This got me thinking of the following question:
What do we think a wide band driver would do? Usually, it leads to beaming, so there are some frequencies over which it will offer less decay than others. In other words, a driver that goes from say 100 to 5000 Hz, and is around 8" will beam around 1500 Hz plus, and the beaming effect will get more pronounced I think as the frequency increases. How would this impact the frequency rolloff off axis? IS a wide band driver a good thing or a bad thing , from the perspective of off axis frequency roll off patterns?
-akhilesh

The system I recently built and displayed at RMAF is based on the Fostex FE-206E, and in the design I went to some length to generate a well energized, tonally fairly well-balanced reverberant field, making a few trade-offs along the way. I did not try to control the pattern tightly, as I don't think this type of driver lends itself to particularly well-controlled radiation patterns. For instance, even with a lot of toe-in (Geddes-style) I was still getting some undesirable sidewall interaction from the 8" diameter Fostex drivers, and had to resort to using a plant along one sidewall.

In my experience a good horn or waveguide-based system does a considerably better job of radiation pattern control, provided attention is devoted to minimizing the pattern discrepancy between woofer and horn where they transition. A good fullrange driver has its attributes, but when it comes to pattern control a waveguide or constant-directivity horn is a much more effective device.

Duke

Predicting the directivity of a full-range driver is probably nearly impossible. In order to be be "full-range", the driver has to operate into break-up mode, then it mechanically crosses over to the whizzer cone or dust cap and the process starts over. The graph above is for a speaker using the FE167E, a 6" whizzer-cone driver. The plots are 0, 30 and 60 degrees. You can speculate as to which part of the driver is producing what frequency and where cross-over points are. In any case, there is a lot more energy off axis than for a normal 6" driver.

My experience is that the speakers work best toed to cross behind the listener. Imaging is still good at this point and the overall balance is better than normal toe-in. Straight forward, zero toe works well for HT, but leaves too much hole in the middle for music.

Bob

Bob

Yes I enjoyed your speakers at GPAF, and have enjoyed your website as well.

The on- and off-axis curves you posted are most informative - thanks! I would guess that somewhere between the top two curves - maybe around 15 degrees ballpark - the first-arrival response is smoothest. Then the rising on-axis energy instead becomes reverberant energy, helping to maintain a better tonal balance for the reverberant field than you'd normally get from "flat on-axis" speakers.

For the sake of a wider listening area, I toe my Fostex's in so that they criss-cross in just front of the listener rather than just behind. Also, the FE206E isn't as smooth as the FE167E (more energy between 2k and 10k), so I use a broad, gentle notch filter to bring that region down just a skosh.

Duke

Hi Wayne,

In all fairness, my FE206E-based speaker isn't exactly a "single-driver" speaker. I'm using a couple of powered woofers to get adequate bottom end extension in a reasonable box size. Since this is of course cheating, the speakers sort of named themselves.

Assuming the picture shows up, the two 6.5" woofers you see are driven by a plate amp on the back of the cabinet. I'm also using a couple of rear-firing drivers to tailor the reverberant field the way I want it. And yes, the stands are too short.

If the picture doesn't show up, here's a link:

http://gallery.AudioAsylum.com//cgi/gi.mpl?u=2112&f=Cheetah1.jpg

Duke

Lori and I are looking forward to attending GPAF again next year. I plan to bring the Cheetahs, and may bring something else as well. I have a couple of other projects in the works, and later today I'll be "making sawdust" - that is, building a prototype box.

Earl was at RMAF in another room, and showed an interesting subwoofer with the Summas. I also had a pair of Summas in my room, and alternated between his and mine.

Duke

Retsel