Friday, September 30, 2011

The Importance of Speaker/Listener Locations

By Norman Varney

The corner stone for high fidelity playback is positioning the speakers and listener at the optimal locations in the room. The idea is to avoid as much room boundary interference as possible, while providing an accurate soundstage. In very basic terms, let's find out why this is so important to the end result. 

Room walls, floors and ceilings react to sound energy with reflections and resonances from the make up of their construction surfaces and cavities. These interferences compete with, and distort, the direct signal sent by the loudspeakers. As speakers are located further away from boundaries, less energy is transferred in which to move room surfaces. In addition, as listeners are distanced further away from boundaries, less energy from room surface resonances and reflections is received by listeners. This mitigation of non-original signal information means improved low-level resolution, dynamic range, spatial cues and timbre accuracy.

There are three types of boundary interferences:

1. Cavity resonances. Try stomping on a wood floor and pounding on a framed wall and listen for them to sound like a drum. This adiabatic compression of a low frequency note is dictated by the mass-air-mass construction of the partition itself. When a loudspeaker plays the frequency in question, the partition will move sympathetically, resulting in that note being returned to the listener from the room surface, after the original event. 

2. Room resonances. Like any kind of enclosed space or musical instrument, a room has resonances defined by its dimensions, mass, compliance and friction. Each axis; length, width and height, has its own frequency in which the lowest (longest) wavelength can fit. Resonance, or room modes, are "standing waves". They are formed when the distance is a multiple of one-half the wavelength. When this occurs, the resonant frequency (and its harmonics) will sound louder than normal in some locations, and quieter in others. Think of the waveform with its pressure peaks and valleys traversing from one surface to the opposite parallel surface, and then reflecting back into the oncoming waves, etc. As they collide,  peaks from one surface run into the valleys from the other, resulting in a cancellation of energy. On the other hand, some peaks will run into other peaks, causing an increase in energy level.

3. Reflections.  Obviously, if we position ourselves and/or speakers near a large surface, will will hear the effects of sound energy being reflected to our ears later in time than the direct signal. The distance between the loudspeaker, the surface, and our ears will determine how much interference will be perceived. Basically, if the reflection is within about 15 dB SPL of the direct, it will be audible. In addition, the construction of the reflecting surface will determine what extent and what frequencies are absorbed and reflected by it.

In rooms of rectangular shape (preferred), simple math will predict what frequencies will resonate. It is correct to think that certain dimensions will offer better results than others. For example, rooms with dimensions divisible by each other will tend to exaggerate those resonant frequencies because they are similar in musical relationship. Once you determine the fundamental resonant frequencies, you can figure out where the peaks and valleys are located in the room along each axis. It is important to figure out the second and third order resonant frequencies for each axis as well because their energy levels are also likely audible. With this information you can avoid placing your speakers and listener in locations that will exasperate the room's unique modes and offer the most linear bass response.

Positioning for Room Modes
All rooms have room modes. Larger rooms have more of them. This means that there is less of a gap between one and the next, which is a good thing. Fewer modes mean that they draw more attention to themselves. Because all modes start and end at the boundaries with high pressure peaks, you have lots of bass there. Essentially, about 3 dB (sounds twice as loud) more bass at a single surface boundary, 6 dB (sounds three times louder) where corners meet, and 12 dB (sounds four times louder) in a tri-corner. People can use this for passive acoustical bass gain, but at the sacrifice of accurate, linear bass response. Same results for listener locations.

Ideally, you want to avoid placing a speaker or listener in a mode peak. Doing either will result in certain frequencies being discernibly louder than all the others. Though it's best to place speakers and listener between these primary room modes, you must always compromise. With speakers, avoid the peaks over the valleys. With the listener, avoid both, with one exception. It is very important to place the speaker/listener footprint exactly between the side walls to allow for symmetry in the horizontal plane. Without this established, the timing, energy levels and frequency response will be different for the left ear than for the right. As you can imagine, this means that you will be sitting in a spot that is a null for the first order resonance frequency of the width mode. This position is also a peak for the second and a null for the third width modes. This is a compromise that must be taken. It will suffer the fewest anomalies; only in the low frequency range and only at certain instances. Any other position will compromise all time arrivals, all energy levels and all frequencies, all of the time.(See Symmetrical vs. Non-symmetrical Layouts)

