my speakers just two inches closer together.

Two RTA Measurements with a Samsung Galaxy S III

A reminder is needed here regarding measurements with RTA devices and real-life soundstage observations. While RTAs show you how smooth your system produces sound, they show you nothing about the height, width, or depth of the soundstage. RTAs are most useful in understanding problematic room resonances and identifying annoying frequency peaks. There is no app that can tell you anything about the size of your soundstage.

With your speakers set in the mathematically-calculated position described in Part 4 of this series, use your RTA app now and measure the smoothness of your system’s response at your sweet spot. This should be your “reference” or “starting point” measurement. Subsequent measurements will show you what changed regarding your system’s overall smoothness as a result of that change. Do this measurement now.

In Part 6 of this series, we will start moving things around and use subjective and objective measurements to decide if a change is desired or a disaster. You will continue to use your RTA app to objectively measure what these changes do. And I will help you understand how to be a better listener. So until next time…

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.

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