Finding the best speaker locations
finding the best location for the midrangeWhen optimizing speaker locations, best results can be achieved by minimizing the difference between the left and right speakers relative to your listening position. This practice is referred to as “minimizing your path length differences.” Figure 1
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Path Lengths are unequal |
Path lengths are equal |
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Picture A |
Picture B |
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Figure 1 |
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In Figure 1 Picture A, the listener is closer to one speaker. This is typical in most automotive speaker installations. In this situation, the sound will appear to come primarily from the closer speaker. This does not help to create a “phantom center image.” A phantom center image is the result of a speaker systems ability to create the illusion of a center vocalist or instrument to originating from a point in between two stereo speakers. In Figure 1 Picture B, the listener is equal distant from both speakers. This situation the listener receives each speaker’s information equally, a necessity for the creation of the phantom center image.
In a automobile, it is difficult to find speaker locations that are equal distant to the listening position. That is, unless you have a cool million dollars for a McClaren F1 Super Car. For the rest of us, we must be content on finding locations that minimize the path length differences for the left and right speakers for both the driver and the passenger. In most vehicles, speakers placed either low and front in the front doors or in the front kick panels will have the least amount of path lengths differences. Typically, kick panel locations offer the best in overall imaging, but are usually more difficult to install the speakers.
The best and easiest way to determine the best locations for your midrange is to test it first. Sound simple enough? All you need is your system working in your car and some test enclosures (can be made out of cardboard). Play the midrange with a full range signal. Play music that you are familiar with that has a good strong center image. Move the speakers around the vehicle (in places where installation is possible) and locate the best placement by ear. Your ears are the best test equipment you can use.
If you do not have any program material that suits this need, we recommend the latest IASCA (International Auto Sound Competition Association) test disc. This is the same program material that the autosound competitors use to tune and evaluate their award winning systems.
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topFinding the best location for the tweeter
Once the best location for the midranges have been found, the next step is to find a location for the tweeter. The goal is to find a location for the tweeter that blends as seamless as possible to the midranges. There are several characteristic of placement you need to consider.
How close should I place the tweeter to the midrange?
For best results, the tweeter should be placed where it blends the best with the midrange. The correct placement would cause the least amount of constructive or destructive interference. Constructive and destructive interference is a description of change in perceived amplitude when two independent acoustical sound waves intersect each other. Just like when two pebbles are dropped in a pond. The waves of water caused by these two pebbles intersect. The intensity of the waves can be compounded or negated depending on the position on the water. Figure 2
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Figure 2 |
The points where the gray and black circles intersect would be points of constructive interference. The places in-between, would be areas of destructive interference. The sonic effect would be that certain frequencies will appear louder to the listener than others. This can offset the spectral balance of the system. From Figure 2, it becomes clear the closer the two original sounds take place, the less chance for interference to occur. From another perspective, if the two sound sources are far enough apart. The interference can also be minimized. The critical factor is the crossover frequency. The crossover frequency is the frequency at which both the midrange and tweeter have about the same acoustical output. Or, the frequency where placement will have the greatest effect on constructive and destructive interference. For best results, the tweeter should be less than 1/2 the wave length of the crossover frequency or greater than 2 wavelengths of the crossover frequency. For a midrange tweeter crossover set to 2,500 Hz, these critical distances are 2-1/2” and 11”. Figure 3.
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Figure 3 |
Where do I place the tweeter to the midrange? There are two different ways of locating the tweeter to the midrange: horizontal array or a vertical array. Figure 4
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Figure 4 |
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The closer to a vertical array you can get to the listening position, the more the tweeter and the midrange will act as a single source. The closer you get to a horizontal array the more confused the image can become. Surpassingly good results can be accomplished with the tweeter mounted either directly above of below the driver. This is possible because both situations can maximize a vertical array effect. Again. as before, testing is believing. Try different mounting locations as well as mounting angles to produce the desired result. A little effort here will be rewarded with awesome sound results.