Positioning for Soundstage
By soundstage, I mean the accuracy in sound representation of the recorded space for width, depth and even height. Once mapping of the room modes is complete, either by modeling or with test instruments, the soundstage must be considered. The relationship of separation between the two speakers and the listener must be precise.  If the speakers are much closer to each other than the distance between them and the listener, there will be a small, narrow soundstage and sound will appear to originate from the speakers. On the other hand, if the speakers are too far apart, you'll have a hole in the middle of the soundstage and again, the sound will seem to come from the speakers. When the speaker/listener positions are correct, the soundstage will become three dimensionally large and solid, well beyond the speaker's edge. There will be a sense of true sound development beyond where the speakers reside and the recorded space will be realized. 

Fine tuning the soundstage is beyond the scope of this article. I will mention that are ways to precisely adjust the toe-in of the speaker angle using the ears and laser alignment tools. You can also adjust for personal preference of soundstage perspective, meaning if you prefer an intimate, front row perspective, or one more laid-back from say row T.  Note that toe-in not only controls balance, spaciousness, focus and intimacy, but also tonal brightness. It is speaker/room specific, due to the unique interactions of the speaker's energy dispersion pattern and the make up of the room.

The drawing above is an indicator of how positioning the speaker/listener footprint off center causes havoc on all signals, all of the time. The point that should be understood is how important it is keep things symmetrical, especially in the horizontal plane. Construction, even furnishings can impact how sound energy is absorbed, reflected and diffused.

Optimal speaker/listener location within the room is paramount to high fidelity playback. Keeping the speakers and listener footprint centered between side walls, away from boundaries, and room modes is the first priority in setting up a sound system. I would prioritize stereo separation as second, toe-in as third, and symmetry of furnishings in the horizontal plane as fourth. Without optimizing this footprint for the specific room, the full potential of the recorded experience cannot be realized. Avoiding room modes and optimizing soundstage go hand in hand. They are the foundation for optimal bass response, dynamic range & low-level detail, and accurate tonality & imaging. Getting this right is the most important aspect of the system. Regardless of the quality of the equipment, the quality of the sound will depend on how well the speaker/listener locations are set up in the room. A/V RoomService offers both modeling and onsite testing (voicing) services. Visit for more information.

Friday, September 16, 2011

General Electrical Maintenance of A/V Equipment

By Norman Varney

It shouldn't come as any surprise that audio/video equipment needs a little TLC in order to perform best. Happily, the TLC required costs very little in time, and next to nothing in dollars. As in most improvements in the A/V chain, start at the source and work your way down. Assuming there are no week links in the chain, an improved signal at the front, means a more accurate signal at the end. This is typically the hierarchy for any recording or playback system. With this in mind, we'll outline a full electrical maintenance practice for routine use. By routine use, I mean once every six months for climate controlled environments. However, in environments which may be exposed to ocean air, high dust content, extreme temperatures and/or humidity, you'll want to schedule this more often, say at least every three months, or after a conditional event.

If you have not done anything like this before, you will be pleasantly surprised at the audible improvements in dynamic response, resolution, speed and authority, soundstage size, image dimensions, reduced noise, etc. As always, what is presented here is to help the end user to optimally experience what the artists intended by delivering the most undistorted signal possible.

