Isolation Ward

I remember them

63.16.47.230

In Reply to: RE: Yes, thanks, posted by rick_m on June 16, 2008 at 21:57:15

Those were Polks, IIRC, and I personally did not like them, perhaps because the speakers, out of necessity, were not vertically aligned. While the concept was to use algebraic summation and cancellation to create a wider soundstage IIRC, the concept was only applied to the midrange drivers and thus there were anomalies to my hearing in the highs and lows (at least on the model I heard). The additional driver cancelled out the center or common signal. Similar ideas were employed by Carver, IIRC, in their electronics.
Again, I find that since it is impossible, or at least very difficult to match drivers at all frequencies and volumes, that such cancellation effects are problematic. Again I believe the widespread use of a felt dampener around tweeters and other drivers serve a similar effect. They physically reduce the sound waves moving at 180 degrees to the direction of the driver. In a multiple driver system where crossover frequencies overlap, the sound emanating from each driver meeting each other at 180 degrees will cause cancellation but again differences in speed and time will create anomalies. Creating a small obstruction to prevent those sound waves in direct opposition from meeting means that the waves will be more reinforcing when their vectors meet at any angle less than 180 degrees.
I've done a little experimentation which seems to indicate this.
In placing that putty dam between drivers, one needs only to make the line long enough to run between an imaginary line running tangent to the outside edge of the drivers. Canting the line will direct the radiated sound towards a direction perpendicular to the putty. Thus, if you want a higher soundstage, you can cant the line, say 30 degrees from horizontal and throw the sound upwards towards the center, and raise the sensation of height.
In a single driver with a phase plug (Lowther), I've experimented again with putty in reshaping the plug. In modeling a sort of tapered flat screwdriver shape, vertically oriented, you can deflect more sound left and right and thus increase the sense of separation gaining in left and right separation.
What is also fascinating is that simple factors like the voice coil wire attachment points on a speaker cone also creates eigenmodes which affect the sound projected. The attachment points create a slight drag on the cone movement and also serves to dampen the cone at that point. If your VC wires are attached close together, I like to rotate the driver so that those attachment points are facing the upper (frequency wise) driver. The "dead" spots should be facing each other so that there is less cancellation and interaction between the drivers.
Many drivers have VC attachment points located at 180 degrees apart. If you can rotate your drivers so that those points are vertically oriented, again you get better left-right dispersion and the dead spots are then usually oriented towards the other drivers, increasing the coherency of the system.
I did this on a $200 pair of Monitor Audio speakers and the owner was stunned and shocked at how much of a difference it made. Again while I am sure that the effects are very audible, I would appreciate comments from anyone else who cares to try this.

Stu

Edits: 09/28/08

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RE: I remember them - rick_m 12:42:02 06/17/08 (0)

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