[embty2002]

Hello,
i have a simple cm70x112 rectangular panel with alpha15 and a 6,5" focal for mid-high.
could i increase my soundstage , changing panel shape?
is it a good idea that?

http://home.kabelfoon.nl/~dezaire/MOB3W/MOB3W.htm#Baffle%20design%20and%20building

about mid-high, a cm 20 wide panel size is better than my actual cm 70?

Many thanks

Giuseppe

[Rudolf]

The 6,5" driver should have a cone diameter of ca. 5". This leads to a value of 873 Hz for "ka=1" in the diagrams below, assembled from http://www.linkwitzlab.com/models.htm#A3:



On the left you see a black driver cone of radius "a" in a round baffle of radius (from top to bottom): b=a, b=2a, b=4a, b=8a.
ka=1 is 873 Hz, ka=10 is 8,73 kHz and ka=0,1 is 87,3 Hz.
Your 6,5" driver in a 70 cm wide baffle would be b=5,6a. So you have to interpolate.

What do we see:
From ka=3 upward the driver response starts to beam (because of the cone size). Baffle width has increasingly less influence, because the beam touches the baffle edges less and less.
Down from ka=3 we have a red zone, which widens with the increasing baffle width. The red zone marks an area, where controlled directivity gets widely lost and the dipole radiates in wiggling lobes to changing directions. This can't be helpful for a precise soundstage.
Below the red zone we see the regular dipole radiation pattern again.
You should try to keep the red zone for your 6,5" driver as small as possible. You can't avoid it completely without changing to a 4-way system. But it would be helpful  if you reduce the baffle width around that driver to b=2a at least.

Note the green marks on the left vertical scale of each diagram. They show the SPL loss of the baffle at 87,3 Hz compared to the driver in an infinite baffle. As you see, a wide baffle is much more efficient than a small one. You need to take that into consideration, because your driver needs to reach down to the crossover with the alpha15.

Rudolf

[JeffB]

Nice explanation Rudolf.

[embty2002]

Thanks Rudolf.
my Focal PC 165 reach 110Hz with cm 70 panel.
do you think that i can reach 110hz with a cm 26 panel?
but, soundstage could increase, please?
thanks

[Rudolf]

... my Focal PC 165 reach 110Hz with cm 70 panel.
do you think that i can reach 110hz with a cm 26 panel?

Certainly not, but you can use the Alpha 15 up to 200 or 250 Hz and cross there. 

but, soundstage could increase, please?

What do you mean by "increase"? Widening? Please explain. 
My above argumentation is more about "improving" the spatial rendering - not widening it.

[Rudolf]

Nice explanation Rudolf.

Thank you Jeff. I wasn't sure, if anybody could follow my rumination. 

[Guy 13]

Thank you Jeff. I wasn't sure, if anybody could follow my rumination. 

Hi Rudolf and all Audio Circle members.
I got/understood more than 50% of your rumination
and that's good enough for me.
Thanks.

Guy 13

[embty2002]

My above argumentation is more about "improving" the spatial rendering - not widening it.

OK, thanks. sorry for my poor english

[Rudolf]

OK, thanks. sorry for my poor english

But I didn't answer your question, right? 

Try to put that "increase spacing and image sound" in other words, or just an example.
Do you want a wider stage, where instruments and voices play?
Are things too mushy - not separated from each other?

[embty2002]

i have a very wide stage, there is a 2,2 meters space between panel. and 1,2 mt from rear wall.
wide is very good.
i would more deep image, and the Qsound of "amused to death" is not working in my stereo, why? 

[Rudolf]

Giuseppe,
you are sure, that you have the recording of ATD with Q-sound? There seem to be recordings that don't have a Q-sound mix.
I googled for <loudspeaker placement "amused to death">. The results tell me, that it depends much more on the room and loudspeaker placement than on the loudspeaker itself. Apparently different rooms place the effects at different locations.
I don't have ATD, but other recordings with phase inversion effects. One key to the effect is symmetry. Have the same next-sidewall-distance for both speakers and sit at equal distance to both speakers. Aim both speakers at your head.
I'm quite sure that a change of baffle shape will NOT help you in this regard.

Rudolf

[Rudolf]

Giuseppe,
you are sure, that you have the recording of ATD with Q-sound? There seem to be recordings that don't have a Q-sound mix.
I googled for <loudspeaker placement "amused to death">. The results tell me, that it depends much more on the room and loudspeaker placement than on the loudspeaker itself. Apparently different rooms place the effects at different locations.
I don't have ATD, but other recordings with phase inversion effects. One key to the effect is symmetry. Have the same next-sidewall-distance for both speakers and sit at equal distance to both speakers. Aim both speakers at your head.

ATD will also tell you in seconds if your listening room set up is average, good, or exceptional.

If you have boundary proximity issues, your speakers have phase or coherence shortcomings, or your speakers and listening position are even slightly asymmetrically arranged, you will experience only half of this recording's extraordinary message. Though the Q-Sound effects require great attention to system set up, the results of spending the time and energy to optimize that alignment are overwhelming. Sounds will be all around you with this recording using just two speakers. There are dripping faucets behind you to the left, dogs barking off your right shoulder, thunder rolling around the room, horse drawn sleighs crossing your listening room—well in front of the plane of the speakers—and even a Genie's voice that surrounds you and fills the entire room. The recording is loaded with myriad of sounds, too many to inventory, with many outside the boundaries of your listening environment!

From http://www.positive-feedback.com/Issue18/waters.htm][url]http://www.positive-feedback.com/Issue18/waters.htm[/url]

I'm quite sure that a change of baffle shape will NOT help you in this regard.

Rudolf