Concentric vs
Single driver
Whizzer AND
Phase Plugs
Whizzer cones have an effect, a lot lower than 7Khz. If you compare the response of the speaker with and without the whizzer cone, not just the frequencies where the whizzer is the sole source of sound.
An 8" driver with 160mm cone and 80mm horn shaped whizzer with and without whizzer, was tested. They found the whizzer cone starts to have a large effect on the off axis response as low as 2.5Khz.
Specifically the presence of the whizzer cone reduced the on axis response from 2.5Khz to about 6Khz by nearly 3dB, but increased the (30 degree) off axis response by several dB. The dispersion between 2.5Khz and 6Khz was greatly improved at the expense of -1db loss of on axis response.
On axis response without the whizzer actually had a +3dB shelf from 2.5Khz to 6Khz, which suggests the main cone of the driver was designed with an increased output in this range (a slight convexed taper) so the response was balanced once the whizzer was placed.
Above 7Khz the response of the single main cone by itself disappears. At 7Khz the output is almost entirely the whizzer cone.
So technically the whizzer is only acting as a second separate cone above 7Khz, but between 2.5Khz and 7Khz it is still acting as a source of sound as well as a directivity modifier for the main cone.
The improvement in dispersion is so great that at 4Khz without whizzer cone the 30 degree off axis response was -9dB with on axis response (severe beaming). With the whizzer cone in place the 30 degree off axis response at 4Khz was only -1.8dB from the on axis response...
Now think concentric driver with a whizzer for better off axis and phase plug for back wave distortion reduction.
My question is can you still keep the acoustic center of the two drivers and use the correct phase plug to stop the back wave (BASS), from the rear/side walls first reflection.
Hypothetically the HF driver would have to be set inside the phase plug or Open Baffle the HF driver backwards.. (I’ve seen that).. and it works if the rest of the driver system is in a box, bipoled the opposite direction.
(I haven’t seen that)
What I’ve seen and herd though was BOTH sides of the driver were in an open baffle. So it was dipole for the bass and bipole for the HF driver (it had it’s own chamber) and it was facing the front wall..
A nightmare to get the timing right.
The acoustic center only stay aligned, IF the driver and structure are placed in a chamber, I don’t think you could get it to work correctly in a listening room. Maybe.. within 1/2" to get it right..
3 years I worked with the old GRs at a buddies.. 90s. (Super Wedge or something).
He gave up.. I didn’t have much of a choice.
Regards
