Placement of a small strip of putty ( you can use Play dough, caulk, even a strip of tape folded over) creates a dam between the two drivers. What this does is that it blocks the sound wave moving towards each other exactly 180 degrees apart. Since no crossover has an exact frequency cut off and the frequencies overlap, a 180 degree confrontation will result in cancellation. However since no drivers are equal in both amplitude and at all frequencies, this creates a region of distortion which muddies the sound.
The putty strip forces the frequencies to meet at a slight angle which creates a reinforcing vector. This is similar to playing pool. Two balls moving directly against each other will hit and have no resulting motion. When moving and meeting at a slight angle they will shoot forward.
This is exactly what we are inducing, and the result is more forward presence with greater detail in the crossover region where the sound will be pushed forward towards the listener.
You can adjust the tonality by experimenting with the height of the strip. Placing the strip closer to the tweeter allows the woofer a greater range of dispersion and creates a slightly warmer tone. Likewise moving the strip towards the woofer allows more space for the tweeter dispersion and the upper frequencies become more pronounced.
You can also play with the angle of the strip. Angling the strip slightly so that it throws more sound upwards and inboard, will throw the upper frequencies higher between the speakers and raise the image height. That angle can be adjusted to adjust the image height.
No 2 involves placing two small teardrops shaped balls of putty directly above and below the tweeter ( or actually any driver). This shape is ideal for the air flow ( if you can picture the side view of an airplane wing). The blunt edge will split the airflow coming off the drivers into a left right symmetry and improve imaging as well as throwing more detail in the center image.
Like the putty, a slight deviation from vertical will throw the air form slightly deviating from horizontal symmetry. You can thus use this technique to lower or raise the center image height, as long as the placement on a stereo pair of speakers are kept in mirror image.
A higher image would require the line running through the teardrop shaped putty pieces be slightly oriented outboard.
No 3 involves woofers or larger drivers. Since most dynamic drivers are circular in nature, the standing nodes involved in speaker break up can occur anywhere in the cone structure and may vary in location at different frequencies. We use a small piece of tape, measuring roughly about one millimeter by about 3 mm, and placed directly top and bottom of the cone. While we normally place them on the outer edge of the cone. It will also work placed vertically over the dust cap closer to the center.
Again this technique forces the eigenmodes present in the cone to break up into a left-right symmetry. Like tweak No 2 the sound waves coming off the cone will be more left-right symmetrical and a better imaging with greater detail is heard. Remember human ears (unless you are lying down) are oriented horizontally and our hearing acuity (for imaging at least) is dependent upon the distance between the ears.
On certain drivers, like Lowthers which employ a super light cone material, the tape size may have to be significantly reduced. Even the slight additional weight can be heard as slowing down the driver speed.
This technique can also be applied to drivers where you know the location of where the voice coil wires are attached to the cone. On many drivers, the attachment points are 180 degrees apart and the point of attachment adds a very slight amount of drag when the speaker is in motion. This dampens the cone at those attachment points and works similarly to adding tape in pushing the cone to break up into two halves. Orienting those points vertically certainly helps the imaging.
On some drivers, the voice coil attachment points are close to each other. Orienting those points so that they point in the direction of the adjacent driver, places the ” dampened” spot so that the crossover overlap is slightly reduced aiding the transition from one driver to the other.
4. Replace mounting screws with non magnetic stainless or brass screws. The typical ferrous screws tend to retain the magnetic field of the drivers and actually can slow down the cone, or dome. replacing them one for one improves the overall performance.
While the reduction on the magnetic influence is primary, all AC signals generate an EMF field, and the brass being more conductive, will help pass that field through faster.
You can remove one screw from one corner and go down to Home Depot or City mill and find an equivalent. The stainless will be a sheet metal screw, usually, and have a slightly tighter thread, but it makes little difference.
Brass being more conductive than steel or stainless is the best option. Not many local stores carry them however, and you may have to go to the internet to find them. Normal wood screws are the 6 by 1 inch variety.
You will hear increased micro dynamics, and better detail in doing this little tweak.
Have fun experimenting and remember with putty, remember everything is reversible
If, as in a mono signal, the signals meet exactly in the middle there is cancellation, being that the mono signal is out of phase with each other. Since no speaker can be perfectly matched, the cancellation is uneven across the frequency bandwidth and thus actually muddies up the center image.
Placing two vertical dividers in the middle of your soundstage a bit taller than your speakers, keeps this left /right signal from combining, and allows the ears to do the actual mix much like headphones. The result is a significantly better stereo imaging with far greater detail being revealed.
In the shop listening room we use two room tunes placed in a v formation point towards the listener, about 60 degrees apart. You can use those room dividers with three sections and get equally good results.