Note: The following procedures should be performed with the power off and dissipated.
  1. AC.  People generally think of power sources as simply a 50 or 60Hz. signal feed for component power supply capacitors. What they don't realize is that as the capacitors used to record or playback musical events must be replenished in a nonlinear fashion due to the transient characteristics of music. This may mean pulling bursts of current off the highest and lowest peaks of the 50 or 60Hz. sinewave, within milliseconds. During this process full wave bridge rectifiers and digital switching supplies can introduce significant noise to the line up to the 50th harmonic. Ideally, the power supply must be unrestricted if it is to deliver continuous and instantaneous current to the electronics. However, there are plenty interfaces in the path between components which impede, restrict and slow down the current's transfer flow. When this happens, loss in dynamic response, resolution and cleanliness of the sound occur.
    1. Service Panel. (For a qualified electrician
      1. *Clean any visible corrosion or carbon deposits seen on the grounding rod junction, buss bars, breakers (replace if old or has tripped several times), or outlets.
      2. **Gas tighten all connections to the grounding rod junction, buss bars, breakers and outlets.
    2. Power Cords. *Clean and tighten both male and female terminations, as well as the receptacles in the chassis of the electronic equipment itself (with power dissipated). 
  2. Source & Accessory Components
    1. Faders, knobs and switches should be turned back and forth weekly to wipe away oxidation and sulfide build up. Use a contact cleaner when needed.
    2. Vacuum all heat sinks, vents and electrical components inside and outside of the chassis very carefully using a soft brush
    3. *Clean all electrical chassis contact surfaces (pins and/or receptacles) for interconnects
    4. *Clean tube pins and receptacles (and replace tubes sooner than the manufacture suggests)
    5. *Clean power contacts, including fuses and fuse holders (with power dissipated)
    6. *Clean cartridge pins and leads
    7. Tighten all electrical connections
  3. Interconnects. 
    1. *Clean all electrical contact surfaces (pins and/or receptacles) of component interconnects.
    2. Tighten any possible electrical connections on the cable itself
Note on unbalanced interconnects like RCA and phone plugs, twist the connector to the right when disconnecting and reconnecting.
    1. Amplifiers.
      1. Vacuum all heat sinks, vents and electrical components inside and out of the chassis very carefully using a soft brush
      2. *Clean all electrical chassis input pins and/or receptacles
      3. *Clean tube pins and receptacles (and replace tubes sooner than the manufacture suggests)
      4. *Clean all speaker output terminals
      5. *Clean power contacts, including fuses and fuse holders (with power dissipated) 
      6. Tighten any possible electrical connections
    2. Speaker Cable.
      1. *Clean all terminations
      2. Tighten any possible electrical connections on the cable itself
    Note on speaker cable connections: A spade termination connected to a binding post will offer the most contact surface area. It will also allow you to make a tight, if not gas-tight, connection. If you have any type of connection that allows you to "screw it down", tighten it as far as you can using just your fingers, and then use a wrench or pliers to cinch it down another quarter turn (careful not to break cheap connectors!).
    1. Speakers.
      1. *Clean all terminal contacts
      2. *Clean any power contacts, including fuses and fuse holders (with power dissipated)
      3. Tighten any possible electrical connections on the binding posts
      4. Tighten all driver units by cinching down until seated. Do so incrementally and in a star pattern so that it may seat concentrically. Do not over-tighten.
    In summary, good signal integrity means flowing unimpeded throughout the chain. The three ingredients for this recipe are; quality materials, large, smooth, clean contact surface areas, and tight connections. Even in controlled climate environments, connections settle, are moved, are vibrated and resonate, which can cause breaks in the connections allowing air contaminants and oxidation to occur, and restrict current flow, resulting in signal losses, alterations and noise introductions to the original signal. Taking the preventative measures described above will help you achieve better performance from your A/V system, and a more accurate, more enjoyable experience.

                                               Acceptable AC THD and harmonics

    * Cleaning refers to wiping the contact surfaces with Lanolin-free isopropal alcohol, or a solvent such as Caig Lab's DeoxIT or Cramolin Contaclean, and/or physically scrubbing or abrading the contact surfaces of impurities. As soon as the surface is confirmed free of contaminants and debris, make a swift connection to avoid possible re-contamination. Light duty (gold plated contacts) applicators may include lint-free cotton cloths and swabs. Medium duty (visible coloration, etc.) may include pipe cleaners and nylon or stainless steel brushes. Heavy duty (high current) may include 100 grit sand paper or heavy steel brush.

    **Gas tight in this context refers to malleable metals being compressed to the point of deformation to create an intermetallic bond. It also means that all oxides and other surface contaminants are absent at the connection point, and that no air molecules can penetrate the seal.