Forgiveness is a great social asset, and it takes a valuable place amongst audiophiles as well. Developing a great audio playback system is, for most of us, a slow and methodical process of identifying and acquiring very specialized and expensive equipment. Equally painstaking is the installation and configuration of the components that yield the best possible performance of the system as a whole. At any point along this long journey, forgiveness is a great asset, whether or not it is acknowledged. No audio system is perfect, the honest among us will admit, and our satisfaction and enjoyment is dependent on our ability to forgive the discrepancies from perfection that destroy the hobby for those who cannot forgive. However, this asset can also become a liability when problems that are quite readily resolved are left to remain because forgiveness has put them out of sound and out of mind. A great remedy for such “deafness” can be the candid opinion of a good friend with good ears and the courage to share what he hears. Such a friend shared with me that my left channel tweeter was calling attention to itself. I reacted to this by making perfunctory corrections and then putting the whole thing out of my mind. Many years later I began hearing what my friend was referring to, and I wondered why it took me so long to experience it myself.
The topic of this paper is sound stage symmetry and a practical way of analyzing it. The premise of two channel audio (stereophony) depends on left/right channel symmetry. Absence of absolute symmetry will, of course, distort the sound stage. The problem can go unnoticed because of the wide stage presentation of many stereo recordings, and, when it is noticed, it is often attributed to the particular recording that evidences it. As the insidious flaw continues untreated, the audiophile revels in the sense of closure to his quest but suffers unknowingly because of it.
The methods discussed in this paper are specifically not to be conducted with a phonograph as a front-end source. The reason for this is that many errors in cartridge alignment, as well as defects of the cartridge or stylus, can cause high frequency asymmetry and disintegration. It is advisable to remove these possibilities from the system analysis for the time being. When everything else is found or made to be functioning perfectly, one can undertake to question his phonograph separately, but that is not the subject of this writing.
Without further ado, let us perform the simple test of listening to a monaural recording. I am a stereo snob who avoids monaural recordings as “beneath me”, but here we submit to them for analysis’ sake. At risk of stating the obvious, all of the sound should seem to emerge from the exact center stage, i.e., exactly midway between the speakers. This statement carries two ideas: all of the sound is clustered together in a small spatial grouping, and the location of this grouping is exactly centered between the speakers. If your system passes this test, go back to stereo listening and have a great life. If the sound is well grouped but is not centered, I suggest reading my previous paper on speaker placement errors. If the sound is not well grouped, for instance, if a part of the spectrum is not located where the rest of the spectrum is, then you have what we will refer to as incoherence. When I tried this experiment, I found that the high frequency portion of the spectrum, cymbals and sibilance, for instance, was displaced to the left from the rest of the spectrum by several feet. This was the left channel tweeter comment my friend made years ago.
If you discover incoherence playing a monaural recording, the cause needs to be identified and fixed. Of course, the list of possible causes is very long, including each electronic component, each cable, each speaker, and numerous aspects of the listening room. The fastest work of sorting this out begins with a very simple operation. Connect each speaker to the same amplifier output. If you are worried about overloading your amplifier, don’t be. You can keep the volume level quite low for this. Your speaker cables will need to be long enough to allow this, which is no problem in most systems. If you happen to have separate left and right channel amplifiers that are placed near their respective speakers with short speaker cables, this may be a problem. In this case I recommend buying or borrowing a pair of low-cost speaker cables so you can run the experiment. Assuming you are able to accomplish this connection, repeat the listening. You can, of course, use a stereo recording this time because one channel is supplied identically to each of your two speakers and it should sound like monaural.
Does the incoherence still exist? If it is gone, the problem is before the speakers. Reconnect the speakers as usual and begin troubleshooting by swapping left and right channel cable connections, one at a time, to identify the component or cable that is the culprit. When the “bad channel” of the culprit is swapped from right to left, the incoherence will also swap sides accordingly.
On the other hand, if connecting both speakers to a single amplifier channel does not eliminate the incoherence, you have eliminated all of the electronics and cabling, except the speaker cables, from the list of possible causes. If you used speaker cables other than those belonging to the system, then you have eliminated the speaker cables from consideration also. Possible causes include the speakers and the listening room.
At this point you may want to swap the left and right channel speakers to see if the incoherence changes direction, but many speakers are far too heavy and precisely placed to make this a practical option. A practical way to proceed is to place a listening chair on the central axis of the system, and move the chair progressively closer to the plane of the speakers. Leaving the speakers each wired to the same amplifier channel, continue listening at each listening position to see if the incoherence resolves as you move closer to the plane of the speakers. If it does, the room is the culprit. If it does not, the speakers are probably the culprit, i.e., they are not operating symmetrically. Possible problems with a speaker include a damaged tweeter or a damaged crossover network. For instance, if the high frequencies are pulled to the left, as was the case in my system, that could be caused by reduced output from the right channel tweeter, possibly pointing to a damaged right channel tweeter or crossover network.
What if a room problem is indicated? Begin by making a list of any left-right asymmetries in the room, including an asymmetry in the placement of the system within the room. The upshot of this is that some sound reflective surface is closer to the sound field on one side than it is on the other. When the high frequencies are pulled away from the rest of the sound group, they are usually pulled in the direction of the closer reflecting surface. Stated alternatively, a reflective surface will have the effect of “pulling” the high frequencies toward it. If your high frequencies are pulled toward the left, for example, look for a reflective surface in the left side of the room that has no identical counterpart in the right side of the room. Once identified, try treating this surface with blankets, pillows, or even sheep skin. If you are treating the culprit, the incoherence should begin to resolve. Continue this work until the sound all seems to be emerging from the center stage, over the entire frequency spectrum. When you are satisfied that the incoherence is gone, reconnect the speakers to their respective amplifier channels. You should notice a pleasing, and perhaps even thrilling, improvement to the sound of stereo recordings. Particular benefits should be noticed in the focus and palpability of center channel sound sources, such as a vocalist or a center stage instrument.
In my case, I wound up identifying a load-bearing post on the left side of my listening room as the problem. I treated it by wrapping it with a blanket and the problem was gone. I suppose I should have suspected that this post would be a problem from the start, but since it was not removable, I simply decided to forgive and forget it. After all the years of living with this insidious problem, I finally corrected it. In the process, I learned two valuable lessons: Never forgive a problem that is easily corrected, and never forget the importance of monaural playback. This isn’t to say that you should necessarily sit around listening to mono recordings. It is simply a reminder that, unless a monaural recording plays back correctly, stereo recordings never will.
The information contained herein is presented in good faith and with all hopes of helping the reader to find the best equipment for an audio system. Neither the author, nor Bella Sound LLC, assumes any responsibility or liability due to loss on the part of the reader, owing to or believed to be owing to the content of this article, or resulting from or believed to be resulting from an application of the information contained herein, regardless the level of expertise engaged thereto.
